Notes on dry and complex glue preparation

 Notes on dry and complex glue preparation #Plastic packaging dry recovery process, glue preparation is one of the key control points, glue is the glue main agent, curing agent and solvent according to the specified proportion and correct operation method to prepare into the machine can be used normally mixed glue liquid. The composite quality accidents caused by abnormal glue distribution are often occurred in printing and packaging enterprises, for example, less addition or no reinforcement agent leads to the serious non-curing of the rubber layer, due to the imbalance of glue proportion, due to the improper curing, resulting in the bag hot sealing place winding, aluminum leakage, etc.; Excessive addition of #solvent, will lead to insufficient glue, peel strength is not up to standard; Residual glue use is not standardized to cause compound bad and so on. The following are the common methods of preparation of two-component dry and complex solvent glue and the matters needing attention are summarized as follows, for the reference of operators and grass-roots managers. First, glue technical data (or glue use manual) important technical data is an essential reference before the use of glue. To properly match the glue, we should get the technical data provided by the glue manufacturer first. This ratio is usually used by the glue manufacturer in the laboratory test, the main agent and the curing agent fully react, and then appropriately increase the amount of isocyanic acid group, the amount of the effective composition of the curing agent, the amount of excess, to offset the consumption of the external uncertainty factors. Generally, the enterprise will issue the process sheet for a single specific product in the composite process, which will make the regulation of glue ratio according to the "#glue technical data" provided by the glue manufacturer and other factors. Some enterprises may also have "glue preparation operation specifications", which will clearly stipulate the proportion of various glue used by the enterprise. In general, glue preparation must be subject to standard basis and standard requirements. In special cases, proportion adjustment must be based on this standard ratio, especially the proportion change of main agent and curing agent. The following table shows the screenshot of a glue technical data and the joint process screenshot of the enterprise. Relationship between solid content and diluent when dilution According to the production process requirements, the working concentration of glue (solid content of mixture) is determined by the amount of glue and the number of wire lines used by the coating roller. Different types of products, such as ordinary two-layer structure, aluminum foil structure or high temperature cooking structure, are different requirements for the use of glue type and glue volume, glue type and glue volume, directly affect the proportion requirements of glue allocation. The production process is determined after considering the technical data of glue, product type, use environment, product detection data and other factors, so the allocation ratio before glue use must be according to the production process requirements, but glue technical data is still an important reference. Iii. Influence of objective conditions The glue ratio is affected by objective conditions, which mainly includes the following aspects: 1. Requirements of composite stripping strength of the product According to the product type, there are specific requirements for stripping strength, in addition to reasonable design of glue, but also through fine tuning of main agent and curing agent proportion to achieve. For example, ordinary aluminum-plated film products, if not the special glue of aluminum-plated film, can reduce the dealuminized aluminum by reducing the proportion of curing agent, so as to improve the stripping strength (other quality risks caused by this operation need to be evaluated). Generally, on the basis of the use of the original curing agent, the proportion of 10%~20% is reduced. If the main agent is under normal use: curing agent =5:1, after adjustment, the main agent: curing agent =5:0.8, in order to ensure the product quality, it is necessary to pass the actual verification, To determine the specific reduction ratio to form standard technical data. For example, in order to reduce the attenuation degree of peel strength after cooking, the proportion of curing agent will be increased to increase the hardness of rubber layer to reduce the anti-stripping strength, which will generally increase 3% ~ 5%. In the ultra-high temperature and high humidity environment (humidity exceeding 90%), even if the proportion of curing agents is increased, it is not recommended to make high-temperature cooking products. 2. Number of coating roller network lines Many packaging manufacturers, dry and coated roller model is limited, even a roller general all products, because the number of mesh lines of the coating roller is not appropriate, the product needs reasonable glue volume, it needs to adjust the working concentration of the glue liquid to stabilize the glue volume. For example, the small coating roller of network wire can achieve a small amount of glue, and the glue preparation should be with a small working concentration, which is realized by increasing the proportion of solvent. The large coating roller of network line can achieve a slightly higher amount of glue, so it is necessary to increase the working concentration of glue and reduce the proportion of solvent to increase the working concentration. Due to the limitation of coating roll, the way of adjusting glue ratio is often increased cost (solvent volatiles loss) or some quality problems (caused by plugging plate compound white point). The coating roller has limitations, and the working concentration can be changed by increasing or reducing the proportion of solvent. 3. Seasonal changes and environmental temperature and humidity Seasonal changes and weather effects, such as the difference in temperature and humidity in winter and summer or the brief return to south China problem, these factors bring environmental temperature and humidity changes to the glue ratio has a relatively large impact, the ideal environment temperature and humidity condition is temperature: 25 + 5. Humidity :50%~60%, non-constant temperature and airtight workshop, in the whole year, this condition is difficult to be constant. In the high temperature and high humidity environment, such as the workshop humidity exceeds 85%, the temperature exceeds 35m. In the process of use, the glue circulation and glue flow in the glue tank, the solvent volatiles, the glue liquid temperature is low, will absorb certain moisture, plus the solvent volatiles, the condensed water droplets mix, will consume part of the curing agent. Therefore, the humidity of the workshop is greater than 85%, and the addition of the curing agent by 5%~10% is usually used to offset the consumption of the curing agent by water. If the workshop temperature is particularly low, although the working concentration (solid content) of the glue liquid remains unchanged, the viscosity will increase, which is not conducive to the coating transfer of the glue liquid. In order to improve the transfer efficiency of the glue, the proportion of the solvent will be increased to appropriately reduce the viscosity, such as increasing the amount of solvent by 10%, and reducing the viscosity of glue by 2 ~ 3s. Due to the decrease of working concentration, although the transfer amount can be appropriately improved, the actual glue volume is also affected by the number of lines, network hole depth, network line roller type, machine speed, adhesive pressure roller pressure, scraper pressure, corona value of rubber film and other factors. It must be determined to verify whether the amount of glue has been reached, otherwise, the method of increasing the viscosity of solvent cannot be used to increase the amount of glue. High solid glue containing low viscosity can be used to solve the problem of glue use under ultra-low temperature. 4. The stability of viscosity glue ratio must be determined according to the solid content of the main agent and curing agent and the actual working concentration, the proportion of the mixing of the working fluid must be determined. Whether it can meet the requirements of the amount of glue in process design, as mentioned earlier, there are many influencing factors, among which the influence of viscosity is very important. Viscosity is not only affected by the characteristics of glue itself, but also by the ratio (solvent addition) and environmental temperature. In order to stabilize the coating, all aspects of the situation are complete, only to ensure the viscosity stability of the glue liquid, can achieve the coating volume stability. In the process of glue use, with the continuous volatilization of solvent, if the solvent cannot be added in time, the proportion of glue is out of balance, the viscosity increases, will generally increase the amount of glue. Therefore, in the normal use of glue, it is also necessary to manually and periodically add solvent or viscosity control instrument to automatically adjust to achieve the stability of glue viscosity, and the stability of glue working concentration to ensure the stability of glue volume. In order to be stable, the viscosity value should be maintained, which will change the proportion of glue and solvent. 5. Abnormal material quality or influence of material properties The abnormal material referred to here is that before the adhesive is added, it has been clearly known that alcohol dissolution in the printing film exceeds the standard or the solvent purity is not standard. For example, isopropanol in the printing film (including ethanol) exceeds 5mg/m2, and the dosage of curing agent can be increased by 1% ~ 3% when glue is used. For example, the solvent purity of ethyl acetate was lower than 99.5%, especially the sum of alcohols and water exceeded 0.2%, in order to cancel their consumption of isocyanate group, which was used to increase the curing agent by 3% ~ 5%. For example, the normal proportion is the main agent: curing agent =5:1, after adjustment, the main agent: curing agent = 5:05. In this case, the quality risk of the composite film produced is very high in other aspects, such as whether the stripping strength of the final printing layer is up to standard and whether the excessive dissolution of residual material is still present. Remember, this method of adjusting the proportion of glue can only be used as an emergency remedy, cannot be used as a conventional operation mode, really need to solve the printing film dissolution and solvent purity problem from the source. The material properties affect, for example, nylon film is easy to absorb moisture. When making nylon film composite, generally increase the amount of curing agent by 3%~5% in the environment, and increase the amount of curing agent by 5%~10% in the high humidity environment (more than 85%). 6. Reuse of residual glue Residual glue usually refers to the glue that has been cleaned out in the glue groove (the glue that has been opened in the bucket is not prepared, as long as the seal is tight, usually can be used normally). The storage time of the remaining glue is generally no more than 48h, fast drying glue is not more than 12h, even if put in the refrigerator of 4 yuan, more than a certain amount of time, will usually be emulsified to become white, this kind of emulsified severe residual glue, can not be used anymore. In order to save costs, the remaining glue stored in a short time can be reused, and generally mixed with new glue. According to the proportion of new glue main agent, curing agent and solvent, the preparation process is prepared to the required working concentration, and the viscosity value is measured after stirring fully. According to the weight of the new glue, the remaining glue that can be reused is mixed into the new glue according to the ratio of 5% to 30%, and the viscosity after full mixing is measured. If the viscosity is lower than the viscosity of the new glue, the main agent and curing agent need to be added in proportion to the initial viscosity until the initial viscosity is reached. (this residual glue is often a large amount of solvent used to clean the roller in the glue solution). If the viscosity is higher than the initial viscosity, new solvent needs to be adjusted to achieve the initial viscosity (this case is that the residual glue solvent is overvolatile, the solid content is high). The proportion of residual glue added needs to consider the product type, ordinary products can be used in appropriate amount, high temperature cooking products are not recommended to be used, specific add amount, but also consider the degree of glue emulsification, the more serious degree of emulsification, the smaller the proportion of adding. No matter how much# glue is added, it will definitely change the proportion of glue and solvent. There is a certain quality risk for the use of residual glue, no matter what proportion is added, it is necessary to combine the product type and daily operation experience. What needs to be emphasized is that the remaining glue can only be mixed with the same manufacturer and the same model of new glue. The same glue manufacturer, the same type, different types of glue can mix, should listen to the glue manufacturer's opinion. Iv. Standardized management Since it is very important to make glue and ensure the stability of glue proportion, it is necessary to standardize the management of glue distribution in practice, dry and complex glue preparation operation specifications, to cover the operation requirements and problems that need to be avoided, you can refer to the following table. Fifth, conclusion In the process of dry and recovery process, the working of adhesive is very important, and the most important part is that the proportion of glue should be according to the process requirements, combined with specific product material structure, production environment conditions, glue performance, product use conditions, etc. More should eliminate the error of artificial glue, for example, avoid the curing agent at will increase or decrease, at will shorten the stirring time; Not to be more due to the operation error leakage reinforcement agent. Good glue distribution operation, is to ensure dry and return production quality of the basic work, must not be careless. At present, there is a special glue mixing system for dry and complex, which realizes the automation or semi-automation of glue distribution, which can more ensure the stability of glue ratio, minimize or eliminate the risk of artificial error of glue manual preparation, better control the cost of solvent use, and provide more guarantee for the stability of dry and return production quality.

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