Select hot melt adhesive should pay attention to what issues (below)

1. Hot melt adhesive selection

Selecting a qualified hot melt can guarantee the quality of the tank. The affinity of the hot melt adhesive to different bonded materials is different. In order to make the hot melt adhesive perform better "stickiness", the following factors should be carefully considered in selecting the hot melt adhesive. (1) Color. Due to the different colors of the adhesive, the color requirements of the hot melt adhesive should be different. If there is no special requirement for the color of the adherend itself, yellow hot melt adhesive is recommended. In general, yellow hot melt adhesives are more viscous than white. (2) Surface treatment of the adherend. The surface treatment of the hot melt adhesive to the adhered material is not as strict as other adhesives, but the dust and oil stains on the surface of the adhered material should also be properly treated so that the hot melt adhesive can better exert the adhesive effect. (3) Working hours. Fast job is a major feature of hot melt adhesives. The working time of hot melt adhesive is generally about 15 seconds. With the extensive application of modern production methods, assembly lines, hot melt adhesives require shorter and shorter working hours. (4) Temperature resistance. The hot melt adhesive is sensitive to temperature, and the temperature reaches a certain degree, the hot melt adhesive begins to soften; below a certain temperature, the hot melt adhesive will become brittle, so the choice of hot melt adhesive must fully consider the change of the ambient temperature. (5) Stickiness. The tackiness of hot melt adhesives is early tack and late tack. Only the early stickiness and the late stickiness can make the hot melt adhesive and the adherend stable. In the production process of hot melt adhesives, it should be ensured that it has anti-oxidation, anti-halogen, anti-acidity and plasticity.

2. Some issues to note in the use of hot melt adhesives

The use of hot-melt adhesive sealing technology can be said to be a lot of books glued book technology, therefore, in the use of hot-melt adhesives can also refer to some glue-binding technology. Because different hot melt adhesives have different characteristics and application requirements, it is necessary to focus on the use of different materials and hot melt adhesives in the tank. For EVA hot melt adhesives, since EVA hot melt adhesive is a thermoplastic adhesive, it differs from ordinary cold adhesives and PUR hot melt adhesives. According to its characteristics, the following issues should be noted during use. .

(1) It is necessary to recognize and grasp various models and different technical performance parameters of EVA hot melt adhesives. Different types of hot melt adhesives have different open, cure, and cooling times. It is also necessary to distinguish between the use of Xiajiao and Dongjiao due to different regions. The opening and curing time will also change with different temperatures. The entire bonding process is completed during the opening time of the hot melt adhesive.

(2) The use of EVA hot-melt adhesives should not be directly heated with open flame, must use spacer oil bath heating (boiling point should be to 100 degrees Celsius) or, with a sealed heating plate heating device. The temperature of the hot-melt adhesive must be strictly controlled within the scope of use. The temperature of the adhesive must not be arbitrarily changed. The maximum allowable tolerance is ±1.0 degrees Celsius under special circumstances.

(3) Before the solid EVA hot melt adhesive is used, it must be warmed up with a preheating device and then released to a plasticized plastic box. During the process of using glue, no solid glue blocks (plastic blocks not preheated) can be directly mixed in the plastic working glue box to prevent the phenomenon of uneven temperature, poor fluidity, or incomplete melting of the glue, resulting in uneven coating. Or bonding difficulties affect quality.

(4) The amount of glue in the preheated glue pan must be properly grasped, and the amount of glue that cannot be used in excess must not be used up. The colloid is repeatedly melted to degenerate and deteriorate the viscosity and affect the adhesive force. It is also not possible to add too little and not enough, causing waiting for the melt to affect normal production. Plastic pots and plastic boxes should be regularly cleaned to ensure that the plastic pot inside the plastic box to prevent impurities in the glue liquid precipitation, accumulation and affect the accuracy of temperature control, to set the system in the work, on time inspection, earnestly implemented.

As for the use of PUR hot melt adhesives, as it is a new material and new technology that has been popularized in recent years, there are still some insufficiencies. Therefore, it is necessary to pay attention to constantly sum up experience in use, and be familiar with the use of equipment and materials. In order to give full play to its good advantages.

(1) In PUR hot melt adhesives, it will be covered with thick adhesive after being used for a period of time, and can only be removed after cleaning. Therefore, it is necessary to pay attention to timely cleaning. The coating device, which is easy to clean at the end of the job, must remove the PUR residue after the gluing is completed to remove the remaining adhesive. In addition, the pressure of the adhesive must be reduced, and the operating temperature must be optimized.

(2) Since the PUR hot melt adhesive is a moisture-cured product, care must be taken in the transportation and application of the hot melt adhesive to avoid exposure to air and moisture. Note that the PUR hot melt equipment must meet the requirements for the isolation of the glue to ensure absolute dryness of the glue. Therefore, PUR hot melt adhesives are always transported in full containers and applied by dedicated melters. The dedicated melter always seals the seal of the tank, avoids contact with air and provides PUR on-demand supply. This access to hot melt adhesives on demand can well avoid system temperature pressures.

(3) New hot melt adhesive products offer lower handling tack, as well as better initial strength and viscosity stability, which are required for the tank fuser. Although manufacturers have made great advances in processing equipment and technology, PUR hot melt adhesives still require more attention than conventional products to determine every detail, especially during maintenance. Although users have certain restrictions on cleaning up PUR chemical products to generate accessories, these removal products are very effective. Care should be taken to remove any residual glue from the cracks and crevices of the equipment, and to remove adhesive residue from dirty tanks, pumps, hoses, and other related equipment.

(4) The environmental protection voices of all walks of life are now relatively strong, and the printing industry is no exception. No matter which new technology and materials are selected, environmental protection issues cannot be ignored. Although special caution is required when using PUR hot melt adhesives, because PUR encounters high heat (typically 140 degrees Celsius or more), it releases isocyanate gas and has a certain influence on human health. In the case of gas, it can irritate the mucous membranes of the eyes, nose and throat. When inhaling large amounts of smoke, it can cause headaches and other symptoms. This is an important issue faced by many users of PUR hot melt adhesives. Therefore, for the operator to have certain protective measures, in addition to control the commonly used operating temperature does not exceed 120 degrees Celsius, from the perspective of environmental protection and safety, the PUR hot melt adhesive heating is best to set the temperature control and exhaust device to promote gas diffusion.

In addition, an environmentally friendly "micro-irradiation" PUR hot melt adhesive can be used. It is reported that this product contains less than 0.1% of the monomeric iso-hydrogen acid salt of the conventional PUR hot melt adhesive. Now this indicator has been set to European statutory indicators. After the micro-irradiation product is melted, the iso-hydrogen salt emitted by the traditional PUR hot-melt adhesive can be reduced by 90%, so it is more conducive to environmental protection and guarantees the health of production personnel.

Author/Lin Qishui Source: China Packaging News