What should be paid attention to when selecting ho

What problems should be paid attention to when selecting hot melt adhesive (Part 2)

II. Problems to be paid attention to in the selection of hot melt adhesive 1. selection of hot melt adhesive

only by selecting and keeping the machine in the power-off state, can the quality of the glue box be guaranteed. The affinity between the hot melt adhesive and different bonded materials is different. In order to make the hot melt adhesive give better play to its "viscosity", the following factors should be carefully considered when selecting the hot melt adhesive. (1) Color. Due to the different colors of the bonded objects, the color requirements of the hot melt adhesive should be different. If the object to be bonded has no special requirements for color, it is recommended to use yellow hot melt adhesive. Generally speaking, yellow hot melt adhesive is more viscous than white adhesive. (2) Surface treatment of the bonded object. The surface treatment of the hot melt adhesive is not as strict as that of other adhesives, but the dust and oil stains on the surface of the adhesive should also be properly treated to make the hot melt adhesive play a better role in bonding. (3) Operation time. Quick operation is a major feature of hot melt adhesive. The operation time of hot melt adhesive is generally about 15 seconds. With the wide application of modern production line, the operation time of hot melt adhesive is required to be shorter and shorter. (4) Temperature resistance. Hot melt adhesive is sensitive to temperature. When the temperature reaches a certain level, the hot melt adhesive begins to soften; Below a certain temperature, the hot melt adhesive will become brittle, so the selection of hot melt adhesive must fully consider the change of ambient temperature. (5) Stickiness. The viscosity of hot melt adhesive is divided into early viscosity and late viscosity. Only when the early viscosity is consistent with the late viscosity can the hot melt adhesive and the bonded object remain stable. In the production process of hot melt adhesive, it shall be ensured that it has oxygen resistance, halogen resistance, acid alkali resistance and plasticization

2. some problems needing attention in the use of hot melt adhesive

the use technology of hot melt adhesive sealing box can be said to draw lessons from the binding technology of many books and periodicals. Therefore, some binding technologies can also be referred to in the use of hot melt adhesive. As different hot-melt adhesives have different characteristics and use requirements, the use technology should be paid attention to for different materials and hot-melt adhesives in the rubber box, although the bellows ring stiffness tester is no exception. As for EVA hot melt adhesive, the bonding material of EVA hot melt adhesive is a kind of thermoplastic adhesive, which is different from both common cold adhesive and pur hot melt adhesive. According to its characteristics, the following problems should be paid attention to in use. In the same year,

(1) it is necessary to understand and master various models and different technical performance parameters of EVA hot melt adhesive. Different types of hot melt adhesives have different opening, curing and cooling times. It should also be distinguished that due to different regions, the opening and curing time of summer glue and winter glue will also change when the temperature is different. The whole bonding process shall be completed within the opening time of the hot melt adhesive

(2) when using EVA hot melt adhesive, do not directly heat it with open fire. Be sure to heat it with a spacer oil bath (boiling point should reach 100 ℃) or with a sealed electric heating plate. The temperature of the hot-melt colloid shall be strictly controlled within the range of use, and the temperature of the used colloid shall not be changed arbitrarily. Under special circumstances, the maximum allowable deviation is ± 1.0 ℃

(3) before using the solid EVA hot melt adhesive, it must be preheated by the preheating device to reach the standard, and then released to the glue box for use. In the process of glue application, it is not allowed to directly mix solid glue blocks (glue blocks without preheating) into the glue box for glue application, so as to prevent uneven glue temperature, poor fluidity or incomplete melting, resulting in uneven glue application or difficult bonding and affecting the quality

(4) the amount of glue in the preheated glue pot should be appropriate. Do not add too much glue. The glue is repeatedly melted for many times, which will deteriorate and age, reduce the viscosity and affect the adhesion. It is also not allowed to add too little and not enough to cause waiting for melting and affect normal production. The glue pot and the glue box shall be cleaned regularly to ensure the cleanness of the glue pot and the glue box, so as to prevent the impurities in the glue liquid from precipitating and accumulating and affecting the accuracy of temperature control. The system shall be formulated in the work, checked on time and implemented carefully

as for the use of PUR hot melt adhesive, as it is a new material and technology popularized and used in recent years, there are still some insufficient factors. Therefore, it is necessary to constantly sum up experience and master the use skills of its equipment and materials in order to give full play to its good advantages

(1) in the pur hot melt adhesive box, because it will be covered by thick adhesive after a period of use, it can only be removed after cleaning, so it should be cleaned in time. For the coating device that is easy to clean at the end of the operation, the residue of PUR must be removed from the sample and the adhesive residue must be removed. In addition, it is necessary to reduce the temperature pressure of the adhesive, and the operating temperature must be in an optimized state

(2) as pur hot melt adhesive is a product that solidifies when wet, great care should be taken during the transportation and application of hot melt adhesive to avoid exposure to air and moisture. Note that pur hot-melt equipment must meet the isolation requirements of glue to ensure the absolute drying of glue. Therefore, PUR hot melt adhesive is always transported in the form of a whole box and applied through a special melter. The special melter always seals the seal of the glue box to avoid the contact between the glue and air, and conveniently provides pur on-demand supply. In this way, hot melt adhesive can be used on demand to avoid the pressure of system temperature

(3) the new hot melt adhesive products provide lower processing viscosity and better initial strength and viscosity stability, which are necessary conditions for the glue box hot melt. Although the manufacturer has made great improvements in processing equipment and technology, PUR hot melt adhesive still needs more attention than traditional similar products to determine every detail, especially during maintenance. Although users have certain restrictions on cleaning up the generated accessories of PUR chemical products, these cleaning products are very effective. Pay attention to remove the residual adhesive from the cracks and crevices of the equipment, and remove the residual adhesive from the dirty rubber box, rubber pump, rubber hose and other related equipment

(4) nowadays, there is a strong voice for environmental protection in all walks of life, including the printing industry. No matter what new process and materials are used, environmental protection issues cannot be ignored. Although extra care is required when using pur hot melt adhesive, due to high heat (generally above 140 ℃), PUR will release isocyanate gas, which will have a certain impact on human health. When people contact this gas, it will stimulate the mucous membranes of eyes, nose and throat, and cause headache and other symptoms when inhaling a large amount of smoke. This is an important problem faced by many users of PUR hot melt adhesive. Therefore, certain protective measures should be taken for operators. In addition to controlling the common operating temperature not to exceed 120 ℃, from the perspective of environmental protection and safety, it is best to set temperature control and exhaust devices for the heating of PUR hot melt adhesive to promote the diffusion of gas

in addition, the environmental friendly "micro radiation" pur hot melt adhesive can be used. It is reported that the product contains less than 0.1% of the monomer of the traditional pur hot melt adhesive. Now this index has been set as the legal index in Europe. After melting, this micro radiation product can reduce 90% of the isohydrides emitted by the traditional pur hot melt adhesive, so it is more conducive to environmental protection and the health of production personnel

author/Lin Qishui source: China Packaging News