How is the graft compatibility used in hot melt adhesives for shoes?
When it comes to shoe materials, many people have headaches for leaking shoes. Especially when it ’s raining or snowing, I do n’t dare to walk on a road with water because of leaking shoes, and it is not a problem to wear rain boots to work. Big head, what's wrong with this shoe leaking?
It turned out that most of the shoes leaked because the shoe material was debonded. It was affected by external factors such as temperature, oxygen, water, acid and alkali salts, impurities, and mechanical damage. Destruction, cracking of the adhesive layer, eventually causing the shoe to leak and leak.
Therefore, composite bonding is one of the key links in shoe production. Throughout every link of shoe production, such as sole bonding, upper bonding, insole bonding, etc., the quality of hot-melt adhesive bonding is very important.
Hot melt adhesives are widely used in the footwear industry due to environmental protection, solvent-free, extremely low VOC, and easy processing, The material that has a more critical effect on the adhesive properties of hot melt adhesives is a highly polar, high peel strength graft compatibility agent.
There are many types of graft compatibilizers and many monomers for grafting. Commonly used are: maleic anhydride (MAH), glycidyl methacrylate (GMA), styrene (St), and methyl methacrylate (MMA ), Butyl acrylate (BA), acrylic acid (AA), epoxy resin, oxazoline, etc. These compatibilizers are only different monomers, the principle is similar: the use of free radical initiation into the monomer and polyolefin mixture Graft reaction can be performed.
Among them, the maleic anhydride (MAH) graft compatibilizer has the strongest polarity of the maleic anhydride monomer, and the graft compatibilizer produced by the same substrate has the strongest polarity, so it is also the most widely used. A lot of applications.
The addition of a highly polar maleic anhydride graft compatibilizer gives the hot melt adhesive a higher peel strength. Increasing the polarity of the polymer can increase the interaction between molecules at the bonding interface and improve the interface bonding conditions, thereby increasing the interface adhesion, and also changing the mechanical and rheological properties of the bonding layer: Cohesive strength and modulus of elasticity, increasing glass transition temperature and bulk viscosity, etc., all have a good improvement in peel strength.
For the bonding of different parts of shoes, different materials of graft-compatible hot-melt adhesives are selected according to different temperatures. Hot-melt adhesive does not overflow when bonding various shoe soles, which makes it more beautiful, firm, and water-resistant. The use of the graft-compatible hot melt adhesive simplifies the process, reduces labor, and greatly improves production efficiency.
2. Classification of Graft-compatible Hot Melt Adhesives
There are five main types of hot melt adhesives for footwear: EVA hot melt adhesive film, TPU hot melt adhesive film, PES hot melt adhesive film, PA hot melt adhesive film, PO hot melt adhesive film. The grafting compatibilizers that can be added include grafted POE, grafted PE, grafted SEBS, and grafted EPDM in addition to the most commonly used grafted EVA.
3. Specific application of graft compatible hot melt adhesive
The application parts of the graft-type compatibility agent hot-melt adhesive are mainly uppers, insoles, shoe labels, foot pads, heels, etc.
(1) No-seam upper fits inside the shoe
Mainly used for sports shoes, for the bonding of uppers, mesh and other materials, for high-frequency machine bonding of upper leather and mesh, without the need for needle and thread sewing, instead of traditional glue, mainly used for EVA Insoles, PU insoles, PU soles, rubber soles, EVA soles, etc. fit the foot pads and heels.
The lasting is to nail the insole on the plant equipped with the upper, and then use an adhesive to make the upper firmly adhere to the insole. Compatible hot-melt adhesive used for banding requires short bonding time and high bonding strength. The bonding process is completed on the banding machine at one time. Most of the graft-compatible hot-melt adhesives are made into rubber strips in advance, and then transported to the bonding site of the upper and the insole. The bonding operation can be completed by heating and pressing for a few seconds.
(3) Sticky outsole
Outsoles account for the largest share of hot melt adhesives used in the shoe industry. Because the outsole and the upper require higher bonding strength, polyester hot melt adhesives with high crystallinity and high cohesive strength are generally used.
(4) Bonding the main heel and Baotou
The graft-compatible hot-melt adhesive is used to adhere the main heel and the toe cap, which can eliminate the drying process necessary for water-based and solvent-based adhesives and shorten the production cycle. If it is a soft toe cap, use a small extruder to squeeze the compatible dosage hot melt adhesive directly to the toe cap on the inner surface of the upper and spread it into a toe cap shape. The hot-melt adhesive becomes a soft toe cap after cooling, and no additional lining is required.
(5) Upper cloth bonding of shoes and cloth rubber shoes
In addition to environmental protection factors, the use of graft-compatible hot-melt adhesives is also important because of its high efficiency, upright shoe materials, moisture resistance, corrosion resistance, and good hygienic performance. The dot coating process keeps the cloth with good ventilation and ventilation, and makes up for the shortcomings of gasoline rubber and latex in these aspects.