Thermoplastic Polyurethane Hot Melt Adhesives
Non-reactive polyurethane hot melt adhesive is heated to a certain temperature and then melted and coated on the bonding substrate, and then cured by cooling. The bonding mechanism and one-component solvent-volatile adhesives, curing process does not occur chemical reaction, mainly using the role of hydrogen bonding in the composition of physical cross-linking, and produce adhesion, the initial adhesion is very good. After heat, the loss of hydrogen bonding, into a molten viscous liquid, so the use of this reversible feature can be repeatedly heated – cooling curing.
Lower melting point of TPU can be made into powder, film, strip hot melt polyurethane adhesives. Thermoplastic polyurethanes for hot melt adhesives are linear or polymers with a few branched chains. The main material of polyurethane is generally made of polyether glycol or polyester glycol, diisocyanate (such as MDI, TDI, IPDI or HDI) and low molecular diol chain extender, etc. The synthesis methods are propriety method and solution method. Aliphatic diisocyanate does not contain benzene ring, the yellowing resistance of its products is better.
In the preparation of polyurethane hot-melt adhesives, the original performance of polyurethane in some aspects still can not meet the requirements, the need to add some substances to modify, such as the addition of viscosity-enhancing resins, thermoplastic resins, plasticizers, antioxidants and ultraviolet absorbers. The addition of tackifying resins and thermoplastic resins improves the bonding strength, heat resistance and wettability of the material, and gives the product certain pressure sensitivity. Tackifier resins can reduce the melting temperature and viscosity of hot melt adhesives, improve the wettability of polyurethane hot melt adhesives to the sticky objects, thus improving the adhesive performance of polyurethane hot melt adhesives, mainly phenolic resins, epoxy resins, terpene resins, rosin glycerides, disproportionated rosin, polymerized rosin, petroleum resins, alkyl phenolic resins, coumarin-indene resins, etc., and thermoplastic resins mainly include SBS, SIS and EVA, etc. Plasticizers can be added to improve the flexibility of the product, improve the cold resistance of adhesives, heat resistance, flame retardant, durability, etc., while improving the physical and mechanical properties of adhesives and construction process performance, but when adding plasticizers and polyurethane should be noted to have good compatibility, to prevent plasticizer migration, exudation, volatilization, etc. The plasticizers added are mainly dioctyl phthalate and trioctyl trimellitate, etc. Add antioxidants and UV absorbers to improve the product’s high-temperature yellowing resistance and sunlight aging resistance. The addition of zinc stearate or calcium stearate in appropriate amount can improve the melt flow rate of polyurethane and increase the fluidity of the product, making it helpful for construction.
The main component of powdered polyurethane hot melt adhesive is still thermoplastic polyurethane resin, which can be mixed and formulated with additives such as colorants, plasticizers and stabilizers. The powder has fluidity, which provides convenience for conveying, dispersing and using, and can be evenly dispersed on the surface of the adhered material without melting.
There are three main methods of preparing polyurethane powder as described below. At present, the first one is mainly used.
①In the absence of oxygen (
Oxygen can cause dust explosion) freeze grinding of TPU elastomers. An impact mill can be used to reduce the temperature with frozen brine, dry ice or liquid nitrogen.
For example, the granular polyurethane resin is mixed with additives, and the material is extruded by a twin-screw extruder at a temperature of 80 to 130°C. After cooling and cutting, the material is crushed in a special pulverizer, and the coarse particles are removed by screening to obtain 40 to 60 μm granules, and the polyurethane powder prepared by this method has good fluidity and stability.
② Use solution polymerization method.
The solvent chosen for this solution polymerization requires that only one reaction component be dissolved, and not the final polyurethane. For example, hydrocarbons that dissolve only isocyanates can be suitable for making powder polyurethane. The recovery of solvent by solution polymerization is energy intensive.
For example, adipic acid adipate diol is dehydrated under vacuum and reacted with HDI to generate prepolymer, then it is reacted with 1,6-hexanediol and neopentyl glycol in toluene solution for chain expansion, and polyurethane solid is precipitated after a period of time, and after removing the solvent, it is dried, ground and sieved to obtain polyurethane hot melt adhesive powder with a melting temperature of 120-126°C and a powder size of 0.3-0.5 mm. The adhesive can be The glue can be heated by infrared heating radiator and used for fabric bonding, the amount of glue applied is about 28g/m2, and the peel strength is 570~690N/m. The glue can also be further processed into film-like.
③Emulsion polymerization method. In the presence of a very small amount of emulsifier or in the case of very low hydrophilic group content, the polyurethane aqueous dispersion is made by emulsion polymerization, and then made into powder after emulsion breaking and drying. The product performance has a large gap with the body polymerization.
Ultramoll PU produced by Germany Bayer is a highly flexible polyurethane powder containing polymer plasticizer, the powder is colorless and odorless, particle size less than 1000μm, it contains (5±3)% PVC, Shore A hardness of 72±3. When Ultramoll PU is applied to injection molded soles to bond PVC and upper materials, the bonding strength can be greatly improved. .
Polyurethane hot melt adhesive film and strip polyurethane hot melt adhesive can be obtained from thermoplastic polyurethane granules by calendering. The films can also be obtained by coating and drying with polyurethane solutions.
The granular polyurethane hot melt adhesive can be extruded into an extruder with a T-shaped die to form an adhesive film, and then water-cooled and wound into a product. For example, the film can be 800 ~ 820mm wide, 0.3 ~ 1.5 mm thick. A polyurethane hot melt adhesive technical indicators are: construction temperature 165 ~ 190 ℃, adhesive film tensile strength ≥ 30MPa, 300% fixed tensile stress ≥ 8MPa, room temperature shear strength ≥ 45MPa, 75 ℃ shear strength ≥ 12MPa, melt flow rate ≥ 6g / min (145 ℃. 2.15kg).
Dongguan Guangshiyuan Polyurethane Material Co.
20 years professional polyurethane auxiliary materials.
10 years of anti-aging and yellowing resistance formula development
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Dongguan Guangshiyuan Polyurethane Material Co., Ltd. was established in 2009, which is deeply engaged in the niche industry of polyurethane raw materials – amine catalysts; we develop and compound various types of amine catalysts, which are suitable for sponge, molding, high resilience, self-crusting, PU toys and various hard and semi-hard foam end products.
Main products: Anti-yellowing agent for sponge; Meriken color essence; Soft foam silicone oil; Amine catalyst for hard and soft foam; Anti-oxidant; Anti-static agent; Porosity-opening agent; Flame retardant; Sponge color paste; Anti-mildew agent; Tin catalyst; Modified MDI; Polyurethane auxiliary; UV absorber; Light stabilizer
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