The hottest polyurethane adhesive

2022-10-24
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Hot melt polyurethane adhesive

1 Overview

hot melt adhesive is a solid at room temperature. When heated to a certain temperature, it melts into a viscous liquid. When cooled to room temperature, it turns into a solid and has a strong bonding effect. Therefore, people call it hot melt adhesive (hot melt adhesive for short). Because hot melt adhesive has the advantages of fast bonding speed, non-toxic, simple bonding process, good bonding strength and flexibility, it has been widely used in wireless book binding, packaging and sealing, shoemaking, textile and other aspects, and has made new developments in variety and performance in recent years. Most of the hot-melt adhesives are prepared from ethylene vinyl acetate (EVA), polyester, polyamide and other hot-melt resins. Due to the poor strength and elasticity of EVA and polyester hot-melt adhesives, they cannot withstand too much external force, and due to the high melting point and hardness of polyamide hot-melt adhesives, they are limited in use. The principle of preparing hot-melt polyurethane adhesive is similar to that of thermoplastic polyurethane elastomer (or rubber), which mainly uses the function of hydrogen bond in the composition to produce physical cross-linking, so that the polyurethane hot-melt adhesive has excellent elasticity and strength. When heated, the hot-melt polyurethane adhesive will lose its hydrogen bonding effect and become a molten viscous liquid. After cooling, it will restore its original physical properties. Therefore, the reversible property of polyurethane resin can be used to make hot melt adhesive with high bonding strength, solvent resistance and wear resistance, which can be used for the bonding of various materials, especially for the bonding of fabrics

polyurethane extreme hot melt adhesives can be divided into two categories: one is thermoplastic polyurethane elastomer hot melt adhesives, and the other is reactive polyurethane hot melt adhesives. The latter is divided into closed type and wet curing hot-melt type. The closed type has been described. As the dissociation temperature of the sealant is above 100 ℃, it will cause bubbles in the adhesive layer, which is only used for maintenance treatment. The wet curing hot-melt polyurethane adhesive is one component, solvent-free, in line with environmental protection laws and regulations, easy to use, and its performance is comparable to that of solvent reactive type, so it has a good development prospect

according to the shape of hot melt adhesive, there are three types of adhesive film, adhesive tape and powder. The adhesive tape is backed by reinforced materials or carriers, while the adhesive film is supported by the adhesive itself

the reasons for the application of hot-melt polyurethane are: high reliability, good chemical and physical uniformity, simple bonding process (reducing production costs), less waste (unused glue can be saved and reused), no mixing problems, and the adhesive can achieve the best physical properties. In addition, because the hot melt adhesive does not use organic solvents, the production site will not be polluted, so it is welcomed by users

2. Thermoplastic hot melt adhesive

thermoplastic polyurethane hot melt adhesive uses more polyester polyols, because its physical properties are superior to those made of polyether polyols. Polyisocyanate adopts MDI and HDI (no discoloration)

(polybutylene adipate MD II hot melt adhesive)

1 Preparation of adhesive film

Add 100g (1/20 mol) of polybutylene adipate (molecular weight 2000) into a 500ml three mouth bottle, heat and melt to 120 ℃. Reduce pressure (vacuum degree 0.67kpa) and dehydrate for 30min under stirring. Add l2.5g (1/20 mole) of MDL pre melted at 60 ℃ into a three port flask, install the reflux condensing pipe, and add 200ml of toluene into the flask four times under stirring within 2h, with the reaction temperature controlled at ℃. Reaction for another 30min, add 100ml of ethyl acetate, stir evenly and stop the reaction. The solid content of glue liquid is 30%. The viscosity measured by the falling ball method is 4pa · s

scrape the film on the glass plate to make the solution volatilize naturally, and then remove it for use after 24h

2. Film properties

(1) the melting temperature of the film is ℃. (2) Peel strength: polyester polyester fabric is greater than 3.92kn/m, and cotton cotton fabric is greater than 4.9kn/m. (3) Hydrolysis resistance: long term immersion in 40 ~ 50 ℃ water (more than 1 month) has no effect on the strength of the adhesive. The peel strength began to decrease after 800 times of bending in ℃ water. Soaking in boiling water has no effect. (4) The storage period is more than 1 year

3. Application

this adhesive film is suitable for the bonding of textiles and glass, such as the bonding of liquid crystal containers on display instruments (computers) with liquid crystal devices

these models are the first choice for plastic mechanical function inspection. MDI hot melt adhesive

(1) tensile strength is (32 ± 2) MPa. (2) The elongation is 600%. (3) Peel strength: cotton cotton cloth 7 ± 1kn/m, polyester polyester 5kn/m. (4) Solvent resistance: insoluble in general organic solvents, slightly soluble in cyclohexanone, and soluble in DMF. (5) The characteristic viscosity is 0.65dl/g. (6) Hot water resistance: in 100 ℃ water for 2h, (1) - (4) all properties have no change; There is no change in the properties of (1) - (4) in water at 40 ℃ for 30 days. Bending 800 times in 40 ℃ water has no effect. (7) The original performance can be maintained after 3 months of atmospheric aging (open air, Beijing month). (8) Damp heat aging (55 ℃, relative humidity 98%, 240h), tensile strength (27 ± 1) MPa, elongation 80%. (9) UV accelerated aging (1000W UV, 1m away, 100h illumination), the film turns yellow, the tensile strength decreases with the thickness, and it is no longer soluble in DMF, indicating that UV accelerated aging and cross-linking have occurred. (10) The storage period is more than 1 year

hdi hot melt adhesive

polyurethane particle size is 0 5mm, dispersed through a sieve onto the undyed cotton fabric with cross twills. When the weight of cotton fabric is 200g per m2, the polyurethane particles used are 28g/m2. After the cotton fabric is covered with rubber particles, heat it with a 1500W infrared radiator for 20s. If so, the rubber particles can be evenly coated on the fabric (the heating area of the infrared radiator is 300cm2, and the distance from the fabric is 10cm). After cooling, it can be used for bonding. Put a piece of cotton knitted fabric on the hot-melt fabric treated above, press it on an iron press at 64kpa and 160 ℃ for 120s, and then press the two fabrics firmly together. The tearing strength of the fabric bonded by this method is 0 69kn/m, with tear strength of 0 after washing with 60 ℃ washing machine 67kn/m, and its tear strength is 0 after washing with boiling water 65kn/m. if perchloroethylene is used for dry cleaning, the tear strength still reaches 0.55 ~ 0.67kn/m. It shows that polyurethane hot melt adhesive particles are successful in bonding fabrics

3. Reactive hot melt adhesive

reactive hot melt polyurethane adhesive appeared in the American market in 1984, marking the new development of hot melt polyurethane adhesive technology. In Europe, the amount of reactive hot melt adhesive used in automobiles was 50 tons in 1986, increased to 300 tons in 1989, with an average annual growth of 80%, and reached 500 tons in 1994, with an average annual growth of 11%. Reactive hot melt adhesive is heated and melted into fluid under the condition of inhibiting chemical reaction, so as to facilitate coating; After the two adherends are bonded and cooled, the adhesive layer condenses and plays a bonding role; Then, with the help of the moisture existing in the air or attached to the surface of the adherend, it reacts with it and expands the chain to produce high cohesion polymer, which significantly improves the adhesion and heat resistance. This kind of adhesive is based on NCO end group prepolymer, combined with thermoplastic resin and tackifying resin that do not react with isocyanate group, antioxidant, catalyst, filler and other additives, so as to ensure that the product has a long service life and storage life

due to the excellent performance of the wet curing reactive hot melt adhesive, it is possible to use the wet curing reactive hot melt adhesive to complete the bonding operation when the hot melt adhesive or reactive adhesive was originally used for bonding. Only because it must be strictly isolated from moisture during manufacturing, storage, transportation and sizing, its promotion is limited and it has not been commercialized in large quantities for a long time. In recent years, due to the breakthrough of technology and equipment, these problems have been gradually overcome and hot melt adhesives have been partially replaced. In the future, with its further improvement and the development of special adhesives, its application will be expanded

1. 100g of polytetrahydrofuran (molecular weight 1000) and 45g of mdl45g were added into the reaction vessel, stirred and heated to 80 ℃ for several hours to prepare the prepolymer, and the viscosity was 5000MPa · s at 25 ℃. After mixing 65g of this prepolymer with polystyrene oligomer, a wet curing reactive polyurethane hot melt adhesive was prepared. The viscosity at 100 ℃ is MPa · s, which has good adhesion strength to polyester film and nylon fabric

2. 850g of prepolymer with liquid NCO end group at room temperature was prepared by polyoxypropylene polyol (molecular weight 400) and MDI. 94g of solid prepolymer made of polyoxypropylene polyol (molecular weight 4000) and MDI was added and mixed evenly at about 120 ℃ to prepare wet curing reactive polyurethane hot melt adhesive. The viscosity is 1200Mpa · s at 130 ℃. The initial shear strength of the hot melt adhesive to wood is 1.8MPa, and the shear strength after curing at room temperature is 7.8mpa

3. Polyester polyol (poly adipic acid terephthalic acid-1,4-butanediol) was synthesized from adipic acid, terephthalic acid and 1,4-butanediol, with a molecular weight of. MDI is used for isocyanate, and the R value is 1 6. The NCO content is controlled at 1.2% - 1.8%. In the prepared prepolymer, molecular weight regulator, stabilizer and catalyst are added to prepare wet curing reactive polyurethane hot melt adhesive. The hot melt adhesive has been applied in the shoemaking industry, as follows

① the outsoles and insoles of the assembly line of running water distribution are pre glued and hardened at room temperature; Expand the chain for 5 days under the conditions of temperature ℃, relative humidity 40%-65% (RH), heat activate at ℃, and press it on the press for S. It is used for bonding the outsole of women's riding boots with six heels. The width of the stripping knife edge is 20mm, and the stripping strength is 100N/cm. It is used for bonding the outsole of 2 1/2 men's leather shoes. The stripping knife edge is 10mm wide and the stripping strength is 99n/cm

② bonding of sandal strips at present, the processing method of sandal strips is to temporarily bond with glutinous rice glue after PU leather is cut into strips. In order to increase the strength, a cloth belt is added in the middle as a reinforcing strip, and then sewed with a sewing machine. This method is complex and unsightly. After 100 ℃ hot melting with this hot melt adhesive, it is applied to synthetic leather cloth. After cooling and hardening, the chain is expanded at room temperature for 5 days, and the strips with different widths are continuously pressed on a special strip pressing machine. The bonded sandal strips are novel, flexible and comfortable, and have good water resistance; Moreover, there is no need to strengthen the cloth belt in the middle, and molding strips of various colors and sizes can be directly selected to make sandal production parts excellent

4. Powdered hot melt adhesive

powdered polyurethane hot melt adhesive is prepared by mixing thermoplastic polyurethane resin with additives such as colorants, plasticizers, stabilizers, curing agents, etc., providing an economical and low-energy manufacturing process. The mixing process of powder is relaxed, which keeps the integrity of resin structure and the stability of performance, so as to ensure its service performance

another advantage of powder is that it has fluidity, which provides convenience for transportation, dispersion and use. Therefore, it does not need the help of pendulum device of other media (such as organic solvent or water), so the powder can be transported and dispersed without melting

there are three main methods for preparing polyurethane powder

1. Grind polyurethane elastomer in the absence of oxygen (oxygen will cause dust explosion). If an impact mill is used, the softer the product to be ground, the lower the operating temperature required. Frozen brine, ice or liquid nitrogen can be used to reduce the temperature

2. In the solvent, the polymerization reaction method is adopted for preparation. The selected solvent requires that only one reaction component can be dissolved, but the final polyurethane product (such as only the hydrocarbon of isocyanate) will not be dissolved. No matter how the solvent is recovered, the polyurethane resin prepared by this solution polymerization method will consume a lot of energy

3. Polyurethane is prepared by lotion polymerization in the presence of a small amount of emulsifier or in the case of very low hydrophilic group content

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