Hot-melt polyurethane adhesive (top)

1 Overview

Hot-melt adhesives are solid at room temperature and melt to a viscous liquid when heated to a certain temperature. After cooling to room temperature, they become solid and have a strong bonding effect. Therefore, people call it hot melt. (Type) adhesive (referred to as hot melt adhesive). Because the hot melt adhesive has the advantages of fast bonding speed, non-toxicity, simple bonding process, good adhesive strength and flexibility, etc., it is widely used in books, such as wireless binding, packaging sealing, footwear, and textiles. Application, and in recent years there have been new developments in variety and performance. Most hot-melt adhesives are made of hot-melt resins such as ethylene-vinyl acetate (EVA), polyester, and polyamide. Because EVA and polyester hot-melt adhesives have poor strength and elasticity, they cannot withstand large external forces. Because of the higher melting point and hardness of the polyamide hot melt adhesive, it is limited in use. The principle of the preparation of hot-melt polyurethane adhesive is similar to that of thermoplastic polyurethane elastomer (or rubber), and it is mainly used to physically cross-link the hydrogen bonds in the composition, so that the polyurethane hot-melt adhesive has excellent elasticity and strength. Hot-melt type polyurethane adhesive loses its hydrogen bonding effect when heated, and turns into a molten viscous liquid, which returns to its original properties after cooling. Therefore, the reversible characteristic of polyurethane resin can be used to make hot melt adhesives with high adhesive strength, solvent resistance and wear resistance, which can be applied to the bonding of various materials, and is particularly suitable for bonding fabrics.

Polyamide hot melt adhesives can be divided into two categories: one is thermoplastic polyurethane elastomer hot melt adhesive, and the other is reactive polyurethane hot melt adhesive. The latter is divided into closed type and moisture curing hot melt type. Closed type has already been described, because the sealant dissociation temperature up to 100 °C above, will cause the glue layer to cause air bubbles, etc., only for maintenance and treatment. The moisture-curing hot-melt polyurethane rubber is a one-component, solvent-free type that meets the environmental protection regulations. It is easy to use and the performance is comparable to the solvent-reaction type. Therefore, the development prospect is very good.

According to the shape of hot melt adhesive, there are three types of adhesive film, tape and powder. The adhesive tape is backed with a reinforcing material or carrier, and the adhesive film is supported by the adhesive itself.

The reasons for the use of hot-melt polyurethanes are: high reliability of use, good chemical and physical homogeneity, simple bonding process (lower production cost), low waste (unused glue can be used after storage), no mixing Problems can make the adhesive achieve the best physical properties. In addition, because the hot melt adhesive does not use organic solvents, the production site will not be contaminated and will be welcomed by users.

2. Thermoplastic hot melt adhesive

Thermoplastic polyurethane hot melt adhesives use more polyester polyols, and their physical properties are superior to those of polyether polyols. Polyisocyanates use MDI and HDI (no discoloration).
(polybutylene adipate-MDII hot melt adhesive)
1. Film Preparation 100 g (1/20 mol) of polybutylene adipate (molecular weight 2000) was placed in a 500-ml three-necked flask and heated to 120° C. by heating. Dewatering under reduced pressure (degree of vacuum 0.67 kPa) for 30 min under stirring. Into a three-neck flask, MDl melted in advance at 60 DEG C was added into a three-necked flask, a reflux condenser was set, and 200 ml of toluene was added to the bottle in 4 hours with stirring, and the reaction temperature was controlled at 110. -115°C. The reaction was continued for 30 minutes plus 100 ml of ethyl acetate, and the reaction was stopped after stirring. The glue solid content is 30%. The viscosity measured by the falling ball method is 4 Pa·s.

The glue liquid was scraped on the glass plate to volatilize the solution naturally and it could be removed after 24 hours.

2. Film properties (1) The film melt temperature is 90-100 °C. (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 water of 40-50°C (more than one month) has no effect on the strength of the rubber. The peel strength began to decrease after flexing 800 times in water at 40-50°C. Soaking in boiling water has no effect. (4) The retention period is more than 1 year.

3. Application of the adhesive film is suitable for adhesion of textiles and glass, for example, for attaching a liquid crystal device to display a liquid crystal container on an instrument (computer).

The MDI hot melt adhesive (1) has a tensile strength of (32±2) MPa. (2) The elongation is 600%. (3) Peeling strength: cotton cloth-cotton 7±1kN/m, polyester-polyester 5kN/m. (4) Solvent resistance: insoluble in common organic solvents, slightly soluble in cyclohexanone, and soluble in DMF. (5) The characteristics of the cement are 0.65dL/g. (6) Heat-resistant water performance: In water of 100°C for 2 hours, there is no change in performance of (1)-(4); in water of 40°C for 30 days, there is no change in performance of (1)-(4). There was no effect on flexing in water at 40°C for 800 times. (7) Atmospheric aging can maintain its original performance for 3 months (open air, Beijing, August-November). (8) Hygrothermal aging (55°C, relative humidity 98%, 240h), tensile strength (27±1) MPa, elongation 80%. (9) Ultraviolet accelerated aging (1000W UV, distance 1m, light 100h), film yellowing, tensile strength decreased with different thickness and varying degrees, and is no longer soluble in DMF, indicating that UV accelerated aging, occurred Cross-linked. (10) The storage period is more than 1 year.

The HDI hot-melt adhesive polyurethane size is 0.3-0.5 mm and is dispersed through a sieve onto an undyed cotton fabric with crossed diagonal stripes. When the cotton fabric has a weight of 200 g per m2, the polyurethane gel used is 28 g/m2. After the cotton fabric is covered with rubber particles, it is heated with a 1500W infrared radiator for 20 seconds. If it is, the rubber particles can be uniformly applied to 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. A piece of cotton knitted fabric is put on the hot-melt fabric after the above treatment. On an iron press, the ironing process is performed at a pressure of 64 kPa and 160° C. for 120 seconds, and the two fabrics are firmly bonded. Together. The tear strength of the fabrics bonded by this method is 0.57-0.69 kN/m, the tear strength after washing in a washing machine at 60°C is 0.57-0.67 kN/m, and the tear strength after washing with boiling water is 0.55-0.65 kN/m. , Such as dry cleaning with perchloroethylene tear strength is still 0.55 ~ 0.67kN / m. It was demonstrated that polyurethane hot melt adhesive particles were used to bond fabrics.