Development of the hottest polyether polyurethane

Development of polyether type polyurethane adhesive for shoes

preface

since the 1960s, polyurethane adhesive has developed rapidly because of its good adhesion and high elasticity. As a general non structural adhesive, it is widely used in the bonding of various materials. In recent years, China has become the world's largest shoe producer, with an annual output of more than 4billion pairs of leather shoes (including synthetic leather shoes). The cold bonding process is the main process used in today's large-scale molded shoe industry. According to the different bonding materials, the adhesives used in cold bonding shoes mainly include neoprene adhesives. According to the bonding materials, polymethyl methacrylate also needs to do a good job in promoting biodegradable plastics in a short time, such as methyl acrylate grafted neoprene adhesives, polyurethane adhesives, etc. The main requirements of shoe adhesives are room temperature curing, strong adhesion and good flexibility. Polyurethane adhesive is more and more used because of its good adhesion performance, adhesive process performance, curing adhesive layer toughness, which will show additional visibility, low-temperature curing performance and light color (even colorless) in this year's K exhibition. Nowadays, in European and American countries, 80% - 90% of shoe adhesives are polyurethane

room temperature curing polyurethane adhesive is a two-component adhesive. In the traditional two-component polyester adhesive, the prepolymer takes polyester as the flexible chain segment. Generally, polyester has high viscosity, and the corresponding adhesive has poor flexibility; And most of them are terminated with diisocyanate. During construction, the isocyanate end group is easy to react with moisture in the air; In addition, the low molecular amine curing agent used for room temperature curing is also not acceptable to shoe manufacturers. Therefore, it is necessary to develop a polyurethane adhesive with good adhesion, meeting the process requirements and easy storage to meet the needs of shoe industry and other industries

this paper explores the use of polyether as the flexible chain segment and hydroxyl terminated polyurethane prepolymer as the basis to prepare adhesive (avoiding the reaction between isocyanate end group and moisture in the air). The product has good flexibility, strong adhesion, low viscosity and easy to apply. At the same time, the effects of the relative molecular weight of Polyether Segment and the amount of curing agent on the properties of the adhesive were studied

2 test part

2.1 main raw materials and instruments

raw materials: tetrahydrofuran, acetic anhydride, perchloric acid, TDI, ethyl acetate (the above are chemically pure), desmodurrf

instrument: NDJ-79 rotary viscometer, xll-100a tensile testing machine

2.2 test

2.2.1 preparation of polytetrahydrofuran

the dosage of tetrahydrofuran is 1.6mol, the dosage of acetic anhydride is 0.5mol, and the dosage of perchloric acid is 0.01 ~ 0.05mol. The reaction time is 2.5h. The acetyl polytetrahydrofuran at the end of the product is saponified with 2 times the amount of 0.5mkoh ethanol water solution, the ethanol is evaporated, and the water layer is discharged with a separating funnel. The oil layer is washed to neutral with water, and the water is evaporated under reduced pressure. The residue is vacuum dried to obtain colorless viscous polytetrahydrofuran. The viscosity average relative molecular weight of polytetrahydrofuran was measured by Ubbelohde viscometer with ethyl acetate as solvent

2.2.2 preparation of hydroxy terminated polyurethane prepolymer chain extension reaction

add the metered above polytetrahydrofuran, TDI and ethyl acetate into a dry three mouth bottle with mixer, thermometer, condensing tube and CaCl2 drying tube, heat it in a water bath, control the reaction temperature of 65 ~ 67 ℃, and react for 3h to obtain hydroxy terminated polyurethane prepolymer, which looks like a light yellow viscous liquid

when nco/oh ratio is 0.85, polyurethane has higher bonding strength. The ratio of raw materials for chain extension reaction is: according to nco/oh=0.85, the amount of TDI and PTF is mixed according to the relative molecular weight of PTF, and PTF (W)/ethyl acetate (W) =1

2.2.3 peel strength test

weigh an appropriate amount of polyurethane prepolymer, add a certain amount of butanone to prepare a 35% glue solution, add 6% desmodurrf[containing 20% thiophosphate tris (4-isocyanate phenyl ester), made in Bayer, Germany] as hardener, and then apply it to 150 × On the 25mm2 surface treated PVC leather (or leather) sample or vulcanized rubber sample, each sample is coated twice, placed at about 60 ℃ for 5 ~ 15min until it cannot be brushed by hand, the sample is closed, properly pressurized, and placed at room temperature for 48h. Use xll-100a tensile testing machine to stretch at the speed of 100mm/min at room temperature to test the peel strength of PVC leather PVC leather and leather vulcanized rubber

3 results and discussion

3.1 control of the relative molecular weight of polytetrahydrofuran

the relative molecular weight of polymer has a great influence on the adhesion performance of adhesive, because it affects the wettability and force of adhesive on the bonded surface, so the relative molecular weight of polymer must be controlled within a certain range

the dosage of perchloric acid has an effect on the relative molecular weight of polytetrahydrofuran. When the dosage of perchloric acid increased, the relative molecular weight of polytetrahydrofuran decreased. This is mainly due to the increase of acetyl cation and chain initiation point in the system with the increase of perchloric acid dosage, which leads to the decrease of the relative molecular weight of the polymer

3.2 effect of relative molecular weight of Polyether Segment on viscosity the relative molecular weight of Polyether Segment directly affects the viscosity of polyurethane prepolymer. The viscosity of polyurethane prepolymer increases with the increase of the relative molecular weight of polyether segment. This is because the relative molecular weight of polyurethane prepolymer in chain extension reaction depends on the ratio of hydroxyl terminated polyether and TDI

the relative molecular weight of polyurethane prepolymer can be controlled by adjusting the ratio between the respective advantages and characteristic sections of multi-component composites. When the amount of TDI is constant, the relative molecular weight of polyurethane prepolymer increases with the increase of the relative molecular weight of polyether segment

3.3 effect of relative molecular weight of Polyether Segment on adhesive force

Polyether Segment, as a flexible segment in the polyurethane molecule of this test, the practice of Jinan experimental machine we see in the world should be called material experimental machine. The relative molecular weight of polyether segment has a significant effect on the adhesive force of polyurethane. When the relative molecular weight of polyether segment is around 2300, polyurethane has the maximum adhesive force. If it is higher or lower than this relative molecular weight range, the adhesive force decreases. When the relative molecular weight of hydroxyl terminated prepolymer (determined by the relative molecular weight of Polyether Segment) decreases, the hydroxyl value increases. When the amount of curing agent is insufficient, the crosslinking density decreases, the chemical bond force, intermolecular force and mechanical force generated in the bonding process are small, and the bonding force is low. The relative molecular weight is too large, the fluidity of the adhesive is poor, and the wettability to the bonded material is poor. Moreover, due to the long hydroxyl distance, the crosslinking density is reduced, and the cohesive strength is low, so the adhesive force is reduced

3.4 effect of the amount of curing agent on the adhesive force

the amount of curing agent has a direct effect on the adhesive force of polyurethane. The polyurethane prepolymer with a polyether segment relative molecular weight of 2300 was tested. When the amount of curing agent desmodurrf was 6% (w/w) of the prepolymer, the polyurethane had the best adhesion. If the amount of curing agent is too small, the crosslinking density decreases and the adhesive force weakens. If the amount of curing agent is too much, the curing speed is too fast, which is not conducive to coating the adhesive, and the wettability of the bonded material is poor, which also reduces the bonding force

4 conclusion

polytetrahydrofuran with viscosity average relative molecular weight around 2300 is used as flexible chain segment to synthesize polyurethane, and its corresponding adhesive has good adhesion to PVC leather PVC leather and leather vulcanized rubber. Desmodurrf is used as room temperature curing agent, and the effect is the best when the dosage is 6% (w/w). The adhesive is suitable for cold sticking shoes and other purposes

source: fine chemicals in the 21st century