Development of the hottest polyurethane lotion adh

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Development of polyurethane lotion adhesive (II)

2 results and discussion

2.1 physical properties of lotion

2.2 effect of reaction temperature

because the reaction between isocyanate group and active hydrogen is very sensitive to temperature, with the rise of reaction temperature, cross-linking reaction is easier than chain growth reaction. At high temperature, the viscosity of the system increases sharply to form gel. In this experiment, the reaction temperature has been tested for many times from 80 ° C to 50 ° C. It is found that the reaction should be controlled at 50 ~ 60 ° C. within this temperature range, the reaction is relatively gentle, and the reaction time is about 3 hours. After forming a certain viscosity, uniform and transparent solution, it is neutralized and emulsified

2.3 selection of synthetic process

castor oil is a glyceride of enoic acid containing hydroxyl, which is a natural product, reflecting that dehydration must be carried out before. Its viscosity is large, and the viscosity increases rapidly in the reaction with TDI. The molecular chain of the resin is linearly increased by chain extender. After grinding and drying, tartaric acid is dissolved in a small amount of butanone and added into the system. The hydrogen atom on the hydroxyl group reacts with the end NCO group of the prepolymer, and -cooh group is introduced into the macromolecular chain. At the same time, tartaric acid also acts as an acid catalyst to a certain extent, inhibiting the cross-linking reaction. The addition of a small amount of butanone solvent can reduce and adjust the viscosity of the system. The last small amount of butanone is added at the same time of adding alkaline aqueous solution, and strong stirring is the key for good emulsification to strengthen pre communication, in-process reconciliation, and post inspection

2.4 effect of tartaric acid dosage

tartaric acid (2,3-dihydroxysuccinic acid) is introduced into the molecular chain structure of polyurethane as a hydrophilic monomer, and polyurethane is dispersed in water to make a self emulsifying lotion. Its hydrophilic group is hydroxyl, so the lotion is anionic. When the dosage is appropriate, the self emulsifying stable lotion can be formed under certain reaction conditions. Table 2 lists the influence of tartaric acid dosage on the stability of lotion. The catalytic effect of tartaric acid in the reaction has been mentioned before. Experiments have found that if tartaric acid is not added or added late, the prepolymer formation reaction is easy to produce gel. It can be seen from table 2 that the amount of tartaric acid accounts for 3% by weight of resin Stable lotion can be formed between 4, with moderate viscosity and certain fluidity

2.5 influence of nco/oh ratio

the main component of sesame oil is glyceride of 9-alkenyl-12-hydroxyoctadecanoic acid, with a content of more than 90%. The hydroxyl value is about 163, containing 4.94% hydroxyl, and the hydroxyl equivalent is 345. According to the hydroxyl standard, it can be considered that the sesame oil contains 70% triglyceride and 30% diglyceride, with an average functionality of 2.7. Because there are many trifunctional components, in order to avoid cross-linking reaction, in addition to controlling the reaction temperature not to be too high, it is also important to select the proportion of nco/oh for prepolymer. Experiments carried out at the ratio nco/oh=1.02 ~ 1.4 show that when nco/oh is less than 1.3, gel does not occur. At this time, the ratio of isocyanate group to total hydroxyl (including chain extender and hydrophilic monomer) is less than 0.8, which ensures that -nco does not react with water

2.6 neutralizer

in principle, all compounds containing alkaline groups can be selected as neutralizers. This system has tested the commonly used alkali sodium hydroxide, ammonia and triethylamine as neutralizers. The results show that the lotion particles obtained by using the first two neutralizers are coarse and have poor uniformity, while when using triethylamine as neutralizer, the lotion particles are small and very uniform

2.7 water resistance

the changes of water absorption and dissolution rate of adhesive film with time are shown in Table 3. The long-chain nonpolar fatty acids of the linseed oil component of the lotion film are hydrophobic. Due to the introduction of hydrophilic groups and the hydrophilicity of ether bonds in the chain extender, the water resistance of the film is reduced. In the four parallel water resistance tests, although the repeatability of the data is not good enough, the trend of the data given is the same. Take test No. 1 as an example to see the changes of water absorption and dissolution rate with time, as shown in Table 3. Table 3 shows that the water absorption and dissolution of the adhesive film tend to slow down after soaking for one day. The dissolved may also be free chain extenders or small molecules such as tartrate

2.8 testing the bonding strength of lotion adhesive to different materials

testing the glass separation strength of soft materials, such as between cord fabrics, between canvas and PVC artificial leather, the results are not ideal, the data is 2 ~ 5n/25mm, the main reason is that the adhesive is difficult to solidify at room temperature, and there is no further study on the results of heating and curing. For the bonding between hard materials, such as PVC hard board, aluminum board, wood board, steel plate and other materials, it is found that the adhesive has good bonding strength to steel plate, and the shear strength tested is related to the heating and curing temperature of the style. Such a base material is 08F steel plate. The size is length x width x thickness =10025x2, in mm, the lap length is 12.5mm, glued twice, dried for half an hour, and placed at room temperature. The traditional halogen and other flame retardant systems are greatly limited. After 24 hours, the shear strength measured strongly depends on the curing temperature. In order to find the best reaction conditions, Adopt the formal experimental design method for optimization

under the condition that the process operation process remains unchanged and the amount of linseed oil remains unchanged, the amount of a-tdi is proposed to change four factors; B-type of chain extender; Dosage of c-tartaric acid; D-reaction temperature. Factor a takes four levels, and the other three factors take two levels. Change the orthogonal table L16 (215) to orthogonal table L16 (41x212) [4] so that four level factors can be arranged on the two-level table. See Table 5 for specific arrangements. The inspection index is that the quality of the flat vacuum heat insulation board bonded with 08F steel plate by adhesive has some differences with that of foreign countries. The shear strength test results are in n/cm2, and the curing temperature is 160 ℃. The amount of linseed oil used in the test is 100 parts by weight. After 16 tests, evenly dispersed lotion with good fluidity was prepared within the variation range of each level of the above four factors, which can be directly used as the top adhesive for bonding a variety of materials. The following is a visual analysis of the influence of each factor on the shear strength. Table 5 shows the sum of test results corresponding to levels 1, 2, 3 and 4 in column J respectively. Divide them by the number of tests to obtain the average test results corresponding to each level of factors in column J respectively. Subtract the minimum value from the maximum value of the average value to the range of each level. The factor with the largest range has the greatest impact on the test results, while the factor with the smallest range has little impact on the test results. Through comprehensive comparison, the optimal reaction conditions can be obtained. Within the range of test changes, the dosage of TDI is 29.2 (parts by weight); The chain extender is 1.4-butanediol; The optimum reaction conditions are tartaric acid dosage of 4.17 parts by weight and reaction temperature of 60 ℃

3 conclusion

(1) a water-based system with linseed oil and toluene diisocyanate as the main raw materials, butanediol or diethylene glycol as the chain extender, tartaric acid as the hydrophilic monomer, triethylamine as the neutralizer can produce a uniform and stable polyurethane lotion adhesive under the process conditions described in this paper

(2) the bonding strength of the adhesive is strongly dependent on the curing temperature

(3) the optimal reaction conditions by orthogonal experimental design are: the amount of linseed oil is 100 parts by weight; The dosage of TDI is 29.2 parts; Tartaric acid is 4.17 parts; 1.4-butanediol as chain extender; The reaction temperature is 60 ℃

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