Incomplete solidification phenomenon and determina

2022-08-22
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Incomplete curing of ammonia resin grade solvent and its determination

the test schedule can be fixed with two-component polyurethane adhesive. After the film is made into a bag, there is a "tunnel" phenomenon near the hot sealing edge, which is easier to peel off after heating, and the adhesive on the film is still sticky after stripping. This accident is called "incomplete curing"

reasons for incomplete curing

first, insufficient curing agent

second, the ripening time is less than, and the bag making operation is carried out in advance. Different isocyanates have different reaction rates, which should be paid special attention to

III. the solvent contains water, free alcohol, acid and other impurities, which consumes the NCO group in the curing agent

IV. when operating in a high humidity environment, the moisture in the air enters the glue. The first two reasons can be controlled through the data obtained from the test. As for the moisture and impurities in the solvent, at present, general printing plants are unable to detect quantitatively, resulting in frequent quality accidents, and the cause of the accident is difficult to define. What quality of ethyl ester can be used in polyurethane adhesive

the national standard GB requires that the purity of ethyl ester should not be less than 99%, and the moisture content should not be less than 0.2%. Obviously, this standard is too wide. Henkel's so-called "ammonia and other materials are not widely used in the field of Construction Engineering". The requirements of the solvent are that the purity is greater than 99.9%, the moisture is less than 300ppm, and the free alcohol is less than 200ppm, which seems too strict. We believe that it is feasible to establish evaluation standards according to the high purity of ethyl ester in China, measure the consumption of water and impurities in ethyl ester on NCO base, and adjust the proportion of curing agent, so as to eradicate incomplete curing accidents

determination of urethane grade solvent

the solvent that can be used for polyurethane adhesive is called urethane grade solvent. Compared with general industrial products, in addition to water, the content of free alcohol and acid must be reduced as much as possible to avoid reaction with NCO group. There is an index to consider whether it belongs to urethane grade solvent, namely "isocyanate equivalent". Isocyanate equivalent refers to the weight of the solvent required to consume 1 mole of equivalent NCO group, and the substances that consume NCO group include the sum of impurities and water contained in the solvent. The isocyanate equivalent of domestic "urethane grade" ethyl ester can reach 5600 grams, and the greater the value, the better the stability. Printing compound enterprises are different from chemical enterprises. In the measurement method we recommend, we use the consumption of "isocyanate value" to measure, which is intuitive and convenient

the test is divided into three steps. First, tmp-td1 adduct (such as yh10 curing agent of GAOMENG company) is used to react with ethyl ester, specifically with water, alcohol and acid in ethyl ester. Then, di-n-butylamine reacts with excess isocyanate to produce urea:

r-nco+hn (C4H9) 2 - rnhcon (C4H9) 2

in the third step, the remaining di-n-butylamine is titrated with hydrochloric acid:

hcl+hn (C4H9) 2- (C4H9) nhhcl

reagent:

① yh10 curing agent

② 2mol/l di-n-butylamine toluene solution. 258g of anhydrous di-n-butylamine was re evaporated, diluted to 1L with anhydrous toluene, and stored in a brown reagent bottle

③ bromocresol green indicator. Dissolve 1 g of bromocresol green in ethanol to prepare a 100 ml solution

④ titrant. 0.5mol/l hydrochloric acid solution

⑤ absolute toluene, absolute ethanol

operation:

at the same time, accurately weigh two parts, that is, judge the worn parts and their specific parts. Yh10 curing agent is required to have the same weight, each gram. Put them into two conical flasks respectively. One of them is for blank test, and the other is to add 20 ml of ethyl acetate to be tested with a pipette to dissolve the curing agent and place it at room temperature for 5 hours. Then add 10 ml of dibutylamine toluene solution with another pipette, shake it violently to mix it, and leave it at room temperature for 50 minutes. After full reaction, add 50 ml of absolute ethanol and 5 drops of bromocresol green indicator into the flask, and titrate with 0.5mol/l hydrochloric acid solution. When the blue color of the sample solution disappears, it appears yellow and remains unchanged for 15 seconds, it is the end point

after the blank test flask is put into the curing agent, add 20 ml of anhydrous toluene, shake well, add dibutylamine solution, place at room temperature for 20 minutes, add ethanol and indicator agent, and then titrate

the value of isocyanate consumed is calculated by the following formula:

nco% = (a-b) × zero point five × 4.2/weight of curing agent (g)

both a and B are the volume consumed by hydrochloric acid titrant (ML), where a is the consumption of ethyl acetate sample and B is the consumption of blank sample

the above-mentioned isocyanate equivalent of 5600 grams of ethyl ester consumes about 4.5% NCO, and the isocyanate equivalent of 2500 grams of ethyl ester consumes 10% NCO base. Of course, it cannot be called "ammonia fat grade" solvent

discussion of analysis results

take the ethyl ester with an isocyanate equivalent of 5600 g as an example, 20 ml of ethyl ester (18 g) consumes 4.5% NCO group in 3 g of curing agent, and the weight ratio of ethyl ester to curing agent is 6:1. The greater the dilution of ethyl ester, the greater the consumption of isocyanate value in the curing agent. Take some varieties of GAOMENG company as an example:

name common working concentration Main: solid: ethyl ester, ethyl ester and curing agent ratio

yh2000d 35% 5:1:6.9 6.9:1

yh501s aluminum coated adhesive 35% 10:1.5:13.2 8.8:1

yh2000s aluminum foil adhesive% 10:1.5: 3 8.. 8: 1

yh501sl 25% 10:1.5:22.5 18:1

yh502 cooking glue 25% 10:1:12 12:1

the ratio of 501s common working concentration ethyl ester to curing agent in the table is about 9:1, and the consumption of nco%:

9 × 4.5/6 =6.75%

the isocyanic acid value of the curing agent is 14%, and the NCO base consumed by the solvent accounts for about half of the total, so it should be safe. The reason is:

first of all, the ratio of NCO group to OH group in the adhesive ratio is about 2:1, and the excess NCO group is used for the consumption of water impurities in the solvent

secondly, the reaction rates of various groups to NCO groups are different. If the relative reaction rate of primary alcohol group is 1, the rate of water is 5 times slower, and the rate of carboxylic acid is 18 times slower than primary alcohol. Even if the relative reaction rate of free alcohol and OH group in the main agent is the same, their reaction probability is also related to the content in the glue

what percentage of isocyanate consumed by ethyl ester is the safety critical point? If it exceeds, how much curing agent should be added? This should be decided by experiment. What is important is that we have the means to monitor the "ammonia grease level, which can also be used to test the anisotropy of non-ferrous metal plates with gbt24183 (2) 009" experimental methods for ear making of metal materials "and gb5125 (2) 008" experimental methods for cup punching of non-ferrous metals ". We have the method of quantitative analysis, which can be used to study more complex dynamic changes, such as the influence of moisture in the gas during production under high humidity conditions on the glue in the ink tray. Here, I hope colleagues in the industry can make wonderful statements

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