Selection of Adhesives for Food and Drug Packaging (4)

2 The solid content is low. Sometimes the solid content of the main agent is unqualified, indicating 75%, only 70% actually measured, indicating 50%, the measured only 42% to 45%; sometimes the solid content of the solid agent is unqualified, it should be 75%, only measured 71% to 72%. Failure of the curing agent is greater than the unacceptable adverse effect of the main agent because it will cause a mismatch in the proportion, the film does not solidify, and is always sticky. Therefore, the peeling force is low, the heat resistance is poor, and the antibiotic is not good. There should be standards for solids content, but there is a ±2% permissible range. Only controlling the lower limit and always having negative tolerances are intentional!
When it comes to the solids content of the glue solution, there is a problem that the detection method is different and the result is also different. At a national technology exchange conference, a company said that his product solids content test method is to take a small area of ​​the film to weigh (set to W1), and then take a small amount of glue sample on it , Take the second weighing (set to W2), the weight of the sample taken is W2-W1, and then put into a 70-75°C oven to dry for 30 minutes, and then take it out for the third time. Weight (set as W3), dry weight of the sample after drying is W3-W1, according to NV% = W3-W1/W2-W1 × 100 to calculate the solid content of the glue (NV%). I think this is wrong.
For the first time, the state has a standard test method for the determination of solids content (also known as non-volatile content), that is, GB/T 2793-1995. Anyone must adopt this unified test method to have fairness, It is fair, reasonable, and accurate. Otherwise, it will be indiscriminate. Secondly, according to his method of inspection, due to the difference in the speed of operation and the degree of proficiency of each person, the resulting value deviates greatly from the actual value. The test result is 50%, which is actually much lower than 50. %. Similarly, the 75% test result is actually well below 75%. This is because:
1 The solid content of the sample at the moment when the sample was weighed and weighed was higher than the solid content of the glue in the original barrel. The reason is that while sampling, it is inevitable that the solvent will continuously evaporate, and the temperature will be high and the operation speed will be much slower. Since there are few samples to be weighed, the denominator (W2-W1) at the time of calculating the solid content is small. A slight deviation will have a great influence on the result value. Therefore, this open sampling method is inaccurate. The resulting value must be higher than the true actual value.
2 Drying under 70°C-75°C for 30min drying conditions, far from drying the solvent in the glue solution, because the solvent in the glue is ethyl acetate, the boiling point is 77.1°C, when the glue layer is thick At the time of baking at 70°C-75°C for 30 minutes, the ethyl acetate could not be fully captured. As a result, at the third weighing, a lot of residual solvent was mistakenly counted on the weight of the dry adhesive, resulting in solid content. Imaginary height. If detected by this method, the true solid content should be higher than 5%, which will impair the practical benefits of using the glue. The basic reason that drives some units to make the solids content low is to reduce costs and increase profits. It is estimated that due to the low solid content of 3% to 4%, the cost per ton can be lower by more than 1,000 yuan, but the user will pay more than 1,000 yuan.
3 The solvent is not pure. This is due to the use of recycled ethyl acetate or deliberately replacing some of the ethyl acetate with toluene for cost reduction. Because of the oversupply, in order to sell it, the raw material cost is used to reduce the cost of ethyl acetate by replacing ethyl ester with cheaper or cheaper toluene. According to the calculation, only by adopting this method on the solvent, the cost per ton of rubber can be reduced by 700 to 800 yuan, but it will have an adverse effect on users and consumers, and there will be residual solvents, odors, and hygienic safety. Potential hazards.
4 The packaging weight is not up to the standard. Under normal circumstances, the main agent is 20kg/barrel and 50 barrels is 1t. However, some plastic production units use the mentality and practice of the purchaser who only counts the number of barrels and do not go to the school scale. There was once a comparison of adhesives used by the supplier, and the two suppliers' glues were all checked on the solids content and the net weight of the package. As a result, it was found that one of the supplier's products was not only 4% lower in solids content. 5%, and the net weight of the package is also low, only 19kg per barrel, 1t will lack 50kg, two projects caused more than 2000 losses. Therefore, to remind all the plastic units, when the purchase, if not a full scale, should also be checked to see if it is genuine. (To be continued)