The influence of the hottest ink on the dry phenom

2022-08-08
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The influence of ink on the dry phenomenon of composite film adhesive layer

some flexible packaging manufacturers often encounter the dry phenomenon of composite products after 24-48 hours of ripening. Some manufacturers have also announced their annual targets. They found that the cured products have wrinkles through bag making and heat sealing, and the glass strength between layers is better by peeling off the crown insulation. I don't know why this is caused. In fact, this is directly related to the non drying of the composite film adhesive layer. The phenomenon of non drying often occurs in spring and summer with high temperature and humidity, and is not easy to occur in dry autumn and winter. The non drying of dry composite film will seriously affect the quality of composite products, and we hope to attract the attention of flexible packaging manufacturers

I. Analysis of the phenomenon that the composite film does not dry:

after the composite product is cured at a certain temperature and time, the adhesive layer of the interlayer peeling composite film still has a certain viscosity, that is, after the peeling of the Rockwell hardness composite film, use your hand to re stick the two layers of film together, and the two layers of film will re stick together. The serious dryness of the composite film adhesive layer will directly affect the peeling strength of the composite film, while the slight dryness will lead to poor heat sealing strength after bag making, viscosity after interlayer peeling, and wrinkles are easy to appear in the heat sealing place. In addition, after the composite film is matured, it is processed and made into bags, and there is no folding phenomenon, but the folding phenomenon of packaging bags does not appear until it is stored for a week or half a month. If this phenomenon occurs, the loss is often large. These phenomena are analyzed as follows:

1. Analysis of adhesives: the main agent of polyurethane adhesive is a high molecular polyester and polyurethane compound terminated with - Oh, which has a certain viscosity. The curing agent of polyurethane adhesive is a polyurethane compound containing - NCO (isocyanogen) terminated. The main agent of polyurethane adhesive has high peel strength only by reacting with isocyanide in the curing agent to produce a cross chain structure. The isocyanide in the curing agent of polyurethane adhesive is very easy to react with substances containing hydroxyl and amino groups (water, alcohols, amines). Its reaction mechanism (see Formula 1):

Formula 1

- NCO + H2O → - nhcooh → - NH2 + CO2

- NCO + - NH2 → - nhconh -

from the two formulas, we can see that one water molecule can react with two - NCO groups, the molecular weight of one water molecule is 18, and the molecular weight of - NCO group is 42, that is, 18 grams of water, can react with 42 × 2 = 48 G - NCO group reaction

generally, the solid content of the curing agent of polyurethane adhesive for dry composite is 75%, and the content of 75% curing agent NCO is about 13%. Then the amount of curing agent that needs to consume 75% of 18 grams of water is 84/13% = 646 grams. We assume that the water content of 20kg ethyl alcohol is 0.2% (according to the national standard), so the water content in 20kg ethyl acetate is 40g. If the reaction is complete, 1.435kg of curing agent will be consumed, and it can be decomposed into 2 carbon oxide and water curing agent in 3~6 months

the reaction speed between the main agent of polyurethane adhesive and curing agent is generally related to the amount, temperature and concentration of catalyst. The more the amount of catalyst is, the faster the reaction speed is. The higher the temperature is, the faster the reaction speed is. The greater the concentration is, the faster the reaction speed is. The same is true for the reaction of water and small molecular alcohols with the curing agent. Their reaction also takes a certain time, but it is 10-20 times faster than that of the main agent and the curing agent. In the actual compounding, the water and alcohol in the solvent will be volatilized in the oven, so what we need to do is to make as much water and alcohol volatilize in the oven as possible, so as to reduce the phenomenon of non drying

from the above analysis, the main reason why the adhesive layer does not dry is that the cross chain reaction between the main agent and the curing agent is not complete, that is, some main agents do not react with the curing agent, because the main agent is a viscous substance, so the adhesive layer of the composite film is viscous. It affects the quality of products. The reason for incomplete crosslinking between the main agent and the curing agent is that a large amount of - NCO groups in the curing agent are consumed by water or alcohols

2. When the PET film containing K coating is compounded, it will also appear dry phenomenon. The dry phenomenon of this kind of products' compounding is often closely related to K coating. Therefore, prevention work should be done during compounding, and the prevention method is to appropriately increase the amount of curing agent (increase by 5-10%)

3. The quality of PET film is poor, and the additive components contained in the film are unstable, which will also cause dryness, because the amine components contained in the additives will also react with the curing agent to produce powdery white substances. But this kind of phenomenon is often relatively rare

4. The use of polyurethane and polyester inks can also easily cause the adhesive layer to dry. Firstly, the polyurethane ink system is analyzed. The composition of polyurethane ink: pigment, polyurethane resin, additives, solvents and so on. The diluent solvent components of polyurethane ink generally include: butanone, ethyl ester, butyl ester, isopropanol, toluene, etc

alcohols with - oh and substances with - NH2 have great interference on post compounding. The polyurethane resin in the ink is also - Oh terminated, and can also react with the curing agent of polyurethane adhesive

5. Fast curing polyurethane adhesives are used. Some fast curing polyurethane adhesives often increase the reaction speed between the main agent and the curing agent by increasing the amount of catalyst, but at the same time, it also improves the reaction speed between water and alcohol and the curing agent. If the water or alcohol in the solvent is a little higher, the curing agent in the glue will be destroyed by water or alcohol before entering the drying channel and there is little left. This will cause inaction

II. Judgment of non drying phenomenon of composite film

through the above analysis, we believe that the non drying of adhesive layer is caused by the following reasons:

1. The proportion provided by the glue manufacturer is inaccurate, the proportion of curing agent is too small or the proportion is misadjusted when preparing glue, and the curing agent is too small or ineffective

2. In addition, the water content of diluted solvent or the content of small molecular alcohol is too high, which consumes a lot of curing agent

3. Film moisture absorption, especially NY and peel paper, is easy to dry; As the cathode material, the price of 4.35v lithium cobalt oxide has risen to 260000 yuan/ton

4. The alcohol solvent contained in the ink used did not volatilize, which completely caused the adhesive layer to dry

5. The adhesive layer does not dry due to the use of polyurethane and polyester inks

6. The environmental temperature and humidity are too high, and the prepared adhesive is placed for too long, resulting in the long-term reaction between the curing agent and water

7. PET film composite containing K coating and the influence of additives in PET film

III. solution to the non drying phenomenon of composite film

1. Generally speaking, the proportion provided by the adhesive manufacturer is a reasonable proportion obtained through a large number of tests by the adhesive manufacturer. Therefore, there will be no inaccurate proportioning. If it is really due to the quality of the adhesive itself, the adhesive must be replaced

2. Reduce the total content of water and alcohol in ethyl acetate (replace ethyl acetate with good quality, and the total content of water and alcohol is less than 0.2%)

3. When compounding NY and cellophane films that are easy to absorb moisture, adjust and increase the proportion of curing agent (5% ~ 10%), and do not use damp films at the same time

4. Try to reduce the amount of residual solvent in printing ink

5. When using polyurethane ink:

the first thing is to solve the composition of dilution solvent in polyurethane ink, and try not to use alcohol dilution solvent. If alcohol diluents must be used during printing, try to minimize the residual solvents during printing

secondly, if there is a white ink backed printing film, and finally add a small amount of hardener to the white ink, the composite fastness can be increased. However, the service life of the ink with hardener is short. If there is surplus and the interval is long, it should not be used again in principle

finally, the purity of ethyl acetate used for diluting adhesives should be high, and the content of water and alcohol should be as low as possible, which is the quality assurance of cooking bags and dry compounding. In addition, when preparing adhesives, appropriately increase the amount of curing agent (the increase proportion is between 5% and 10% of the curing dose, that is, adding 1 kg of curing agent requires adding 0.05-0.5 kg of curing agent) to ensure that the main agent of adhesives and curing agent are fully crosslinked

6. We must control the compound environment, such as placing exhaust fans indoors and strengthening indoor air circulation, but be careful not to blow against the compound machine. When compounding, always pay attention to the scraper and guide roller near the rubber groove to see if there are water drops, and reduce the speed at the same time, because the speed is too fast, and the local temperature near the rubber groove is too low, which should cause water vapor condensation

7. Shorten the storage time of the prepared adhesive. When preparing the adhesive, reduce the amount of preparation each time, increase the number of preparation, shorten the storage time, and increase the drying channel temperature to reduce the amount of residual solvent. In this way, the influence of water and alcohol on the curing agent will be reduced, and as much water and alcohol as possible will volatilize in the drying channel

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