Solvent-free laminating process significant advantages of cost reduction, energy efficiency, production safety and stability, improve product quality, is a worthy of strong advocacy, very practical value of the production process. The current solvent-free laminating process has not reached full maturity, flexible packaging enterprises in the application process there are still some easily overlooked technical risks, resulting in quality problems. Industry professionals analyzed three of the more common solvent-free composite technology risk control points.
 

Point I: solvent-free laminating to increase the amount of A glue technical risk
Solvent-free composite two-component (A glue and B glue) adhesive mixing ratio generally refers to the weight ratio of A glue and B glue, rather than the volume ratio of the two. The mixing ratio of two-component adhesive is generally determined by the adhesive manufacturer, because different brands and different uses of adhesive ratios are generally different. Although there are many domestic solvent-free adhesive manufacturers, but A glue and B glue weight ratio options are not many, the more common A:B has 100:80, 100:75, 100:50, 100:45, etc.. But in the flexible packaging enterprises in the actual solvent-free composite production, two-component adhesive ratio will appear out of proportion, which will have an impact on the quality of solvent-free composite flexible packaging products.
Case: the composite structure of OPP/VMPET/PE flexible packaging bags, after printing, solvent-free composite process has not appeared after the quality problem, but in the slitting bag, the sealing edge has appeared in the phenomenon of curling.
The structure of the composite flexible packaging bags using a brand of low-viscosity solvent-free adhesive, the actual composite production of A, B glue ratio of 100:67 (Note: According to the above, and closer to the normal ratio of 100:75). In analyzing the cause of the failure, I found that the bag rolled edge at the same time also accompanied by the phenomenon of the inner layer of adhesive is not dry. Originally thought to be the degree of maturation of the composite film is incomplete due to the extension of the maturation time and then slitting bag, bag curling problem still exists, and the opening of the serious deterioration.
In the dry laminating process, there is “improve the curing agent (-NCO component) can improve the composite strength”, the industry is very easy to “copy” this idea to the solvent-free laminating process, which led to a more serious quality accidents.
In fact, in the solvent-free laminating process, whether it is -OH excess or -NCO excess, may lead to the phenomenon of solvent-free adhesive is not dry, just -OH excess caused by permanent non-drying, and -NCO excess caused by transient non-drying, which can also react with water molecules in the air and continue to solidify. Judgment of the two is a simple method, the non-dry composite layer is peeled off, exposed to be placed in the air, if the adhesive layer becomes dry after 24 hours, then it shows that the -NCO component is excessive; still sticky, then it shows that the -OH component is excessive.
Through the above analysis, and then determine the cause of the case, while combining A, B glue ratio situation, it is not difficult to find the bag curling is mainly caused by the A glue (i.e. -NCO) excess, due to the solvent-free composite film volume is larger, usually prolong the effect of the ripening time is not obvious (here must be differentiated from the ripening temperature of the case of low), and then must be introduced to the moisture can react with -NCO to participate in the crosslinking curing reaction.
Some people say that placing a few buckets of water in the ripening room to control the relative humidity of the ripening room can achieve the effect of introducing moisture to react with -NCO. However, the author believes that this is only helpful for the aging of the end and surface of the composite film rolls, and the effect on the middle of the composite film rolls is very small, because in the aging environment, it is difficult for the moisture in the air to penetrate into the middle of the composite film rolls, which will cause the overall aging effect to deviate.
The author believes that a more effective approach is to composite film rolls in the slitting machine for a rewinding and then ripening, while increasing the humidity of the workshop environment (using humidifiers), so that the composite film layers and surface adsorption of a portion of the moisture in the ripening of the moisture will penetrate into the adhesive layer with an excessive amount of -NCO crosslinking curing reaction occurs, thus making the non-drying adhesive layer to further full curing, and then effectively lift the flexible packaging bags! The phenomenon of crimping is effectively lifted.

Point two: solvent-free lamination in the PE film peel strength decay risk control
Film blow molding will add a certain amount of talcum agent, in order to reduce the friction between the film, film and equipment, so that the film surface is smoother, so that the composite film in the production process as well as the packaging machine runs more smoothly. Usually, PE film will be moderately added to the excessive amount of talcum agent, which can be solvent-free composite film to a certain extent to solve the phenomenon of abnormal increase in the coefficient of friction after aging, but this will also lead to the peel strength of the composite film attenuation occurs, serious, in the completion of the aging of the composite film can be detected at the completion of the peel strength of the composite film does not meet the standard, and most of the cases are in the composite film placed in the process or in the process of circulation of the flexible packaging bag, only to Peel strength attenuation. I hereby analyze two actual cases as a reference.
Case 1: composite structure for the BOPA / PE film
Main parameters: a brand of solvent-free adhesive, glue coating amount of 1.5g/m2, 40 ℃ temperature ripening 24 hours.
The composite film peel strength of the tracking test data are as follows:
Detected on October 13th: transverse peel strength is 15.37N/m.
Detected on November 4: the transverse peel strength was 4.62N/m.
After peeling off the composite layer, there was a layer of foggy substance on the surface of PE film which could be wiped off by hand, as shown in Fig. 1.
January 18 detection: lateral peeling strength of 4.69N/m.
Close to the last test data, indicating that the peel strength of the composite film has reached a stable value.
Usually, flexible packaging companies only shortly after the ripening of the peel strength of the composite film for testing, rarely tracking test placed in the process of the composite film or the circulation process of the peel strength of the flexible packaging bag whether the attenuation, should be noted here.
Case 2: composite structure for the matte OPP / PET / antistatic PE
Main parameters: a brand of solvent-free adhesive, glue coating amount of 1.5g/m2, 42 ℃ temperature ripening 24 hours.
The same selection of three time points for peel strength tracking test, the test results are: longitudinal peel strength of 2.08N/15mm (PET film fracture), 1.82N/15mm, 1.79N/15mm; transverse peel strength of 2.97N/15mm, 2.75N/15mm, 2.69N/15mm, respectively.
Longitudinal peel strength attenuation is serious, transverse peel strength attenuation is not obvious, and in the last test was also found on the surface of the PE film there is a layer of white material that can be wiped off by hand, with a solvent wipe shows that the adhesive layer on the PE film side.
From the above two cases can be seen, the migration of solvent-free adhesives in the PE film will be smooth agent out of the migration, which is the main reason for the peel strength of the composite film attenuation, the author suggests that can be used to resist the migration of solvent-free adhesives smooth agent to add formulations, so that you can not only solve the problem of the coefficient of friction of the PE film in solvent-free composite changes can be resolved, you can also solve the problem of peel strength of the attenuation.

Point three: pay attention to identify the odor characteristics of solvent-free adhesives
There have been people asked the author: “structure OPP/VMPET/PE composite film, the use of solvent-free composite has a residual odor, while the use of dry composite is not, may I ask what is the reason?”
Caused by the flexible packaging pouches produce odor more factors, such as residual solvents, ink resins, film raw material resins, adhesives, etc., although solvent-free lamination does not exist in the process risk of solvent residue, but the solvent-free adhesives in the resin and the formulation of a certain odor characteristics, some of which are in the composite curing, and even also some after the packaging contents still have a certain impact. For flexible packaging companies, we must pay attention to identify the solvent-free lamination of the composite film after the odor, prevention is better than cure.
On the composite film odor detection methods, GB/T 10004-2008 “packaging plastic composite film, bags dry composite, extrusion composite” standard has relevant provisions.
(1) In the GB/T 10004-2008 standard provides for packaging sensory index testing methods: open the box and lining of the packaging film, instantly smell whether there is an odor.
(2) GB / T 10004-2008 of 6.6.16.2 provides, take 10cm × 10cm of a film, cut into strips, into a vessel containing 150ml of distilled water, seal the lid, into the oven or water bath at 60 ℃, 30min after removing, open the lid, smell the odor of the water vapor, to determine whether there is an odor.
(3) Method 2 is actually less used, usually take a certain area of the composite film, cut up and encapsulated into a 500ml glass bottle, baked at a temperature of 60 ~ 80 ℃ for 30min, sensory detection of whether there is an odor. The bag can also be sealed into the air or the actual contents of the bag, rotating at a temperature of 50 ~ 60 ℃ for several hours, tear open the package, sensory testing whether there is an odor.
The odor of the composite film mainly comes from the solvent-free adhesive, so the general odor characteristics of solvent-free adhesive, can be used to identify the following methods.
(1) Take a certain amount of different brands of A adhesive and B adhesive, sensory testing for comparison.
(2) The same structure of raw materials composite film, with different solvent-free adhesive composite, take samples according to the composite film odor judgment method 2 for identification.
(3) will be mixed according to the instructions proportion of solvent-free adhesive added to the glass bottle (the bottom of the bottle pad Zhang plastic monolithic film, adhesive curing convenient to take out), at 40 ~ 50 ℃ crosslinking reaction 24 ~ 48 hours, to identify its odor characteristics. This method is more suitable for practical applications, including the odor characteristics of the resin itself, the low molecular weight components that are not fully reacted may produce the odor characteristics, crosslinking and curing may exist when the odor characteristics of the side reaction products.