First, the composite film appeared “point”
Solvent-free composite process implementation, the composite film appears “point” is a relatively common anomaly. Its causes are physical and chemical reasons.
Physical causes of the “point” and chemical causes of the “point” whether from the external appearance, formation mechanism and solutions are different. Therefore, this “point” is not the other “point”, should be carefully screened and treated separately, can not be “the same”.

1, the physical causes of the formation of “points”
(1) Appearance: irregular distribution, often the number of different areas of the ink layer thickness is different.
Cause analysis: the amount of glue is too small. Coated glue is not enough to fill the gap in the ink layer in the composite film and the pits on the surface of the material, the formation of the “point”. In fact, no glue and the formation of the “gap”.
Solution: increase the amount of glue.
(2) Appearance characteristics: some “points” periodically concentrated and repeated in a fixed area of the pattern.
Reason analysis: because in the transfer steel roller, transfer roller, coating steel roller, coating roller, a roller on the adhesion of foreign objects, or a roller on the mechanical defects, resulting in a specific area on the amount of glue transfer bad, and the formation of the “point”.
Solution: According to the length of the periodic recurrence, compared to the circumference of the rollers, to find out where the problem is the roller, and clean up foreign objects or repair defects.
2、Chemical reasons for the formation of the “point”
External characteristics: irregular distribution, but the distribution of a wide range of “points” of different sizes, especially in wet weather, good barrier (such as aluminized film) is more likely to occur when the material structure of the composite.
Cause analysis:
Two-component solvent-free adhesive in the isocyanate (-NCO) component and the water in the air to produce derivatization reaction, the generation of carbon dioxide gas, because these gases can not be precipitated from the barrier of good composite film, silt collection in the formation of composite film between the “point”.
Therefore, these points are actually carbon dioxide “bubbles”.
3, how to avoid the composite membrane “point”?
(1) Avoid “points” in the laminated film caused by insufficient glue or uneven glue application by the following measures:
Reasonably set the amount of glue applied to various composite structures.
Pay attention to keep the coating unit rollers clean, clean up the adhering foreign matter in time.
Often check the surface condition of each roller of the coating unit, and replace the roller with defective surface in time.
Reasonably set the level of glue in the storage tank, often observe the status of the glue in the tank, and deal with the abnormal phenomena such as the mixture of glue siltation, viscosity, lumps, and so on in a timely manner.
(2) through the following measures to avoid the composite film due to the reaction of water and glue in the air caused by the “bubble”:
Control composite operation, curing environment humidity, general relative humidity control in 70% or less;.
Regularly replace the glue mixer storage drum desiccant, to ensure that the air inside the storage drum is dry.
Glue drums (especially curing agent components) open, if there is a surplus of glue, should be closed tightly in time, and as soon as possible will be the surplus of glue with out;
Create a relatively closed space for solvent-free laminating process operation, which is conducive to the control of temperature and humidity.

Second, the composite film peeling force is not enough
Composite film peeling force is not enough, according to the phenomenon can be divided into categories: into batches of full-width peeling force is not enough, local peeling force is not enough (such as local curing or curing bad), transfer phenomenon (such as the transfer of ink or the transfer of the aluminum layer) and so on. The causes are various, but mainly belong to the physical causes.
How to effectively reduce the phenomenon of insufficient peel strength of composite film?
Try to use qualified materials (qualified surface tension, strong adhesion of the adhesive layer), if necessary or possible, install online corona equipment.
Choose the most suitable brand of adhesive for your company's product characteristics.
Strictly in accordance with the instructions and requirements of the use of adhesives, adhesive warehousing, and in accordance with the relevant regulations and requirements of the correct use of adhesives.
Try to use automatic mixing machine mixing, strictly according to the regulations of the correct use of mixing machine, and ensure that the mixing machine is in a normal state.
Table 1 Reasons and solutions for insufficient peeling force of composite film

On the composite film “transfer” phenomenon, there are “ink transfer” and “aluminum transfer” two kinds, sometimes a single phenomenon, sometimes at the same time. But the performance is often one of them, because when one of the phenomena (the weakest strength) appeared, the other is often covered up and ignored.
1, the reasons for the generation of transfer
Any change in the shape of the object will produce stress. Solvent-free adhesive curing process, in fact, is also the adhesive from the liquid state into a solid state, this process produces “deformation stress”. Composite film to produce “ink transfer” or “aluminum transfer” is the direct cause of the adhesive curing process “deformation stress” caused by: when the ink or aluminum layer and plastic film between When the adhesion between the ink or aluminum layer and the plastic film is much smaller than the deformation stress generated during the curing of the adhesive, it is easy to produce transfer.
2、Prevention and improvement methods
Transfer phenomenon can be prevented, improved or resolved through a variety of initiatives.
First, the use of surface corona better substrate for printing, to ensure that the printing ink adhesion is higher; composite aluminized film when the choice of higher adhesion of aluminized film.
Secondly, through such as fine-tuning the ratio of A/B glue, adjust the order of the three-layer composite, reduce the curing temperature appropriately (extend the curing time to ease the “deformation stress” intensity) and a series of technological adjustment measures to prevent, improve or solve the phenomenon of ink transfer / aluminizing transfer.

Third, the composite film friction coefficient increases
Composite film friction coefficient increases, often occurs in PE, CPP film as a heat sealing layer in the composite structure, especially when the heat sealing layer is thinner more likely to occur, but also caused by the results of curing the composite film smoothness is not good or to affect the opening of the bag after making.
1. Causes
The heat sealing film material itself is not enough to add smooth agent, the film itself is not good smoothness.
Solvent-free adhesive contains a pre-polymer as a “polyether” component, it is in contact with the film, under certain conditions will react with the film in the smooth agent (the intensity of the reaction has a greater relationship with the temperature), excessive consumption of film in the smooth agent, resulting in an increase in the coefficient of friction of the composite film, smoothness is not good.
Smooth agent in the main component - amine and solvent-free adhesives in the NCO component (A glue) reaction (the formation of urea, and then the formation of polyurea), the film in the smooth agent is too much consumption, resulting in increased friction coefficient of the composite film.
2、Measures to prevent or improve the increase of friction coefficient of composite film
According to the order from easy to difficult, can use a variety of initiatives to solve or improve:
In order to meet the peel strength as well as to ensure that the premise of not out of the point, appropriate reduction in the amount of adhesive coating (close to the critical);.
Appropriately reduce the operating temperature and control the curing temperature (e.g., ordinary compounding 33 ~ 38 ℃), in the summer time can be considered room temperature curing;
Procurement of smoothness of better film (or blowing film to increase the amount of smooth agent added).
Choose a more suitable brand or model of adhesive.
Appropriately reduce the laminating film winding tension.
Fourth, the printing ink is “halo”
In the implementation of solvent-free composite process, the phenomenon is not a common anomaly (but once encountered, the consequences may be very serious), there does not seem to be a fixed or standardized terminology, some people figuratively referred to as “ink-glue miscibility”, some people call it “ink staining “.
1, the problem case (Figure):
(1) Problem samples 1: after compounding the red ink edges produce halo phenomenon, replace the red ink, the phenomenon disappeared.

(2) Problem sample 2: green ink and adhesive “miscible”, replace the green ink, the phenomenon disappears.

Cause analysis:
This is a physical phenomenon. Solvent-free adhesive formula design, will contain some permeability components, when it comes into contact with the ink, if the ink also contains easy to dissolve in the components of the composition, it will cause the second dissolution of the ink, resulting in the formation of “halo” (or “miscible” phenomenon). phenomenon).
Solution:
This printing ink is “miscible” phenomenon, generally by adjusting the ink to solve.

Fourth, the conclusion
Through the analysis of the above process anomalies, giving us an important revelation. That is, in the implementation of solvent-free composite process, the “new composite structure” of the process test, is an important part of the essential.
1, what is called “new composite structure”?
The so-called “new composite structure”, is the first time this enterprise products using solvent-free composite process product structure, including substrates, inks, glues, facilities and other elements, as long as there is a change in one of the elements, have become “new structure”.
2, the content of the process test
A small amount of process test on the product to be used in solvent-free laminating process, to adjust and confirm the compatibility and matching of the elements in the process system, and to confirm the most suitable tension, pressure, gluing amount and other relevant parameters in the operation process, and to confirm the suitability of the subsequent processing.
3、The significance of process test
Discover potential problems, early adjustment and solution to avoid unnecessary losses.
Provide relevant basis for subsequent production to ensure smooth and efficient mass production.