9 questions about nylon membrane

1. Why is the nylon membrane easy to absorb moisture?

Nylon is mainly composed of a dibasic acid, a diamine-free or a polycondensation of an amino acid group. Because the polyamide molecule contains a very broad amide group, in the production, not the molecules in the polyamide can crystallize and molecularly coordinate, and there are also some non-crystalline polyamide polar genes, which are partially amorphous. The amide group in the polyamide molecular chain can coordinate with water, that is, it has water absorption and can absorb water molecules with strong polarity. When it is serious, a water film is formed on the surface of the film to make the nylon film barrier and airtight. Greatly dropped.

2. Why does the nylon film sometimes produce color migration and color penetration after printing?

Color migration and color infiltration are two different concepts:

1) The color migration is mainly because the small molecules of the pigment in the ink layer do vigorous brilliance movement under a certain temperature, thereby separating from the lattice formed by the weak intermolecular force, and following other organic molecules to do the migration movement and spreading the color;

2) Color penetration means that the plastic printing substrate is superposed on top of each other, and the surface of the lower substrate is printed with the pattern printed on the substrate.

The main reason is that in the plastic film polymer printed with the ink film, the polymer moves vigorously to form a gap with pores. When the temperature rises, the pores also expand and become larger, and at this time, the pigment molecules also make a sharp brown. When they move, they will spread and penetrate through the pores. In particular, green lotus, pink, etc. are more prone to color penetration.

The diffusion and penetration of the pigment molecules is mainly carried out in the amorphous region during the thermal movement of the polymer chain of the plastic film. Nylon film, non-linear polyethylene and other types of film are amorphous plastics, due to their low crystallinity, large molecular gap, especially in high temperature and humidity environment, easy to heat deformation, large water absorption, hot water solution. Therefore, the plastic film of this type is more susceptible to the penetration of certain colors.

3, nylon membrane composite PE, the peel strength can be ok when the machine is off, but the reason for easy peeling and tearing after curing for 16h?

There are several phenomena:

1) Whether the corona surface treatment degree of raw materials (printing materials and heat sealing materials) is up to standard (PA-52dny, PET-48dny, PE-40dny);

2) Additives (auxiliaries) for printing and heat-sealing materials. Too much to be heated and floated to degrade the composite layer and easily peel off;

3) The amount of glue is not enough. Generally, the blank small bag should have 2.5g/m2 below 200g, the ordinary bag should be 3g/m2, the boiled bag should reach 4.5g/m2, and the retort bag should be more than 5g/m2. (refers to the amount of dry glue) refer to GB/T10004---2008 standard;

4) The smoothing dose of the PE film is too high, that is, the additive content is above 500 ppm, and the thickness of the film is thick (more than 60 um). The additive is added too much and the peeling degree is low;

5) The curing conditions do not meet the requirements, or the curing time is too short. The thorough cross-linking of different adhesives is different. In order to ensure the complete cross-linking of the glue, different curing processes should be adopted for different grades of glue and different uses;

6) Climate conditions. Generally, more than 80% humidity is very unfavorable for dry compounding, and should generally be controlled at 23 ° C ± 3 ° C and humidity 65% ​​± 5%;

7) The intrinsic quality of the adhesive. The first is the percentage of curing agent. Generally, the percentage of curing agent is less than 2%. The viscosity of the water should be greatly reduced. Secondly, the proportion of curing agent should not be too large. If it is too large, the composite film will be brittle and tear.

(Solvent-free compounding is very strict on the curing process, and is discussed separately)

4. Why does the nylon membrane composite CPP have a sporadic blistering phenomenon?

In this case, the glue bubbles are too high or the nylon membrane is damp, and the residual solvent in the composite layer is too much. In the humid climate of the south, this is a common problem in cooking and packaging. At this time, it is necessary to increase the circulation amount of the glue in the glue tank, to suppress the occurrence of bubbles, or to increase the drying temperature of the printing and laminating machine, or Increase the curing agent by no more than 5% in the glue, and when the weather is good (humidity is less than 70%), the printed nylon film should be compounded immediately, or wrapped in aluminum foil. Do not leave it for too long (within 5 minutes) to prevent the nylon film from absorbing water. Get wet and create bubbles.

5. What is the reason why the nylon membrane is used as a surface layer composite and re-cooked to cause delamination?

Due to the water absorption of nylon, nylon membranes are more problematic for surface layer printing, composite re-cooking or cooking, which seriously affects the peel strength. Therefore, general boiling-type adhesives do not dare to use adhesives below 121 °C. In BOPA/PE (115 °C), BOPA/CPP121 °C structure, only 135 ° C retort adhesive can be used, that is, the temperature resistance of the glue is increased by one grade and the amount of sizing is appropriately increased. It is better to use a waterproof coating to prevent moisture from entering the nylon membrane. A small amount of yellowing after the nylon film is cooked will cause color difference in the package, so pay special attention.

6. What is the reason for BOPP film material combination, which will generate bubbles after a period of time and BOPP will not?

BOPA is a kind of material with good barrier property, and there are many residual solvents in the printing compounding process. After curing, it cannot be volatilized through the film and remains in the film interlayer. This is due to the residual moisture and the curing agent in the adhesive. The isocyanate group reacts to form a carbon dioxide-based gas residue. However, BOPP has a weak barrier property. By curing, some of the solvent remaining in the film interlayer is volatilized from the surface layer of BOPP. Therefore, in general, the BOPP film has less bubbles after composite ripening.

7. Does the OPA/AL/RCPP material combination crack or even break in the aluminum foil at the seal?

BOPA film and aluminum foil are all materials with certain ductility, but the phenomenon of cracking occurs in the heat sealing of the packaged bag. Generally, the extension of the heat-sealing knife applied to the packaging material exceeds the acceptable level of the material. The resulting heat seal layer is thus crushed. If the automatic packaging double roller heat sealing, it should also consider whether the uneven shape of the double roller is too sharp and pierce the extrusion to break the aluminum foil layer into a black line crack.

8. When using BOPA/AL/PE (15.07.60um) composite, the edge of the bag heat sealing is easy to produce delamination?

Since the heat sealing temperature of the bag is high, and the heat sealing temperature of the heat sealing position is generally increased by two heat sealing. In the heat sealing position, it is in a blank transparent state. Low molecular substances (slip agents, etc.) in the film will permeate up to the surface at a high temperature, causing degradation and delamination of the adhesive. On the other hand, the oil in the production process of AL is not completely removed, and a large heat-peeling distance is generated during heat sealing to cause delamination.

9. Why is there a nylon film combination, and the printing ink containing the sauce bag is easy to fade?

Material combination B0PA/AL/LDPE or PA/CPE. In fact, no matter which kind of film combination has a phenomenon. Fading mainly caused by contents. Pickles are solid-liquid coexisting foods containing various seasonings. The chemical composition is the same as that of mustard bags. Many of them are highly permeable chemicals. For this reason, the inner layer can not be used with LDPE or CPE, and it is better to use a cold-resistant CCPP (rogue co-polypropylene) which can withstand 10 degrees below zero without brittleness, so that the chemical change is less likely to penetrate into the ink layer.