Classification of nylon film production process
Polyamide film: a linear polymer containing many repeating amide groups (- CO-NH -) in the PA molecular chain segment, with a specific gravity of 1.14 g / cm3. Polyamide (PA) refers to the polymer with amide group in the main chain, which is usually called nylon.
At present, nylon films used in China are all made of nylon 6 obtained by ring opening polymerization of caprolactam. And nylon film on the production and molding process is divided into: salivation method (CPA), blowing tube membrane method (IPA), biaxial stretching method (BOPA). Drawing method can be divided into synchronous drawing and asynchronous drawing.
Nylon film is a kind of directional film, and its properties are as follows:
A. After longitudinal and transverse stretching, the polymer molecules have a high degree of orientation, so they lose the heat sealing property, such as BOPP, pet, BOPA, etc;
B. The crystallinity is increased, the physical and mechanical properties are greatly improved, and the transparency is also improved;
C. The initiation tear strength is large, but the secondary tear strength is greatly reduced.
1. Why is nylon film easy to absorb moisture?
Nylon is mainly made of dibasic acid, diamine or amino acid group by condensation polymerization. Because polyamide contains a wide range of amide groups, but in the production process, not all the molecules in the polyamide can crystallize and coordinate with molecules, and there are some amorphous polyamide polar genes. The amide groups in the amorphous polyamide molecular chain can coordinate with water, that is to say, it has water absorption, and can absorb water molecules with strong polarity. In serious cases, it will form a The barrier and air tightness of nylon film are greatly reduced by water film.
2. Why does nylon film sometimes produce color migration and color penetration after printing?
Color transfer and color penetration are two different concepts
1) The color transfer is mainly that the small molecules of pigment in the ink layer do intense Brownian motion under the action of a certain temperature, thus breaking away from the lattice formed by the weak intermolecular force, and following other organic molecules to do the migration movement together to disperse the color;
2) Color penetration refers to that the plastic printing substrate is superimposed on top and bottom, and the pattern printed on the upper substrate is printed on the surface of the lower substrate.
The main reason is: in the plastic film polymer printed with ink film, the polymer moves violently to form interstitial pores. When the temperature rises, the pores also expand and enlarge. At this time, pigment molecules also do intense Brownian motion, and they will diffuse and penetrate through the pores. In particular, blue lotus and peach red are more prone to color penetration.
The diffusion and penetration of pigment molecules mainly occurs in the amorphous region of the polymer chain of plastic film during thermal movement. Nylon film, non-linear polyethylene and other types of films belong to amorphous plastics. Due to their low crystallinity and large molecular gap, they are easy to thermal deformation, absorb large amount of water and hydrolyze when heated, especially in high temperature and humidity environment. Therefore, this type of plastic film is more prone to some color penetration phenomenon.
3. The peeling strength of the composite PE is good when it is off the machine, but it is easy to peel and tear after curing for 16 h?
There are several phenomena as follows:
1) Whether the corona surface treatment degree of raw materials (printing materials and heat sealing materials) reaches the standard (pa-52dny, pet-48dny, pe-40dny);
2) There are too many additives (additives) in printing and heat sealing materials, which make the composite layer degraded and easy to peel off;
3) Not enough glue. Generally, the blank small bag should be 2.5g/m2 below 200g, the ordinary bag should be 3G / m2, the boiling bag should be 4.5g/m2, and the cooking bag should be more than 5g / m2. Refer to GB / t10004-2008 standard;
4) The smooth dosage of PE film is too high, that is, the additive content is more than 500ppm, and the thickness of PE film is too thick (more than 60um). Too much additive addition causes low peeling degree;
5) The curing conditions did not meet the requirements or the curing time was too short. The complete crosslinking of different adhesives is different. In order to ensure the complete crosslinking of glue, different curing processes should be adopted according to different brands of glue and different uses;
6) Climate conditions. Generally, the humidity over 80% is very unfavorable for dry lamination, which should be controlled at 23 ℃± 3 ℃ and 65% ± 5% humidity;
7) The intrinsic quality of the adhesive. The first is the percentage content of curing agent. Generally, the percentage content of curing agent is less than 2%. The viscosity of prepared water will be greatly reduced. Secondly, the proportion of curing agent should not be too large. If it is too large, it will cause embrittlement and tear of the composite film.
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