Q: What is polyamide (nylon PA) film?
Polyamide (PA) refers to a polymer with amide groups on the main chain, commonly known as nylon. At present, nylon films used in China are made of nylon 6 obtained by ring opening polymerization of caprolactam, which belongs to oriented film. Nylon film can be divided into salivation method (CPA), drum blowing film method (IPA) and biaxial tensile method (BOPA). Drawing method is divided into synchronous drawing and asynchronous drawing.
Nylon film belongs to directional film. The performance characteristics of directional film mainly include:
① After vertical and horizontal stretching, polymer molecules have high orientation, so they lose heat sealing, such as BOPP, pet, BOPA, etc;
② The crystallinity is improved, the physical and mechanical properties are greatly improved, and the transparency is also improved;
③ The induced tear strength is large, but the secondary tear strength is greatly reduced.
Q:Why does nylon film absorb moisture easily?
Nylon is mainly formed by polycondensation of dibasic acid, diamine or amino acid group. Because the polyamide molecule contains a very wide range of amide groups, but not all the molecules in the polyamide can be crystallized and coordinated in production. There are also some amorphous polyamide polar groups. The amide groups in this part of amorphous polyamide molecular chain can coordinate with water, that is, water molecules with strong water absorption and strong polarity can be absorbed, In severe cases, a layer of water film will be formed on the membrane surface, which greatly reduces the barrier and air tightness of nylon membrane.
Q:Why does nylon film sometimes produce color migration and color penetration after printing? What treatment measures have been taken for severe cases?
Color migration and color penetration are two different concepts:
1) Color migration mainly refers to the intense Brownian movement of small pigment molecules in the ink layer under the action of a certain temperature, so as to break away from the lattice formed by weak intermolecular force, follow other organic molecules to do migration movement and disperse color;
2) Color penetration means that the plastic printing substrate is overlapped up and down, and the pattern printed on the upper substrate is pad printed on the surface of the lower substrate.
The main reason is: in the plastic film polymer of the printing ink film, the polymer moves violently to form interstitial pores. When the temperature rises, the pores also expand and become larger. At this time, the pigment molecules also do violent Brownian motion, and they will diffuse and form infiltration through the pores. In particular, green lotus color and peach color are more prone to color penetration.
The diffusion and penetration of pigment molecules are mainly carried out in the amorphous region during the thermal movement of polymer chain of plastic film. Nylon film, non-linear polyethylene and other types of films belong to amorphous plastics. Because of their low crystallinity and large molecular gap, especially in the environment of high temperature and humidity, they are prone to thermal deformation, large water absorption and thermal hydrolysis. Therefore, this type of plastic film is more prone to penetration of some colors.
Q:When BOPA / Al / PE composite is used, delamination is easy to occur along the hot sealing edge of bag making?
Because the bag making heat sealing temperature is high, and the heating temperature of the heat sealing position is generally increased through two heat seals. In the heat sealing position, it is in a blank and transparent state. Low molecular weight substances (such as smoothing agent) in the film will penetrate and float to the surface at high temperature, causing degradation and delamination of the adhesive. On the other hand, the oil stain in the production process of all was not completely removed, and there was a large thermal stripping distance during heat sealing, resulting in delamination.
Q:Why is the printing ink with nylon film combination and jam bag easy to fade?
Material combination BOPA / Al / LDPE or PA / CPE. In fact, no matter what kind of film combination, some phenomena occur. Discoloration mainly caused by contents. Pickles are solid-liquid foods containing various condiments. Their chemical components are as complex as mustard bags. Many of them are highly permeable chemicals.
Therefore, LDPE or CPE cannot be used for the inner layer, and CCPP (salivary co polypropylene) with good cold resistance is better to be used, which can withstand minus 10 ℃ without brittleness, so the probability of chemical change due to penetration into the ink layer is lower.
Q:Does the aluminum foil of BOPA / Al / rcpp material combination crack or even break at the seal?
BOPA film and aluminum foil are materials with certain ductility, but the heat sealing moment when they are processed into packaging bags breaks. Generally, the extension applied by the heat sealing knife to the packaging material has exceeded the acceptable degree of the material, so the heat sealing layer is crushed. In case of automatic packaging double roller heat sealing, it shall also consider whether the concave convex shape of the double roller is too sharp to pierce and squeeze, causing the aluminum foil layer to break into black line crack shape. First of all, we should standardize treatment.
Q:What is the reason why BOPP will not produce bubbles after compounding for a period of time?
BOPA is a good barrier material, and there are too many residual solvents in the process of printing and compounding. After curing, it can not volatilize through the film and still remains in the film interlayer. This is because the residual water reacts with the isocyanate group of the curing agent in the adhesive to form a gas residue dominated by carbon dioxide.
The barrier property of BOPP is weak. Through ripening, part of the solvent remaining in the film interlayer volatilizes from the surface of BOPP. Therefore, generally, there are fewer bubbles after composite curing of BOPP membrane.
Q:Why is it easy to produce delamination when nylon membrane is used as surface composite and then boiled in water?
Due to the water absorption of nylon, the problems of surface printing, composite RE boiling or cooking of nylon film are more serious, which seriously affects the peel strength. Therefore, the adhesive with resistance below 121 ℃ cannot be used as the general boiled adhesive.
In the structure of BOPA / PE (115 ℃) and BOPA / cpp121 ℃, only cooking adhesive with 135 ℃ resistance can be used, that is, the temperature resistance of adhesive can be improved by one grade and the glue amount can be appropriately increased. It is better to use a waterproof coating to prevent moisture from invading the nylon membrane. A small amount of yellowing of nylon film after cooking will cause color difference in the packaging bag, which should be paid special attention.
Q:Why is there sporadic foaming in the finished product of nylon membrane composite CPP?
This situation is mostly caused by too high glue bubbles or damp nylon film, and too much residual solvent in the composite layer. In the humid climate in the south, this is a common problem in cooking and packaging. At this time, increase the circulation of glue in the glue tank to curb the occurrence of bubbles;
Or increase the drying temperature of the printing and compounding machine, or add no more than 5% curing agent in the glue, and when the weather is good (humidity is less than 70%), the printed nylon film should be compounded immediately, or wrapped with aluminum foil paper. It is recommended not to put it aside for too long (within 5min) to avoid water absorption and moisture of the nylon film and bubbles.
Q:The peeling strength of nylon film composite PE is OK when it is off the machine, but it is easy to peel and tear after curing for 16h? What treatment measures have been taken for severe cases?
1) Whether the corona surface treatment degree of raw materials (printing materials and heat sealing materials) meets the standard (pa-52dny, pet-48dny, pe-40dny);
2) There are too many additives (additives) in printing and heat sealing materials, which float up when heated, so that the composite layer is degraded and easy to peel off;
3) Insufficient glue. Generally, there should be 2.5g / ㎡ for blank small bags below 200g, 3G / ㎡ for ordinary bags, 4.5g / ㎡ for boiled bags, and 5g / ㎡ for cooking bags. (refers to the amount of dry glue) refer to GB / t10004 --- 2008 standard;
4) The smooth dose of PE film is too high, that is, the additive content is more than 500ppm, and the film thickness is too thick (60%) μ M) too much additive is added to cause low peeling degree;
5) The curing conditions do not meet the requirements, or the curing time is 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) Climatic conditions. Generally, humidity exceeding 80% is very unfavorable for dry compounding, which shall be controlled at 23 ℃± 3 ℃ and 65% ± 5%;
7) Internal quality of adhesive. The first is the percentage content of the curing agent. Generally, the percentage content of the curing agent is less than 2%, and the viscosity of the prepared water will be greatly reduced. The second is that the proportion of the curing agent should not be too large. If it is too large, it will cause embrittlement and tear of the composite film.