PA - A linear polymer containing many repeating amide groups in the molecular chain with a specific gravity of 1.14 g / cm 3 Polyamide (PA) refers to a polymer with an amide group in the main chain, commonly referred to as nylon (Nylon).
At present, the nylon film used domestically is a oriented film made of nylon 6 obtained by the ring-opening polymerization of lactam, while the production of nylon film is divided into three types: CPA, IPA ), Biaxial stretching method (BOPA) .The stretching method is divided into synchronous stretching and asynchronous stretching two different processes.
Nylon film is oriented film, and the performance characteristics of oriented film are:
A, the vertical and horizontal stretching, polymer molecules have a high degree of orientation, so lose heat sealing, such as BOPP, PET, BOPA, etc .;
B, improve the crystallinity, physical and mechanical properties greatly improved, transparency also increased;
C, lead to a great tear strength, but secondary tear strength greatly reduced.
1, why nylon membrane easily absorb moisture?
Nylon mainly consists of dibasic acid, two amine-free or amino acid by polycondensation from the polyamide molecule contains a very wide range of amide, but not in the production of polyamide molecules can crystallize and molecular coordination, There are some non-crystalline polyamide polar genes exist, this part of the non-crystalline amide amide amide chain can coordinate with the water, that is, has a water-absorbing, strong absorption of water molecules, in severe cases A layer of water film will be formed on the surface of the film, which will greatly reduce the barrier property and air tightness of the nylon film.
2, why the nylon film sometimes produce color printing color migration and infiltration?
Color color penetration and migration are two different concepts:
1) Color pigment ink migration mainly small molecules do vigorous Brownian motion effect at a certain temperature, so that by departing from the lattice formed between a weak intermolecular forces, following migration other organic molecule do move together, spreading color;
2) color penetration refers to the upper and lower substrates laminated plastic printing, the printing surface of the lower substrate is patterned on the printed substrate.
The main reason is: the plastic film polymer printed with ink film, the polymer strenuous exercise, the formation of interstitial pores, when the temperature rises, the pores also expand, but at this time, the pigment molecules also make violent Brown Movement, they will spread through the pores to form infiltration, especially green lotus, pink and more prone to color penetration phenomenon.
Diffusion and penetration of pigment molecules are mainly carried out in the non-crystalline region during the thermal movement of the polymer chains of the plastic film, which are amorphous plastics, because of their low crystallinity, molecular interstices Large, especially in high temperature and humidity environment, easy thermal deformation, water absorption, when heated hydrolysis, so the type of plastic film is more prone to some color infiltration.
3, nylon film composite PE, peel strength under the machine can be, but after curing 16h is easy to peel tear reason?
There are several phenomena:
1) Corona treatment of raw materials (printing materials and heat sealing materials) is satisfactory (PA-52dny, PET-48dny, PE-40dny);
2) printing and heat sealing materials additives (additives) Too much heat to float the composite layer degradation and easy to peel off;
3) The amount of plastic is not enough.General small white bags should be less than 200g 2.5g / ㎡, ordinary bags should reach 3g / ㎡, boiled bags should reach 4.5g / ㎡ and cooking bags should be more than 5g / ㎡. Refers to the amount of adhesive) reference GB / T10004 --- 2008 standard;
4) The slippery dosage of PE film is too high, ie the content of additive is above 500PPm, and the film thickness is too thick (60um or above)
5) Curing conditions do not meet the requirements, or curing time is too short. Completely different cross-linking of different adhesives are not the same, in order to ensure complete cross-linking glue, according to different grades of glue, different uses of different curing process;
6) Climatic conditions Generally, humidity exceeding 80% is very unfavorable for dry compounding, and should generally be controlled at 23 ℃ ± 3 ℃ and humidity of 65% ± 5%;
7) The intrinsic quality of the adhesive. The first is the percentage of the curing agent content, the percentage of the average curing agent content of less than 2%, with the water viscosity will be greatly reduced, followed by the curing agent ratio can not be too large, such as the result is too large Composite film embrittlement tear.
(Solvent-free compound curing process requirements are very strict, the other discussion)
4, Why nylon membrane composite CPP, finished sporadic bubbly phenomenon?
This situation is mostly caused by excessive glue bubbles or nylon membrane damp, as well as the composite layer caused by too much residual solvents in the humid southern climate environment, which is a common problem of cooking and packaging, then to increase plastic tank The amount of glue in the circulation, to curb the occurrence of bubbles, or increase the printing and laminating machine drying temperature, or in the glue to increase not more than 5% curing agent, and the weather is good (less than 70% humidity) Printed Nylon film to be immediately complex, or wrapped with aluminum foil, do not set aside for too long (5min or less), so as to avoid damp nylon membrane moisture, resulting in bubbles.
5, nylon membrane used as a complex surface and then easy to delaminate delamination reasons?
Due to the water absorption of nylon, Nylon film for surface printing, complex and then boiled or cooking more serious problems, seriously affect the peel strength, so the general boiling type of adhesive can not use the adhesive below 121 ℃ .BOPA / PE (115 ℃) , BOPA / CPP121 ℃ structure, can only be used 135 ° C cooking adhesive resistance, that is, the temperature of the glue to improve a grade and the appropriate increase in the amount of glue. It is best to use a waterproof coating is more ideal to prevent moisture intrusion into the nylon membrane Nylon membrane cooking a small amount of yellowing phenomenon, the color difference will produce bags, pay special attention.
6, BOPA film material combinations, bubbles after a period of time and BOPP will not be the reason?
BOPA is a material with good barrier property. However, the residual solvent in the printing compound process is too much, and the cured solvent can not volatilize through the film but remains in the film interlayer because of the residual moisture and the curing agent in the adhesive Of the isocyanate group, resulting in carbon dioxide-based gas residue.BOPP barrier is weak, through the aging, part of the residual solvent in the film interlayer volatilized from the surface of the BOPP out.Therefore, the general BOPP film produced after the maturation of bubbles less some.
7, OPA / AL / RCPP material combination in the sealing aluminum foil cracks or even broken?
BOPA film and aluminum foil are some ductile materials, but in the process of processing bag instant heat crack appeared phenomenon is generally heat sealing knife applied to the package material has exceeded the degree of extension of the degree of acceptance, So the heat seal layer is crushed.If it is self-packaging double-roll heat seal, you should also consider whether the double-roll uneven shape is too sharp and piercing extrusion rupture of the aluminum foil into black line crack.
8, the use of BOPA / AL / PE (15.07.60um) composite, easy to produce bag sealing edge delamination?
As the bag heat sealing temperature is higher, and generally by two heat sealing to increase the heat sealing position of the heating temperature in the heat sealing position are in a transparent state in the film of low molecular weight (slip agent, etc.) On the other hand, AL oil pollution in the production process has not been completely removed, heat sealing has a greater thermal stripping distance occurred off Floor.
9, why there is a nylon membrane combination, the printing ink inside the bag filled with soy sauce easy to fade?
Material combinations B0PA / AL / LDPE or PA / CPE. In fact, no matter what kind of film combinations are some phenomena. Mainly caused by the content of the fade. Pickles are built with a variety of condiments solid-liquid coexistence of food, including chemical Composition with the same vegetable bags, is very complex, there are many high-permeability chemicals.To this end, the inner layer can not be LDPE or CPE, the best cold-resistant CCPP (salivary polypropylene) can withstand minus 10 degrees Not brittle, so that penetration into the ink layer and the probability of chemical changes smaller.