Theoretical analysis of the heat-sealing performance of PE film subjected to electronic shock

Polyethylene is a non-polar material, and its film has low surface tension. Generally, the surface tension of the film can be reached by corona treatment.
Better printing results can be obtained above 38dyn/cm. This development is to select appropriate raw and auxiliary materials and reasonable process formulas,
After the PE film of extrusion blow molding is corona treated, the treated surface does not affect the double-sided (folded) heat seal strength and other comprehensive properties
can.
Corona treatment (Corona treatment) is a kind of high-frequency and high-voltage that accelerates electrons to leave the electrode and encounters molecules in the air.
The formation of oxygen free radicals, a process in which free radicals and high-speed electrons pass through the surface of a polymer film. during this process,
A series of physical and chemical changes occur on the surface of the PE film:

①A lot of uneven layers are formed on the surface of the film, making the surface rough.
② Free radicals and high-speed electrons act on the surface of the film to break the bonds of the surface layer molecules, causing free radicals to accelerate the reaction.
③Oxygen radicals oxidize the C—C bond to generate carbonyl (-CO), hydroxyl (-OH), carboxyl (-COOH), and other poles.
The group.

④ The table forms cross-links.


From the analysis of the corona treatment mechanism, it can be seen that the PE film has undergone a series of chemical changes on the corona surface and the surface molecular shape
Part of the PE material is broken, and the molecular chains undergo cross-linking and reorganization. Therefore, for most PE materials, after corona treatment,
As the surface of the PE film changes, the strength of the surface layer is reduced, and the changed surface layer after heat sealing is easy to peel off from the whole
Falling down, resulting in the insufficiency of heat sealing. At present, there are two ways to solve the problem of heat seal strength decrease after corona:
The first is to squeeze a layer of heat-sealing material on the surface layer of the PE film after printing. The advantage of this method is that it can ensure the film surface
It is hygienic, but the cost is relatively high and the manufacturing cycle is relatively long. The second method is to use special materials for the structure
Formula design, blending and extruding raw and auxiliary materials with special properties to achieve the goal of not affecting the heat sealing performance after corona treatment
.
There are two theoretical foundations in the actual selection and application of materials: First, the damage to the amorphous region by electronic shock is greater than the damage to the crystalline region.
The degree of badness is high. But it should be noted that the use of high crystallinity resin will increase the haze of the film, decrease the transparency, and decrease the gloss.
It must be adjusted when designing the formula; second, the branch of the molecule with a long branched-chain structure stretches in space, which protects the main chain to a certain extent.
It reduces the degree of rupture of the main chain caused by electronic shocks. Third, the amount of corona directly affects the processing degree of the PE film.
If the amount of corona is too large, the advantages of the first and second resins will be lost, so the amount of corona should be properly controlled. The amount of corona can be
It is calculated by the following formula:
D=P/(B*V)
D-Corona amount (W.min / m2)
P-Generator power (W)
B-Corona width (m)
V-Movement speed of film (m/min)
Fourth, the produced film must be used within a certain period of time, because the amount of corona will degrade with the extension of the film placement time.
Reduce, especially when stored in a humid environment. (The curve of corona attenuation versus film storage time is shown below)
Based on the above analysis, the material selection for the corona layer of the polyethylene double-sided heat-sealable film can be basically drawn up. HDPE (70-80% knots) can be selected.
Crystallinity), LLDPE (10-20% metallocene linear polyethylene) resin with long-chain branched structure, with good heat-sealing compatibility
Suitable EVA, an appropriate amount of anti-reflection agent, etc. can be blended.
The product has no special requirements for production equipment and can be produced with a single-layer extruder or two-layer or three-layer co-extrusion film blowing unit.
Considering the application performance and comprehensive cost, it is more appropriate to choose a three-layer co-extrusion blown film unit. (Author: Niewen Mei Zhang Jiaren Week
Baohua)
Ink fastness is not good, easy to discolor
The factors that cause low ink adhesion of the liquid packaging film are:
1. The corona treatment of the substrate can not reach more than 40 dyne/cm, the surface is dense, smooth and ink affinity
Poor.
2. The oily material in the color masterbatch is not enough, although the gloss is improved, the friction coefficient is reduced,
However, the printing fastness is reduced, and the heat-sealing fastness is reduced, so the choice of color masterbatch is very important. Improve oil
The bonding fastness of the ink to the printing substrate enhances the compatibility of the binder in the ink with the printing substrate film. Choose to print
Brush substrate film has good swelling or good solubility solvent, increase the content of the binder in the ink, add it to the ink
The amount of tackifying resin to improve the adhesion of the ink.
3. The addition of solvent is out of adjustment and does not meet the actual standard.
4. The ink is too old and contains impurities and must be filtered.
5. The added solvent contains water.
The liquid packaging film makes noise during printing, and it sticks after rewinding
After the plastic film is rolled by gravure, it is divided and cut into packaging bags. After stacking, the printing surface
The ink or the ink sticks to the blank surface of the printing and cannot be separated (pull it hard to cause the ink to fall off, resulting in
Product scrap). It should be based on the possible causes of adhesion, that is, sticky ink, too high humidity, too much pressure, etc.
Start analysis.
Discussion on the Effect of Resin on Ink Performance and Analysis of Dirt Removal Techniques of Imposition Film Base
Its surface tension can only reach about 38 dynes. The resin structure should be non-polar, such as a chlorinated polypropylene resin binder. For PET,
For surface polar substrates such as PA, polyurethane resin binders can be used. Now the polyurethane ink binder system is specially used for
PP, PE adhesion promoter.
Or using a small amount of chlorinated polypropylene resin and polyurethane resin can often solve the problem of adhesion on non-polar substrates.
The versatility of the resin binder, and at the same time solves the problem of excessive toluene solvent residue that is likely to occur when the chlorinated polypropylene resin is used as the binder.
Advocating green and environmental protection Today, this breakthrough is particularly important, and it can be seen.
The pigment particles do not exist alone but are dispersed in the binder medium. Microscopically, the best wetted and dispersed state of a pigment particle is complete.
All are evenly wrapped in a resin binder. And attached to the surface of the substrate, the color display is that light enters the package through the resin connecting material film layer
The surface of the paint is reflected in the consumer's eyes.
Whether the transparency of the resin is good or not, the color number directly affects the color expression of different pigments, and at the same time, whether the resin wets and disperses the pigment sufficiently, directly
It will affect the uniform coating of the resin to the pigment and also affect the hue of the ink itself. Anti-adhesiveness is an important physical property index of printing ink.
Printing is a kind of high ink supply and good tone reproducibility.
Fast printing speed printing method, most of the inks used are solvent-based volatile drying inks, and then the ink is transferred to the substrate for printing after fishing.
In the drying tunnel, after the organic solvent is quickly evaporated and dried, the roll will be rewarded. As we all know, the surface temperature of the printing film is generally 40℃~
Between 60 ℃, and due to the existence of rewinding pressure, if the ink itself has poor anti-adhesive properties, it will cause serious rewinding adhesion quality accidents and oil
Mexican customers caused irreparable economic losses.
The good and bad anti-adhesive properties of the ink are not only related to the thoroughness after the solvent gradient volatilizes during the printing process, but also directly from a film with the resin binder used.
The nature of the resin molecule is related, and the film-forming property is good. The resin binder can impart good dryness to the ink. After the solvent evaporates and is completely dried, the film is completely formed.
Excellent anti-tack resistance after winding, in gravure printing.
In the printing process, the amount of ink-filled is large, the film layer is thick when transferred to the base material, and the ink hole volume is small. The amount of ink-filled is small, and the film layer transferred to the base material is thin, so the
On the base material, there is a series of shades, bright colors, and poor resolubility ink. In the fishing shallow net part, the roller rotates at a high speed in the ink tank! Residual oil
The ink is not easy to be re-dissolved by the ink in the ink tank, which will cause the cells to be printed lighter and lighter, and eventually cause blockage accidents. The ink is too good for resolubility.
In the overprinting process, the printed ink is easy to be dissolved by the ink solvent in the fish, causing the problem of ink cross-color! After the ink has been stored for a period of time! In rong
The upper part is thin, the viscosity is low, the color and density are relatively poor, and the lower part is thick! High viscosity, good color, and density, gravure printing
Because the ink is a fluid with low viscosity because the pigment is poorly dispersed in the binder, the density of the pigment or filler is too large, and it is easy to be thick after long-term storage.
There are precipitation problems, all of these problems will affect the performance of the ink, even after fully shaken.
It needs to be wiped several times to allow the residue to cover the photosensitive layer and re-develop. If it is heavy, you need to use a trimming knife to repair or scrap the entire fish, to prevent
A similar situation occurs. There are mainly the following two methods that can be used. Within the scope permitted by the conditions. Use a soft cloth dipped in alcohol to wipe the dirt on the base, because
Alcohol is relatively pure and contains a certain amount of water, so the dirt is easy to wipe off after absorbing water.
Extrusion compounding, as a production method in flexible packaging products, has the same and different characteristics as dry compounding. It has low investment, low cost, high production efficiency, and operation.
It has many advantages such as simple operation. Therefore, it still occupies a very important position in plastic composite processing, but it is inevitable that this or that will occur in the actual production process.
For problems, such as the effect of substrate surface treatment on the peel strength, the coated substrate is subjected to corona treatment in advance. The surface tension after treatment should be ≥38 dynes or more,
This can improve the adhesion of the base material to the melt-extruded resin.
The effect of ink on the peel strength of extrusion compound. In actual production, sometimes there are parts with no ink or less ink. The peel strength is good, while ink and ink are better.
It is a phenomenon that the peel strength of many parts is relatively poor, which is caused by the poor adaptability of the ink used or the ink not being completely dried.
Special attention should be paid to the influence of resin additives on quality. The additives in the resin, especially the slip agent, have a great influence on the peel strength of the extrusion compound.
When LDPE resin is used for extrusion compounding, extrusion coating grade resin particles that contain no or less lubricant should be used. (E.g. Beijing Yanshan 1C7A, Shanghai Jinshi
1C8A). In addition, the high water content in the resin can easily cause poor plasticization during the extrusion process.
Extrusion temperature control is extremely important to product quality. The extruder barrel temperature and T die temperature are the key and core of the extrusion compounding process. The temperature is too low and the plasticization is poor.
The molten film that flows out at too high a temperature will be fully oxidized, and polar molecules will be generated on the surface, and the affinity to the substrate will be better. Generally, the temperature of the barrel is controlled at 150~340 degrees.
In between, the temperature of the T-mode is controlled between 310 and 340 degrees.
The air gap has a certain effect on the quality. The air gap refers to the distance from the extrusion die to the composite cooling steel roller and the contact line of the pressure roller. The size of the air gap affects the extrusion composite
The peel strength also has a great influence. Therefore, the size of the air gap should be adjusted according to the actual situation of the product during extrusion and compounding. Generally speaking, the air gap should be controlled at
The range between 50mm and 100mm is preferably greater than 100mm, and the peel strength will directly decrease.

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