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First, compound is not strong

That is, the composite strength is very low or zero, can not meet customer requirements, resulting in product obsolescence. Due to the particularity of PE film production process, low surface tension, high content of smooth agent, surface pollution, etc., may lead to weak composite.

Low surface tension

Under normal circumstances, the surface tension of dry composite PE film must reach 38dyn/cm above can be used.

Practice has proved that if the surface tension value of PE film is lower than 38dyn/cm, it may cause the phenomenon of low composite strength. The composite strength below 36dyn/cm is very low or zero. At the same time, the composite strength is also related to the thickness of PE film, if less than 30 microns, at 36-38dyn/cm can barely composite, thickness at 30-50 microns, surface tension value 37dyn/cm, depending on its composite structure, such as: OPP/PE, composite effect can basically meet the requirements. However, when the thickness is greater than 50 microns, it can not be used below 38dyn/cm. Here are some data sets for reference:

The surface tension value of the film is very large when it is just produced, but as the time goes by, its surface tension value gradually decreases. Under normal circumstances, PE film can be stored for 3-6 months, but the storage period should not be more than 2 months in the summer hot and humid season. Practice has proved that the surface tension value of PE film is closely related to the surrounding environment and the thickness of the film. The higher the ambient temperature and humidity, the faster the surface tension value decreases, the thicker the film, the faster the decline. Therefore, the placement of PE film should not be more than 3 months, especially in the Meiyu season, more attention should be paid to the ventilation and breathable storage. If for some reason the time is too long, when re-using, in addition to the volume by volume inspection, but also according to the purpose of composite products to consider whether to continue to use, so as to avoid losses.

Effect of additives

In polymerization or PE film in film formation, according to its different uses, generally need to add a certain amount of additives, such as antistatic agent, smooth agent, opening agent, etc. These additives are not static after film formation or compound, especially smooth agents. Smootheners generally use erucic acid amide or oleic acid amide. There are two reasons for the decline of compound strength due to smootheners:

(1) PE film placement time is not long, the smooth agent migration to the surface of PE film, forming a thin layer of dense layer, this layer of dense layer barrier adhesive and PE film surface combination, resulting in adhesive can not contact with PE molecules, composite initial adhesion is very low, with the increase of curing time, composite strength is little change, composite strength is always very low or zero. If you carefully understand the production of PE film resin, this phenomenon, generally can be avoided. For special requirements must use high smooth PE film, under normal circumstances should not be placed too long, if for some reason caused by the use of PE film, before the compound test or PE film in 60-70℃ temperature for more than 8 hours, at this time the smooth agent will be partially failed, then to compound generally will not appear low compound strength problem, But PE film has no high smooth.

(2) The initial adhesive strength of the composite is OK, but with the increase of curing time, the composite strength is lower and lower, and there is a layer of white powdery substance between the two layers. This is due to the selection of high smooth PE raw material in the production of PE film. Due to the high content of smooth agent in the film, during the process of high temperature (40-50℃) curing, the movement of smooth agent molecules in the film is intensified, and a large number of smooth agent molecules migrate to both sides of the film. With the extension of time, the amount of migration to the surface gradually increases. Its migration destroys the physical bonding process between the adhesive and PE molecules, and destroys the newly formed not very firm bonding force. The longer the time, the stronger the destructive force, the lower the composite strength. In this case, the method of increasing the curing temperature is generally adopted to accelerate the crosslinking speed of the adhesive, so that the reaction speed exceeds the migration speed of the smooth agent, in order to make up for the negative impact caused by too much smooth agent in the PE film.

In the production process, in many cases will encounter a variety of almost contradictory requirements of customers, such as automatic packaging, which requires high composite strength, but also requires low friction coefficient, which is itself a pair of contradictions, in order to solve this contradiction, generally adopt multi-layer co-extrusion film method, each layer according to the different use of different ingredients, in order to meet the various requirements of customers.

Surface contamination

Membrane in the production process will not suffer from pollution, but one kind of pollution is easy to be ignored, that is the Dyne fluid pollution. Many PE film manufacturers, have adopted self-matching Dyne solution to test the surface tension of the film. Dyne liquid is generally selected glycol only diethyl ether mixture, which is a ****** transparent liquid, if accidentally contaminated the guide roller, due to its volatilization rate is very slow, the film through the guide roller will be polluted, Dyne liquid into the surface of PE film, and PE molecules closely combined, composite, it does not cross linked with adhesive molecules, resulting in local composite strength of zero. This condition is extremely difficult to detect on prior examination.

Two, compound white spots

This phenomenon is easy to occur in PE opalescent film, the general opalescent film is after adding a certain amount of white master material that is: concentrated titanium dioxide. Due to the quality of the color masterbatch is different, containing titanium dioxide particle size is different, hardness is not the same, resulting in the composite production of opalescent film quality is different, surface brightness is different. If the milky white film surface feel rough, from the side to see pitting, the use of such a film composite products will mostly appear white spot phenomenon. Usually the solution to this problem is: one is to improve the amount of adhesive coating. The second is to print a new layer of white ink. No matter what kind of way to increase the cost, so PE film must be strictly tested before use.

Three, compound product hair astringent

This phenomenon has happened in many manufacturers. The compound product automatic packaging machine does not run smoothly, or the bag made is difficult to open.

Dry composite is generally used two liquid reaction type adhesive, composite to high temperature curing, in order to achieve composite strength. The smoothness agent in PE film will change due to the change of curing temperature, at a certain temperature, the smoothness agent will undergo chemical changes and lose the smoothness effect, the higher the temperature, the greater the change, the greater the loss of the smoothness agent, will lead to astringent products, can not be used. Therefore, the temperature of the curing chamber must be strictly controlled at about 40℃, and can not be increased at will. In addition, according to the different uses of the product, choose different ingredients to avoid the product astringent due to the improper selection of resin brand.

Four, bad heat sealing

After entering a process or entering the hands of customers, sometimes there will be local heat sealing temperature is too high, bad heat sealing phenomenon, serious can not be saved. The reasons for this result include corona breakdown, high content of smoothing agent and excessive amount of recycled material.

Corona breakdown

Film in the production process through the high pressure discharge roll, due to various reasons may cause local breakdown of the film, this phenomenon is often a longitudinal, the position is generally fixed, the surface tension value of the PE film at the heat seal is generally high, because the breakdown of the thermal surface and composite surface formed a material with polar groups, this material does not have heat seal, so, In the bag-making or automatic packaging, there will be a phenomenon of poor local heat sealing. In order to avoid the occurrence of this phenomenon, PE film in the factory inspection to add a composite surface tension value detection item.

The content of smooth agent is high

Due to the high content of the smooth agent in the heat sealing layer of PE film, it will lead to a large amount of precipitation on the surface of PE film to form a dense layer, which hinders the heat sealing of PE film. This may occur if an expired PE film is used. Therefore, according to the specific requirements of customers to choose the appropriate resin brand, for high smooth products as far as possible not to use expired film. After this phenomenon occurs, it is recommended to use solvents to wipe the hot cover repeatedly, the effect will be improved.

Recycled material

In order to save cost, in the production of PE film, often add a certain amount of recycled material, and recycled material is generally after no less than two high temperature regeneration, and there is a certain amount of impurities, after re-film, its heat sealing performance is greatly reduced, heat sealing temperature generally increased by 5-10℃, experimental results show that when the amount of recycled material added in the heat sealing layer is 30%, The heat sealing temperature of PE film is increased by 3-5℃, and the heat sealing temperature is increased by 6-10℃ when the amount is added by 50%. Generally, film manufacturers are required not to add recycled materials in the heat sealing layer as far as possible.

There are many problems encountered in the process of dry compound, but often the cause of the formation of the same problem is many, so after the problem, we must carefully analyze, multi-consideration, after the experiment can be concluded.