In dry compounding, there are often problems such as weak compounding, white spots after compounding, the astringency of the compound product, and poor heat sealing.
There are many reasons for these problems. The following only discusses the problems arising from the dry compounding of the PE film.
1 Insufficient compound
Tags: PE film
That is, the composite strength is low, which cannot meet the requirements of customers, resulting in product scrap. Due to the particularity of the PE film production process, the table
Low surface tension, high slip agent content, surface contamination, etc. may cause weak composites.
1) low surface tension
Under normal circumstances, the surface tension of the dry composite PE film must reach 38dyn/cm or more before it can be used. at the same time,
The composite strength is also related to the thickness of the PE film. If the thickness is less than 30μm, the surface tension is 36~38dyn/cm, which can be reluctant.
complex. When the thickness is 30~50μm and the surface tension value is 37dyn/cm, the composite effect depends on its composite structure, such as OPP /
PE, the compound effect can basically meet the requirements. But when the thickness is greater than 50μm, when the surface tension is less than 38dyn/cm, the composite
Basically, the products out can not be used.
The surface tension value of PE film is very large when it is just produced, but with the passage of time, its surface tension value gradually decreases.
drop. Under normal circumstances, PE film can be stored for 3 to 6 months, but the storage period should not exceed two months in the hot and humid summer season.
The practice has proved that the surface tension value of the PE film has a very close relationship with the surrounding environment and the thickness of the film: the higher the environmental temperature and humidity, the higher the
The faster the surface tension value decreases; the thicker the film, the faster the decrease.
2) The influence of additives
When PE is polymerized or PE film is formed, depending on its use, a certain amount of additives is generally required, such as antistatic
Electric agent, slip agent, anti-blocking agent, etc. These additives are not static after film formation or compounding, especially slip agents.
There are two reasons for the decrease in composite strength caused by slip agents.
① After the PE film is placed for a short time, the slip agent will migrate to the surface of the PET film to form a very thin dense layer, which is dense
The layer blocks the bonding between the adhesive and the surface of the PE film, resulting in the adhesive being unable to contact the PE molecules, resulting in a significant decrease in the initial adhesion of the composite.
low. Even with the lengthening of the curing time, the composite strength always remains low. If you carefully understand the resin production of PE film,
This phenomenon can generally be avoided. For the PE film that must use a high slip agent with special requirements, it should not be placed under normal circumstances
It's too long. If the PE film is used for an extended period of time due to some reason, it is best to try a small test or place the PE film in
At a temperature of 60~70℃ for more than 8 hours, the slip agent will partially fail at this time, and the composite will generally not have low composite strength.
However, PE film no longer possesses high smoothness.
②The initial composite adhesion is acceptable, but as the curing time increases, the composite strength becomes lower and lower, and a white layer appears between the two layers
Powdery substance. This is due to the selection of high-slip PE raw materials in the production of PE film. Due to the high content of slip agent in the film, the
During the curing process at high temperature (40~50℃), the movement of slip agent molecules in the film is intensified, and a large number of these molecules migrate to both sides of the film.
As time increases, the amount of migration to the surface gradually increases, and its migration destroys the physical bonding between the adhesive and the PE molecule.
Process, destroy the newly formed weak bond force. The longer the time, the stronger the destructive force and the lower the composite strength. Encounter
In this case, the method of increasing the curing temperature is generally adopted to accelerate the cross-linking speed of the adhesive, so that the reaction speed exceeds the slip.
The migration speed of the agent compensates for the negative effects caused by too much slip agent in the PE film.
In the actual production process, when there are too many additives in the PE film, it is recommended that the temperature of the hot steel roll not be too high during compounding, because the temperature is too high.
High can easily cause the additives to migrate outwards and reduce the peel strength. Generally, the temperature of the steel roll should be below 50°C. Complex with many additives
When the product is peeled off, the foggy appearance can be clearly observed.
In the production process, in many cases, customers will encounter various nearly contradictory requirements, such as automatic packaging, which requires
High composite strength requires a low coefficient of friction. This in itself is a pair of contradictions. To resolve this pair of contradictions, generally
Multi-layer co-extrusion film production method, each layer selects different ingredients according to different uses to meet the various requirements of customers.
3) Contamination on the surface of the film causes the composite strength to decrease
PE film is generally not polluted during the production process, but one of the pollutions is easily overlooked, that is, the pollution of dyne solution.
dye. Many PE film manufacturers use their own dyne solution to test the surface tension of the film. Dyne fluid is generally used
A mixture of alcohol and monoethyl ether, which is a colorless and transparent liquid. If it drops on the guide roller accidentally, its volatilization speed is very slow.
The film will be contaminated when it passes through the guide roller. The dyne solution is immersed on the surface of the PE film and is tightly combined with the PE molecules. After compounding, it will not be
The binder molecules are cross-linked, resulting in zero local composite strength. This situation is extremely difficult to find in the pre-inspection.
2 White spots appear after compounding
This phenomenon is very easy to occur on PE milky white film, generally milky white film is added with a certain amount of white masterbatch, namely concentrated titanium
White powder. Due to the different quality of the color masterbatch, the particle size and hardness of the titanium dioxide contained in it are different, which leads to
The quality of the milky white film produced is different, and the surface brightness is also different. If the surface of the milky film feels rough, there are pitting from the side,
Most of the products compounded with this kind of film will have white spots. Usually, there are ways to solve this problem: one is to increase the stickiness
The coating amount of the mixture; The second is to reprint a layer of white ink. No matter which method is adopted, it will increase the cost, so PE film before use
Must be strictly inspected. The white spots after compounding may also be caused by the glue itself. It is recommended to replace the glue for a small test.
Mass production can be carried out after meeting the quality requirements.
3 After compounding, the finished product appears astringent
This phenomenon has occurred in many manufacturers. The compounded product does not run smoothly on the automatic packaging machine, or the bag is opened
Difficulty in the mouth.
Dry compounding generally uses two-component reactive adhesives, which must be cured at a high temperature after compounding to achieve higher compound strength.
degree. The slip agent in the PE film will change due to the change of curing temperature. At a certain temperature, the slip agent will undergo chemical changes.
And lose the smoothing effect, the higher the temperature, the greater the change, the greater the loss of smoothing agent, which will eventually cause the product to become astringent.
can not be used. Therefore, the temperature of the curing chamber must be strictly controlled at about 40°C and cannot be increased arbitrarily. In addition, according to the production
For different purposes of the product, choose different ingredients to avoid the product becoming astringent due to improper selection of resin grades. From the astringent problem
We should analyze and find effective countermeasures. In terms of compound technology, we should do:
After 10h or longer, perform post-processing.
4 Poor heat seal
After the compound enters the last processor enters the hands of the customer, sometimes the local heat sealing temperature is too high, the heat sealing is not good, etc.
The phenomenon, when it is serious, it cannot be saved. The reasons for this result are corona breakdown, high slip agent content, and the number of recycled materials added.
Too big to wait.
1) Corona breakdown
When the PE film passes through the high-voltage discharge roller during the production process, it may cause the partial breakdown of the film due to various reasons. This phenomenon
It is often a longitudinal strip, and the position is generally fixed. The surface tension value of the PE film at the poor heat seal is generally very high.
The breakdown hot cover forms a substance with polar groups like the composite surface. This substance does not have heat-sealability. Therefore, in
Poor partial heat sealing will occur during bag making or automatic packaging. In order to avoid this phenomenon, it is recommended that the PE film be inspected in the factory
A test item for the surface tension value of the compound surface is added during the test.
2) High content of slip agent
As the content of the slip agent in the heat seal layer of the PE film is too high, it will cause a large amount of it to precipitate, forming a dense layer on the surface of the PE film, which prevents
This hinders the heat sealing of the PE film. This may happen if an expired PE film is used. Therefore, according to the customer’s specific
It is required to select an appropriate resin grade, and try not to use expired films for high-slip products. After this phenomenon occurs, it is recommended
Use solvent to wipe its hot cover repeatedly, the effect will be improved.
3) Recycled materials
In order to save costs, a certain amount of recycled materials is often added to the production of PE film. Recycled materials are generally not less than two passes
High-temperature regeneration, there is a certain amount of impurities. After re-forming the film, its heat-sealing performance will be greatly reduced, and the heat-sealing temperature should be generally increased.
5~10℃. Experiments have proved that when the addition amount of the heat-sealing layer reclaimed material is 30%, the heat-sealing temperature of the PE film should be increased by 3~5℃.
At 50%, the heat-sealing temperature should be increased by 6~10℃, so it is generally required that the film manufacturer should not add recycled materials in the heat-sealing layer as much as possible.