LDPE blown film production problems

October 13, 2008 on 8:32 pm | In Tech | 1 Comment

Most of thermoplastics can blow by blow method to produce thin film, blown film is thin plastic tube Jicheng, while it is hot and then use compressed air to blow plastic inflation, then in the shape of cooling after the tube-like film to be manufactured This film’s performance at a film directed with the membrane between the cast: strength than cast film, and sealing membrane worse than the cast.

Blow production of the film there are many varieties, such as low density polyethylene (LDPE), polypropylene (PP), high-density polyethylene (HDPE), nylon (PA), ethylene-vinyl acetate copolymer (EVA), and so on, Here we have used for low density polyethylene (LDPE) film production process and its Common blown failure to carry out a brief introduction.

Polyethylene blown film material of choice

1. The selection of raw materials should be used blown-grade polyethylene resin particles containing Shuanghua’s agent amount, to guarantee the opening of film.

2. Resin particles melt index (MI) can not be too large to melt index (MI) too much, the viscosity of the molten resin is too small, narrow the scope of processing, processing conditions difficult to control, the resin film poor, is not easy to process into Membrane; In addition, the melting index (MI) too much, polymer molecular weight distribution is relatively narrow, less intensity of the film. Therefore, the choice should be melting index (MI) smaller and relatively wide distribution of molecular weight resin raw materials, such films can meet the performance requirements but also ensures that the processing characteristics of the resin. Blow polyethylene film selection of the general melting index (MI) in the range of 2 ~ 6g/10min between the polyethylene material.

Blow process control points

Blown film process is as follows:

Hopper feed on a plastics extrusion materials → Inflation traction Central cooling wind → → herringbone traction roller traction splint → → → film to deal with Corona rolling

However, it is worth pointing out that the blow with the performance of the film production process parameters have a great relationship, in the course of blown film, it is necessary to strengthen the technological parameters of control, regulate the operation process to ensure the smooth progress of production, and Access to high-quality film products. In polyethylene blown film production, mainly to do a good job the following technical parameters of control:

1. Extruder temperature

Blow low density polyethylene (LDPE) film, the general temperature control in crowding 160 ℃ ~ 170 ℃, and must guarantee evenness nose temperature, high temperature extrusion, resin easy to break down film and brittle hair, in particular, So that the longitudinal tensile strength decreased significantly; the temperature is too low, the non-performing plastic resin and can not carry out smooth expansion of the stretch, the film’s low tensile strength and surface gloss and transparency of the poor, even as timber-like ring The pattern is not as well as the melting of the nuclei (fish-eye).

2. Inflation over

Inflation is more than blown film production process control of one of the main points, Inflation refers to the film after the bubble with a diameter of the tube Inflation did not ring the ratio between the diameter. Inflation for the film than the horizontal expansion of the multiple film is actually a horizontal stretch, stretch plastic molecules will have a certain degree of orientation, than Inflation increased, so that the horizontal strength of the film. However, more than Inflation can not be too much, otherwise easily lead to instability in the bubble film, film and prone to wrinkles. As a result, more than Inflation should be the same with traction than it appropriate, in general, low-density polyethylene (LDPE) films than Inflation should be controlled at 2.5 to 3.0 is appropriate.

3. Traction than

Traction than the film refers to the speed traction control and speed crowding ring between the ratio. Traction than the vertical draw ratio, so that the film cited in the direction of taking on the role of orientation with. Traction than the increase, the vertical will also increase the strength and thickness of the film, but if too much traction than, the thickness of the film difficult to control, the film might even pull off, resulting in broken membrane phenomenon. Low density polyethylene (LDPE) film of traction control than the average between 4 to 6 is appropriate.

4. Dew point

Frost also known as the dew point line, referring to the sticky plastic flow into the high-elastic boundaries of the state. Blown in the process of low density polyethylene (LDPE) in the population die from the molten state was out of time, good transparency. When I leave the mold, to wind through the ring of membrane Cooling of the bubble areas Inflation cooling, air cooling to a certain angle and speed of the nose from blowing out of plastic foam, bubble film of high temperature and cooling air Contact, the film bubbles heat the cold air will be taken away, the temperature will drop significantly to the low density polyethylene (LDPE) following the flow temperature, making it the cooling and solidification of blurred. Paoshang blow in the film we can see a transparent and blurred the line between, that is, dew point (or cream that line).

Blown in the process, the dew point of the film on the level of performance to a certain extent. If the dew point, Inflation at the top of the bubble film, the film’s Inflation in the liquid under, so that only Inflation film thinning, and the elements are not subject to the direction stretch, when the film close to Inflation In the cast film. On the other hand, if the dew point is relatively low, Inflation is under the solid-state, this time in a high-elastic-plastic, blowing as horizontal expansion on the same stretch, so that the orientation of molecules, so that the film Inflation close to the performance of Directed film.

The basic properties of the technical requirements

1. And specifications error

Polyethylene film width, thickness should be in line with the requirements of the film Bohou uniform, Wang, vertical Thickness small deviation, and the bias is more evenly distributed.

2. Appearance

Polyethylene plastic film demands a good, non-obvious “Shuiwen” and the “cloud”; film on the surface should be smooth with no wrinkles or only a small number of live-fold; does not allow air bubbles, piercing and cracking phenomenon; no The black spots, impurities, crystal and stiff block; not allowed to have a serious hang-line materials and silk patterns exist.

3. Mechanical properties

After the blow as a result of the polyethylene film used for printing or processing complex, is subject to mechanical force, the requirements of the polyethylene film should be good mechanical properties, including tensile strength, elongation at break, tear Strength several indicators such as the split should be line with the standards.

4. The size of the surface tension

In order for printing ink and adhesive compound used in polyethylene film has a good surface wetting and adhesion, the requirements of the polyethylene film surface tension should be up to the required standard, otherwise it will affect the printing and production of complex smoothly. In general, the surface tension of the polyethylene film should at least reach up to 38 as a result of more than 40 reached as a result of the above better.

Low density polyethylene (LDPE) film blow common faults and solutions

1. Film is too sticky, poor openings


① resin material model right, not a blown-class low-density polyethylene resin particles, which does not speak agent or agents of the content on the low side openings;

② resin melting temperature is too high, too much liquidity;

Inflation ③ than too much, resulting in the opening film of variation;

④ cooling too slow to film cooling enough traction in the roller pressure occurred bonded with each other;

⑤ speed traction too.


① replacement resin raw materials, or to the Division of Sino-Canadian fighting a certain amount of open agent;

② out due to lower temperature and the temperature of resin;

③ due to lower than Inflation;

④ to increase air flow and improve cooling effect, to accelerate the speed of film cooling;

⑤ appropriate to reduce the speed of traction.

2. Poor transparency of the film


① out of the low temperature, non-performing plastic resin, resulting in blow after the film’s poor transparency;

② than Inflation is too small;

③ cooling effect of the poor, thus affecting the transparency of the film;

④ resin materials in the water with excessive;

⑤ traction too fast, lack of film cooling.


① out to raise the appropriate temperature, so that the plastic resin can be uniform;

② appropriate to raise more than Inflation;

③ to increase air flow and improve cooling effect;

④ of raw materials for processing and drying;

⑤ appropriate to reduce the speed of traction.

3. Film appear fold


① uneven film thickness;

② enough cooling effect;

Inflation ③ than too much, causing instability in the bubble film, or so swing back and forth, and prone to wrinkles;

④ splint miter angle is too large, bubble film in the short distance to be flattening, the film is also prone to wrinkles;

⑤ traction on both sides of the pressure roller different side of the high-low side;

⑥ the guide roller between the axis parallel to the non-affected the stability of the peace Zhanxing film, which appeared fold.


① adjust the thickness of the film to ensure uniform thickness;

② improve the cooling effect, be able to guarantee the full film cooling;

③ due to lower than Inflation;

④ words were appropriate to reduce the angle between the splint;

⑤ traction roller pressure adjustment to ensure uniformity of film loading;

⑥ check the orientation of the shaft axis, and parallel to each other.

4, a thin mist Shuiwen


① out of the low temperature, bad plastic resin;

② resin damp, moisture content is too high.


① adjustment extruder temperature settings, and appropriate to raise the temperature out.

② resin will dry raw materials, the general requirements of the resin water should not exceed 0.3 percent.

5. Uneven film thickness


① I die gap of a direct impact on the uniformity of film thickness uniformity, if I die gap uneven, and some parts of some of the big gap, and some small parts of some of the gap, resulting in more capacity out of a small, formed The film thickness is inconsistent, and some parts of thin, and some parts of thick;

I-mode ② non-uniform temperature distribution, high-low, so that after the blow of the film Bohou uneven;

③ wind cooling of the air supply ring around the volume of inconsistency, caused by the cooling effect of uneven thickness of the film so that the emergence of the phenomenon of uneven;

④ than Inflation and traction than the inappropriate, so that the film thickness of the foam difficult to control;

⑤ speed traction is not constant, constant change, of course, will affect the thickness of the film.


① nose adjustment mouth gap mode, to ensure uniformity throughout the line;

② adjustment mode nose mouth temperature, so that I die temperature part of the uniform;

③ conditioning cooling device to ensure that the air out of the air flow evenly;

Inflation adjusted ④ and traction than the ratio;

⑤ mechanical inspection gear, so that the traction to maintain a constant speed.

6. The thick-film thickness


① I-mode space and out of large volume, the thick-film thickness;

② air cooling ring too much air flow, film cooling too quickly;

③ traction too slow.


① mouth gap adjustment mode;

② appropriate to reduce wind ring style, so that the film Inflation further, making it the thickness of some of the thinning;

③ appropriate to increase the speed of traction.

7. Thin-film thickness


① I die gap too small, too much resistance, the thin-film thickness;

② wind cooling of the air volume is too small ring, the film is too slow cooling;

③ traction too fast, over-stretched thin, so thin thickness.


① mouth gap adjustment mode;

② appropriate ring wind increased wind, speed up the cooling of the film;

③ appropriate to reduce the speed of traction.

8. The film sealing poor


① low dew point, the orientation of polymer molecules, so close to the performance of films directed film, resulting in the reduction of sealing performance;

② than Inflation and traction than the inappropriate (too much), stretch-oriented films took place, thereby affecting the sealing performance of the film.


Central air-conditioning ① the size of the stroke volume, so that the dew point higher, as much as possible in the plastic melting point under Inflation and traction to reduce Inflation and traction caused by the orientation molecular stretching;

② Inflation and traction than the ratio should be smaller, than if Inflation is too large and too fast traction, the film’s over-stretching horizontal and vertical, so that the film’s performance will be become two-way stretch, the film And sealing will deteriorate.

9. Film tensile strength of vertical difference


① resin melting temperature is too high, will film the tensile strength of the vertical drop;

② traction slow vertical orientation film role enough so that the vertical variation of the tensile strength;

③ than Inflation too, with more than traction does not match the film so that the horizontal orientation of the role and increase the tensile strength, tensile strength and vertical will be worse;

④ film cooling too fast.


① appropriate to lower the temperature of molten resin;

② appropriate to increase the speed traction;

Inflation adjusted ③ than bring it into line with traction than the suit;

④ due to lower cooling rate.

10. Horizontal film tensile strength poor


① traction too fast, with the wind than the expansion of a similar amount, so that fibrosis have a vertical, horizontal on the strength of variation;

② cooling loop cooling wind speed is too slow.


① appropriate to reduce the speed of traction, and make it more than matched by Inflation;

② ring wind increased wind, so that the film Inflation cooled quickly to avoid the higher

The high-temperature shells were stretching orientation.

11. Vesicle membrane instability


① extrusion temperature is too high, the flow of molten resin too, the viscosity is too small, prone to fluctuations;

② out of the low temperature, less material;

③ Central air cooling air flow instability, uneven film cooling bubble;

④ by the strong currents of foreign interference and influence.


① out to adjust the temperature;

② out temperature adjustment;

③ check the wind cooling loop to ensure that air traffic around the uniform;

④ prevent and reduce the flow of outside interference.

12, the film surface rough, uneven


① low temperature extrusion, plastic resins bad;

② out too fast.


① to adjust the temperature setting out, and appropriately raise the temperature of extrusion, plastic resins to ensure good;

② appropriate to reduce the speed of extrusion.

13. Films have a peculiar smell


① resin has a smell of raw materials;

② out of the molten resin temperature is too high, resulting in decomposition of resin, resulting in smell;

③ bubble film cooling enough film of the hot air inside the bubble did not rule out clean.


① replacement resin raw materials;

② out temperature adjustment;

③ improve the cooling efficiency of the air cooling ring, so that the membrane vesicles full cooling.

Hint:If there is any inconsistency or conflict between the English and Chinese versions, the Chinese version shall prevail for all purposes.

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  1. Thank you,

    Sir for such a nice fruitfull reading material.And hope to provide me a good reading materails on 5layer blown film at same EmailID.

    Comment by Dharmendra — April 3, 2010 #

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