Analysis and discussion of defects and problems of TPV material extrusion

Original release | Meite Polymer Nova

Nowadays, due to ease of processing TPV, range of its application is becoming wider and wider. For extrusion molding, wires and cables, extruded pipes, profiles, sealing tapes, water cutting, mud tanks, etc. are used. To ensure normal extrusion, it is usually necessary to bake TPV raw materials at 80°C for 2 hours and clean extrusion screw . But even if above steps are followed, there may still be poor extrusion. Now, author summarizes common extrusion defects as follows and gives appropriate treatment measures.

1. Horizontal stripes

Source: Network

Some will be called trembling lines and vibrating lines, which refer to stripes perpendicular to direction of rods. The frequency of bands varies from high to low. There are two reasons for this. The second is that extrusion machine, including roller press, extrusion unit and tractor, have certain fluctuations. When size and fineness of surface remain unchanged, following attempts can be made:

1.1. Correctly reduce set temperature of screw and die;

1.2, increase rod pull speed;

1.3. Replace raw materials with a lower melt flow rate;

1.4 Check if machine is shaking, and if so, fix it.

Impact resistance note: As for vibration (vibration, vibration), in terms of TPV materials, this is usually reason for insufficient melt strength, and can also be said that reason is due to slow cure rate TPV. For example, a TPV with a relatively low cure rate is more likely to result in vibrating lines, and this is more likely to occur in high temperature conditions. A very interesting situation arises: when degree of stretching is relatively large, when cure rate of TPV material is very high, especially in case of low temperature in winter, horizontal bulges will be more obvious, which is better judge. Because this defect is more obvious, size is greatly reduced.

Second, vertical stripes

refers to stripes parallel to direction of edges.

2.1, matrix not polished evenly;

2.2. Material has accumulated in die that may scratch surface of product;

2.3 Stereotypes don't grind smoothly.

3. Accumulation of material on die

TPV is not like a one-piece PVC extrusion die that has no buildup. It is a mixture of PP and EPDM. There will always be accumulation in place of extrusion head. It's just a matter of how much and accumulation. The condition problem, there are two kinds of accumulation conditions: oily paste and fluffy flaky mass. Some customers need an ointment because accumulated material will not be carried away with product and will not affect appearance of product; Accumulation because too much accumulation needs to be turned off for cleanup. The condition is mainly determined by raw material. Besides, it's about how much. Obviously, less material accumulated, better. To achieve a state of less material accumulation, following adjustments can be made:

3.1. Sand die outlet position as smoothly as possible;

3.2. Before extruding product, lubricate mold and die, for example, wash raw material containing a certain proportion of PPA before extruding product, and then extrude normally;

3.3. In event that this does not affect bonding of surface of product or there is no need for such bondingIn any case, material supplier must add appropriate amount of lubricant to material.

Recommended Reading: Analyzing and Solving Die Deposits in Extrusion

Fourthly, surface of product is rough

Generally speaking, if surface of product is rough, curing rate will be higher and physical properties will be better. But some products require high fineness on surface, you can start from following points:

4.1. Increase processing temperature, including screw temperature and die temperature;

4.2. Reduce extrusion speed and pull speed;

4.3. Suppliers must reduce cure rate of raw materials accordingly.

Toughness Brother Note: If TPV contains a certain amount of water, it will affect appearance of extrusion. In severe cases, it will be very rough, and pores will appear in cut. If it is slightly lighter, surface will be damaged. It is still relatively flat, but contains some extruded silver wire, as shown in picture below:

TPV sealing strip taken by Huawei mate 20pro

5. Sawtooth position at sharp corners

Sawtooth means that material is not continuous and there is a break that results in failure.

5.1. Where matrix has a sawtooth shape, chamfer corner R so that sharp corner takes form of an arc of a circle;

5.2. Enlarge flow channel in mold and increase discharge back pressure;

5.3 Replace raw materials with higher melt strength. In general, phenolic TPV has higher melt strength than peroxide TPV.

Six, size deviation

6.1.Deviation of overall size, change extrusion speed or pull speed of main screw;

6.2.Local size deviation, modified die for single-channel flow, modified flow channel for multi-channel.

Seven, easily deformed

After molding, cross-sectional shape of product changes, mainly due to insufficient or too slow cooling of material.

7.1. Reduce cooling water temperature or lengthen cooling water tank to make cooling more complete;

7.2. To keep surface of extruded product of high quality, reduce temperature of die;

7.3 Suppliers are required to increase cure rate of TPV materials.

Finally, composition of TPV is that PP is a continuous phase and EPDM is a dispersed phase. In low hardness TPV, because PP is less continuous, it is necessary that extruder has strong plasticizing ability. When meltability is relatively weak, extruded appearance may not be delicate or even have particles. Increasing extrusion temperature has a certain effect, but effect is not very obvious. Therefore, it is still necessary to consider matching screw design, aspect ratio and extrusion volume of extruder.

Disclaimer: All text/images and other manuscripts marked "Source: XXX" are intended to provide additional information and facilitate industry discussion under this heading and do not constitute agreement with them. The content of article is for reference only. If there is any infringement, please contact us to have it removed. All texts/figures and other manuscripts in which author is indicated at beginning of article are originals with this heading number, if necessary, it is necessary to obtain authorization with this heading number.