Why do some TPE products change color during processing?

We all know that TPE materials are suitable for a variety of processing methods and are easy to operate, but sometimes due to improper handling of certain details, it will cause defects in the finished product. Tereflex will explain to you why some TPE products change color during processing.

In the process of TPE processing, some friends will have inconsistent background color of injection molded products, which mainly causes the following reasons:

1. Materials:

1) The quality of the material itself is poor.

2) Improper storage is contaminated.

3) High content of moisture and volatiles.

2. Equipment:

1) The equipment is not cleaned, and dust or other dust is deposited on the hopper, resulting in material pollution and discoloration.

2) Temperature control failure caused by the imbalance of the thermostat or heating system.

3) There are foreign objects stuck in the barrel or screw groove, and the plastic is discolored by continuous grinding.

Second, the mold.

1) Poor mold exhaust.

3) There are residues of lubricant and release agent in the material or in the mold.

4) The size of the nozzle hole, sprue and runner is too small.

3. Technological aspects.

1) The screw speed is too high.

2) The temperature of the barrel and nozzle is too high.

3) The injection pressure is too high and the speed is too fast.

The influencing factors of injection molding machine on the discoloration of TPE plastic parts are:

1.The equipment is not in a hurry, it needs to be cleaned, dust or other dust, multiplied on the hopper is the material is contaminated and dyed and discolored.

2.Thermocouples, thermostats, or heating systems are out of balance, causing temperature control to malfunction.

3.There are obstacles in the barrel, which is easy to promote the degradation of TPE plastics, and there are metal foreign bodies stuck in the barrel or luochu, which are constantly grinding to discolor the plastics.

The influencing factors of discoloration of plastic parts may be caused by molds.

5.The mold is poorly vented, the plastic is adiabatic compressed, and it reacts violently with oxygen at high temperature and high pressure, burning the plastic.

6.The mold gate is too small.

7.Too much lubricant in the material or in the mold, too much release agent. If necessary, the barrel should be cleaned regularly to remove additives such as antistatic properties that are worse than the heat resistance of plastics.

8.The size of the nozzle holes, sprues and runners is too small.

In this regard, there are first oxidation problems, thermal conductivity after heating, pH value changes, temperature and humidity changes, etc., so special attention should be paid to processing.

TPE discoloration Categories: TPE News Thermoplastic elastomers (TPEs) have the physical and mechanical properties of vulcanized rubber and the process properties of thermoplastics. Since there is no need for hot vulcanization, the product can be produced using universal plastic processing equipment.

This feature makes the rubber industry produce.

If it is not handled properly during the production process, some chemical reactions will occur, resulting in discoloration.

The temperature is not to the plasticizing temperature.

The discoloration and dark lines of TPE injection molded products refer to the discoloration or dark streaks on the surface of the products due to overheating and degradation of materials or other reasons, and the main reasons for their appearance are three aspects: materials, molds and processes.

Reason 1: Poor thermal stability of the material.

Suggestion: Choose materials with good thermal stability or add heat stabilizers to materials.

Reason 2: There are ** materials in the material.

Recommendation: Stop using ** material.

Reason 3: The nozzle is inconsistent with the R-value of the die, resulting in material build-up that is carried into the mold cavity during each injection.

Recommendation: Make the nozzle consistent with the die r-value.

Reason 4: The plasticization of the material is uneven, and there are unmelted particles in the product, and dark lines appear.

Suggestion: Increase the back pressure to make the plasticization even.

Reason 5: There are foreign substances in the material, such as: dust from the mold, the hopper heater or barrel falls off due to corrosion and plating layer, and the barrel or nozzle contains previously used residual resin.

Recommendation: Clean the barrels, nozzles, or clean hoppers.

Reason 6: The barrel or screw is defective (such as bumps or chips) that cause the material to remain for a long time and decompose.

Recommendation: Repair and, if necessary, replace.

We generally analyze the color difference of TPE products from the following five aspects.

1. Injection molding machine and mold factors.

To choose an injection molding machine with the same capacity as the injection molding product, if the injection molding machine has problems such as material dead ends, it is best to replace the equipment. For the color difference caused by the mold pouring system and exhaust groove, it can be solved by the maintenance of the corresponding part of the mold. It is recommended to solve the problems of injection molding machines and molds before organizing production to reduce the complexity of the problem.

2. TPE material and masterbatch.

Controlling the raw material TPE is an important part of solving the color difference. Especially in the production of light-colored products, we cannot ignore the influence of the different thermal stability of TPE materials on the color fluctuation of the products. Since most injection molding manufacturers do not produce filler masterbatches or masterbatches themselves, the focus can be on production management and raw material inspection.

That is, to strengthen the inspection of raw materials warehousing; In production, the same product is produced by the same manufacturer, the same brand of masterbatch and masterbatch as much as possible; For the masterbatch, we should conduct a sampling test before mass production, not only to proofread with the last time, but also to compare in this time, if the color difference is not large, it can be considered qualified, as the batch of masterbatch has a slight color difference, the masterbatch can be remixed and then used, in order to reduce the color difference caused by the uneven mixing of the masterbatch itself. At the same time, we also need to focus on testing the thermal stability of raw material resin and masterbatch, and it is recommended that manufacturers replace those with poor thermal stability.

3. The masterbatch is unevenly mixed with the TPE main material.

The poor mixing of the same color masterbatch of the TPE main material will also make the color of the product changeable. After the TPE and masterbatch are mechanically mixed evenly, when the material is sent to the hopper through the lower suction, due to the electrostatic action, the masterbatch is separated from the TPE main material, and it is easy to adsorb on the hopper wall, which is bound to cause the change of the amount of masterbatch in the injection cycle, resulting in color difference. This situation can be solved by the method of manual stirring after the raw materials are sucked into the hopper.

For the production of colored products by adding toner, the most effective way is not to use a suction machine, but to use a hot air dryer, and use manual feeding to prevent the color difference caused by the separation of toner and masterbatch.

Fourth, the injection molding process adjustment.

When the injection molding process parameters need to be adjusted due to non-color difference, the injection temperature, back pressure, injection cycle and masterbatch addition should not be changed as much as possible, and other process parameters should be adjusted to observe the impact on the color. As much as possible, avoid the use of injection molding processes that cause strong shear effects, such as high injection speed and high back pressure, to prevent color difference caused by local overheating or thermal decomposition. Strictly control the temperature of each heating section of the barrel, especially the nozzle and the heating part immediately adjacent to the nozzle.

Fifth, the amount of masterbatch.

Before making color difference adjustment, it is also necessary to know the trend of product color change with temperature and masterbatch. With the change of production temperature or masterbatch quantity, the color change law of different masterbatches is different. The law of change can be determined through the color testing process.

Unless the color variation of this masterbatch is known, it is not possible to adjust the color difference very quickly, especially when producing with new masterbatches.