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What should I pay attention to during the injection moulding of thermoplastic elastomer TPR? According to the characteristics of the material and the supply situation, the appearance and process performance of the material should generally be tested before moulding. The supplied granules often contain varying degrees of moisture, melts and other volatile low molecules, especially with hygroscopic tendency of TPR water content is always more than the limit allowed for processing.

It is therefore necessary to dry the material before processing and to determine the moisture content. At high temperatures the moisture content of TPR is required to be below 5%, or even 2%-3%, so it is commonly used to dry the material in a vacuum oven at 75°C-90°C for 2 hours. Already dry material must be properly sealed and stored to prevent the material from the air again moisture absorption and loss of drying effect, the use of drying chamber hopper can be continuously for the injection moulding machine to provide dry hot material, to simplify the operation, to maintain clean, improve the quality, increase the rate of injection are favourable. The loading quantity of drying hopper is generally taken as 2.5 times of the hourly quantity of material used by the injection moulding machine.

TPR Colouring:

SBC based TPEs are superior in colour to most other TPR materials. Therefore, they require only a small amount of masterbatch to achieve a particular colour effect and the resulting colour is purer than other TPRs. Generally speaking, the viscosity of the masterbatch should be lower than that of the TPR because the melt index of TPR is higher than that of the masterbatch, which will facilitate the dispersing process and result in a more uniform colour distribution.

For SBS-based TPEs, polystyrene-based colour carriers are recommended. For harder SEBS-based TPR, polypropylene (PP) colour carriers are recommended. For softer SEBS-based TPR, low-density polyethylene (LDPE) or ethylene vinyl acetate copolymers (EVAC) can be used. For softer varieties, PP colour carriers are not recommended as the hardness of the composite will be compromised.

For some overmoulding applications, the use of polyethylene (PE) colour carriers may adversely affect the adhesion to the substrate.

Need to clean the barrel before injection moulding

Before the newly purchased injection moulding machine is used for the first time, or when it is necessary to change the product, change the raw material, change the colour or find out that there is a decomposition phenomenon in the plastic, it is necessary to clean or dismantle the barrel of the injection moulding machine.

Cleaning barrel generally use heating barrel cleaning method. Cleaning materials generally use plastic raw materials (or plastic recycling materials). For TPR material, can be processed by the new material to replace the transition cleaning material.

TPR moulding temperature

In the process of injection moulding, whether the temperature is set accurately is the key to the appearance and performance of the product. The following are some suggestions for temperature setting in TPR processing and injection moulding. The temperature in the feed area should be set fairly low to avoid clogging of the feed opening and to allow entrained air to escape. When using masterbatches, the temperature in the transition zone should be set above the melting point of the masterbatch to improve mixing. The temperature in the area closest to the injection nozzle should be set close to the desired melt temperature. Therefore, it has been tested that the usual temperature range for TPR products is 160°C to 210°C for the cylinder and 180°C to 230°C for the nozzle in each zone.

The mould temperature should be set higher than the condensation temperature in the injection zone, as this will avoid contamination of the mould with moisture which may cause streaks on the surface of the product. Higher mould temperatures usually result in longer cycle times, but it improves the weld line and the appearance of the product, so the mould temperature range should be designed to be between 30 and 40.

Mould filling, pressure holding and cooling

In the process of filling the mould cavity with products, if the filling performance of the products is not good, it will happen that the pressure will be reduced too much, the filling time will be too long, the filling will not be enough and so on, which will make the products have quality problems. In order to improve the filling performance of the products in the moulding, and improve the quality of the moulded products, it can be generally considered from the following aspects:

Changing to another series of products

Change the gate position

Changing the injection pressure

Changing the geometry of the part

The control of injection pressure is usually divided into the control of primary injection pressure, secondary injection pressure (holding pressure) or more than three times of injection pressure. The proper timing of pressure switching is very important to prevent overpressure in the mould, overflow or lack of material, etc. The specific volume of the moulded product depends on the melt pressure and temperature when the gate is closed during the holding pressure phase.

If the pressure and temperature are the same every time you switch from the holding pressure to the cooling phase of the moulded part, the specific volume of the moulded part will not change. At a constant moulding temperature, the most important parameter determining the product size is the holding pressure, and the most important variables affecting the product size tolerance are the holding pressure and temperature.

For example, the holding pressure is lowered immediately after the end of mould filling, and then increased when the surface layer is of a certain thickness, so that large products with thick walls can be moulded with a low clamping force, eliminating craters and flying edges.

The holding pressure and speed are usually 50%-65% of the maximum pressure and speed when filling the mould cavity, i.e. the holding pressure is about 0.6-0.8MPa lower than the injection pressure. due to the lower holding pressure than the injection pressure, the load on the pump is low during the considerable holding time, which prolongs the service life of the oil pump, and at the same time, reduces the power consumption of the oil pump motor.

A certain amount of metering is pre-adjusted so that a small amount of melt (buffer volume) remains at the end of the screw near the end of the injection stroke, and a small amount of melt is replenished by applying a further injection pressure (secondary or tertiary injection pressure) in accordance with the filling situation in the mould. In this way, it is possible to prevent the product from denting or to regulate the shrinkage of the product.

The cooling time depends mainly on the melt temperature, the wall thickness of the product and the cooling efficiency. In addition, the hardness of the material is also a factor. Harder varieties will solidify faster in the mould compared to very soft varieties. If cooling is done from both sides, the cooling time required per 0.100' wall thickness will typically be approximately 10 to 15 seconds. Overmoulded products will require longer cooling times because they can be cooled more efficiently with a smaller surface area. The cooling time required per 0.100' wall thickness will be approximately 15 to 25 seconds.

Effect of injection moulding process conditions:

Incomplete plastic moulding

Improperly regulated feed, missing or excess material.

Injection pressure too low, short injection time, plunger or screw returned too early.

Slow injection speed.

Material temperature too low.

Overflow (flying edge)

Injection pressure too high or injection speed too fast.

Excessive dosing.

TPE thermoplastic elastomer main application areas, TPE thermoplastic elastomer as the industry material of the rising star, in recent years has been more and more recognized by the industry. TPE thermoplastic elastomer is non-toxic and non-irritating, both rubber and plastic double features, its high elasticity, aging resistance, oil resistance and other excellent performance, has become the industry recognized as a substitute for traditional rubber and PVC, PP, PE and other general thermoplastic resin new polymer materials. In the end, what are the main application areas of TPE thermoplastic elastomer next to summarise the following points:

TPE materials are applicable to a very large number of areas, almost involving many aspects of our working life, as follows:

First, the medical field: TPE materials are safe, non-toxic and biodegradable, compared with PVC has obvious advantages, so the medical field is one of the main areas of application of TPE materials, it is widely used in pharmaceutical packaging, disposable syringes, infusion bags, all kinds of catheters, medical equipment accessories;

Second, sports equipment: TPE is one of the commonly used materials in the field of sports, it can be given to the racket handle to do wrapping, or sports equipment handle wrapping, in addition to indoor fitness equipment such as tension bands, tension tubes, yoga mats, grip and other indoor fitness equipment, as well as frogs shoes, Frisbee, goggles, and other outdoor sports equipment are often used as raw materials TPE;

Third, instruments and tools: TPE material can provide non-slip shock-absorbing function for the product, improve the comfort and durability of the product. It is often used in all kinds of tools, such as pliers, shovels, drills, meters and so on;

Fourth, home daily use: TPE also has a place in the field of daily necessities: our common ice grid, non-slip carpet, toothbrush wrapping rubber, bathroom shower material, luggage coating material, water pipes, kitchen utensils wrapping rubber, are made of TPE;

Fifth, adult products: TPE material is non-toxic, mild and non-irritating, direct contact with the human body will not lead to allergies, so it is very suitable to serve as adult materials, in the industry, TPE is often used to make solid dolls and other products;

Six, electronic products: TPE material is soft, good ductility, not easy to break, and has good fire performance, so it is very suitable for the production of various types of wire, such as data lines, headphone cables, audio cables, etc., at the same time, TPE is also often used as a raw material for the production of mobile phone cases;

Seven, the automotive field: in recent years, with the rapid growth of the domestic automotive industry, TPE has been formed in the automotive-centric applications market, maintaining an average annual growth of 15% to 20% of the high-speed growth momentum. TPE is used in a large number of automotive body, interior and exterior, structural components and special purpose, and the market share continues to expand, the automotive field has become one of the main growth points in recent years TPE;

Eight, children's toys: traditional toys made of PVC materials contain toxicity, direct contact with the baby will stimulate the baby's skin, affecting the baby's physical health. With the escalation of parental care of children, they are on baby products and toys of the safety and health level of strict requirements, TPE soft high toughness and environmental protection and non-toxicity of the characteristics of the children's toys just in line with the parents of the stringent requirements.

The elongation at break of a TPE material refers to the concept of tensile strength and tensile strength and is usually expressed in Arabic numerals. For example, if a material has an original length of 100mm, it is stretched by an external force, and it breaks when it is stretched to 300mm, then the elongation of that material is 300%. So what are the factors that affect the elongation at break of TPE?

The factors that affect the elongation at break of TPE are as follows:

Stone powder filling: under the premise of other factors are consistent, the larger the ratio of stone powder filling, the smaller the elongation at break.

Substrate: Under the premise of other factors are the same, the elongation at break of TPE of SEBS substrate is greater than that of TPE of SBS substrate, in SEBS substrate, the elongation at break of SEBS substrate with large content of butadiene is better than that of SEBS substrate with small content of butadiene.

Plastic ratio: under the premise of other factors are the same ah, the larger the proportion of plastic, the smaller the elongation at break of the material.

Oil filling ratio: under the premise of other factors, the larger the oil filling ratio, the larger the elongation at break of the material.

TPE material formulation system has a large variation of space, which determines the TPE material has a large elongation at break space, different hardness and physical properties of the TPE material elongation at break is generally in the 200-1600% or so.

TPE material injection moulding process, if the filling performance of the products is not good, it will happen that the pressure reduction is too big, the filling time is too long, the filling is not enough, etc., so that the products have quality problems.

Then TPE material injection moulding will encounter what problems?

TPE material injection moulding will encounter what problems, you can refer to the following content:

Drying:

According to the characteristics of the material and the supply situation, the appearance and process performance of the material should generally be tested before moulding. Supplied granules often contain varying degrees of moisture, melts and other volatile low molecular matter, especially with hygroscopic tendency of TPE water content is always more than the limit permitted by the processing. Therefore, it is necessary to dry them before processing and to determine the water content.

Colouring:

TPEs based on SBC are superior in colour to most other TPR materials. Therefore they require only a small amount of masterbatch to achieve a particular colour effect and the resulting colour is purer than other TPRs. Generally speaking, the viscosity of the masterbatch should be lower than that of the TPR. This is because the melt index of TPR is higher than that of the masterbatch, which will facilitate the dispersion process and allow a more uniform colour distribution.

Cleaning the barrel:

The barrel of the injection moulding machine needs to be cleaned or dismantled before the initial use of the newly purchased injection moulding machine, or when it is necessary to change the product, change the raw material, switch the colour or find that there is decomposition in the plastic in the production.

Moulding temperature:

In the process of injection moulding, whether the temperature setting is accurate or not is the key to the appearance and performance of the products.

As we all know, TPE material is a thermoplastic elastomer material modified on the basis of SEBS, which is often widely used in common transparent toys, sports equipment, home appliance shells, handles and other industries. However, some outdoor use of TPE products, due to radiation, ozone, ultraviolet light and other long-term action, it is likely to occur aging and not durable problem, so that the TPE material will soon lose its performance. Therefore, improving the durability of TPE plastic products is worth our attention.

Tips to make TPE plastic products more durable are as follows:

If the TPE plastic products are stained during the use, you can use water to rinse, and then dry with a rag. If there are oil stains, glue, dust or dirt, we, on the other hand, can apply toothpaste and windex to the surface of the item to wipe it, which can effectively remove the stains without residue.

TPE plastic products should not be placed in the sun for a long time, which will make the structure of the TPE raw materials change, TPE products will therefore appear cracking, gradually hardening and other aging phenomena. So TPE plastic products are not suitable for long-term outdoor use.

In daily use, do not use sharp objects to cut TPE plastic products, because the tear strength of TPE raw material is poor. Also don't press the TPE plastic products under heavy objects for a long time, otherwise it will easily cause its bending and deformation.

In the general environment, TPE plastic products are less likely to be aging problems, but in high temperature, humidity, outdoor long-term use of the occasion, in order to ensure the use of additional heat-resistant stabilizers (antioxidant), so as to more effectively improve the aging resistance of TPE products.

The molding process affects TPE shrinkage:

Holding pressure increases, shrinkage decreases.

Injection temperature remains constant, injection pressure increases, shrinkage is decreasing accordingly.

The mold temperature is set high, the shrinkage rate increases.

Melt temperature increases, shrinkage decreases.

Product cooling time in the mold cavity increases, shrinkage decreases.

Holding pressure for a long time, shrinkage decreases, but the gate closure will no longer affect the shrinkage.

Internal stress shrinkage, generally within a day after the finished product is molded, stabilized in about 3 days. Plunger injection molding machine molding shrinkage is also greater.

TPE products injection molding speed, shrinkage will also have signs of increase, but the impact is very small.

There are many kinds of POM, such as: reinforced pom, toughened pom, flame-retardant pom, abrasion-resistant pom, weather-resistant pom, oil-resistant pom, hydrolysis-resistant pom, high (low) temperature-resistant pom, heat-resistant pom, high-viscosity POM, high-toughness POM, high-stiffness pom, high-hardness pom, glass-fiber-reinforced pom, low-warping pom, low latent pom, fatigue-resistant pom, Creep-resistant pom, high-flow pom, heat-stabilized pom, anti-static pom, flexible pom and other modified products.