What is "TPV Raw Material" to Take You to Learn More
Source：德创化工Time：2020-03-30Hits：2954
Several processing methods of TPV TPV have slight moisture absorption characteristics, and should be dried before extrusion or blow molding. Before putting the materials into the drying oven, the temperature of the dryer should be raised to 100℃. The TPV is then kept in a drying oven for 2-3 hours. Contact with the environment with high relative humidity should be avoided, because the material will absorb moisture and make the processed products void. If after a long period of shutdown, the raw materials remaining in the extruder barrel should be discharged before resuming the operation. Extrusion equipment should be thoroughly cleaned before and after processing TPV. Injection molding equipment or extruder barrel shall be cleaned mechanically or completely replaced and emptied with polyethylene or polypropylene.
Several Processing Methods of TPV
I extrusion
According to the requirements, the soft and hard parts can be coextruded, the sealing performance of the flexible part of the sealing strip is good, the flexible barb has good adaptability to slotting, the slotting tolerance requirement is loose, the hardware part is convenient to insert and saves working hours. Light specific gravity, easy processing, small Mick number. There are many specifications and varieties, which can be made into various colors according to requirements to meet various requirements of customers. It has excellent weather resistance, good sealing performance, wear resistance and durability.
1 extrusion micro foaming
II. Injection Molding
Injection molding is to convert thermoplastic raw materials into products that can be used and maintain their original properties through injection molding. Therefore, preparation of injection molding process parameters is an important link to ensure injection molding processing.
The key factors that should be paid special attention to in the preparation of injection molding process parameters are: temperature, pressure and time.
1 Injection molding temperature control: The temperatures to be controlled in the process of injection molding include barrel temperature, nozzle temperature and mold temperature.
The main purpose of controlling the temperature of the charging barrel and the nozzle is to fully plasticize and flow the materials in the charging barrel. The purpose of controlling the mold temperature is to make the melted material have higher fluidity in the mold filling process, and to help the melted material to quickly fill all parts of the mold cavity; At the same time, the material filled with the mold cavity can be fully cooled and shaped. The control of mold temperature has great influence on the internal performance and apparent quality of products.
2 Pressure Control: During the processing of injection molded products, the pressure to be controlled includes injection molding pressure and plasticizing pressure (i.e. back pressure).
Injection pressure: the pressure is transmitted to the tail end of the barrel through the hydraulic system of the injection machine (electric injection machine uses servo motor) to push the screw forward, that is, the pressure applied to the tail end of the screw is called injection pressure. In injection molding, the injection pressure plays a role in overcoming the flow resistance of molten plastic from the charging barrel to the mold cavity, in the filling process, giving the molten mold filling rate and compacting the molten material.
Plasticizing pressure: refers to the pressure on the top of the screw when the screw rotates backward, which is called plasticizing pressure, also called back pressure. It can also be said that overcoming the resistance caused by the screw feeding rotation is called back pressure. Under normal circumstances, an appropriate increase in back pressure can make the melt temperature uniform, the pigment mixing uniform, and the gas in the melt can also be discharged.
In normal production operation, the back pressure should be as small as possible on the premise of maintaining good product quality.
3 time control: the time to be controlled in the injection molding process includes injection time, pressure maintaining time, plasticizing time, cooling time and cycle time.
Injection time: the time required for the molten material in the charging barrel to basically fill the cavity under the action of injection pressure is called injection time.
Holding time: is the time to press the plastic in the cavity. However, it should be noted that the holding time has an effect on the dimensional accuracy of the product before the melting material at the gate is frozen, but has no effect after the melting material at the gate is frozen.
Plasticizing time: The time required from the screw to start rotating the feed until the set metering position is called plasticizing time. The length of time is directly affected by back pressure and screw speed. It must be noted that the plasticizing time must be completed within the cooling time.
Cooling time: cooling time refers to the time required for the full molding of the product at a constant temperature after filling the cavity with the solid plastic melt. The length of cooling time mainly depends on the thickness of the product, and at the same time, it is the principle to ensure that the product will not cause changes when demoulding.
Cycle time: cycle time refers to the time required from the mold closing of the injection machine to the end of product demolding. The cycle time includes the aforementioned several times, i.e. injection time, holding time and cooling time (cooling time includes plasticizing time). The length of cycle time is related to the rationality of process parameter setting. It is also related to the continuity and automation of the production process.
Third, blow molding
The blow molding process is divided into four basic steps: first, forming a tube blank; Secondly, after the mold is closed, compressed air is introduced into the mold to inflate; Third, cooling and shaping; Fourth, deflate and open the mold to obtain the product.
The main technological factors affecting blow molding and product quality are: parison temperature, mold temperature, cooling time, blowing rate, blow molding air pressure and blowing ratio.
1. parison temperature
The parison temperature is generally controlled between the glass transition temperature and the softening temperature (or melting temperature), and is offset to the softening temperature side.
2. Mold temperature
The mold temperature is related to the glass transition temperature (Tg) of the raw materials. The Tg is higher and the mold temperature can be higher. On the contrary, the mold temperature should be lower.
3. Cooling time
The cooling time of hollow blow-molded products is generally 1/3~2/3 of the molding time, which is to prevent deformation of products caused by elastic recovery of polymers.
4. Blowing rate
The blowing rate of hollow blow molding should be as high as possible, which can shorten the blowing time and obtain a more uniform wall thickness and a better container surface.
5. Blow molding air pressure
Blow molding air pressure is related to plastic melt viscosity, product size and parison wall thickness.
6, inflation ratio
Blow-up ratio refers to the ratio of the outer diameter of the product (the transverse maximum dimension shall prevail for non-cylindrical products) to the outer diameter of the parison.
Blow molding equipment
Generally, the main machines of blow molding equipment are injection machines and extruders, followed by blow molding dies. Blow molding dies are usually composed of two halves. Due to the low pressure of blow molding dies, common mold materials include aluminum, zinc alloy, beryllium copper, cast iron, steel, etc.
Four, the problems encountered in the molding and solutions 1TPV has a very heavy odor reasons can be summarized as follows
(1) processing, temperature control problems
(2) odors generated by cross-linking agents and additives in the products, such as aging agents, oxidizing agents, etc.
(3) different brands
(4) the taste of oil
(5) Is the vacuum port vacuumized
Resolution:
It is suggested to raise the cost and do more post-treatment. If it is the odor generated by the auxiliary agent, it can be mixed and eliminated one by one, and the auxiliary agent with less odor can be used. Or directly change the tasteless material. If you want to remove the taste directly, you can use activated carbon and some mineral adsorption fillers such as porous zeolite can solve these problems.
2 Rough Phenomenon: Rough Surface
Cause:
(1) Poor plasticization and mixing
(2) poor liquidity
(3) the material be affected with damp be affected with damp
Resolution:
(1) Use an extruder with good mixing effect to increase the set temperature and use a fine filter screen
(2) increasing the set temperature
(3) fully drying before molding
3 scaling phenomenon: sediment is retained at the edge of the mouth shape
Cause:
(1) the material be affected with damp be affected with damp
(2) the characteristics of the material itself
Resolution:
(1) fully drying before molding
(2) using lubricant, coating the die with teflon, and modifying the material
4 unstable extrusion quantity: unstable extrusion quantity
Cause:
(1) The melting point in the extruder is unstable
(2) The temperature of extruder fluctuates greatly
(3) Slipping of Screw and Pellets
Resolution:
(1) changing extrusion conditions and screw shape
(2) improving the temperature control precision
(3) preheating the granules and increasing the temperature of the barrel under the filler hopper
5 deformation phenomenon: product deformation
Cause:
(1) uneven cooling
(2) Double-layer extrusion with different shrinkage
Resolution:
(1) uniform cooling
(2) Adjust shrinkage rate
6 Stripe Phenomenon: Stripes Appear at the Same Position
Cause:
(1) Mouth damage and scaling
(2) the appearance of dissimilar materials
(3) The welded parts have not been eliminated
Resolution:
(1) cleaning the mouth shape
(2) The interior of the cleaning machine barrel, the screw rod and the machine head
(3) increase the length from the joint (welding) part to the die, and increase the end pressure of the die and the resin temperature.
The above contents on several processing methods of TPV are shared here. Finally, it is necessary to know whether customers have certification or specified standard requirements for TPV. Some customers require a third-party test report, such as mechanical performance, electrical performance, flame retardant performance, and sanitary performance. Some reports are obtained relatively quickly and at low cost, while others are relatively long in time and high in cost.
