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injection molding thermoplastic elastomers.
by：Dajin caster
2020-06-13
At present, all five types of thermoplastic rubber on the market (TPEs)
Can be injection molded into parts with high elasticity.
These five categories include styrenics, Polyolefine, polypolyester, polyurethane and polyamide.
Although there is a certain overlap in the application of TPEs, due to the unique advantages of the material, each class has an area it mainly occupies (s).
Styrenic materials launched in 1965 provide terminals
The overall flexibility of the user is the widest range.
Over the years, durometer as low as 15 Shore A and as high as 70 Shore D has been successfully formed.
The application of molded items includes footwear, automotive supplies, medical supplies and general-purpose items.
Thermoplastic polymer (TPOs)
The fastest growing market at an average rate of nearly 20% a year (ref. 1).
Due to the various oil-based polymer and composite technologies used in the manufacture of materials, these elastomer provide a wide range of processing properties and physical properties.
The main applications include many different automotive products such as exterior body parts, side molding of the body, air duct and industrial products.
Copolyester rubber provides a class of materials with physical properties between rubber and engineering plastics for molder.
They have excellent flexibility, creep resistance and operate over a wide range of temperatures.
Their main applications include automotive supplies such as constant speed drive joint boots, electrical components, and medical products.
All kinds of thermoplastic polyurethane rubber (TPUs)
The hardness values range from 30 bank A to 70 Bank D.
Their main applications include automotive products, casters and industrial products such as drive belts, soft
Hammer Head and washer.
Finally, it can be considered that nylon TPEs is a kind of elastic nylon that is not reinforced.
These materials have excellent low temperature impact properties and good wear resistance.
The main applications of these materials include seals and washers, low temperature bellows and boots, and auto parts.
The injection molding process itself may be a difficult process depending on many factors.
These main factors include material and machine properties and the design of the parts.
Although other materials are injection molded, this process can be described as producing 3D parts from polymer materials continuously.
The production of parts is done by first melting the material (
Generally referred to as plasticization)
The material is then injected into the mold under pressure and solidified in the form of a cavity in the mold.
The history of injection molding dates back to 1872, when the United StatesS.
Patents have been issued for the design of machines using pistons (ref. 2).
The TPE material may be formed on the plunger machine today, however, with a reciprocating spiral type machine, the melting homogenizing effect is better.
It was not until 1956 that the first reciprocating machine was available, the one chosen today.
Generally, the machine can be broken down into three pieces.
These three components are made up of injection units, molds and process control systems.
The polymer in the form of particles or powders is supplied to the machine through the Hopper.
The material must be continuously fed through the hopper and entered down into the injection device.
When the screw rotates, the material is transmitted through the barrel to the front of the screw.
As it moves, the material is heated by a series of heater bands outside the barrel.
The combination of heating and shear should form a uniform melting.
When the material is delivered, the pressure is generated in front of the screw tip.
This pressure forces the screw to return until a predetermined amount of material is developed.
The screws will stop temporarily (
How much time depends on the cooling time)
And then will stand up (non-rotating)
Push the material into the cavity.
The material is then cooled under reduced internal pressure.
When the part is set enough, the clamping device will open and the part will fall off.
Figure 1 shows the cavity pressure distribution over time during the molding process.
Molded thermoplastic rubber if you follow some simple guidelines, the molding of five different types of TPEs may be relatively easy.
First of all, almost all TPEs have different theological properties than most thermoplastic materials.
Since all TPEs are fairly rubber in nature, the viscosity of the material is usually more affected by shear than by temperature (figure 2).
When the material goes through a higher shear rate, the viscosity drop becomes more intense.
Because of this, since the shear rate can be controlled more easily, the reciprocating injection molding machine should be used as much as possible.
Styrenic TPEs are sold commercially in two different categories depending on the composition of the intermediate block.
Table 1 compares the differences between these two classes.
Under normal circumstances, the non-saturated styrenic material (
Ding benzene-styrene)
High shear rates should not and should not be experienced.
However, the saturated midblock type (styrene-ethylene-butylene-styrene)
To ensure sufficient surface appearance and good physical performance, a higher shear rate is indeed required.
The cylinder temperature of the non-saturated material shall be within the range of 280 [degrees]F -400 [degrees]
Depending on the grade of the material.
Usually, a higher mold temperature leads to a better surface appearance.
Depending on the surface area and processing conditions of the part, the injection pressure of the unsaturated resin can vary from 3,000 psi to 20,000 psi.
The injection pressure time should be as short as possible so that there is no excessive packaging of the part.
According to the length of the runner and the size of the part, the injection speed should be from slow to moderate.
30-normal screw speed
80 rpm should be used so that the screws stop before the next injection.
25-back pressure
50 psi should be sufficient to form a uniform melting.
The processing stability of the saturated style is higher and therefore more tolerant.
The cylinder temperature of these materials is generally from 380 [degrees]F -500 [degrees]
F with mold temperature of 80 [degrees]F -175 [degrees]F.
The injection speed should be fast, so freeze-
No off will appear, and the appearance of the surface will be optimized.
Depending on the compound, the screw speed and return pressure may be slightly higher than the unsaturated resin.
Table 2 gives a more complete breakdown of the preferred processing conditions for these two types of styrenic materials.
Depending on the specific morphology, olefin elastomer or TPOs can be divided into three different categories.
Initially, TPOs was prepared by mechanically mixing olefinic-type materials, specifically polyethylene, polypropylene and ethylene-propylene rubber.
Another kind of TPO, called thermoplastic vulcanization rubber (TPV)
, Including the composite process of partially cured elastic phase in the thermoplastic carrier.
Finally, a single-phase olefinic elastic material (
Melted rubberMPR)
It is reported that this shows a single glass transition temperature (ref. 3).
However, the behavior of these three types of materials is indeed somewhat similar in the molding process.
Cylinder temperature should change from 375 [degrees]
F High 450 [:degrees]
Depending on the grade of the material.
Mold temperature can run from low to 35 [degrees]
F. Certain grades to 175 [degrees]F.
To ensure adequate filling, the injection speed should range from moderate to fast.
TPOs is not easy to absorb water, but should be stored in a relatively dry place.
If the material gets wet, it should be dry at 200 [degrees]F for 1-3 hours.
Table 3 reports the preferred conditions for this rapidly growing category of materials.
In order to obtain the best performance, the copolyester elastomer must be dried before molding ([is less than]0. 1%).
In general, copolyester is not as shear-sensitive as some other types of TPEs.
Their viscosity can be controlled by increasing or lowering the barrel temperature.
When the mold temperature is hot enough, the injection pressure as low as 3,000 psi can be used (150 [degrees]F).
Higher pressure will reduce shrinkage due to higher packaging.
For thin-walled molding, the injection rate should be high, while for thicker parts, the injection rate is moderate enough.
Table 4 the appropriate molding conditions for co-polyester TPEs are recommended.
Polyurethane TPEs (or TPUs)
Two types of goods are usually considered.
The tensile strength of polyester-based tpu is higher than that of polyester-type TPEs, with better ozone, oxygen, oil and solvent resistance.
However, ether
The base TPEs has better low temperature performance and better resistance to hydrolysis and microbial attack.
Both classes have similar processing conditions.
The material is hygroscopic and must be dried before processing ([is less than]. 05%).
The mold temperature is between 90 [degrees]F -150 [degrees]
F is sufficient for optimal surface appearance and physical performance.
When the material is properly treated, the melt should deviate slightly-
White to very light yellow.
If there are bubbles in the melt, there may be moisture.
Excessive melting temperatures can lead to a \"very transparent\" cleaning process.
During the shutdown, the barrel should be cleaned using materials such as polyethylene or polystyrene to prevent material degradation.
Table 5 reports on the recommended processing conditions for tpu.
If following some important guidelines, it is also easy for the polyamide TPEs to be injection molded.
The material must be dry before molding, generally less.
08% moisture content.
By using a polymer (such as nylon 6, 11, or 12) as the structural part of the part, it is easy to complete the insertion molding without the need for an adhesive.
The universal screw works well in producing full melting homogenization.
Regrind can be used safely at level 20
25% as long as the material is properly dried.
Table 6 gives a more complete decomposition of the preferred processing conditions for polyamide TPEs.
Finally, in many traditional designs, all TPEs that are commercially available today can be easily formed.
Processing of softer durometer compounds ([is less than]45A)
The modified gate design is sometimes required for easy disassembly.
The angle of eating water. 0 [degrees]
It is usually satisfactory for most softer compounds.
In addition, in order to increase the pull force, more \"positive\" gate pull pins are sometimes needed.
For deeper stretching and softer compounds, it may be necessary to peel off the plate and/or air to break the vacuum generated by shrinkage.
The thimble should also be as large as possible so that they do not penetrate the parts.
The runner should be a full circular configuration and be as short as possible so that there will be enough traffic for all lenses.
Door size should always start from an early age (
Size depends on the part)
Expand if necessary.
In order to obtain the best release from the mold cavity, the surface of the mold cavity should be honed by steam.
Highly polished or chrome plated mold surfaces can cause sticking together and are not recommended.
As long as the runner itself is \"fairly short\" and at least 1 inch in diameter, insulated runners can be used.
Hot runner has also been successfully used in systems where the runner diameter is greater. 5 inch.
Injection molding TPEs may be relatively easy if certain guidelines are followed.
Some of the more important guidelines are as follows: * most TPEs are sensitive to shear.
Increasing or lowering the back pressure of the material changes the viscosity of the material.
* Since the material is sensitive to shear, the screw retraction time should be adjusted so that it can end before the next shot.
* The injection pressure time should be as short as possible to avoid excessive packaging.
* The holding pressure should be 1/3 to 1/2 of the injection pressure so that the gate will be sealed and there will be no excessive packaging.
* For better parts to top out, the mold cavity should be honed by steam.
* Universal screws work fine for all TPE materials.
* Always follow the manufacturer\'s advice on drying materials.
Under normal circumstances, the co-polyester, polyurethane and polyamine are moisture-absorbing, while styrenics and polyolene are not.
Note 1: it should be noted in the processing guide table that as the TPE level becomes soft (
Within the same class)
Processing parameters will fall into the lower range reported.
For example, the 35 Shore a styrenic TPE will have lower injection pressure, processing temperature and subsequent higher flow performance than the 50 shore D material. References [1]Walker, B. M. , Rader C. P.
2nd edition of the manual of thermal plastic elastic materials.
\"Thermoplastic Polyolefine elastomer, Shide C. D. , p.
48, Van Nostrand Reinhold, New York1988). [2]Rubin, I. I.
Injection molding;
Theory and Practice, Willie, New York, USA (1973). [3]
German patent DRP 858,310. [4]Walker B. M. , Rader C. P.
2nd edition of the manual of thermal plastic elastic materials.
\"Single-phase fused machined rubber\", Wallace J. G. , p.
143, Van Nostrand Reinhold, New York1988).
Can be injection molded into parts with high elasticity.
These five categories include styrenics, Polyolefine, polypolyester, polyurethane and polyamide.
Although there is a certain overlap in the application of TPEs, due to the unique advantages of the material, each class has an area it mainly occupies (s).
Styrenic materials launched in 1965 provide terminals
The overall flexibility of the user is the widest range.
Over the years, durometer as low as 15 Shore A and as high as 70 Shore D has been successfully formed.
The application of molded items includes footwear, automotive supplies, medical supplies and general-purpose items.
Thermoplastic polymer (TPOs)
The fastest growing market at an average rate of nearly 20% a year (ref. 1).
Due to the various oil-based polymer and composite technologies used in the manufacture of materials, these elastomer provide a wide range of processing properties and physical properties.
The main applications include many different automotive products such as exterior body parts, side molding of the body, air duct and industrial products.
Copolyester rubber provides a class of materials with physical properties between rubber and engineering plastics for molder.
They have excellent flexibility, creep resistance and operate over a wide range of temperatures.
Their main applications include automotive supplies such as constant speed drive joint boots, electrical components, and medical products.
All kinds of thermoplastic polyurethane rubber (TPUs)
The hardness values range from 30 bank A to 70 Bank D.
Their main applications include automotive products, casters and industrial products such as drive belts, soft
Hammer Head and washer.
Finally, it can be considered that nylon TPEs is a kind of elastic nylon that is not reinforced.
These materials have excellent low temperature impact properties and good wear resistance.
The main applications of these materials include seals and washers, low temperature bellows and boots, and auto parts.
The injection molding process itself may be a difficult process depending on many factors.
These main factors include material and machine properties and the design of the parts.
Although other materials are injection molded, this process can be described as producing 3D parts from polymer materials continuously.
The production of parts is done by first melting the material (
Generally referred to as plasticization)
The material is then injected into the mold under pressure and solidified in the form of a cavity in the mold.
The history of injection molding dates back to 1872, when the United StatesS.
Patents have been issued for the design of machines using pistons (ref. 2).
The TPE material may be formed on the plunger machine today, however, with a reciprocating spiral type machine, the melting homogenizing effect is better.
It was not until 1956 that the first reciprocating machine was available, the one chosen today.
Generally, the machine can be broken down into three pieces.
These three components are made up of injection units, molds and process control systems.
The polymer in the form of particles or powders is supplied to the machine through the Hopper.
The material must be continuously fed through the hopper and entered down into the injection device.
When the screw rotates, the material is transmitted through the barrel to the front of the screw.
As it moves, the material is heated by a series of heater bands outside the barrel.
The combination of heating and shear should form a uniform melting.
When the material is delivered, the pressure is generated in front of the screw tip.
This pressure forces the screw to return until a predetermined amount of material is developed.
The screws will stop temporarily (
How much time depends on the cooling time)
And then will stand up (non-rotating)
Push the material into the cavity.
The material is then cooled under reduced internal pressure.
When the part is set enough, the clamping device will open and the part will fall off.
Figure 1 shows the cavity pressure distribution over time during the molding process.
Molded thermoplastic rubber if you follow some simple guidelines, the molding of five different types of TPEs may be relatively easy.
First of all, almost all TPEs have different theological properties than most thermoplastic materials.
Since all TPEs are fairly rubber in nature, the viscosity of the material is usually more affected by shear than by temperature (figure 2).
When the material goes through a higher shear rate, the viscosity drop becomes more intense.
Because of this, since the shear rate can be controlled more easily, the reciprocating injection molding machine should be used as much as possible.
Styrenic TPEs are sold commercially in two different categories depending on the composition of the intermediate block.
Table 1 compares the differences between these two classes.
Under normal circumstances, the non-saturated styrenic material (
Ding benzene-styrene)
High shear rates should not and should not be experienced.
However, the saturated midblock type (styrene-ethylene-butylene-styrene)
To ensure sufficient surface appearance and good physical performance, a higher shear rate is indeed required.
The cylinder temperature of the non-saturated material shall be within the range of 280 [degrees]F -400 [degrees]
Depending on the grade of the material.
Usually, a higher mold temperature leads to a better surface appearance.
Depending on the surface area and processing conditions of the part, the injection pressure of the unsaturated resin can vary from 3,000 psi to 20,000 psi.
The injection pressure time should be as short as possible so that there is no excessive packaging of the part.
According to the length of the runner and the size of the part, the injection speed should be from slow to moderate.
30-normal screw speed
80 rpm should be used so that the screws stop before the next injection.
25-back pressure
50 psi should be sufficient to form a uniform melting.
The processing stability of the saturated style is higher and therefore more tolerant.
The cylinder temperature of these materials is generally from 380 [degrees]F -500 [degrees]
F with mold temperature of 80 [degrees]F -175 [degrees]F.
The injection speed should be fast, so freeze-
No off will appear, and the appearance of the surface will be optimized.
Depending on the compound, the screw speed and return pressure may be slightly higher than the unsaturated resin.
Table 2 gives a more complete breakdown of the preferred processing conditions for these two types of styrenic materials.
Depending on the specific morphology, olefin elastomer or TPOs can be divided into three different categories.
Initially, TPOs was prepared by mechanically mixing olefinic-type materials, specifically polyethylene, polypropylene and ethylene-propylene rubber.
Another kind of TPO, called thermoplastic vulcanization rubber (TPV)
, Including the composite process of partially cured elastic phase in the thermoplastic carrier.
Finally, a single-phase olefinic elastic material (
Melted rubberMPR)
It is reported that this shows a single glass transition temperature (ref. 3).
However, the behavior of these three types of materials is indeed somewhat similar in the molding process.
Cylinder temperature should change from 375 [degrees]
F High 450 [:degrees]
Depending on the grade of the material.
Mold temperature can run from low to 35 [degrees]
F. Certain grades to 175 [degrees]F.
To ensure adequate filling, the injection speed should range from moderate to fast.
TPOs is not easy to absorb water, but should be stored in a relatively dry place.
If the material gets wet, it should be dry at 200 [degrees]F for 1-3 hours.
Table 3 reports the preferred conditions for this rapidly growing category of materials.
In order to obtain the best performance, the copolyester elastomer must be dried before molding ([is less than]0. 1%).
In general, copolyester is not as shear-sensitive as some other types of TPEs.
Their viscosity can be controlled by increasing or lowering the barrel temperature.
When the mold temperature is hot enough, the injection pressure as low as 3,000 psi can be used (150 [degrees]F).
Higher pressure will reduce shrinkage due to higher packaging.
For thin-walled molding, the injection rate should be high, while for thicker parts, the injection rate is moderate enough.
Table 4 the appropriate molding conditions for co-polyester TPEs are recommended.
Polyurethane TPEs (or TPUs)
Two types of goods are usually considered.
The tensile strength of polyester-based tpu is higher than that of polyester-type TPEs, with better ozone, oxygen, oil and solvent resistance.
However, ether
The base TPEs has better low temperature performance and better resistance to hydrolysis and microbial attack.
Both classes have similar processing conditions.
The material is hygroscopic and must be dried before processing ([is less than]. 05%).
The mold temperature is between 90 [degrees]F -150 [degrees]
F is sufficient for optimal surface appearance and physical performance.
When the material is properly treated, the melt should deviate slightly-
White to very light yellow.
If there are bubbles in the melt, there may be moisture.
Excessive melting temperatures can lead to a \"very transparent\" cleaning process.
During the shutdown, the barrel should be cleaned using materials such as polyethylene or polystyrene to prevent material degradation.
Table 5 reports on the recommended processing conditions for tpu.
If following some important guidelines, it is also easy for the polyamide TPEs to be injection molded.
The material must be dry before molding, generally less.
08% moisture content.
By using a polymer (such as nylon 6, 11, or 12) as the structural part of the part, it is easy to complete the insertion molding without the need for an adhesive.
The universal screw works well in producing full melting homogenization.
Regrind can be used safely at level 20
25% as long as the material is properly dried.
Table 6 gives a more complete decomposition of the preferred processing conditions for polyamide TPEs.
Finally, in many traditional designs, all TPEs that are commercially available today can be easily formed.
Processing of softer durometer compounds ([is less than]45A)
The modified gate design is sometimes required for easy disassembly.
The angle of eating water. 0 [degrees]
It is usually satisfactory for most softer compounds.
In addition, in order to increase the pull force, more \"positive\" gate pull pins are sometimes needed.
For deeper stretching and softer compounds, it may be necessary to peel off the plate and/or air to break the vacuum generated by shrinkage.
The thimble should also be as large as possible so that they do not penetrate the parts.
The runner should be a full circular configuration and be as short as possible so that there will be enough traffic for all lenses.
Door size should always start from an early age (
Size depends on the part)
Expand if necessary.
In order to obtain the best release from the mold cavity, the surface of the mold cavity should be honed by steam.
Highly polished or chrome plated mold surfaces can cause sticking together and are not recommended.
As long as the runner itself is \"fairly short\" and at least 1 inch in diameter, insulated runners can be used.
Hot runner has also been successfully used in systems where the runner diameter is greater. 5 inch.
Injection molding TPEs may be relatively easy if certain guidelines are followed.
Some of the more important guidelines are as follows: * most TPEs are sensitive to shear.
Increasing or lowering the back pressure of the material changes the viscosity of the material.
* Since the material is sensitive to shear, the screw retraction time should be adjusted so that it can end before the next shot.
* The injection pressure time should be as short as possible to avoid excessive packaging.
* The holding pressure should be 1/3 to 1/2 of the injection pressure so that the gate will be sealed and there will be no excessive packaging.
* For better parts to top out, the mold cavity should be honed by steam.
* Universal screws work fine for all TPE materials.
* Always follow the manufacturer\'s advice on drying materials.
Under normal circumstances, the co-polyester, polyurethane and polyamine are moisture-absorbing, while styrenics and polyolene are not.
Note 1: it should be noted in the processing guide table that as the TPE level becomes soft (
Within the same class)
Processing parameters will fall into the lower range reported.
For example, the 35 Shore a styrenic TPE will have lower injection pressure, processing temperature and subsequent higher flow performance than the 50 shore D material. References [1]Walker, B. M. , Rader C. P.
2nd edition of the manual of thermal plastic elastic materials.
\"Thermoplastic Polyolefine elastomer, Shide C. D. , p.
48, Van Nostrand Reinhold, New York1988). [2]Rubin, I. I.
Injection molding;
Theory and Practice, Willie, New York, USA (1973). [3]
German patent DRP 858,310. [4]Walker B. M. , Rader C. P.
2nd edition of the manual of thermal plastic elastic materials.
\"Single-phase fused machined rubber\", Wallace J. G. , p.
143, Van Nostrand Reinhold, New York1988).
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