Design of Injection Molding Machine and Tools for SUMIKASUPER LCP

Selection of Injection Molding Machinery

SUMIKASUPER LCP can be molded using both the standard inline type and plunger type (ram fed) of injection molding machines. Since the molding temperatures for the E4000 and E6000 series are <400 deg C, there are no problems with heater capacity, even when standard injection molding machine is used. However, as the E5000 series requires a higher molding temperature (up to 420 deg C), high temperature machine is required (specifications for handling 450 deg C).

Screws and Cylinders

  • As the filler content of SUMIKASUPER LCP is quite high, it is preferable that materials with good abrasion resistance be used.
  • It is preferable that standard full flight screws be used. Sub-flight screws and high mixing screws are not recommended for usage, as metering time will be extended.
  • It is recommended that screw heads with backflow prevention (check valve) be utilized.
  • The moldability of SUMIKASUPER LCP is sensitive to temperature. Therefore, as the PID control method provides good controllability, this method is recommended for the control of cylinder temperature.

Nozzles

  • Nozzle materials must be suited to the particular screw and cylinder utilized.
  • Open nozzles should always be used. Shut-off nozzles should not be used, as they have excessive dead space that can trap and retain resin.
  • The nozzle heaters used must have independent temperature control employing the PID control method. The PID control method provides good controllability.
  • When extension nozzles are used, they should be designed with consideration for consistent temperature distribution.

Injection Unit and Control System

  • Both standard open loop control and closed loop control types of molding machines can be used for SUMIKASUPER LCP.
  • For molding thin-walled products, it is preferable to use a molding machine that possesses superior response for the initial injection, as SUMIKASUPER LCP sets rapidly and possesses high shear rate dependence for melt viscosity.

Molding Machine Capacity

  • In general, the best results are obtained from molding machines that are capable of continuously metering 1/3 - 3/4 of the total injection capacity. If there is insufficient continuous metering capability, then excess remaining resin may cause variou molding defects.

Resin Temperature Control

For most LCPs', including SUMIKASUPER LCP, the physical properties, such as mechanical characteristics and melt viscosity, are highly dependent upon molding temperature. Therefore, unless temperatures are controlled correctly, the desired physical properties may not be obtained. Injection molding machines are usually designed in a manner such that the temperature of resin inside the cylinder and the cylinder temperature setting can equalize easily, for the molding temperatures used by general purpose resins (purpose resins (-30 deg C). However, within the higher molding temperature range of SUMIKASUPER LCP (320-400 deg C), a temperature differential may occasionally occur between the temperature setting and the resin temperature.
For the above reason, in order to achieve the best performance from SUMIKASUPER LCP, the operator must have a thorough understanding of resin temperatures inside the cylinder. The temperatures for each grade of SUMIKASUPER LCP product must be controlled accurately, in order to maintain the resin at its optimum temperature. The abovementioned resin temperature can be easily measured using a spot type non-contact infrared radiation thermometer that enables the measurement of temperatures for minute areas (The measurement spot size should be smaller than the diameter of a strand).

Figure : Resin Temperature Control

High-speed Injection Molding Technology

SUMIKASUPER LCP possesses special low flash production characteristics. Flash is not readily produced during molding due to the low melt viscosity and rapid speed of setting. However, during the molding process for ultra thin-walled products (<0.2mmt), resin does set in areas that contain very thin walls, thus hindering the achievement of sufficient flow length in certain products. To remedy this situation, a molding machine should be utilized that possesses superior response capability for the initial injection; such as equipment that an accumulator is installed.

Mold Design

Injection molding, which is the process under share, causes the orientated molecules of SUMIKASUPER LCP to the flow direction. elastic modulus, but also anisotropic properties.When designing tools, both flow patterns and anisotropy within cavities, must be considered carefully.

Sprue

  • The appropriate angle for use when drawing out the sprue is 1°~2° (per side).
  • In order to allow for the removal of cold slug, a cold slug well (4-5mmΦx5mm or more) should be installed at the end of the sprue.
  • A sprue lock should be installed in order to provide better sprue removal.
Figure : Sprue

Runner

  • Standard runners having either a circular, semicircular or trapezoidal cross-sectional shape can be utilized. However, it is recommended that runners having a circular or trapezoidal cross-sectional shape be utilized, as they are most efficient in terms of pressure loss and processability.
    As SUMIKASUPER LCP possesses outstanding moldability, runner diameters can be decreased.
    Standard runner diameter : 2-5mmΦ
    Guideline for runner diameters : 2/3-1/2 of that used for PPS and PBT (smallest : 2mmΦ)
  • When using multi-cavity tool, it is recommended that runners be correctly balanced so that individual cavities will fill simultaneously with resin.
  • Cold slug wells should also be installed at the ends of runners.

Gate

  • As the weld strength of SUMIKASUPER LCP is lower than that of other engineering plastics, it is necessary to ensure that gate locations are limited to only 1-2 places, in order to avoid the formation of welds.
  • Side Gates
    The appropriate land length is 1 mm or less, with a width of no more than 5mm. Guidelines for land depths are 0.7x the thickness of the molding, with a minimum depth of 0.2mm.
  • Pinpoint Gates
    The appropriate gate diameter ranges from 0.3-1.5mm, with a land length of up to 1mm.
    If the gate diameter is increased, stringing and gate warpage may occur.
  • Submarine (Tunnel) Gates
    Although the utilization of film gates and ring gates is possible, they are not commonly used in SUMIKASUPER LCP molding.
Figure : Gate

Extraction Taper

  • The ideal angular ranges for the extraction taper are: 0.5°(1/90) -1°(1/60) for thin-walled moldings; and 1°(1/60) -2°(1/30) for thick-walled moldings.
  • Using MR grades, moldings can be released from tool easier than general grades. The releasing force with MR grades is nearly the half of that with general grades However, the extraction taper must be enlarged when molding products that have greater depths.

Air Venting (Gas Drainage)

  • As SUMIKASUPER LCP is often molded under high-speed injection molding conditions, the installation of mold air venting is recommended, in order that the air remaining in the mold can be discharged effectively.
  • When welds occur in thin-walled products or at the ends of the flow, short shots defect tend to occur. Therefore, it is recommended that air venting be installed to remedy this problem.
  • SUMIKASUPER LCP has low melt viscosity and excellent moldability. However, as solidification occurs extremely rapidly, flash defect will not occurred easily, even with the installation of air venting.
  • The recommended depth for air vents ranges from 0.005-0.02mm.

Anisotropy (Mold Shrinkage)

  • As the difference between molding direction (MD) and transverse direction (TD) properties (anisotropy) has a substantial effect on SUMIKASUPER LCP mold shrinkage, the mold shrinkage must be specified for the correctable direction, based on the mean value of the MD and TD values.
  • For compact size and / or thin-walled molding, it is recommended that the design shrinkage be specified as 0% in the molding direction (MD).

Table 1 : Anisotropy

Item Thickess Direction Unit E5008L E5008 E4008 E6008 E6006L
Molding shrinkage 3mm MD % 0.05 0.08 0.10 0.18 0.19
TD % 0.81 1.25 1.32 1.16 0.74
1mm MD % 0.13 0.05 0.06 0.09 0.10
TD % 0.43 0.70 0.78 0.80 0.49
Flexural strength 3mm MD MPa 137 130 138 136 156
TD MPa 58 56 57 61 92
Flexural modulus 3mm MD GPa 13.4 12.6 12.7 12.2 11.4
TD GPa 3.7 3.3 3.0 4.4 4.7

Figure 5 : Mold Shrinkage Rate of E6008

Figure 5 : Mold Shrinkage Rate of E6008

Figure 6 : Mold Shrinkage Rate of E5008

Figure 6 : Mold Shrinkage Rate of E5008

Tool Material

  • The standard grades of SUMIKASUPER LCP contain glass fiber as filler. Therefore, for tools that require high dimensional accuracy, as well as for those used in mass production, tools should be made of a steel alloy with rigidity equivalent to SKD11 and a hardness of HRC55 - 62 (i.e., HPM31, PD613 and RIGOR).
  • As SUMIKASUPER LCP emit almost no corrosive gases, mold corrosion does not occur, thus general-purpose tool material can be used.

Usage of Hot Runners

The following precautions must be observed when using hot runners:
During long-term continuous molding, some resin will generally tend to remain within the dead spaces of the molding machine and hot runner manifold. This residual resin deteriorates and may cause discoloration. Due to its extremely low melt viscosity, SUMIKASUPER LCP will tend to remain within these dead spaces.
In order to address this deficiency with SUMIKASUPER LCP, the use of hot runners is recommended. In particular, it is important to ensure that residual resin does not accumulate, in order to prevent the occurrence of black specks and cold slag.

Precautions for the Usage of Hot Runners with SUMIKASUPER LCP

  • The system must be capable of producing high levels of heating with a uniform temperature distribution.
    Heater: an integrated type of heating unit is preferable. The manifold and nozzle temperatures should not be maintained at too high. The areas coming into contact with the tool (gate areas) must be maintained at high temperatures.

      Temperature specification of hot-runner (MAX)
    E6000 Series ~380 deg C
    E4000 Series ~400 deg C
    E5000 Series ~420 deg C
  • The hot runner layout must be as free as possible from dead space within the flow channels.
    (To avoid resin retention and the resulting production of black specks.)
    External heating should be used, rather than internal heating, and the use of narrower flow channels will help to reduce the creation of dead space.
  • The hot runner layout should be designed such that cold slag cannot easily mix into the hot resin.
    (To avoid cold slag being contaminated into the molding.)
    When using open gates, it is recommended that the installation of sub-runners be considered (sprue-less molding).

Usage of Hot Runners

The table below provides details of hot runner usage for SUMIKASUPER LCP.

Table 2 : Hot Runner Usage for SUMIKASUPER LCP

  Runner section Gate seal Application to
SUMIKASUPER LCP
Remarks
Internal
heating
External
heating
Thermally
constant
ON,OFF
at every
heat shot
ON,OFF
at every
heat shotF
Complete
hot-runner
Sprue-less
molding
Juuo614 system
Meisei Kinzoku
- - - - Φ4
Electromagnetic
induction heating
Mini-Runner
Seiki Kogyo
- - - - - *1
Spear
System
B type
(conventional)
- - - × ×  
EH type - - - × *2
Mold Master
Master Shot
- - - × △~◯  
Saito Koki
Plagate System
- - - ×  

◎: Examples of application to SUMIKASUPER LCP exist
◯: Application to SUMIKASUPER LCP is possible.
△: No example of application to SUMIKASUPER LCP
×: Application to SUMIKASUPER LCP is impossible.

*1: When it has multi-point gate and uses extension nozzle for mini-runner, it is preferred to control temperature of each extension nozzle separately. As for E5000 series which are molded at high temperature, it is desirable to exercise temperature control of each nozzle separately.
*2: For tip section, internal heating system is employed.
Inquiries about SUMIKASUPER LCP