Injection Casting
The so-called injection casting method is to maintain a lower locking force after the injection of material, and then increase the clamping force. As shown in the table, there are three comparison of injection methods.
7. Molding
The mold temperature must be considered together with the material temperature, injection rate, and injection pressure, and the cooling time will affect the thickness of the substrate, thereby affecting the "Cycle Time".
8. Punching
Generally, European injection molding machines have a "needle valve nozzle" designed at the top of the barrel. After the injection and pressure holding are completed, the needle valve will close and the nozzle will retreat in the early cooling period. At this time, the punch perforation operation is only carried out in the final cooling period, and we call this method "Hard Cut".
Japanese injection molding machines do not use the design of the valve nozzle and the barrel does not need to be retracted, as the punch is already perforated in the early stages of the cooling period. Therefore, the perforation operation is completed before the plastic has fully cooled down, and we call this method "Soft Cut". The benefits of soft cutting are:
(1) Plastic can flow stably and improve temperature stability;
(2) Piercing while the plastic is still very soft can avoid stress at the edge of the inner hole caused by hard cutting;
(3) This method does not require the barrel to retract during perforation, thus reducing mechanical losses.
The standard inner hole diameter of a general die is 34mm, and in DVD production, a 22mm diameter die inner hole is also used.
9. Take out
There are two ways to use a robotic arm to bounce off or clip out the water sun and discard it.
10. Conditioning
When the disc base is taken out of the mold, the temperature is still very high. If placed on an unbalanced cooling device, uneven cooling will lead to the generation of warping. Not only should there be enough time for cooling, but also the amount of dust falling in the cooling area should be considered, because even in a 1000 level purification area, there is still a chance of contamination when the disc base stays in it for dozens of minutes, especially when placed horizontally, Therefore, it is mostly necessary to have a "De ionized Blower" under the sink cover of the high-efficiency filter screen (HEPA), which charges the air flowing through the needle tip to prevent dust from adhering to the wall due to charging and not flying randomly. The grounding work of the machine itself should also be implemented to avoid accumulating excessive charges and generating discharge sparks. Therefore, the best cooling device is a Rotation Vertical Cooling Buffer that rotates the upright edge of the disc base forward
四、 Operation and problem analysis
In practical operation, we all hope to have a faster production rate, that is, a short "Cycle Time", and the factors that reduce the production cycle include: (a) birefringence; (b) Warping; (c) Geometric shaping of grooves
1. In Line Optical Scanner
(1) Test Light Source
The in line 100% detection machine measures the light intensity of penetration and reflection using light sources such as lamps, solid-state lasers, or light-emitting diodes (LEDs), along with some optical filters and photo arrays. We can obtain conditions such as transmittance, reflectivity, warping, and defects on the substrate.
(2) Vibration Stability after Disc Landing
Generally, in line optical testing machines need to complete the testing of one disc within 1-2 seconds, so the disc base should be stable on the "Chuck" of the testing machine before starting the measurement. This is the function of delay time.
In the past, when CD-R was first mass-produced in 1998, the recordable disc copying line was equipped with three in line optical inspection machines to inspect the substrate, dye disc, and finished disc. However, most of the current copying lines have cancelled the configuration of the first machine, which does not measure the substrate online, and the testing of the substrate is mostly done by offline optical inspection machines.
2. Off Line Optical Tester
The difference between an external optical testing machine and an internal optical testing machine is that it can perform more complex optical measurements. With some spatial metrology settings and a combination of polarizers, we can estimate the width and depth of the groove by measuring the intensity of scattered light at different angles, But this estimated value (relative value) needs to be compared with the absolute value measured by the Atomic Force Microscope (AFM) to confirm whether it has achieved considerable accuracy.
(1) Optical reading head
It is worth mentioning that the pickup up head (PUH) for general commercial photolithography has a different light source illumination method from optical testing machines. Optical testing machines that use parallel beams with a diameter of one millimeter inside and outside the line are different from those that require focusing (NA) in PUH.
(2) Transparency (transmittance/reflectance)
Excessive heating can cause the plastic to burn and cause yellowing, and incomplete drying of the plastic can also cause white spots on the disc base. Under normal operation, maintaining appropriate "Screw Circular Velocity" and "Injection Velocity" will maintain good transparency of the plastic.
(3) Tilt/Finishing
The main cause of warping is the temperature difference between the two halves of the mold, followed by the cooling rate of the substrate in the mold, the mold cavity pressure during cooling, and the air blow before mold opening. Of course, the substrate removed after mold opening is still very hot, and without proper cooling, it will also cause warping. Subsequent drying, sputtering, bonding, UV curing, and printing of the dye substrate will also affect the size of warping. Generally speaking, the term 'warp' mostly refers to axial 'radial tilt', and there is also 'tangential tilt'.
(4) Birefringence
Optical "birefringence", also known as "recurrence", refers to the fact that the refractive index varies in different directions within the material's structure, resulting in "polarization components" in different directions. Although passing through the same plastic thickness only results in phase differences. When there is a variation in birefringence in the disc base, the laser reading the signal by the optical head will have different phases on each polarization component after being reflected by the disc. The strength of this interference interference will further affect the reading of signal strength. Therefore, we need to reduce the amount of birefringence and maintain consistency in the birefringence on the inner and outer diameters.
The causes of birefringence include: (a) the cooling rate of plastic molecules during forming, and whether there is residual stress; (b) Will the timing of the punch cut cause stress on the inner ring material; (c) Will the selection of injection molding methods cause problems with the flow and shrinkage of melted plastic in the mold; (d) The density variation of plastic.
The influence of birefringence is: (a) changing the polarization phase of the laser, causing the signal of the reverse optical reading head to mutate; (b) weakening the tracking force of PUH; (c) Prone to scattering; (d) The recording effect of recordable optical disc products is poor, with variations in hole burning formation, which naturally weakens the compatibility with the disc drive.
The adjustment of birefringence is shown in the figure. Increasing the material temperature or increasing the locking force will reduce the birefringence of the inner and outer diameters, while adjusting other parameters (such as reducing the injection rate, reducing the mold temperature, extending the cooling time, and delaying the punch cutting time) can promote the consistency of the birefringence on the inner and outer diameters.
(5) Replication rate
Increasing the mold temperature, barrel temperature, injection speed, or locking force can all increase the replication rate of the disc base groove. However, the locking force must reach a certain value or above and be maintained for sufficient time to have a better replication rate. However, the maintenance time of high locking force should not be too long to avoid the difference in shrinkage rate between the "PC substrate" and the "Nickel Stamper", which leads to a high difference in outer ring shrinkage rate and poor molding.
(6) Requirements for groove geometry
For the comparison of recording and injection molding conditions for recordable optical discs, it is hoped that there should be a clear groove contour in the recording aspect, but the actual injection molding cannot achieve this ideal value. In order to solve problems such as water marks, the tolerance rate for groove geometric errors must be moderately relaxed.
(7) Penetration rate
The penetration rate of the substrate can be directly measured on online and offline testing machines, and defects related to the substrate can also be observed through direct sputtering of the metal layer. It should be noted that the groove width and depth required for various dye processes will vary, as there will be different scattering amounts under the irradiation of a parallel beam of one centimeter diameter, resulting in different measured penetration rates, Therefore, using an offline signal testing machine (such as CATS Pulstec, etc.) to measure reflectivity that truly takes into account "numerical aperture" (NA) is correct.
(8) Shrinkage rate
For the calculation of shrinkage rate, we must rely on observations such as atomic force microscopy to calculate the geometric size changes of the inner and outer diameter grooves, which are basically represented by the vertical distance ratio. However, some people also add horizontal data, and even use the groove product to calculate.
The shrinkage rate of general plastics is about 95% to 98%, and different parameter sizes have different effects on the shrinkage rate. Please refer to the diagram.
3. Problem analysis
(1) Mechanical Properties
A. Cloud/Release Mark
The generation of water marks mostly occurs at the moment of mold opening, mainly due to the additive factors of "horizontal shrinkage difference" and "warping". It is possible to occur everywhere on the inner and outer diameters of the disc base, but the probability of appearing in the inner ring is relatively high.
Just like driving a new car, it is necessary to take care of the initial wear and tear of the engine. It is recommended to inject 100 to 200 pieces of each compression mold at the beginning of use. It is recommended to first use a smaller locking force and a longer injection cycle, and then start increasing the locking force and accelerating production speed for mass production after smooth production.
B. Weight/Thickness
The greater the holding pressure, the thicker the disc base thickness. Other factors that affect the disc base thickness include mold locking force, mold temperature, and material temperature. The basic concept is that the stability of about 60 disc bases will only be achieved after starting the injection molding after the machine is warmed up, and even if there is any brief shutdown during mass production, the thickness and size of 5-20 disc bases will be unstable during the machine covering.
The evaluation of the quality of injection molding machines and whether they have achieved the optimization of injection molding control adjustment can be determined by the maximum variation of disc base weight during mass production, which is 6 δ) The size is determined by.
C. Bore size, eccentricity, and balance
Die punching deviation and disc base punching deviation can cause shaking during track reading, especially when the disc rotates at 52X high speed, making it difficult to track. In addition, the variation in density and different thicknesses in various directions caused by injection molding of the disc base can cause the mass center of the disc base to shift from the physical size center, resulting in "Unbalance" and "Focus" problems during rotation. This is commonly seen in the noise generated by high-speed rotation of the disc.
(2) Cosmetic Defects
In terms of appearance defects, they include threads, contamination (moisture, impurities...), scratches, surface contamination, incomplete forming, oversaturation, and flow marks inside the disc based plastic. Basically, we need to pay attention to the position of the inner ring code of the mold, which is used to identify the direction and inner diameter distance of the defect. If it occurs in the same position, it is mostly a problem with the mold. If it occurs in a different position, it may be caused by materials, pollution, and unstable surrounding supply. Reasoning operations are carried out in sequence until the cause is found. Generally, plastic suppliers provide a manual for problem-solving as a reference.
4. Comparison between Atomic Force Microscope and High Line Optical Testing Machine
The working principle of Atomic Force Microscope (AFM) is to suspend a very thin probe (Probe) for a short distance in the channel orbit due to the repulsive force between atoms (van der Waals force). The small amplitude of the probe will cause the reflected laser behind the rocker to oscillate with a large amplitude, so this small change in height will be reflected in the light detection array for recording, When the probe tip continuously passes through several grooves and accumulates a three-dimensional image, the directly measured values will be more accurate than those obtained by optical diffraction measurement using optical testing machines. However, AFM can only measure small areas, while diffraction testing can measure the full width of the groove in seconds. The former is absolute while the latter is relative, and comparison and correction between the two are necessary to make sense.
5、 The Evolution of Toyo Injection Molding Machines
At present, the most popular model of Toyo Machinery's fully electric injection molding machine is the ST50discPRO, which has been renamed as the S model, Representing 'Standard model' The meaning of. In addition to inheriting the previous design of having a purification sink cover at the top of the injection molding, the injection molding machine comes with its own mold purification cover, and there is also a shielding design on the nozzle, adopting a simplified vacuum pump and additional lubricating oil pump. In addition to such thoughtful design, the most important thing is that it has a locking output of 50 tons; The most sturdy steel body; In addition, a tension plate is added to the dynamic mold to more evenly guide the locking force into the mold: the control of the punch is also independently driven by a servo motor, which can achieve a more perfect cut in soft cutting operations and maintain the uniformity of the inner hole.
With the development of the high-quality market, Toyo has developed an injection molding machine called "ST50discPRO-H", which adds a servo motor to each of the four pull rod ends of the ST50discPRO-S. These four servo motors, combined with high-precision four quadrant pressure detectors inside the mold, perform cycle control, and can accurately adjust the force on each pull rod separately, making the locking force more evenly distributed in various radial directions of the disc base, Completely reducing the imbalance problem of the disc base, it is very suitable for high-speed (48X and above) recordable disc CD-R and DVD-R (4X and above) disc base production.
In addition, the Disc BOX upright injection molding machine has the advantages of minimal floor area, avoiding density variation of plastic caused by gravity, and simplicity in applying locking force vertically, while the cycle cycle can be accelerated to 2.8s/DVD.
The DiscPRO-V injection molding machine adopts a design of twin screws and twin molds, which is different from the single screw and twin molds designed by other factories because the single barrel is responsible for the injection of two molds. In the case of asymmetric "Sprue Bush", there may be uneven filling, which can easily lead to imbalance of the disc. Therefore, only twin screw and twin mold can achieve central symmetrical injection molding.
