JPH03116560A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To suppress hydrolysis of polycarbonate resin as well as to maintain good releasing property of the resin on molding by specifying the hydroxyl value of fatty acid ester included as a releasing agent in the polycarbonate resin, and molding the resin at lower temp. CONSTITUTION:0.005 - 0.5pts.wt. of the releasing agent essentially comprising esters of fatty acid with hydroxyl value of <=5mgKOH/g is incorporated into 100pts.wt. of polycarbonate resin. This polycarbonate resin without containing a heat stabilizer is subjected to injection molding at >=280 deg.C and <=326 deg.C into a molded substrate, on which a recording layer is to be formed. By specifying the resin temp. during injection molding as well as specifying the hydroxyl value of the releasing agent, hydrolysis of the polycarbonate resin can be prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to optical information recording media such as various write-once optical disks on magneto-optical disks, and digital audio disks (so-called compact disks). In particular, the present invention relates to improvements in optical information recording media using injection molded polycarbonate resin substrates.

[Summary of the invention]

In an optical information recording medium using an injection molded polycarbonate resin as a substrate, the present invention stipulates the hydroxyl value of the fatty acid ester contained in the polycarbonate resin as a mold release agent, and suppresses the molding temperature to prevent hydrolysis. The purpose of the present invention is to provide an optical information recording medium that has fewer defects and is highly reliable.

[Conventional technology]

Polycarbonate resin is used as a substrate for optical information recording media that record and reproduce information by irradiating laser light, such as magneto-optical disks, various write-once optical disks, rewritable optical disks, and even digital audio disks. It is common to use an injection molded product. This is an injection molded body of polycarbonate resin.
Heat resistant and easy to mold, deformation after molding 5
This is because it has characteristics such as less deterioration, excellent mechanical properties such as impact resistance, and superior mass productivity and low cost compared to glass substrates.

[Problem to be solved by the invention]

By the way, when injection molding the polycarbonate resin mentioned above to make a substrate, a mold release agent is added because if the mold release resistance is high when the mold is released from the mold, it can cause warping of the molded product, optical distortion, etc. is common.

Paraffin, silicone oil, fatty acid ester, fatty acid partial ester (particularly fatty acid monoglyceride), and the like are conventionally known as mold release agents for polycarbonate resins.

Some of these have a sufficient mold release effect with a small amount, while others are not effective unless added in a large amount. For example, silicone oil, which needs to be added in a large amount, may interfere with film adhesion. , some of which may cause film corrosion.

Fatty acid monoglycerides and the like exhibit excellent mold release effects in small amounts, but it has been found that they can trigger hydrolysis of polycarbonate resins when storage tests are carried out under high temperature and high humidity conditions.

When polycarbonate resin is hydrolyzed, the decomposed products precipitate into the molded product as fine white spots, causing laser light dispersion (local birefringence abnormality), reduced film adhesion, and deterioration of substrate strength.

Therefore, the present invention was proposed in view of the conventional situation, and aims to ensure good mold release properties and at the same time suppress the hydrolysis of polycarbonate resin.
The purpose of this is to provide a highly reliable optical information recording medium with few defects.

[Means for Solving the Problem] As a result of various studies to achieve the above-mentioned object, the present inventors found that the cause of hydrolysis of polycarbonate resin is that fatty acid monoglyceride, which is a mold release agent, has at the molecular terminal. It was found that the presence of this hydroxyl group promotes hydrolysis.

Therefore, in the optical information recording medium of the present invention, a fatty acid ester that does not have a hydroxyl group at the molecular end is used as a mold release agent, and at the same time, the molding temperature is suppressed to suppress the increase in hydroxyl groups due to decomposition of the fatty acid ester. shall be.

That is, in order to achieve the above-mentioned object, the optical information recording medium of the present invention contains a mold release agent mainly composed of fatty acid ester and having a hydroxyl value of 5 mgKOH/g or less.
0.0% per part by weight. A polycarbonate resin containing 5 to 0.5 parts by weight of OO and no heat stabilizer was heated at 280°C.
As described above, the present invention is characterized in that a molded article formed by injection molding at 326° C. or lower is used as a substrate, and an information recording layer is formed on the substrate.

In the optical information recording medium of the present invention, the polycarbonate resin used as the substrate material is prepared by combining aromatic bisphenols (e.g. bisphenol A) with a solvent (ethylene chloride) in the presence of an acid binder (e.g. an alkali such as sodium hydroxide). , chloroform, carbon tetrachloride, dichloroethane, trichloroethane, etc.) by interfacial polymerization, which is synthesized by reacting with phosgene in halogenated hydrocarbons such as chloroform, carbon tetrachloride, dichloroethane, and trichloroethane. Branched polycarbonate resin using a trifunctional or higher polyfunctional organic compound having a phenolic hydroxyl group, terminal length using a monofunctional organic compound such as a long-chain alkyl acid chloride or a long-chain alkyl ester substituted phenol as a terminal stopper. Styrene is added to a chain alkyl polycarbonate resin, a terminal long chain alkyl branched polycarbonate resin using both the above-mentioned branching agent and terminal capping agent, and a modified polycarbonate resin obtained using bisphenol or vinylphenol having an unsaturated double bond. Those obtained by graft polymerization, those obtained by graft polymerization of polycarbonate resin to modified styrene having phenolic hydroxyl groups, and mixtures thereof are used. Moreover, the viscosity average molecular weight of the polycarbonate resin used for injection molding is about 13,000 to 30,000.

A mold release agent is added to the polycarbonate resin, and the mold release agent used here is mainly composed of a fatty acid ester having no alcoholic hydroxyl group. In addition,
Fatty acid esters that do not have alcoholic hydroxyl groups are full esters in which alcoholic hydroxyl groups and fatty acids are reacted in equimolar amounts during the fatty acid ester synthesis step, or are reacted with an excess of fatty acids, resulting in unreacted (residual) alcohol. Refers to substances with extremely low content. Or, plants and animals;
It also exists in ester waxes contained in natural products such as insects and minerals. In the present invention, the hydroxyl value of the mold release agent is 5 ■K OH/g or less.

If the hydroxyl value of the mold release agent exceeds 5 mg KOH/g, hydrolysis of the polycarbonate resin will be accelerated and defects in the substrate will increase.

Specifically, butyl stearate, stearyl stearate, hehenyl behenate, methyl laurate, isopropyl palmitate, 2-ethylhexyl stearate,
Examples include synthetic products such as pentaerythritol tetrastearate and pentaerythritol tetrabehenate, and beeswax containing long-chain fatty acid ester as a main component and having high purity of the component.

The amount of the above mold release agent added is 100% of the polycarbonate resin.
The ratio is 0.005 to 0.5 parts by weight.

If the amount of the mold release agent added is less than the above range, it will be difficult to ensure good mold release properties, and there is a risk that warpage, optical distortion, etc. will occur in the substrate. On the other hand, if there is too much mold release agent,
There is a risk that problems such as poor film adhesion to the information recording layer may occur.

In addition, the polycarbonate resin used for injection molding is
It is preferable that it does not contain a phosphorus compound such as a phosphite ester as a heat stabilizer.

However, this means that no heat stabilizer is actively added to the polycarbonate resin to prevent it from decomposing due to heat; for example, if traces of phosphorus compounds are included due to other factors. Even if a polycarbonate resin contains a small amount (for example, s ppm or less) of a heat stabilizer, it is considered to be included in the polycarbonate resin that does not contain a heat stabilizer as referred to herein.

The above-mentioned polycarbonate resin is put into an injection molding machine in the form of a pellet, fluidized by a heater, and then extruded into a mold to be molded into a substrate. It is better to keep the temperature as low as possible, and it is preferable to keep it to 326°C at most. If the resin temperature is too high, not only will the fatty acid ester contained as a mold release agent decompose and accelerate the hydrolysis of the polycarbonate resin, but the resin itself will decompose due to heat, increasing contamination. . However, if the resin temperature is too low, there is a risk that the optical properties (birefringence, etc.) of the substrate will be impaired, so the lower limit needs to be about 280°C.

(Action) The main component of the mold release agent is fat M that does not have alcoholic hydroxyl groups.
Ester (full ester) with a hydroxyl value of 5m
gKOH/g and the resin temperature during injection molding is 326'C or less, thereby suppressing hydrolysis of the polycarbonate resin.

In addition, keeping the resin temperature at 326°C or less during injection molding helps prevent contamination due to thermal decomposition of the polycarbonate resin, and also eliminates the need for a thermal stabilizer, which is also beneficial in terms of corrosion of the recording layer. It is.

〔Example〕

The present invention will be explained below based on specific experimental results.

First, we will explain the configuration of the injection molding machine used in this experiment.

As shown in Figure 1, the injection molding machine has a resin injection section (1) for melting polycarbonate resin and feeding it into the mold, and a mold section (2) for forming a cavity according to the shape of the optical disk substrate. , and a mold clamping mechanism (3) that applies pressure to the mold part (2).

The resin injection section (1) includes an input hopper (11) into which resin pellets as raw materials are charged, and a heating cylinder (12) in which a heating heater is provided around the periphery and a screw is disposed inside.
) and a nozzle (13), the resin pellets supplied from the input pump (11) are sequentially melted, and the nozzle (13)
This molten resin is sent out from the tip.

In addition, the mold part (2) has a movable mold (2) as shown in FIG.
The stamper (23) is fixed to the movable mold (21) by an inner stamper holder (24) and an outer stamper holder (25). There is. The fixed mold (22) is mounted on a fixed platen (
26), and the resin injection part (1) is located in the center.
A resin injection port (27) connected to the nozzle (13) and having an opening (27a) at its tip is provided. and,
A mold holder (28) fixed to a fixed platen (26) is provided on the outer periphery of the fixed mold (22), and a movable mold is attached to the tip surface (28a) of this mold holder (28). (21
) are brought into contact and the mold is closed, and a cavity (29) is formed between the two molds (21) and (22).
) will be formed as a predetermined space.

The mold part (2) is provided with a mold clamping mechanism (3) that moves the movable mold (21) back and forth, and in this example, a so-called booster ram type mold clamping mechanism is used as the mold clamping mechanism (3). It has been adopted. This booth clam type mold clamping mechanism is a mechanism in which a booth clam with a diameter smaller than the diameter of the main ram is inserted coaxially with the central axis of the main ram in order to advance the main ram at high speed, and is widely used in medium-sized injection molding machines etc. It is used. A servo valve mechanism (31) is connected to this mold clamping mechanism (3), and a mold clamping pressure regulator (
32). The mold clamping pressure regulator (32) is connected to the aforementioned mold clamping mechanism (3) via the pressure detector (33), and the mold clamping mechanism (3)
) is applied to the movable mold (21) by the operation of
The pressure is detected by the pressure detector (33), and the clamping pressure regulator (32) is controlled by this detection signal to adjust the servo valve mechanism (31). In addition, the above-mentioned mold clamping pressure regulator (3
A program setting device (34) is also connected to 2), and by storing the application timing of the clamping pressure of the movable mold (21) in the program setting device (34), the program setting device (34) The output of the mold clamping positive regulator (32
), the servo valve mechanism (31) is operated to control the hydraulic pressure and operating time of the mold clamping mechanism (3) to close the gap between the movable mold (21) and the fixed mold (22). It is set to change the clamping pressure of the movable mold (21) during the process of injecting molten resin into the cavity (29) or after the injection process is completed. In addition, it is preferable that the change in mold clamping pressure can be controlled digitally, and it is also possible to control the mold clamping pressure with a fast response (for example, from 140 kg/cm to 0 kg/cm).
/c- in which decompression is completed within 0.5 seconds) is preferable.

The mold clamping mechanism (3) is not limited to the aforementioned booster ram type mold clamping mechanism, but may also be a toggle type mold clamping mechanism. The toggle type mold clamping mechanism increases the force of the mold clamping cylinder using a link mechanism called a toggle to obtain a large mold clamping pressure, and can obtain high mold clamping pressure with a small cylinder and perform high-speed mold clamping.

An optical disk substrate made of polycarbonate resin is molded using an injection molding machine having the above-described configuration, and the molding method will be described below.

In this experiment, to create an optical disk substrate, the second
As shown in the figure, the outer peripheral portion (21a) of the movable mold (21)
) is provided on the outer periphery of the fixed mold (22).
The mold is kept in a closed state in contact with the tip end surface (28a) of the resin injection part (28), and in this state, the polycarbonate resin (4) melted in the resin injection part (1) is injected into the resin injection port (27) through the nozzle (13). ) into the cavity (29).

The mold temperature is arbitrary, but from the viewpoint of improving skew characteristics and productivity, it is preferably set to a temperature equal to or lower than the thermal deformation temperature of the optical disk substrate, and is usually set at about 50 to 120°C.

The molten resin (4) enters the cavity (29) during injection.
), but in this embodiment, the filling pressure due to injection is set to be slightly higher than the clamping pressure applied to the movable mold (21).

Therefore, when injecting the molten resin (4) into the cavity (29) of the mold part (2) in the closed state,
As shown in Figure 3, the movable mold (2
1) is moved back by Δl in the direction of arrow a in FIG.
It is pushed open at T2 in the figure.

In this way, the filling pressure is set to be slightly higher than the clamping pressure applied to the movable mold (21), and both molds (
By making the gap between 21) and (22) change, the pressure inside the cavity (29) becomes uniform due to the change in the gap, and the molten resin (4) flows into the cavity (29).
(2) It is possible to mold an optical disk substrate with high dimensional accuracy by filling every corner of the disk. In addition, the mold (
21) and (22) open, the cavity (29)
The internal pressure does not become extremely high, and the molten resin (4)
This is also advantageous in terms of improving birefringence since no unnecessary stress is generated. However, 2. If the clamping pressure applied to the movable mold (21) is too small, the transferability may be insufficient, so it is preferable to take this point into account and set the clamping pressure appropriately.

In addition, as mentioned above, the molds (21) and (22
) are pushed open, the molds (21) and (2
2) There is a risk that the molten resin (4) may enter into the minute gaps between the two, causing so-called flashing. Therefore, here, the inner circumferential surface (25a) of the ring-shaped outer peripheral stamper holder (25) provided on the movable mold (21) corresponding to the outer peripheral edge of the disk substrate, and the disk substrate diameter of the fixed mold (22) are shown. By arranging the stepped portion glue (peripheral surface (22a)) corresponding to the disk substrate so that it intersects with the disk substrate surface in a direction substantially perpendicular to the disk substrate surface, the structure reduces the occurrence of flash.

When the above-mentioned filling of the molten resin (4) is completed, since the clamping pressure of the movable mold (21) is maintained at this stage, a predetermined pressure is applied uniformly to the entire surface of the resin (4).
As shown in Figure 4, the mold (21) shrinks due to cooling.
), (22) will become tighter.

As a result of the above, the molten resin (4) in the cavity (29) is molded into a disk substrate with the desired thickness T3, and the stamper (
23), a pre-formed focus and guide groove (pre-group) is transferred. However, at this stage, the resin (4) is not completely solidified, and the outer peripheral portion is solidified as a skin layer, while the inside is still in a fluid state as a core layer.

Therefore, before the resin (4) completely solidifies, the mold clamping pressure applied to the movable mold (21) is reduced to zero or reduced to a low pressure, and the pressure is violently released (so-called decompression). (Lesson) to do.

To rapidly release mold clamping pressure, for example, when using the booster ram type mold clamping mechanism described above, the mold clamping pressure regulator (
32) to operate the servo valve mechanism (31) to rapidly discharge the oil in the cylinder chambers of the main ram and booster ram. Similarly, in the case of a toggle-type mold clamping mechanism, all you need to do is release the pressure in the mold clamping cylinder and the mold clamping pressure in the link mechanism.In addition, when using a general-purpose injection molding machine, the pressure The applied pressure may be suddenly released by, for example, opening a valve.

This rapid release of mold clamping pressure is extremely effective in controlling birefringence.

After controlling the initial birefringence by releasing the clamping pressure of the movable mold (21) at a predetermined timing in this manner, the resin (4) is completely solidified while maintaining this state. At this time, the molds (21) and (22) are made of resin (4
) and release only the clamping pressure.

Finally, the molds (21) and (22) are opened and the molded optical disk substrate is taken out.

Even if the removed optical disk substrate is used as is, the birefringence gradually approaches zero due to changes over time, but when annealing treatment is performed, the birefringence stabilizes near zero. The practical annealing temperature condition is approximately 70 to 120°C.

The above method can be said to separate the transfer securing zone and birefringence control zone during the molding process, and therefore, these conditions can be controlled independently, and the conflicting demands of birefringence and transfer characteristics can be simultaneously satisfied. It becomes possible to mold optical disk substrates.

Fruit 3 ([ According to the injection molding method described above, the hydroxyl number is 4.8 m
gKOH/g, 12.3mgKOH/g, 25.21g
A polycarbonate resin to which 0.04% by weight of a KOH/g mold release agent (behenyl behenate) was added was injection molded to form a substrate A with a diameter of 120+nm (hydroxyl number 4.
8■KOH/g), substrate B (hydroxyl number 12.3m
gKOH/g), substrate C (hydroxyl number 25.2 m
g KOH/g) was obtained.

Note that the hydroxyl value of the mold release agent was determined by the pyridine-acetic anhydride method.

These substrates were left in an environment of 85° C. and 90% relative humidity, and changes over time in the number of white spots due to hydrolysis of the polycarbonate resin were examined. The results are shown in FIG. 5, in which curve A corresponds to substrate A, curve B to substrate B, and curve C to substrate C, respectively.

As a result, the hydroxyl value of the mold release agent has a large effect on the number of white spots, and while substrate A, which has a low hydroxyl value, shows almost no increase in white spots over time, as the hydroxyl number increases, the number of white spots increases over time. It was found that there was a significant increase in the number of white spots.

In the experiment, we mainly investigated the effects of the heat stabilizer and the resin temperature during injection molding.

First, a polycarbonate resin that does not contain a heat stabilizer,
Heat stabilizer (trisnonylphenyl phosphite) 1
A substrate is injection molded using polycarbonate resin containing 5 ppm and 55 ppn+, and a film thickness of 50
A magneto-optical disk was prepared by sequentially laminating a transparent dielectric layer (SixNn film) with a thickness of 600, a recording layer (TbFeCo layer) with a thickness of 600, and an ultraviolet curing resin layer with a thickness of 5 μm.

When we investigated the defects that occur in the recording layer when these magneto-optical disks were stored at 80°C and 85% relative humidity, we found that the number of defects increased when a thermal stabilizer was included, as shown in Figure 6. was found to be significant.

In addition, in Fig. 6, the curved line indicates the case where no heat stabilizer is included.
Curve E is heat stabilizer i5ppm, curve F is heat stabilizer i5ppm
This corresponds to the case of spps.

Next, contamination due to resin temperature was investigated. The results are shown in FIG. In the figure, curve G represents the case where no heat stabilizer is included, and curve H represents the case where 15 ppm of heat stabilizer is included. The number of contaminants has a diameter of 0.
The number of foreign particles and deterioration with a size of 5 to 1 μm was counted, and the number was expressed as the number of particles per 1 g of substrate.

When a heat stabilizer is included, no increase in contamination is seen up to around 345°C, whereas when a heat stabilizer is not included, an increase in contamination is seen when the temperature exceeds 326°C. .

Therefore, when molding a polycarbonate resin that does not contain a heat stabilizer, it is necessary to suppress the resin temperature to 326° C. or lower.

Substrate J molded with the addition of a mold release agent mainly composed of behenylbehenate (hydroxyl value 4.0I1gKOH/g)
and a mold release agent mainly composed of stearic acid monoglyceride (
Regarding the substrate K formed by adding a hydroxyl value of 310 mgKOH/g, defects occurring in the substrate were investigated when it was stored under conditions of 85° C. and 85% relative humidity. At the same time, the resin temperature was varied during the molding process, and the differences caused by this were also investigated. Note that no thermal stabilizer was added to any of the substrates.

The results are shown in FIG. In the figure, curve J is for substrate J (resin temperature 338"C), and curve J is for substrate J (resin temperature 325"C).
C), the curve Kg corresponds to the substrate K (resin temperature 338°C), and the curve Kg corresponds to the substrate K (resin temperature 325''C).

At any resin temperature, it was more advantageous to use behenylbehenate as a mold release agent, but especially when behenylbehenate was used as a mold release agent and the resin temperature was 325.
'C, the increase in defects in the substrate was slight.

The present invention has been described above based on specific experimental results, but the present invention also applies to magneto-optical disks 2, various write-once optical disks, etc.
Can be used with all types of optical information recording media,
Furthermore, the structure of the medium is not limited at all.

[Effects of the Invention] As is clear from the following explanation, in the present invention, the hydroxyl value of the mold release agent and the resin temperature during injection molding are specified, so that the It is possible to provide an optical information recording medium that can prevent hydrolysis, has few defects, and has excellent long-term reliability.

[Brief explanation of drawings]

FIG. 1 is a schematic side view showing an example of an injection molding machine. Figures 2 to 4 are schematic cross-sectional views showing the injection molding process according to the process order, with Figure 2 showing the mold closed state, Figure 3 the molten resin filling process, and Figure 4 the mold closing state, respectively. show. FIG. 5 is a characteristic diagram showing the difference in the change over time of white spots in the substrate due to the difference in the hydroxyl value of the mold release agent. FIG. 6 is a characteristic diagram showing the change over time in the number of defects occurring in the recording layer in a case where a thermal stabilizer is included and a case where a thermal stabilizer is not included. Figure 7 is a characteristic diagram showing the relationship between resin temperature and contamination when injection molding is performed using polycarbonate resin that does not contain a heat stabilizer, compared to when injection molding is performed using polycarbonate resin that contains a heat stabilizer. be. FIG. 8 is a characteristic diagram showing the temporal change of defects occurring in the substrate, comparing the case where hehenylbehenate is used as the mold release agent and the case where stearic acid monoglyceride is used as the mold release agent.

Claims (1)

[Claims] Mainly fatty acid ester, hydroxyl value 5mgKOH
/g or less of mold release agent per 100 parts by weight of resin.
A molded article obtained by injection molding a polycarbonate resin containing 05 to 0.5 parts by weight and not containing a heat stabilizer at 280°C or higher and 326°C or lower is used as a substrate, and an information recording layer is formed on the substrate. An optical information recording medium.