JPH0345687B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a filler-containing thermoplastic resin injection molded product having excellent flatness and smoothness, and more specifically to a hard material used for recording and storing programs and data in external storage devices of computers. The present invention relates to an injection molded article using a thermoplastic resin that is particularly suitable for use as a substrate for magnetic, optical, and magnetic recording media. [Prior Art] As a magnetic recording medium, one in which magnetic layers are provided on both sides of a disc-shaped aluminum substrate via an underlayer is well known as a so-called hard disk (rigid magnetic recording medium). . Such hard disks are 3000-3600rpm
During operation, the flying head aerodynamically floats on the surface of the hard disk and does not touch the hard disk, but when starting and stopping the flying head contacts the disk (contact start).・In addition to the stop type, there are also types in which the head and disk are not in contact with each other at all times, and types in which the head and disk are in constant contact. In any of these formats,
In order to perform magnetic recording accurately, it is necessary to keep the distance between the head and the disk or the state of contact between the head and the disk constant. For this purpose, the surface of the disk must be smooth, and
The disk needed to have good flatness without warping or waving. Furthermore, in the contact start/stop method, at the start of operation (at the start)
At the end of operation (when stopped), the flying head and disk come into contact, so the impact and friction of the head caused by contact, especially when stopped, can cause the magnetic layer to wear out or peel off from the substrate, resulting in damage to the magnetic or mechanical parts. Decrease in strength and shortening of usable life often occur, and for this reason, strong adhesion between the substrate and the magnetic layer is required. Therefore, looking at hard disks obtained from the aforementioned disc-shaped aluminum substrate, first of all, in order to manufacture such an aluminum substrate,
Punching from aluminum plate, rough cutting, tempering,
It had to go through extremely complicated processes such as mirror polishing using diamond cutting, cleaning, and inspection, making it extremely expensive. In addition, since an aluminum-based substrate is used, it is heavy, and a powerful motor must be used to rotate the disk, which poses problems in terms of miniaturization and cost reduction of the device. In addition, the greater the weight, the greater the impact upon starting and stopping, which tends to cause the magnetic layer to peel off. Furthermore, in a disk in which a magnetic layer is provided on a substrate made of aluminum or its alloy by plating or sputtering, the interface between the substrate made of aluminum or its alloy and the magnetic layer, or the interface between the substrate and the underlayer provided under the magnetic layer. This was a problem as corrosion occurred, leading to a decline in performance. As mentioned above, there are problems that arise due to the use of aluminum-based substrates, namely, complicated manufacturing processes,
In an attempt to solve the problems of weight and corrosion at interfaces, attempts have been made to obtain disk substrates by injection molding polyetherimide. [Problems to be Solved by the Invention] However, although the surface smoothness of the substrate made of polyetherimide and the like is good, there are some problems with the flatness, and furthermore, the coefficient of thermal expansion of polyetherimide is 50 to 60. ×10 ^-6 /℃ and 20 to 23 × of aluminum
10 ^-6 /°C, and therefore, when a metal magnetic film is formed on a polyetherimide substrate by sputtering at a temperature not exceeding 200°C, cracks occur in the magnetic film, making it difficult to apply sputtering. It was hot. In order to create a magnetic disk with a high recording density, it is advantageous to form a metal magnetic thin film layer by sputtering, ion plating, vacuum evaporation, etc.; If it becomes difficult, no increase in recording density can be expected. [Means and effects for solving the problems] The present invention has been made in view of the above points ^. It is made of an amorphous resin with a linear expansion coefficient of ⁶ /℃ or less and a filler of 5 to 80% by weight, and the flatness is 29μ per 38mm span.
Provided is an injection molded article of thermoplastic resin suitable for use as a substrate for magnetic, optical/magnetic recording media, etc., having a smoothness of 0.2 μm or less. Flatness in the present invention was evaluated by measuring the maximum height (warp or bulge) per standard dimension (span) of 38 mm in the plate-shaped molded product using a three-dimensional dimension measuring device. In the case of a donut-shaped disc, the waviness (maximum height) on the circumference of the disc and the waviness (maximum height) in the radial direction from the center are measured and evaluated. As a measuring device
A circumferential undulation measuring device manufactured by Kosaka Laboratory Co., Ltd., model PU-DP10, etc. may be used. When measuring the undulation (maximum height) on the circumference, the reference dimension (span) is not the distance on the circumference but the distance between the center and the measurement point. For example, in the case of a donut-shaped disk with a radius of rmm, the maximum height obtained as above is
X _nax (mm) is converted to the size of a donut-shaped disk with a radius of 38 mm using the following formula, and the amount of warpage per span of 38 mm is used as a value indicating flatness. Flatness = X _nax ×38/r In the case of a donut-shaped disk with a radius of 38 mm, the maximum height obtained by measuring as above is, of course, the value indicating the flatness around the span of 38 mm. Become. The smoothness in the present invention is defined by JIS B
0601, using Surfcom 550A manufactured by Tokyo Seimitsu Co., Ltd., stylus tip 2.5 μm R, stylus measuring force 0.5 g.
It refers to the maximum height (Rmax) obtained by measuring at f or less. When used as a substrate for a hard magnetic recording medium, the better the planarity and smoothness, the more the distance between the magnetic head and the magnetic layer of the hard magnetic recording medium can be kept constant, and the more accurately magnetic recording can be performed. The filled thermoplastic resin injection molded article according to the present invention has a flatness of 29 μm or less per 38 mm span, preferably 18 μm or less, more preferably 6 μm or less, and a smoothness of 0.2 μm or less. The above flatness
If the thickness exceeds 25 μm, when the injection molded product is used as a substrate and a magnetic layer is provided on it as a hard magnetic recording medium and rotated, the fluctuation in the distance between the magnetic head and the magnetic layer due to the vibration of the plate surface in the vertical direction becomes large. High-precision magnetic recording becomes difficult. In addition, the above smoothness
If it exceeds 0.2 .mu.m, when the same hard magnetic recording medium as mentioned above is driven in rotation, the distance between the magnetic head and the magnetic layer will vary greatly due to the unevenness of the surface of the plate, making it difficult to perform high-precision magnetic recording. As the thermoplastic resin used in the injection molded article of the present invention, an amorphous resin is used because it has good reproducibility of the molded product in mold dimensions and has a low molding shrinkage rate. Furthermore, from the viewpoint of dimensional stability, a resin having specific values for hygroscopicity, heating deformation temperature, and linear expansion coefficient is used. ASTM for hygroscopicity
At D570, water absorption at 23°C for 24 hours is 0.7% or less, preferably 0.35% or less. Regarding heating deformation temperature, ASTM D 648 states that bending stress is
The measured value at 18.6 Kg/cm ² is 100°C or higher, preferably 140°C or higher, more preferably 170°C or higher.
The coefficient of linear expansion measured according to ASTM D 696 is 50×10 ^-6 /°C or less, preferably 15×
10 ^-6 /°C to 30×10 ^-6 /°C. Specific examples of thermoplastic resins preferred in the present invention include polyetherimide, polyether sulfone, polyphenylene ether, polycarbonate, acrylonitrile-styrene copolymer,
Examples include ABS resin. An example of polyetherimide is the formula Examples include those having a structural unit shown in the following.
In addition, as an example of polyether sulfone, the formula Examples include those having a structural unit shown in the following.
In addition, as an example of polyphenylene ether,
formula() Examples include structural units represented by the following. The filler in the present invention can be in various shapes such as powder, fiber, and plate. Here, the powdered filler also includes spherical (bead-shaped) filler. The powder filler preferably has an average particle diameter of 50 μm or less, more preferably 20 μm or less, and still more preferably 0.2 μm or less. The fibrous filler preferably has an average diameter of 1 to 20 μmφ and an average length of 0.1 to 6 mm. Specific examples of fillers include organic fillers such as glass beads, powdered carbon, titanium oxide, iron powder, and copper powder.
Inorganic or metal powder; fibers such as glass fiber, carbon fiber, copper wire, aramid fiber; mica,
Examples include plate-shaped bodies such as aluminum foil. These fillers may be used alone or in combination of two or more. The content of filler in the injection molded body is from 5 to 80% by weight. Within this range, the effects of adding the filler, such as good flatness and prevention of cracking of the magnetic layer during high-temperature processing such as sputtering, can be suitably achieved. The molded article of the present invention can be made into an excellent magnetic recording medium by forming a magnetic layer by a method such as coating, plating, sputtering, ion plating, or vacuum evaporation, and further providing a protective layer thereon as necessary. can do. The filler-containing thermoplastic resin injection molded article of the present invention can be manufactured by a method in which the surface of the mold in which the surface of the injection molded article is to be formed is previously heated by high-frequency induction to a temperature higher than the heating deformation temperature of the thermoplastic resin, and then injection molded. can. It is impossible to release the mold from the mold while keeping the surface of the thermoplastic resin at a temperature higher than the heat deformation temperature of the thermoplastic resin.In order to obtain the desired molded product without deformation, the mold must be cooled and the temperature of the molded product must be lowered. It is necessary to cool and solidify the resin to a temperature lower than the heating deformation temperature of the thermoplastic resin before releasing it from the mold. However, injection molds are usually made of steel and are many times larger in weight and capacity than the shape of the molded product, and require a large amount of heat and time for heating and cooling. Therefore, if the principle of high-frequency induction heating is used for heating, it is possible to selectively heat the surface layer of the mold, and it is also possible to rapidly heat and cool the mold surface. According to this method, the influence of thermal expansion, contraction, etc. on the entire mold is eliminated, and there is no appearance of unevenness. The heating deformation temperature referred to here is measured by the method specified in JIS K 6871, but when specifying the mold surface temperature, the bending stress is 18.6 kg/
This is the heating deformation temperature when a load is applied to a test piece so that the temperature becomes cm ² . Here, we will explain why an injection molded product with a smooth surface could not be obtained using the conventional method using a cooled mold. In the conventional method, the plasticity of the thermoplastic resin is generally used in injection molding of thermoplastic resin molded products. In other words, the thermoplastic resin is heated and fluidized using a screw, etc., and then molded into a mold. The basic principle is to obtain molded products by cooling and solidifying. That is, in order to release and take out the molded product from the mold after solidification, it is cooled below the heating deformation temperature of the thermoplastic resin and taken out from the mold. Therefore, the mold is generally maintained at a temperature lower than the heating deformation temperature. Furthermore, in order to increase productivity, the mold is cooled to a temperature on the verge of condensation using a refrigerant.
Even when the mold is cooled and heated and stored at the temperature of the molten resin, in principle the mold temperature is controlled so as not to exceed the heating deformation temperature of the thermoplastic resin. In other words, when the mold surface and thermoplastic resin come into contact, the thermoplastic resin is rapidly cooled at the contact surface, and the fluidity of the thermoplastic resin becomes extremely poor. Transferability is poor and the surface of the molded product is extremely uneven. In addition, in the case of a filler, the filler and thermoplastic resin generally have poor compatibility, so it is thought that minute voids are created at the interface between the filler and the thermoplastic resin, resulting in silver streaks when injection molded. That is, the filler appears on the surface of the molded product, resulting in severe unevenness, silver streaks, etc., and a molded product with poor surface smoothness. On the other hand, according to a method in which the mold surface temperature is higher than the heating deformation temperature of the thermoplastic resin, molding can be performed while retaining the plasticity, and good transferability is achieved without causing flow marks or silver streaks. Therefore, it is possible to transfer the mirror surface of the mold extremely well and obtain an injection molded product with an extremely smooth surface.In addition, since only the mold surface is heated using the high-frequency induction heating method, productivity can be improved. . Observation of the surface of the molded product obtained by this method reveals that a thermoplastic resin skin layer of 1 to 100 μm is formed. Next, this method will be explained with reference to the drawings. First, as shown in FIG. 1, a high-frequency induction heating inductor is installed between the stationary mold and the movable mold. When an inductor was sandwiched between the movable mold and the stationary mold, and a high frequency was oscillated while the inductor was sandwiched, as shown in Figure 2, only the mold surface (points A and B) suddenly changed. It can be confirmed that the temperature increases, and the temperature inside the mold (point C and point D) hardly increases due to high frequency induction heating. In the case of the example shown in FIG. 2, the mold is not cooled with cooling water, but simply shows an example of the change over time in the temperature distribution of the mold due to high-frequency induction heating. After that, the mold was opened, the inductor was extracted from between the fixed and movable molds, the mold was closed again, and the filled thermoplastic resin was injection molded in the same manner as normal injection molding. An injection molded product with good surface smoothness and excellent flatness was obtained. [Example] Next, the present invention will be explained in more detail by giving examples. Test methods in the following Examples and Comparative Examples will be described below. Flatness: For flat molded products, the amount of deformation such as blistering and warping is measured over a span of 38 mm using a three-dimensional dimension measuring device (AE 122 Micro cord manufactured by Mitoyo Seisakusho Co., Ltd.). For disc-shaped compacts, use a circumferential waviness measuring device (Circumferential waviness measuring device PU-DP10 model manufactured by Kosaka Institute Co., Ltd.)
Values measured using the method described above (converted to a span of 38 mm). In either case, flatness is evaluated using maximum warp and waviness. Smoothness Maximum height (R _nax ) obtained using Surfcom 550A manufactured by Tokyo Seimitsu Co., Ltd., with a stylus tip of 2.5 μm R and a stylus measuring force of 0.1 gf according to JIS B 0601. Hygroscopicity Water absorption (%) at 23°C for 24 hours under ASTM D 570. At heating deformation temperature ASTM D 648, bending stress is 18.6Kg/
Measured value in cm ² . Linear expansion coefficient Value measured according to ASTM D 696. Example 1 A polyetherimide resin containing 20% by weight of glass beads with an average particle size of 18 μm [Ultem manufactured by GE, which has a structural unit represented by the above formula (), was molded using a conventional so-called disc specification precision injection molding material. Using a molding machine with a clamping force of 150 tons and an injection cylinder and screw capable of heating up to 490℃, we produced a donut with an outer diameter of 130 mm, a thickness of 1.9 mm, and a hole of 40 mm in diameter in the center, as shown in Figure 3. A disk-shaped hard magnetic recording medium substrate was molded. The smoothness R _nax of the surface of the mold on which the molded product was to be formed was 0.02 μm. The gate is a disk gate. The inductor is made by spirally forming an 8mm diameter copper tube into a donut shape at 12mm intervals.
It was made by casting with epoxy resin to a thickness of 1 cm and solidifying it into a flat plate. As for the injection molding conditions, the cylinder temperature was set so that the temperature of the glass bead-added polyetherimide resin was 420°C. Before injecting the glass bead-added polyetherimide resin into the mold, the above-mentioned inductor was sandwiched between the molds, and a 7kHz,
A 50 kW high frequency oscillator oscillated for 20 seconds, then the mold was opened, the inductor was pulled out from between the molds, and the mold was closed again. During this time, make sure that the mold cooling water does not flow inside the mold. Then, as with normal injection molding, polyetherimide resin containing glass beads is injected into the mold for 1 second at an injection pressure of 100 kg/ ^cm2 , then cooling water is passed through it, and after cooling for 30 seconds,
I took out the molded product. The total cycle time was 80 seconds. The flatness and smoothness values of the donut disc-shaped molded product obtained here are shown below. In addition, for other physical properties, the mold was replaced with one that conformed to the prescribed test method, and other conditions were the same as those used for producing the donut disc-shaped molded product, and test pieces were prepared and tested. Summer. Flatness: 5.8μm Smoothness: 0.1μm Hygroscopicity: 0.27% Heating deformation temperature: 207℃ Linear expansion coefficient: 30×10 ^-6 /℃ In addition, the donut disk-shaped hard magnetic recording medium substrate obtained above was used. After removing the adsorbed moisture in a vacuum container at 120° C. for 10 minutes, magnetron sputtering was performed for 1.5 minutes using chromium as a target to obtain a substrate with an underlayer. Next, a 0.06 μm thick Co ₈₀ Ni ₂₀ magnetic layer was provided on this underlayer by magnetron sputtering. When the surface of this hard disk subjected to magnetron sputtering was observed using a scanning electron microscope, it was found that the magnetic layer was uniformly adhered to the hard disk, with no cracks or the like. Furthermore, a carbon protective layer with a thickness of 0.03 μm was provided. Using the magnetic disk thus obtained, a contact start stop (CSS) test was conducted according to a conventional method.The results are shown below. CSS frequency output reduction rate (%) 10000 0 20000 0 30000 0 50000 0 80000 2 Examples 2, 3 The polyetherimide resin in Example 1 was replaced with polyether sulfone resin (Example 2), polyphenylene ether resin (Example 3), a molded article was obtained and tested in the same manner as in the example. The results are shown below. When the surface of the hard disk subjected to magnetron sputtering was observed using a scanning electron microscope, it was found that the magnetic layer was evenly adhered to the hard disk, with no cracks or the like.

[Table] Examples 4, 5, 6 Molded bodies were obtained and tested in the same manner as in Example 1, except that the type and amount of filler added were changed as shown below. The results are shown below.

[Table] Comparative Example 1 A donut-shaped substrate of an aluminum-magnesium alloy (AA 5086) having the same dimensions as in Example 1 was subjected to magnetron sputtering for 1.5 minutes using chromium as a target to obtain a substrate with an underlayer. Next, a 0.06 μm thick Co ₇₈ Ni ₂₂ magnetic layer was provided on this underlayer by magnetron sputtering, and a 0.02 μm thick carbon protective layer was further provided to produce a magnetic disk. The results of the CSS test for this magnetic disk are shown below. CSS number output reduction rate (%) 10000 0 20000 0 30000 7 50000 15 Comparative example 2 The same polyetherimide used in Example 1 was used, no filler was added, and the same molding machine and mold as Example 1 were used. A molded product was obtained by molding at a resin temperature of 400°C, a mold temperature of 100°C, cooling for 2 seconds, a total molding cycle of 45 seconds, and an injection pressure of 100 kg/cm ² . The physical properties are shown below. Flatness: 32 μm Smoothness: 0.1 μm Hygroscopicity: 0.26% Heating deformation temperature: 200°C Linear expansion coefficient: 56×10 ^-6 /°C In addition, a magnetic layer was applied to the molded product under the same conditions as in Example 1, and it was examined under an electron microscope. As a result of observation, it was confirmed that microcracks had occurred in the magnetic layer. CSS frequency output reduction rate (%) 10000 0 20000 0 30000 5 50000 14 Comparative example 3 Using the same polyetherimide, filler type and additive amount of resin as used in Example 5, and the same forming material and mold. The molded product was then molded at a resin temperature of 450°C, a mold temperature of 180°C, a cooling time of 80 seconds, and a total molding cycle of 100 seconds. The physical properties of the molded article at that time were flatness of 5.5 μm and smoothness of 6 μm. Although the appearance is nicer and smoother than ordinary glass fiber-added polyetherimide molded products, the lack of smoothness makes it difficult to accurately input and output recorded signals even when used in hard disk drives. [Effects of the Invention] The thermoplastic resin injection molded article according to the present invention has excellent planarity and smoothness, and is therefore particularly suitable for use as a substrate for magnetic recording media. In some cases, highly accurate magnetic recording is possible based on the flatness and smoothness of the substrate.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an apparatus used in a manufacturing method for manufacturing a filled thermoplastic resin injection molded article of the present invention. FIG. 2 is a graph showing an example of the temperature distribution of the mold in the apparatus shown in FIG. FIG. 3 is a plan view showing a substrate for a hard magnetic recording medium as an example of the molded article of the present invention. Reference numeral 1 designates a stationary mold, 2 a movable mold, and 3 an inductor in a high frequency generator. Points A and B indicate the surface of the mold, and points C and D indicate the inside of the mold. 4 is a substrate, and 5 is a hole.

Claims (1)

[Claims] 1. Addition of 5 to 80% by weight of filler to an amorphous resin having a hygroscopicity of 0.7% or less, a heat distortion temperature of 100°C or more, and a linear expansion coefficient of 5×10 ^-6 /°C or less The flatness is 29 μm or less per 38 mm span.
An injection molded thermoplastic resin body suitable for use as a substrate for magnetic, optical, and magnetic recording media, characterized by a smoothness of 0.2 μm or less. 2 Filler is organic, inorganic or metal powder,
The injection molded article according to claim 1, which is made of one type or a combination of two or more types of fibers or plate-like bodies.