JPH09300402A - Method of manufacturing turntable for CD - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent eccentricity and improve adhesion at low cost and with high precision. [Composition] Injection molding of a donut-shaped CD turntable in which resin is injected and density distribution is performed at equal angles around a reference axis in the same phase, and a step of inserting the CD turntable into a molding die is performed. A step of closing the mold to form a cavity with the CD turntable, and injecting and injecting a molten resin material having a large elastic coefficient into the cavity, and joining the resin material to the surface of the CD turntable by fusion heat. Then, the cavity is formed into a shape having the same phase at equal angles around the reference axis, and the cavity is mass-produced with high accuracy and low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a CD turntable. More specifically, the present invention relates to a method of manufacturing a CD turntable that isotropically distributes density from an axisymmetric gate.

[0002]

2. Description of the Related Art The rotation speed of a compact disk (hereinafter referred to as a CD) such as a CD-ROM, which is a recording medium, is increased from double speed to triple speed. Such speeding up should continue to progress in the future. The CD is placed closely on the turntable. In order to protect the surface of the CD and provide cushioning and friction between the CD and the turntable,
A thin film layer is formed on the surface of the turntable with an elastic material such as rubber.

The turntable is usually made of metal, but as shown in JP-A-64-30001, a turntable made of resin has been proposed. The surface accuracy required for the turntable can be easily obtained by the recent highly accurate molding technology. The thin film layer must be formed to have a uniform thickness to avoid wobbling. It is known from the publication that a printing technique is used as a technique for forming a thin film layer having a uniform thickness on the surface of a turntable. Although the mask printing can form a thin film layer of a uniform thickness to a considerable extent, it is still insufficient. In the case of printing, the adhesive strength between the thin film layer and the turntable surface is
Is insufficient.

The adhesive strength can be sufficiently enhanced by integrating the turntable and the thin film layer by the different material integral injection molding technique. The thin film layer must also have a high coefficient of friction. The coefficient of friction depends on the density of the thin film layer. The variation in the density of the thin film layer affects the runout during high speed rotation. When forming a thin film layer by injection molding,
It is known that if the pressure distribution in the cavity is not uniform, the density will not be uniform.

For example, it is known that the density of an elastomer doubles when the pressure doubles at a certain temperature. Such properties are generally found in resin materials to some extent. If the density is not uniform, for example, if the density distribution is not axisymmetric, centrifugal shake may occur during high speed rotation. Reworking the rotating body that causes centrifugal shake to prevent centrifugal shake is unsuitable for mass-produced products that require extremely low costs.

[0006]

SUMMARY OF THE INVENTION The present invention has been made based on such a technical background, and achieves the following objects.

An object of the present invention is to provide a method for manufacturing a CD turntable in which the density distribution is axially symmetrical even if a resin thin film layer is formed on a resin turntable by injection molding of different materials.

Another object of the present invention is to provide a method of manufacturing a CD turntable in which no runout occurs even if a resin thin film layer is formed on a resin turntable by injection molding of different materials.

Still another object of the present invention is to provide a method of manufacturing a CD turntable which has a large bonding strength without causing a runout even if a resin thin film layer is formed on a resin turntable by injection molding of a different material. It is in.

Still another object of the present invention is to provide a CD having a large joining strength and a large friction coefficient even if a resin thin film layer is formed on a resin turntable by injection molding of a different material without causing runout.
It is to provide a method of manufacturing a turntable for use.

Still another object of the present invention is to provide a method of manufacturing a turntable for a CD, which has an axisymmetric density distribution even when a resin thin film layer is formed on a resin turntable by injection molding of a different material and is inexpensive. To do.

[0012]

Means for Solving the Problems To solve the above-mentioned problems, the following means are adopted.

The method of manufacturing a CD turntable according to the first aspect of the present invention includes the steps of injecting a resin to injection-mold a doughnut-shaped CD turntable in which the density is distributed in the same phase around the reference axis at equal angles. CD molded in the process
A turntable for molding into a molding die, a step of closing the molding die to form a cavity between the molding die and the turntable for CD, and a molten resin material having a large elastic coefficient in the cavity. And injecting the resin material into the surface of the CD turntable by heat of fusion to form a bonding layer, wherein the cavities have the same phase around the reference axis at equal angles. Is formed in.

A method of manufacturing a CD turntable according to a second aspect of the present invention is characterized in that, in the first aspect, a plurality of injection / injection gates communicating with the cavity are arranged at the same phase at equal angles.

According to a second aspect of the present invention, in the method of manufacturing a CD turntable according to the second aspect of the present invention, the supply holes for supplying the molten resin material to the injection / injection gate are arranged in the same phase at equal angles. Is characterized by.

A method of manufacturing a CD turntable according to a fourth aspect of the present invention is characterized in that, in the second aspect, the resin material is an elastomer having a different density depending on a pressure when melted.

A method of manufacturing a turntable for a CD according to a fifth aspect of the present invention is the same as the fourth aspect of the present invention, in which the elastomer and the C are used.
It is characterized by being fused with the D turntable.

The method of manufacturing a CD turntable according to the sixth aspect of the present invention is the same as the first aspect of the present invention, wherein the difference in density of the bonding layers at the axially symmetrical positions is ΔL (micron) as the allowable range of the runout of the CD turntable. When the average radius of the bonding layer is represented by R, the mass of the CD turntable is represented by M, and a constant having a dimension of volume is represented by V, per unit volume of the bonding layer in an axially symmetric position is represented. The resin material is injected such that the density difference Δρ is smaller than the difference represented by the following equation ΔL = K · Δρ K = (V / M) · R.

According to a seventh aspect of the present invention, in the method of manufacturing a CD turntable according to the sixth aspect of the invention, the supply holes for supplying the molten resin material to the injection / injection gate are arranged at the same phase at equal angles. Is characterized by.

The method of manufacturing a CD turntable according to the eighth aspect of the present invention is characterized in that, in the sixth aspect, the resin material is an elastomer having a different density depending on the pressure when melted.

In the method of manufacturing a CD turntable according to the present invention, since the cavities are formed exactly in the same phase around the reference axis at equal angles, eccentricity is prevented. By fusion bonding, the joining layer is joined firmly to the turntable body, that is, integrally. Since it has a large friction coefficient and is formed by mirror finishing, it has a large adsorption force both in the radial direction and in the radial direction.

Since the bonding layer is formed within the range of the density error which is proportional to the allowable error of the runout, runout is prevented. The molding condition is easily judged by the molding standard of the density difference having a simple relation to the eccentricity amount, and high-precision molding is possible.

[0023]

Next, an embodiment of the present invention will be described. FIG. 1 shows a CD-RO on a turntable manufactured by the method for manufacturing a CD turntable of the present invention.
The state where M is placed and rotated is shown. The turntable 1 is made of resin and is produced by injection molding. As the resin forming the turntable 1, various hard engineering plastics are used. The resin used can be selected from the group of engineering plastics such as ABS resin, PP and polycarbonate.

The turntable 1 integrally has a small diameter portion 2 on the upper surface side in the center. The turntable 1 integrally has a shaft portion 3 on the lower surface side in the center. Small diameter part 2 and shaft part 3
Share the center line J of the rotation axis of the turntable 1 as a center line. That is, the small diameter portion 2 and the shaft portion 3 are formed coaxially.

The turntable 1 has a density distribution in the same phase around the reference axis at equal angles. Since the illustrated turntable 1 is isotropic (isotropic), the equiangles have the same phase for every arbitrary angle. The bonding layer 4, which is a thin film layer, is bonded to the surface of the turntable 1. The bonding layer 4 has a donut shape and is formed in the outer peripheral area of the surface of the turntable 1.

The thickness of the bonding layer 4 is uniform over the entire area, and is 0.
2 to 0.5 mm. The bonding layer 4 is axisymmetric with respect to the reference axis J. The material of the bonding layer 4 has rubber elasticity and a large friction coefficient. Elastomer is used as a material for the bonding layer 4 having high strength. The elastomer can be selected from a group of elastomers including various elastomers such as polyester elastomers and polyether elastomers.

The combination for heat fusion of the material selected from the engineering plastic group of the turntable 1 and the material selected from the elastomer group of the bonding layer 4 has been well studied and known by the present inventors. . The fusion is a state in which both materials are intricately formed in a sea-island shape or a sea-island like shape by photographing with an electron microscope. Fusion is a state in which both materials are melted and enter each other in the form of protrusions in cluster units. It has been determined by the present inventor that such fusion occurs when high pressure is applied under a temperature condition in which two selected foreign materials are present.

The smoothness of the surface formed by molding the bonding layer 4 is comparable to that in the mirror-polished state. The CD5 is placed on such a surface. The bonding layer 4 and the CD 5 are in close contact with each other in the vertical direction (normal direction orthogonal to the surface), and due to the large friction coefficient of the bonding layer 4, they are in close contact with each other even with respect to positional displacement on the surface.

The inner peripheral surface of the central hole of the CD 5 fits the outer peripheral surface of the small diameter portion 2 to some extent, and is slidably fitted in the axial direction. The CD 5 is movable in the radial direction with respect to the turntable 1 in the order of microns. Shaft 3
Is driven to rotate by a motor (not shown).

FIG. 2 shows a first embodiment of the method for manufacturing a CD turntable according to the present invention. The mold device 6 is composed of a fixed side element 7 and a movable side element 8. The turntable 1 has already been molded and produced in a separate process.
The turntable 1 is inserted into the fixed side element 7,
It is precisely positioned with respect to the stationary element 7. The turntable 1 and the movable-side element 8 are shown in the closed state.
And form a cavity 9.

The cavity 9 can also be formed by the turntable 1, the fixed side element 7 and the movable side element 8.
The cavity 9 is a closed space surrounded by a ring-shaped surface 11, an inner peripheral surface 12, an outer peripheral surface 13 and an upper surface 14 of the turntable 1 formed on the bottom surface of the movable element 8.

The outer peripheral surface 13 can also be formed by the inner peripheral surface of the fixed-side element 7. The cavities 9 have a shape having the same phase for each equal angle, and specifically have a disk shape, that is, a disk shape. Disk-shaped cavity 9 shown
Is isotropic, and therefore has the same phase for every arbitrary angle.

As shown in FIGS. 2 and 3, injection injection gates 21 are provided at three locations. Injection injection gate 21
Are in phase with each other if they rotate about the reference axis J at equal angles. In this case, the rotation angle with the same phase is 120
Degrees. Each injection injection gate 21 has an axial supply hole 2
It is the open end of 2 and opens to the cavity 9.

Axial supply holes 22 arranged at three positions
Are equidistant from the reference axis and have the same phase when they are oriented in the axial direction and rotate about the reference axis J. The axial supply holes 22 are gathered to the reference axis J via the radial supply holes 23 and connected to one central axis common hole 24. The radial supply hole 23 faces in the radial direction.

Radial supply holes 2 arranged at three positions
3 have the same phase when they rotate about the reference axis J at an equal angle. The central shaft supply hole 24 is oriented in the axial direction. Axial supply hole 22, radial supply hole 23, central shaft supply hole 2
Such a spool and a supply hole, which is a runner, composed of 4 have the same phase if they are rotated at an equal angle around the reference axis, and match with themselves.

In the mold closed state of FIG. 2, the molten resin is injected into the central shaft supply hole 24 at an appropriate pressure. A case where the most preferable material, elastomer, is selected as the bonding layer 4 of the turntable manufactured by the method for manufacturing a CD turntable of the present invention will be described.

The molten elastomer flows into the radial supply holes 23 at the same pressure, flows radially, bends at the outer end, and flows axially. The flow velocity and flow pressure of the molten elastomer in the axial supply hole 22 and the radial supply hole 23 are equiangular and in the same phase around the reference axis J.

The pressure of the molten elastomer reaching each injection and injection gate 21 and the inflow velocity of the molten elastomer per unit time flowing into the cavity 9 are equal. The molten elastomer injected into the cavity 9 at three points expands from each injection and injection gate 21 in a substantially radial direction with a uniform pressure distribution and an expansion speed.

The regions where the three flows that expand and flow from the three locations interfere with each other are equiangular and in the same phase. Cavity 9
The density distribution inside is not uniform. If the pressure of the molten elastomer is high, it behaves like an ideal gas because the density becomes large, but it is not an ideal fluid because the viscous resistance is large.

As the distance from the injection injection gate 21 increases, the pressure drops and becomes lower. Adjacent radial feed holes 23
At the middle position of, the pressure becomes the lowest and the density becomes low. Thus, the density distribution is not uniform, but the reference axis J
Are equiangular around and in phase.

The final density distribution is generally determined by the pressure when a certain time has elapsed from the time when the molten elastomer completely filled the cavity 9. Such pressure adjustment is performed by an adjusting mechanism generally attached to the injection molding machine.

The opening area of each injection injection gate 21, the cross-sectional area of each axial supply hole 22 and each radial supply hole 23 should be corrected by performing test injection and measuring the deflection of the molding turntable. You can The density distribution of the turntable 1 is isotropic with sufficient accuracy because the material used is hard engineering plastic.

Next, the relationship between the allowable range of the formed runout and the density error will be examined. The runout of the first embodiment may be analyzed by the density difference per unit length in the circumferential direction shown in FIG. The bonding layer 4 at the position (a) is a bonding layer portion around the injection injection gate 21. The bonding layer 4 at the position (b) is a bonding layer portion that is 180 degrees out of phase with the injection injection gate 21.

Due to the density difference, both bonding layer portions are slightly outwardly distorted and inclined, but in the following analysis due to this inclination, they are secondary correction terms and are ignored. In the figure, the density of the left bonding layer is represented by ρL, the density of the left bonding layer is represented by ρR, and the density difference is represented by Δρ. Since ρL is larger than ρR (larger), Δρ = ρL−ρR> 0 If the rotation speed is v, the average radius is R, the mass of the turntable 1 is M, the reciprocal of the time (cycle) of one rotation is ω, and the volume per unit length is V, the centrifugal force difference ΔF on both sides Is
It can be expressed by the following equation.

[0045]

[Equation 1] This centrifugal force difference can be expressed by the following equation as a vector in the horizontal direction in the drawing.

[0046]

[Equation 2] The centrifugal run-out length when making a half turn (from 0 to π / 2) is
By integrating this ΔF twice, an approximate value ΔL (positive) is obtained. If the integration is performed twice and the integration constant is zero, ΔL = (Δρ · V / M) · R The constant per unit length {(V / M) · R} is expressed as K. ΔL = K · Δρ The value ΔL is a linear function of the density difference and is not related to speed. The swing value ΔL and the density difference are simply proportional. ΔL
Is 10 micron, the accuracy of the density difference in molding is Δρ <10 micron / K 2. A calculation using the specifications of an ordinary CD-ROM allows a density difference of about 0.1 gram per unit length.

[0047]

According to the method for manufacturing a CD turntable of the present invention, it is possible to mass-produce high-precision turntables at low cost. It is easy to adjust the molding conditions for higher accuracy by adjusting the density difference.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a turntable manufactured by a method for manufacturing a CD turntable according to the present invention.

FIG. 2 is a cross-sectional view showing a first embodiment of a method for manufacturing a CD turntable of the present invention.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a cross-sectional view for analysis.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Turntable 4 ... Bonding layer 9 ... Cavity 11 ... Ring surface 12 ... Inner peripheral surface 13 ... Outer peripheral surface 14 ... Upper surface 15 ... Outer peripheral surface 21 ... Injection injection gate 22 ... Axial supply hole 23 ... Radial supply hole 24 ... Central axis supply hole

Claims (8)

[Claims] 1. A step of injection-molding a doughnut-shaped CD turntable in which resin is injected and density distribution is performed at equal angles around a reference axis in the same phase, and the CD turntable molded in the step is molded. Inserting into a mold, closing the mold to form a cavity between the mold and the CD turntable, and injecting a molten resin material having a large elastic coefficient into the cavity to melt the resin. Bonding the resin material to the surface of the CD turntable by heat to form a bonding layer, and the cavities are formed in the same phase shape at equal angles around the reference axis. Manufacturing method of turntable for CD. 2. The method for manufacturing a CD turntable according to claim 1, wherein a plurality of injection and injection gates communicating with the cavity are arranged at the same phase for each equal angle. 3. The method for manufacturing a CD turntable according to claim 2, wherein the supply holes for communicating the molten resin material through the injection / injection gate are arranged in the same phase at equal angles. . 4. The method for manufacturing a CD turntable according to claim 2, wherein the resin material is an elastomer having different densities depending on pressure when melted. 5. The method for manufacturing a CD turntable according to claim 4, wherein the elastomer and the CD turntable are fused together. 6. The density difference between the bonding layers at axially symmetric positions according to claim 1, wherein the allowable range of runout of the CD turntable is ΔL (micron),
When the average radius of the joining layer is represented by R, the mass of the CD turntable is represented by M, and a constant having a dimension of volume is represented by V, a density difference per unit volume of the joining layer at an axisymmetric position is represented. A method of manufacturing a CD turntable, characterized in that the resin material is injected so that Δρ becomes a value smaller than a difference represented by the following equation ΔL = K · Δρ K = (V / M) · R. . 7. The method of manufacturing a CD turntable according to claim 6, wherein the supply holes for communicating the molten resin material through the injection / injection gate are arranged in the same phase at equal angles. . 8. The method for manufacturing a CD turntable according to claim 6, wherein the resin material is an elastomer having a density that varies depending on pressure when melted.