JPS63183949A - Plastic omposition used in optical data storage member - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to material compositions for use in making optically clear plastic parts useful as video disc structures.

Information markings are also referred to as light reflective elements and light non-reflective elements arranged sequentially in tracks on the surface of the video disc member. A light reflective element and a light non-reflective element are arranged to represent a frequency modulated signal. The width of the frequency band is 0.
In the preferred embodiment, ranging from 25 Mz to 10 Mz, the video disk member is used to store frequency modulated signals representing composite video signals. The composite video signal includes a chrominance signal as well as a luminance signal.

In one mode of operation of this video disc, the reading beam passes through the protective layer and is modulated by information indicators. The reflective layer enhances both the light reflectance of the light reflective element as well as the light scattering of the light non-reflective element.

In another mode of operation, the read beam is incident on the underside of the video disk substrate member and passes through the body of the substrate. After passing through the body of the substrate, the read beam is incident on the information label and is modulated by the information label it carries. In this second mode of operation, the reflective layer still enhances the reflection from the light reflective areas and also enhances the scattering from the previously non-reflective areas.

With such a video disc structure, various aspects of improvements are described below to improve the quality of the video images played from the video disc and displayed on standard television receivers.

The first improvement is that before the reading beam enters the information sign,
The objective is to improve the radial error tracking signal by improving the clarity and birefringence in the thick video disc body passing through it. A typical video disk member has a thickness of 0, IOIMM to 2.5MM.
is within the range of Such birefringence of the substrate body is measured in nanometers. Nanometer is a measure of the delay of light as well as the distortion of light as it passes through a transparent body.

2 at a temperature of approximately 480”F based on manufacturer’s instructions
Using molding times of seconds injection cycles produced video disk members with commercially unacceptable properties. These video disk members were not flat, but rather umbrella-shaped in cross section. This umbrella was measured at the center of the disc. For this purpose, the distance between the center of the disk and a plane passing through at least two points on the outer circumference of the disk was measured. This distance is called the crown of the disc. In the example mentioned above, this crown was 10M1'l.

Another unacceptable characteristic is that the information storage area of this video disc has a uniform and large birefringence value. Various values of birefringence were measured from as low as 4 nanometers to as high as 100 nanometers. A substantially uniform value of birefringence of ±5 nanometers throughout the information storage area is preferred.

Such conventional disks are brittle, prone to surface scratches, and prone to internal stress lines, resulting in surface cracks.

A final characteristic that is unacceptable for video disc members is the presence of morning glory marks, blisters, and other surface defects. All these characteristics influence the quality of the modulated light beam that is reproduced after reflection from the surface of the video disc.

The preferred video disc construction is made by injection molding.
Made from a piece of transparent plastic. The video disc structure includes an information bearing surface having light reflective areas and first non-reflective areas arranged sequentially in alternating positions in the form of a track. The entire body is transparent, but the light reflective areas and the non-reflective areas are formed during the injection molding process.

The light reflective area is planar, and the first non-reflective area is an area extending above and below this planar area. In a preferred embodiment, the first non-reflective region is raised. All the tops lie in a common plane separated from a planar region comprised of light reflective regions. In another embodiment, the information-bearing surface of the video disc member is comprised of planar members in successive positions arranged in alternating planes. Because of the rotational speed of the video disk member and the maximum resolution of the objective lens used to collect the reflected light from each planar region, the discontinuities between these planar regions are as in the preferred embodiment. It acts to fix the light reflective area and the first non-reflective area.

In a preferred embodiment, a protective layer is applied over the zero-order reflective layer that reflects light or prevents light by applying a reflective layer over the light reflective area and the first non-reflective area. Form. An incident light beam passes from the underside of the video disc member through the injection molded body and is modulated by light reflective areas and non-reflective areas.

For rigid video disc components, the board body thickness is 0.
．． It falls within the preferred range of 101MM to 2.5MM.

That is, the incoming beam must pass through the thickness of the substrate with the intensity, directivity, and focus substantially unchanged before hitting the light-reflecting and non-reflecting members. , the intensity is modulated by entering the light reflecting member and the light non-reflecting member. The modulated read beam is reflected by the reflective layer and passes back through the substrate body of the video disc. The first and second passes of the light beam and the modulated reflected beam through the body of the video disc, respectively, ensure that the intensity, directivity and focus of the reading light beam remain unchanged, while the intensity, directivity and focus of the reflected modulated beam remain the same. It is preferable that the quality remains the same and there is no noise.

In fact, the incident light beam and the reflected, modulated light beam are influenced by the composition of the substrate body of the video disc. Defects in the video disk substrate body introduce noise signals into the reflected, modulated read beam. These distortions appear as noise in the reflected signal, which degrades the quality of the image when displayed on a standard television receiver.

A preferred composition for plastic video disc construction is specially prepared polymethyl methacrylate (hereinafter referred to as PMMA).

FIG. 1a schematically shows an optical device 2 used in a typical conventional video disc player device.

Optical arrangement W2 includes a reading laser 3, which is used to generate a reading beam 4 which is used to read the frequency modulation encoded signal stored on the video disc 5. The reading beam 4 is polarized in a predetermined direction. A reading beam 3 is directed onto the video disc 5 by an optical arrangement W2. Another function of the optical device 2 is to image the light beam into a spot 6 at the point of incidence on the video disc 5.

A portion of the information-bearing surface 7 of the video disc 5 is shown in an enlarged view in FIG. 1b. Each of the plurality of information tracks is indicated by a line 9. This line is drawn through a plurality of light-reflecting elements 10 and light-non-reflecting elements 11 in successive positions. Such elements 10, 11 will be explained in more detail later. Clockwise rotation below 4 is indicated by arrow 12.

The reading beam 4 has two degrees of freedom of movement, one of which is radial, as indicated by the double arrow 14. Each arrow 13.1
The arrowheads at both ends of 5 indicate that the reading beam 4 can be moved in both directions, both radially and tangentially.

Furthermore, the optical device 2 has a lens 15 . This lens is
It is used to shape the beam 4 so that it completely fills the entrance aperture 16 of the microscope objective 17. Using an objective lens, a spot 6 of light is formed at the point of incidence on the area 10.11 of the information track 9. Improved results have been observed when the entrance aperture 16 is overfilled by the reading beam 4. As a result, the light intensity of spot 6 becomes maximum.

After the beam 4 has been properly formed by the lens 15, it passes through a beam splitting prism 20. The transmitted portion of beam 4 is applied to quarter wave plate 22 . This plate changes the polarization of the incident light forming the beam 4 by 45°.The zero-order reading beam 4 is incident on the fixed mirror 24. This mirror directs the reading beam 4 onto a first pivoting mirror 26 . First pivot mirror 2
The action of 6 is to move the light beam in the direction of the first degree of freedom of movement, which is tangential to the surface 7 of the video disc 5, so that due to the eccentricity when manufacturing the disc 5, the reading beam 4 is The goal is to correct for any incoming time-based errors.

The tangential directions are forward and backward along the information track 9 on the video disc 5, as indicated by the double arrow 14.

A first pivot mirror 26 directs the light beam to a second pivot mirror 28 . The second pivot mirror 28 is used as a radial tracking mirror. In response to the composite tracking error signal, the point of incidence 6 of the reading beam 4 is controlled by slightly changing its physical position with respect to the reading beam 4, so that the information-bearing member 10.11 is moved along one information track 9. The function of the tracking mirror 28 is to track in the radial direction. The second pivoting mirror 28 has one degree of freedom of movement which directs the light beam towards the disk 50 in the direction indicated by the double arrow 13.
Move radially on the surface. The reading beam 4 then enters the previously mentioned entrance aperture 16 and is focused by a lens 17 onto a spot 6 on the information track 9 of the video disc 5.

In a typical reproduction mode, a focused light beam is incident on a light reflective region 10 and a first non-reflective region 11 at successive locations representing frequency modulated information. In a preferred embodiment, the first non-reflective member 11 is a light scattering element carried by the video disc 5. The reflected beam 4' is a modulated light beam. The modulated reflected beam 4' is light that corresponds to the frequency modulated signal represented by the light reflective element and the non-reflective element 10.11 in the track 9. When this modulated light beam is reflected by a light reflective member 10 and a first non-reflective member 11 located in successive positions on the video disc 5, it is focused by a microscope objective lens 17 at 0.
The reflected reading beam 4' returns along a portion of the same path as previously described for the incident reading beam. This passage connects the second pivot mirror 28, the second pivot mirror 26 and the fixed mirror 2.
Contains sequential reflections from 4. In order to use the common path of the reading optics 2, we use the number 4 for the incident light beam;
The number 4' is used for the reflected beam. The reflected reading beam 4' passes through a quarter wave plate 22. The quarter-wave plate 22 changes the polarization by an additional 45°, resulting in a total change in polarization of the reflected read beam 4′ by 90° relative to the incident read beam 4. Then reflected reading beam 4
' is incident on the beam splitting prism 20, and this prism changes the direction of the 90° shifted portion of the reflected reading beam 4' and makes it incident on the tracking error signal reproducing circuit 30.Circuit 30 generates a radial tracking error signal, which will be explained later.

FIG. 2 shows the video disc member 5 partially in cross-section and partially in perspective. The video disc 5 has a substrate member 53, which has a first or entrance surface 55 and a second or information-bearing surface 57. upper surface 57
includes a planar surface portion 58 which includes a segment 10 which acts as a light-reflecting portion of the information track 9; furthermore, the upper surface 57 includes a non-planar surface area 59 which contributes to the light scattering of the information track. It acts as member 11. Each light reflection segment) 10 is Ila.

It is located between a pair of light scattering regions as shown in 11b.

A highly reflective layer 60 is formed over the surface 57 and a protective coating 61 is formed over the highly reflective layer 60.

FIG. 6 schematically shows a portion of the information-bearing surface 57, which includes a plurality of tracks 9a, 9b, 9c. Each information track is a ring-shaped area between pairs of structural lines 63,65. The track 9a as a whole consists of a pair of structural lines 6
3a, 65a, track 9b is generally between structure lines 63b, 65b, and track 9C is generally between structure lines 63c, 65c.

The width of each ring-shaped area 9a, 9b, 9c is radial and is defined by lines 67a, 67b, respectively.

It is represented by the length of 67c. Ring-shaped area 9a
, 9b, 9c are measured in the circumferential direction and vary by 2πR with respect to the radius of the ring-shaped member, as is well known.

The planar portion 58 of the information storage surface 57 is further 9a.

It includes a planar inter-track protection region 69 that separates adjacent tracks as shown in 9b. In a plan view of an information track as shown in 9a, a planar reflective area is indicated at 10;
The scattering area is indicated by 11.

In the embodiment shown in FIGS. 2 and 3, the light scattering region 11 is shown as having a trapezoidal cross section, having a leading edge 71 and a trailing edge 73, and an egg-shaped planar upper surface. For purposes of illustration in FIG. 2, the light scattering region 11 having a trapezoidal cross-section is shown as an egg-shaped truncated cone, the surface 59 of which is an egg-shaped upper surface 75.
and side surface 77.

In FIG. 3, the upper surface 75 of all the light scattering members 11 is
It is shown that it terminates in a single plane, denoted by . It is shown that all light reflective areas 10 terminate in a single plane, indicated by line 81. A highly reflective layer 60 is covered with a protective layer 61. If you look at this figure, you can see that the protective layer 61 is attached to the substrate body 53.
It will be appreciated that it is much thinner. An objective lens, shown in side view, images the reading beam 4 onto a light-reflecting region 10 .

In FIG. 4, the video disc structure 5 is shown in substantially the same cross-sectional view, but the light scattering region 11 is shown as a recess from the surface 57, and the semicircular line 57 in brackets 83 is shown.
It is rated as a. Viewed in perspective (not shown), this recess is a hemispherical void in surface 57. It is shown that the reading beam 4 is imaged partly onto the light-reflecting region 101 and partly onto the light-scattering region 11 .

FIG. 5 shows a third embodiment of a video disc structure 5 designed for use in the video disc player shown in FIG. Substrate 53 has a first or inlet surface 55 and a second or information-bearing surface 57 . A planar light reflecting area 10 is shown at 58. Light scattering region 11 is shown as a curved surface region 59. A reflective layer 60 is formed on top surface 57. A protective layer 61 is shown formed over reflective layer 60. An objective lens images the reading beam 4 partly onto a planar, light-reflecting portion 58 of the information-bearing surface 57 and partly onto a curved portion 59 of the information-bearing surface 57 .

Example 1 A video disk structure is formed using PMMA without any special preparation as the molding material.

The molding temperature for the injection molding cycle is set at 480'F and the injection molding cycle time is 2 seconds. The initial molding temperature is determined by the manufacturer of the injection molding material.

Inspection of the video disk structure produced by injection molding in this manner revealed that it was umbrella-shaped with a raised crown of about 10 mm.

Measurements of birefringence have ranged from a minimum of 4 nanometers at the outer radius to a maximum of 100 nanometers at the center of the disc. This video disc structure is very fragile and has numerous surface marks. It was recognized that there is. 3.
It broke when I bent it with a radius of 5 inches.

Examples 2 to 5, described below, were carried out using the injection molding machine described in Example 1, using PMMA without any special preparation.

Example 2 All PMMA mixtures were used in an injection molding machine.

The temperature of the melt was increased to 508'F and the injection molding time was 2
It took seconds. Video disc structures made with this injection molding cycle were found to have a 5 mm crown. The disks exhibited varying values of birefringence starting from a small value of 4 nanometers at the outer radius to a maximum value of 50 nanometers at the center of the disk. The disc had a number of surface marks.This test showed that increasing the temperature of the melt reduces the absolute value of birefringence. Surface defects also increased with increasing temperature.

Example 3 The injection molding cycle composition was entirely PMMA. The temperature of the melt was raised to below 536°C and the temperature was 2°C for 4 hours during injection molding.
It took seconds. Video disc structures made by this method were found to be nearly flat with a 2 mm crown. The values of birefringence start from a minimum of 4 nanometers at the outer radius and increase to 3 nanometers at the center of the disk.
It changed to the maximum value of 0 nanometers. The video disc remained brittle and had an increased number of marks on the surface compared to the disc made by the method described in Example 2.

Example 4 The composition of the injection molding melt was 100% PMMA.

The melt temperature was maintained at 536"F and the injection molding time was reduced to 1 second. This resulted in a nearly flat video disc structure with a crown of zero mm. The value of birefringence was: from a small value of 4 nanometers at the periphery of the disk to 15 nanometers at the center of the disk.The video disk structure remains fragile, and Example 3
Additional surface marks occurred compared to those seen in the video disc structure described in .

This test showed that because the temperature of the injection molding melt is high, it is possible to shorten the injection molding time. These high temperatures reduce the resistance to melt flow into the injection molding cavity.

Furthermore, this test showed that increasing the temperature of the injection molding melt and shortening the injection molding time significantly increased the brittleness.
It was found that surface defects increased.

Example 5 The composition of the injection molding melt is 100% PMMA.

The temperature was kept below 536°C and the cycle time was reduced to 0.5 seconds. Video disk structures made by this method were found to be substantially flat, with a crown of zero millimeters. The value of birefringence is 4 from the outer radius to the inner radius.
It continued to decline at a gradient of nanometers to 10 nanometers.

As for the characteristics of the disc, the brittleness continued to increase and the surface markings increased compared to the disc structure made by the method described in Example 4.

If PMMA is specially prepared to have the melt flow rate, particle size, and dimensional stability described below, as well as a monomer-free system and a lubrication system, PMMA alone can be used to produce plastic videos.・Able to create disk structure, PM
It has been found that properties can be made at least as good as plastic video disk structures made from the preferred composition of MA and acrylic rubber.

The melt flow rate PMMA is processed to have a melt flow rate of about 23 to 23 grams per 10 minutes, as measured by ASTM No. D12, 8 Condition I. Lower melt flow rates result in a more viscous polymer and require increased pressure to force the polymer into the mold. The increased pressure creates a difference in the density of the polymer within the disk, which causes the disk to curl back into an umbrella shape after being released from the mold. At the desired melt flow rates stated above, the density of the polymer in the disc is approximately uniform, resulting in a relatively small, uniform composite with no warping of the disc after release from the mold. Has refraction.

Melt flow rates greater than those stated above result in unacceptable environmental characteristics of the plastic disk member. For example, plastics become too brittle, melt at relatively low temperatures, and have relatively low hardness, robustness, and tensile strength. If, at a desired melt flow rate, the disk becomes significantly brittle, this brittleness can be minimized by making the disk thicker. The disks can be made thicker by making the mold thicker or by fitting two disks into one disk.

Particle Size Foreign particles in the PMMA will deflect the light beam as it passes through the disk and must be eliminated; this means that UV absorbers, toners or other foreign particles are not added to the polymer during manufacture. or PMM
This can be achieved by filtering the polymer in A such that the particle size is no larger than 1 to 10 microns.

The presence of PMMA monomers in the monomers and stability polymers causes disc blistering during molding and blistering of aluminum reflective coatings after vacuum spraying; It should be eliminated. If the polymer is fragmented, P during molding
MMA monomer may also be produced. For this reason, the polymer should be stable and should not degrade under the processing or molding conditions described herein.

Lubrication A suitable lubricant is mixed with the PMMA to facilitate release of the disk structure from the mold. When the lubricant runs out and the mold is opened, there is a risk that it will splatter and contaminate the surface of the disk, so to avoid this, the lubricant should be selected to have a vapor pressure lower than the molding temperature. . Examples of suitable lubricants include stearyl alcohol, stearic acid, metal stearates such as zinc or calcium stearate, crystalline paraffin wax and montan wax.

The lubricant is added in an amount of about 0.5 to 0.8% by weight of the plastic to facilitate release from the mold and to ensure good adhesion between the plastic disc and the vacuum-deposited aluminum. Should.

The specially prepared PMMA described above was injection molded under the same preferred processing conditions as described above.

In FIG. 7, an optically readable element 5 with one information track 9 is shown in cross section.

The information track 9 mechanically connects the spacer element 114 with a spacer element 112 having a light-reflecting area 10 and a light-scattering area 11 . A spacer member 114 mechanically retains an optically clear member 116 made in accordance with the present invention. This shows the case where the reading beam 4 is imaged on the light scattering member 11. In this embodiment, optically clear member 116 acts as a dust cover for the overall protective sheet member;
Protect member 5 from the environment. Optically clear member 1 shown as having a uniform thickness over its length
It is important that 16 be of such composition that it does not interfere with the intensity, directivity and/or focus of reading beam 4. In this embodiment, an optically clear member 116 is placed between the source of the reading beam 4 and the video disc member 5 to image the reading beam 4 onto the information track 9. is read.

[Brief explanation of the drawing]

FIG. 1a is a block diagram of a conventional video disc player, showing the relationship between the video disc and other electronic circuitry used in the player. FIG. 1b is a highly enlarged schematic diagram of a portion of the video disc shown in FIG. 1a, FIG. 2 is a perspective view in cross-section of a portion of the video disc structure shown in FIG. 1a, and FIG. The video shown in Figure 2
FIG. 3 is a radial cross-sectional view of the disk taken along line 3-3;
The objective shown in FIG. 1 is also shown in side view. FIG. 4 is a radial sectional view showing a second embodiment of the video disc structure, FIG. 5 is a radial sectional view showing a third embodiment of the video disc structure, and FIG. FIG. 7 is an enlarged view of a portion of the surface of the video disk member shown, and FIG. 7 is a cross-sectional view illustrating the reading of a recording through an optically clear member made in accordance with the present invention.

Claims (5)

[Claims] (1) A clear, substantially monomer-free polymethyl methacrylate material for injection molding an optical information storage member, wherein the material is; during the injection molding the monomers are formed; Material stability and US standard ASTM
Approximately 20 per 10 minutes measured under number D1238 condition I
A plastic composition for use in an optical information storage member, characterized in that it has a melt flow rate of from 23 grams to 23 grams and a material purity free of foreign particles with dimensions of 1 to 10 microns or more. (2) In the material described in claim 1,
A plastic composition for use in optical information storage elements, characterized in that said material further comprises a lubricant having a low vapor pressure under injection molding conditions. (3) In the material described in claim 2,
A plastic composition for use in an optical information storage member, characterized in that the lubricant is distributed in the material in an amount of 0.5 to 0.8% by weight of the material. (4) A clear, substantially monomer-free, polymethyl methacrylate member for injection molding optical information storage materials having defined surface discontinuities, the material comprising: The sheet member defining the transparent area for the regenerating beam has sufficient material stability to prevent the formation of the monomer during the injection molding and American Standard ASTM No. 1238 conditions. an optical material characterized by having material properties including a melt flow rate of about 20 to 23 grams per 10 minutes, measured at clear sheet material. (5) In the optically clear sheet member described in claim 4, the member further includes an optically clear sheet member having an optical birefringence value in the range of 4 to 20 nanometers. .