Video disc molding composition

A conductive molding composition for the compression molding of high density information discs (video discs). The composition includes a polyvinylchloride-based resin containing sufficient carbon black particles to obtain a desired conductivity (bulk resistivity of about 500 ohm-cm at 900 mHz or less,) from about 1 to 5 weight percent of a stabilizer, from about 0.5 to 3 weight percent of a lubricant, from about 1 to 5 weight percent of a plasticizer and from about 0.1 to 1 weight percent of an organo-silicone compound having polar groups.

This invention relates to the manufacture of high density information 
discs, also known as video discs. More particularly, this invention 
pertains to a molding composition for video discs which maximizes 
performance properties while at the same time reduces the number of 
components and simplifies manufacture. 
BACKGROUND OF THE INVENTION 
Martin et al., in U.S. Pat. No. 4,228,050, have disclosed an improved 
conductive molding composition for the compression molding of high density 
information discs, also known as video discs. This composition, in 
essence, comprises a polyvinylchloride-based resin containing sufficient 
conductive carbon black particles to provide the requisite conductivity, 
i.e., a bulk resistivity of below about 500 ohm-cm at 900 mHz. The 
formulation additionally contains additives such as stabilizers, 
lubricants, plasticizers, processing aids and the like. The composition 
disclosed by Martin et al. contains a large number of such additives which 
are required to stabilize the finished disc. It has been found in 
developing this formulation that care must be used in selecting each 
additive because not only its own stability must be taken into account, 
but one must examine the stability of each additive vis-a-vis the other 
additives, their degradation products, their potential reactions with each 
other, as well as with or between each other. Obviously, the more 
ingredients that are present the more complex the problem becomes and 
potentially the greater the possibility that reactions will occur, for 
example, during the heat and pressure encountered in compression molding 
of the disc. 
Even the complex composition disclosed by Martin et al. is inadequate to 
prevent deterioration of the disc upon exposure to conditions of elevated 
temperature and relative humidity. This deterioration affects the playback 
characteristics of the disc so that they are no longer excellent and maybe 
even progress to where they are unacceptable. In order to offset this 
deterioration, the discs, after they are pressed, are treated to remove 
any material on the surface of the disc. For example, they may be washed, 
with an aqueous cleaning solution containing an oxidizing agent, a base 
and a fluorosurfactant as disclosed in U.S. Pat. No. 4,275,100 to Datta, 
and then rinsed with water and dried. In addition to the treating steps, 
the discs are further coated with a methylalkylsiloxane lubricant which is 
doped with a diloxane dopant as disclosed in U.S. Pat. No. 4,355,062 to 
Wang et al. Discs thus washed and lubricated have been found to possess 
excellent playback characteristics over extended periods of time, even 
under conditions of high temperature and high relative humidity. 
There exists, however, a need to simplify the formulation of the video disc 
molding composition thereby reducing the number of chemical reactions 
which can occur during and after manufacture and/or reduce the number of 
processing steps required for the disc's manufacture for an obvious 
savings in cost and time. In accordance with this invention, there is 
provided an improved conductive molding composition for the video disc 
which significantly reduces the number of ingredients required, eliminates 
the required further treating or washing operation and the use of doped 
lubricants, while retaining and even improving the playback performance 
characteristics of the finished discs. 
SUMMARY OF THE INVENTION 
I have found an improved conductive molding composition having a high 
thermal stability and which is readily processable, such as by compression 
molding, to produce high density information discs of improved quality and 
which have improved surface characteristics resulting in excellent 
playback quality. This molding composition comprises a 
polyvinylchloride-based resin containing sufficient finely divided 
conductive carbon black particles to obtain a desired conductivity (a bulk 
resistivity of below about 500 ohm-cm at 900 mHz), from about 1 to about 5 
percent by weight of the total composition of a stabilizer, from about 0.5 
to about 3 percent by weight of a lubricant, from about 1 to about 5 
percent by weight of a plasticizer and from about 0.1 to about 1 percent 
by weight of an organo-silicone compound having polar groups.

DETAILED DESCRIPTION OF THE INVENTION 
Because of the uniqueness and very small dimension of the information on 
high density information discs, a composition suitable for molding such 
discs must have a uniform dispersion of conductive particles and the other 
additives in the resin so that the molded article will have a uniform 
surface free of defects, minimum shrinkage and warp characteristics and a 
high heat distortion temperature. The composition must be readily 
processable to form a very small relief pattern over the surface of a 12 
inch disc; and sufficient additives must be added to overcome the 
stiffness and brittleness imparted by the large quantity of conductive 
particles present. However, if too large a quantity of total additives are 
present, the additives bleed to the surface, causing non-uniformity and 
staining, which adversely affect the disc quality and may even render the 
disc unplayable by filling up the tiny grooves or information tracks 
monitored by the playback stylus. 
According to the present invention, the improved molding composition 
thereof includes from about 65 up to about 85 weight percent of the total 
composition of a vinyl chloride based resin, from about 12 up to about 19 
percent by weight of the total composition of finely divided conductive 
particles, particularly carbon black, from about 1 up to about 5 percent 
by weight of the total composition of a stabilizer, from about 0.5 up to 
about 3 percent by weight of the total composition of a lubricant, from 
about 1 up to about 5 percent by weight of the total composition of a 
plasticizer, and from about 0.1 up to about 1 percent by weight of the 
total composition of an organo-silicone compound having polar groups. 
The resin employed in the molding composition of this invention can be a 
homopolymer or copolymer of vinyl chloride, or a mixture of the two. 
Suitable polymers include polyvinylchloride homopolymer, a vinyl 
chloride/propylene copolymer, and a vinyl chloride/vinyl acetate 
copolymer. A preferred resin for use in this molding composition is a 
homopolymer of vinyl chloride commercially available from the B. F. 
Goodrich Company as BFG-346, which has a weight average molecular weight 
of approximately 84,000, a number average molecular weight of 
approximately 38,000 and a T.sub.g of approximately 88.degree. C. In order 
to produce the desired characteristics in the video disc, the resin of the 
molding composition should have a high heat distortion temperature, 
preferably 140.degree. F. (60.degree. C.) or higher for the unfilled 
resin. 
Conductive particles suitable for use in the molding composition include 
highly electrically conductive, finely divided carbon blacks which 
preferably have a low bulk density to reduce loading requirements. 
Presently preferred products are commercially available from the Armak 
Company, as Ketjenblack EC, and from the Cabot Carbon Company as CSX-200, 
which carbon blacks have an apparent bulk density of about 140-160 grams 
per liter and an average particle size of about 300 Angstroms. These 
carbon black particles have a high surface area and high proportion of 
voids within the particles as measured by dibutylphthalate absorption. 
This characteristic enables current to flow between the conductive 
particles in a non-conductive polymer matrix in a highly effective manner. 
Other carbon blacks or conductive particles may be employed if they meet 
the electrical requirements. Denser carbon particles will usually require 
higher loading, e.g., up to about 35-40 percent by weight for an 
equivalent conductivity, which must be at least 500 ohm-cm at 900 mHz in 
order for the video signals to be reconsituted on playback with a metal 
tipped stylus. The particle size of these conductive carbon black 
particles is not critical, but in general the particle size should be less 
than 500 Angstroms to prevent the formation of a grainy surface in the 
plastic matrix. As previously indicated, an amount of from about 12 up to 
about 19 weight percent of a carbon black, such as Cabot's CSX-200 is 
preferred. 
Antioxidant stabilizers suitable for use in the present conductive molding 
composition include organo-metallic compounds derived from metals 
including tin, lead, zinc, barium and cadmium, such as 
dibutyltin-.beta.-mercaptopropionate, dibutyltin maleate and the like. 
Epoxides, phosphites and alkylated phenols such as t-butylcatechol can 
also be employed. Generally, these stabilizers are employed in a minor 
amount, i.e., about 1 to about 5 percent by weight of the total molding 
composition. A preferred stabilizer is T-49 available from M & T Chemicals 
Inc. under the trademark of Thermolite-49, which is an organotin maleate. 
The stabilizers act primarily to neutralize volatiles formed as 
decomposition products of the resin. 
A lubricant is also added to the PVC-based resin molding composition of 
this invention. Suitable lubricants include fatty acids and esters, such 
as stearic acid, fatty acid esters of alcohols and acids, polyfunctional 
acid and alcohol esters, soaps including calcium stearate, fatty acid 
amides such as stearic acid amide, oleamide, ethylene and bis stearamide 
and the like, and silanes such as dimethyl siloxane. Sufficient lubricant 
is added to prevent high shear heating during processing and to prevent 
the composition from sticking to the mold during processing. A preferred 
lubricant for the molding composition of this invention is an ester of a 
stearate, such as an alkyl stearate or vinyl stearate, which is employed 
in an amount of from about 0.5 up to about 3 percent by weight of the 
total composition. 
The improved molding composition of this invention also includes a small 
amount of a plasticizer. The plasticizer is employed in amounts of from 
about 1 up to about 5 weight percent of the total composition. A 
preferable plasticizer is diundecyl phthalate. 
In addition to the above-described resin, conductive particles, stabilizer, 
lubricant and plasticizer, the improved conductive molding composition of 
this invention further includes a small amount of a silicone, particularly 
an organo-silicone, and preferably an organo-silicone having polar groups. 
This organo-silicone is employed in amounts of from about 0.1 up to 1 
weight percent of the total molding composition. Preferable 
organo-silicones containing polar groups include 
bis(hydroxyalkyl)disiloxanes, such as 1,3-bis(4-hydroxybutyl)-1,3 
didecyldimethyldisiloxane, an organo-functional silane available from 
Union Carbide Corporation as Y-9602, a polyalkylene oxide modified 
dimethyl polysiloxane available from Union Carbide Corporation as L-722, 
and a similar silicone alkylene oxide copolymer available from Union 
Carbide Corporation as L-7676. 
A presently preferred conductive molding composition for use in making high 
density information discs comprises from 12-19 weight percent of the 
molding composition of Cabot's CSX-200 conductive carbon black particles, 
from 1.0-5.0 weight percent of the molding composition of T-49 
stabilizers, from 0.5-3.0 weight percent of the molding composition of 
vinyl stearate lubricant, from 1.0-5.0 weight percent of the molding 
composition of diundecyl phthalate plasticizer, from 0.1-1.0 weight 
percent of the molding composition of a bis(hydroxyalkyl)disiloxane, with 
the remainder of the composition being a polyvinylchloride homopolymer (B. 
F. Goodrich-346) having a T.sub.g of over about 60.degree. C. 
The present molding composition can be prepared by mixing all of the solid 
ingredients first in a blender, such as a Henschel mixer, until the 
temperature reaches about 120.degree. F. (about 49.degree. C.) and then 
adding any liquid ingredients which coat the solid particles. The mixing 
is continued until the temperature reaches about 160.degree. F. 
(41.degree. C.). The composition is then collected and charged to a Buss 
Condux extruder or other suitable apparatus to melt the ingredients under 
shear. The composition is then extruded through the Buss Condux extruder, 
operating at 150 rpm with the material temperatures in the four zones of 
the extruder ranging between 120.degree. and 180.degree. C. The rate of 
flow of the material through the extruder is controlled to produce a good 
quality composition with optimum melt mixing. Thereafter, the material is 
passed through a 1/8" die, pelletized and stored for molding. The molded 
articles (high density information discs) can be made by compression 
molding in the conventional manner, e.g., forming a preform, compression 
molding, using a 30-60 second cycle at about 325.degree.-380.degree. F. 
(163.degree.-190.degree. C.) and removing the flash. 
Video discs, fabricated as above from the improved molding composition of 
this invention, have surfaces which are not stained, as is the case with 
many video discs of the prior art. Stained disc surfaces have often been 
caused by the bleeding of additives to the disc surface which not only 
cause a staining but often non-uniformities on the disc surface as well. 
In addition to being non-stained, it has been found that the surfaces of 
the discs molded from this improved composition are hydrophobic, having 
little affinity for water, even under atmospheric conditions of high 
temperature and high relative humidity. Due to the non-stained and 
hydrophobic character of the surfaces of these discs, it has been found 
that the discs need no further treatment, such as a cleaning or washing as 
disclosed in U.S. Pat. No. 4,275,100. 
The hydrophobic nature of the surfaces of these discs is attributed to the 
bleeding to the disc surfaces of the organo-silicone compound having polar 
groups. This is illustrated by the single FIGURE of the drawing wherein a 
sample from the inner, non-grooved portion of an as-pressed disc 
fabricated as set forth above was examined by secondary ion mass 
spectrometry (SIMS). The FIGURE is a graph of the ion concentration as a 
function of the depth for 28.sub.Si+ and 30.sub.Si+ of the sample from the 
as-pressed disc. It is readily apparent from the graph that the largest 
concentration of silicon ions is at the disc surface, thus indicating 
bleed-out of the organo-silicone compound to the disc surface, and 
consequent hydrophobic nature of the disc surface. Due to the hydrophobic 
nature of the disc surface, it has additionally been found that a 
lubricant such as that disclosed in U.S. Pat. No. 4,275,101 is sufficient 
and that doped lubricants, such as disclosed in U.S. Pat. Nos. 4,330,583 
and 4,355,062, are not required, even if the disc is to be subjected to 
atmospheric conditions of high relative humidity and high temperature. 
The following specific Examples are included in order to illustrate the 
invention and the improvements thereof with greater particularity. However 
it is to be understood that these Examples are not intended to limit the 
invention in any way. 
EXAMPLE I 
A molding composition was prepared by dry blending the following 
ingredients in a Henschel mixer: 78.75 parts of BFG-346 polyvinylchloride 
homopolymer; 3.0 parts of T-49, an organotin maleate stablizer; 1.0 part 
of vinyl stearate lubricant; 2.0 parts diundecyl phthalate plasticizer; 
and 0.25 part of 1,3-bis(4-hydroxybutyl)-1,3 didecyldimethyldisiloxane as 
the organo-silicone having polar groups, for a period of approximately 10 
minutes. Thereafter, 15.0 parts of Cabot Carbon Company CSX-200A carbon 
particles were added to the Henschel mixer and the total ingredients of 
the formulation were dry-blended therein for an additional ten minutes, or 
until the temperature reached about 190.degree. F. (87.8.degree. C.). 
The compounded mixture was allowed to cool to room temperature and then fed 
to a Buss Condux extruder from which the same was melt-extruded in the 
form of a pelletized molding composition. Thereafter, video discs were 
compression molded from this composition as set forth above and as 
disclosed in U.S. Pat. No. 4,228,050. 
The as-pressed video discs were lubricated with a heretofore known and used 
video disc lubricant having the following formula: 
##STR1## 
wherein x is an integer of about 2-4, and as disclosed by Wang et al. in 
U.S. Pat. No. 4,275,101, referred to hereinabove. The lubricant was 
applied to the surfaces of each disc, without any prior processing or 
treating of the disc, by spraying with a heptane solution of the lubricant 
followed by evaporation of the heptane. 
For this Example and the Examples that follow, carrier distress, which is a 
measure of the distortion, loss of signal or dropout of the audio, video 
and color information coming from the video disc is an important factor. 
The carrier distress time is measured by adding the amount of time in 
seconds (but discounting intervals of less than 10 microseconds) during 
disc playback when the r.f. output of the player arm is less than 150 
millivolts peak-to-peak, and the time when the r.f. output gives above 8.6 
megahertz or below 3.1 megahertz in frequency, indicating a defect. Such 
defects are noted by the viewer as dropouts, up to a complete loss of the 
picture and sound information. The present acceptable level of carrier 
distress for a video disc is 3 seconds in one hour of playback time. 
Another important measure of the quality of the video discs fabricated in 
this and the following Examples is a factor known as the small skips (less 
than 8 grooves) event, which is a measure of the quality of the grooves in 
the disc surface. If the grooves in the disc surface are of such a poor 
quality that the playback stylus skips a number of them, the disc has a 
defect which is noted by the viewer as a complete loss of picture and 
sound information. For the small skips event, the r.f. output of the 
player arm normally detects 8 daxi-codes per groove (or revolution) of the 
disc. However, if less than 8 daxi-codes per groove are detected, a defect 
is indicated in one or more grooves of the disc. The small skips event is 
determined and reported by adding together the number of times (events) 
that the playback stylus skips less than 8 grooves (1 to 8) during disc 
playback. A present desirable level of the small skips event for a video 
disc is 30 events in 1 hour of playback time. 
Carrier distress and the small skips event information for the initial play 
of the discs obtained and lubricated in accordance with this Example were 
measured and determined. This information is set forth hereinbelow in the 
Table. 
The discs were then subjected to a hot condensation stress by being placed 
in a chamber maintained at 95% relative humidity and 100.degree. F. 
(37.7.degree. C.) for a period of 1 hour and played again. The carrier 
distress and small skips event data are set forth hereinbelow in the 
Table. 
Also shown in the Table is the percent of the discs which passed the 3 
seconds in 60 minutes of playback time criteria referred to hereinabove, 
as well as the percent of the discs which passed the less than 30 events 
in 1 hour of playback time criteria referred to above. 
EXAMPLE II 
In this Example, a molding composition was prepared and video discs were 
compression molded therefrom as set forth in Example I above with the 
exception that the organo-silicone compound having polar groups employed 
was Union Carbide Corporation's L-7676 (0.25 part). The pressed discs were 
lubricated and treated as in Example I. Thereafter, carrier distress and 
small skips event information for the initial play and the first play 
following stress testing were measured and determined. These data are set 
forth hereinbelow in the Table. 
EXAMPLE III 
In this Example, a molding composition was prepared and video discs were 
fabricated therefrom as in Example II above, with the exception that the 
lubricant used was Loxiol G-30 (1.0 part), a monofatty acid ester of 
varying molecular weight alcohols and acids of Henkel International GmbH. 
The video discs fabricated from this molding composition were lubricated 
and treated as in the preceeding Examples. Thereafter, carrier distress 
and small skips event information for the initial play as well as the 
first play following the stress testing of the video discs were measured 
and determined. These data are set forth hereinbelow in the Table. 
EXAMPLE IV 
A molding composition was prepared as in Example III above with the 
exception that the organo-silicone compound having polar groups used was 
Union Carbide Corporation's Y-9602 (an organofunctional silane). Video 
discs were fabricated from this molding composition and were lubricated 
and treated as in the previous Examples. Carrier distress and small skips 
event information for the initial play, as well as the first play 
following stress testing for these video discs, were measured and 
determined. These data are set forth hereinbelow in the Table. 
EXAMPLE V 
In this Example, a molding composition was prepared and video discs were 
compression molded therefrom as set forth in Example I above, with the 
exception that the organo-silicone compound having polar groups employed 
was Union Carbide Corporation's L-722, which is a polyalkylene oxide 
modified dimethylpolysiloxane and which was used in the amount of 0.25 
part. The video discs molded from this composition were lubricated and 
treated as in the above Examples. Carrier distress and small skips event 
information for the initial play, as well as the first play following 
stress testing for these so-lubricated and treated video discs were 
measured and determined. These data are set forth hereinbelow in the 
Table. 
EXAMPLE VI 
A molding composition was prepared and discs were fabricated therefrom as 
set forth above in Example V with the single exception that the 
organo-silicone compound having polar groups (Union Carbide Corporation's 
L-722) was employed in an amount of 0.5 part, with the amount of the resin 
employed being proportionately less than that used in Example V. The 
fabricated discs were lubricated and treated as in the previous Examples. 
Carrier distress and small skips event information for the initial play, 
as well as the first play following stress testing for these discs were 
measured and determined. These data are set forth hereinbelow in the 
Table. 
Control A 
A molding composition was prepared using the following ingredients: 77.5 
parts of BFG-346 polyvinylchloride homopolymer; 15.0 parts of Cabot Carbon 
Company's CSX-200A carbon particles; 2.0 parts of T35, a 
dibutlytin-.beta.-mercaptopropionate stabilizer; 1.0 part of Mark 275, a 
liquid dibutlytin maleate stabilizer; 0.75 part of Acryloid K-175, a 
commercially available processing aid of Rohm and Haas Company; 0.5 part 
of Loxiol G-30 lubricant, a monofatty acid ester of varying molecular 
weight alcohols and acids; 0.25 part of Loxiol G-70, a polyfunctional 
complex ester of saturated fatty acids; 1.0 part of calcium stearate 
lubricant; and 2.0 parts of diundecyl phthalate plasticizer. This molding 
composition is similar to that disclosed by Martin et al. in U.S. Pat. No. 
4,228,050 and was prepared as disclosed by Martin et al. and set forth 
hereinabove. Video discs were compression molded from this composition as 
set forth above and as disclosed by Martin et al. The thus obtained video 
discs were lubricated and treated as in the previous Examples. Carrier 
distress and small skips event information for the initial play, as well 
as the first play following stress testing of these video discs, were 
measured and determined. These data are set forth hereinbelow in the 
Table. 
Control B 
Video discs were fabricated from the molding composition of Control A 
above. The as-pressed discs were then further treated and processed by the 
previously known and commercially used disc treating process as disclosed 
in U.S. Pat. No. 4,275,100 to Datta, which includes a washing, rinsing and 
drying treatment. Following this treatment, the discs were then lubricated 
with the previously known and commercially used doped lubricant as 
disclosed in U.S. Pat. No. 4,355,062 to Wang et al. Following disc 
treatment and lubrication, carrier distress and small skips event 
information for the initial play, as well as the first play following 
stress testing for these discs, were measured and determined. These data 
are set forth hereinbelow in the Table. 
TABLE 
______________________________________ 
Carrier Distress 
(sec. per 60 min. Playback Time) 
Initial Play 1st Play After Stress 
% % 
Example Median Range Pass Median 
Range Pass 
______________________________________ 
I 0.04 0.02-0.1 100 0.89 0.05-2.5 
100 
II 0.6 0.2-5.0 92 0.8 0.1-3.5 92 
III 0.18 0.09-3.5 92 0.8 0.1-5.3 92 
IV 0.31 0.17-28.8 
91 1.5 0.32-28.0 
82 
V 0.2 0.1-2.0 100 0.5 0.1-6.0 92 
VI 0.4 0.25-12.0 
83 0.8 0.3-7.0 83 
Control A 
0.03 0.01-0.19 
100 178.0 35.0-588.0 
0 
Control B 
0.1 0.09-0.22 
100 0.35 0.17-3.8 
83 
______________________________________ 
Small Skips Event 
(events per 60 min. Playback Time) 
Initial Play 1st Play After Stress 
Example Median Range % Pass 
Median 
Range % Pass 
______________________________________ 
I 6 0-41 75 19 2-120 70 
II 10 2-134 75 12 0-132 75 
III 6 2-92 75 6 0-162 80 
IV 4 2-72 85 6 0-120 90 
V 7 0-110 85 9 0-80 85 
VI 5 0-95 90 8 0-73 80 
Control A 
7 0-145 83 32 3-168 50 
Control B 
7 0-54 75 18 0-110 66 
______________________________________ 
From a review of the above Examples and Table, it can be readily seen that 
this invention provides not only a savings in materials (fewer number of 
components in the molding composition and no need to use a dopant in the 
lubricant), but also a savings in the disc processing (no need for 
treatment or processing of as-pressed discs, such as washing or cleaning, 
rinsing, and drying) as well, over prior art compositions and processing.