High density information disc

High density information discs comprising a conductive carbon loaded polyvinylchloride disc is lubricated with a fractionated methyl alkyl siloxane lubricant which contains a quinuclidene additive.

This invention relates to an improved high density information disc 
lubricant. More particularly, this invention relates to an improved high 
density information disc lubricant containing a quinuclidene additive. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 3,833,408 to Matthies, herein incorporated by reference, 
describes the application of methyl alkyl siloxane compositions as 
lubricants for conductive information discs comprising a molded plastic 
disc having audio and video signal information in the form of geometric 
variations in a spiral groove. These discs are coated first with a 
conductive material which acts as a first electrode of a capacitor, then 
with a dielectric layer and a final layer of lubricant. A metallized 
stylus acts as a second electrode of the capacitor. The information 
signals are monitored by the stylus which notes changes in capacitance 
between the stylus and the disc surface as the information signals, in the 
form of a surface relief pattern, pass beneath the stylus. 
Further developments in this system have produced a disc which is made of a 
conductive plastic material, e.g., a polyvinylchloride homopolymer or 
copolymer resin containing sufficient amounts of conductive carbon 
particles so that the disc can provide capacitance readout. The plastic 
resin at the surface of the disc surrounds the carbon particles to produce 
a dielectric surface layer. This development has eliminated the need for 
separate coatings of metal and a dielectric layer on the surface of the 
disc. 
The stylus, formerly made of metallized sapphire, has also been improved so 
that metallized diamond can be used. Diamond is a harder, longer wearing 
material than sapphire but also requires improved lubrication of the disc 
surface. 
High density information discs are also being developed which do not 
require a conductive surface or a grooved surface, the stylus being 
maintained in synchronization with the information pattern track by means 
of electrical signals rather than by the groove walls. 
These changes in the materials used for the high density information discs 
and the stylus have changed the requirements for the lubricant system and 
improved lubricants were required. Wang et al, in copending application 
Ser. No. 065,065 filed Aug. 9, 1979, which is a continuation of Ser. No. 
937,819 filed Aug. 29, 1978, now U.S. Pat. No. 4,275,101, have described 
an improved lubricant system which comprises a fractionated, purified 
methyl alkyl siloxane of the formula 
##STR1## 
wherein R.sub.1 and R.sub.2 are alkyl groups of 4-20 carbon atoms, x is an 
integer of 2-4 and y is an integer of 0-2 and wherein the sum of x and y 
is 4 or less. These lubricants have improved long term stability and 
resistance to temperature and relative humidity changes in the atmosphere. 
High density information discs of the above type are subject to a 
phenomenon called carrier distress. Since the polyvinylchloride 
composition from which the discs are made is a heavily filled, heavily 
lubricated and heavily plasticized composition, degradation products that 
are produced during molding and on storage from reactions of the disc 
materials and excess, incompatible additives, bleed to the surface of the 
disc, forming a thin layer of organic and inorganic materials. This layer 
interferes with playback by collecting in the grooves and by building up 
on the stylus. The result can be locked grooves, or dropouts of 
information as the disc is played. This problem has been somewhat 
alleviated by cleaning the discs after molding and prior to lubrication 
with aqueous solutions which remove at least some of the surface layer. 
However, with time, additional materials bleed to the surface of the disc. 
This bleedout can be accelerated by exposure of the disc to high 
temperatures, on the order of about 100.degree. F., and high relative 
humidity, e.q., 90 percent and above. Lubrication of the disc has 
heretofore had little or no effect on reducing carrier distress. However, 
it would be highly desirable to be able to reduce carrier distress by 
means of a permanent layer on the disc surface. 
SUMMARY OF THE INVENTION 
We have found that when methyl alkyl siloxane lubricants are doped with 
compatible quinuclidene additives, the carrier distress of high density 
information discs, after exposure of the discs to high temperature and 
high relative humidity, is considerably reduced. 
DETAILED DESCRIPTION OF THE INVENTION 
The quinuclidenes useful in the present invention have the formula 
##STR2## 
wherein R at each occurrence is an electron donating group in the position 
.beta. with respect to the nitrogen atom. Suitable electron donating 
groups include, for example, H, alkyl groups of 1-5 carbon atoms, 
Si(CH.sub.3).sub.3, halogen and the like. 
The above quinuclidenes, when added in small amounts to a methyl alkyl 
siloxane lubricant as described hereinabove, improve the stability of high 
density information discs, particularly after exposure of the disc to high 
temperature and high relative humidity. The exact reason for this 
improvement is unknown at the present time. 
The amount of a quinuclidene added to the lubricant is not critical and the 
minimum amount that will be effective to reduce carrier distress is 
preferred. At the present time amounts of from about 5 to about 20 percent 
by weight of the methyl alkyl siloxane lubricant has been found to be 
satisfactory. 
The quinuclidene additive described above is soluble in the methyl alkyl 
siloxane lubricant. The two materials can be mixed together and applied in 
conventional manner, as by spraying from a solvent, e.g., heptane, in 
which the methyl alkyl siloxane lubricant is soluble. The solvent is then 
evaporated, leaving a film about 200-400 angstroms thick on the surface of 
the disc. The two materials can also be applied to the disc surface 
separately but this is less desirable since it requires a separate step. 
The present lubricant system, once applied, is stable with respect to 
atmospheric effects and provides high uniformity and reproducibility for 
high density information discs. In addition, this system provides 
excellent lubricity.

The invention will be further illustrated by the following Example but the 
invention is not to be limited to the details described therein. In the 
Example, percent is by weight unless otherwise noted. 
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. The present acceptable level 
of carrier distress for a video disc is 3 seconds in one hour of playback 
time. 
EXAMPLE 1 
A molding composition was prepared by mixing 78 parts of Geon 110.times.346 
polyvinylchloride of the B. F. Goodrich Company; 13 parts of Ketjenblack 
EC carbon black of the Armak Company; 1.5 parts of 
dibutyltin-.beta.-mercaptopropionate commercially available as T35 from M 
& T Chemical Company, Inc.; 1.0 part of Mark 275 Stabilizer of Argus 
Chemical Co., a dibutyltin maleate stabilizer; 2.0 parts of Acryloid K-147 
and 0.75 part of Acryloid K-275, acrylic modifiers of Rohm & Haas Co.; 0.5 
part of Loxiol G-30 and 0.25 part of Loxiol G-70, lubricants of Henkel 
International GmbH; 1.0 part of calcium stearate and 3.0 parts of 
diundecyl phthalate. 
Video discs were compression molded from the above composition at about 
360.degree. F. (182.2.degree. C.). A first control group of six discs was 
lubricated in the standard manner by spraying with the fractionated methyl 
alkyl siloxane as in Formula (1) above as a 0.06 percent solution in 
heptane. 
A second group of 6 discs was lubricated with the fractionated methyl alkyl 
siloxane as in Formula (1) above containing 10 percent by weight of 
quinuclidene. 
The discs were played once, then stressed by storing for one hour in a 
chamber maintained at 100.degree. F. and 95 percent relative humidity and 
played again. The carrier distress was measured for each disc. The data, 
normalized to seconds of carrier distress for one hour of play, are 
summarized in Table I below. 
TABLE I 
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Carrier Distress, sec./hr. 
Initial Play 
After Stressing 
Group Range Median Range Median 
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Control 0.0 0.0 3.4-31.6 
15.4 
Example 0.0-0.4 0.0 0.2-6.4 
0.6 
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It is apparent the discs treated according to the invention performed 
better after stressing.