Background of the Invention

The invention relates to a composition and method for repairing surfaces defects, including scratches or gouges, on a plastic object, particularly on a laser-readable object such as an audio compact disc or computer memory disc.

Laser-readable discs store information through a series of laser-induced pits in the surface of a plastic disc. The pits are "read" by a laser and converted to a signal which is processed by a signal processor into the music, video or text which was encoded by the pits. The disk on which the information is stored typically is coated with a translucent or transparent plastic layer. When this layer becomes scratched or gouged, the laser may no longer be able to read the information in the affected section, and the signal may be interrupted or distracted. Depending on the seriousness of the defect, the disc may no longer be usable.

It is an object of the present invention to provide a composition and method uniquely suited to repairing surface defects, such as scratches or gouges, in laser- readable plastic discs.

Summary of the Invention

The invention is a composition useful for repairing defects on the surface of a translucent plastic object and 5 a method for repairing a plastic object using the composition. Using the present composition and method, a scratch or gouge on the surface of the object is smoothed and filled in a single step. The composition and method are particularly useful for repairing surface scratches, 10 gouges or other defects on laser-readable objects, such as audio compact discs, video laser discs or computer memory discs.

The composition comprises a mixture of a wax having a

15. refractive index compatible with the refractive index of the plastic, an organic solvent, an emulsifier and an abrasive material. The abrasive material acts to smooth the edges of the scratch, gouge or other defect and the wax simultaneously fills the scratch, gouge or defect with

20 a material having approximately the same refractive index as the plastic. The organic solvent is present to dissolve or disperse the wax, and the emulsifier is present to keep the abrasive in suspension, thereby forming a uniform, easily applied material.

25

The method of the invention involves applying a composition containing a mixture of a wax, an organic solvent, an emulsifier and an abrasive material to a scratch, gouge or other defect in a plastic object such

30 that the edges of the defect are smoothed out and the defect is filled with the wax. As a result, a laser can pass over the defect without disruption in reading the information encoded on the disc.

Detailed Description of the Invention

A preferred aspect of the present invention provides a composition and method for repairing surface defects in laser-readable discs. The composition and method are designed to smooth the edges of the defect and fill it with a wax material having a refractive index compatible with the refractive index of the plastic material from which the disc is formed. Use of the present composition and method results in a smooth repair which does not distract the reading laser.

To accomplish this, the composition of the invention comprises a wax material selected to have a refractive index at room temperature (about 25°C) compatible with the refractive index of the plastic material which forms the disc; an organic solvent for dissolving or dispersing the wax; a mildly abrasive material for smoothing the edges of the defect; and an emulsifier for suspending the abrasive material in the composition. These ingredients are mixed together to form a liquid or paste which can be applied easily to the disc, for example, with a cloth or other applicator.

The wax can be any natural or synthetic wax which has a refractive index which is the same as or closely approximates the refractive index of the disc material. Most audio compact discs, computer memory discs (CD-ROM) and video laser discs are formed from polycarbonate; which has a refractive index at 25°C of about 1.586. Therefore, to repair a defect in a polycarbonate disc, a wax having a refractive index between 1.4 and 1.6 can be used. Waxes having a refractive index in this range include carnauba wax (1.455), polyethylene wax (1.51) or polypropylene wax (1.49), for example. A mixture of waxes also may be used.

Such waxes are readily available from a number of sources, for example, from Reed Wax, Reading, MA. The amount of wax in the formula should be sufficient to fill the scratch or defect, and which forms a stable mixture, i.e., does not separate from the formula upon standing.

Generally, an amount in the range of from about 10 to 15% by volume based on the total volume of the material is effective for this purpose.

Any organic solvent can be used provided it does not dissolve the disc material and is compatible with the wax used. Since the composition is designed to be applied by individuals, non-toxic solvents are preferred. Solvents which can be used for this purpose include, for example, mineral spirits, or non-toxic alcohols, such as ethanol or isopropanol. Such solvents are readily available from a number of sources, for example from Exxon Corporation. The amount of solvent in the formula should be sufficient to dissolve or disperse the wax, and form a stable paste or liquid. Generally, an amount of solvent in the range of form about 30% to about 60% by volume is effective for this purpose.

The emulsifier can be any surface active material which aids in forming a stable emulsion or suspension of the abrasive particles in the formula. Fatty acid salts, such as calcium stearate or calcium oleate, are particularly useful for this purpose. Such surface active agents are readily available from a number of sources, for example, from Witco Corporation. The amount of emulsifier should be sufficient to form a stable emulsion, dispersion or suspension. Generally, an amount of emulsifier in the range of from about 1% to about 10% by volume is effective for this purpose.

The abrasive material can be any abrasive compound which can polish the plastic surface without damaging it. Abrasive typically used in the glass polishing art, especially those used for polishing plastic lenses are particularly useful for this purpose. The abrasive particles preferably are less than 2 microns in diameter, and are round in shape. Platelet shaped particles can be used, but are less desirable. The amount of abrasive material used in the formula depends upon the type and morphology of the abrasive particles. For example, if the abrasive consists of large (e.g., 1-2 microns or greater) particles and/or platelet shaped particles, then less abrasive should be used. If the abrasive material consists of fine (e.g., less than 1 micron) particles and/or round particles, then more should be used. A preferred abrasive material is aluminum oxide particles having a particle size of about 0.75 microns and a round shape. Such particles are commercially available, for example, from Micro Abrasives Corporation. Generally, the amount of abrasive material in the formula preferably is in the range of from about 10% to about 50% by volume.

The composition of the invention is prepared by combining the wax, solvent, emulsifier and abrasive material to form a paste or liquid. The ingredients can be mixed in any order. A preferred method of making the composition involves melting the wax, and blending solvent and emulsifier while gently heating, then blending the melted wax and solvent mixture with agitation to form a smooth paste or liquid. The blend is allowed to cool, then is mixed with the abrasive material until a uniform dispersion is obtained.

A currently preferred formula for carrying out the present invention to repair polycarbonate discs comprises the following Formula I.

FORMULA I

Amount By Volume Ingredient

11.00% Carnauba wax (yellow flake #1,

Reed Wax) 33.50% mineral spirits (Coastal Pale Oil

105, Exxon Corp.)

5.50% calcium stearate (Witco

Corporation)

50.00% 0.757 Al~0, round particles

(Microgrft"*PXA 411, Micro

Abrasives Corp. )

100.00%

The formula was made according to the following procedure: the wax, mineral spirits and emulsifier are blended while gently heating to form a smooth paste; the paste was allowed to cool and was blended with the abrasive particles to form a uniform dispersion.

In another aspect, the present invention comprises a method of using the composition to repair defects or scratches in plastic objects. The method involves applying the composition to the surface to be treated and gently rubbing with a soft cloth or other applicator until the defect is smoothed and filled. The abrasive material polishes and ooths the edges of the defect forming a "beveled" edge, while the wax material fills the defect. The surface then is smoothed over and any excess material carefully removed. Alternatively, the composition first may be applied to a cloth or other applicator, and then applied to the surface to be treated.

The following example describing the repair of laser- readable audio compact discs using the composition proves

the efficacy of the composition and method. Several audio compact discs were provided which had been scratched with a sharp object to produce scratches and gouges on the surface thereof sufficient to cause skipping or interruption of the recording. Each disc was played on a compact disc player to confirm that the defect caused skipping or interruption of the sound. The scratches were examined under a stereoscopic microscope to visually note their severity. Each disc then was treated by applying a small amount of the composition of Formula I to the scratched area, and rubbing gently with a soft cloth. The progress of the repair was observed under a stereoscopic microscope. The disc was considered "repaired" when the edges of the scratch were beveled or rounded and the scratch itself filled in with the composition, which was verified visually under the microscope. Each disc was replayed on the same compact disc player. As a result of the treatment, each disc played without skipping or interruption in the repaired area.

Equivalents

One skilled in the art will be able to ascertain many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed within the scope of the following claims.