While the name of the vinyl record seems to be a dead giveaway as to its composition, underneath it is a complex mixture of a significant number of additives. Each additive contributes a particular physical aspect to the performance of the vinyl album in order to provide optimal pressing and playback.
Composition of Vinyl Records – reposted with permission fromvinyltoplastic.com
The thermoplastic resin that is used to produce vinyl albums (and singles) comprises mostly of the copolymers of vinyl chloride (PVC) and vinyl acetate (PVA) in an approximate ratio of two parts PVA copolymer to one part PVC monopolymer. This mixture makes up between 75%-96% of the weight of the album, with the remaining 4%-25% being the additives, most of which are all critical to the pressing and playback process and the album’s longevity.
PVC is an ideal base material being flexible and 10-20% crystalline making it quite strong. It is low cost, not too brittle, supports a smooth and, therefore, quiet playback surface, can be pressed into the microgrooves, and allows a stylus to ride within the grooves with minimal damage. However, PVC and PVA alone do not create an ideal material for pressing and playback. That is where all the additives come into play.
These additives include:
- Heat stabilizers
The above additives are not chemically bonded to the PVC/PVA mix but are simply incorporated within it. The whole vinyl resin production process maybe summarized in the following simplified diagram.
The final percentage and selection of the various additives is generally a closely held secret of each pressing manufacturer as it affects both the cost and performance of their finished product. I am also sure that other additives not listed above are incorporated into the resin mix, particularly into audiophile formulations like the SuperVinyl of Mobile Fidelity or the JVC Super Vinyl of yesteryear.
Vinyl Resin Additive Percentages
The percentages of each additive can vary quite widely, with fillers, if used, generally taking up the largest percentage.
These additives are essential for the pressing of a vinyl album, and without them, it would not be possible. PVC has low thermal stability and at temperatures above about 70C, will break down due to the Hydrogen Chloride (HCL) gas that is given off during the higher temperature production processes of typically 155C for extrusion and 120C for molding presses. These stabilizers not only help protect the press stampers from staining and etching by scavenging the HCL gas, but they can also act as stamper-releasing agents and protect the vinyl against UV and general pollution over time.
Stabilizers typically make up between 0.5-1.5% of the resin mix by weight. They are often a combination of a number of metal salts of fatty acids or similar organometallic compounds, often referred to as ‘metallic soaps’. The metals include; lead, tin, barium, and cadmium, and the fatty acids include; lauric or stearic acid. Other co-stabilizers like organophosphate esters and phenolic antioxidants may also be added to improve overall chemical stability, reduce the use of heavy metals and further enhance UV protection.
It should be noted that the organometallic compounds are similar in nature to the soap scum in showers and bathtubs. So take care when cleaning vinyl with anything acidic. This is a good reason for using acid-free record sleeves.
Lubricants are added to the resin mix to improve the flow of the resin during processing and aid in the release from the stampers. These lubricants are sometimes referred to as ‘mold-release agents. They are typically hard natural waxes like Carnauba or Montan or synthetic waxes like Stearamide or distearyl amide. This lubricant also aids in reducing friction, heating, and wear at the contact points of the stylus and hence helps to reduce surface noise.
Excessive cleaning and the use of strong solvents on the surface of the vinyl is therefore not recommended.
To reduce the cost of expensive virgin polymer and reduce waste vinyl pressing materials, some manufacturers add a filler to the resin to bulk it out up to about 20%. These include various cellulose-derived products and even diatomaceous earth, with the most common being recycled vinyl. It is not unknown that some albums are to be pressed on 100% recycled vinyl! In some instances, these fillers are used to add wear resistance but generally, their addition results in an increase in background noise. Recycled vinyl can be the worst offender as any contaminants that it contains cannot be removed when the album is cleaned, being in the vinyl’s matrix. Buying 100% virgin vinyl albums is obviously the way to go.
While the PVC-PVA mix supports good flexible properties, the addition of plasticizers improves the viscosity and melting properties of the resin mix. This in turn, improves the moldability and flexibility of the vinyl, helping it to flow into the microgrooves in the stamper discs and making the final disc more durable by improving its flexibility. These additives could include; phthalate esters epoxidized soybean oil or even toluene.
Care should be exercised when cleaning vinyl records with solvents such as alcohol, as they can dissolve these plasticizers, especially at higher concentrations of 60% and more.
Some pressing houses include conditioners in their vinyl resin mix to aid with; surface lubrication resulting in lower stylus friction and noise, static control, and even adding resistance to microbial contamination. Typical chemicals would be quaternary ammonium salts with long fatty-acid derived chains, sometimes referred to as quats or surfactants like; alkyl dimethyl benzyl ammonium chloride, alkyl didecyl dimethyl ammonium chloride, and dialkyl dimethyl ammonium chloride.
When cleaning your album, these properties can be neutralized by household soaps and detergents (also known as anions). The good news is that some record cleaning solutions include quats in their mix, and they may also be found in some ‘anti-static’ record sleeve material.
The PVC/PVA resin mix is clear/milky-white in its natural state. However, it is usual to add a colorant to observe surface defects and scratches. Carbon black was and still is the most common additive being about 0.25-0.5% by weight. It has the additional advantage of distributing electrical static charge and is not soluble in water, so cleaning fluids cannot easily remove it from the vinyl’s surface. These days carbon black is often replaced with a solid color titanium dioxide colorant or pigments. Some of these colors are not without a downside as they can cause an increase in surface noise. Even carbon additives can contain various “unfriendly” trace (metal) elements that can give rise to additional surface noise. That is why some audiophile and UHQR pressings now use carbonless dyes like those used in MoFi SuperVinyl or press on clear vinyl like the Clarity Vinyl from Classic Records (now owned by Acoustic Sounds).