Below is my understanding of the chemical makeup of vinyl phonographic records (excludes shellac, lacquer, and polystyrene discs). I’m sure it is incomplete as I am no expert, but I have read numerous papers and patents and spoken with people who were in the industry to gather the most information possible. Specificity is difficult as there were numerous resin recipes used over the years and most of them are proprietary. Much of what I present is from what was done at RCA (USA) and Victor (Japan). I would love to hear from others in the field so we can expand the knowledge base. My objective is to understand the composition since “what something is made of helps us decide how best to handle and preserve it”. Hence, I have included notes on possible conflicts with cleaning methods (mindful that this is a controversial topic).
Composition of Vinyl Records -
The thermoplastic resin used to produce vinyl (non-shellac) phonograph records consist mostly of copolymers of vinyl chloride (PVC) and vinyl acetate (PVA). The ratio typically used is 2 parts PVA copolymer to one part PVC monopolymer and the total vinyl polymer can be 75-96% of the record weight. The other 4%-25% are additives that are critical to the production, performance, and stability of the product. Most of these additives are not covalently bound; they are merely incorporated within the polymer matrix and therefore may be leeched out.
The additives include:
1. Heat stabilizers. Record production would not be possible without heat stabilizers whose main function is to neutralize the HCl gas generated at production temperatures. PVC has low thermal stability and degrades in a dehydrochlorination reaction at temperatures above 70 deg C (extruder temps are typically 155C and molding presses are typically at 120C). The reaction is autocatalytic: the released HCl catalyzes further breakdown. In addition to heat, UV and pollution exposure can initialize this reaction over time so it is important not to remove these stabilizers. In fact, it has been shown aging of records can be monitored by measuring the amount of effective stabilizer remaining in the disc (Pickett and Lemcoe, 1959). By scavenging the HCl gas released at pressing, the stabilizers also protect the press stampers from staining and etching, giving them a longer life.
The stabilizers are typically metal salts of fatty acids or similar organometallic compounds (often called “metallic soaps”). The metals are typically lead, tin, barium and/or cadmium and the fatty acids are typically lauric or stearic acid. They typically make up 0.5-1.5% of the resin mix and often, more than one type are added. Some of these compounds also act as releasing agents.
Organophosphite esters may be added as co-stabilizers as they reduce the amount of heavy metal compounds needed in the record. *1 Other stabilizers (e.g. phenolic antioxidants) that protect the polymer during its useful life (e.g. free radical scavengers, UV protection) are sometimes also included.
The organometallic compounds are essentially the components that form soap scum in bathtubs and showers. Hence, it is reasonable when cleaning vinyl records to avoid household cleaning agents (including formulations containing Vinegar) that remove soap scum. Acidic cleaners, in general, might best be avoided so as not to promote the dehydrochlorination reaction, reduce the amount of effective stabilizer, or otherwise reduce the useful life of the product. For the same reason, acid-free record sleeves are strongly advised.
It is customary to add a lubricant to the resin mix to promote the flow of the resin during processing. The lubricant is typically a hard wax, natural (e.g Carnauba or Montan wax) or a synthetic (e.g. distearyl amide type waxes). Fatty acid esters also served as lubricants (the cationic type doubled as “conditioners”). Lubricants typically comprise 1% or less of the resin mixture. The lubricant also promotes release from stamper. Some refer to these as “mold releasing agents”, but it should be noted that they are integrated into the resin mix, not something added to the stamper. Because the lubricant is evenly dispersed within the record, it also reduces friction at the finished record surface, for example, reducing heat and potential PVC breakdown as a stylus moves across. Hence, removal of lubricants is not desirable. Hard wax removal requires heat and/or strong solvents so these should be avoided (e.g. no steam cleaning). Additional friction at the record surface may result in audible noise: RCA found that too much or too little wax lubricant in their mix produced non-uniformity that resulted in noisy records.*2
It is customary to add a colorant so that the record surface is more easily observed (for defects, etc.). Carbon black is the most common as it also offers durability to the product and it is typically included at 0.25 -0.5%.*4 Carbon Black has the additional benefit of distributing electrical charges and increasing the rate at which such charges are dissipated (reducing static charge). Carbon Black is insoluble in water and most solvents so it is not something easily removed without destroying the record. Some resin recipes (transparent, colored records, and others *3) deliberately omit carbon black from the mix and may add another colorant, often titanium oxide (white base) and/or a desired pigment colorant.
Some resin producers added fillers, mostly to reduce the amount of expensive virgin polymer they had to include but also for added wear resistance. All kinds of fillers have been used over time, everything from cellulose-derived products to diatomaceous earth, some producing greater background noise than others. The most common modern filler is recylcled vinyl. Because this vinyl is used, any contaminants present get incorporated into the new vinyl product, often resulting in a noisy record. These contaminants are embedded within the vinyl matrix and are not easy to remove without damaging record. Therefore, it is often recommended to purchase 100% virgin vinyl records. Most of the other fillers in old records are inert and not easily removed or effected by most cleaning agents.
Plasticizers change the viscosity and melting properties of the resin mix, improving moldability and flexibility of the final product. They essentially decrease the attraction between polymer chains allowing for a flexible record that is more resistant to breakage. For the most part, the PVA –PVC copolymer in the resin provides these properties when mixed with the PVC monopolymer. However, additional plasticizer compounds have historically been included in resin mixes for increased flexibility and durability. RCA used epoxidized soybean oil (ESBO)*2 which has the added advantage in that it is also an HCl scavenger (stabilizer activity). Others have used traditional plasticizers, like phthalate esters. The amounts and types of included plasticizers vary greatly, depending on when and where the record was produced, but typically make up less than 1% of the mix (sometimes 0%). In the early 1970’s, there was a cost cutting move to make thinner, more flexible records and these included higher plasticizer levels; some even found toluene (up to 3%) allowed for thinner records *5. Most of the added (non-polymer) plasticizers are solvent soluble. Studies by preservationists on PVC artifacts has shown plasticizer extraction with solvents, including alcohol (at concentrations 60% and higher) *6. Hence, it is reasonable to keep alcohol (and other solvent) concentrations as low as possible in cleaning solutions.
6. Conditioner: A few producers included a conditioner in the mix to aid in lubrication and control static. The typical conditioners are quaternary ammonium salts with long fatty-acid derived chains (called quat. surfactants or “quats”)*2. Some quats have the added benefit that they have biocidal properties. Resin formulations that include them result in records that have lower surface friction, lower potential for static charge, and resistance to microbial contamination. These properties can be neutralized by anions, so it is useful to avoid common household dish soaps and detergents that typically include the anionic detergent SDS. The quats on the surface can be replenished (or added to records that don’t include them) by including them in cleaning solutions. Quats are also incorporated into many “ant-static” record sleeves.
Pickett, A.G. and Lemcoe M.M (1959) Preservation and Storage of Sound Recordings, Society of Amer. Archivists.
*1 Lead-stearate was once used, supporting the notion that records can contain lead.
*2 “Disc record and method of compounding disc record composition”, (1974) RCA Corp., US Patent # 3960790
*3 One modern producer (the maker of Quiex SV-P) deliberately excludes carbon black from their resin mix as they claim that “Carbon Black contains trace metals that become magnetized and cause electrical distortions in cartridges during playback that smears the sound.” This claim is controversial.
*4 “Conductive phonograph record containing thermoplastic resin and carbon black” 1961 Miller, H.B. US Patent #2997451
*5 “Phonograph record composition and process” (1974) Sands, A., US Patent #3846361
*6 Munoz C.M. et. al (2014) “A model for finding cleaning solutions for plasticized poly(vinyl chloride) surfaces of collections objects” J. Amer. Inst. of Conservation, 53 (4), pp. 236-251.