You are correct, Richard. Switching to styrene from vinyl for 7 inch production had NOTHING to do with quality improvement. It had EVERYTHING to do with cost. Styrene is actually a terrible material from which to make records. In its fairly pure form, styrene is very brittle which makes it easily broken as well as easily abraded. Try bending and marking the transparent lids of your CD jewel boxes to see how easily damaged styrene can be. There was only one supplier (Richardson) of the modified styrene material that US record makers used. They supplied the material in pelletized form, ready to be loaded into the extruders of the presses. Styrene flows like water when heated sufficiently, so it lends itself to injection molding. Vinyl never gets this liquid (without burning up) and it must be compression molded. The Richardson compound was highly modified to work (just barely) as a record material. Although improved somewhat, the innate problems of brittleness and easy abrasion remained. The compound was actually slightly more expensive than vinyl, but it could be used in completely automated injection presses which operated in a very much faster cycle than compression presses. Injection presses also don't need steam to operate, and they require only a small amount of cooling water. This netted out to a noticeable cost savings overall in the manufacturing process.
But styrene records NEVER molded quite correctly - every manufacturer was constantly fighting the problem of incomplete mold filling. Properly controlled, this wasn't usually an audible problem because the unmolded area was at the very top of the groove where the stylus didn't usually touch. But when the process got a little out of control, the unmolded area became larger than usual, the part of the groove touched by the stylus would be improperly formed, and this resulted in all kinds of distortion on playback.
Styrene is much smoother than vinyl in its surface microstructure, so a well-molded styrene record will sound absolutely silent on first play - NO surface noise. The problem is the abrasion of the stylus. Styrene has miserable wear properties compared with vinyl, and a SINGLE play with a 5-gram tracking force will cause visible abrasion and scoring of the groove walls. The only proper way to deal with a styrene record is record it to tape or digital storage the FIRST time you play it. Because it will get noisier with each successive playing.
Today, I try to shy away from buying 45s containing 1980s music because they are likely made of styrene. The wear problem was a HUGE bugaboo for jukebox operators and for radio station DJs (remember, there was no digital audio in the late 1970s - DJs actually played records). Record companies were getting inundated with field complaints about worn out 45s from these markets. The solution was to run parallel production of vinyl 45s for these markets only! How the hell this saved the record companies money, only a stupidly overpaid executive can figure out. Yes, for every new release of a single, TWO orders were put out - one for styrene commercial production and one for vinyl DJ and juke production. RCA no longer had any 7 inch vinyl production capacity, so we had to farm out those orders to small independent pressing plants.
So far as I know, only the USA manufacturers used styrene for 7 inch production. RCA Records was the last of the major US pressing plants to switch to styrene around 1983 (can't remember exactly). The other major factories had been using styrene for up to 5 years or so earlier. So many of the commercially sold 45s from the late 1970s on, and MOST of the 45s from 1983 onward in the USA were made of styrene. So if I want original pressings of circa 1980s music, I try to find either DJ copies or the 45s that were made in Canada - no styrene production up there, eh. Canadian eBay to the rescue.
You can easily tell a styrene 45 from a vinyl one. Styrene records have their outer edge molded rather than cut as with vinyl. Looking closely, you will see the mold parting line running just at the center of the molded edge of a styrene record. Vinyl was usually colored black with the inclusion of carbon black which makes the records opaque. There are some exceptions to this, especially in today's 45s which, interestingly, are ALL made of vinyl. Again. Styrene is always colored with a dye which makes the black records slightly translucent when you hold them up to bright light. Also, vinyl records have the paper label actually molded into the vinyl, just as is done with the LPs. Styrene records are molded without the label, then the label is either directly printed onto the record or a paper label is pasted on. You can feel the edge of a pasted-on label whereas a molded-in label has the edge buried down into the vinyl. A few euro pressing plants (notably Philips) experimented for a while with directly printed labels on vinyl, but these records also generally have the artwork also embossed in relief in the label area. Similar to the way the early Edison DDs were embossed - how's that for returning this topic to antique audio
) and have a limited edition pressed for the collector community. It might be a fun project.