GPW wrote:..I believe ( please correct me Fish) that the only big difference between Primer and paint is the colored pigment … basically …sorta’ ish ‘ ...
..sorta..kinda-ish..in an approximate sort of way..
All below is greatly simplified..so some my note some "yah, but's.." that arise from the simplification.
First..a diagram of a latex film formation
"Primer" and "Paint" are just words. Words that describe an enduse, but the enduse is what dictates what a product is made of...that..and what the intended market will pay. What the market will pay has the largest influence on product components and ultimate performance**. The house paint and primer market is notorious for demanding a hard "low-cost" approach..and yet they want ultimate performance(better, cheaper, faster..pick two). Price-performance is where suppliers & paint mfg's make their money. With the constraint of tight cost control, the development chemist (me..and those I worked with) are tasked with using a palette of lower-cost monomers and minimizing the use of moderately-priced monomers. Combine potential monomer mixes with an extensive palette of processing options and you get prototype products that might address the needs of any particular customer-end-use.
Example: A customer (Sherwin Williams***, Valspar, Behr..........) comes to us and says.. "We need a latex base**** that has superior adhesion to raw wood, pine pitch, light grease/dirt, and painted surfaces, it dries tack free, it has some flexibility under impact testing, topcoats well, and is compatible with & can support a very high loading of TiO2. Minimal moisture transmission is a definite plus that we'd pay a little more for."
****A "latex base" is typically a mixture of 2, 3, 4 unique latexes (latices) that yield a prototype "product". One latex, a unique-proprietary product-by-process made up of multiple monomers, may have great adhesion properties, but it too soft to offer a tack-free surface when applied and dry...and it's expensive. Another product-by-process (PBP) latex is hard, offering a tack-free surface when dry, and is cheap to make...often this is a latex with high styrene content. Yet another latex (made of multiple monomers) is known to have great compatibility properties with coatings applied on top of it. Mix the three latices together and you get a prototype that has good adhesion, is compatible with topcoats, and is cheap enough to meet the cost constraints implied by the customer.
An additional tool in the chemist's pocket is to build the latex having a core-shell morphology. As I mentioned above, a latex is a polymer billiard ball suspended in a water(aqueous) matrix. That polymer billiard ball started out as a monomer that was fed into a water solution and polymerized in that aqueous matrix. Let's say monomer A, that yields a soft-gummy surface when polymerized and laid down as a coating, is known to yield great adhesion, but is very expensive. Monomer B is a hard monomer..it yields a hard, tack-free surface when polymerized, and is cheap to purchase and process. If you mix monomer A & B and then feed it into the water/soap/resin/free radical polymerization initiator solution and polymerize it, you'll end up with a copolymer (co..two monomers mixed together in the same polymer chain) billiard ball suspended in an aqueous matrix. That copolymer ball will have a uniform composition of the two monomers. This process wastes the expensive momoner A as great adhesion to some surface isn't needed inside the ball..it's only needed at the point where the ball meets the surface it's applied to. Using this process, to get great adhesion you have to use more of monomer A, driving the cost up and the tack-free properties of the final film down. If you take a core-shell approach, your polymer billiard ball has a morphology like a candy M&M. You keep the monomers separate and feed the reactor/polymerize the hard monomer B first, then feed the soft-expensive monomer A into the reactor and polymerize it as a thin shell covering the hard polymer B ball. You now have a latex that can offer great adhesion and a tack free coating surface at minimal cost. Core-shell latices have different performance properties than just mixing a polymer A latex with a polymer B latex.
The advantage/disadvantage balance is brutal in chemical-polymer research. If you try to maximize one property in a product, it invariably decreases some other property you really need. In that vein..the above, "take a primer and add some stuff to get what you want" sounds good, but it isn't that simple...95% of the time.
**You want ultimate performance..look to products made for very special applications and customers with big pockets..the military & others. Ultimate performance is nearly always available..for an ultimate price.
***Some paint mfgs buy all their raw material latexes/additives on the open commodity/specialty market and then use them to formulate their own products. I worked at one of those suppliers..the best(and most expensive) one out there..so the industry customer surveys indicated for decades. A number of the paint manufacturers, like SW, are backward integrated and make their own base polymer latexes at less cost than buying them on the open market. SW and others would buy from us when they needed performance and they couldn't figure out how to make(reverse-engineer) what we made..and we'd charge them accordingly. Two different polymer manufacturers could make the same polymer formula and end up with one product that works as expected and one that fails miserably in use. The key is in intellectual property which yields a "product by process"...how you make it matters as much as what you make it out of.
OK..having said all that..what was the question:
"GPW":..I believe ( please correct me Fish) that the only big difference between Primer and paint is the colored pigment … basically …sorta’ ish'
In a simplified form:
1) An (aqueous) Primer is a mix of polymer latices + pigment for color (if any) + LOTS of opacifier (TiO2, talc..etc) all highly optimized for opacity, adhesion, stain-blocking, topcoat compatibility, tack-free film, latex stability....
2) An (aqueous) Paint is a mix of polymer latices + pigment for color + sufficient opacifier(TiO2, talc..etc) all highly optimized for opacity, adhesion, appearance, gloss level, stain resistance, washablility, UV resistance, water resistance, long-term performance, roller application performance, viscosity stability........................................................
3) An (aqueous) Varnish is a mix of polymer latices with no pigment, or opacifier highly optimized for adhesion, crystal-clear appearance, gloss level, UV resistance, water resistance, long-term performance, viscosity stability........................................................
4) An (aqueous) Semi-transparent Stain is a mix of polymer latices with pigment for color, no opacifier or a slight amount highly optimized for adhesion, semi-transparent appearance, gloss level, UV resistance, substrate permeability, water resistance, long-term performance, viscosity stability........................................................
5) An (aqueous) Opaque Stain is a mix of polymer latices with pigment for color, sufficient opacifier highly optimized for adhesion, opaque appearance, gloss level, UV resistance, substrate permeability, water resistance, long-term performance, viscosity stability........................................................
The base latices in all the above will be different, with different additives, different optimizations in formula and/or process, different ASTM tests...............
So
"GPW":..I believe ( please correct me Fish) that the only big difference between Primer and paint is the colored pigment … basically …sorta’ ish'
"Big difference"..yah..sort of, but under that thin generalization, no, not really. From a development and performance standpoint paints and primers are very different animals with very different requirements that require very different approaches.
FWIW..as a wild guess..The developing the old Glidden Gripper could easily keep a team of 4-6 scientists and engineers busy full time for a year or more to design and optimize. If it truly has changed or the original formula has been taken off the market, there has to be a compelling cost or regulatory reason. It may be that PPG moved the production to one of their own facilities, are using the old formula, and they don't know how to make it. Having experienced several company-sold events, the company that got bought often loses considerable IP talent. When you move a plant..the experienced, older folks don't move and that IP is lost. The new company may or may not follow the old reactor design, formulas, processes, or have access to the right raw materials, or know how to use them. The result is they screw up the value that they paid for in the purchase and spend years and millions$ trying to get back to normal, if they ever do. BTDT...hard to watch. Companies prefer not to value people..and that preference costs them dearly...but the execs all cash big checks with buying/selling divisions..so it's all good..I guess.