What is Silicone?
“Silicone, also called polysiloxane, any of a diverse class of fluids, resins, or elastomers based on polymerized siloxanes, substances whose molecules consist of chains made of alternating silicon and oxygen atoms. Their chemical inertness, resistance to water and oxidation, and stability at both high and low temperatures have led to a wide range of commercial applications, from lubricating greases to electrical-wire insulation and biomedical implants (such as breast implants). The silicones differ from most industrial polymers in that the chains of linked atoms that make up the backbones of their molecules do not contain carbon, the characteristic element of organic compounds. This lack of carbon in the polymer backbones makes polysiloxanes into unusual “inorganic” polymers—though in most members of the class two organic groups, usually vinyl (CH2), methyl (CH3), or phenyl (C6H5), are attached to each silicon atom. A general formula for silicones is (R2SiO)x, where R can be any one of a variety of organic groups” (Britannica). Silicones, in the uncured state, range from liquid (water-like) to clay-like materials. Silicone consistencies can be reported in flow rates, viscosity, or plasticity measurements.
Problems with Silicone Painting
Release Agent Residue
Before casting (pouring) a silicone kit in a glove-mold, release agent is applied to the glove-mold. Release agent prevents the silicone that is being cat into the mold from sticking to the mold. When the kit has cured inside the mold, it is demolded (removed) from the mold. At this time, the kit has to undergo a cleaning process to remove the release agent, in order for the silicone paint to stick to the kit.
The softer the silicone the more problems can occur. When chemicals get added to soften the silicone, the weaker the silicone molecular bonds become.
Platinum-catalyzed silicone older than several weeks to a few months can cause adherence issues.
Chemical Nature of Silicone
Platinum catalyzed silicone is not naturally adhesive. The cured polymer chain ends that link to others don't bond well to fresh silicone, less so as it ages and cures. Platinum-cure silicone can be finicky: Some doll kits are easily cleaned with warm water and Dawn dish soap while other kits need acetone solvents followed by a warm Dawn dish soap wash.
Silicone has a shelf life (about 6 months). Try new material as soon as possible to check for any problems with shelf life or material properties.
Cure-Inhibition VERSUS Adherence-Problem
It is highly recommended that you have test strips of silicone that you are painting with. Drip some of the silicone you prepared onto your new bag of sponges and gloves (any disposable tools) that you are using to paint your silicone doll as part of your trouble shooting method.
Differentiating between Cure Inhibition and Adherence Problems
Causes of Cure Inhibition
1) contaminants on a model surface prevent the liquid silicone from properly curing (hardening). [Contamination]
2) Part A and Part B of the silicone paint base weren’t mixed correctly. The reaction mechanism was not properly achieved. [chemical Reactions)
Prevention of Cure Inhibition
1) use a scale to measure your Part A and B evenly
2) use clean tools and new disposable tools. Watch for the shelf life as indicated on your material containers and material data sheets.
3) avoid overloading your paint base with thinners and paint pigments
FIX Cure Inhibition
1) thoroughly remove the uncured paint form the doll kit; wash it off.
Rubber toys (old Barbies), adhesive glues (envelopes), art supplies (paints, erasers), balloons, rubber bands, automobile tires and floormats, bicycle handle bar grips, carpet backing, computer mouse pad, certain cosmetic sponges; elastic underwear, socks, clothing; electric cords, handles, raincoats, telephone receiver headrests, toothbrush handles with rubber strips, kitchen gloves, zippered plastic storage bags, water toys, thongs, ear plugs, swim goggles, band-aids, pacifier, diapers, shoes, teething toys, rubber pants, rubber cement, books (ink), crayons, stickers, masking tape, electronics, remote controls, phone chargers, ear buds, keyboards, blood pressure cuffs, respirators, razors (lubricating strips), hairbands, feminine products, hair dryers, toilet paper, scissor handles, yarn, ribbon/ lace, puzzles, dolls, flexible toys, toys with rubber wheels. Sweatshirts/ hoodies, hat bands, watches, bras, jeans, athletic shorts, rubberwood furniture (parawood/ Malaysian oak), faux Christmas trees and greenery, newspaper, lottery tickets, non-slip items, shower curtains, vacuums. Binoculars, upholstery, flashlights, cameras, mattresses, microfiber blankets, dog and cat toys, pet brushes, kitchen utensil handles, can openers, turkey basters, spatulas, drain plugs
(includes latex), oils, solvents, PVC, wood
Certain metals such as Lead, silver, tin, mercury
Causes of Adherence Problems
Adherence problems occur when the silicone on the kit is not bonding with the silicone paint base you are applying. The silicone will cure (harden) on your test strip but the paint layer will peel off. Something is between the 2 layers.
Contamination should be one of the first considerations. Any grease, oil or other impurity on the surface can potentially cause loss of adhesion. Oils from skin contact could be enough to cause a problem. Tools and work areas may have been improperly cleaned. Manufacturers sometimes change a production process that does not affect the component performance or tolerances but can unintentionally affect the bonding of that component. Controlling the cleaning process is the best method to ensure occurrence of this potential problem does not arise. (Design World)
Prevent Adherence Problems
by proper Surface preparation, which is essential for bond consistency. Ask your kit supplier/ sculptor/ vendor what preparations have been done prior to you receiving the kit. Our kits come ready to paint as each kit undergoes an extensive cleaning regiment. However, sometimes problem still occur. Contact us immediately if you experience problems.
prevent problems by checking each layer as you apply them.
FIX Adherence Problems by removing peeling layers carefully and give it a clean edge where peeling stops. Apply new layer after cleaning the problem spot thoroughly.
Some systems are very sensitive to minor changes in the mix ratio. Many materials are stoichiometrically balanced and an off-ratio mix may cause the material to cure erratically and/or not perform to its optimal capability. Use a scale to mix your silicone A and B.
Even some materials that are not as sensitive to the mix ratio may exhibit slightly different characteristics when the ratio is varied. Materials that do cure with an off-ratio mix may have slightly different finished hardness and tensile strength thus effecting the final performance. (Design World)
Fillers or other residues could settle. Ensuring a homogenous mix of each component prior to mixing (for two parts) is vital to achieve maximum properties.
Avoid the use of alcohol and other chemicals during the paint process as those can leave residue and prevent adherence. Using cleaners to prepare a kit is ok but should be washed off.
Diluting the Part A and B Silicone paint mix too drastically with a solvent (i.e. Novocs, or OSS, or pigments) can loosen the molecular bonds as well. SmoothOn says, when adding the solvent to Psycho Paint, add between 200%-400% NOVOCS™ solvent by weight; when adding it to Sil-Poxy, add between 300%-500% NOVOCS™ solvent by weight.
According to SmoothOn, materials should be stored and used in a warm environment (73° F / 23° C).
Products that help the silicone paint base to bond with the silicone kit
1) Inhibit X (Smoothon)
3) OSS (Odorless silicone solvent)
4) Platsil Gel