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Silicone resin coating compositions

IP.com Disclosure Number: IPCOM000248571D
Publication Date: 2016-Dec-20
Document File: 5 page(s) / 285K

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Abstract

Heat resistant liquid coating compositions comprising a phenyl methyl silicone resin as binder are described. The silicone resin was used as a 70 w% solution in 1-methoxy-2-propylacetate. Several compounds were screened as a curing catalyst. N-(3-(Trimethoxysilyl)propyl)ethylenediamine was found to be the most effective catalyst with acceptable pot life. Full resistance to solvents was already developed after 20min at 180°C. The coatings withstood exposure to 500°C without any visible damage. Furthermore, the silicone resin was blended with various organic resins. Especially acrylic resins and short-oil alkyds showed good compatibility.

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Silicone resins, their preparation and their use as binder for coatings

Silicone resins can be prepared as described in the literature 1. They are commercially available as solid

flake resins or solvent solutions. Typical solvents are aromatic solvents like toluene,

xylene/ethylbenzene which are used in the production process, too. Solutions in other solvents can be

prepared by completely removing the aromatic solvents (e. g. in a thin film evaporator) and re-dissolving

the remaining silicone resin in another solvent like n-butylacetate, 1-methoxy-2-propylacetate or similar

acetates.

A silicone resin was prepared by typical silane condensation reactions in toluene as described in the

literature. Afterwards the toluene was removed by evaporation under reduced pressure and the neat

resin was dissolved in 1-methoxy-2-propylacetate. A 70 weight% silicone resin solution A in 1-methoxy-

2-propylacetate was obtained. The viscosity of the solution was between 300 and 600 mm2/s. Further

structural analysis by 29Si-NMR revealed the average composition to be app. 6 mol% Me2SiO2/2, 42 mol%

MeSiO3/2, 52 mol% PhSiO3/2. The calculated Ph/Me-ratio was 0.96. The remaining valencies were

determined by 1H-NMR to be SiOH and SiOEt. Accurate determination was not possible due to

interference of resonances, but estimated SiOH and SiOEt were around 3 w%. Molecular weight of the

resin was determined by SEC in THF vs. Polystyrene as standard: Mw = 3700 g/mol, Mn = 1500 g/mol.

This silicone resin solution A was examined as a binder for coatings. As catalysts

- Titanium-containing compounds like titanium-tetra-n-butoxide or Titanium-bis acetylacetonato

dipropoxide

- Zinc-containing compounds like zinc-di-2-ethylhexanoate

- Nitrogen-containing non-silicone compounds like 1,1,3,3-tetramethylguanidine or 1,8-

Diazabicyclo[5.4.0]-7-undecen (DBU)

- Acids like p-toluene sulfonic acid, acid di-butylphosphate and the like

were screened, too.

Tin-containing compounds like dibutyl tin diacetate might work as well, but were excluded due to their

toxicological profile.

When applied with a thin film applicator/doctor blade (100 µm wet) on a steel panel the following

values were obtained (see table 1).

1 B. Pachaly, F. Achenbach, C. Herzig, K. Mautner, Silicone, S. 1183ff, Sonderdruck aus Winnacker/Küchler,

Chemische Technik: Prozesse und Produkte, Band 5: Organische Zwischenverbindungen, Polymere

Catalyst (1 % level)

None Tetra-n-butoxy titanium

Bis(ethylaceto- acetato)diiso- butoxy-titanium

1,1,3,3- tetramethyl- guanidine

1,8-Diaza- bicyclo[5.4.0]-7- undecen (DBU)

N-(3- (Trimethoxysilyl) propyl)ethylene- diamine

acid mixture of mono and di- butylphosphate

Dry-to-touch time

> 6h, but < 24h Rapid reaction/gelling

2h Rapid reaction/gelling

Rapid reaction/gelling

2h 2h

Pencil hardness (24h@ambien t temp)

< 6B nd nd nd nd 3B nd

Pencil hardness (7d@ambient temp)

5B nd nd nd nd B nd

Film appearance after curing 20min/180°C

ok na Some cracks na na ok Some cracks

Pencil Hardness (after cur...