Smart-Formulation-Journal-2012

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8 Liquid Silica Nanocomposites from Evonik – Scratch Resistance and Transparency for Coatings Systems Liquid silica nanocomposites from Evonik are used primarily where coatings are required to exhibit high scratch and abrasion resistance without sacrificing transparency. Also, these products should be easy to formulate. Furthermore, secondary properties such as barrier effect, reduced shrinkage during curing and improved adhesion on substrates with hydroxyl function can be achieved in various coatings systems without compromising the degree of gloss. The properties can only be achieved by conventional means by using several layers. Manufacture of silica nanocomposites Using a modified sol-gel process, it is possible to manufacture composites from silica nanoparticles and organic resins which, despite being 50 % w / w filled, are water white. Starting from water glass, spherical silica nanoparticles, approximately 20 nm in diameter and with a very narrow size distribution, can be cultured in an aqueous environment. These particles then have their surfaces modified to permit a stable transfer into their future organic matrix. The results are transparent products that do not exhibit any sedimentation. Improving properties with silica nanocomposites Silica nanocomposites should be regarded as an additive to the binder in a coating formulation. In addition to the main property of scratch and abrasion resistance while maintaining transparency, silica nanocomposites improve other properties of the coating. Thus, they reduce shrinkage during curing and improve barrier effects. The particles in the cured film are statistically distributed, i. e. the average distribution is identical at the surface, in the middle and at the bottom. Nanocomposite particle distribution This is quite different from surface active products such as waxes or silicone oils which are only effective at the coating / air interface and thus have only a temporary effect on scratch and abrasion resistance. Silica nanocomposites, in contrast, offer permanent protection as they are firmly bound in the cured film matrix. Because they are distributed throughout the whole film, the initial recommendation is 5 to 10 % w / w relative to the solids of a coating formulation. The liquid nanocomposites from Evonik also have the advantage that they only cause a slight increase in the viscosity of the coating formulation. This is achieved by customized surface modification of the nanoparticles. On substrates such as glass and aluminum, the glassy nanoparticles improve adhesion. This effect is utilized in, for example, printing on high quality glass bottles. Silica nanoparticles are also suitable for applications where a barrier effect is required, especially where excellent transparency is needed. The barrier effect in an organic coating is increased by the inorganic silica particles. Diffusion of oxygen or water vapor is thus significantly lower when compared to an unmodified clearcoat. The degree of gloss of the formulation is not affected by the silica nanoparticles. Unlike surface waxes, which are added as matting agents, the nanoparticles do not settle out on the surface but are, as already described, distributed statistically throughout the entire film. It is thus possible to obtain coatings with improved hardness, scratch and abrasion resistance without being restricted by considerations on the degree of gloss. Use of silica nanocomposites Incorporation of the liquid composites is easy. Like standard binders, the products are thoroughly stirred in together with the main binder at the start of the production process. Dispersing or bead milling is unnecessary. Moderately polar solvents such as xylene or toluene should not be used alone in formulations. These solvents are, however, generally very compatible when used in blends with popular solvents such as esters, ketones and alcohols. Certain additives can result in incompatibilities with silica nanocomposites. These manifest themselves in, for example, agglomeration, flocculation or increased viscosity of the coating formulation. To save laboratory time when developing coatings with silica nanocomposites, compatibility lists are available from us on request for the additives most commonly used with NANOCRYL®, NANOPOX® and NANOPOL®. These lists give recommendations for the compatibility of additives with the silica nanocomposites in terms of short- and long-term shelf-life. Silica nanocomposites for various coatings systems Optimized silica nanocomposites have been developed by Tego for the different curing mechanisms in coatings. NANOCRYL®, a range of silica nanocomposites in various commonly used UV-curable acrylate monomers, has Evonik been specially developed for radical-curing UV coatings. Product Overview NANOCRYL® Name NANOCRYL® C 130 NANOCRYL® C 140 NANOCRYL® C 145 NANOCRYL® C 150 NANOCRYL® C 153 NANOCRYL® C 155 NANOCRYL® C 165 Monomer SiO 2 -content[% w / w] Viscosity, 25 °C 50 275 mPa•s Hexanedioldiacrylate 50 175 mPa•s Trimethylolpropaneformalacrylate Tripropyleneglycoldiacrylate Trimethylolpropanetriacrylate Ethoxylated trimethylolpropanetriacrylate Propoxylated glycerinetriacrylate Alkoxylated pentaerythritoltetraacrylate 50 200 mPa•s 50 3.3 Pa•s 50 1.0 Pa•s 50 1.75 Pa•s 50 2.5 Pa•s Listing status of individual products available on request. NANOPOX® materials are manufactured from epoxide resins and suitable reactive diluents. Smart Formulating Journal | Issue 9 | April 2012
9 Product Overview NANOPOX I Product Overview NANOPOX II Product Overview NANOPOL Name NANOPOX® C 450 NANOPOX® C 460 SiO 2 - content [% w / w] Base resin EEW [g / equiv.] Viscosity 25 °C 40 DGEBA 295 60,000 mPa•s 40 DGEBA/ DGEBF 290 45,000 mPa•s Characterization aromatic aromatic, crystallizationfree Name NANOPOX® C 620 SiO 2 - content [% w / w] Base resin EEC Cycloaliphatic epoxy resin for cationic UV-curing EEW [g / equiv.] Listing status of individual products available on request. Viscosity 25 °C 40 4.0 Pa•s Name NANOPOL® C 764 NANOPOL® C 784 Solvent SiO 2 -content [% w / w] Viscosity 25 °C Methoxypropylacetate 50 < 50 mPa•s N-butylacetate 50 < 50 mPa•s Listing status of individual products available on request. Listing status of individual products available on request. These NANOPOX® products can be heat-cured anhydrously, room-temperature cured with amines, or force cured. The product NANOPOX® C 620 is suitable for cationic UV-curing. NANOPOL® is a solvent-based product which is universally applicable. It is equally suited for use in 1-pack stoving enamels and in 2-pack PUR or UV coatings. Contact Marco Heuer marco.heuer@evonik.com High Technology in the Store Cupboard DYNAPOL® Specialty Coating Resins for Exterior and Interior Protection of the Classic Food Can Saturated copolyesters have been used for many years as binders in the area of packaging. The reason is the “modular construction system” of polyester chemistry: By an appropriate choice of monomers and their quantitative assembly in the formulation of the polyester, the customer gets exactly the properties he wants. Evonik currently has about 35 monomers available for synthesis into customized polyesters. One outstanding feature here is the balance between flexibility and hardness that can be achieved by adjusting the formulation. In addition, the copolyesters are odorless and tasteless, and therefore suitable even for packaging with direct food contact. Frequent changes and new trends in the packaging market have resulted in polyesters, of all the available binders, increasingly coming into focus due to their excellent properties. Interest in, and demand for, polyesters in the packaging market has risen significantly. Under the DYNAPOL® brand name, Evonik markets copolyesters used as binders in flexible packaging (film primers, printing inks), coil coatings (facade elements, refrigerators), and can coatings (food cans, metal packaging). On the subject of cans, it is interesting that no less a personage than Napoleon announced a competition about 200 years ago to find a process for preserving food. The Evonik’s Coatings & Additives Business Unit ensures reliable protection against corrosion, wear, and scratching. Under the DYNAPOL® brand name it markets specialty coating resins that protect metal packaging both externally and internally. 1 2 winning entry, based on the idea of sealing food in airtight containers, came from a Parisian confectioner. The thin metal shell is now well established in many application areas, from the preservation of food and drink to the storage of chemical products. The can is tough, heat resistant, 100 percent recyclable, and to be found in every store cupboard. The biggest challenge in the area of can coating is the internal coating of food cans, particularly at the stage where pre-coated metal plate is shaped into can bodies. The coating must be flexible enough to withstand the shaping process without damage. A typical tin can contains several coating layers, up to three outside and one inside. The exterior layers protect the can from corrosion and the color printing of the advertising space from scratches. “In production, coatings are first applied on thin tinplate and stoved. The body and lid of the can are then stamped and formed from the coated metal sheet. The coating must be sufficiently flexible or it will crack and flake off. If it’s too flexible, on the other hand, it doesn’t offer enough hardness and protection,” says Rainer Spittka of Technical Service, Pre-Coated Metal. Evonik’s polyester resins, designed with just this balancing act in mind, offer both optimal protection and high flexibility. For food cans, the requirements on the exterior 3 4 5 Dynapol in Every Layer 1 Internal seam of the can: A special DYNAPOL® grade covers the weld seam of the can. 2 Interior coating of the can: This protective layer prevents acids in the food from attacking the metal, and metal particles from entering the food. 3 Stamping enamel: The clear white coating protects the metal against corrosion and serves as a primer for pin-sharp printing. 4 Printing can be in any desired color. 5 Overprint varnish protects the print during sterilization and later against abrasion and scratching. coating are particularly high; once filled, the cans face the next test of their durability: sterilization. To preserve the food, the packaging must be treated at 130 degrees Celsius and high pressure in the sterilization chamber. Only if the exterior coating has come through this step undamaged is the can ready for sale. And DYNAPOL® is useful inside the can as well, because most foods contain ingredients that attack tinplate, such as vinegar, lactic acid, oils, and salts. If the can contains sauerkraut or chilli, for example, it must also be protected from the inside. The inner coating layer prevents the acids in the food from attacking the metal, and metal particles from entering the food. The development, testing, and statutory approval of suitable coating systems for food contact applications takes several years. This sensitive field of application therefore uses mainly “classics” such as the high molecular weight DYNAPOL® L 912 and DYNAPOL® L 952 grades. However, relatively new products such as the medium molecular weight DYNAPOL® LH 815-05 and DYNAPOL® LH 318-02 grades have also been successfully launched on the market. Contact Rainer Spittka rainer.spittka@evonik.com Smart Formulating Journal | Issue 9 | April 2012
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Smart-Formulation-Journal-2012

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