Ontario Specialty Coatings Corporation

THE LEADER IN DIGITAL IMAGING COATING TECHNOLOGY

Silica:

Colloidal: A stable dispersion of non-porous, dense phase primary particles in water. Range in size from 10 nm to over 100 nm. Porosity arises from the packing of the primary particles atop and next to each other. Hydrophilic nature is due to the presence of silanol groups. Colloidal silicas can be chemically modified to have anionic or cationic charge.

Properties: 10% - 40% solids solution                     

                  pH: 3.5 - 9.0                   

Fumed: Produced by flame hydrolysis of silica tetrachloride or tetrafluoride. Small primary non-porous particles ranging in size from approximately 7 nm to 40 nm. Particles adhere through hydrogen bonding and form aggregates which in turn bond together to form micron sized agglomerates. Porosity is created by the packing of primary particles into secondary structures. The surface area of fumed silicas are considered to be totally external, thereby resulting in a very large specific surface area to mass ratio. The hydrophilic nature is due to the presence of silanol groups.

Properties: BET Surface Area: 50 - 380 gsm                     

                  pH: 3.5 - 4.5

Precipitated: The production process of precipitated silica is similar to fumed, although the primary silica particles are precipitated from solution. This process results in a material having a much lower bulk density (higher internal surface area). Hydrophilic nature due to silanol groups.

Properties: BET Surface Area: 50 - 650 gsm, (internal and external)

                  Agglomerate Size: 4 - 100 microns                     

                    pH: 5.5 - 7.0     

Silica-Gel: Small primary particles, approximately 25 angstroms in size, that are chemically welded together to provide a porous, three dimensional structure.

Properties: BET Surface Area: 200 - 800 gsm, (internal and external)

                   Particle Size: 2 - 3000 microns

                   Pore Diameter:25- 300 angstroms 

                   Pore Volume: 0.4 - 2.1 cc/g

Levels of Silica Products used in Ink Jet Coating Formulations

Colloidal Silica:

Clear Coatings: Usually comprises 100 parts of pigment component. Combined with photographic gelatins, polyvinyl alcohol, and polyvinylpyrrolidone.

Translucent and Opaque Coatings: 5 - 50 parts of pigment.

Fumed Silica: 5 - 25 parts of pigment component. Usually included to provide additional surface area in combination with precipitated silica and/or calcium carbonate. Usage is minimized due to cost.

Precipitated Silica: 20 - 80 parts of pigment component. Usually serves as the majority silica component in the coating due to cost, which usually lower than other silica types. Is usually combined with fumed silica and/or calcium carbonate.

Silica Gel: 5 - 80 parts of pigment component. Usually serves as a significant part of the pigment component. However, cost is high, and works well in combination with calcium carbonate.

Silica Suppliers:

Colloidal Silica:         Eka Chemicals

Fumed Silica:            Degussa Corporation

                                 Cabot Corporation

Precipitated Silica:   Degussa Corporation

Silica Gel:                 Grace Davison Corporation        

Precipitated Calcium Carbonate (PCC):

A new, specially designed, precipitated calcium carbonate pigment has been produced by Specialty Minerals Incorporated, Bethlehem, Pa., which has many of the desirable ink jet printing properties of dry silica pigments, but with few, if any, of the disadvantages. Specialty Minerals has been able to produce a PCC with a unique surface morphology and chemistry which enables the pigment to bind to the ink jet dyes with sufficient strength to maintain these dyes on the surface of the coating just like silica. Testing conducted by Ontario Specialty Coatings showed that JetCoat 30 based coatings provided excellent ink jet printability and are as good, or superior, to most commercial silica based premium ink jet coated papers.

JetCoat 30 has been designed for use in high quality, premium coated ink jet papers also produced on-line as part of the paper making process or on a separate, off-line paper coating machine.

Physical Properties:

Solids: 25%

Density: 9.6 wet lbs. per gallon

Charge: cationic

JetCoat 30 offers several important advantages over conventional silica pigments in ink jet coatings.

- Hercules high shear rheology is very low compared to silica. Coatings containing JetCoat 30 can be run on rod, blade, or air knife coaters, as well as on a metering size press. Runnability on roll coaters has not been fully tested, but the high shear rheology indicates that this pigment should run successfully.

- JetCoat 30 comes as a predispersed slurry which is easy to handle and combine with other ingredients. High shear mixing is recommended, but may not be necessary, depending on the exact composition of the coating formulation.

- The binder demand of JetCoat 30 is very low, which significantly reduces coating costs. Typical silica coatings require 25 - 30 parts of PVOH binder to inhibit dusting. Coating formulations using levels of PVOH as low as 3 parts have been designed and used. Typical binder loading for JetCoat 30 is 7 parts of PVOH. Ultimate binder demand will vary depending on the binder used and the composition of the coating.

- JetCoat 30 is much more cost effective than silicas. Depending on the type of silica, JetCoat 30 is about 35% to 80% less expensive.

- JetCoat 30 is compatible with most binders and additives currently used in ink jet coatings. However, it is always advisable to test the compatibility of ingredients in the laboratory prior to running larger scale coating trials.