Natural zeolite pigment
papermaking and paper coating
استخدام الزيوليت فى صناعة الورق واحبار الطباعة
. Background Information
Pigments are used in papermaking and paper coating to improve the appearance, optical properties and printability of papers.
Commonly used pigments include kaolin clay, calcium carbonate, titanium dioxide, alumina trihydrate and polystyrene.
These pigments are useful in manufacture of conventional printing and writing papers and paperboards that are printed or imaged by common processes including offset lithography, gravure and xerography.
Ink jet printing technology has undergone several changes in addressing the demands of existing and future digital printing applications that require high quality printed images.
High quality ink jet printing typically occurs on coated paper; therefore, to produce such high quality printed images the coating composition and the ink formulation must be considered.
Jet inks typically contain 2.5% by weight of organic dyes. The dye is fixed to the paper surface either by evaporation of a base such as ammonia, by migration of a base such as diethanolamine into the paper, or by changes in ionic environment when the ink meets the coating material layer.
The paper must exhibit unique properties in order to produce a high quality printed image when the ink is fixed to the paper surface.
Once the ink drop is accepted by the paper, the ink must adhere to the paper and spread minimally in all directions to generate sharp edges for print contrast1 and image fidelity.
The paper must be smooth to give high print densities2. In addition, the paper should minimize bleeding3 and wicking while promoting the absorption of ink to set the dye onto the coated surface since this promotes higher print densities.
Ink jet droplets must be adsorbed quickly to avoid image smearing and multiple drop splatter.
Zeolites are crystalline, hydrated aluminosilicates of the alkali and alkaline earth metals.
More particularly, zeolites are framework silicates consisting of interlocking tetrahedrons of SiO4 and AlO4.
In order to constitute a zeolite the ratio of silicon and aluminum to oxygen must be ½.
The alumino-silicates structure is negatively charged and attracts the positive cations that reside within. When exposed to higher charged ions of a new element, zeolites will exchange the lower charged element contained within the zeolite for a higher charged element.
Unlike most other tectosilicates, zeolites have large vacant spaces or cages in their structures that allow space for large cations such as sodium, potassium, barium, and calcium and relatively large molecules and cationic molecules, such as water, ammonia, carbonate ions, and nitrate ions.
In most useful zeolites, the spaces are interconnected and form long wide channels of varying sizes depending on the mineral. These channels allow ease of movement of the resident ions and molecules into and out of the structure.
Zeolites are characterized by
1) a high degree of hydration,
2) low density and large void volume when dehydrated,
3) stability of the crystal structure of many zeolites when dehydrated,
4) uniform molecular sized channels in the dehydrated crystals,
5) ability to absorb gases and vapors,
6) catalytic properties,
7) cation exchange properties.
The use of natural zeolites in paper making has a long history, but has been almost unique to Japan where zeolite has been used as filler to improve bulkiness and printability.
Natural zeolites have also been used as fillers for paper in Hungary.
These natural zeolites however are a low brightness material and this renders it unsatisfactory for application in the United States on coated ink jet paper where high brightness is expected.
Numerous families of natural zeolites exist and each has varying characteristics. Unfortunately, natural zeolites exhibit nonuniform properties that makes them difficult to work with in many applications because ores from one location can vary with any other.
It is however possible to manufacture zeolites with uniform properties. The preferred zeolite for use in the present invention is a processed form of the natural mineral clinoptilolite which is a hydrated sodium potassium calcium aluminum silicate having the formula (Na, K, Ca)2-3Al3(Al,Si)2Si13)36—12H2O.
This zeolite is within the family Heulandite that also includes the mineral heulandite which is a hydrated sodium calcium aluminum silicate.
The physical characteristics of raw clinoptilolite are listed :-
- Color : colorless, white, pink, yellow, reddish and pale brown.
- Luster : vitreous to pearly on the most prominent pinacoid face and on
- Transparency: Crystals are transparent to translucent.
- Crystal System is monoclinic; 2/m.
- Crystal Habits include blocky or tabular crystals with good monoclinic
crystal form. More tabular and proportioned than heulandite. Also
commonly found in acicular (needle thin) crystal sprays.
- Cleavage: perfect in one direction parallel to the prominent pinacoid
- Fracture is uneven.
- Hardness : 3.5-4, maybe softer on cleavage surfaces.
- Specific Gravity : approximately 2.2
- Streak : white.
The coated and calendered unprinted paperboard samples were tested for brightness with the following results:
There was a gain in brightness from the control (0 parts zeolite pigment) with 5 and 10 parts of zeolite pigment, then the brightness dropped with higher levels of zeolite pigment.
This is encouraging for two reasons:
(1) there is an increase in brightness with the addition of small amounts of zeolite pigment
(2) this increase in brightness could allow for more intense calendering of the formulations with 5 and 10 parts zeolite pigment to increase gloss
A zeolite pigment that possesses the desirable combination of
particle size distribution,
internal void volume,
rheology and hardness
could also be useful in overcoming the limitations of conventional and other specialty pigments in various papermaking and paper coating applications including but not limited to:
(1) toner bond improvement in laser and other dry toner imaged digital papers;
(2) elimination of smudging and improvement of print quality in direct print flexography on coated linerboard used in corrugated containers;
(3) elimination of print through on newsprint and ultra light weight coated papers;
(4) improvement of dot fidelity and print quality on coated rotogravure printing papers;
(5) low abrasion extender for titanium dioxide pigments;
(6) improvement of coefficient of friction of paper and paperboard;
(7) production of technical specialty papers such as anti-tarnish, gas filtration, and absorbent papers with improved properties and lower cost of manufacture;
(8) more economical microparticulate retention system chemistry;
(9) additive to improve the efficiency of deinking systems.