Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-08-26
2004-04-27
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
Reexamination Certificate
active
06726807
ABSTRACT:
TECHNICAL FIELD
This invention relates to the manufacturing of novel calcium silicate hydrate (“CSH”) crystalline structures, and to pigment products, and novel to paper products produced therewith.
BACKGROUND
The paper industry currently utilizes many different types of fillers as a substitute for pulp fiber, as well as to provide desired functional and end-use properties to various paper and paper products. For example, clay has long been used as a filler or fiber substitute. Importantly, the use of clay also provides an improvement in print quality. However, one disadvantage of clay is that it is relatively low in brightness. And, the use of clay in papermaking leads to a decrease in tensile strength of the paper sheet, and to reductions in paper sheet caliper and stiffness.
Calcined clay was introduced to the paper industry in an effort to improve brightness and opacity in paper. However, one significant economic limitation of calcined clay is that it is relatively expensive. Also, physically, calcined claim is highly abrasive.
Titanium dioxide, TiO
2
, is another example of a filler commonly used in papermaking. Most commonly, titanium dioxide is used to improve opacity of the paper sheet, and, in some cases, it is used to improve sheet brightness as well. Use of titanium dioxide is limited, though, because it is extremely expensive. Unfortunately, it is also the most abrasive pigment on the market today. This is important because highly abrasive pigments are detrimental in the paper industry since they wear down critical paper machine components, such as forming wires, printing press plates, and the like, ultimately leading to high life cycle costs due to the constant repair and maintenance costs.
When calcined clay was first introduced, it was touted as a titanium dioxide extender. Although it did succeed in extending TiO
2
, it is nonetheless abrasive, and it is more expensive than either standard clay or market pulp fiber.
More recently, and particularly since the mid 1980's, ground calcium carbonate(GCC) has been used as a low cost alkaline filler. Although GCC improved sheet brightness, one downside to GCC was that it too is abrasive. Moreover, use of GCC reduces tensile strength, caliper and stiffness of paper sheets. Consequently, a paper sheet containing GCC tends to be rather limp.
Finally, one of the most commonly used alkaline paper fillers is precipitated calcium carbonate(PCC). PCC is presently one of the best compromise solutions for providing a high brightness filler at an economically feasible price. However, a significant downside to the use of PCC in paper sheets is that PCC provides a lower light scattering power than either TiO
2
or calcined clay. Also, it often reduces sheet strength and stiffness.
Thus, the paper industry still has an unmet need, and continues to look for, a multi-functional pigment that can simultaneously provide two or more of the following attributes:
a) cost that are less than TiO
2
;
b) better optical properties than calcined clay;
c) better optical properties than GCC;
d) better optical properties than PCC;
e) minimal tensile strength loss associated with increased filler usage;
f) at least some improved strength characteristics, such as sheet stiffness.
In addition to the just stated criteria, if a paper filler could also simultaneously improve sheet porosity (i.e., provide a more closed sheet) yet provide higher sheet caliper, it would be a very highly desired filler material. To date, no single paper filler with such attributes has been brought to the market. Consequently, the development and commercial availability of such a filler would be extremely desirable.
Finally, the current industry demand for printing papers, especially the rapidly increasing demand for ink jet paper, requires a high performance paper. The performance of such paper would be enhanced by the availability of a pigment that would provide excellent water and oil absorption capacities, so that the paper could quickly capture and prevent ink from spreading or bleeding, as well as aid in surface drying of the ink.
Some of the key requirements for an ideal papermaking pigment can be summarized as set forth in Tables 1, 2 and 3 below.
TABLE 1
Idealized Paper Filler Attributes
Filler
Sheet
Sheet
Scattering
Scattering
Attribute →
Opacity
Coefficient
Power
Brightness
Industry
HIGHER
HIGHER
HIGHER
EQUAL OR
Requirement →
than pulp
than pulp
than pulp
HIGHER
or
or
or
than pulp
carbonate
carbonate
carbonate
or
fillers
fillers
fillers
carbonate
fillers
TABLE 2
Key strength parameters for an “Ideal” pigment.
Sheet
Sheet
Attribute →
Caliper
Bulk
Porosity
Smoothness
Stiffness
Tensile
Industry
HIGHER
HIGHER
HIGHER
HIGHER
HIGHER
HIGHER
Requirement →
than
than
than
than pulp
than pulp
than pulp
pulp
pulp
pulp
sheet
sheet
sheet
sheet
sheet
sheet
alone or
alone or
alone or
alone
alone
alone
with
with
with
or with
or with
or with
CaCO
3
CaCO
3
CaCO
3
CaCO
3
CaCO
3
CaCO
3
fillers
fillers
fillers
fillers
fillers
fillers
TABLE 3
Key printing requirements for an “Ideal” pigment.
Sheet
Ink
Show
Print
Attribute →
Penetration
Through
Through
Industry
LOWER
LOWER
LOWER
Requirement →
than pulp
than pulp
than pulp
sheet
sheet
sheet
alone or
alone or
alone or
with
with
with
CaCO
3
CaCO
3
CaCO
3
filler
filler
filler
Currently, the papermaking industry uses various combinations of available fillers in order to optimize the properties as may be desired in a particular papermaking application. However, because currently available fillers reduce sheet strength to at least some extent, the industry relies on strength additives, such as starch and/or polymers, to maintain the desired paper strength properties when fillers are utilized. Unfortunately, because different pigments have different particle charge characteristics, additions of multiple pigments and additives in the paper making system often create an extremely complicated chemical system which may be somewhat sensitive and difficult to control.
In summary, there remains a significant and as yet unmet need for a high quality, cost effective filler which can be used to simultaneously achieve desired optical properties and sheet strength in paper products. Further, there remains a continuing, unmet need for a method to reliably produce such a pigment which has desirable optical properties and which provides significant cost benefits when compared to the use of titanium dioxide or other pigments currently utilized in the production of paper.
OBJECTS, ADVANTAGES AND NOVEL FEATURES
Accordingly, an important objective of my invention is to provide a process for the manufacture of unique calcium silicate hydrate (“CSH”) products, which provide crystalline structures with desired brightness, opacity, and other optical properties.
Another important and related objective is to provide an economical substitute for current paper fillers such as titanium dioxide.
A related and important objective is to provide a method for the production of novel paper products using my unique calcium silicate hydrate product.
An important objective is to provide a new calcium silicate hydrate product with low bulk density, good chemical stability (particularly in aqueous solutions), and a high adsorptive capability, among other properties.
These and other advantages, and novel features of my multi-phase calcium silicate hydrates, the method for their preparation, and the improved pigments and paper products produced therewith will become evident and more fully appreciated from full evaluation and consideration of the following detailed description, as well as the accompanying tables and drawing figures.
SUMMARY
I have now discovered the process conditions required to reliably produce unique calcium silicate hydrate products with particularly advantageous properties for use as a filler in papermaking. The products are produced by reacting, under hydrothermal conditions, a slurry of burned lime (quick lime) and a slurry of fluxed calcined diatomaceous earth (or other appropriate starting siliceous material). Preferably, a fine
Chin Peter
G.R. International, Inc. (A Washington Corporation)
Goodloe, Jr. R. Reams
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