Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1997-11-06
2002-05-14
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000, C428S537500, C106S436000, C106S464000, C106S465000, C106S474000, C106S475000, C106S486000
Reexamination Certificate
active
06387500
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to dry mixtures, slurries, coating formulations, and coated paperboards and paper, and in particular, relates to the use of dark colorants such as carbon black, in dry mixtures, slurries, coating formulations, and coated paperboards and paper.
Paper is distinguished from board or paperboard primarily on basis weight (or grammage). The term “paper” is generally applied to sheets having basis weights of 20 to 170 g/m
2
while the term “board” or “paperboard” refers to basis weights of 130 to 450 g/m
2
. As there is some overlap in basis weights, a further distinction is based on stiffness and end uses. At equivalent basis weights, a board will be stiffer and more rigid than paper. Board or paperboard is typically used for packaging applications. Paperboards are generally formed from both bleached and unbleached pulp as well as recycled fiber. Examples include unbleached kraft and recycled board. Generally, coated paperboard is used in printed packaging applications. The primary objective in coating paperboard is to improve the appearance and smoothness of the surface before printing. When paperboard surface brightness is low and/or has a mottled appearance and a good quality print is desired, mills may apply two or more coatings to form a glossy surface suitable for printing. For example, coated recycled multi-ply boxboard usually consists of a “white” fiber top liner, a middle brown liner and a gray bottom liner. Depending on the finish used, the brightness of the top liner can range from 35 to 65% and is typically unsuitable for printing. Double or triple coatings can be employed to hide surface imperfections.
To obtain a suitable coated surface for printing, the pigments chosen must provide a cost effective means of achieving the required degree of opacity for even coverage (reduced mottle) at a specified brightness (usually in the range of 70 to 80%). In addition, the coating should preferably exhibit good ink receptivity and have acceptable physical properties. A wide variety of white or near white pigments are available for use in coating applications. These include various grades of clays, including structured and calcined clays, natural and synthetic calcium carbonate, precipitated silicas, aluminum trihydrate, plastic (polystyrene) pigments, and titanium dioxide. Pigments such as No. 2 and calcined clays are often used in the base coating to provide leveling. Although expensive, titanium dioxide, because of its excellent opacifying properties, is often used either in the top coat and/or in the base coat to achieve good coverage and high brightness. However, because of its high cost, mills often try to replace or extend the use of titanium dioxide with less expensive pigment alternatives. The coating weight applied depends on the tradeoffs between a variety of considerations such as cost, acceptable percent weight increase, available drying capacity, and surface physical properties.
Conventionally, the base coat is applied to the paperboard to achieve a dried coating weight in the range of about 4 to 30 g/m
2
and more typically in the range of 6 to 20 g/m
2
. Thereafter, the base coated paperboard is dried and then recoated with a top coat to achieve a dried top coating weight in the range of about 4 to 30 g/m
2
and more typically in the range of 6 to 20 g/m
2
. The purpose of the top coating is to provide a uniform surface of high brightness (as well as exhibiting good ink receptivity so that good print quality can be attained) and high gloss (as well as smoothness). Achieving these objectives is difficult when the top layer of the paperboard is composed of unbleached pulp or contains large amounts of recycled fiber so that the surface is either highly mottled and/or dark in color. In such cases, because of its excellent hiding power and high brightness, the coating may contain substantial amounts of costly titanium dioxide pigment. Typically, a mixture of pigments is used to attain the required degree of coated properties, such as opacity and brightness. These pigments are generally various grades of kaolin clays, including structured and calcined clays, natural and synthetic calcium carbonate, precipitated silicas, aluminum trihydrate, and titanium dioxide. Titanium dioxide generally represents from 0 to about 25% of the total weight of white pigments employed.
Accordingly, there is need to find ways to reduce the amount of expensive pigments like titanium dioxide present in a paperboard or paper coating without substantially altering the mottle and/or brightness of the coatings. Also, there is a need to reduce Mottle Index in a more cost effective manner.
SUMMARY OF THE INVENTION
A feature of the present invention is to provide a coating on a substrate which reduces the mottle on the substrate, without reducing the brightness unacceptably.
Another feature of the present invention is to provide a coated paperboard or paper having a coating which is present in an amount to reduce mottle on the paperboard or paper without reducing the brightness unacceptably.
Another feature of the present invention is to provide dry mixtures which can be formed into slurries and ultimately into coatings on substrates like paperboard and paper.
Another feature of the present invention is to provide a method to decrease the amount of white or near white pigment in a coating located on a substrate, like a paperboard or paper.
Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention.
To achieve these and other advantages, and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention relates to a multi-layered coating comprising at least a first layer and a second layer. The first layer contains at least one dark colorant, at least one white or near white pigment, and at least one binder. The second layer contains at least one white or near white pigment and at least one binder. The dark colorant is present in the coating in an amount sufficient to reduce mottle on a substrate, while retaining at least 50% of the brightness compared to the substrate having the same multi-layered coating but with no dark colorant present. The dark colorant is preferably non-structured.
The present invention also relates to a multi-layered coated paperboard or paper containing the same ingredients as in the coating described above.
The present invention, in addition, relates to a dry mixture containing at least one dark colorant, at least one white or near white pigment, and at least one binder. Again, the dark colorant, when the dry mixture is formed into a coating, is present in an amount sufficient to reduce mottle on a paper or paperboard to which it is applied, while retaining at least 50% of the brightness compared to the paperboard or paper coated with the same coating having no dark colorant present.
The present invention also relates to a multi-component system for forming a coating on a paperboard or paper. In this system, a first slurry and a second slurry are prepared. The first slurry contains a solution or suspension having at least one dark colorant and the second slurry contains a solution or suspension having at least one white or near white pigment. A binder can be present in the first and/or second slurry or can be present in a separate slurry. The slurries, once combined, can form a coating for a paperboard or paper. The amount of the dark colorant present, when formed into a coating, is an amount sufficient to reduce mottle on the paperboard or paper while retaining at least of the brightness compared to the paperboard or paper coated with the same coating having no dark colorant present.
The present invention further relates to a slurry containing at least an aqueous or non-aqueous solution, at least one dark colorant, at least one white or near white pigment, and at least one binder. The dark colora
Cabot Corporation
Thibodeau Paul
Zacharia Ramsey
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