Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-07-29
2004-06-15
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S244000, C525S237000, C525S238000, C525S241000, C525S232000, C525S309000, C525S310000, C523S201000
Reexamination Certificate
active
06750297
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an artificial pigment, specifically to an artificial pigment with excellent dry pick resistance and to a method of preparing the same.
(b) Description of the Related Art
Conventional coated paper is manufactured by coating an inorganic pigment such as clay, calcium carbonate, aluminum hydroxide (Al(OH)
3
), titanium oxide (TiO
2
) on paper. In preparing coated paper, a natural binder such as casein or starch and an artificial binder such as styrene-butadiene latex, polyvinyl alcohol or acrylic latex are used as an adhesive. Also, many kinds of additives such as a dispersion agent, a thickener, or a water-resistance agent are used. However, the most important components in manufacturing coated paper are an inorganic pigment and a binder. In order to obtain balanced properties of coated paper, an appropriate inorganic pigment and a binder should be used.
The most commonly used inorganic pigments are clay and calcium carbonate. Clay having plate shape has merits of high paper gloss and printing gloss. Calcium carbonate has merits of fluidity, dry pick resistance, Ink set-off, brightness of paper, and opacity.
Besides the inorganic pigment, an artificial pigment can be used in order to obtain coated paper with high quality. Conventionally, a latex of styrene polymer or an acryl-styrene copolymer is used as an artificial pigment. The artificial pigment has very high glass transition temperature so that it can increase the paper gloss of coated paper, opacity and micro smoothness. However, since the artificial pigment has little dry pick resistance and high binder demand, if a sufficient amount of binder is not used, material properties such as dry pick resistance of coated paper and printing gloss can deteriorate.
Recently, in order to improve productivity and save drying energy, as high concentration of solid content of coating color proceeded, viscosity of a composition for paper coating increased. Because of this, fluidity of coated paper decreased and thus it brought a reduction of work-operation.
In addition, to increase the manufacturing speed of paper, there has been considerable research to improve productivity and to provide an increase in printed materials by increasing coating speed. When coating speed is increased, shear strength during coating also increases and thus high-shear fluidity becomes more important. A high-shear means a shear speed of more than one, one thousands of a second and a low-shear means a shear speed of less than one, one hundreds of a second. The low-shear viscosity affects the transfer of the coating color and the coating.
As mentioned above, there is a problem that low-shear/high-shear fluidity of the coating color is a previous requirement for a high concentration of coating color and an increase in coating speed. In order to solve the above problem, there are two solutions: one is replacing a natural soluble binder having a large thickening effect, such as starch or casein, with an artificial binder and the other is increasing the ratio of ground calcium carbonate with fine particles that has a lower viscosity in terms of a pigment. However, although calcium carbonate has many merits, it is unfavorable in terms of paper gloss, printing gloss and smoothness so that it is difficult to increase weight. Also fluidity problems can be solved by controlling particle size of a binder. As the particle size of a binder decreases, the high-shear viscosity is lowered. This principle is applicable to the artificial pigment. That is, fluidity can be controlled by changing the particle size of an artificial pigment used so that it is easier to cope with the high concentration and change of coating speed than that of using an inorganic pigment only.
In addition, the artificial pigment has a better water-retention property than an inorganic pigment. The water-retention property is a property of coating color to maintain moisture against exterior strength. When the water-retention property is low, the solid content of the coating color continuously increases during coating so that work-operation has problems and irregular binder distribution in the coating layer such as binder migration can occur. However, since an artificial pigment is conventionally more surface-hydrophilic than an inorganic pigment, the moisture-holding property is excellent and thus, the work-operation and the quality of coated paper can be improved.
Recently, due to an increase in printed materials, the tendency of using high-speed printing, particularly in offset printing is gradually increasing. Also, as a requirement of coating color, the importance of dry pick resistance and reduction of the binder content is continuously increasing. That is, the coated paper should resist strong mechanical strength against the surface of the coated paper of pigments in order not to incur picking from the coating layer and the falling off of pigment during printing. That is, the coated paper should have a clear printing appearance. Since the destruction of the paper surface is more severe as the printing speed is increased and content of binder is lowered, a pigment adhesive having excellent dry pick resistance is required in order to prevent the above problem.
In addition, the importance of ink set-off is increasing. Ink set-off is a property, which represents ink-drying speed after printing. In the case of multi-color printing, printing is usually done with four colors of blue, black, red, and yellow. As the ink set-off increases, the time period to print the next color can be short, thus it improves the productivity of the printing. If the ink is not well dried and goes to the next step, print mottle or a post-smear phenomenon can occur.
Gloss is an important factor to increase commercial value and quality of printing paper. Gloss is divided into paper gloss of coated paper and printing gloss after printing. As the value of both of these factors increases, the paper develops a good appearance. Conventionally, as the particle size of a binder used in the coating color is increased, the arrangement of the inorganic pigments is made easier, so that paper gloss increases. Also, as the glass transition temperature of the binder is increased, paper gloss increases. Another method increase paper gloss is to lower the content of the binder in the coating color. However, when the paper gloss is increased by only the above methods, the dry pick resistance is decreased.
Another method increase paper gloss is to use an artificial pigment. Although the conventional artificial pigment has a high glass transition temperature and can increase paper gloss, they have demerits of low dry pick resistance and printing gloss. In order to complement these demerits, there can be provided artificial pigment having dry pick resistance. But, such a pigment has a lower paper gloss than an artificial pigment having a high glass transition temperature, or it has a high paper gloss but insufficient dry pick resistance.
Meanwhile, in order to increase the printing gloss, the porosity should be lowered and thus, it is required to hold the solvent on the surface, until after printing, until stability is achieved. Thus small particle size of the binder, a low glass transition temperature and a high binder content of the coating color are desired. In this case, ink set-off should be lowered. Also, when an artificial pigment having high glass transition temperature is used, since porosity increases, printing gloss reduces.
In addition, wet-pick resistance is also an important printing property in offset printing. In the offset printing, damping water is used. If the wet-pick resistance decreases, pigments can be exfoliated by the application of a strong physical strength during printing.
Another printing property required in offset printing is wet ink receptivity. As described above, since damping water is used in the offset printing, if the coated paper does not effectively absorb water during printing, ink that does not have compatibility with wa
Cha Wan-Sik
Choi Ho-Yeul
Han Chang-Sun
Yeu Seung-Uk
Asinovsky Olga
Birch & Stewart Kolasch & Birch, LLP
LG Chem Ltd.
Seidleck James J.
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