Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2000-09-15
2003-02-11
Medley, Margaret (Department: 1714)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S447000, C524S588000, C524S837000, C524S858000
Reexamination Certificate
active
06517941
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating composition that is applied to the surface of a substrate to make coated paper.
2. Related Art
Paper is living necessaries, and has long been used for various purposes. In recent years, value-added coated or laminated paper excellent in various properties such as water resistance, glossiness, solvent resistance and heat resistance is extensively made by subjecting paper to a treating or finishing process, for example, a coating or laminating process, proper to the intended use of the paper.
Owing to an increase in the number of office automation apparatus such as computers, ink-jet printers have widely been spread. It is now very common to conduct color printing to produce photographic images or the like of good image quality. Recording paper for ink-jet printers is required to be excellent in not only such physical properties as glossiness and water resistance but also ink penetration. To make such recording paper more penetrate to aqueous inks for use in ink-jet printing, silica is often mixed into the hydrophilic binder component of a coating composition that is applied to the surface of paper to make recording paper for ink-jet printing. However, the recording paper coated with such a coating composition is disadvantageous in that it is poor in water resistance.
To improve the water resistance of recording paper for ink-jet printers, extensive studies have been made so far. For instance, there has been made such a proposal that a binder having high water resistance and colloidal silica are mixed into a coating composition useful for making recording paper in order to reconcile ink penetration with water resistance in the recording paper.
Although such recording paper is excellent in both ink penetration and water resistance, it is not easy to recycle the recording paper. As public concern for environmental problem as grown, the recycling of paper has become an important issue in recent years. The above recording paper has such a shortcoming hat it requires great cost for its recycling.
SUMMARY OF THE INVENTION
The present inventor has now found that recording paper excellent in glossiness, water resistance, solvent resistance, heat resistance, thermal blocking resistance, and ink penetration. can be obtained by the use of a coating composition comprising a specific hydrosol emulsion and colloidal silica. The present inventor has also found that, since paper coated with such a coating composition is readily soluble in an alkali, it is easy to dispose the coated paper after use as regenerable waste. The present invention has been made based on these findings.
An object of the present invention is therefore to provide a coating composition with which it is possible to make coated paper that is excellent in such properties as glossiness, water resistance, solvent resistance, heat resistance, thermal blocking resistance and ink penetration and that can readily be recycled.
A coating composition according to the present invention comprises a hydrosol emulsion and colloidal silica, wherein the hydrosol emulsion is obtained by neutralizing, with an alkali, a synthetic resin emulsion prepared by dispersing, in water, particles of a synthetic resin having carboxyl group and an alkoxysilyl group.
DETAILED DESCRIPTION OF THE INVENTION
Coating Composition
The coating composition according to the present invention is useful for making coated paper, especially one required to have high gloss, high resistance to water and heat, and good ink penetration essential to ink-jet printing. Paper coated with the coating composition of the present invention can readily be recycled after use.
In the coating composition according to the present invention, the synthetic resin particles and the colloidal silica are combined through the alkoxysilyl group contained in the synthetic resin to form a colloidal-silica-combined hydrosol emulsion. By virtue of the existence of this composite, paper coated with the coating composition shows high gloss and excellent resistance to water, solvents and heat. In addition, it is believed that, since this composite swells and dissolves in an alkali in the course of the disposal of the coated paper for recycling, the recycling of the coated paper can easily be achieved.
The coating composition of the present invention comprises, at least, a specific hydrosol emulsion and colloidal silica.
(a) Hydrosol Emulsion
The hydrosol emulsion for use in the present invention is obtained by neutralizing, with an alkali, a synthetic resin emulsion prepared by dispersing, in water, particles of a synthetic resin having carboxyl group and an alkoxysilyl group.
In the present invention, the synthetic resin emulsion can be prepared by subjecting, at least, a (meth)acrylic alkyl ester, an ethylenically unsaturated carboxylic acid, and an organoalkoxysilane having radically polymerizable unsaturated bond to emulsion polymerization. Alternatively, the synthetic resin emulsion can also be obtained by subjecting, at least, a (meth)acrylic alkyl ester and an ethylenically unsaturated carboxylic acid to emulsion polymerization, and mixing the polymer produced and an organoalkoxysilane having no radically polymerizable unsaturated bond.
Any purposive technique selected properly can be used for conducting the emulsion polymerization. Examples of methods of emulsion polymerization include a batch process in which water, a surfactant serving as an emulsifier and a monomer component are charged to a polymerizer, the temperature of the mixture is raised, and proper additives such as a polymerization initiator are added to the mixture to make the polymerization proceed; a monomer-dosing process in which water and a radically polymerizable surfactant serving as an emulsifier are charged to a polymerizer, the temperature of the mixture is raised, and a monomer component is added dropwise to the mixture; and an monomer emulsion dosing process in which, in the above monomer-dropping process, the monomer component is firstly emulsified by the use of a surfactant serving as an emulsifier and water, and the emulsion formed is added dropwise to the mixture.
By conducting emulsion polymerization by such methods, it is possible to obtain the synthetic resin emulsion in which particles of a synthetic resin having carboxyl group and an alkoxysilyl group are dispersed in water.
The synthetic resin emulsion obtained is neutralized with an alkali to obtain the hydrosol emulsion. This neutralization can be conducted through the application of a conventional technique or operation for neutralization properly selected. An alkali of any purposive type can be used for the neutralization in a proper amount, and an aqueous sodium hydroxide solution or ammonia, for example, may be used.
In the present invention, the (meth)acrylic alkyl ester is a monomer that will constitute the skeleton of the synthetic resin to be used for preparing the above-described synthetic resin emulsion, and any purposive one can be used. Examples of such (meth)acrylic alkyl esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, iso-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and cyclohexyl acrylate. These alkyl esters can be used either singly or in combination of two or more members.
In the present invention, it is preferable to use a hydroxyl-group-containing (meth)acrylic alkyl ester. This is because, when such an alkyl ester is used, the resultant coated paper swells and dissolves in an alkali more easily, so that it is possible to recycle the coated paper more easily and successfully. When a hydroxyl-group-containing (meth)acrylic alkyl ester is used as the (meth)acrylic alkyl ester, the synthetic resin emulsion prepared is to contain hydroxyl group in addition to the carboxyl group and the alkox
Clariant Finance (BVI) Limited
Hanf Scott E.
Medley Margaret
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