Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2003-01-28
2004-08-17
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S457000, C428S461000, C428S476300, C428S483000, C428S500000, C428S520000, C427S372200, C427S388100, C524S442000, C524S449000, C524S543000, C524S555000, C524S556000, C524S559000, C524S560000
Reexamination Certificate
active
06777096
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous polyolefin resin dispersion.
BACKGROUND ART
With a recent trend toward the restriction of the use of organic solvents from the viewpoint of environmental protection, resource saving, hazardous material regulations under the Japanese Fire Defense Law and improvement of office environments, various aqueous resin dispersions have been developed. Aqueous resin dispersions containing olefin compounds will be described below.
It is known that an aqueous dispersion of a resin containing an olefin compound in a lower proportion is generally obtained by emulsion polymerization or dispersion polymerization in the presence of an emulsifying agent or a protective colloidal compound. However, a reaction pressure for the polymerization is increased, as the content of the olefin compound in the resin is increased. In consideration of equipment and safety, it is difficult to obtain a stable aqueous dispersion by the aforesaid method. A resin containing the olefin compound in a greater proportion is generally obtained by high-pressure radical polymerization in a high-pressure ethylene plant or the like and, in general, is not provided in the form of an aqueous dispersion.
On the other hand, where the resin containing the olefin compound in a greater proportion is copolymerized with an unsaturated carboxylic acid at a higher copolymerization ratio, the resin can be provided in the form of an aqueous dispersion. For example, aqueous dispersions of ethylene-unsaturated carboxylic acid copolymer resins such as ethylene-acrylic acid copolymer resins and ethylene-methacrylic acid copolymer resins each containing about 20 wt % of an unsaturated carboxylic acid are conventionally known. Particularly, the aqueous dispersion of such resins can easily be prepared by employing an alkaline metal compound or ammonia and, therefore, this method is widely used. Where the content of the unsaturated carboxylic acid in the ethylene-unsaturated carboxylic acid copolymer resin is increased, the water compatibilization of the resin is facilitated, but the amount of carboxyl groups reactive with various compounds is increased. This significantly reduces the blend stability of the aqueous dispersion when an additive, particularly a compound reactive with the carboxyl groups, is added to the aqueous dispersion after the preparation.
Therefore, an attempt is made to reduce the content of the unsaturated carboxylic acid in the ethylene-unsaturated carboxylic acid copolymer resin. However, the water compatibilization of the resin becomes more difficult, as the content of the unsaturated carboxylic acid is reduced. For example, Japanese Unexamined Patent Publications No. 2000-72879 and No. 2000-119398 disclose aqueous dispersions of ethylene-unsaturated carboxylic acid copolymer resins each containing 5 to 30 wt % of an unsaturated carboxylic acid and preparation methods therefor, but virtually provide only those containing the unsaturated carboxylic acid in proportions of not smaller than 15 wt % as examples. Where a polyolefin resin containing an unsaturated carboxylic acid in a smaller proportion, more specifically, an ethylene-unsaturated carboxylic acid copolymer containing the unsaturated carboxylic acid in a proportion of smaller than 10 wt %, particularly smaller than 5 wt %, is to be dispersed in an aqueous medium, the resin is first dissolved in an organic solvent or melted to be made into a liquid form, and then mechanically dispersed in the aqueous medium in the presence of a nonvolatile water-compatibilizing agent such as an emulsifying agent, a protective colloid or a wax. For example, a method for dispersing a polyolefin resin in water by addition of a carboxyl group containing polyolefin wax is stated in Japanese Examined Patent Publication No. SHO58 (1983)-42207. Further, methods for dispersing a polyolefin resin in water with the use of various emulsifying agents are stated in Japanese Unexamined Patent Publications No. SHO62(1987)-252478, No. HEI5(1993)-163420, No. HEI7(1995)-82423 and No. HEI9(1997)-296081. However, these aqueous dispersions each essentially contain a highly hydrophilic emulsifying agent or a protective colloidal compound. A coating film formed from such an aqueous dispersion is liable to have a significantly reduced water resistance because the emulsifying agent or the protective colloidal compound remains in the coating film after drying thereof. Further, the coating film containing the emulsifying agent or the protective colloidal compound is not preferable environmentally and hygienically with a possibility of bleed-out. Where a low molecular weight compound such as the polyolefin wax or the protective colloidal compound is used in combination with the polyolefin resin, the intrinsic properties of the polyolefin resin are deteriorated. Hence, there is a demand for finely and homogeneously dispersing a polyolefin resin in an aqueous medium virtually without the addition of a compound which may remain in the resulting coating film after drying.
It is an object of the present invention to solve the aforesaid problem and to provide an aqueous polyolefin resin dispersion which is virtually free from a nonvolatile water-compatibilizing agent such as an emulsifying agent or a protective colloidal compound, and excellent in storage stability, low-temperature film formability and blend stability with respect to any other aqueous polymer dispersion and any of various additives with capability of forming a coating film excellent in transparency and water resistance.
DISCLOSURE OF THE INVENTION
As a result of intensive studies to achieve the aforesaid object, the inventors of the present invention have found that, where an aqueous dispersion comprises a polyolefin resin having a specific composition, a basic compound and an aqueous medium, the polyolefin resin can stably be dispersed in the aqueous medium without addition of a nonvolatile water-compatibilizing agent such as an emulsifying agent or a protective colloidal compound even if the content of an unsaturated carboxylic acid in the polyolefin resin is low, and attained the present invention.
The following is the summary of the present invention.
An aqueous polyolefin resin dispersion according to the present invention comprises a polyolefin resin, a basic compound and an aqueous medium, wherein the polyolefin resin comprises a copolymer of an unsaturated carboxylic acid or an anhydride thereof, an ethylenic hydrocarbon and a specific compound, wherein the specific compound is at least one of compounds represented by the following formulae (I) to (IV):
wherein R1 is an hydrogen atom or a methyl group, R2 is an alkyl group having a carbon number of not greater than 10, and R3 is a hydrogen atom or an alkyl group having a carbon number of not greater than 10.
With this arrangement, the polyolefin resin can be dispersed in the aqueous medium as having a number average particle diameter of not greater than 1 &mgr;m virtually without addition of a nonvolatile water-compatibilizing agent even if the unsaturated carboxylic acid is contained in the polyolefin resin in a smaller proportion. Therefore, the aqueous dispersion is excellent in storage stability and low-temperature film formability, and is capable of forming a coating film excellent in transparency and water resistance. In addition, the aqueous polyolefin resin dispersion is excellent in blend stability with respect to any other aqueous polymer dispersion or an additive such as metal ions, inorganic particles or a cross-linking agent and, therefore, can advantageously be employed for a variety of applications such as coating agents and anti-corrosive coating materials.
Where the aqueous polyolefin resin dispersion according to the present invention is employed as a coating agent to be applied on a base film, thin coating is possible, and the resulting coated film is excellent in water resistance, cleanliness, alkali resistance, adhesion between the coating film and the base film and heat-sealability, because no nonvolatile
Kajimaru Hiroshi
Okamoto Shoji
Onishi Hayami
Shiba Kenjin
Fildes & Outland, P.C.
Jackson Monique R.
Unitika Ltd.
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