Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2002-08-29
2004-02-10
Metzmaier, Daniel S. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C516S079000, C516S134000, C516S917000, C516S919000, C524S004000, C524S005000, C106S802000, C106S823000
Reexamination Certificate
active
06689818
ABSTRACT:
This invention relates to dispersant compositions, and more particularly, to dispersant compositions which exert improved dispersing, anti-foaming and viscosity-reducing effects when added in small amounts in dispersing inorganic particulates such as ceramic particulates (e.g., alumina, ferrite) and calcium carbonate.
BACKGROUND OF THE INVENTION
Prior art methods of forming ceramic sheets involve dissolving a binder such as polyvinyl butyral resin in an organic solvent, admixing a finely divided ceramic raw material in the solution, and milling the mixture in a ball mill or suitable mixer for a long time for dispersion. After defoaming, the dispersion is applied to a film support of polyester or the like to a certain thickness to form a green sheet, which is fired.
Because of the flammability and environmental problems of organic solvents, it was recently proposed to use aqueous binders to avoid the use of organic solvents. Water-soluble binders including polyvinyl alcohol and water-soluble polyurethane were developed as disclosed in JP-A 60-180955. They have found more frequent use.
Often a slurry is prepared by dispersing ceramic powder in water and blending a water-soluble binder therein. In the process of preparing a powder slurry, it is crucial to control the dispersion of fine particles. The quality of finished ceramic articles is largely affected by the degree of dispersion of fine particles. Then a choice of a dispersant is very important.
Nevertheless, aqueous binders raise problems due to their high surface tension. When ceramic particles are dispersed, the penetration of the binder or dispersant is retarded so that the ceramic particles will agglomerate together, or even when they are dispersed, the resulting slurry has a high viscosity which causes uneven coating when the slurry is applied. Emulsifiers or water-soluble polymers in the aqueous binders cause the slurry to generate foams, which reveal themselves as pinholes in articles formed from the slurry. As a result, the formed articles are very weak.
Under the circumstances, polyacrylic acid and ammonium salts of &bgr;-naphthalenesulfonic acid-formaldehyde condensates are often used as the dispersant. For certain types of powder, some dispersants are ineffective, and some have dispersing effects, but the dispersed slurry increases its viscosity with the passage of time. After a certain time has passed since the initial dispersion, the slurry cannot be dispersed again, that is, becomes unusable.
More recently proposed replacement dispersants are interdigital polymers such as graft products of allyl alcohol-maleic anhydride-styrene polymers with polyoxyalkylene monoalkyl ether. They have good dispersing effects and change little with time, but have so high a foaming ability that formed ceramic bodies have many pinholes and are very weak. This necessitates the combined use of anti-foaming agents.
The anti-foaming agents used in the art are mineral oil and silicone base agents. The mineral oil base agents are relatively low repellent, but lack retention and water solubility. Their safety problem becomes a concern in these days. On the other hand, the silicone base anti-foaming agents have good and long-lasting anti-foaming effects, but have the shortcomings of high repellency, formation of craters, and an increased rate of defectives. The addition amount is thus limited.
When such an anti-foaming agent is used to prevent pinholes, repellency is developed due to poor compatibility. In green sheets formed from such slurries, the development of craters presumably resulting from repellency is a problem.
Under the circumstances, it would be desirable in the electronic material art to have a dispersant which is compatible with aqueous binders without a need for anti-foaming agents, that is, has minimized foaming ability, viscosity-reducing effects, and good dispersing effects, and experiences no change of viscosity with time.
SUMMARY OF THE INVENTION
An object of the invention is to provide a dispersant composition which exerts improved dispersing, anti-foaming and viscosity-reducing effects when added in dispersing inorganic particulates such as ceramic particulates and calcium carbonate and which experiences little change with time.
We have found that a dispersant composition comprising a specific acetylene glycol and a graft product of an allyl alcohol-maleic anhydride-styrene copolymer with a polyoxyalkylene monoalkyl ether is compatible with aqueous ceramic binders, has improved dispersing and viscosity-reducing effects, experiences little change with time, and has minimized foaming ability. Using this dispersant composition, the above-discussed problems of the prior art are overcome.
According to the invention, there is provided a dispersant composition comprising
(A) 20 to 80% by weight of at least one acetylene glycol selected from acetylene glycols of the formula (1):
wherein R
1
and R
2
each are a C
1-5
alkyl group, and ethoxylated acetylene glycols of the formula (2):
wherein R
1
and R
2
each are a C
1-5
alkyl group, m and n each are a positive number of 0.5 to 25, and m+n is 1 to 40, and
(B) 20 to 80% by weight of a graft product of an allyl alcohol-maleic anhydride-styrene copolymer with a polyoxyalkylene monoalkyl ether, comprising (a) polyoxyalkylene monoalkyl ether units of the formula (3):
wherein R
3
is a C
1-5
alkyl group and p is a positive number of 5 to 50, (b) maleic anhydride units, and (c) styrene units, in a compositional ratio a:b:c of 25-40:25-40:25-40 in mole percent, the graft product having a weight average molecular weight ({overscore (Mw)}) of 1,000 to 50,000.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Component (A) in the dispersant composition of the invention is at least one acetylene glycol selected from acetylene glycols of the formula (1) and ethoxylated acetylene glycols of the formula (2).
Herein R
1
and R
2
each are a C
1-5
alkyl group, m and n each are a positive number of 0.5 to 25, and m+n is 1 to 40.
Examples of the acetylene glycol having formula (1) include
2,5,8,11-tetramethyl-6-dodecyne-5,8-diol,
5,8-dimethyl-6-dodecyne-5,8-diol,
2,4,7,9-tetramethyl-5-decyne-4,7-diol,
4,7-dimethyl-5-decyne-4,7-diol,
2,3,6,7-tetramethyl-4-octyne-3,6-diol,
3,6-dimethyl-4-octyne-3,6-diol, and
2,5-dimethyl-3-hexyne-2,5-diol.
Examples of the ethoxylated acetylene glycol having formula (2) include ethylene oxide derivatives of the above-exemplified acetylene glycols, such as ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (molar number of ethylene oxide added 10 moles), ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol (molar number of ethylene oxide added 4 moles), ethoxylated 3,6-dimethyl-4-octyne-3,6-diol (molar number of ethylene oxide added 4 moles), and ethoxylated 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (molar number of ethylene oxide added 6 moles).
The molar number of ethylene oxide units added to the acetylene glycol on each side is 0.5 to 25 moles, and the total molar number of addition is 1 to 40 moles. If the total molar number of ethylene oxide added exceeds 40 moles, the foaming ability increases, resulting in formed articles having pinholes and lacking strength.
The acetylene glycols (A) may be used alone or in admixture of two or more. When the dispersant composition of the invention is prepared, the acetylene glycol (A) is used in an amount of 20 to 80% by weight, preferably 30 to 60% by weight of the entire composition. A composition with more than 80% by weight of the acetylene glycol is low in dissolving power, allowing repellency (craters) to occur when ceramic sheets are formed. A composition with less than 20% by weight of the acetylene glycol has less anti-foaming effects, allowing for foaming, which results in pinholes.
In the dispersant composition of the invention, the acetylene glycol (A) is compounded with a graft product of an allyl alcohol-maleic anhydride-styrene copolymer with a polyoxyalkylene monoalkyl ether, designated as component (B). The graft product (B) is constructed from (a) polyoxyalkylene monoalkyl ether units of the formul
Nakamura Norio
Shinohara Shuichiro
Birch & Stewart Kolasch & Birch, LLP
Metzmaier Daniel S.
Nissin Chemical Industry Co. Ltd.
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