Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-09-28
2003-09-30
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S267000, C523S161000, C528S326000, C528S327000, C430S114000, C430S118600, C428S407000, C428S402240
Reexamination Certificate
active
06627696
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dispersion composition and a method for producing the same. More particularly, it relates to a dispersion composition which can be utilized in the technical fields where a particulate material insoluble in organic solvent is dispersed and used, for example, the field of paint, printing ink, liquid developer (wet toner) or ink jet ink where a pigment or a dye as a particulate material is dispersed and utilized, the field where a medicine as a particulate material is dispersed and utilized, and the field where a catalyst or a polymerization initiator as a particulate material is dispersed and utilized, and to a method for producing the same. The present invention further relates to a dispersion composition utilizable also in the field of coloring materials comprising a polymeric compound in which a particulate material is included by drying, such as dry toners, powdered paints, and plastics, and to a method for producing the same.
Hitherto, in the field of utilizing pigments or dyes which are particulate materials insoluble in organic solvents, a fine dispersion of particles has been made resulting in improved storage stability. For example, British Patent No. 2001083 discloses the use of a specific polyester amine as a pigment dispersant in paints or inks.
Furthermore, JP-A-8-30040 discloses a liquid developer prepared by dispersing in a non-aqueous solvent an urethane-based microencapsulated colored resin particle containing a pigment or a dye.
Moreover, JP-A-3-160464 discloses a solid self-dispersion type coloring material comprising a mixture of a pigment or a dye and a self-dispersion type graft polymer which forms particles upon self-dispersing in a high insulation carrier liquid, and mentions use of silicone-based graft polymers.
However, in the dispersion compositions using general dispersion stabilizers and pigment dispersants disclosed in the above British Patent No. 2001083, the type of organic solvent or pigment used is limited. Moreover, stabilization of the dispersion has been attempted by steric repulsion of the resins, however since the amount of electric charge generated at the surface of the pigment is small, in the case of dilute pigment dispersion, sedimentation occurs when stored for a long time and thus it lacks dispersion stability.
Furthermore, the solid self-dispersion type coloring material using urethane-based microencapsulated colored resin particles or self-dispersion type graft copolymers have the problem of sedimentation in long-term storage when they are used for liquid developers or ink jet inks because of their large dispersion particle diameter.
Moreover, the polymer toners have a large particle diameter because they are obtained by dispersing a reactive silicone monomer, an isocyanate and a coloring material and then polymerizing them, and the silicone-containing polymer used for the improvement of dispersibility dissolves in the organic solvent in the ink to cause sedimentation of toner particles in the ink.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a dispersion composition which is enhanced in dispersion stability of a particulate material, solves the problem of sedimentation, expands the kind of usable organic solvent or insoluble particulate materials and is wide in use, especially useful for liquid developers or ink jet inks which utilize the electrostatic force.
The above object can be attained by a dispersion composition comprising a particulate material dispersed in an organic solvent where a graft copolymer in which the graft chain comprises a polysiloxane and an alkylene group (hereinafter referred to as “graft copolymer A”) is adsorbed to at least a part of the outer surface of said particulate material.
DESCRIPTION OF THE INVENTION
According to the research conducted by the inventors, it has been found that by adsorbing the graft copolymer A to at least a part of the outer surface of a particulate material, the particulate material can be made finer and electric charge can be generated at the surface of the particulate material, whereby steric repulsive force between the particulate materials per se is enhanced, and sedimentation of the particulate material is inhibited and dispersion stability is enhanced.
The graft copolymer A in the present invention is a copolymer of such a type that a branch (graft chain) of a homopolymer grows at a backbone (main chain) of another homopolymer. This graft chain is composed of a polysiloxane and an alkylene group. The polysiloxane means a chain of siloxane bond (—Si—O—). By bonding the polysiloxane through the alkylene group, the portion of polysiloxane is sufficiently extended for an organic solvent, especially, an organic solvent having a resistivity of not less than
10
9
&OHgr;·cm (e.g., aliphatic hydrocarbons or silicone solvents), and the particulate material can be finely and stably kept. Furthermore, since the graft copolymer A is adsorbed to the surface of pigment so as to cover the particulate material, electric charge can be generated.
Moreover, the dispersion composition of the present invention can be produced by mixing a dispersion comprising a particulate material dispersed using a graft copolymer having a particle diameter of 0.01-1 &mgr;m in an organic solvent in which said graft copolymer is soluble with an organic solvent in which said graft copolymer is insoluble, thereby precipitating the graft copolymer to adsorb the graft copolymer to at least a part of the outer surface of the particulate material.
In the dispersion composition of the present invention, it is essential that the graft chain bonded to the graft backbone (main chain) in the graft copolymer A adsorbed to the particulate material comprises a polysiloxane and an alkylene group. More preferred is a structure where the polysiloxane is bonded to the main chain through the alkylene group. The structure of the graft chain comprising a polysiloxane and an alkylene group is represented by the following formula.
X: A linkage group containing at least one of urethane group, amide group and ester group.
R
1
: An alkylene group of 1-18 carbon atoms.
R
2
: An alkyl group of 1-4 carbon atoms.
R
3
: H or CH
3
n : An integer of 5-200.
The alkylene group is not particularly limited as far as the carbon number is 1 or more, but an alkylene group of 1-18 carbon atoms is preferred. An alkylene group of more than 18 carbon atoms is not preferred since the solubility of the graft polymer increases and the self-dispersion becomes difficult. An alkylene group of 1-12 carbon atoms is especially preferred. The polysiloxane is preferably polydimethylsiloxane and the molecular weight thereof is preferably 370-15000. Bonding of the alkylene group in the graft chain to the graft backbone (main chain) is conducted through an ester group, an amide group, an urethane group or the like. The ester group is especially preferred which can be simply obtained.
In the case of the general graft copolymers having a graft chain comprising only a polysiloxane shown in JP-A-6-160464, there is no extension of the graft portion in the organic solvent, and dispersion particle diameter of the particulate material increases and it sediments when used for preparation of jet ink and the like.
In the dispersion composition of the present invention, it is essential that the graft copolymer A adsorbed to the particulate material has a particle diameter of 0.01-1 &mgr;im and self-disperses in an organic solvent. If the particle diameter is more than 1 &mgr;m, it becomes difficult to improve the dispersion stability of the particulate material, and if it is less than 0.01 &mgr;m, the particulate material cannot be covered. More preferred range of the particle diameter is 0.015-0.5 &mgr;m, and further preferred is 0.015-0.25 &mgr;m. For obtaining the finer and very stable dispersion composition, the particle diameter is preferably 0.015-0.09 &mgr;m.
The term “self-disperse” employed in the present specification means that the graft copolymer A does not di
Nishimura Miyuki
Takao Nagayuki
Hitachi Maxell Ltd.
Hu Henry S.
Wilson Donald R.
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