Dispersant for plaster

Details Dispersant for plaster Dispersant for plaster

1997-08-26

2001-07-24

Marcantoni, Paul (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Inorganic settable ingredient containing

C106S785000, C106S820000, C106S823000

Reexamination Certificate

active

06264739

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a dispersant for plaster. In particular, the present invention relates to a dispersant for plaster which can impart proper dispersion to a plaster composition, and has an excellent effect on the foam stability of the composition.
2. Description of the Related Art
Among various dispersants for plaster, such as salts of condensates of naphthalenesulfonic acid with formaldehyde (hereinafter referred to as “the naphthalene compounds”), salts of condensates of melaminesulfonic acid with formaldehyde (hereinafter referred to as “the melamine compounds”), and salts of polycarboxylic acids (hereinafter referred to as “the polycarboxylic acid compounds”). By using these naphthalene compounds, water during mixing step can be reduced and drying time shortened.
In making plaster boards, at first, plaster powder, a dispersant-water mixture, a hardening improver or the like and very fine foam are continuously introduced into a mixer. The mixture is discharged after agitation for about 10 seconds, and is sandwiched by paper boards. But, even if enough foam is introduced, some of the foam breaks which creates undesirable spaces or voids in the plaster board. So, generally twice the amount of foam is introduced. Furthermore, the broken foam concentrates on the faces of the boards which prohibits bonding.
DISCLOSURE OF THE INVENTION
SUMMARY OF THE INVENTION
The present inventors have made extensive studies on the cause of the above problem and have solved it. As a result of studies, they have found that foam breaking is caused by dispersants. By using the dispersant of the present invention, the problem is solved. Thus, the inventors have found that the usual naphthalene compounds have strong power for destroying foam.
Thus, the present invention relates to an dispersant for plaster comprising a copolymer prepared by copolymerizing a monomer (a) represented by the following formula (A) with a monomer (b) selected from the group consisting of the compounds represented by the following formula (B) and those represented by the following formula (C), or mixtures of (B) and (C):
wherein R
1
and R
2
may be the same or different from each other and each represents a hydrogen atom or a methyl group; ml is an integer of 0 to 2; AO represents an oxyalkylene group having 2 to 3 carbon atoms; n is a number of 2 to 300; and X represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,
wherein R
3
, R
4
and R
5
may be the same or different from one another and each represents a hydrogen atom, a methyl group or a group represented by the formula: (CH
2
)
m2
COOM
2
(wherein m2 is an integer of 0 to 2; and M2 represents a hydrogen atom, an alkali metal atom, ½ an alkaline earth metal atom, an ammonium group, an alkylammonium group or a substituted alkylammonium group); and M1 represents a hydrogen atom, an alkali metal atom, ½ an alkaline earth metal atom, an ammonium group, an alkylammonium group or a substituted alkylammonium group, and
wherein R
6
represents a hydrogen atom or a methyl group; and Y represents a hydrogen atom, an alkali metal atom, ½ an alkaline earth metal atom, an ammonium group, an alkylammonium group or a substituted alkylammonium group.
Preferably the dispersant copolymer is a copolymer prepared by copolymerizing monomer (A) with a mixture of monomers (B) and (C), and more preferably a copolymer of monomer (A) and (B).
In formula (A), n refers to not only the number of alkylene oxide molecules added of one compound represented by the formula (A), but also the average number of alkylene oxide molecules added of a mixture of compounds represented by the formula (A) which are different from one another only in the number of alkylene oxide molecules added. In the former case, n is an integer of 2 to 300, while in the latter, n is an integer of 2 to 300, preferably an integer of 110 to 300. In the latter, the above-mentioned mixture has a distribution with respect to the number of alkylene oxide molecules added. The mixture having an average number of alkylene oxide molecules added of 2 to 300 may contain also a compound having a number of alkylene oxide molecules added of less than 2 and/or a compound having a number of alkylene oxide molecules added of more than 300.
The present invention includes a dispersant for plaster comprising, as an essential component, a copolymer prepared by copolymerizing a monomer (a) represented by the following general formula (A) with at least one monomer (b) selected from among the compounds represented by the following general formula (B) and those represented by the following general formula (C):
general formula (A)
 (wherein, R
1
and R
2
: hydrogen or a methyl group,
m1: an integer of 0 to 2,
AO: an oxyalkylene group having 2 to 3 carbon atoms,
n: an integer of 2 to 300,
X: hydrogen or an alkyl group having 1 to 3 carbon atoms),
general formula (B) general formula (C)
 (wherein, R
3
-R
5
: hydrogen, a methyl group or (CH
2
)
m2
COOM
2
R6: hydrogen or a methyl group,
M
1
, M
2
and Y: hydrogen, alkali metal,
alkaline earth metal,
ammonium, alkylammonium or
substituted alkylammonium,
m
2
: an integer of 0 to 2).
Further, the present invention relates to a method for improving the quality of a plaster board which comprises adding a copolymer prepared by copolymerizing a monomer (a) represented by the above formula (A) with a monomer (b) selected from the group consisting of the compounds represented by the above formula (B) and those represented by the above formula (C) to a plaster composition, and use of a copolymer prepared by copolymerizing a monomer (a) represented by the above formula (A) with a monomer (b) selected from the group consisting of the compounds represented by the above formula (B) and those represented by the above formula (C) for improving the fluidity of a plaster composition.
Furthermore, the present invention relates to a plaster composition comprising a copolymer prepared by copolymerizing a monomer (a) represented by the above formula (A) with a monomer (b) selected from the group consisting of the compounds represented by the above formula (B) and those represented by the above formula (C), surfactant and water.
The dispersant according to the present invention has oxyalkylene chains, which imparts strong protection against calcium ions which dissolve out from the slurry. The dispersant is also an adduct of 2 or more oxyalkylene groups so it stablizes the foam. Thus, a copolymer of poly(meth)acrylic acid without oxyalkylene groups or a poly(meth)acrylic acid adduct containing only one mole of oxyalkylene and a hydroxy ethylmethacrylate does not maintain good foam stability. Furthermore, an inventive dispersant containing 100-300 mole oxyalkylene groups are excellent foam stabilizers.
DETAILED DESCRIPTION OF THE INVENTION
Examples of the monomer (a) represented by the formula (A) to be used in the present invention includes esters of polyalkylene glycols having one end etherified with alkyl [for example, methoxypolyethylene glycol, i.e., an adduct of methanol with ethylene oxide (n is-from 2 to 300), methoxypolyethylenepolypropylene glycol, ethoxy polyethylene glycol, ethoxypolyethylenepolypropylene glycol, propoxypolyethylene glycol and propoxypolyethylenepolypropylene glycol] with acrylic acid, methacrylic acid and products of dehydrogenation (or oxidation) of fatty acids; and adducts of acrylic acid, methacrylic acid and products of dehydrogenation (or oxidation) of fatty acids with ethylene oxide and/or propylene oxide.
The number of the oxyalkylene groups constituting the oxyalkylene chain of the above polyalkylene glycol, or the (average) number of alkylene oxide molecules added of the above adduct is from 2 to 300. When both ethylene oxide and propylene oxide are added, they may be added in any manner such as random addition, block addition, alternating additions of random and block and others. When the number of the oxyalkylene groups constituting the oxyalkylene chain of the p

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