JP2919970B2 - Inorganic material slurry - Google Patents

Abstract

There is disclosed a high solids, aqueous suspension of a cationically dispersed particulate inorganic material, characterised in that the particulate inorganic material has a particle size distribution such that not more than 10 % by weight of the particles have an equivalent spherical diameter (esd) smaller than 0.25 microns.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cationically dispersed, high solids aqueous suspension of an inorganic pigment or filler, such as calcium carbonate.

Dispersed inorganic pigments and fillers in which the particles have an overall positive charge are known. Such cationic dispersion suspensions are useful in the paper industry (EP-0278602A) and in paper coating.

It has been found that the use of inorganic pigments or fillers with a particular particle size distribution can improve the rheology of the cationic dispersion suspension.

Thus, according to the present invention, a high solid aqueous solution of a cationic dispersed particulate inorganic material characterized by having a particle size distribution such that the equivalent sphere diameter (esd) of particles of 10% by weight or less of the particulate inorganic material is smaller than 0.25 micron. Provide a suspension.

Preferably, the high solids suspension is at least 60% by weight solids.

The inorganic material is preferably a material which, when ground to a granular mass, exists in the form of regular, substantially spherical particles having a low average particle aspect ratio. Thus, the material may be any form of calcium carbonate, natural or synthetic. Precipitated calcium carbonate (PCC) and chalk can be used, but particularly preferred is ground marble. Other possible inorganic materials are gypsum, talc and calcined kaolin clay. However, it should be recognized that other materials of the flat plate structure, for example, layered lattice silicates such as kaolin clay, are within the scope of the present invention.

Preferably, the inorganic material used in the present invention is BET N ₂
Less than about 7.5 m ² g ⁻¹ , more preferably less than about 6.5 m ² g ⁻¹ , and preferably at least 2
It has a specific surface area of m ² g ⁻¹ .

The particulate material also preferably has a particle size distribution such that less than 1% of the particles have an esd of greater than 10 microns and at least 65% have an esd of less than 2 microns.

Prior to dispersion, the inorganic material may be ground to a desired particle size distribution. The milling conditions can be adjusted in a manner known per se in order to produce materials of varying distribution.

Cationic slurries made in accordance with the present invention can form slurries having a predetermined viscosity with a higher solids content than slurries where the inorganic material has a broader particle size distribution.

When the inorganic material is a pigment or filler that retains a neutral or positive charge, for example, marble, talc, gypsum or calcined kaolin clay, the particles of the material are made of anionic and cationic polyelectrolytes. The dispersion may be carried out using a dispersant containing the combination. Here, the cationic polyelectrolyte is used in an amount sufficient to render the particles cationic. When unprocessed, the choke particle has no positive charge due to natural anionic species absorbed on the particle surface,
The chalk can be vigorously agitated to remove such anionic species, and using a combination of anionic and cationic polyelectrolytes tends to effectively disperse the chalk in high solids. is there.

Diluting the high solids aqueous suspension of the present invention (if necessary) to a solids concentration of at least 45% by weight;
And it can be "prepared" into paper coatings by the addition of an adhesive that should be non-ionic or cationic in nature.

For a thorough discussion of the components of paper coatings and how to apply such coatings to paper, see James P. Casey, “Pulp and Paper: Ch.
Emistry and Technology ", Second Edition, III
Volume, Chapter XIX. For further consideration, The B
ritish Paper & Board Industry Federation, London
n, TWRDean, 1979, “An Operat.
or's Guide to Apueous Coating for Paper and Board "
Is shown in

The aqueous suspension according to the invention is preferably stirred vigorously before or after suspension. In general, the vigorous mixing of inorganic materials
It should be sufficient to provide at least 10 kJ / kg of energy, preferably no more than about 50 kJ / kg. Generally, energy input is 1k of inorganic material
Will be 18-36 kJ per g.

The paper paint can be used for a method of coating a sheet member. The coated paper thus formed is particularly suitable for recycling.

The ground marble for use in the present invention is preferably formed by grinding a lot of marble in an aqueous suspension without a chemical dispersant using a particulate grinding medium. In addition, milling is achieved by dewatering the suspension of the milled marble, for example, filtering without a flocculant, followed by drying the pigment, and milling the dried product in a conventional mill. .

The particulate pigment is dispersed in a combination of an anionic polyelectrolyte and a cationic polyelectrolyte. Preferably, the anionic polyelectrolyte is a water-soluble vinyl polymer, an alkali metal or ammonium salt thereof or an alkali metal or ammonium salt of polysilicic acid. Most preferably, the anionic polyelectrolyte is poly (acrylic acid),
Poly (methacrylic acid), substituted poly (acrylic acid) or substituted poly (methacrylic acid) or alkali metal or ammonium salts of any of these acids. The substituted poly (acrylic acid) may be a partially sulfonated polymer. Particularly effective anionic polyelectrolytes are alkali metal or ammonium salts of copolymers of acrylic acid and sulfonic acid derivatives of acrylic acid, wherein the proportion of sulfonic acid derivative monomers is 5% to 20% of the total number of monomer units. Is preferred.

The number average molecular weight of the anionic polymer electrolyte is preferably at least 500, and more preferably 100,000 or less. The amount used is generally from about 0.01% to about 0.5% by weight, preferably from about 0.1 to 0.2% by weight, based on the weight of the dry pigment.

The cationic polyelectrolyte may be a water-soluble substituted polyolefin containing a quaternary ammonium group. The quaternary ammonium group may be on the linear polymer chain or on a branch of the polymer chain. The number average molecular weight of the substituted polyolefin is preferably at least 1500,
It is preferably not more than 000,000, more preferably in the range of 50,000 to 500,000. The amount required will generally be from about 0.01% to about 1.5% by weight, based on the weight of the dry pigment. Beneficial results have been obtained when the substituted polyolefin is a poly (diallyldi (hydrogen or lower alkyl) ammonium salt). Lower alkyl groups, which may be the same or different, may have, for example, up to four carbon atoms, each preferably being methyl. For example, ammonium salt, chloride, bromide, iodide, HSO ₄ ^- and the salts, CH ₃ SO ₄ ^- or may be a salt or nitrite with. Preferably, the salt is chloride. Most preferably, the cationic polyelectrolyte is poly (diallyldimethylammonium chloride). Alternatively, the water-soluble substituted polyolefin may be a product obtained by copolymerizing epichlorohydrin and an aliphatic secondary amine, and the product has the following general formula.

In the formula, R and R ′ may be the same or different and are each hydrogen or a lower alkyl group having 1 to 4 carbon atoms, preferably methyl or ethyl, and X is Cl
^{-, Br -, I -,} HSO 4 -, CH 3 SO 4 - is or nitrite ions.
The preferred number average molecular weight of the epichlorohydrin product is between 50,000 and 300,000.

Further, the cationic polymer electrolyte may be a water-soluble organic compound in which the majority is a basic group, and the number average molecular weight is preferably at least 10,000, and more preferably 1,000,000 or less. Most preferably, the number average molecular weight is at least 50,000. These water-soluble organic compounds may be described as polyacidic organic bases, preferably compounds of only carbon, hydrogen and nitrogen, and which have increased solubility in water, thus allowing them to be removed from clay in aqueous suspension. It does not contain other functional groups that increase the likelihood of leaving, such as hydroxy or carboxylic acid groups. Preferably, the organic compound is polyethyleneimine (PEI) having a number average molecular weight of 50,000 to 1,000,000. Further, examples of water-soluble organic compounds that may be used include polyethylene diamine, which may be ethylene dihalide or a copolymer of formaldehyde and ethylene diamine.

The cationic polyelectrolyte is used in an amount sufficient to render the inorganic particles cationic. Typically, the zeta potential of the particles is at least +20 mV after treatment,
Typically +50 mV, typically + 50-60 mV
It is as follows. These potentials were measured using a "Pen Kem Laser Z" meter using a diluted (0.02 wt%) solids suspension using an indicator electrolyte of potassium chloride ( ^10-4 M).

The weight ratio of the cationic polyelectrolyte to the anionic polyelectrolyte used is preferably from 2: 1 to 20: 1, more preferably from 2: 1 to 10: 1.

In the slurry production method of the present invention, the raw pigment is generally obtained as a filter cake having a relatively high solid content. A dispersant is then added to the cake to provide a dispersed high solids slurry (45-80% solids by weight) that may be mixed vigorously thereafter.

If the pigment is to be dispersed using a combination of anionic and cationic polyelectrolytes, it is mixed with the anionic polyelectrolyte before mixing with the cationic polyelectrolyte. This would result in a more fluid suspension at a higher solids concentration.

When aqueous suspensions are to be used for paper coating, other conventional paper coating adjuvants such as insolubilisers (eg melamine formaldehyde resins), lubricants such as calcium stearate and, if present, cationic latex. A catalyst that catalyzes crosslinking may be included: a preferred such catalyst is sodium bicarbonate. The amounts of these adjuvants required are known to those skilled in the art.

The adhesive used to make the paper coating should be a non-ionic or cationic adhesive. Such adhesives are contrasted with the anionic adhesives commonly used in paper coatings where the pigment is anionic. Thus, cationic casein and cationic starch adhesives can be used as well as cationic or non-ionic latex. Such cationic and nonionic adhesives are readily available. The particular cationic or non-ionic adhesive used will depend, for example, on the printing method to be used, for example offset printing requires an adhesive that must be water-insoluble. For paper to be used in offset printing, the amount of adhesive is preferably 7 to 25% by weight, based on the weight of the pigment, whereas for gravure paper, the adhesive is 4 to 4%, based on the weight of the pigment. Should be used in an amount of ~ 15% by weight. The precise amount of adhesive required will depend on the nature of the adhesive and the material being coated, but can be readily determined by one skilled in the art.

The paint may be coated on the sheet member using a normal paper coating machine under standard paper coating conditions. Paper coated with a cationic paint according to the present invention has been found to provide generally similar results to paper obtained with conventional anionic systems.

Coated paper that can be made using the present invention is a convenient paper when used as "broken paper" or recycled paper in the papermaking process. Generally, large volumes of paper are recycled at some point in the manufacture for some or other reasons. Also, the advantages of the paper of the present invention in recycling are of paramount importance to the papermaking industry. Such paper recycling methods include a process of reducing paper to a recyclable state in a fibrous state and a paper-making composition (paper-making composi).
step).

Such papermaking compositions include conventional papermaking pulp,
For example, bleached sulphite pulp may be mentioned; broke fibers and pulp will generally be used in a ratio of 10:90 to 60:40.

Also included in the papermaking composition are fillers, such as calcium carbonate fillers and retention aids.
d). Since the broke fibers contain some of the paint-derived calcium carbonate, reducing the amount of calcium carbonate filler to give a total amount of filler of 5-20% by weight of the total papermaking composition Is possible. Preferably, the weight of the added dry broke (fibers and fillers) ranges from about 5 to 30% by weight of the fibers.

When the broke fibers used are obtained from the coated paper according to the invention, it makes it possible to reduce the amount of retention aid used in the papermaking composition.

The aqueous slurries of the present invention are particularly suitable for paper fillers, and EP-278602A of the applicant is hereby incorporated by reference.

 The following examples illustrate the invention.

EXAMPLES Two calcium carbonate pigments were prepared by grinding low solid sand of marble powder. By adjusting the milling conditions, the products with different distribution widths were compared. Cedigraph data was obtained as shown in Table I below (percentages are by weight): Both samples were filtered to give a 70-75% solids filter cake. Then, the cake is pre-treated with sodium polyacrylate (molecular weight 4000) to disperse the cations,
Subsequently, a large amount of polydadomac having a molecular weight of 500,000 (that is, poly (diallyldimethylammonium chloride)) was added. The weight ratio of cationic polymer to anionic polymer was maintained at 3.2-3.5: 1. The suspension was diluted with water until the viscosity reached a viscosity of about 600 mPa.s, as measured at 100 rpm using a Brookfield viscometer, and the solids content of the suspension was measured.

Thus, in this example, the ground marble having a broad particle size distribution obtained about 4 units lower solids for a given rheology when the cations were dispersed.

Claims (7)

(57) [Claims] 1. An aqueous suspension for a paper coating composition comprising a particulate calcium carbonate pigment in an amount such that the solids content is at least 60% by weight, said particulate calcium carbonate pigment comprising 7.5 m ² g
Less than ^-1, has a specific surface area measured by BET N ₂ method, and the particles of 1 wt% or less equivalent spherical diameter (esd) greater than 10 microns, said particles at least 65 wt% of the equivalent spherical Having a particle size distribution such that the equivalent sphere diameter of less than 2 microns and less than 0.25 microns equivalent sphere diameter of less than 10% by weight of the particles, and wherein the particulate calcium carbonate pigment comprises a cationic polyelectrolyte and an anion Characterized in that the cationic polymer electrolyte is cationically dispersed by a dispersing agent in combination with the cationic polymer electrolyte, and the cationic electrolyte is used in an amount sufficient to make the pigment particles cationic. Said aqueous suspension. 2. The calcium carbonate pigment is used in an amount of 2.0 to 6.5 m ² g.
_2. The aqueous suspension according to claim 1, having a specific surface area measured by the BET N2 method in the range of ^-1 . 3. The amount of the cationic polyelectrolyte used is:
About 0.01 to about 1.5 based on the dry weight of calcium carbonate
Weight percent and the amount of anionic polyelectrolyte used is such that the weight ratio of the cationic polyelectrolyte to the anionic polyelectrolyte is in the range of about 2: 1 to 20: 1. The aqueous suspension according to claim 1, wherein the aqueous suspension comprises: 4. The aqueous suspension is subjected to vigorous stirring before or after the dispersion of the calcium carbonate pigment, so that 10 to 50 kJ of energy per kg of calcium carbonate is applied to the aqueous suspension. The aqueous suspension according to any one of claims 1 to 3. 5. A paper coating composition comprising the aqueous suspension according to claim 1 and a nonionic or cationic adhesive. 6. A coated paper comprising a coating formed from the paper coating composition according to claim 5. 7. A papermaking method comprising the step of recycling coated paper which has been made into a fibrous recyclable state and subsequently contained in a papermaking composition, said coated paper comprising the paper according to claim 6. The papermaking method as described above.