NO752021L - - Google Patents

Abstract

Pigmented latex for use 1. paper coating masses.

Description

The present invention relates to a strong mono-

dlspers latex of a non-film-forming polymer and a method for its production.

A feature of the present invention relates to a stable/strong monodisperse latex of a non-film-forming copolymer of a. α,O-ethylenically unsaturated, emulsion polymerizable, hard monomer

and at least 1% by weight of an α,β-ethylenically unsaturated amide which is copolymerizable therewith.

Another feature of the present invention concerns

a method for the production of a latex, which is charac-

cert by (1) dispersing the hard monomer and ethylenic

unsaturated amide in an aqueous environment containing a surfactant 1 in an amount from 0.1 - 0.9, preferably 0.1 - 0.75, of the critical micelle concentration of the surfactant and (2) subjecting the dispersion to emulsion polymerization conditions.

Another feature of the present invention by

relates to a method for the production of a monodisperse latex which is characterized by polymerizing in an aqueous environment a mixture consisting of a surface-active agent in an amount from 0.1 - 0.9 of the critical ml cell concentration of the surface-active agent under emulsion polymerization conditions, periodically adds an emulsion polymerizable, ethylenically unsaturated,

hard monomer and at least 1% by weight based on total monomer of an o,$-ethylenically unsaturated amide which is copolymerizable with the hard monomer. The copolymer of the resulting monodisperse latex is present 1

form of non-film-forming, separated particles..

With the method where the monomer is added periodically (continuously) during the polymerization, latexes can be produced that have excellent pigment properties in a high yield in a safe monomer, i.e. without the risk of an uncontrolled turnover that can find

place by a completely satsvl's procedure.

Latexes according to the present invention have an average particle diameter that is usually in the range from approx. 0.25 - 1 nm, and no more than 10% by weight of particles with diameters outside this range, are usable as plastic pigments for paper coating. Paper coatings containing these latexes have a surprisingly high degree of adhesion to the paper. The result is that the amount of necessary binder can be significantly reduced. Since the latex according to the present invention is highly monodisperse, it is very useful as an internal calibration standard in electron microscopy and so" model systems for the study of colloidal properties.

The highly monodisperse latexes of the present invention contain discrete particles of a water-insoluble, non-film-forming copolymer of a hard monomer and an α,O-ethylenically unsaturated amide.

By "strongly monodispersed latex" is meant an aqueous dispersion of copolymer particles of carbon size, where the standard particle size deviation is less than 2%, preferably less than 1%. The expression "colloidal size" means that the diameters of the <0>latex particles are in the range from approx. 0.1 - 2 ym.

The term "non-film-forming" means that the separated polymer particles of the latex do not flow together and form a film at ambient temperature and at use temperatures of the latex, for example super calendering temperatures, if the latex is to be used as a pigment in paper coatings. When the required temperature varies with the application, it is usually preferred that the copolymer does not flow at temperatures below 60°C. If the separated particles melt or flow together before or during use, they may be completely unusable as pigments in beat printing materials due to poor opacity properties. In a similar way, when used as cold welding standards, be significantly reduced. On similar

manner, it is critical that the copolymer particles of the latex are insoluble in water and binder, if such is used, in the coating materials.

The copolymer of the highly monodispersed latex contains from 50 to 99, preferably from 77 to 98, wt% of an emulsion polymerizable, o,B-ethylenically unsaturated hard monomer; from 1 - 20, preferably from 2 - 10, % by weight of emulsion polymerizable, α,O-ethylenically unsaturated amide and up to 40, preferably from 0 - 20% by weight, of an emulsion polymerizable, α,β-ethylenically unsaturated, soft monomer.

Preferred emulsion polymerizable hard monomers which can be polymerized and/or copolymerized with each other in any amount and/or with other monomers to give such polymers include, for example, α,β-ethylenically unsaturated monomers, such as monovylyldenecarboxylic monomers; esters of ct,B-ethylenically unsaturated carboxylic acids which polymerize to form non-film forming polymers; α,β-ethylenically unsaturated esters of non-polymerizable carboxylic acids; et, B-ethylenically unsaturated nitriles; and other polymerizable vinyl monomers, such as vinyl chloride and vinyl bromide. Especially preferred are monovylyldenecarboxylic aromatic monomers, especially styrene and mixtures of styrene and acrylonitrile.

The above-mentioned monomers are usually classified as hard monomers, since they homopolymerize or copolymerize with each other to form polymers that are non-film-forming as required by the present invention.

Examples of suitable amides are emulsion polymerizable, α,β-ethylenically unsaturated amides, which are copolymerizable with the hard monomer, preferably such amides which are water soluble. Suitable amides include, for example, acrylamide, methacrylamide, amides of acids such as fumaric acid, maleic acid, itaconic acid, eitraconic acid, N-substituted amides such as W-methylacrylamide, N,N-dimethylacrylamide, N-isopropylacrylamide, N-(2- hydroxyethyl)acrylamide and M-substituted amides of the above-mentioned acids where the substituents are alkyl or hydroxyalkyl. Acrylamide is preferred.

Smaller amounts, such as less than 40% by weight based on the polymer, of other ethylenically unsaturated monomers which usually polymerize to form film-forming polymers (so-called soft monomers) are optionally copolymerized with the above-mentioned hard monomers. The soft monomers include, for example, conjugated aliphatic dienes; alkyl acrylates; unsaturated esters of saturated carboxylic acids; esters and half-esters of α,β-ethylenically unsaturated polycarboxylic acids; and other copolymerizable vinyl monomers containing a single polymerizable ethylenically unsaturated group, such

such as vinylidene fluoride, vinylidene chloride and vinylidene fluoride. The maximum concentrations of these monomers are primarily determined by the temperature reached during use of the latex and the extent to which a given monomer lowers the softening point of the resulting copolymer. If a strong monodisperse latex of an interpolymer of styrene, butadiene and acrylamide is used as a plastic pigment in a

coating compound, the content of the skin diene 1 copolymer is usually not higher than 20% by weight. If, however, the interpolymer of styrene/butadiene/acrylamide contains more than the normal amount

of cross-linking, the butadiene can be present in concentrations greater than 20% by weight, the maximum concentration of butadiene being

depending on the relevant degree of cross-linking. Increasing cross-linking is usually promoted by irradiation or by using a suitable cross-linking agent such as unsaturated polyester or polyethylene unsaturated monomer* Examples of polyethylene unsaturated monomers are divinylbenzene, trivinylbenzene and divinylnaphthalene. With respect to the use of the aforementioned soft monomers, these may be used in any concentration suitable provided the resulting polymer is non-film forming as required by the present invention.

It will further be understood that in order to be suitable

must the monomers which are to be copolymerized with the amide monomer be lntered above the amide functionality so that the amide groups are present as such in the resulting latex copolymer.

Preferred polymers of strong monodisperse latex

are copolymers containing from SO - 98% by weight of fine or more of the above mentioned hard monomers, from 0 - 49% by weight of Sn or more of the above mentioned soft monomers and from 2 - 10% by weight of

one or more of the above-mentioned amides, and preferably those containing 3-8 carbon atoms. Particularly preferred copolymers are copolymers containing 77-98% by weight of monovylnylidene carbocyclic aromatic monomers such as styrene and ar-(t-butyl)-styrene, 0-20% by weight of α,0-ethylenic unsaturated nitriles such as acrylonitrile and methacrylonitrile, and 2 - 10% by weight of a, B-ethylenically unsaturated amide such as acrylamide and methacrylamide. Examples of particularly preferred copolymers are styrene/acrylamide copolymers, styrene/acrylamide/acrylamide copolymers, styrene/methacrylamide copolymers and styrene/acrylonitrile/methacrylamide copolymers. With the preferred copolymers, it is sometimes advantageous to copolymerize from 1-15% by weight of polyethylene unsaturated monomer, such as divinylbenzene, to increase resistance to high temperatures.

If the latex is used as a plastic pigment in coating materials, the latex particles should be in the form of particles

which has an average diameter in the range from 0.25 - 1.0 tun,

and so that no more than 10% by weight of the particles based on the total weight of the particles making up the polymer pigment have diameters that lie on

outside this range, preferably not higher than 4% by weight. An amide pigment containing an unusually large number of particles

(>10 by weight) which have diameters smaller than 0.22 µm do not have the desired bonding or opacity properties. The average particle diameter of the amide pigment is preferably in the range from 0.3 - 0.8 µm.

The highly monodisperse latex is produced by

an emulsion polymerization which is carried out in such a way as to ensure that the concentration of the surfactant is not higher than the critical molecular concentration (hereinafter referred to as CMC) of the surfactant. Usually the amount of surfactant is sufficient to give 0.1 - 0.90 CMC, preferably 0.1 - 0.75 CMC and most advantageously 0.125 - 0.50 CMC.

X in connection with the present invention means critical micelle concentration (CMC), the concentration of a surface-active agent in water which is necessary for the formation of micelles. The relationship between the concentration of surfactant and

CMC appears in D.C. Blaokley, B£gh Polymer Latioes.Vol. 1, 270-271 (1966). The amount of surfactant required to provide the desired sub-CMC varies with each surfactant. The values of CMC are 1 gram unit of surfactant per 100 grams of aqueous solution. Dihexyl sodium sulfosuccinate has

for example a CMC in the range 0.3 - 1.5 g per 100 g of aqueous solution depending on the sample chosen, while a sample of sodium lauryl sulfate consistently shows a CMC value of 0.075 g per 100 g aqueous solution.

It is also desirable that the unsaturated amide is present in a stabilizing amount in the aqueous phase during the polymerisation. It is thus advantageous to add the amide already at the start of the polymerisation or at an early point in time. An amide length which ensures at least a fine weight % of the amide in the resulting water-soluble copolymer is usually found to be a stabilizing amount. The stabilizing function of the amide is believed to be the result of in situ formation of a water-soluble copolymer of the amide and the hard monomer which acts as an emulsion stabilizer. The water-soluble copolymer is believed to be present in

quantities in the area from o.a. 1-30% by weight based on the weight thereof

water-insoluble copolymer, preferably from 2 - 15% by weight. The water-soluble copolymer contains sufficient polymerized acrylamide to make the copolymer water-soluble, usually from 50-99, preferably from 65-80, by weight based on the water-soluble copolymer.

In the polymerisation According to the present invention, monomeric components are polymerised 1 narvar of sub-CMC amounts (less than CMC) of the surfactant and an unsaturated amide such as acrylamide. Since there are no micelles (sub-CMC) available as polymer ligation sites, polymer ligation is assumed to initially take place in dissolved monomer molecules. The monomer thus reacts with free radicals during formation

of monomer radicals that grow and then flocculate to form identifiable copolymer particles. The degree of flocculation is regulated by the amount of surfactant and age

for the production of a population: of polymer particles of uniform size (hereafter referred to as "Kimlatex"). Further growth of the germ latex is achieved by chain transfer and combination with the structure of the germ latex particles. The transfer of monomer to polymer within the bud latex particles is believed to take place mainly at the expense of monomer that is absorbed or encapsulated by the bud latex particles. Such transfer continues until another radical enters the particle from the aqueous phase and thereby terminates the polymerisation.

In the preferred embodiment, the polymer solution zone is flushed with inert gas and then water-soluble catalyst, water, surface-active agent and monomer are added. The resulting reaction mixture is brought to a suitable reaction temperature, usually from

30 - 98°C, and the reaction proceeds to completion. In this preferred embodiment, it is sometimes advantageous to add a buffer, such as sodium bicarbonate, to the reaction mixture prior to polymerisation and to add catalyst during the final stages of

the polymerization to force the polymerization to completion. In a particularly preferred batch method, it is desirable to use the latex produced in the above manner as a germ latex

for producing a latex of a larger and more desired particle size. In such cases, the germ latex is added to the polymer

sation zone or is produced in this insitu before the polymerization of the remaining monomer. The polymerization of the remaining monomer is achieved as described above, preferably in a batch manner.

In another preferred embodiment, the polymerization zone is flushed with inert gas and then water and surfactant are added. These components are brought to a suitable reaction temperature, usually from 30 - 98°C, preferably from 65 - 92°C, and the continuous addition of monomer and catalyst begins. Alternatively, the polymerization tank can be heated to reaction temperature shortly after the continuous addition of

the monomer. The catalyst can also be added all at once before or at the beginning of the polymerisation.

It is not critical how quickly the monomer is added. However, it is usually desirable to add at such a rate that the addition of total monomer is completed within 2-24 hours, preferably from 2-5 hours. In this embodiment, it is

It is also often desirable to add a buffer, such as sodium bicarbonate, to the reaction mixture, preferably in an amount of from 0.1 to 0.6% by weight based on the total amount of monomer, before the polymerisation and to add a substantial excess of catalyst during the last steps of the polymerisation to force the polymerisation to completion.

Other methods, which include modifications and/or combinations of the above-mentioned methods, can also be used provided that (1) the monomers are added periodically, preferably continuously, during polymerisation, (2) the old monomer is present in the aqueous phase during the polymerisation and (3) ) the surfactant is always present in the amounts stated above less than the CMC of the surfactant.

As polymerization catalysts, one or more can be used per oxygen compound known to act as free radical catalysts. Suitable are usually persulphates including ammonium, sodium and potassium persulphates), hydrogen peroxide, or perborates, persllcates or percarbonates. Organic peroxides can also be used, either alone or in addition to inorganic peroxides or sulphoxylate compounds. The choice of catalyst is partly dependent on the given combination of monomers to be polymerised. As expected, some of the monomers react better to one type of catalyst than another. Generally, however, the per-sulfates are preferred. A catalytic amount of catalyst is preferably from 0.01 - 3.0% by weight based on the weight of the total monomer addition.

In order to achieve the polymerisation at a temperature which is lower than the temperature at which coagulation or coalescence of the latex takes place, it may be desirable to activate the catalyst. The activation can best be achieved by using a redox system where a reducing agent is used which is present 1 en

o amount of 6.001 - 6% based on the weight of total monomers in addition to the peroxygen catalyst. The redox systems can be activated by adding

the presence of a small amount (a few parts per million) of polyvalent metal ions. Ferro ions are usually used or a tertiary amine which is soluble in the reaction medium can also be used as an activator.

Suitable surfactants According to the present invention are water-soluble cationic surfactants, water-soluble anionic surfactants and mixtures thereof together with non-ionic surfactants. It is preferred to use anionic surfactants. In those cases where a mixture of anionic and non-ionic surfactants is used, it is desirable that the main amount is anionic.

After the aqueous dispersion is cooled to ambient temperature, the aqueous dispersion of polymeric particles can be separated from unwanted contaminants, such as coagulant by-product, by filtering the aqueous dispersion of polymeric particles through a stainless steel filter having a perforated filter surface equivalent to standard 16 mesh after U.S. Standard Sleeve Series.

The filtered aqueous dispersion of polymeric particles prepared according to the process described above and which usually contains from 20 - 60% by weight, preferably from 40 - 50% by weight, of non-film-forming polymeric dry substances can be used in the form of latex or can be obtained as dry particles, for example by spray drying, and can be used as indicated below.

A paper coating compound can, for example, be produced by dispersing the polymeric particles (amide pigment)

in aqueous dlspersion in an aqueous medium containing binder or by mixing the aqueous dlspersion with the aqueous medium containing binder, thus eliminating the separation of the particles from the aqueous dlspersion. Suitable ratios between binder and pigment in the Horse Smoothing Mass vary from 1.3 - 11.5 parts by volume of binder, on a dry matter basis, to 38.8 parts by volume, on a dry matter basis, of pigment. Preferred proportions vary from 6.7 - 10 parts by volume of binder to 38.8 parts by volume of polymer particles.

Amide pigment alone or a combination of inorganic pigment and/or conventional plastic pigment together with amide pigment is covered by the present invention. In such a combination, the amide pigment ©t 1 is used in such an amount that the coating properties are improved in terms of resistance to tearing and in terms of the coating's resistance to sticking to the calender rolls, compared to a coating composition which only contains inorganic pigment and/or conventional pla&plgment as pigment. The old pigment preferably makes up at least 5% by weight of the total amount of pigment.

Suitable binders according to the present invention include coating materials which are non-solvents for the polymer pigment used and which can be adapted to the paper coating method

so that you get a continuous, smooth, glossy layer suitable for printing. Examples of suitable binders include natural binders such as starch, modified starch, soybean, protein

and casein and commonly known synthetic binders. Suitable modified starches include oxidized, enzyme-treated or hydroxy-ethylated starch. Suitable synthetic binders include styrene/-

hutadlen copolymer latex latexes of polymers of alkyl esters of α,B-ethylenically unsaturated carboxylic acids such as alkyl acrylates and methacrylates, in particular such aqueous dispersions of the polymers containing a small amount of a copolymerized, ethylenically unsaturated carboxylic acid? latexes of copolymers of butadiene and acrylonitrile, latexes of copolymers of vinyl acetate and alkyl acrylates, latexes of copolymers of butadiene and methyl methacrylate, latexes of copolymers of vinyl chloride and vinylidene chloride, latexes of vinyl chloride polymers, latexes of vinylidene chloride copolymers; aqueous dispersions of polybutadiene, polyvinyl acetate, polyvinyl alcohol and other synthetic polymers which are usually used as pigment binders in paper coating compounds. Such binders are

usually film-forming at room temperature and they must be film-forming at the temperatures used during the coating operation.

The coating mass is applied to the paper substrate using conventional techniques such as trailing blade air knife, reverse blade, roller coater, spraying devices and the like.

After the horse ironing compound has been applied, the surface of the substrate is dried and often post-treated by calendering or super calendering. It is critical that the temperature of the coating does not exceed the softening point of the amide particles, otherwise the particles will lose a separate crack ... • ^ ,m. ■■

Tcter or suitable size and. shape. When this

takes place, the opacity and lightness of the don coated surface is reduced..

The use of amide pigment as at least part of the pigment in paper coating compositions reduces the time required to dry coating compositions having such a composition and improves the finish and visual gloss of papers coated with such compositions.

When the solvent sensitivity of a given amide pigment is a problem, a coating containing amide pigments can be applied to paper substrates as a base coat and such raw paper is then coated with a coating compound containing an inorganic pigment that is not as sensitive to solvents. With such a method, it will be necessary to use less inorganic pigment in the horse-brushing compound to achieve a surface with the desired gloss and opacity, and the total coating weight is usually reduced by approx. 23%.

The following examples illustrate the invention. If nothing else is stated, all parts and percentages are by weight. Parts by weight are based on 100 parts by weight of total monomers if nothing else is stated.

Example 1

Step 1

The following ingredients are added to a 284 gram bottle of citrate, e.g

The bottle is flushed with nitrogen, sealed and rotated in a water bath at 65°C for 16 hours. The resulting aqueous dispersion of polymer particles (latex) is cooled, filtered and found to be a stable, highly monodisperse, 30.1 weight latex having an average particle diameter of 0.37 µm with a particle size standard deviation of less than 1% .

Step 2

Latex from step 1 is used as germ latex.

the ingredients are polymerized in a citrate bottle and obtained as indicated in step 1. The resulting product is a stable, monodisperse, 30.8% by weight polymer latex of styrene/acrylamide (95/5) copolymer having an average particle size of 0.54 µm with a standard particle size variation of less than 1%.

A coating composition for paper is prepared by mixing 100 parts (on a dry matter basis) of the copolymer latex (0.54 µm) with 26 parts (on a dry matter basis) of boiled, ethylated starch. The dry matter f content is adjusted to 30% and >pH to 7.9 by adding

aqueous ammonia. Enough of the mixture is applied to a paper substrate

with the help of a Meyer stick so that you get 7.5 g/m dry coating. The coated paper is cut to a width of 17.8 µm and passed through the nip of a laboratory super calender at 212 kg/cm and at various temperatures starting at 66°. The degree of sticking to the steel roll in the supercalender is qualitatively evaluated by listening to the sound of the paper sticking to the roll, the degree of waviness of the paper and the effect that the supercalendering has on the resulting treated paper. It is noted that the coated paper containing copolymer latex can be supercalendered at temperatures 11-23°C higher before the paper sticks or curls, compared to similar coated papers containing conventional 8tyrene/acrylic acid (97/3) copolymer pigment.

Four sheets of paper coated with the mixture containing copolymer latex and four sheets coated with another similar mixture except that they contain conventional styrene/acrylic acid (97/3) copolymer pigment Instead of the copolymer latex, calendered through four nips at 212 kg/om and 66°C. After conditioning at standard TAPPI conditions, the resulting paper is analyzed for gloss, lightness, opacity, color receptivity and tear resistance. The results appear in table X.

(1) Viscosity in centipois with No. 4 spindle at 23°C.

(2) "TAFPI Standard Method T480-OS-72." (3) °TAPPI Standard Method T452-OS-58."

(4) "TAPPI Standard Method T425-os-60.M

(3) "TAPPI Uoeful Method 553." (6)<a>TAPPI Suggested Method T499-su-64" where tension "B" and a pressure of kilograms are used.

Color numbers are indicated in ( ).

Example 2

Step 1

The following ingredients are added to a 2-11 liter, 3-necked flask equipped with a tube rack, Nj supply tube and cooler

The reaction mixture in the flask is stirred and the bottle is flushed with N2 1 for 10-20 minutes. The temperature of the reaction mixture is brought to 65°C and held there while maintaining a positive pressure of L for 6 hours. The resulting latex is cooled and filtered for use in step 2.

Step 2

When using the latex 1 step 1 as seed latex, the following components in the flask are obtained as indicated in step li

The resulting product is a stable monodisperse latex of styrene/acrylamide copolymer having an average particle size of 0.54 µm with a particle size standard deviation of less than 1 µm.

The coating method 1 example 1 is used for the production of a number of coated papers and these are analyzed as in example 1. The results appear in table XX.

Example 3

Step 1

To a 75.7 liter reactor which is equipped with pipework, ^-supply pipe°9en fcjØl«* the following components are added at 30°C:

The reactor is flushed with N, for 20 minutes then 57.6 parts of styrene are added. The reactor is heated to 65°C and kept at this temperature for 7 hours under a Nj atmosphere. The resulting latex is cooled and filtered for use in step 2.

Step 2

The latex in step 2 is used as seed latex and the following components are added to the reactor as in step 1 and heated to 65°C for 15 hours.

v*

The resulting product is a stable, monodisperse latex of amide pigment having an average particle size of 0.52 um

with less than. 1% of the particles that have diameters outside the range 0.3-0.8 µm. Based on total polymer, it is found that 96.4% exists as water-insoluble latex copolymer particles and 3.6% is water-soluble styrene/acrylamide copolymer containing more than 50% polymerized acrylamide.

For the sake of comparison, a plastic pigment (sample no. A^) is prepared according to the method 1 example 1 1 U.S. patent» no.

3,595,323. Another pigment for comparison (Sample No. A2) is prepared in a similar manner except that. the monomer mixture of the pigment varies. As a control (Sample No. C), a pigment prepared from styrene/acrylic acid in the same manner as described in U.S. Pat.

3,819,557.

When using the coating method indicated in example 1, except that the calendering is carried out at 178 kg/cm and a temperature of 178 kg/cm, a number of coated papers are produced using the above-mentioned peg mounters and analyzed as in example 1. The results appear in Table III.

It appears from the results in table ZZZ that the coatings containing the amide pigments according to the present invention have a higher resistance to stripping than the coatings containing conventional plastic pigments.

Example 4

When using the amide pigments (sample no. 1) 1 example 3, a number of coating compounds are produced by combining the pigment with coating compounds containing varying amounts of kaolin clay and binder which is a mixture of styrene/butadiene copolymer latex and starch. When applying the coating method in example 1, except that the super calendering is carried out at 143 kg/rem at 52°C, a number of coated papers are produced and these are analyzed as in example 1. The results appear in table XV.

Example 5

By applying the method in example 2, a number of highly monodisperse latexes are produced by using different amounts of different monomers as indicated in table I. The results appear in table V. (1) Parts by weight are indicated as dry matter parts even though DHSS, KjS-Og and Na HCO, are added as aqueous solutions. Water parts by weight indicates the total amount of water in the reaction mixtures.

(a) dlhexyl sodium sulfosuccinate (d) acrylamide

(b) styrene (e) methacrylamide

(c) methyl methacrylate (£) diacetanoacrylamide Example 6

A strong monodisperse latex is produced by using a cationic emulsifier.

Step 1

To a 2-liter, 3-necked flask equipped with pipework, ^-supply pipe and cooler, add the following constituent parts

The reaction mixture 1 flask is stirred and the flask is flushed with N2 for 10-20 minutes. The temperature of the reaction mixture is brought to 65°C and maintained at this temperature while maintaining a positive pressure of ^ for 5 hours. The resulting product is cooled and filtered to give a strong monodisperse, 33.5 solids § polymer latex having an average particle size of 0.2375 µm with a standard particle size deviation© of 0.65%.

Step 2

When using the latex in step 1 as klm latex, the following components are polymerized in the flask and obtained as indicated in step 1.

The resulting product is a stable, monodisperse, 49.6% solids polymer latex of styrene/acrylamide copolymer having an average particle size of 0.4 µM\

Example 7

41.1 parts of deionized water are added to a reactor of 113.6 liters which is equipped with &2 inlet, piping and cooler. The reactor is then flushed with nitrogen while heating to 88°C. 0.2 part dlhexyl sodium sulfosuccinate dissolved in 1.66 parts water, 0.1 part sodium persulfate dissolved in 0.83 parts water and 0.06 parts sodium bicarbonate dissolved in 1.25 parts water are then added to the reactor.

After the contents of the reactor have reached 88°C, 46.9 parts of styrene and 4.2 parts of an aqueous solution of 463 acrylamide are added separately to the reactor. After 10% of the monomers have been added to the reactor, the monomer additions are stopped and a catalyst addition consisting of 0.25 parts sodium persulphate dissolved in 3.33 parts water is started. After one exothermic peak has been reached, the monomer addition is started again and is terminated during a total monomer addition time of 3*i hour. The catalyst addition should be regulated so that it is finished 30 minutes after the monomer additions have finished. After all additions have been completed, the reaction mixture is digested for 11 hours. The resulting latex is cooled and filtered to yield 47.8% solids and an average particle size of 0.525 µm with a particle size standard deviation of less than 5%.

A coating mass is produced by mixing

25 parts (dry basis) of the above latexes and 75 parts clay pigment with 8 parts (dry basis) styrene/butadiene latex binder and 4 parts (dry basis) boiled ethyl starch. The dry matter content of the mixture is adjusted to 51.5% and the pH to 7.3

vad addition of aqueous ammonia. Enough of the mixture is applied to a paper substrate by means of a Meyer stick so that 14.4 - 15.3 g/m<2>dry coating is obtained.

Four sheets (sample no. 1) of coated paper

with the composition containing the amide pigment and four sheets (Sample No. C) coated with another similar composition, except that it contains conventional styrene/acrylic acid (97/3) copolymer filler instead of the amide filler, are supercalendered through 4 nips at 143 kg/linear cm and 52°C. After conditioning at standard TAPPI conditions, the resulting papers are analyzed for gloss, brightness, opacity, color acceptability and resistance to fading. The results appear in table VI.

Claims (19)

1. Pigment comprising a water-insoluble copolymer of an emulsion polymerizable, α,B-ethylenically unsaturated hard monomer, characterized in that the copolymer contains at least 1 weight of an emulsion polymerizable, α,B-ethylenically unsaturated amide and that the pigment is in the form of -film-forming, separated particles having an average particle diameter in the range from 0.25 to 1 µm with no more than 10% by weight of the particles having diameters outside this range. 2. Pigment as stated in claim 1, characterized in that it has from 1 to 30% by weight, based on the pigment, of a water-soluble copolymer of the emulsion polymerizable, ethylenically unsaturated hard monomer and at least 50% by weight of the amide. 3. Pigment as stated in claim 1 or 2, characterized in that the hard monomer is a monovinylidene aromatic monomer. 4. Pigment as specified in claim 1, characterized in that the monovinylidene aromatic monomer is styrene. 5. Pigment as stated in claim 1 or 2, characterized in that the hard monomer is a mixture of a monovinylidene aromatic monomer and an α,β-ethylenically unsaturated nitrile. 6. Pigment as stated in claim 1 or 2, characterized in that the hard monomer is methyl methacrylate. 7. Pigment as stated in any one of claims 1 to 6, characterized in that the amide is acrylamide. 8. Pigment as stated in claim 1, characterized in that the water-insoluble copolymer is a copolymer of from 50 to 99% by weight of the hard monomer, from 1 to 20% by weight of the amide and up to 40% by weight of an emulsion polymerizable, a ,B-ethylenically unsaturated, soft monomer. 9. Latex, characterized in that the solid comprises the pigment from any of claims 1 to 8, and that the particles have a standard particle size deviation of less than 2%. 10* Coating compound comprising a binder and a pigment, characterized in that at least part of the pigment is 1 form of the pigment from any of claims 1 to 8. 11. Coating composition as specified in claim 10, characterized in that part of the pigment is an inorganic pigment. 12. Coated paper, characterized in that it has attached to it the horse-ironing mass from claim 10 or II. 13. Method for producing the latex according to claim 9, characterized in that (1) dispersing the hard monomer and the amide in an aqueous phase containing surfactant in an amount of from 0.1 to 0.75 of the critical micelle concentration of the surfactant, the hard monomer being inert to the amide and the proportion of amide relative to hard monomer is sufficient to provide a water-insoluble copolymer containing at least 1% by weight of the amide; and (2) subjecting the dispersion to emulsion polymerization conditions such that at least a stabilizing amount of the amide is present in the aqueous phase during polymerization. 14. Method as set forth in claim 13, characterized in that the hard monomer is a monovinylidene aromatic monomer. 15. Method as stated in claim 13, characterized in that the hard monomer is styrene. 16. Method as stated in claim 13, characterized in that the hard monomer is methyl methacrylate. 17. Method as stated in claim 13, characterized in that the amide is acrylamide. 18. Process for producing a pigment according to any one of claims 1 to 8, characterized by (1) dispersing the hard monomer and the amide in an aqueous phase containing surfactant in an amount which is from 0.1 to 0.90 of the critical molar concentration of the surfactant, the hard monomer being inert to the amide and the proportion of amide in relation to hard monomer is sufficient to providing a water-insoluble copolymer Bora containing at least 1% by weight of the amide; and (2) subjecting the dispersion to emulsion polymerization conditions such that at least a stabilizing amount of amidote is present in the aqueous phase during polymerization. 19. Method as indicated in claim 18, characterized in that the hard monomer and the amide are added in portions to the aqueous environment during the polymerisation.