DK154154B - Paper product containing organic particles as a coating or a filler - Google Patents

Description

DK 154154 B

The present invention relates to a paper product containing organic particles as a coating or filler, which organic particles have a size of from 0.1 to 2 µm and are water-insoluble copolymer particles consisting essentially of the free-radical-catalyzed copolymerization product of ( 1) at least one ethylenically unsaturated monomer and (2) a water-soluble prepolymer having an RSV value of 0.1 to 2.5 (1M NaCl, 1%, 25 ° C) where the prepolymer portion of the copolymer particles is present on the surface of the particles.

Paper or other cellulose substrates are often coated to improve the appearance and printability. The coatings usually comprise an inorganic pigment such as iodine, calcium carbonate or titanium dioxide, and a binder which binds the pigment particles to the substrate. The coating applied provides a smooth, ink-susceptible surface suitable for printing. In addition, the inorganic pigment particles scatter the light and render the coated substrate opaque and white. Such particles are also used as filler to improve the opacity and strength of the paper.

Further, from SE Publication No. 362,912, it is known to use organic polymer particles, such as fine particles of polystyrene 20 or polystyrene copolymers having a size of 0.3-0.8 µm, as substitutes or partial substitutes for inorganic particles in paper coatings or as fillers. These polymer particles are referred to by those skilled in the art as "organic pigments". However, it is desirable to achieve better compatibility between the organic pigments, the paper cellulose and the 25 binders traditionally used in paper coatings.

This is achieved with the initially stated paper product which is characterized by the monomer (1) being styrene or combinations of styrene and divinylbenzene, and the prepolymer (2) being prepolymers prepared by addition polymerization of 30 acrylamide or a mixture of acrylamide and an anionic or nonionic vinyl monomer, wherein the amount of prepolymer (2) used to prepare the copolymer particles is from 2 to 10 parts by weight per 100 parts by weight of the monomer used (1) and the copolymer has a Tg of 75 ° C or more.

Paper products according to the invention, wherein the particles are present in a coating, will usually comprise a binder material such as that used for inorganic pigments. The organic particles in the products of the invention are suitably compatible with such binders, as well as they are more compatible with cellulose than the known organic pigments.

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polystyrene.

In practicing the present invention, an aqueous solution of the water-soluble prepolymer, which may be either an anionic prepolymer or a nonionic prepolymer, is first prepared. The prepolymers may be homopolymers or copolymers of two or more monomers. These polymers will then be described in more detail.

To the aqueous solution of the prepolymer is added a free radical polymerization initiator and the desired monoethylenically unsaturated monomer, and free radical graft copolymerization is carried out at a temperature of about 10 40 ° C to approx. 90 ° C. The exact temperature used during graft copolymerization can be determined by one skilled in the art and will depend on the initiator and monomer used. A very stable latex is produced. In some cases, if desired, the water can be removed by drying to produce free-flowing graft copolymer particles.

The initial function of the water-soluble anionic or nonionic prepolymer is to stabilize the slurry and prevent coagulation of the individual particles. After initial graft copolymerization is performed, some homopolymerization of the monomer may occur within the particle. A substantial portion of the anionic or nonionic prepolymer will be grafted onto the surface of the graft copolymer particles. Substantially stable latexes of the graft copolymer particles are prepared according to the present invention without the need for additional stabilizer.

The water-soluble anionic and nonionic prepolymers used in the present invention are prepared by the addition polymerization of acrylamide or a mixture of acrylamide and anionic or nonionic vinyl monomer and may be well known in the art of water-soluble polymers of the addition type. Examples of non-ionic monomers are α, β-ethylenically unsaturated amides such as acrylamide, methacrylamide, Ν, Ν-dimethylacrylamide, N-methylacrylamide, N-methylol acrylamide and diacetone acrylamide. Other suitable nonionic monomers are hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and N-vinylpyrrolidone. Monomers which can be used to prepare anionic prepolymers are α, β-ethylenically unsaturated mono- and polycarboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid and fumaric acid. Other suitable monomers that can be used to prepare anionic prepolymers are vinylsulfonic acid, allylsulfonic acid, styrene sulfonic acid, and 2-sulfoethyl methacrylate.

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Nonionic prepolymers include homopolymers and copolymers of the aforementioned nonionic monomers such as e.g. polyacrylamide, homopolymers of acrylamide, polymethacrylamide, homoplymer of polymethacrylamide, copolymers of acrylamide and hydroxyethyl acrylate, 5 copolymers of methacrylamide and hydroxypropyl acrylate, and copolymers of acrylamide and hydroxyethyl methacrylate.

Other suitable water-soluble nonionic polymers which can be used in the present invention are poly (vinyl alcohol) and poly (ethylene oxide).

Examples of anionic prepolymers are copolymers of acrylamide and acrylic acid, copolymers of methacrylamide and acrylic acid, copolymers of acrylamide and methacrylic acid and copolymers of methacrylamide and methacrylic acid. It will be obvious to one skilled in the art that these prepolymers are only anionic in their neutralized form. In order to take advantage of the anionic properties, it is necessary to use these prepolymers in neutralized form. This is not a problem when the organic pigments produced from these anionic prepolymers are used in paper coating, since the paper coating processes are usually carried out at an alkaline pH.

Other suitable water-soluble polymers are the naturally occurring polymers, such as starch (non-ionic), the non-ionic and anionic derivatives of starch, and the naturally occurring polymers made water-soluble by derivatization, such as hydroxyethyl cellulose (non-ionic). ) and the sodium salt of carboxymethyl cellulose 25 (anionic).

Water-soluble anionic and non-ionic prepolymers are prepared easily and quickly by adding the desired monomers in the desired amounts and a water-soluble, free-radical polymerization initiator, both in aqueous solution, simultaneously to a reaction vessel containing 30 water and held on a temperature of from approx. 80 ° C to approx. 90 ° C. Suitable free radical polymerization initiators are those used to prepare the graft copolymer particles of the present invention, and are hereinafter referred to. The amount of initiator used will be the amount needed to produce water-soluble prepolymers having an RSV (reduced specific viscosity) of from approx. 0.1 to approx. 2.5, preferably from 0.1 to 1, measured in a 1% solution in 1M NaCl at 25 ° C (1M NaCl, 1%, 25 ° C).

There are two main requirements for the graft copolymer particles used in the present invention. They must be (1) water-insoluble and 4

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(2) have a sufficiently high melting point or softening point that they do not deform substantially under the heat or pressure conditions or both to which they are subjected during use. The graft copolymer preferably has a second order conversion temperature (glass conversion temperature, Tg) / equal to or greater than 75 ° C.

In some cases, it is desirable that the prepolymer portion of the graft copolymer particles contain a group which is reactive. Such reactivity will usually increase the bonding properties of the particles with respect to bonding to each other and to the surface on which they are applied.

10. Reactive groups may be introduced into some monomers prior to preparation of a prepolymer, they may be introduced into a prepolymer after preparation thereof, or they may be introduced into the graft copolymer particles after preparation thereof.

Reactive groups may be introduced by an aldehyde, such as formaldehyde, glyoxal, and glutaraldehyde, with monomers containing amide function such as acrylamide and monomers containing hydroxyl groups such as hydroxyethyl acrylate and with prepolymers containing amide function such as poly (acrylamide), or hydroxyl groups such as poly (vinylal alcohol). When using dialdehydes such as glyoxal, the reactive group will be an aldehyde. When formaldehyde is used, the reactive group will be the N-methyloI group.

The amount of aldehyde used to produce graft copolymer particles with appropriate reactive groups will be about 0.25 mole to approx. 3 moles, preferably approx. 1 mole to approx. 2 moles, for each mole of 25 amide or hydroxy If un ction. The reaction will be carried out at a temperature of from ca. 20 ° C to approx. 60 ° C at a pH of approx. 8 to 10 with the exception that when formaldehyde is used as aldehyde, the reaction is carried out at a pH of about 2 to 3.

The presence of reactive groups on the surface of the particles 30 of the present invention improves the adhesiveness of reactions between particles or between particle and substrate.

The amount of water-soluble prepolymer used to prepare the graft copolymers of the present invention can range from 2 to 10 parts per 100 parts by weight of monomer or monomer mixture.

As mentioned above, graft copolymerization is carried out by adding the graft copolymerizable monomer to a solution of water-soluble prepolymers in the presence of a polymerization initiator. The prepolymer may be present in the reaction vessel initially or added simultaneously with the monomers. The polymerization initiator is added 5

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usually simultaneously with the monomer.

A large number of chemical polymerization initiators can be used to prepare the latexes used in the present invention, with peroxy compounds being particularly useful. The initial stage of the polymerization involves the formation of a graft copolymer between the monomer and the water-soluble prepolymer. The initiator probably first introduces free radical sites on the prepolymer. Addition of monomer to these sites then leads to the desirable graft copolymer particles.

Suitable water-soluble initiators include those activated by heat, such as sodium persulfate and ammonium persulfate. Polymerizations carried out with these initiators usually proceed at temperatures of 70-95 ° C. Other suitable water-soluble initiators include the so-called redox initiator systems, such as 15 ammonium persulfate sodium bisulfite ferroion and t-butyl hydroperoxide sodium formaldehyde sulfoxylate. Redox initiators are activated at relatively low temperatures, and polymerizations using these systems can be carried out at temperatures of from 20 ° C to 80 ° C.

The amount of initiator to be used may be determined by a person skilled in the art. Usually, from about 0.1 part to approx. 5 parts initiator for every 100 parts monomer used.

In the present description and examples, all parts and percentages are by weight unless otherwise specified.

EXAMPLE 1A

The prepolymer used in this example was a 92% acrylamide-8% acrylic acid copolymer. The Brookfield viscosity of a 12.5% solution of the prepolymer in water was 1286 centipoise measured at 26 ° C.

A 12-liter reaction vessel was equipped with a stirrer, a 30 thermometer, a cooler and 3 addition funnels. The reaction vessel was filled with 2250 g of distilled water. One funnel was charged with 3500 g of styrene, another funnel was charged with 80 g of ammonium persulfate dissolved in 400 g of distilled water, and a third funnel was charged with 2200 g of an 8% aqueous solution of the above prepolymer. The water in the reaction vessel was heated to 78 ° C. The contents of the 3 funnels were added dropwise to the reaction vessel over a period of approx. 3 hours. During this period, the contents of the reaction vessel were kept at a temperature of from 80-95 ° C. The resulting latex, 46.8% solids, was cooled to room temperature (about 25 ° C).

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EXAMPLE 1B

Example 1A was repeated with the following exceptions: The prepolymer solution used was 2400 g of a 7.3% aqueous solution thereof, the ammonium persulfate solution consisted of 60 g of 5 ammonium persulfate dissolved in 250 g of distilled water and the resulting latex diluted with 1100 g of distilled water. producing a latex having a solids content of 39.5%.

EXAMPLE IC

Example 1B was repeated with the following exceptions: The initial container of distilled water of the reaction vessel was 3150 g instead of 2250 g, and the ammonium persulfate solution consisted of 48 g of ammonium persulfate dissolved in 200 g of distilled water. In this example, no additional water was added to produce latex as in Example 1B. The resulting latex had a solids content of 39.6%.

EXAMPLE ID

Example 1C was repeated with the following exception: The ammonium persulfate solution consisted of 46.4 g of ammonium persulfate in 210 g of distilled water. The resulting latex had a solids content of 41%.

EXAMPLE 1E

Example 1C was repeated with the following exception: The ammonium persulfate solution consisted of 38.4 g of ammonium persulfate in 160 g of distilled water. The resulting latex had a solids content of 41%.

EXAMPLE 2A

The latexes of Examples 1A, 1B, 1C, 1Dog1E were combined and a coating color was prepared from a portion thereof. To a 30 vessel equipped with a high shear stirrer, 26.5 kilograms of a 70% aqueous suspension of a clay pigment commercially available under Ultrawhite 90, 6.8 kg of a 2% aqueous solution of a water-soluble sodium carboxymethyl cellulose of medium viscosity (degree of substitution about 0.9) and 15.5 kg of a 47.7% polyethyl acetate latex binder. The pH of the resulting mixture was adjusted to 8.8 with concentrated NH 4 OH. 11.1 kg of the total latexes from Examples 1A-1E were added with high shear stirring. The pH was then adjusted to 8.5 with concentration 7

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NH4 OH. The total dry matter content of the resulting coating color was 56.4%. It is identified as coating color 3.

EXAMPLE 2B

Example 2A was repeated with the following exceptions: 11.6 kg of polyvinyl acetate latex binder was used instead of 15.5 kg and an additional 0.8 kg of water was added to produce a coating color with a dry solids content of 55.7%. This is identified as coating color 4.

10

EXAMPLE 2C

Example 2A was repeated with the following exceptions: 7.7 kg. polyvinyl acetate latex binder was used instead of 15.5 kg and an additional 1.5 kg of water was added to produce a coating color with a dry matter content of 56.9%. This is identified as coating color 5.

EXAMPLE 2D

To a vessel equipped with a high shear stirrer, 64.8 kg of an aqueous clay suspension as used in Example 2A, 4.6 kg of water, 6.8 kg of 2% aqueous solution of sodium carboxymethyl cellulose as used in Example 2A and 15.5 kg of a 47% polyvinyl acetate latex binder as used in Example 2A. The pH of the resulting mixture was adjusted to 8.5 with concentrated NH 3 OH. This coating color, identified as coating color 1, had a dry matter content of 55.8%.

EXAMPLE 2E

Example 2D was repeated with the following exceptions: The amount of aqueous clay suspension added was 58.3 kg, the amount of added water was 1.6 kg, the amount of added polyvinyl acetate latex binder was 15.5 kg, and 9.4 were also added to this mixture. kg of a 48% aqueous dispersion of organic polystyrene pigment. This coating color, identified as coating color 2, had a dry matter content of 55.9%.

Table I below shows pigment, sodium carboxymethyl cellulose and binder composition of the above coating colors.

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TABLE 1

Pigment Polyvinyl - (parts by weight) acetate -

5 Coating Poly Example Binder CMC J

clay color Clay styrene 1A-1E (parts by weight) (parts by weight) 1 100 - 16 0.3 2 90 10 - 16 0.3 3 90 - 10 16 0.3 10 4 90 - 10 12 0.3 5 90 - 10 8 0 , 3 (1) Sodium carboxymethyl cellulose used as viscosity enhancing additive.

15

Each coating color was applied to a commercially obtainable "50-lb". cardboard commodity using the blade coating on a pilot coating machine. Various tests were performed on the coated paper. Tests for lightness, opacity and whiteness were performed on 20 unglazed, coated paper. All other tests were performed on coated sheets of paper which had been glossed by passing the coated paper through a heated calender (71 ° C) 4 times (4 presses) at 2625 N / cm roll slot (1500 µl). These tests and the results are given in Table II below.

25 30 35

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EXAMPLE 3

A 1-liter water jacket resin boiler was provided with a stirrer, a thermometer, a cooler and 3 addition funnels. One funnel was charged with a solution of 97.5 g of acrylamide dissolved in 390 g of distilled water, the second funnel was charged with a solution of 2.5 g of acrylic acid dissolved in 10 g of distilled water, and the third funnel was charged with 2.5 g of ammonium persulfate. dissolved in 47.5 g of distilled water. The resin kettle was charged with 117 g of distilled water and heated to 85 ° C-87 ° C under nitrogen supply. The contents of the three funnels were added dropwise to the 10 resin kettle over a period of 2 3/4 hours to produce a prepolymer solution. The prepolymer was the 97.5% acrylamide-2.5% acrylic acid copolymer. The RSV value of the prepolymer was 0.34 (0.1M NaCl, 1%, 25 ° C). The prepolymer had an RSV value of 0.29 measured in a 1% solution in 1M NaCl at 25 ° C (1M NaCl, 1%, 25 ° C). The prepolymer solution 15 had a solids content of 15.8% by weight. This prepolymer was diluted with distilled water to a 10% solids content.

A 1-liter resin boiler with water jacket was provided with a stirrer, a thermometer, a cooler and 2 addition funnels. The boiler was charged with 163 g of the above 10% prepolymer solution and 20,326 g of distilled water. A funnel was charged with 327 g of styrene and it

second with 8.6 g of ammonium persulfate dissolved in 34.5 g of distilled water. The boiler content was heated to 85 ° C with circulating hot water in the water jacket. The contents of the two funnels were added dropwise to the resin boiler over a period of 2½ hours. After the addition was complete, the contents of the resin kettle were stirred for 15 minutes at 89-91 ° C.

followed by cooling to room temperature. The resulting latex was filtered through a 100 mesh screen. The resulting latex contained a small amount of aggregate and to break this aggregate the latex was passed through a hand homogenizer. The latex had a solids content of 41%, 30 and the particles had a particle size of 0.6 microns. Particle size was determined from turbidity readings according to the method of A.B.Loebel (Official Digest, 200, February, 1959). The latex was mixed with a glyoxal amount equivalent to the amount of acrylamide used to prepare the prepolymer.

EXAMPLE 4

Three coating colors were produced. These coating colors are identified as coating colors 6, 7 and 8. These coating colors were prepared by perfect blending of the components shown in Table 5 11

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III using high shear shaking. pH adjustments are also shown in the table. In the table, "g" means grams.

10 15 20 25 30 35 12

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TABLE Hl

Coating color 6 7 8 5 Example 3 latex composition - - 61 g

Polystyrene pigment (48% aqueous dispersion) - 52 g of 10 CMC ^ (3% aqueous solution) 13.3 g 13.3 g 13.3 g

Polyvinyl acetate latex binder (47.7% dry matter) 51.9 g 51.9 g 51.9 g 15

Distilled water 25.3 g 9 g

Clay pigment (70% aqueous dispersion) 178.6 g 142.8 g 142.8 g pH adjusted with concentrated NH 4 OH to 9 9 9% dry matter 55.4 55.7 55.2 (1) CMC sodium carboxymethyl cellulose, water soluble, medium viscosity, degree of substitution approx. 0.9 - used as a viscosity enhancing additive.

30 35 13

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Table IV below shows compositions of pigment, sodium carboxymethyl cellulose and binder in the above coating colors.

TABLE IV

Pigment Polyvinyl (parts by weight) acetate-1 ')

Coating Poly- Particle Binder CMC

color of clay Styrene from Ex.3 (parts by weight) (parts by weight) 10 6 100 - 20 0.3 7 80 20 - 20 0.3 8 80 20 20 0.3 (1) Sodium carboxymethyl cellulose - used as a viscosity-increasing additive.

Each coating color was applied to the felt side of a "55-lb. Paper base stock" using the Meyerstang. The coated sheets were dried in an oven with air circulation at 100 ° C for 45 seconds. In the case where the paper was coated with coating color 6, all samples except gloss (which was performed as shown) were performed on the coated sheets of paper which had been calendered by passing the coated sheets through a heated calender (71 ° C ) 4 times (4 nip) at 438 N per cm roller slot. In the cases where the paper was coated with coating colors 7 and 8, all tests except gloss (which was performed as shown) were performed on the coated sheets of paper which had been calendered by passing the coated sheets through a heated calender (71 ° C) 4 times (4 nips) at 438 N cm roller slot.

30 35 14

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EXAMPLE 5

A 10% solution of a water-soluble prepolymer was prepared by dissolving 43.7 g of poly (acrylamide) in 393.1 g of distilled water. Poly (acrylamide) had an RSV value of 0.45 (1M Nacl, 1%, 25 ° C).

A 1 liter resin boiler with water jacket was provided with a stirrer, a thermometer, a cooler and 3 addition funnels. The kettle was charged with 108.8 g of the prepolymer solution and 986 g of distilled water. One funnel was charged with 436 g of styrene, the second funnel was charged with 328 g of the prepolymer solution, and the third funnel was charged with a solution of 12 g (NH 4 SgOg) dissolved in 48.4 g of distilled water.

The boiler content was heated to 85-86 ° C (under a layer of nitrogen) by recirculating hot water in the jacket. The contents of each funnel were added three times to the boiler over a period of 2 hours. Additional catalyst, 1 g (NH 2) 2 S 2 O 2 dissolved in 4 g distilled water, was added to the resin boiler to complete the polymerization. The resulting latex, after filtration through a 100 mesh screen, had a solids content of 25.6% and the latex particles had a particle size in the range of 0.5 to 0.8 microns. Particle size was measured by transmission electron microscopy.

EXAMPLE 6

A 1-liter resin boiler with water jacket was provided with a stirrer, a thermometer, a cooler and 2 addition funnels. The boiler was charged with 1854 g of a prepolymer solution and 3685 g of distilled water. The prepolymer solution was an aqueous solution of a 97.5% acrylamide-2.5% acrylic acid copolymer. The solution contained 10% by weight of the prepolymer and the prepolymer had an RSV value of 0.39 (1M NaCl, 1%, 25 ° C). One funnel was charged with 3532 g styrene and 176.6 g divinylbenzene. The second funnel was charged with a solution of 97.4 g ammonium persulfate dissolved in 390 g distilled water. The boiler content was heated to ca. 92-94 ° C under a nitrogen layer. The contents of each of the two funnels were added dropwise to the boiler over a period of 4 hours. The latex was stirred for 15 minutes after these additions were completed and then filtered through a 100 mesh screen. The latex had a solids content of 40%. Particle size was approx. 0.7 microns. Particle size 35 was determined from turbidity reading according to the method of A.B.Loebel (Official Digest, 200, February 1959).

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EXAMPLE 7

A 2-liter resin boiler with water jacket fitted with a cooler, two thermometers, 2 addition funnels, a burette, nitrogen introduction and mechanical stirrer, was charged with 986 g of distilled water, 5 108 g of a 10% aqueous solution of poly (acrylamide) having an RSV value of 0.45 (1M NaCl, 1%, 25 ° C). One funnel was charged with 328 g of a 10% solution of a poly (acrylamide) having the same RSV value as above, the second hopper was charged with 436 g of styrene and the burette was charged with a solution of 12 g of ammonium persulfate 10 dissolved in 48.4 g of distilled water.

The boiler content was heated to 85 ° C with recirculating hot water through the jacket. The contents of the two funnels and the burette were added three times to the boiler over a period of 2 hours. An exotherm was observed after ca. 90 minutes and was easily controlled by cooling.

After the addition was complete, the prepared latex was stirred for 15 minutes. A slight styrene odor was detected and 1 g of ammonium persulfate dissolved in 4 g of distilled water was added to complete the polymerization.

The latex was filtered through a 100 mesh screen. The recovered 20 latex had a solids content of 25.6%. The latex was concentrated to 38.4% solids. The latex particles had a particle size in the range of 0.5-0.8 microns measured with a Coulter Counter.

The aforementioned latex was reacted with glyoxal as follows: 599 g of the latex having 38.4% solids was placed in a reaction flask, and the pH was adjusted from 1.6 to 9.0 by 50 ml of 1M NaOH.

85.5 g of a 40% aqueous solution of glyoxal was added to give a pH of 5.7. The pH was re-adjusted to 8.8 with 1M NaOH. Sufficient water was added to the reaction mass to give 29.7% reaction solids. The latex was stirred for 55 minutes at which time a visible increase in viscosity was observed. The pH was adjusted from 7.9 to 3.0 with 2 ml of concentrated hydrochloric acid.

EXAMPLE 8

A 97.5% acrylamide-2.5% acrylic acid copolymer was prepared.

The copolymer had an RSV value of 0.34 (0.1M NaCl, 1%, 25 ° C). A 2-liter resin skull with water jacket equipped as in Example 7 was charged with 217 g of distilled water and 108.8 g of a 10% aqueous solution of the above copolymer. One funnel was charged with 218 g styrene and the second funnel was charged with 5.7 g ammonium persulfate dissolved in 23 g 17

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distilled wand. The boiler content was heated to 86 ° C by recycling hot water through the jacket. The contents of the two funnels were added to evidence over a period of 2.5 hours. An exotherm was observed after 1.75 hours which was easily controlled by cooling. The 5 ilatex produced was filtered through a 100 mesh screen. The latex had a solids content of 41.1%. The particles had a particle size of 0.64 microns. Particle size was measured from turbidity reading according to the method of A.B.Loebel (Official Digest, 200, February, 1959).

EXAMPLE 9

A latex was prepared according to the procedure of Example 8 except that the copolymer used was a 90% acrylamide-10% acrylic acid copolymer having an RSV value of 0.44 (0.1M NaCl, 1%, 25%). ° C). The latex had a solids content of 41.1%. The particles have a particle size of 0.62, determined in the same manner as in Example 8.

Example 10 264.1 g of the latex of Example 8 was mixed with 49.2 g of a 40% aqueous solution of glyoxal (19.7 g of glyoxal). The resulting 20 aqueous solution had a solids content of 41%.

EXAMPLE 11 249 g of the latex of Example 9 was mixed with 42.5 g of a 40% aqueous solution of glyoxal (17.1 g of glyoxal). The resulting aqueous solution had a solids content of 41%.

EXAMPLE 12

Four coating colors were produced. These coating colors are identified as coating colors 9, 10, 11 and 12. These 30 coating colors were prepared by thoroughly mixing the components shown in Table VI. pH adjustments are also shown in the table. Each coating color was applied to the felt side of a "55-lb paper base stock" using a Meyer rod. The coated sheets were dried in an oven with air circulation at 100 ° C for 45 seconds. The coated sheets were calendered by passing them through a heated calender (71 ° C) at 1310 N / cm roll slot. Gloss measurements shown in Table VII were performed on sheets passed through the calender 2 times (2 nip), 3 times (3 nip) and 4 times (4 nip). In the case where the paper is coated with coating color 10, all tests are done after the coated sheets are 18

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passed through the calendar 4 times (4 nips). In the case where the paper is coated with coating colors 9 and 12, all other tests are performed after passing the coated sheets through the calender 3 times (3 nips). In the case where the paper is coated with coating color 11, all other 5 tests are performed after the coated sheets are passed through the calender twice. The experimental results are shown in Table VII.

TABLE VI

Coating color 9 10 11 12 10

Example 10 latex composition 61 g -

Example 11 iatex composition 61 g

Polystyrene pigment (48% aqueous dispersion) - - - 52 g 20 CMCC (3% aqueous solution) 13.3 g 13.3 g 13.3 g 13.3 g

Polyvinyl acetate latex binder (47.7% dry matter) 52.4 g 52.4 g 52.4 g 52.4 g Distilled water 2.1 g 2.1 g 27.3 g 11/1 g

Clay pigment (70% aqueous dispersion) 142.8 g 142.8 g 178.6 g 142.8 g 30 Initial pH 3.6 3.7 4.8 5.0 pH adjusted with concentrated NH 4 OH to 9.0 9 , 0 9.0 9.0 1 35 CMC sodium carboxymethyl cellulose, water soluble, medium viscosity, degree of substitution approx. 0.9, used as a viscosity enhancing additive.

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EXAMPLE 13

A 1-liter water jacket resin boiler was equipped with a stirrer, a thermometer, a cooler and 3 addition funnels. The boiler was charged with 2.5 g of water-soluble sodium carboxymethyl cellulose of low viscosity and degree of substitution approx. 0.7 and 300 g of distilled water. The funnels were charged with 250 g of styrene, 2.4 g of sodium formaldehyde sulfoxylate in 50 g of distilled water and 3.4 g of 70% tert-butyl hydroperoxide in 50 g of distilled water. The boiler content was heated to 73 ° C by recycling hot water in the jacket. To the boiler were added 10% of styrene and 20% of 10 each of the catalyst solutions. When there was evidence of latex formation (about 10 minutes), the rest of the funnel contents were added dropwise over a period of 3 hours. The yield was 566.7 g of a white latex containing 38.5% dry matter. The product had a 60 r.p.m. Brookfield viscosity of 370 cps. and an average particle size (method according to Loebel, Official Digest, 200, February, 1959) of 0.35 microns.

EXAMPLE 14

A 1-liter water jacket resin boiler was equipped with a stirrer, a thermometer, a cooler and 3 addition funnels. One funnel 20 was filled with a solution of 90 g of acrylamide dissolved in 360 g of distilled water, the second funnel was filled with a solution of 10 g of acrylic acid in 40 g of distilled water and the third funnel was filled with 3.75 g of ammonium persulfate dissolved in 71 g of distilled water. The resin kettle was charged with 195 g of distilled water and heated to 86-89 ° C under nitrogen.

The contents of the 3 funnels were added dropwise to the resin boiler over a period of 2 hours, followed by heating the reaction mass to 88.5-90 ° C for 15 minutes. The copolymer solution was cooled to room temperature. The RSV value of the copolymer was 0.38 (1M NaCl, 1%, 25 ° C). Total solids were 14.2%. This prepolymer was diluted with distilled 30 water to 10% solids content.

A 2-liter water jacket resin boiler was provided with a stirrer, a thermometer, a cooler and 2 addition funnels. The boiler was charged with 108.8 g of the above 10% prepolymer solution and 217 g of distilled water. One of the hoppers was charged with 218 g of styrene and the other 5.7 g of ammonium persulfate dissolved in 23 g of distilled water. The boiler content was heated to 86.5 ° C by circulating hot water through the jacket. The contents of the two funnels were added dropwise to the resin boiler over a period of 2½ hours. After the addition was complete, the contents of the resin kettle were stirred for 15 minutes at 21

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88-90 ° C, followed by cooling to room temperature. The resulting latex was filtered through a 100 mesh screen. No grains were isolated. The resulting latex had a solids content of 41.5% and a particle size of 0.7 microns (method of Loebel, Official 5 Digest, 200, February, 1959).

EXAMPLE 15

A portion of the latex prepared in Example 14 was treated with glyoxal as follows: 180.8 g of the latex was placed in a beaker. Glyoxal, 12.6 g of a 40% aqueous solution (5.02 g of glyoxal), was added. The resulting pH was 1.8 and total solids were 41.4%. The reaction with glyoxal was carried out by taking 100 g of the aforementioned latex-glyoxal mixture, adjusting the pH from 1.8 to 8-8.5 with 5M NaOH, stirring for 15 minutes, diluting to 10% dry matter and adjusting the pH value to 2 with concentrated sulfuric acid.

EXAMPLE 16

The compositions of Examples 14 and 15 were evaluated as fillers ten! paper. Handmade sheets were manufactured on a Noble & Wood 20 handmade sheet metal appliance. The pulp consisted of a 50:50 blend of bleached hardwood pulp: bleached softwood pulp that was turned to a Canadian standard free condition of 500 cm. The paper was prepared at a pH of 4.5 (1% alum). The latexes were assessed at addition levels of 4% and 8% (on a dry basis) using 0.05% of a high molecular weight cationic pdlyacrylamide as a retention aid. The results of the paper test are summarized in Table VIII below. The results given are averages of test results obtained with 4 sheets of paper.

TABLE VIII

30 Dry Break- Blast-

Gram Weight Strength Strength

Filler (g / m2) (N / cm) kPa visibility

Ex. 14 (4%) 67.2 33.6 219 86.3 (8%) 68.2 31.7 185 88.2 35

Ex.15 (4%) 67.7 32.0 224 86.4 (8%) 69.0 31.9 200 88.4 (1) TAPPI Standard T-425 (Hunter Opacity Meter) 22

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EXAMPLE 17

A reaction vessel was charged with 506.2 kg of demineralized water and 175.2 kg of a prepolymer solution. The prepolymer solution was an aqueous solution of a 97.5% acrylamide-2.5% acrylic acid copolymer.

The solution contained 13% by weight of the prepolymer and the prepolymer had an RSV value of 0.44 (1M NaCl, 1%, 25 ° C). The contents of the reaction vessel were heated to ca. 89 ° C and over a period of 4 hours was slowly and simultaneously added (1) a mixture of 431.3 kg styrene and 22.7 kg divinylbenzene and (2) a solution of 12 kg ammonium-10 persulfate dissolved in 48.1 kg demineralised water. The resulting latex was stirred and filtered to remove agglomerates. The latex had a solids content of 39.3%. Particle size was approx. 0.52 microns determined by turbidity measurement according to the method of A.B.Loebel (Official Digest, 200, February 1959).

EXAMPLE 18

Two coating colors were produced. The coating colors are identified as the coating colors 13 and 14. The coating colors were prepared with thorough mixing of the components shown in Table X.

20 pH adjustments are also shown in the table. Each coating color was applied to the felt side of a "55-lb paper base stock" using a Meyer rod. The coated sheets were dried in an oven with air circulation at 100 ° C for 45 seconds. The coated sheets were calendered by passing them through a heated calender (71 ° C) at 1310 N 25 cm slit. Gloss determinations, shown in Table XI, were performed on sheets passed through the calendar 2 times (2 nip), 3 times (3 nip) and 4 times (4 nip). In cases where the paper was coated with coating color 13, all other tests were performed after the coated sheets were passed through the calender 2 times (2 nips). In the case where the paper was coated with coating color 14, all other tests were performed by passing the coated sheets through the calender 4 times (4 nips). The test results are shown in Table XI below.

35 23

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TABLE X

Coating Color 13 14 Example 28 Latex Composition 63.6 g CMC3 (3% aqueous solution) 13.3 g 13.3 g 10 Styrene-butadiene latex binder (50% dry matter) 50.0 g 52.3 g

Distilled water 19.5 g 45 g 15 Pigment (70% aqueous dispersion) 142.8 g 178.6 g

Initial pH 5.85 6.0 20 pH adjusted with concentrated NH 4 OH to 8.5 8.5 (1) CMC sodium carboxymethyl cellulose, water-soluble, medium viscosity, degree of substitution approx. 0.9, used as a viscosity enhancing additive.

30 35

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While the organic pigments of the present invention are particularly suitable for paper coatings, they can also be used as paper fillers. When used as pigments in paper coatings, they can be used alone or in combination with other organic pigments or in combination with inorganic pigments or in combination with inorganic pigments and other organic pigments.

When used in paper coatings in combination with inorganic pigments such as clay, the amount used will be from approx. 5% to 1D0% by weight of the inorganic pigment.

Further, the organic pigments of the present invention can be used in paints, inks and the like. Together with a suitable binder, they can also be applied as coatings on glass surfaces, metal surfaces, wood surfaces, gypsum surfaces, plastic surfaces and the like.

The organic pigments used in the present invention are essentially spherical graft copolymer particles. According to the present invention, graft copolymer particles may be prepared which will have a particle size in the range of about 0.1 microns to approx. 2 mi.

Particularly suitable water-soluble prepolymers for use in the preparation of graft copolymer particles of the present invention are (1) the homopolymers of α, β-ethylenically unsaturated amides, in particular poly (acrylamide) and poly (methacrylamide), and (2) copolymers of (a) from 98% by weight to approx. About 50% by weight of an α, β-ethylenically unsaturated amide, in particular acrylamide and methacrylamide, and (b) from ca. 2 to approx. 50% by weight of an α, β-ethylenically unsaturated acid, in particular acrylic acid and methacrylic acid, Podecopolymer particles, which are particularly suitable as organic pigments, either as paper fillers or as a component of a paper coating composition, derived from styrene pod copolymerization or a mixture of styrene and divinylbenzene and a homopolymer (1) or copolymer (2) as described above. Also, graft copolymer particles having reactive groups on the surface thereof, as described above, are also particularly suitable for use as organic pigments.

Binders used in the preparation of coating compositions of the present invention will be non-solvent for the organic pigments and are adapted for use in paper coating processes to produce a sticky, smooth, glossy layer. Suitable binders are well known in the art and include the natural binders and 26

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synthetic binders. Suitable natural binders include starch, soybean protein and casein. Modified starch binders such as oxidized, enzyme-converted and hydroxyethylated starch can be used. Suitable synthetic binders are styrene-butadiene copolymer latexes and 5 polymer latexes of alkyl esters of α, β-ethylenically unsaturated acids such as the acrylic acrylates and methacrylates, and copolymers thereof with a small amount of a copolymerized ethylenically unsaturated carboxylic acid. Other suitable binders are the copolymer latexes of butadiene and acrylonitrile, copolymer latexes of vinyl acetate and the alkyl acrylates, copolymer latex1 of butadiene and methyl methacrylate, copolymer latexes of vinyl chloride and vinylidene chloride, latexes of vinyl chloride copolymer polybutadiene, polyvinyl acetate and poly vinylal carbon.

The amount of binder used to prepare 15 coating compositions for use in the practice of the present invention is the amount that binds the pigment component thereof to the coated paper substrate so that the pigment is not removed from the coated paper during normal handling or under further processing. such as printing. One skilled in the art can determine the amount of binder to be used. The binder used will usually be in the range of approx. 2 volume parts for approx. 30 parts per volume 100 parts by volume of the pigment used.

25 30 35

Claims (5)

A paper product containing organic particles as a coating or filler, which organic particles have a size of 5 from 0.1 to .2 µm and are water-insoluble copolymer particles consisting essentially of the free radical-catalyzed copolymerization product of (1) at least one ethylenically unsaturated monomer and (2) a water-soluble prepolymer having an RSV value of from 0.1 to 2.5 (1M NaCl, 1%, 25 ° C) where the prepolymer portion of the copolymer particles is present on the surface of the particles, characterized in that the monomer (1) is styrene or combinations of styrene and divinylbenzene, and the prepolymer (2) is made up of prepolymers prepared by addition polymerization of acrylamide or a mixture of acrylamide and an anionic or nonionic vinyl monomer. wherein the amount of prepolymer (2) used to prepare the copolymer particles is from 2 to 10 parts by weight per 100 parts by weight of the monomer used (1) and the copolymer has a Tg of 75 ° C or more Re. Paper product according to claim 1, characterized in that in combination with styrene, divinylbenzene is used in an amount which is at least sufficient to produce cross-linked copolymer particles. Paper product according to claim 1, characterized in that the prepolymer (2) is polyacrylamide. Paper product according to claim 1, characterized in that the prepolymer (2) is a copolymer of from 98% to 50% acrylamide and from 2% to 50% acrylic acid. Paper product according to any one of claims 1-4, characterized in that an aldehyde is chemically bonded to the prepolymer portion of the particles. 35