MXPA97008770A - Composition of brightness coating b - Google Patents

Abstract

The present invention provides a low gloss coating composition, having a sheet gloss at 75 ° of 50% or less, which is useful in improving the printing quality of inks applied to the low gloss coated substrate. This low gloss coating composition is particularly useful in increasing the difference in brightness, or delta gloss, between the coated substrate with the low gloss coating composition and the ink applied to the glossy coated substrate.

Description

LOW BRIGHT COMPOSITION COMPOSITION FIELD OF THE INVENTION The present invention relates to a low gloss coating composition useful for improving the printing quality of the inks applied on a substrate of this low gloss coating composition. BACKGROUND Obtaining good print quality on substrates coated with low gloss compositions, such as paper or cardboard, has been difficult. For example, it has been a problem to obtain an adequate difference between the gloss of the coating on the substrate and the brightness of the ink applied to the coated substrate. This difference in brightness between the ink and the coated substrate is named as a delta gloss. A large delta brightness helps the ink applied to the low gloss coated substrate to be visually emphasized. It has also been difficult when applying ink to a low gloss coated substrate, to obtain a uniform density and brightness of the ink in all areas of the substrate, where the ink is applied. These variations in the density and brightness of the ink on the substrate are referred to herein as "mottled". Another problem commonly encountered on low gloss coated substrates is that the ink applied to the substrate tends to penetrate the low gloss coating, resulting in poor ink gloss and delta gloss. The resistance of the coating composition to the penetration of the ink is referred to herein as "ink firmness". Such properties as the brightness delta, mottled, and firmness to the ink can be used to qualitatively and quantitatively measure the print quality. Low gloss coated substrates, where print quality problems occur, frequently include any coated substrate where the surface has a 75 ° sheet gloss of 50 percent or less. Substrates coated with low gloss include, for example, paper, cardboard, paper products used for newspapers, billboards, books or magazines; and construction substrates, such as wall paper, wallboard or ceiling tiles. In the paper industry, examples of substrates coated with low gloss include silk and matte and opaque paper grades. Others have tried to improve print quality on low gloss coated substrates through various techniques. For example, others have tried to improve print quality by formulating low gloss compositions with particular mixtures of clays, carbonates, especially pigments, such as talc or alumina; or with special binders, such as highly carboxylated styrene / butadiene latexes. Another approach has been the use of special glazing techniques to improve print quality. However, the improvements in print quality, particularly the brightness delta, with the use of these techniques, have tended to be smaller than those desired. U.S. Patent Nos. 5,283,129 to Renk et al., Hereinafter referred to as "Renk", discloses a low gloss coating composition for lightweight paper containing delaminated clay, calcined clay, bleaching pigment, starch binder, Starch and lubricant interlacing agent. Renk reveals that the whitening pigment can be partially replaced with hollow-core plastic pigments, primarily to increase the opacity of the paper. Although it is described that the plastic pigments also help to increase the brightness of the ink, experience shows, as detailed below, that the brightness delta is only slightly improved, because the plastic pigments also contribute to increase the brightness of the sheet of the coating composition in the glaze. U.A. Patent No. 5,510,422 to Blankenship et al., Later named "Blankenship", discloses the use of certain core and shell polymer particles, which contain at least one core phase having at least one gap, at least one cover phase enclosing the core and at least one channel, which connects the gap with the outside of the particles. These particles are described as being useful as opacifying agents in coatings. However, Blankenship discloses neither the use of these core and shell particles in the low gloss coating compositions nor the use of any coating composition to improve the delta gloss. It is convenient to provide a low gloss coating composition, which improves the printing quality of the ink applied to a substrate coated with the low gloss composition. This invention addresses this problem by incorporating in the low gloss compositions certain polymer particles having at least one opening from the outside to the interior of the particle. It is unexpected that these particles improve the print quality such as the brightness delta, in the low gloss composition. EXPOSITION OF THE INVENTION The present invention provides a low gloss coating composition, which comprises: one or more polymer particles and one or more pigments, wherein the polymer particles comprise at least one core phase of the polymer that it contains when less a hole; at least one cover phase of the polymer surrounding, at least partially, the core; and at least one channel connecting the gap in the core phase to the outside of the particle; wherein the coating composition comprises 1.0 part by weight up to 50 parts by weight of the polymer particles per 100 parts of the pigment, and wherein the coating composition has a sheet gloss at 75 ° of 50 percent or less. DETAILED DESCRIPTION The low gloss coating composition of the present invention has a sheet gloss at 75 ° of 50 percent or less; preferably from 7 to 50 percent, more preferably from 10 to 40 percent, and especially preferred from 15 to 35 percent. As used herein, "75o sheet gloss" means the gloss measured at a 75 ° angle to the sheet coated with the low gloss coating composition. By "polymer particles", we mean particles that have a certain morphology. The polymer particles contain at least one opening on the outside of the particle, which is connected to the interior of the particle by a channel. More particularly, the polymer particles contain at least one gap, at least one core phase, at least one cover phase and at least one channel, where the core phase surrounds the gap, the cover phase encloses, at least partially the core, and the channel connects the outside of the particle to the gap. By "non-broken polymer particles" or "swellable polymer particles" are meant the particles that can be modified to form the polymer particles useful in the present invention.The polymer particles are present in the low gloss coating composition in an amount of 1 part by weight to 50 parts by weight, more preferably 2 parts by weight to 20 parts by weight, and especially preferred 3 parts by weight to 15 parts by weight, based on 100 parts by weight of the pigment in The composition of the polymer particles can be prepared by emulsion polymerization techniques well known to those skilled in the art Sequence emulsion polymerization techniques are preferably used in multiple stages to form swellable polymer particles which are then they try to form the polymer particles useful in the present invention, for example, the particles of the polymer useful In the present invention, they can be produced by the method disclosed in the U.S. Patent No. 4,985,064. In this U. A. Patent, No. 4,985,064, the multi-stage polymer particles are swollen with a solvent. If the multi-stage particles contain a sufficient amount of acid or base, these particles, with suitable properties, such as cover thickness and cover permeability, will separate into phases under neutralization, to form the polymer particles. The polymer particles can also be produced from swellable polymer particles, which, when swollen, "break" to form voids and channels in the particles. Sequential emulsion polymerization techniques for obtaining these swellable polymer particles are described in the patents of U. U.A., Nos. 4,427,836, 4,920,160, 4,594,363, 4,469,825; and 4,468,498, 4,880,842, 5,157,845, 5,041,464, 5,036,109 and 5,409,776. These polymerization methods can be modified to form swellable polymer particles, which will break upon swelling, to thereby produce the polymer particles of the present invention. Preferably, the particles of the swellable polymer are formed by preparing at least one core of the polymer, which can be swollen, enclosing, or partially or completely with a swelling agent, which can permeate the shell and swell the core. This core swells in a controlled manner to form at least one hole in the core and "break" the particle so that one or more channels are formed to connect the gap to the outside of the particle. The swelling of the polymer particles to form the voids or channels can be done before or after adding the polymer particles to the low gloss coating composition. While the core phase of the polymer can be obtained in a single step or the step of the polymerization in sequence, and the phase of the polymeric cover can be the product of a single stage in sequence or the stage that follows the nucleus stage, the obtaining of the phase of the nucleus can involve a plurality of stages in sequence, followed by the obtaining of the phase of the polymer shell which may involve a series of stages in sequence as well. The molecular weight of the polymer formed in a given step can vary from 100,000 or less, if a chain transfer agent is used, to several million. The first step in obtaining the polymer particles useful in the present invention, may optionally be the preparation of a seed polymer containing small dispersed polymer particles, insoluble in the aqueous emulsion polymerization medium. This seeding polymer may or may not be inflatable and provide particles that form the nuclei in which the core phase is formed. The core phase of the polymer is preferably formed from the aqueous emulsion polymerization of one or more monoethylenically unsaturated monomers. Examples of suitable monoethylenically unsaturated monomers include styrene, vinyltoluene, ethylene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, acrylamide, methacrylamide, and various alkyls (cl ~ c2?) 'Hydroxyalkyls (C1-C20) Esters of (C3-C20) alkenyl of (meth) acrylic acid, such as methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, methacrylate of 2-ethylhexyl, benzyl acrylate, benzyl methacrylate, lauryl acrylate, lauryl methacrylate, palmityl acrylate, palmityl methacrylate, stearyl acrylate, stearyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylic acid, methacrylic acid , itaconic acid, aconitic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, acryloxypropionic acid, methacryloxypropionic acid, acryloxy acetic acid or, methacrylic anhydride, methacryloxyacetic acid, monomethyl acid maleate, monomethyl acid itaconate, monomethyl fumarate, or combinations thereof. As used herein, "(meth) acrylic" means both acrylic and methacrylic and "(meth) acrylate" means acrylate or methacrylate. (C1-C20) At least one core phase is inflatable using techniques known to those skilled in the art. Preferably, the core is susceptible to swelling through the use of an inflatable compound, which is incorporated into the core by techniques such as absorption, encapsulation or polymerization. For example, the swellable compound can be a functional monomer, which polymerizes as all or part of the core phase and which is susceptible to swelling. Functional monomers include, for example, the monoethylenically unsaturated compounds, which contain groups susceptible to neutralization such as acid or base, or groups susceptible to hydrolysis. The swellable compound can also be a non-polymerizable compound, which is incorporated into the polymer particles through techniques such as absorption or encapsulation, and is susceptible to neutralization or hydrolysis. Preferably, the amount of the swellable compound in the polymer particles should be at least 0.5 weight percent, more preferably 1 to 70 weight percent, based on the total weight of the uninflated polymer particles. When a functional monomer is used as the swelling compound, preferably the core contains at least 5 mole percent of the functional monomer, based on the total moles of the monomer in the core phase. More preferably, the core phase contains at least 10 molar percent; and especially preferred from 30 to 60 mole percent of a functional monomer, based on the total moles of the monomer in the core phase. Examples of functional monomers include acid-containing monomers, such as acrylic acid, methacrylic acid, itaconic acid, aconitic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, acryloxypropionic acid, methacryloxypropionic acid, acryloxyacetic acid, methacrylic anhydride, methacryloxyacetic acid, monomethyl acid maleate, monomethyl acid itaconate, monomethyl fumarate, vinyl sulphonic acid, acrylamidopropanesulfonic acid, or combinations thereof; monomers containing bases, such as vinyl pyridine, 2- (dimethylamino) ethyl (meth) acrylate, 2- (tere. -butylamino) ethyl (meth) acrylate, 3- (dimethylamino) propyl (meth) acrylamide 2- (diethylamino) ethyl (meth) acrylate; 2- (dimethylamino) ethyl (meth) acrylamide; or hydrolysable monomers, such as esters of alkyl (meth) acrylate (C-Cg), which include methyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-hydroxyethyl acrylate or vinyl esters , such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurate or vinyl decanoate, or combinations thereof. Preferably, the functional monomer is a functional monomer of an acid or a base, and more preferably is an acidic functional monomer.

If the swellable compound is a non-polymerizable compound, preferably the polymer particles will contain from 0.5 to 70 weight percent, more preferably from 1 to 30 weight percent and especially preferred from 5 to 20 weight percent of the non-polymerizable compound , based on the total weight of the polymer particles without swelling. Suitable non-polymerizable compounds include, for example, compounds containing a base or an acid, such as the carboxylic, aliphatic or aromatic Cg-C? 2f acids or the aliphatic or aromatic Cg-Ci2 amines, and the hydrolyzable compounds. The core phase, if obtained by a one-step process or a process involving several steps, preferably has an average particle size of 20 to 1000 nanometers and more preferably 100 to 500 nanometers in the non-bloated condition. If the core is obtained from a sow polymer, this sowing polymer preferably has an average particle size in the range of 20 to 200 nanometers. After obtaining the core phase, a step or more subsequent steps of the emulsion polymerization is performed to form a shell phase of the polymer in the core phase. The cover phase encloses or surrounds, at least partially, the core phase. Preferably, the cover phase completely surrounds the core phase. One or more monomers are polymerized to form the cover phase on the core phase. Preferably, the monomers are any of these monoethylenically unsaturated monomers, mentioned above, to obtain the core phase. More preferably, the cover phase comprises one or more of alkyls (C-C2?) Hydroxyalkyls (C-C2?) Esters of (C3-C20) alkenyls of (meth) acrylic acid. It is also more preferable that the cover phase be a copolymer containing two or more different monomers. The amount and type of polymerized monomer in the shell phase will allow the core to swell and allow the shell to form the channel connecting the gap to the outside of the particle with swelling. The cover phase will preferably have a glass transition temperature (Tg) of -40 to 105 ° C, more preferably of -10 to 105 ° C and especially preferred of 35 to 80 ° C. The polymer particles, in an unswollen state, preferably have a weight ratio of the core polymer to the shell polymer of 1: 1 to 1:20, preferably 1: 1 to 1:10 and more preferably 1: 2. up to 1: 8 Monomeric mixtures to obtain the shell phase also preferably contain less than 15 mole percent and more preferably 0.1 to 8 mole percent of the functional monomer, based on the total moles of the monomer in the shell phase. The presence of some functional monomer in the shell phase promotes the permeability of the shell to the swelling agent. Any of the polymer steps may optionally contain polyethylenically unsaturated monomers, such as ethylene glycol di (meth) acrylate, allyl (meth) acrylate, diethylene glycol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane trimethacrylate, or divinylbenzene. The amount of the polyethylenically unsaturated monomers is preferably 0 to 15 molar percent and more preferably 0 to 3 molar percent, based on the total moles of the monomer in the polymer stage. The average particle size of the polymer after swelling is 100 to 4500 nanometers, preferably 150 to 2500 nanometers and more preferably 200 to 2000 nanometers and especially preferred 300 to 1500 nanometers. The water uptake of the polymer particles is preferably 0.1 to 4.0 grams of water per gram of the polymer particles and more preferably 0.2 to 3.0 grams of water per gram of the polymer particles.

Once formed, the particles are swollen by contact with the swelling agent. Depending on the type and amount of the swelling compound in the core, the exposure time of the swelling agent is 0.5 to 24 hours. This swelling agent causes the core to swell to form at least one void in the core phase and one or more channels connecting the void to the outside of the particle. During the swelling step, it has been found that the polymer particles can be efficiently formed if the concentration of the particles in the aqueous medium is preferably 15 to 25 weight percent and more preferably 15 to 25 weight percent. It is preferred that the amount of the swelling agent added be sufficient to completely neutralize or hydrolyze, as the case may be, the swelling compound in the core phase. The selected swelling agent must be able to interact with the swelling compound to swell the core. If the core is completely surrounded by the shell polymer, the swelling agent must also be capable of permeating the shell either independently or in the presence of another compound, which aids in permeation. For example, if an acid functional monomer or a non-polymerizable acid compound is incorporated into the core, an organic or inorganic base can be used to swell the core. If a base functional monomer or a non-polymerizable base compound is incorporated into the core, an organic or inorganic acid can be used to swell the core. If a hydrolysable functional monomer or a non-polymerizable hydrolysable compound is incorporated into the core, an aqueous inorganic acid or base can be used to swell the core. Examples of swelling agents that can be used include any base in a gaseous or aqueous medium, such as ammonia, amines, sodium hydroxide, potassium hydroxide, lithium hydroxide or combinations thereof; or acids in a gaseous or aqueous medium, such as formic acid, acetic acid or combinations thereof. Factors that can affect the swelling and formation of the polymer particles include, for example, cover thickeners, "softeners" of the shell, the amount of the swelling compound in the core, the permeability of the shell to the swelling agent, and the time and temperature of exposure of the particles to the swelling agent. These variables can be altered to promote swelling and formation of the gap and channel within the polymer particle. For example, if the glass transition temperature (Tg) of the core or shell is above normal ambient temperature, it may be necessary to heat the polymer particle above its Tg or add a solvent to soften the polymer particles and effect the swelling Also, as the amount of the swelling compound is increased in the core, less time will be needed to inflate the particles. If the amount of the swelling compound is low in the core, the temperature during swelling can be increased to facilitate this swelling. The degree of swelling is also dependent on the hardness of the cover since, as the hardness increases, it will be more difficult to inflate the polymer particles. In a preferred embodiment of the invention, the polymer particles are formed by the method disclosed in the patent of E. U. A., No. 5,510,422 of Blankenship et al. These particles are produced by forming a core containing an acidic functional monomer, which completely encapsulates the core in the shell polymer, which is permeable to the basic swelling agent, and the contact of the resulting polymer particle with a basic swelling agent. , watery or gaseous, to form a hole and break the particles in a controlled manner. In this preferred embodiment, the core phase contains at least 5 mole percent, more preferably at least 10 mole percent and especially preferred 30 to 60 mole percent acidic acid monomer, based on the total moles of the monomer in the core phase.

Preferred acid functional monomers are acrylic acid, methacrylic acid, maleic acid, maleic anhydride or vinyl sulphonic acid. In addition to the specially shaped polymer particles, the low gloss coating composition contains pigments. The type and amount of the pigment is selected to provide a formulation having a 75 ° sheet gloss of 50% or less. The pigment in the coating composition imparts to the coating such properties as softness, low gloss, brilliance and opacity. The pigment is preferably added to the coating composition at a level of 70 parts by weight to 99 parts by weight, more preferably from 80 to 90 parts by weight per 100 parts of the dry coating composition. The pigment is preferably inorganic such as clays, which vary from fine to coarse in their particle size; calcined clay; carbonates, such as ground or precipitated calcium carbonate, titanium dioxide; pigments, especially of low gloss, such as talc, silica, aluminum silicate, hydrated alumina, aluminum trihydrate; or their combinations. Preferred pigments are clays, carbonates or combinations thereof. The low gloss coating composition may also contain other components, such as binders, solvents, water and other additives common to low gloss coating compositions. The amounts and types of components and additives are selected according to techniques well known to those skilled in the art, to provide a composition having a sheet gloss at 75 ° of 50 or less. The binder is typically added to the low gloss coating composition to provide adhesive and cohesive strength. The binder is preferably added to the coating composition in an amount of 4 to 30 parts by weight, more preferably 6 to 25 parts by weight and especially preferred of 7 to 21 parts by weight, based on 100 parts of pigment in the coating composition. The binder can be natural or synthetic. Natural binders include, for example, starch, modified starch, casein or soy protein. Synthetic binders include, for example, the homopolymers or copolymers of ethylene, vinyl alcohol, vinyl acetate, styrene, (meth) acrylic acid, butadiene or esters of C 1 to C 2 'alkyl (meth) acrylates "carboxymethyl cellulose; Combinations Preferred binders include styrene-butadiene copolymers, styrene and acrylic acid, ethylene and vinyl acetate, and vinyl alcohol and vinyl acetate.

The coating composition preferably contains water, solvent or combinations thereof. The water or solvent is preferably added in an amount to supply 40 to 80 weight percent, more preferably 45 to 75 weight percent, and especially preferred 50 to 70 weight percent solids, based on total weight of the composition. Solvents that can be used in the coating composition include, for example, aliphatic or aromatic hydrocarbons, aliphatic or aromatic alcohols. Examples of solvents include hexane, pentane, hexanol, pentanol, xylene, toluene, benzene, mineral spirits and combinations thereof. Although the coating composition can be formulated using solvents, it is preferable that this coating composition be aqueous. The coating composition may optionally contain other additives well known to those skilled in the art, such as dispersing agents; optical brighteners; insolubilizers; opacity agents, rheology modifiers; lubricants; defoamers; corrosion inhibitors; agents against irrigation; agents that adjust the pH; regulatory agents; antioxidant agents; or their combinations. These optional additives typically comprise from 0.01 to 10 parts by weight per 100 parts by weight of the pigment in the coating composition. The low gloss coating composition is obtained by techniques well known to those skilled in the art. Preferably, a pigment dispersion is prepared, followed by the addition of the binder, polymer particles and other additives, to achieve the desired solids, pH and viscosity. In one embodiment of the present invention the unswollen or unbroken polymer particles can be added to the low gloss composition, before being modified, to form gaps and channels in the particles. For example, unswollen polymer particles can be added to the composition and then contacted in the composition with a swelling agent, to form voids and channels in the particles. The unruptured polymer particles, which have partially swollen, can also be added to the composition and then contacted in the composition with a swelling agent to form polymer particles. The low gloss coating composition is useful for improving the print quality of the ink applied to the low gloss composition. By "ink" is meant any coating applied to the low gloss composition, which is different from the low gloss coating composition, which include coatings such as varnishes and paints. Printing properties that can be improved include, for example, delta gloss, ink firmness, or mottling. Preferably, the polymer particles provide a change in the brightness delta (brightness delta?) Of the composition not containing polymer particles of at least 2.0, more preferably at least 2.5 and especially preferred at least 3.2 The coating composition of Low gloss can be applied to substrates that need a low gloss surface. Preferably, the ink is then applied to portions of the coated substrate. For example, the ink can be printed on the coated substrate to form images, such as words or illustrations. Substrates that can be coated include, for example, paper, cardboard, paper products used for newspapers, advertisements, posters, books or magazines; and construction substrates, such as wall paper, wallboard or roof slabs. Preferably, the low gloss coating is used to coat paper, cardboard or paper products. The amount of the low gloss coating composition applied to the substrate is generally from 0.15 to 45 g / m2, more preferably from 1.5 to 30 g / m2 and especially preferred from 3.0 to 21 g / m2.

The low gloss coating composition can be applied to the substrate by techniques well known to those skilled in the art. For example, the coating may be printed, sprayed or applied with a roller applicator, a sheet coater, an air knife, a bar coater, or a brush.

EXAMPLES Some embodiments of the invention will now be described in detail. In the examples, particle size measurements were obtained using a Brookhaven BI-90 Particle Sizer, which employs the light scattering technique. The brightness of the sheet and the brightness of the print were measured at an angle of 75 °, using a Technidyne T480 Glossmeter gloss meter, supplied by Technidyne, located in New Albany, Indiana. The test method for measuring brightness was the Tappi Test Method T-480, published in "Tappi Test Methods 1994-1995" by Tappi Press, located in Atlanta, Georgia. Also, in the examples, the amount of the core acid issued and the water uptake of the particles at the break, were measured by centrifuging about 30 grams of the polymer particles neutralized with a Sorval top-table centrifugal machine at 8,000 RPM during 1.5 hours The supernatant fluid was separated, emptied and weighed. Also the weight of the particles of the centrifuged polymer was obtained. The supernatant fluid was titrated with 0.5N HCl, with the use of a Radiometer Automatic Titrator device, to determine the ejected core acid. The core acid expelled (pKa from around 6. 5) was calculated by Equation 1: ml of Title x Acid 0.5N% of expelled core acid = [] x 100 (theoretical meq of acid) xg of solids Equation 1 where "theoretical acid meq" is the theoretical milliequivalence of the acid in the nucleus in 1 gram of polymer particles, "g of solids" are the grams of polymer solids, after centrifuging. The water uptake of the polymer particles is calculated by Equation 2: (((g of sample - g of envelope) - g solids) - (0.4 x g of solids)) Water uptake = g of solids Equation 2 where: "g of sample" are the grams of the centrifuged sample, "g of envelope" are the grams of the supernatant liquid, "g of solids" have the same meaning as in Equation 1. The value of 0.4 in Equation 2 it is an approximation of the correction for the interstitial water in the stopper. This was determined separately in a polymer of similar composition and particle size. The following abbreviations are used in the Examples: Table 1 - Abbreviations Example 1 - Core Synthesis A 5 liter flask, equipped with paddle stirrer, thermometer, nitrogen inlet and reflux condenser, was charged with 1700 grams (g) of deionized water (DI water). The water was heated to 85 ° C under a nitrogen atmosphere. Then 82 grams of a monomer emulsion was added to the flask. This monomer emulsion was prepared from 335 g of DI water, 3.5 g of sodium dodecylbenzenesulfonate, 23% of active ingredient (SDS), 364.5 g of methyl methacrylate and 4.35 g of methacrylic acid. After stirring the kettle for 5 minutes at 80 ° C, a solution of sodium persulfate of 2.75 g of sodium persulfate dissolved in 15 g of deionized water was added to the flask. The temperature of the reaction mixture was allowed to rise to 1 or 2 ° C. To the previously prepared monomer emulsion, 7 g of SDS and 241 g of methacrylic acid were added. Ten minutes after the addition of the sodium persulfate solution to the flask, a linear stepwise addition of the remaining emulsion of monomers over 2 hours was started. The temperature was maintained at 80 ° C during the addition of the monomer emulsion. Twenty minutes after completing the addition of monomers, the mixture was cooled to 25 ° C. The polymer was filtered through a 100 mesh screen. The filtered polymer dispersion had a pH of 3.1, 22.27 weight percent solids and an average particle diameter of 330 nm.

Example 2 - Synthesis of the Polymer Particles, Ratio in Weight of the Core to the Cover of 1: 2 To a 5-liter flask, equipped with paddle stirrer, nitrogen inlet, reflux condenser and thermometer, was added 400 grams of water DI and 1526.7 grams of the core obtained in Example 1. The mixture was heated to 60 ° C under a nitrogen atmosphere and then 20 grams of an iron sulphate solution (0.15 weight percent active) was added, followed by the addition of 1.2 grams of sodium persulfate dissolved in 100 grams of DI water. An emulsion of monomers of 200 grams of DI water, 6 grams of SDS, 272 grams of ethyl acrylate, 397.8 grams of methyl methacrylate and 10.2 grams of methacrylic acid were gradually added to the flask at a rate of 2.2 grams per minute. . Concurrently with the addition of the monomer emulsion, a solution of 2.8 grams of sodium bisulfite in 200 grams of DI water, and a separate solution of 2.6 grams of sodium persulfate dissolved in 200 grams of DI water were gradually added; each solution was added at a rate of 2.2 grams per minute. After 10 minutes in the monomer emulsion charge, this monomer emulsion charge was increased to 4.4 grams per minute, after twenty more minutes, the charge rate of the monomer emulsion was increased to 11.7 grams per minute. The temperature of the reaction mixture was maintained at 60 ° C through the addition of the monomer emulsion. Upon completion of the charges, the reaction mixture was kept at 60 ° C for fifteen minutes and then cooled to room temperature and filtered through a 100 mesh screen. The polymer product had 30.5 weight percent solids and an average particle size of 475 nm. The product of the resulting polymer was swollen and "broke" by mixing 200 grams of the polymer product with 7.44 grams of ammonia (28 weight percent active) and 97.56 grams of deionized water. Half of this mixture was heated at 60 ° C for one hour and the other half was kept at room temperature for 24 hours. Both samples were analyzed in the percentage of the expelled core acid and the water uptake. The heated sample had 66 percent of its core acid expelled and a water uptake of 2.22 grams of water per gram of polymer particles. The sample swelled at room temperature and had 68 percent of its core material expelled and had a water uptake of 2.22 grams of water per gram of polymer particles.

Example 3 - Synthesis of the Polymer Particles with a Core to Cover Ratio of 1: 4. To the equipment of Example 2 were added 850 grams of DI water and 954.2 grams of the core obtained in Example 1. The mixture was heated to 60 ° C under a nitrogen atmosphere and then 20 grams of an iron sulphate solution was added ( 0.15 percent by active weight), followed by the addition of 1.2 grams of sodium persulfate dissolved in 100 grams of DI water. A monomer emulsion of 250 grams of deionized water, 5.25 grams of SDS, 340 grams of ethyl acrylate, 497.25 grams of methyl methacrylate and 12.75 grams of methacrylic acid was gradually added to the flask at a rate of 2.2 grams per minute. Concurrently with the addition of the monomer emulsion was gradually added a solution of 3.25 grams of sodium bisulfite in 250 grams of DI water, and a separate solution of 3.25 grams of sodium persulfate dissolved in 250 grams of DI water; each solution was added at a rate of 1.9 grams per minute. After 10 minutes in the monomer emulsion charge, this charge was increased to 4.4 grams per minute. After twenty more minutes, the monomer emulsion loading rate was increased to 9.4 grams per minute. The temperature of the mixture was maintained at 60 ° C through the addition of the monomer emulsion. Upon completion of the charges, the mixture was maintained at 60 ° C during fifteen minutes and then cooled to room temperature and filtered through a 100 mesh screen. The polymer product had 30.5 weight percent solids and an average particle size of 560 nanometers. The resulting polymer product was swollen and broke by mixing 200 grams of the polymer product with 4.48 grams of ammonia (28 weight percent active) and 97.56 g of DI water. Half of this mixture was heated at 60 ° C for one hour and the other half was kept at room temperature for 24 hours. Both samples were analyzed in the acid percentage of the expelled core and the water uptake. The heated sample had 59 percent of its core acid expelled and a water uptake of 1.63 grams of water per gram of polymer particles. The sample, swollen at room temperature, had 46 percent of its core material expelled and a water catchment of 1.17 grams of water per gram of polymer particles.

Examples 4 to 19 Polymer particles were prepared in a manner similar to the process of Example 3, except that the monomer composition, the weight ratio of the core to the shell, the particle size of the core and the general particle size were varied. The particle size of the core varied primarily by adjusting the level of the surfactant in the emulsion polymerization.

Table 2 - Polymer Particle Compositions for Examples 4 to 19 Not swollen.

The polymer particles useful in the present invention were evaluated in low gloss paper coatings in their optical properties. The procedure used was as follows: The polymer particles were formulated in low gloss paper coating compositions. Each low gloss paper coating composition was prepared by first making an aqueous paste consisting of inorganic pigments, deionized water and dispersants, shown in the following Table 3.

Table 3 - Composition dß Low Glitter Paper Coating 1 Ti-Pure® R-900, supplied by DuPont 2 Hydrocarb® 90, supplied by Omya Inc. 3 Ansilex®, supplied by Engelhard 4 Supplied by Rohm and Haas Company 5 Dow-615, supplied by Dow Chemical Company 6 Pengum 290, supplied by Pengum.

Sufficient deionized water was added to the pigment slurry to obtain 72 + 2 weight percent solids. After forming the aqueous paste, the styrene and butadiene latex and the starch were added to the polymer to be evaluated. The pH of each coating composition was adjusted to approximately 8 with aqueous ammonium hydroxide (28 weight percent active). ). Then deionized water was added to adjust the concentration of the solids in each composition between 52 and 58 weight percent. For each coating composition in Table 3, a control composition was prepared, using the ingredients shown in Table 4.

Table 4 - Control Coating Compositions Control compositions were prepared by the same method used to obtain the coating compositions in Table 3, except that the Test Polymer was not added. The ingredients were the same used in the Table 3, except that Rhoplex® ASE-75 was used, which was supplied by Rohm and Haas. The viscosity of the coating compositions was measured using a Brookfield LVF viscometer, shaft number 4, at 60 rpm. The compositions varied in viscosity from about 1000 to 6000 centipoise.

Each coating composition in Tables 3 and 4 were applied to a number of paper sheets having dimensions of approximately 23 cm by 30 cm in the following manner. The coating composition was laid out by hand on the paper sheet using a Meyer # 5 or # 6 wire wound bar. The coating composition was applied to the paper sheet in an amount of about 14.8 g / m2 of the paper sheet. The coating composition was applied to the wire side of the paper sheet in the machine direction of this paper sheet. The coiled wire rod was obtained from RDS, Inc. located in Webster, New York. The sheet of paper was a basic sheet material typical of North America, which has an approximate weight of 61 g / m2. Each sheet of coated paper was dried in the oven 80 ° C for one minute and then conditioned overnight at 22 ° C and 50% relative humidity. The weight of the coating on the paper sheet was determined after conditioning overnight, subtracting the average weight of several sheets of uncoated paper (of the same dimensions as the coated sheets) from the weight of the coated paper sheet. The various sheets of paper closest to the target weight of 14.8 g / m2 were then evaluated on the optical properties.

The selected sheets were satinated, with one pass, at a rate of approximately 183 meters per minute, using a laboratory satin machine, designed to simulate over-satin conditions. The satin was made at a temperature of 52 ° C and at a pressure previously selected to produce a constant brightness of the sheet. After glazing, each sheet was evaluated in brightness. Several measurements of the brightness of the sheet were taken on a line below the middle of each sheet. The brightness measurements for all selected sheets were averaged. The result of 1 sheet brightness for the different coating compositions are presented in Table 6. The brightness delta, the difference in brightness between a printed and an unprinted area of a substrate was determined for each coating composition as follows. Several coated satin sheets having a lower average sheet gloss were cut in the center of the sheet to obtain a strip of dimensions of 4.7 cm by 23 cm. The strip was printed to cover the entire surface area with ink, using a Prüfbau printer, obtained from Prüfbau, located in Munich, Germany. The settings on the Prüfbau printer were as follows: Table 5 - Printer settings Prüfbau The type of ink used was black, adjusted for heat, which was obtained from Wikoff, located in Fort Mili, South Carolina. After printing, the strips were heat dried at about 50 ° C for 2 minutes. The strips were conditioned overnight at 22 ° C and 50% humidity. The brightness of the print was measured at several locations below the center of the printed strip, using the same procedure as for the brightness of the sheet. The average print brightness for each coating composition is shown in Table 6. The brightness delta was calculated by subtracting the average gloss of the sheet from the average brightness of the print. The higher the value of the brightness, there will be more contrast in the brightness between the printed and unprinted areas of a sheet. The results of the delta gloss for each of the compositions are shown in Table 6. The "Delta Glitter?" shown in Table 6 is the difference between the brightness delta of the coating composition containing the test polymer and the appropriate control composition.

Table 6 - Gloss Properties of the Coating Composition 7 Satin pressure measured in kilonewtons per meter. 8 Registered trademark of Rohm and Haas Company.

Examples 20-28 of Table 6 show that low gloss coating compositions containing the polymer particles are effective in increasing the brightness of a substrate coated with the low gloss composition as compared to a substrate. coated with the corresponding control, which does not contain the test polymer. The results in Table 6 show that the polymer particles increase the brightness delta in a variety of low gloss coating compositions. Table 6 also shows that the polymer particles are more effective in increasing the delta gloss compared to the polymers containing voids, but they are not "broken", hereinafter referred to as "hollow sphere pigments". For example, Ropaque OP-84, HP-91 and HP-543 in Table 6 (Comparative Examples 21, 22 and 25) are hollow sphere pigments, and showed lower brightness delta as compared to Examples 23 and 26. Hollow sphere pigments are available from Rohm and Haas Company. In addition to the improvements in the brightness delta, the results in Table 6 show that the low gloss coating compositions, which contain the polymer particles, generally maintain or decrease the brightness of the sheet, which developed during the gloss, named at once as the "development of the brightness of the sheet", in comparison with the corresponding control. The polymer particles of various acid contents, coating compositions and particle sizes were evaluated in a low brightness composition in their effectiveness in improving the brightness delta. The effect of the delta brightness varying these parameters is shown in Tables 7, 8 and 9. The procedure for measuring the sheet brightness, the brightness of the print and the brightness delta, was the same as used in Examples 20-28. The coating composition used for the Examples in Tables 7 to 9 was the composition A shown in Table 3. The results in Table 7 show that the low gloss coating compositions, which contain the polymer particles, which have Different amounts of the swelling compound in the core are effective in increasing the brightness of a substrate coated with the low gloss composition, compared to a substrate coated with the control composition, which does not contain the test polymer. Examples 30-31 and 33-34 in Table 7 also show that as the amount of the functional acid monomer is increased in the core of the polymer particle, the delta gloss of the coating composition improves.

Table 7: Effect of Polymer Acid Content on Delta Brightness 9 Parts per acid monomer in the core per 100 parts of polymer particles ** Did not swell or expel acid The results in Table 8 show that low gloss coating compositions, containing polymer particles having different coating compositions, are effective in increasing the delta gloss of a substrate coated with the low gloss composition, as compared to a substrate coated with the control composition, which does not contain the test polymer. Examples 35-43 in Table 8 also show that polymer particles having glass transition temperatures (Tg) ranging from 19 to 54 ° C, were effective in increasing the delta gloss of a substrate coated with Composition A in comparison with a substrate coated with Control Composition A.

Table 8 - Effect of Cover Composition on the Delta Gloss The results of Table 9 show that low gloss coating compositions, containing polymer particles of varying size, are effective in increasing the brightness of a substrate coated with the low gloss composition, as compared to a substrate coated with a control composition that does not contain the test polymer. Examples 44-51 in Table 9 show that the polymer particles, which have an average swollen particle size of 487 to 1280 nm, were effective in increasing the delta brightness of Composition A, as compared to Control Composition A . Table 9 - Effect of the Particle Size in the Delta Brightness The unswollen polymer particles, which were added to a low gloss coating composition, and then swelled and broke in the low gloss coating composition, were evaluated for their effectiveness in improving the brightness delta. The following procedure was used: A low gloss coating composition was prepared according to the method for obtaining Coating Composition A in Table 3, except that the test polymer did not swell or break until after it was added to the composition. The test polymer used was prepared according to Example 19. The prepared composition was divided into two parts and each part was neutralized with aqueous ammonia (28% by active weight) at the pH shown in Table 10. The coating compositions then they were kept at room temperature for at least one hour. The two coating compositions and the Control Composition A were evaluated in the delta gloss, according to the same processing used for Examples 20-28 in Table 6. Example 54 in Table 10 shows that the polymer particles that They were broken in the low gloss coating composition, are effective in increasing the brightness delta on a substrate coated with the composition, as compared to the Control, which does not contain polymer particles (Comparative Example 52). Comparative Example 53 shows that sufficient swelling agent must be added to the low gloss composition to swell and break the polymer particles in order to obtain an improvement in the delta brightness compared to the Control.

Table 10 - Performance of Neutralized Polymer Particles in the Coating Composition The polymer particles were evaluated for their effectiveness in maintaining or decreasing the brightness of the sheet when applied in a low gloss coating composition to a substrate, which is then satinated. The test polymers were formulated in the coating composition A, according to the method used for Examples 20-28 in Table 6. Each coating composition was then coated and satined on a paper substrate, according to the method used in Examples 20-28 in Table 6, except that the constant satin pressure of 72 kN / m was used. The gloss of the sheet of each paper substrate was measured according to the procedure previously described. Table 11 shows that the particles of the polymer maintain or decrease the development of the brightness of the sheet compared to the Control, which does not contain the test polymer (Comparative Example 55). Table 11 also shows that the hollow sphere pigments (Comparative Examples 56-58) increase the brightness of the sheet compared to the control.

Table 11 - Development of Leaf Gloss at Constant Pressure of Satin Registered trademark of Rohm and Haas Company.

Claims (12)

CLAIMS 1. A coating composition, of low gloss, which comprises: one or more polymer particles and one or more pigments; wherein the polymer particles comprise at least one core phase of the polymer, which contains at least one gap; at least one cover phase of the polymer, which surrounds, at least partially, the core; and at least one channel that connects the hole in the core to the outside of the particle; wherein the coating composition comprises

1. 0 to 50 parts by weight of the polymer particles by 100 parts of the pigment, and in which the composition of the coating has a sheet gloss at 75 ° of 50 percent or less.

2. The low gloss coating composition of claim 1, wherein the polymer particles contain at least 0.5 percent by weight of an inflatable compound, based on the total weight of the non-swollen polymer particles.

3. The low gloss coating composition according to claim 1, wherein the polymer particles contain, at least in one core phase, as polymerized units, at least 5 molar percent of a functional monoethylenically unsaturated monomer , which has at least one functional group, selected from the group consisting of a basic, acidic and hydrolysable group.

4. The low gloss coating composition according to claim 1, wherein the polymer particles contain, at least in one core phase, as polymerized units, at least 5 molar percent of an acid functional monomer, unsaturated monoethylenically. The low gloss coating composition according to claim 1, wherein the polymer particles contain, at least in one layer of the shell, one or more monomers, selected from the group consisting of alkyl (C -C2? )? hydroxyalkyl (C1-C20) and (C3-C20) alkenyl esters of (meth) acrylic acid. 6. The low gloss coating composition according to claim 1, wherein the polymer particles have a weight ratio of core to shell ranging from 1: 1 to 1:20. 7. The coating composition, of low gloss, in which the polymer particles have an average size of swollen particles of 200 to 2000 nanometers. 8. The low gloss coating composition according to claim 1, wherein the composition is obtained by a process comprising: a) forming a mixture comprising polymer particles without breaking; wherein these unbroken polymer particles comprise at least one core phase of the polymer containing an inflatable compound; and at least one cover phase of the polymer, which surrounds, at least partially, the core, and b) adding a swelling agent to the mixture, to form at least one gap in the core phase and at least one channel connecting the core. hollow in the core to the outside of the particle. 9. A method for improving the print quality of a substrate, which comprises: applying to the substrate the low gloss coating composition of claim 1. The method of claim 9, wherein the print quality Improved is the brightness delta. 11. A method for obtaining a low gloss coated substrate, comprising: applying to the substrate the low gloss coating composition of claim 1. 12. A low gloss coated substrate produced by the method of claim 12.