MX2008010292A - Microspheres - Google Patents

Abstract

The invention relates to thermally expandable thermoplastic microspheres comprising a polymer shell made from ethylenically unsaturated monomers encapsulating a propellant, said ethylenically unsaturated monomers comprising from 20 to 80 wt%of acrylonitrile, from 20 to 80 wt%of monomers selected from the group consisting of esters of acrylic acid, from 0 to 10 wt%of methacrylonitrile, from 0 to 40 wt%of monomers selected from the group consisting of esters of methacrylic acid, the total amount of acrylonitrile and esters of acrylic acid constituting from 50 to 100 wt%of said ethylenically unsaturated monomers, and said propellant comprising at least one of methane, ethane, propane, isobutane, n-butane and isopentane. The invention further relates to the production and use of the microspheres.

Description

MICROSPHERES The present invention relates to thermoplastic microspheres that can be expanded in thermal form, the production and use thereof, and an aqueous paste comprising said microspheres. Expandable thermoplastic microspheres comprising a thermoplastic polymeric shell encapsulating a propellant gas are commercially available under the trademark EXPANCEL® and used as a foam agent in many different applications. In said microspheres, the propellant gas is usually a liquid having a boiling temperature not higher than the softening temperature of the thermoplastic polymer shell. Upon heating, the propellant gas is evaporated to increase the internal pressure at the same time the cover is softened, resulting in a significant expansion of the microspheres. The temperature at which the expansion starts is called T¡nic¡o > while the temperature at which the maximum expansion is reached is called Tmax. The expandable microspheres are marketed in various forms, for example, as free flowing dry particles, as an aqueous paste or as a partially drained wet mass. The expandable microspheres can be produced by polymerization of unsaturated monomers edénicamente in the presence of a propellant gas. Detailed descriptions of various expandable microspheres and their production can be found, for example, in U.S. Patents. Nos. 3615972, 3945956, 4287308, 5536756, 6235800 (corresponding to EP 1067151), 6235394 and 6509384, in EP 486080, EP 1054034, EP 1288272 and EP 1408097, in WO 2004/072160 and in document which remains open JP No. 1987-286534. An important application for the microspheres that can be expanded is in the production of paper, as described, for example in the Patents of E.U.A. Nos. 3556934 and 4133688, JP Patent 2689787, Patent Remaining Open JP No. 2003-105693, WO 2004/1 13613, International Patent Applications No. WO 2006/068573 and WO 2006/068574, and in the document Ó. Soderberg, "World pulp &paper technology 1995/96, The intemational review for the pulp &paper industry", p. 143 to 145. Other important applications for the expandable microspheres are printing inks, vinyl foams (e.g., plastisols), non-woven and artificial skin. In some applications, it is desirable that the microspheres have a comparatively low TiN. However, the polymeric coating in commercially available microspheres with a low Tissue are usually made from a monomer mixture comprising halogen containing monomers such as vinylidene chloride. Said microspheres, usually suffer from high amounts of residual monomers, discoloration and poor chemical resistance, such as solvents and plasticizers used in artificial skins and plastisols. Attempts to make microspheres with low TiN and high expansion capacity without halogen-containing monomers have not yet satisfactorily resulted in these problems. Even in microspheres without halogen-containing monomers there may be a problem with unsatisfactory polymerization production, particularly if initiators are used that provide a high reaction rate. This leads to the presence of residual monomers in the microspheres and even when the acrylonitrile-like monomers can be removed by suitable subsequent treatments, this is an additional step during the manufacturing process and the residual monomers also constitute a loss of raw material. It is an object of the present invention to provide expandable microspheres with high expansion capacity and low T0nic00 without high amounts of halogen-containing monomers. It is another object of the present invention to provide microspheres that can be expanded with low stain, high chemical resistance and high luminosity.

It is still another object of the present invention to provide expandable microspheres that can be produced with a high production in the polymerization process. It is still another object of the present invention to provide expandable microspheres useful in making paper or printing inks, for example, as a foaming agent therein. It is a further object of the present invention to provide a process for the production of paper. It is still a further object of the present invention to provide an aqueous paste comprising expandable microspheres useful in the production of paper. Surprisingly, it has been found possible to fulfill these objects by combining a monomer composition determined for the polymeric shell with a certain group of propellant gases. One aspect of the present invention relates to thermally expandable thermoplastic microspheres comprising a polymeric shell made from ethylenically unsaturated monomers encapsulating a propellant gas, said ethylenically unsaturated monomers comprising from 20 to 80% by weight of acrylonitrile, from 20 to 80% by weight of monomers selected from the group consisting of acrylic acid esters, from 0 to 10% by weight of methacrylonitrile, from 0 to 40% by weight of monomers selected from the group consisting of of esters of methacrylic acid, and the total amount of acrylonitrile and acrylic acid esters constitute from 50 to 100% of said edenically unsaturated monomers, and said propellant gas comprises at least one of methane, ethane, propane, isobutane, n-butane and isopentane. The ethylenically unsaturated monomers preferably comprise from 30 to 70% by weight, more preferably from 35 to 65% by weight of acrylonitrile. The ethylenically unsaturated monomers preferably also comprise from 20 to 70% by weight, more preferably from 25 to 60% by weight of the monomers selected from the group consisting of acrylic acid esters. Acrylic acid esters preferably have only one carbon-to-carbon double bond. Possible esters of acrylic acid include, for example, methyl acrylate, ethyl acrylate and mixtures thereof, among which methyl acrylate is particularly favorable. The ethylenically unsaturated monomers thus preferably comprise from 20 to 80% by weight, more preferably from 30 to 70% by weight, particularly more preferably from 35 to 65% by weight of the monomers selected from the group which consists of methyl acrylate, ethyl acrylate and mixtures thereof, of which, methyl acrylate is particularly preferred. The total amount of acrylonitrile and acrylic acid esters, preferably constitutes from 65 to 100% by weight, more preferably from 75 to 100% by weight, particularly more preferably from 90 to 100% by weight of ethylenically unsaturated monomers. The ethylenically unsaturated monomers can be substantially free of methacrylonitrile, although in the case that they include the amount thereof, it is preferably from 0 to 5% by weight, more preferably from 0 to 2% by weight. The ethylenically unsaturated monomers may be substantially free of methacrylic acid esters, although where included, the amount thereof is preferably from 0 to 30% by weight, more preferably from 0 to 25% by weight , particularly more preferably from 0 to 10% by weight or even from 0 to 5% by weight of the ethylenically unsaturated monomers. The amount of methacrylic acid esters can also be from 0 to 5% by weight or even from 0 to 2% by weight of the ethylenically unsaturated monomers. Examples of possible methacrylic acid esters include one or more of methyl methacrylate, isobornyl methacrylate, ethyl methacrylate, butyl methacrylate or hydroxyethyl methacrylate, of which, methyl methacrylate is most preferred. It is preferred that the ethylenically unsaturated monomers be substantially free of vinylidene chloride. If included, the amount thereof is preferably less than 10% by weight, more preferably less than 5% by weight, or even less than 1% by weight of the monomers ethylenically unsaturated. It is also preferred that the ethylenically unsaturated monomers be substantially free of any halogen-containing monomers. If included, the amount thereof is preferably less than 10% by weight, more preferably, less than 5% by weight, or even less than 1% by weight of the ethylenically unsaturated monomers. Preferably, the ethylenically unsaturated monomers comprise small amounts of one or more crosslinking multifunctional monomers, such as one or more of divinyl benzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate. , 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, 1,3-butanediol di (meth) acrylate, di (meth) acrylate of neopentyl glycol, di (meth) acrylate of 1,1-decanediol, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, hexa (meth) acrylate) of dipentaerythritol, triallylformal tri (meth) acrylate, allyl methacrylate, tri (meth) acrylate trimethylol propane, di (meth) acrylate tributanediol, PEG # 200 di (meth) acrylate, PEG # 400 di (meth) acrylate, PEG # 600 di (meth) acrylate, 3-acryloyloxy glycol monoacrylate, triacryl formal, triallyl isocyanate, triallyl isocyanurate, etc. Particularly preferred are crosslinking monomers which are at least tri-functional, examples of which include pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallylformal tri (meth) acrylate) , tri (methyl) acrylate of trimethylol propane, triacryl formal, triallyl isocyanate and triallyl isocyanurate. The amounts of functional crosslinking monomers may, for example, be from 0.1 to 10% by weight or from 0.1 to 1% by weight or from 1 to 3% by weight of ethylenically unsaturated monomers, from 0.1 to 1 % by weight being particularly preferred in the case where the one or more multifunctional monomers are at least tri-functional and from 1 to 3% by weight being particularly preferred in case the one or more multifunctional monomers are di-functional . If the ethylenically unsaturated monomers are different from acrylonitrile, the monomers selected from the group consisting of acrylic acid esters, and one or more multifunctional crosslinking monomers are included, the amount thereof, preferably from 0 to 10% by weight , more preferably from 0 to 5% by weight. Examples of such other types of monomers that may be included are nitrite-containing monomers, such as α-ethoxyacrylonitrile, fumaronitrile or crotonitrile; vinyl pyridine; vinyl esters, such as vinyl acetate; show us such as styrene, halogenated styrenes or a-methyl styrene; die such as butadiene, isoprene and chloroprene; the unsaturated carboxylic compounds similar to acrylic acid, methacrylic acid and salts thereof; or other unsaturated monomers similar to acrylamide, methacrylamide or N-substituted maleimides. In one embodiment of the present invention, the ethylenically unsaturated monomers consist substantially of acrylonitrile, the monomers selected from the group consisting of acid esters acrylic, preferably one or more of methyl acrylate or ethyl acrylate, and one or more crosslinking multifunctional monomers. The softening temperature of the polymeric cover, normally corresponds to its glass transition temperature (Tg), is preferably within the range of 0 to 100 ° C, more preferably at a temperature of 30 to 80 ° C. The propellant gas is a hydrocarbon or mixture of hydrocarbons preferably having a boiling temperature not higher than the softening temperature of the thermoplastic polymeric shell. The boiling point at atmospheric pressure, preferably is within the range of -50 to 100 ° C, more preferably from -20 to 50 ° C, particularly more preferably from -20 to 30 ° C. The propellant gas may consist substantially of at least one of methane, ethane, propane, isobutane, n-butane and isopentane, although it may additionally comprise one or more other hydrocarbons, for example, in an amount from 0 to 50% by weight of the propellant gas. Examples of said hydrocarbons include, n-pentane, neo-pentane, cyclopentane, hexane, isohexane, neo-hexane, cyclohexane, heptane, isoheptane, octane and isooctane. In addition to these, other types of hydrocarbons may also be used, such as petroleum ether or chlorinated or fluorinated hydrocarbons, such as methyl chloride, methylene chloride, dichloroethane, dichloethylene, trichloroethane, trichlorethylene, trichlorofluoromethane, perfluorinated hydrocarbons, ethers containing fluorine, etc. Propellant gases Preferred include isobutane, alone or in a mixture with one or more other hydrocarbons. The amount of isobutane in the propellant gas is preferably from 50 to 100% by weight, more preferably from 75 to 100% by weight. The Tissue pa to the expandable microspheres is preferably from 50 to 100 ° C, more preferably from 80 to 95 ° C. The Tmax, for the microspheres that can be expanded preferably, is from 90 to 170 ° C, more preferably from 110 to 150 ° C. In addition to the polymeric cover and the propellant gas, the microspheres may additionally comprise aggregated substances during the production thereof, usually in an amount of from 0 to 20% by weight, preferably from 1 to 10% by weight. Examples of such substances are solid suspending agents, such as one or more of starch, crosslinked polymers, agar gum, cellulose derivatives similar to, for example, methyl cellulose, hydroxypropyl methylcellulose, hydroxyethylcellulose and carboxymethylcellulose, silica, colloidal clays similar to , for example, gypsum and bentonite and / or one or more salts, oxides or hydroxides of metals such as Al, Ca, Mg, Ba, Fe, Zn, Ni and Mn, for example, one or more of cum phosphate, carbonate of cum, magnesium hydroxide, barium sulfate, cum oxalate and hydroxides of aluminum, iron, zinc, nickel or manganese. If present, these solid suspending agents are usually located primarily on the outer surface of the polymeric shell.

However, even if a suspension agent has been added during the production of the microspheres, they may have been washed at a later stage and could be substantially absent from the final product. The preferably expandable microspheres have a volume average diameter of 500 μm, more preferably 5 to 50 μm, more preferably 10 to 50 μm, most preferred 10 to 50 μm. The amount of propellant gas in the microspheres that can be expanded preferably is from 5 to 40% by weight, more preferably from 10 to 40% by weight, most preferred from 15 to 40% by weight, particularly more preferred from 20 to 35% by weight. The term "expandable microspheres" as used herein, refers to expandable microspheres that have not been previously expanded, i.e. unexpanded, expandable microspheres. A further aspect of the present invention relates to a process for the production of expandable thermoplastic microspheres as described above. The process comprises polymerizing ethylenically unsaturated monomers as described above in a preferably aqueous suspension in the presence of a propellant gas as described above to produce the microspheres comprising a polymeric shell encapsulating said propellant gas. With regard to the types and amounts of monomers and propellant gas, the above description of the expandable microspheres refers to that. The production may follow the same principles as those described in the US Patents. mentioned above 3615972, 3945956, 4287308, 5536756, 6235800, 6235394 and 6509384, and EP 486080, EP 1288272, WO 2004/072160 and JP which remains open No. 1987-286534. In one embodiment of the present invention, the microspheres are produced in a batch process and the polymerization can then be conducted as described below in a reaction vessel. For 100 parts of monomer phase (which suitably includes monomers and propellant gas, the proportions of which determine the proportions of monomers in the polymeric shell and the amount of propellant gas in the final product), one or more polymerization initiators, preferably in an amount of 0.1 to 5 parts, the aqueous phase, preferably in an amount of 100 to 800 parts, and one or more solid colloidal suspension agent, preferably in an amount of 1 to 20 parts, are mixed and homogenized. The size of the droplets of the monomeric phase obtained determines the size of the final expandable microspheres according to the principles described in, for example, US Pat. No. 3615972, which can be applied to all similar production methods with various suspending agents. The temperature is suitably maintained from 40 to 90 ° C, preferably from 50 to 80 ° C, while the proper pH depends on the suspension agent used. For example, a high pH, preferably from 5 to 12, more preferably from 6 to 10, is suitable if the suspending agent is selected from salts, oxides or hydroxides of metals such as Ca, Mg, Ba, Zn, Ni and Mn, for example, one or more of calcium phosphate, calcium carbonate, magnesium hydroxide, magnesium oxide, barium sulfate, calcium oxalate and zinc, nickel or manganese hydroxides. A low pH, preferably from 1 to 6, more preferably from 3 to 5, is suitable if the suspending agent is selected from starch, methylcellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, gum agar, silica, colloidal clays or oxide or hydroxide of aluminum or iron. Each of the above agents has different optimal pH, depending on, for example, the solubility data. In order to improve the effect of the suspending agent, it is also possible to add small amounts of one or more promoters, for example, from 0.001 to 1% by weight. Typically, said promoters are organic materials and can, for example, be selected from one or more of water-soluble sulfonated polystyrenes, alginates, carboxymethylcellulose, tetramethyl ammonium hydroxide or chloride or resinous complex of water-soluble amine condensation products, as the water-soluble condensation products of diethanolamine and adipic acid, the water-soluble condensation products of ethylene oxide, urea and formaldehyde, polyethyleneimine, polyvinyl alcohol, materials such as gelatin, glue, casein, albumin, glutin and the like, nonionic materials such as methoxy cellulose, ionic materials normally classified as emulsifiers, such as soaps, alkyl sulfates and sulfonates, and long chain quaternary ammonium compounds. Conventional radical polymerization can be used and the initiators are suitably selected from one or more organic peroxides such as dialkyl peroxides, diacyl peroxides, peroxy esters, peroxy bicarbonates or azo compounds. Suitable initiators include dicetyl peroxydicarbonate, di (4-tert-butylcyclohexyl) peroxydicarbonate, dioctanoyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, tert-butyl peracetate, tert-butyl perlaurate, tert-butyl perbenzoate, tert-butyl hydroperoxide, eumeno hydroperoxide, eumenoperoperoxide, diisopropylhydroxy dicarboxylate, 2,2'-azobis (2,4-dimethyl valeronitrile), 2-2'-azobis (isobutyronitrile), 1, 1'-axobis (cyclohexane-1-carbonitrile) ), dimethyl 2,2'-azobis (2-methylpropionate), 2,2'-axobis [2-methyl-N- (2-hydroxyethyl) propionamide] and the like. It is also possible to initiate polymerization with radiation, such as high energy ionizing radiation. When the polymerization is essentially complete, the microspheres are usually obtained as an aqueous paste or dispersion, which can be used as such or dried by conventional means, such as filter bed, pressure filter, sheet filtrate, rotary filtrate, filtrate band or centrifugation to obtain a so-called wet agglutination. However, it is also possible to dry the microspheres by any conventional means, such as, spray drying, shelf drying, tunnel drying, rotary drying, drum drying, pneumatic drying, turbo rack drying, disk drying or fluidized bed drying. If appropriate, the microspheres can at any stage be treated to reduce the amount of residual unreacted monomers, for example, by any of the methods described in WO 2004/02160 or E.U.A. 4287308 mentioned above. A further aspect of the present invention relates to the expanded microspheres obtained by expanding expandable microspheres as described above., for example, at a particle diameter 2 to 5 times larger than the diameter of the unexpanded microspheres. The density of the expanded microspheres can, for example, be from 0.005 to 0.06 g / cm3. The expansion is performed by heating the microspheres that can be expanded to a temperature above the spot. The upper temperature limit is established when the microspheres begin to collapse and depends on the exact composition of the polymeric coating and the propellant gas. In most cases, a temperature from 80 ° C to 150 ° C is adequate. The density of the expandable microspheres can be controlled by selecting the temperature and time for heating. The expansion can be effected by any suitable means for heating in any suitable device, as described, for example, in EP 0348372, WO 004/056549 or WO 2006/009643. The expandable and expanded microspheres of the present invention are useful in various applications, such as papermaking, printing inks (such as water-based inks, solvent-based inks, plastisols, UV curing inks, etc.) ., for example, for textiles, carpets, etc.), putty sealers, toy clays, under body coatings, adhesives, separation of adhesives, artificial skin, genuine leather, paint, non-woven materials, paper and cardboard, coatings (for example, anti-skid coating, etc.) for various materials such as paper, cardboard, plastics, metals and textiles, explosives, cable insulation, thermoplastics (such as polyethylene, polyvinyl chloride, and ethylene vinyl acetate) or elastomers thermoplastics (such as styrene-ethylene-butylene-styrene co-polymer, styrene-butadiene-styrene co-polymer, thermoplastic polyurethanes and thermoplastic polyolefins), rubber of styrene-butadiene, natural rubber, vulcanized rubber, silicone rubber, thermoset polymers (such as epoxies, polyurethanes and polyesters). In some of these applications, expanded microspheres are particularly advantageous, such as in sealants, sealants, toy clays, genuine skin, paint, explosives, cable insulators and thermoset polymers (such as epoxies, polyurethanes and polyesters). In some cases, it is also possible to use a mixture of expanded microspheres and which can be expanded from the present invention, for example, under body coatings, silicone rubbers and lightweight foams. Yet a further aspect of the present invention relates to an aqueous paste comprising the expandable thermoplastic microspheres as described above, preferably in an amount of from 5 to 55% by weight, more preferably from 20 to 55% by weight. 55% by weight. Said paste is useful for various applications of the expandable microspheres, including, for example, for papermaking. The paste preferably also comprises at least one thickening agent, preferably compatible with the production of paper. Examples of such thickening agents include at least partially water-soluble polymers, selected from the group consisting of starch, gums, celluloses, chitins, chitosan, glucans, galactans, pectins, mannans, dextrins, co-polymers made from monomers comprising acrylic acid and salts thereof (preferably, up to 50 mol%, more preferably up to 20 mol% acrylic acid or salt thereof), homopolymers and copolymers made from monomers comprising methacrylic acid, esters or amides thereof, various rubber latexes, polyvinyl chloride and copolymers, poly (vinyl esters) and copolymers, (for example, with ethylene), alcohol (polyvinyl), polyamines, polyethyleneimine, polyethylene oxides / polypropylene, polyurethane and pre-condensates of aminoplast and fenoplast, such as urea / formaldehyde, urea / melamine / formaldehyde or phenol / formaldehyde and polyamidoamine epichlorohydrin resins. Examples of suitable gums include guar gums, tamarind gums, carob gums, pea gums, karaya gums, calalu, acacia, xanthan, etc., and mixtures thereof, of which, guar gums are particularly preferred. . Examples of suitable celluloses include derivatives such as optionally CMC (carboxymethylcellulose) chemically modified and cellulose esters similar to EHEC (ethyl hydroxyethyl cellulose) and HEC (hydroxyethylcellulose), and mixtures thereof. Chemically modified cellulose derivatives include, for example, those modified with various functional groups such as quaternary amines, other amines, sulfates, sulfonates, phosphates, phosphonates., polyethylene oxide and polypropylene oxide. The polymer at least partially soluble in water can be straight chain, branched or crosslinked. The average molecular weight can vary within wide limits, depending on the type of polymer. In most cases, the preferred average molecular weight is at least 500, more preferably at least 2000, and more preferably at least 5000. The upper limit is not critical and in most cases, the average molecular weight is preferably up to 50,000,000, more preferably up to 10,000,000, more preferably up to 1,000,000. Particularly preferred polymers include starch, CMC, EHEC, guar gum, polyamidoamine epichlorohydrin resins, polymers of acrylic acid with other monomers (for example, with acrylamide), and homopolymers and co-polymers of polyacrylamides, polyamine, alcohol (polyvinyl) and polyethylene / polypropylene oxides. One or more of the at least partially water-soluble polymers effective as a thickening agent are preferably present in an amount to stabilize the slurry against substantially settling or floatation of the microspheres to a range where they can not be dispersed again. In many cases this can be achieved by adding a sufficient polymer to obtain a preferred viscosity of the pulp from about 150 to about 1000 mPas at a temperature of 25 ° C, more preferably from about 200 to about 600 mPas at a temperature of 25 ° C. (refers to the measurement with an Antón viscometer for DV-1 P equipped with an L3 axis). The amount required to stabilize the paste depends on the polymer and other circumstances such as pH. In many cases, a preferred content of the polymer soluble at least partially in water in the pulp is from about 0.1 to about 15% by weight, more preferably from about 0.1 to about 10% by weight, particularly more preferably from about 0.5% to about 10% by weight. All the thickening agents and other additives described in any of WO 2006/068573 and WO 2006/068574 mentioned above can be used in the aqueous paste of the present invention in the preferred amounts also described herein. Particular aspects of the present invention relate to the use of expandable microspheres as described above in printing inks, and in the production of paper from a substance containing cellulose fibers, artificial skin and nonwoven. When used in printing inks, in particular water-based printing inks, expandable microspheres, preferably wet unexpanded microspheres, are added to standard formulations well known to those skilled in the art. Said formulations usually include one or more agglutinators and one or more thickening agents. Other components may be included, for example, pigments, anti-foam agents, fillers, chemicals to prevent peeling or clogging, etc. Printing inks can also be based on acrylate dispersions or plastics comprising expandable microspheres. After printing, the microspheres can be expanded by heating, before or after drying the ink. Said printing inks are particularly suitable for printing on textiles and carpets. When used in artificial skin, the expandable microspheres, preferably the dry unexpanded microspheres, are used in standard formulations in known standard procedures by those skilled in the art, for example in the surface layer or artificial multi-layer body, for example, suede-like or any other type of structure. The artificial skin can be produced by any standard procedures, such as the paper release process, direct coating of tissues and nonwovens, or the coagulation process, from any standard material, such as polyurethane (PU), polyvinyl (PVC) and mixtures thereof. Normally, the artificial skin produced by any of the above processes is coated with PU or PVC paste containing microspheres that can be expanded and then heated to expand the microspheres. In the production of paper, the microspheres that can be expanded to increase the volume of paper are preferably used, although alternatively they can serve for other purposes. The microspheres are then preferably added to a substance containing cellulose fibers, which is then drained and dried, where the microspheres expand. In most cases, expansion helps increase the volume of paper. A special aspect of the present invention relates to a process for the production of paper comprising the steps of adding microspheres that can be expanded in thermal form as described above to a substance containing cellulose fibers, draining the substance on a cable to obtain paper, and dry the paper applying heat, and in this way also raise the temperature of the microspheres enough for them to expand and increase the volume of the paper. The amount of expandable microspheres added to the substance is preferably from 0.1 to 20% by weight, more preferably from 0.2 to 10% by weight of dry microspheres of the dry content in the substance. Any type of paper machine known in the art can be used. The term "paper", as used herein, means that it includes all types of cellulose-based products in sheet or network form, including, for example, cardboard, paperboard and paper. The present invention has been found to be particularly advantageous for the production of cardboard, paper and paperboard, particularly with a basis weight of from 50 to 1000 g / m2, preferably from 150 to 800 g / m2. The paper can be produced as single-layer or multi-layer paper. If the paper comprises three or more layers, the expandable microspheres can be added to the portions of the substances forming one or more of these layers, for example, only for portions of the substance that do not form any of the two layers outside. The substance preferably contains 50 to 100% by weight, more preferably 70 to 100% by weight of cellulose fibers, based on the dried material. Before draining, the substance in addition to the expandable microspheres may also contain one or more filling materials, for example, mineral fibers similar to kaolin, white clay, titanium dioxide, gypsum, talc, chalk, earth marble or precipitated calcium carbonate, and optionally other additives commonly used, such as retention aids, adjusting agents of dimensions, aluminum compounds, dyes, strong resins by wet, agents for optical rinsing, etc. Examples of the aluminum compounds include aluminum, aluminates and polyaluminum compounds, for example, polyaluminum chlorides and sulfates. Examples of retention aids include cationic polymers, anionic inorganic materials in combination with organic polymers, for example, bentonite in combination with cationic polymers or cationic or anionic polymers. Examples of dimension adjusting agents include cellulose reactive dimension adjusting agents, such as alkyl chitin dimers and succinic alkenyl anhydride, and non-reactive cellulose dimension adjusting agents, such as rosin, starch and other agents of adjustment of polymeric dimensions similar to styrene copolymers with vinyl monomers such as maleic anhydride, acrylic acid and their alkyl esters, acrylamide, etc. During drying, the paper, and thus also the microspheres, are preferably heated to a temperature of from 50 to 150 ° C, more preferably from 60 to 1 10 ° C. This results in the expansion of the microspheres and therefore also an increase in the volume of the paper. The magnitude of this volume increase depends on several factors, such as the origin of the fibers of cellulose and other components in the substance, although in most cases from 5 to 70% or more percent by weight of the microspheres retained in the dry paper, compared to the same type of paper produced without adding the microspheres which can be expanded or any other expansion agent. Any conventional means of drying may be applied involving the transfer of heat to the paper, such as contact drying (for example, by heated cylinders), drying by forced convection (for example, by hot air), infrared techniques, or combinations of the same. In the case of contact drying, the temperature of the contact surfaces, for example, the cylinders, is preferably from 20 to 150 ° C., more preferably from 30 to 130 ° C. The paper can pass a series of several cylinders, for example, up to 20 or more, of temperature increase. The cellulose fibers in the substance can, for example, come from pulp made from any type of plants, preferably wood, such as hardwood and soft wood. The cellulose fibers can also originate partially or completely from recycled paper, in which case, it has been found that the present invention provides unexpectedly good results. The expandable microspheres can be added in any form, although from a practical point of view it is preferred to add them in the form of an aqueous paste as described above.

The present invention will be further described in connection with the following examples which, however, will not be construed as limiting the scope of the present invention. If not stated otherwise, all parts and percentages refer to parts and percentages by weight. The degree of monomer conversion was determined by gas chromatography (GC). Approximately 0.2 g of dispersion were extracted directly from the reactor and are dissolved in 10 g of N, N-dimethyl acetamide containing THF as an internal standard. The monomer conversions were calculated from the GC results in relation to the initial monomeric feed. The expansion properties of the microspheres were evaluated on a Mettler TMA 40 with a TC15 TA processor and a PC with STAR6 software that uses a heating index of 20 ° C / min and a load (net.) Of 0.06 N. T¡ n is the temperature at which the expansion begins, Tmax is the temperature at which the maximum expansion is obtained and the density TMA is the density of the microspheres at the temperature Tmax. The particle size and the size distribution were determined by dispersing laser light on a Malvern Mastersizer Hydro 2000 SM apparatus on the wet samples. The average particle size is presented as the median diameter of volume d (0.5). The amount of propellant gas was determined by thermal gravimetric analysis (TGA) in a Mettler Toledo TGA / SDTA851e.

All samples were dried before analysis in order to exclude as much moisture as possible and if present, also from residual monomers. The analyzes were carried out under a nitrogen atmosphere using a heating index at a temperature of 20 ° C min "1 starting at 30 ° C.

EXAMPLE 1 A reaction mixture containing stabilized organic droplets of Mg (OH) 2 in water was created by mixing the phases and stirring vigorously until an adequate droplet size had been achieved. The water dispersion contained 4.4 parts of Mg (OH) 2, 0.009 parts of bis (2-ethylhexyl) sodium sulfosuccinate and 279 parts of water. The organic drops contain 0.6 parts of di (4-tert-butylcyclohexyl) peroxydicarbonate, 27.9 parts of isobutane, 100.0 parts of methyl acrylate and 0.3 parts of trimethylolpropane trimethacrylate. The polymerization was carried out at a temperature of 56 ° C in a sealed reactor under stirring. After cooling to room temperature, the samples of the obtained microsphere paste were removed for the determination of monomer conversion and particle size distribution. The rest of the material was filtered, washed and dried followed by a TMA analysis. The dry particles contain approximately 2% by weight of the propellant gas. The particles fused together and expansion did not occur during heating.

EXAMPLES 2-14 The microspheres were prepared in a plurality of polymerization experiments performed as in Example 1, except for monomers and propellant gases, which were aggregated according to Table 1. The amounts of water and Mg (OH) 2 in the examples varied between 220-280 parts and 3.6-4.4 parts, respectively. This is due to the small differences in the recipes in the different polymerization reactors although it does not influence the thermal properties of the polymerized particles. In Examples 11, 12 and 14, before handling the particles outside the reactor, the amount of residual monomers was reduced by treatment with 2.6 parts of NaHSO 3 for about 4 hours at a temperature of 70 ° C, after which , the temperature was lowered to room temperature and the particles were isolated and analyzed. For Examples 2, 4, 5, 7, 9, 10 and 14, after cooling to room temperature, a sample of the obtained microsphere paste was removed for determination of the monomer conversion (see Table 2). The particles obtained have a particle size ranging from about 13 pm to 33 pm and were contained between 12 and 27% by weight of propellant gas. The analytical results are in Table 1. In Example 2, the particles were partially fused together and in Examples 9 and 10, the particles showed poor expansion or no expansion. The degree of monomer conversion for Examples 2, 4, 5, 7, 9, 10, 14, is shown in Table 2.

EXAMPLE 15 - 17 The polymerization experiments were carried out as in Example 1, except that monomers and propellant gas were used according to Table 1 and dilauryl peroxide as initiator and that the polymerization was carried out overnight at a temperature of 62 ° C. The amounts of water and g (OH) 2 were 280, 350 and 270 parts, and 4.8, 3.4 and 4.8 parts, respectively. For example 16, after cooling to room temperature a sample of the obtained microsphere paste was removed for determination of the monomer conversion (see Table 2). For the rest of the reaction mixtures, 0.2 parts of NaHSO 3 and subsequently 1 1 parts of water were added. After stirring for 1 hour at a temperature of 40 ° C a second addition of NaHSO 3, and water was made and the temperature was raised to 70 ° C for another 4 hours.

TABLE 1 Analytical results for Examples 1 to 17 and the amounts of different chemicals used, expressed as parts by weight AN = acrylonitrile, MA = methyl acrylate, MMA = methyl methacrylate, IB = sobutane, IP = isopentane EXAMPLES 18 TO 20 The microspheres were prepared as in Example 1, except for the monomers that were added according to Table 2, and that the n-pentane was used as the propellant gas.

TABLE 2 Analytical results for Examples 18 to 20, and the amounts of the different chemicals used, expressed as parts by weight pentane EXAMPLE 21-22 The microspheres were prepared as in Example 1, except for the monomers that were added according to Table 3. The particles obtained have a particle size of 15 pm and 14pm and contain 18% and 22% by weight of the gas propellant, respectively. The degree of monomer conversion was determined in the reaction mixture by GC and the results can be found in Table 3.

TABLE 3 Monomeric conversion and residual monomers in the reaction mixture after polymerization Undetermined Due to the difficulty in extracting representative samples, for example, due to agglomeration, some inaccuracies in the data presented in Table 3 may not be excluded. However, the trends are clear and show that co-polymerizations of acrylonitrile with methyl acrylate provide extremely high monomer conversions compared to co-polymerizations with methyl methacrylate. It can also be seen that at very high acrylonitrile / methyl acrylate ratios, the conversion of acrylonitrile is lower. The luminosity of the dried microspheres of Examples 6, 7 and 16, was analyzed in accordance with ISO 2470 with a Zeiss Elrepho Reflectometer; the measurement of the diffuse blue reflection capacity factor, light with a wavelength of 457 nm and using the reference paper 59.65.

However, due to the need for a sample holder for powders, the reflectivity of the microspheres could only be measured through a glass disc, providing a decrease in reflection capacity of approximately 11% (percentage units). ). Therefore, the numbers are provided with the reduction of the reflection capacity included, which means that the true values for the brightness are approximately 1 1 units of higher percentage. A commercial microsphere product having a polymeric cover of 58% vinylidene chloride, 33% acrylonitrile and 9% methyl methacrylate and isobutane as the propellant gas was used as reference. The results are in Table 4.

TABLE 4 Shine of the microspheres EXAMPLES 23 TO 26 The microspheres were prepared in a plurality of polymerization experiments performed as in Example 1, except for the monomers, which were added in accordance with the Table . The particles obtained were between 22 and 34 pm. Examples 23 and 25 contain about 20% by weight of isobutane while Examples 24 and 26 contain about 9% and virtually no isobutane, respectively. The residual monomer levels were low and can be compared with the corresponding methyl acrylate polymerizations. The expansion properties are presented in Table 5, which shows that the particles of Examples 25 and 26 lack expansion.

TABLE 5 Analytical results for examples 23 to 26 and the amounts of monomers used, expressed as parts by weight AN = acrylonitrile, EA = ethyl acrylate, BA = butyl acrylate, IB = isobutane EXAMPLE 27 A single-layer paper card with a basis weight of approximately 80 g / m2 was produced on a pilot paper machine with a machine speed of 4 m / min and does not have a process water reticulated. The pulp consisted of 42.5% by weight of hardwood, 42.5% by weight of softwood pulp and 15.0% of filler material (GCC) and was struck up to a Schopper-Riegler value of 25 ° SR and subsequently dispersed to produce a pulp / substance paste. An aqueous paste of expandable microspheres was added to the substance before mixing in a box in an amount of about 2.0% by weight of dry microspheres of the dry substance in the substance. As a retention aid, Composil® (Eka Chemicals) was used and AKD was used as dimension adjustment agent. In the drying section, the paper mesh was heated by cylinders having a temperature profile from 65 to 122 ° C. The expandable microspheres of Examples 11, 12 and 17 were tested. Gohseran L-3266 ™ (polyvinyl alcohol modified by sulfonic acid) was added to the microsphere pastes to stabilize them against flotation or sedimentation (Example 11 and Example 2a , in Table 6 below). Starch (Solvitosa C5 ™ from Avebe Starches North Europe) was added as a thickening agent to a portion of the microsphere paste of Example 12 (Example 12b). The commercially available microsphere pastes, with microspheres having a polymeric coating of 73% vinylidene chloride, 24% acrylonitrile and 3% methyl methacrylate and having isobutane as a propellant gas, and with Avev Solvitosa C5 ™ (starch) Starches North Europe as a thickening agent, were tested as the reference microspheres. In order to determine the retention of the microspheres, the paper samples were taken before the pressure section for the determination of the amount of microspheres. This was done by quantifying the amount of isobutane present in the paper by GC and from this the amount of microspheres was calculated. The retention was calculated from the addition of microspheres and the content of microspheres in the paper. In addition, dry paper samples were taken for volume and thickness determination. The results are shown in Table 6. In the same way, a single-layer paper card with a basis weight of approximately 300 g / m2 was produced. The microspheres of Examples 1 1, 12 and 16 (Gohseran L-3266 ™ as the thickening agent) were tested with the reference microspheres. The results are shown in Table 7.

TABLE 6 Base weight of approximately 80 g / m2 metar.rilatn TABLE 7 Base weight of approximately 300 g / m2 AN = acrylonitrile, MA = methyl acrylate, VDC = vinylidene chloride, MMA = methyl methacrylate The results show that the general trend is that the paper volume increases of the chlorine-free microspheres of the invention can be compared with the volume increases of the chlorine-containing microspheres. It also seems that a large particle diameter provides a very high volume increase.

EXAMPLE 28 The microspheres of Example 16 were tested in printing ink creating a homogeneous dispersion by mixing 16.1 parts of the wetted microspheres (74.4% dry weight), 73.9 parts of vinyl acetate / ethylene copolymer copolymer dispersion binder (Mowilith DM-07 Celanese, 60% by dry weight), 66.3 parts of co-polymer emulsion binder of methyl methacrylate-ethyl acrylate (Primal ECO-16 from Rohm and Haas, 45.5% by dry weight), 10.0 parts of glycerol, 0.8 parts of mineral oil based on defoamer (Nopco ENA-515 of Cognis) and 29.9 parts of water, using a Silverson mixer. Then, 3.0 parts of polymeric acrylic dispersion thickening agent (Alcoprint PT-XN from Ciba) was added, followed by further mixing with a dissolution mixer until the thickening was completed and a uniform mixture was obtained. This resulted in an impression containing 12% by dry weight of microspheres. The screen impressions were processed, which were dried overnight at room temperature. Then, the thicknesses of the unexpanded impressions were measured with a coating thickness gauge (Elcometer 355 Standard) and it was found to be 40 μ. The impressions were expanded for 60 seconds at a temperature of 90-150 ° C in a hot air oven dryer from Mathis laboratory. The thicknesses of the expanded impressions were measured and the expansion factors were calculated by dividing between the thicknesses of the unexpanded impression. An expandable printing ink, created from commercially available microspheres having polymeric covers of 73% vinylidene chloride, 24% acrylonitrile and 3% methyl methacrylate and having isobutane as the propellant gas, was tested for same way. The expansion factors are presented in Table 18.

TABLE 18 Microsphere expansion factors in printing ink The results show that the expansion factor of the chlorine-free microsphere ink of the present invention is higher compared to the expansion factors of the chlorine-containing microspheres, especially in the region between the temperatures of 100 and 140 ° C.

Claims (20)

1. NOVELTY OF THE INVENTION CLAIMS 1 . Thermoplastic microspheres that can be expanded in thermal form, comprising a polymeric shell made from ethylenically unsaturated monomers encapsulating a propellant gas, said ethylenically unsaturated monomers comprising from 20 to 80% by weight of acrylonitrile, from 20 to 80% by weight of monomers selected from the group consisting of acrylic acid esters, from 0 to 10% by weight of methacrylonitrile, from 0 to 40% by weight of monomers selected from the group consisting of acid esters methacrylic, the total amount of acrylonitrile and acrylic acid esters constitute from 50 to 100% by weight of said ethylenically unsaturated monomers and said propellant gas comprises at least one of methane, ethane, propane, isobutane, n-butane and isopentane .
2. 2. The microspheres according to claim 1, further characterized in that said esters of acrylic acid have only a carbon-carbon double bond.
3. 3. The microspheres according to any of claims 1-2, further characterized in that said ethylenically unsaturated monomers comprise from 30 to 70% by weight of acrylonitrile and from 20 to 70% by weight of monomers selected from the group consisting of acrylic acid esters.
4. 4. The microspheres according to any of claims 1 to 3, further characterized in that said ethylenically unsaturated monomers comprise from 35 to 65% by weight of acrylonitrile and from 25 to 60% by weight of monomers selected from the group which consists of esters of acrylic acid.
5. 5. The microspheres according to any of claims 1 to 4, further characterized in that the amount of acrylonitrile and acrylic acid esters constitutes from 75 to 100% by weight of said ethylenically unsaturated monomers.
6. 6. The microspheres according to any of claims 1 to 5, further characterized in that said ethylenically unsaturated monomers comprise from 20 to 80% by weight of monomers selected from the group consisting of methyl acrylate, ethyl acrylate and mixtures thereof. same.
7. 7. The microspheres according to claim 6, further characterized in that said ethylenically unsaturated monomers comprise from 20 to 80% by weight of methyl acrylate.
8. 8. The microspheres according to any of claims 1 to 7, further characterized in that said ethylenically unsaturated monomers comprise one or more multifunctional crosslinking monomers.
9. 9. - The microspheres according to claim 8, further characterized in that said ethylenically unsaturated monomers comprise one or more crosslinking monomers that are at least tri-functional.
10. 10. The microspheres according to any of claims 1 to 9, further characterized in that said ethylenically unsaturated monomers are substantially free of or comprise less than 10% by weight of halogen-containing monomers. 1.
11. The microspheres according to any of claims 1 to 10, further characterized in that said propellant gas comprises isobutane.
12. 12. The microspheres according to claim 1, further characterized in that said propellant gas comprises from 50 to 100% by weight of isobutane.
13. 13. The process for the production of thermally expandable microspheres according to any of claims 1 to 12, comprising the polymerization of ethylenically unsaturated monomers in the presence of a propellant gas to produce the microspheres comprising a polymer cover encapsulating said propellant gas, said ethylenically unsaturated monomers comprise from 20 to 80% by weight of acrylonitrile, from 20 to 80% by weight of monomers selected from the group consisting of acrylic acid esters, from 0 up to 10% by weight of methacrylonitrile, from 0 to 40% by weight of the monomers selected from the group consisting of esters of methacrylic acid, the total amount of acrylonitrile and esters of acrylic acid constitutes from 50 to 100% by weight of said ethylenically unsaturated monomers , and said propellant gas comprises at least one of methane, ethane, propane, sobutane, n-butane and isopentane.
14. 14. An aqueous paste comprising thermally expandable microspheres according to any of claims 1 to 12.
15. 15. The aqueous paste according to claim 14, further characterized in that it additionally comprises at least one of a thickening agent being a polymer at least partially soluble in water selected from the group consisting of starch, gums, celluloses, chitins, chitosan, glucans, galactans, pectins, mannans, dextrins, co-polymers made from monomers comprising acrylic acid and salts thereof, homopolymers and copolymers made from monomers comprising esters or amides of acrylic acid, homopolymers or copolymers made from monomers comprising methacrylic acid, esters or amides thereof, various rubber latex, poly (vinyl chloride) and copolymers, poly (vinyl esters) and copolymers, alcohol (polyvinyl), p oliamines, polyethyleneimine, polyethylene / polypropylene oxides, polyurethane, and precondensates of aminoplast and fenoplast, and polyamidoamine epichlorohydrin resins.
16. 16. - Expanded microspheres obtained by the expansion of the expandable microspheres according to any of claims 1 to 12.
17. 17. - A use of thermally expandable microspheres according to any of claims 1 to 12 in the production of paper from a suspension containing cellulose fibers.
18. 18. - A use of microspheres that can be expanded in thermal form according to any of claims 1 to 12 in printing inks.
19. 19. Use of microspheres that can be expanded in thermal form according to any of claims 1 to 12 in the production of artificial skin.
20. 20. Use of microspheres that can be expanded in thermal form according to any of claims 1 to 12 in the production of non-woven fibers. twenty-one . - A process for the production of paper, comprising the steps of adding microspheres that can be expanded in thermal form according to any of claims 1 to 12, to a solution containing cellulose fibers, draining the suspension on a cable for get paper, and dry the paper by applying heat and in this way, also raising the temperature of the microspheres enough for them to expand and increase the volume of the paper.

    22. - The method according to claim 21, further characterized in that the microspheres that can be expanded in thermal form are added in the form of an aqueous paste according to any of claims 14-15.