Patent Application
20070010386
The present invention relates to a packaging material comprising an at least two-layer laminate of sized paper or sized cardboard and at least one water-impermeable film or foil for packaging liquids, and to the use of paper products which have been engine sized and which have been laminated on one or both sides with a plastics film or metal foil, for producing containers for packaging liquids, in particular beverages.
EP-B-0 292 975 discloses the use of an emulsion of an alkylketene dimer in combination with a cationic rosin size and an agent imparting insolubility, such as alum, for producing cardboard for packaging liquids. The cardboard is produced by adding size and alum to an aqueous slurry of cellulose fibers and draining the paper stock on a wire.
EP-A-1 091 043 discloses a process for producing a coated packaging cardboard, an aqueous slurry of cellulose fibers being engine sized with an aqueous dispersion of a rosin size, a synthetic size, such as alkylketene dimer, and at least one aluminum compound and the aqueous slurry being drained on a wire. The aqueous dispersions of engine sizes can, if appropriate, comprise a dispersant, e.g. cationic starch, casein, cellulose derivatives, polyvinyl alcohols, polyacrylamides or polyethylenimines. The cardboard is usually coated after the sizing.
Paper products laminated on both sides with a liquid-impermeable layer and intended for packaging foods are disclosed in WO-A-02/090206. The paper products are engine sized with aqueous dispersions of alkylketene dimers. The amount of alkylketene dimers is at least 0.25, preferably 0.25-0.4, % by weight, based on the weight of the dry paper products.
Further multilayer packaging materials whose base layer consists of paper or cardboard are described, for example, in WO-A-97/02140, WO-A-97/02181 and WO-A-98/18680.
The prior art also discloses the use of size mixtures comprising aqueous dispersions of alkylketene-dimers and polymer sizes for the engine sizing of paper and cardboard, cf. DE-A-32 35 529, WO-A-94/05855 and WO-A-96/31650.
The prior German application 10237913.0 discloses a process for producing cardboard for packaging liquids. In this process, the cardboard is produced by engine sizing of an aqueous slurry of cellulose fibers with at least one engine size in the presence of at least one retention aid and at least one cationic polymer and, if appropriate, a water-soluble aluminum compound and drainage of the paper stock on a wire. Sizes described are alkylketene dimers, alkyl- and alkenylsuccinic anhydrides, alkyl isocyanates, combinations of rosin size and alum and combinations of reaction products of rosin size with carboxylic anhydrides and alum.
It is an object of the present invention to provide further packaging materials based on paper products, where the packagings should have in particular improved edge penetration and improved adhesion of the laminates to paper or cardboard.
We have found that this object is achieved, according to the invention, by a packaging material comprising an at least two-layer laminate of a sized paper or sized cardboard and at least one water-impermeable film or foil for producing containers for packaging liquids, if the paper or the cardboard is in each case engine sized with a polymer size.
The present invention also relates to the use of paper products which are obtainable in each case by
engine sizing of a paper stock comprising an aqueous slurry of cellulose fibers with at least one polymer size as an engine size or with a polymer size and an aqueous dispersion of an alkylketene dimer or a mixture thereof in the presence of a retention aid and, if appropriate, of a water-soluble aluminum compound and, if appropriate, at least one cationic polymer,
drainage of the paper stock on the wire of a paper machine,
drying of the paper product and
lamination of the paper product on one or both sides with a plastics film or metal foil, for producing containers for packaging liquids, in particular beverages.
All cellulose fibers usually used in the paper industry, for example fibers of wood pulp and all annual plants, can be used for producing sized paper or sized cardboard. Mechanical pulp is understood as meaning, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semichemical pulp, high-yield pulp, refiner mechanical pulp (RMP) and wastepaper. Pulps which can be used in bleached or in unbleached form are also suitable. Examples of these are sulfate, sulfite and soda pulps. Unbleached pulps, which are also referred to as unbleached kraft pulp, are preferably used. The fibers may be used alone or as a mixture with one another.
In the engine sizing of paper or cardboard, sizing is carried out during the process for the production of these materials, by adding an engine size to the paper stock and draining said paper stock on the wire of a paper machine with sheet formation. According to the invention, the engine size used is a polymer size comprising synthetic polymers. The polymer sizes disclosed in JP-A-58/115 196 are aqueous polymer dispersions which are a paper size and at the same time increase the strength of paper. These dispersions are prepared by polymerization of, for example, styrene and alkyl acrylates in the presence of starch and free radical polymerization initiators in an aqueous medium. The starch used in each case is digested or degraded before the polymerization, so that it is soluble in water. The polymers of these dispersions are graft polymers of styrene and alkyl acrylates on starch or modified starch.
Further polymer sizes are disclosed in EP-B-0 257 412 and EP-B-0 267 770. They are prepared by copolymerization of acrylonitrile and/or methacrylonitrile and at least one acrylate of a monohydric, saturated C3- to C8-alcohol by an emulsion polymerization method in an aqueous solution which comprises a degraded starch, in the presence of free radical initiators, preferably hydrogen peroxide or redox initiators. The degraded starches have viscosities ηi of from 0.04 to 0.50 dl/g. Such starches are obtained, for example, in an oxidative, thermal, acidolytic or enzymatic degradation of a natural or cationically or anionically modified starch. Natural starches from potatoes, wheat, corn, rice or tapioca are advantageously used. An enzymatically degraded potato starch is preferred. The degraded starches act as emulsifiers in the copolymerizatiori of, for example, styrene and n-butyl acrylate in an aqueous medium. The aqueous solution in which the copolymerization is carried out comprises, for example, from 1 to 25% by weight of at least one degraded starch. For example, from 10 to 150 preferably from 40 to 100, parts by weight of the abovementioned monomers are polymerized in 100 parts by weight of such a solution. Instead of acrylonitrile and/or methacrylonitrile, it is also possible to use styrene in the copolymerization, cf. WO-A-94/05855. Aqueous dispersions of copolymers having a mean particle diameter of, for example, from 50 to 500 nm, preferably from 100 to 300 nm, are obtained. These polymer dispersions are presumably graft polymers of the monomers used in each case on degraded starch.
Further polymer sizes based on copolymers of styrene and C3- to C8-alkyl (meth)acrylates are disclosed in WO 02/14393. They are prepared by copolymerization of said monomers in an aqueous medium in the presence of degraded starch and free radical polymerization initiators by a two-stage process.
Other suitable polymer sizes are those aqueous polymer dispersions which can be prepared in the presence of synthetic polymeric protective colloids. They are obtainable, for example, by copolymerization of from 2 to 32 parts of a mixture of
First, a solution copolymer is prepared by copolymerizing the monomers of groups (1) and (2) and, if appropriate, (3) in a water-miscible organic solvent. Suitable solvents are, for example, C1- to C3-carboxylic acids, such as formic acid, acetic acid and propionic acid, or C1- to C4-alcohols, such as methanol, ethanol, n-propanol or isopropanol, and ketones, such as acetone. Preferably used monomers of group (1) are dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate and dimethylaminopropyl acrylate. The monomers of group (1) are preferably used in protonated or in quaternized form. Suitable quaternizing agents are, for example, methyl chloride, dimethyl sulfate and benzyl chloride.
Monomers of group (2) which are used are nonionic, hydrophobic, ethylenically unsaturated compounds which, if they are polymerized by themselves, form hydrophobic polymers. These include, for example, styrene, methylstyrene, C1- to C18-alkyl esters of acrylic acid or methacrylic acid, for example methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate and isobutyl acrylate, and isobutyl methacrylate, n-butyl methacrylate and tert-butyl methacrylate. Acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate and vinyl butyrate are also suitable. Mixtures of the monomers of group (2) can also be used in the copolymerization, for example mixtures of styrene and isobutyl acrylate. The solution copolymers serving as an emulsifier can, if appropriate, also comprise monomers of group (3) incorporated in the form of polymerized units, for example monoethylenically unsaturated C3- to C5-carboxylic acids or their anhydrides, e.g. acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride or itaconic anhydride. The molar ratio (1): (2): (3) is 1:2.5 to 10:0 to 1.5. The copolymer solutions thus obtained are diluted with water and serve in this form as a protective colloid for the polymerization of the abovementioned monomer mixtures of the components (a) and (b) and, if appropriate, (c). Suitable monomers of group (a) are styrene, acrylonitrile, methacrylonitrile or mixtures of styrene and acrylonitrile or of styrene and methacrylonitrile. Monomers of group (b) which are used are acrylates and/or methacrylates of C1- to C18-alcohols and/or vinyl esters of saturated C2- to C4-carboxylic acids. This group of monomers corresponds to the monomers of group (2) which are described above. Preferably used monomers of group (b) are butyl acrylate and butyl methacrylate, e.g. isobutyl acrylate, n-butyl acrylate and isobutyl methacrylate. Monomers of group (c) are, for example, monoethylenically unsaturated C3- to C5-carboxylic acids, acrylamidomethylpropanesulfonic acid, sodium vinylsulfonate, vinylimidazole, N-vinylformamide, acrylamide, methacrylamide and N-vinylimidazoline. From 1 to 32 parts by weight of a monomer mixture of the components (a) to (c) are used per part by weight of the copolymer. The monomers of the components (a) and (b) can be copolymerized in any desired ratio, e.g. in a molar ratio of from 0.1:1 to 1:0.1.
The monomers of group (c) are, if required, used for modifying the properties of the copolymers.
Sizes of this type are described, for example, in EP-B-0 051 144, EP-B-0 058 313 and EP-B-0 150 003.
Preferably used polymer sizes are aqueous polymer dispersions which are obtainable by copolymerization of
from 20 to 65% by weight of styrene, acrylonitrile and/or methacrylonitrile,
from 80 to 35% by weight of acrylates and/or methacrylates of monohydric saturated C3- to C8- alcohols and
from 0 to 20% by weight of other monoethylenically unsaturated copolymerizable monomers, such as acrylamide, methacrylamide, vinylformamide, acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid or basic monomers, such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl acrylate or dimethylaminopropyl methacrylate, the basic monomers generally being used in the form of hydrochlorides or in a form quaternized with methyl chloride, dimethyl sulfate or benzyl chloride, in the presence of free radical initiators by an emulsion polymerization method in an aqueous solution of a degraded starch as a protective colloid.
Other preferably used polymer sizes are aqueous polymer dispersions which are obtainable by copolymerization of
from 60 to 90% by weight of styrene and/or methylstyrene,
from 10 to 40% by weight of 1,3-butadiene and/or isoprene and
from 0 to 20% by weight of other monoethylenically unsaturated copolymerizable monomers, such as acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide or N-vinylpyrrolidone,
in the presence of free radical initiators by an emulsion polymerization method in an aqueous solution of a degraded starch as a protective colloid.
The polymer sizes are preferably cationic or anionic. The charge of the aqueous dispersions is based either on the type of comonomers incorporated in the form of polymerized units in the copolymers (for example, the polymer size dispersion is cationic when basic monomers are used, whereas they are anionic as a result of incorporation of, for example, acrylic acid or its salts in the form of polymerized units) or on the charge of the protective colloid used in each case. For example, the use of cationic starch as an emulsifier leads to cationic polymer size dispersions.
For the engine sizing of paper or cardboard, for example, from 0.1 to 2.0, preferably from 0.2 to 0.75, % by weight, based on dry paper product, of polymer size (i.e. 100% strength polymer) are used.
The engine sizing of paper and cardboard can additionally be carried out in the presence of aqueous dispersions of reactive sizes, such as alkylketene dimers, C5- to C22-alkyl- and/or C5- to C22-alkenylsuccinic anhydrides, chloroformic esters and C12- to C36-alkyl isocyanates, and in the presence of combinations of rosin size and alum or of combinations of reaction products of rosin size with carboxylic anhydrides and alum. Instead of alum or in combination with alum, it is possible to use other aluminum-comprising compounds, such as polyaluminum chlorides or the polyaluminum compounds disclosed in EP-B-1 091 043.
Among the reactive sizes, C12- to C22-alkylketene dimers, e.g. stearyldiketene, lauryldiketene, palmityldiketene, oleyldiketene, behenyidiketene or mixtures thereof, are preferably used.
Suitable succinic anhydrides are, for example, decenylsuccinic anhydride, octenylsuccinic anhydride, dodecenylsuccinic anhydride and n-hexadecenylsuccinic anhydride.
The reactive sizes are usually used in the form of an aqueous dispersion. For example, alkylketene dimers are dispersed in an aqueous solution of a cationic starch, or nonionic or anionic emulsifiers are used for stabilizing the alkylketene dimers. The reactive size dispersions formed are cationically or anionically charged or neutral, depending on the type and amount of the emulsifiers, or mixtures of emulsifiers compatible with one another, which are used.
For example, anionic emulsifiers can be added to alkylketene dimer dispersions which were emulsified with the aid of cationic starch in water. If the charge of the anionic emulsifiers predominates over the charge of the cationic emulsifiers, an anionically charged alkyl diketone dimer dispersion is obtained. Anionically charged aqueous alkylketene dispersions are preferably prepared by emulsifying alkylketene dimers in aqueous solutions of anionic emulsifiers. For example, condensates of naphthalenesulfonic acid and formaldehyde, sulfonated polystyrene, C10- to C22-alkylsulfuric acids, ligninsulfonic acid, phenolsulfonic acid, naphthalenesulfonic acid or the sodium, potassium or ammonium salts of said acids can be used as anionic emulsifiers. Copolymers of acrylic acid and maleic acid, homopolymers of acrylic acid, homopolymers of methacrylic acid, copolymers of isobutene and maleic acid and/or acrylic acid, hydrolyzed copolymers of isobutene or diisobutene and maleic anhydride are also suitable emulsifiers for the preparation of anionic alkylketene dimer dispersions. The acid groups of the homo- and copolymers can, for example, be partly or completely neutralized with sodium hydroxide solution, potassium hydroxide solution or ammonia and used in this form as anionic emulsifiers. The molar mass MW of the homopolymers and of the copolymers is, for example, from 1 000 to 15 000, preferably from 1 500 to 10 000. The emulsifiers are used, for example, in amounts of up to 3.5, preferably up to 2, % by weight, based on the reactive size to be dispersed.
The reactive sizes are alternatively used in the engine sizing of the paper products to be used according to the invention as substrate material for the packaging materials. They are used in particular when packaging materials having particularly good edge penetration are desired. They are then employed in amounts which are usually required for the production of sized paper products, e.g. from 0.1 to 2.0, preferably from 0.1 to 0.5, % by weight, based on dry cellulose fibers. For example, from 0 to 90, preferably from 50 to 90, parts by weight of reactive sizes are used per 100 parts by weight of polymer size. If mixtures of a polymer size dispersion and of an aqueous dispersion of a reactive size are used, the mixtures comprise, for example, from 5 to 50, preferably from 10 to 30, % by weight, based in each case on the polymer content, of polymer (100% strength).
If reactive sizes are used together with a polymer size, the reactive sizes, preferably alkylketene dimer dispersions, can first be added to the paper stock and then the polymer size dispersions can be metered. However, the alkylketene dimer dispersion and at least one polymer size dispersion can also be added simultaneously to the paper stock and the latter then drained with sheet formation, or a mixture of a reactive size, such as at least one alkylketene dimer dispersion, and at least one polymer size dispersion is added to the paper stock and the latter is then drained with sheet formation.
The polymer sizes can of course also be used as surface sizes by applying them, for example with the aid of a size press, to the surface of the paper or spraying them onto the surface of the paper.
The draining of the paper stock is additionally effected in the presence of a retention aid. Apart from anionic retention aids or nonionic retention aids, such as polyacrylamides, cationic polymers are preferably used as retention aids and as drainage aids. A significant improvement in the runability of the paper machines is achieved thereby. Cationic retention aids which may be used are all products commercially available for this purpose. These are, for example, cationic polyacrylamides, polydiallyldimethylammonium chlorides, polyethylenimines, polyamines having a molar mass of more than 50 000, polyamines which, if appropriate, are modified by grafting-on of ethylenimine, polyetheramides, polyvinylimidazoles, polyvinylpyrrolidines, polyvinylimidazolines, polyvinyltetrahydropyridines, poly(dialkylaminoalkyl vinyl ethers), poly(diallkylaminoalkyl (meth)acrylates) in protonated or in quarternized form, and polyamidoamines obtained from a dicarboxylic acid, such as adipic acid, and polyalkylenepolyamines, such as diethylenetriamine, which are grafted with ethylenimine and crosslinked with polyethylene glycol dichlorohydrin ethers according to DE-B-24 34 816, or polyamidoamines which have been reacted with epichlorohydrin to give water-soluble condensates, and copolymers of acrylamide or methacrylamide and dialkylaminoethyl acrylates or methacrylates, for example copolymers of acrylamide arid dimethylaminoethyl acrylate in the form of the salt with hydrochloric acid or in a form quaternized with methyl chloride. Further suitable retention aids are microparticle systems comprising cationic polymers, such as cationic starch and finely divided silica, or comprising cationic polymers, such as cationic polyacrylamide, and bentonite.
The cationic polymers which are used as retention aids have, for example, Fikentscher K values of at least 140 (determined in 5% strength aqueous sodium chloride solution at a polymer concentration of 0.5% by weight, a temperature of 25° C. and a pH of 7). They are preferably used in amounts of from 0.01 to 0.3% by weight, based on dry cellulose fibers.
If appropriate, at least one cationic polymer may also be added to the aqueous slurry of cellulose fibers, in addition to the abovementioned substances. Examples of cationic polymers are polymers comprising vinylamine units, polymers comprising vinylguanidine units, polymers comprising dialkylaminoalkyl(meth)acrylamide units, polyethylenimines, polyamidoamines grafted with ethylenimine and/or polydiallyidimethylammonium chlorides. The amount of cationic polymers is, for example, from 0.001 to 2.0, preferably from 0.01 to 0.1, % by weight, based on dry cellulose fibers.
Polymers comprising vinylamine units are known, cf. U.S. Pat. No. 4,421,602, U.S. Pat. No. 5,334,287, EP-A-0 216 387, U.S. Pat. No. 5,981,689, WO-A-00/63295 and U.S. Pat. No. 6,121,409. They are prepared by hydrolysis of open-chain polymers comprising N-vinylcarboxamide units. These polymers are obtainable, for example, by polymerization of N-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide and N-vinylpropionamide. Said monomers can be polymerized either alone or together with other monomers.
Suitable monoethylenically unsaturated monomers which are copolymerized with the N-vinylcarboxamides are all compounds copolymerizable therewith. Examples of these are vinyl esters of saturated carboxylic acids of 1 to 6 carbon atoms, such as vinyl formate, vinyl acetate, vinyl propionate and vinyl butyrate, and vinyl ethers, such as C1- to C6-alkyl vinyl ethers, e.g. methyl or ethyl vinyl ether. Further suitable comonomers are esters, amides and nitriles of ethylenically unsaturated C3- to C6-carboxylic acids, for example methyl acrylate, methyl methacrylate, ethyl acrylate and ethyl methacrylate, acrylamide and methacrylamide and acrylonitrile and methacrylonitrile.
Further suitable carboxylic esters are derived from glycols or polyalkylene glycols, in each case only one OH group being esterified, e.g. hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and monoesters of acrylic acid with polyalkylene glycols having a molar mass of from 500 to 10 000. Further suitable comonomers are esters of ethylenically unsaturated carboxylic acids with amino alcohols, for example dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, diethylaminopropyl acrylate, dimethylaminobutyl acrylate and diethylaminobutyl acrylate. The basic acrylates can be used in the form of the free bases, of the salts with mineral acids, such as hydrochloric acid, sulfuric aicd or nitric acid, of the salts with organic acids, such as formic acid, acetic acid, propionic acid or the sulfonic acids, or in quaternized form. Suitable quaternizing agents are, for example, dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride and benzyl chloride.
Further suitable comonomers are amides of ethylenically unsaturated carboxylic acids, such as acrylamide, methacrylamide and N-alkylmono- and diamides of monoethylenically unsaturated carboxylic acids having alkyl radicals of 1 to 6 carbon atoms, e.g. N-methylacrylamide, N,N-dimethylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-propylacrylamide and tert-butylacrylamide and basic (meth)acrylamides, e.g. dimethylaminoethylacrylamide, dimethylaminoethyl methacrylamide, diethylaminoethylacrylamide, diethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, diethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and diethylaminopropylmethacrylamide.
N-Vinylpyrrolidone, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, N-vinylimidazole and substituted N-vinylimidazoles, e.g. N-vinyl-2-methylimidazole, N-vinyl4-methylimidazole, N-vinyl-5-methylimidazole and N-vinyl-2-ethylimidazole, and N-vinylimidazolines, such as N-vinylimidazoline, N-vinyl-2-methylimidazoline and N-vinyl-2-ethylimidazoline, are furthermore suitable as comonomers. Apart from being used in the form of the free bases, N-vinylimidazoles and N-vinylimidazolines are also employed in a form neutralized with mineral acids or organic acids or in quaternized form, the quaternization preferably being carried out with dimethyl sulfate, diethyl sulfate, methyl chloride or benzyl chloride. Diallyldialkylammonium halides, e.g. diallyldimethylammonium chloride, are also suitable.
The copolymers comprise for example,
Polymers comprising vinylamine units are preferably prepared starting from homopolymers of N-vinylformamide or from copolymers which are obtainable by copolymerization of
In most cases, the degree of hydrolysis of the homo- and copolymers is from 80 to 95 mol %. The degree of hydrolysis of the homopolymers is equivalent to the content of vinylamine units in the polymers. In the case of copolymers which comprise vinyl esters in the form of polymerized units, hydrolysis of the ester groups with formation of vinyl alcohol units may occur in addition to the hydrolysis of the N-vinylformamide units. This is the case in particular when the hydrolysis of the copolymers is carried out in the presence of sodium hydroxide solution. Acrylonitrile incorporated in the form of polymerized units is likewise chemically changed in the hydrolysis. Here, for example, amido groups or carboxyl groups form. The homo- and copolymers comprising vinylamine units may if appropriate comprise up to 20 mol % of amidine units, which are formed, for example, by reaction of formic acid with two neighboring amino groups or by intramolecular reaction of an amino group with a neighboring amido group, for example of N-vinylformamide incorporated in the form of polymerized units. The molar masses MW of the polymers comprising vinylamine units are, for example, from 500 to 10 million, preferably from 1 000 to 5 million (determined by light scattering). This molar mass range corresponds, for example, to K values of from 5 to 300, preferably from 10 to 250 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25° C. and a polymer concentration of 0.5% by weight).
The polymers comprising vinylamine units are preferably used in salt-free form. Salt-free aqueous solutions of polymers comprising vinylamine units can be prepared, for example, from the salt-containing polymer solutions described above with the aid of ultrafiltration through suitable membranes at cut-offs of, for example, from 1 000 to 500 000, preferably from 10 000 to 300 000, Dalton. The below-described aqueous solutions of other polymers comprising amino and/or ammonium groups can also be obtained in salt-free form with the aid of ultrafiltration.
Derivatives of polymers comprising vinylamine units can also be used as cationic polymers. Thus, it is possible, for example, to prepare a multiplicity of suitable derivatives from the polymers comprising vinylamine units by amidation, alkylation, sulfonamide formation, urea formation, thiourea formation, carbamate formation, acylation, carboxymethylation, phosphonomethylation or Michael addition of the amino groups of the polymer. Of particular interest here are uncrosslinked polyvinylguanidines, which are obtainable by reaction of polymers comprising vinylamine units, preferably polyvinylamines, with cyanamide (R1R2N-CN, where R1 and R2 are H, C1- to C4-alkyl, C3- to C6-cycloalkyl, phenyl, benzyl, alkyl-substituted phenyl or naphthyl), cf. U.S. Pat. No. 6,087,448, column 3, line 64 to column 5, line 14.
The polymers comprising vinylamine units also include hydrolyzed graft polymers of, for example, N-vinylformamide on polyalkylene glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylformamides, polysaccharides, such as starch, oligosaccharides or monosaccharides. The graft polymers are obtainable by subjecting, for example, N-vinylformamide to free radical polymerization in an aqueous medium in the presence of at least one of said grafting bases, if appropriate together with other copolymerizable monomers, and then hydrolzying the grafted-on vinylformamide units in a known manner to give vinylamine units.
Suitable cationic polymers are also polymers of dialkylaminoalkyl(meth)acrylamides. Suitable monomers for the preparation of such polymers are, for example, dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide, diethylaminoethylacrylamide, diethylaminoethylmethacrylamide and diethylaminopropylacrylamide. These monomers can be used in the form of the free bases, of the salts with inorganic or organic acids or in quaternized form in the polymerization. They can be subjected to free radical polymerization to give homopolymers or, together with other copolymerizable monomers, to give copolymers. The polymers comprise, for example, at least 30, preferably at least 70, mol % of said basic monomers incorporated in the form of polymerized units.
Further suitable cationic polymers are polyethylenimines which can be prepared, for example, by polymerization of ethylenimine in aqueous solution in the presence of acid-eliminating compounds, acids or Lewis acids as a catalyst. Polyethylenimines have, for example, molar masses of 2 million, preferably from 200 to 1 000 000. Polyethylenimines having molar masses of from 500 to 750 000 are particularly preferably used. The polyethylenimines can, if appropriate, be modified, for example, alkoxylated, alkylated or amidated. They can also be subjected to a Michael addition or a Stecker synthesis. The polyethylenimine derivatives obtainable thereby are likewise suitable as cationic polymers.
Polyamidoamines grafted with ethylenimine and obtainable, for example, by condensation of dicarboxylic acids with polyamines and subsequent grafting-on of ethylenimine are also suitable. Suitable polyamidoamines are obtained, for example, by reacting dicarboxylic acids of 4 to 10 carbon atoms with polyalkylenepolyamines which comprise from 3 to 10 basic nitrogen atoms in the molecule. Examples of dicarboxylic acids are succinic acid, maleic acid, adipic acid, glutaric acid, suberic acid, sebacic acid and terephthalic acid. In the preparation of the polyamidoamines, mixtures of dicarboxylic acids may also be used, as may mixtures of a plurality of polyalkylenepolyamines. Suitable polyalkylenepolyamines are, for example, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenetriamine, dipropylenetetramine, dihexamethylenetriamine, aminopropylethylenediamine and bisaminopropylethylenediamine. For the preparation of the polyamidoamines, the dicarboxylic acids and polyalklenepolyamines are heated to relatively high temperatures, for example to temperatures in the range from 120 to 220° C., preferably from 130 to 180° C. The water formed during the condensation is removed from the system. In the condensation, lactones or lactams of carboxylic acids of 4 to 8 carbon atoms can, if appropriate, also be used. For example, from 0.8 to 1.4 mol of a polyalkylenepolyamine are used per mole of a dicarboxylic acid. These polyamidoamines are grafted with ethylenimine. The grafting reaction is carried out, for example, in the presence of acids or Lewis acids, such as sulfuric acid or boron trifluoride etherates, at, for example, from 80 to 100° C. Compounds of this type are described, for example, in DE-B-24 34 816.
The optionally crosslinked polyamidoamines, which are, if appropriate additionally grafted with ethylenimine before the crosslinking, are also suitable as cationic polymers. The crosslinked polyamidoamines grafted with ethylenimine are water-soluable and have, for example, an average molecular weight MW of from 3 000 to 2 million Dalton. Conventional crosslinking agents are, for example, epichlorohydrin or bischlorohydrin ethers of alkylene glycols and polyalkylene glycols.
Other suitable cationic polymers are polyallylamines. Polymers of this type are obtained by homopolymerization of allylamine, preferably in the form neutralized with acids, or by copolymerization of allylamine with other monoethylenically unsaturated monomers which are described above as comonomers for N-vinylcarboxainides.
In addition, water-soluble crosslinked polyethylenimines which are obtainable by reacting polyethylenimines with crosslinking agents, such as epichlorohydrin or bischlorohydrin ethers of polyalkylene glycols having from 2 to 100 ethylene oxide and/or propylene oxide units and also have free primary and/or secondary amino groups are suitable. Amidic polyethylenimines which are obtainable, for example, by amidation of polyethylenimines with C1- to C22-monocarboxylic acids are also suitable. Further suitable cationic polymers are alkylated polyethylenimines and alkoxylated polyethylenimines. In the alkoxylation, for example, from 1 to 5 ethylene oxide or propylene oxide units are used per NH unit in the polyethylenimine.
The abovementioned catonic polymers have, for example, K values of from 8 to 300, preferably from 15 to 180 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25% and at a polymer concentration of 0.5% by weight). At a pH of 4.5, they have, for example, a charge density of at least 1, preferably at least 4, meq/g of polyelectrolyte.
Preferred cationic polymers are polymers comprising vinylamine units and polyethylenimines. Examples of these are:
vinylamine homopolymers, from 10 to 100% hydrolyzed polyvinylformamides, partly or completely hydrolyzed copolymers of vinylformamide and vinyl acetate, vinyl alcohol, vinylpyrrolidone or acrylamide, in each case having molar masses of 3 000-2 000 000, and
polyethylenimines, crosslinked polyethylenimines or amidated polyethylenimines, which have in each case molar masses of from 500 to 3 000 000.
The polymer content of the aqueous solution is, for example, from 1 to 60, preferably from 2 to 15, in general from 5 to 10, % by weight.
Cardboard is usually produced by draining a slurry of cellulose fibers. The use of kraft pulp is preferred. Furthermore, the use of TMP and CTMP is of particular interest. The pH of the cellulose fiber slurry is, for example, from 4 to 8, preferably from 6 to 8. The drainage of the paper stock can be carried out batchwise or continuously on a paper machine. Cationic polymer, engine size and retention aid can be added in any chosen sequence. However, a procedure in which first the retention aid and then the cationic polymer, preferably polyvinylamine, and then at least one reactive size, such as alkylketene dimer, alkyl- or alkenylsuccinic anhydride, in combination with an aluminum compound or a mixture of these sizes and a polymer size are added to the aqueous cellulose fiber slurry is preferred. According to another embodiment, first at least one polymer size, then the retention aid and finally the cationic polymer are metered.
In the production of the paper products to be used according to the invention, other assistants usually suitable may be present, for example fixing agents, dyes, bactericides and dry and/or wet strength agents for paper.
After the drainage of the paper stock and drying of the paper product, an engine sized cardboard having a basis weight of from 80 to 400, preferably from 120 to 220, g/m2 is obtained. The cardboard is laminated on one or both sides with a plastics film or metal foil, such as aluminum foil.
Suitable plastics films may be produced from polyethylene, polypropylene, polyamide or polyester. The films or foils can be bonded to the sized paper products, for example, with the aid of an adhesive. In such cases, films or foils which are coated with an adhesive are generally used and the laminate is pressed. However, the surface of the sized paper products can also be coated with an adhesive and the film or foils then applied to one or both sides and the resulting laminate pressed. However, the films or foils can also be processed with the cardboard directly by the action of heating and pressure to give a laminate, from which the suitable structures for production of the packaging for liquids are then cut out. The packagings are preferably used in the food sector, for example for packing beverages, such as mineral water, juices or milk, or for the production of beverage vessels, such as cups. In the case of these packagings, it is important that they have good edge penetration, i.e. the cardboard should absorb very little or virtually no liquid. The adhesion of films or foils to the paper products sized with polymer sizes is better than that of films or foils to paper products which are sized exclusively with alkylketene dimers.
In the examples which follow, percentages are by weight, unless evident otherwise from the context. The K values were determined according to H. Fikentscher, Cellulose-Chemie 13 (1932), 58-64 and 71-74, in 5% strength aqueous sodium chloride solution at 25° C. and a pH of 7 at a polymer concentration of 0.5% by weight. The molar masses MW of the polymers were measured by light scattering.
Determination of the Edge Penetration
The cardboard produced in each case was laminated on both sides with a polyethylene adhesive tape. The thickness of the cardboard was then determined. Test strips measuring 25×75 mm were then cut from the cardboard and weighed in each case. In order to determine the edge penetration, the test strips were dipped in a bath which comprised a 30% strength hydrogen peroxide solution thermostated at 70° C. The test strips were removed from the bath after a residence time of 10 minutes. Excess hydrogen peroxide was absorbed by means of filter paper. The test strips were once again weighed. The edge penetration in kg/m2 was then calculated from the increase in weight.
Ink Flotation Time
The ink flotation time (measured in minutes) is the time which a test ink requires according to DIN 53126 for 50% strike-through through a test sheet.
Cobb Value
The determination was carried out according to DIN 53 132 by storing the paper sheets for a period of 60 seconds in water. The water absorption is stated in g/m2.
0.75%, based in each case on dry paper stock, of a cationic starch (Solvitose BPN) was added as a retention aid to a paper stock having a consistency of 10 g/l and comprising 100% unbleached pine sulfate pulp having a freeness of 20° SR (Schopper-Riegler), and the pH of the mixture was brought to 7. In each case the amounts of stearyldiketene stated in the table, in the form of an aqueous dispersion (Basoplast® 4118MC), and an aqueous dispersion of the polymer sizes likewise stated in table 1 were then metered. The fiber slurries were thoroughly mixed in each case and drained on a Rapid-Köthen sheet former. Sheets having a basis weight of 150 g/m2 were obtained.
The following polymer sizes were used:
Polymer size A: Basoplast® 250D (aqueous dispersion of a copolymer, prepared by emulsion polymerization of acrylonitrile and n-butyl acrylate in the presence of degraded cationic starch as an emulsifier and hydrogen peroxide as an initiator).
Polymer size B: Basoplast® 265D (aqueous dispersion of a copolymer, prepared by emulsion polymerization of styrene and n-butyl acrylate in the presence of degraded cationic starch as an emulsifier and hydrogen peroxide as an initiator).
Polymer size C: Basoplast® PR8172 (aqueous dispersion of a copolymer, prepared by emulsion polymerization of styrene and n-butyl acrylate in the presence of cationic starch as an emulsifier and hydrogen peroxide as an initiator).
The sheets were then dried on a steam-heated drying cylinder at 90° C. to a water content of 6-10%. After the drying, the Cobb value of the sheets was determined. The sheets were then laminated on both sides with an adhesive tape polyethylene having a density of 0.918 g/cm3 (heating of the laminate under pressure to 30° C.). The edge penetration of the three-layer laminate was then determined. The results are shown in table 3.
0.75%, based in each case on dry paper stock, of a cationic starch (Solvitose BPN) was added as a retention aid to a paper stock having a consistency of 10 g/l and comprising 100% unbleached pine sulfate pulp having a freeness of 20° SR (Schopper-Riegler), and the pH of the mixture was brought to 7. In each case the amounts of stearyldiketene shown in table 2 were then metered in the form of an aqueous dispersion (Basoplast® 4118MC). Thereafter, in each case the aqueous fiber slurries were thoroughly mixed and were drained on a Rapid-Köthen sheet former to give a paper product having a basis weight of 150 g/m2.
The sheets were then dried on a steam-heated drying cylinder at 90° C. to a water content of 6-10%. After the drying, the Cobb value of the sheets was determined. The sheets were then adhesively bonded on both sides to a polyethylene adhesive tape (pressing of the laminate under pressure). The edge penetration of the three-layer laminate with respect to hydrogen peroxide was then determined. The results are shown in table 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103222677 | May 2003 | DE | national |
| 1020040019924 | Jan 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/04820 | 5/6/2004 | WO | 11/10/2005 |
