WO2015040242A1

WO2015040242A1 - Adhesive formulations for paper and methods of making and using the same

Info

Publication number: WO2015040242A1
Application number: PCT/EP2014/070265
Authority: WO
Inventors: Barry Sproule; Chafiq Belouadi
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2013-09-23
Filing date: 2014-09-23
Publication date: 2015-03-26
Anticipated expiration: 2016-03-23

Abstract

An adhesive formulation for paper is disclosed, comprising a first polymer obtained by polymerization of monomers including (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or combinations thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35; and a second polymer obtained by polymerization of monomers including at least 50% by weight of a vinyl formamide monomer. Methods of making the formulation, using it with paper, and paper bonded with the formulation are also disclosed.

Description

ADHESIVE FORMULATIONS FOR PAPER AND

METHODS OF MAKING AND USING THE SAME

TECHNICAL FIELD

The present disclosure relates generally to formulations for use in adhesive applications for paper, and methods of making the same.

BACKGROUND

Adhesive binding formulations are used to adhere paper substrates. For example, adhesive binding formulations are used to bind paperboard or cardboard substrates such as those used to form corrugated cardboard boxes. Typically, adhesive binding formulations for adhering corrugated cardboard substrates include starch. One issue with formulations including starch is that they can have undesirably high viscosities and can take large amounts of energy to dry the formulation after it has been used to bond the cardboard substrates. Therefore, it is desirable to reduce the amount of starch used in adhesive binding formulations while still maintaining adhesive strength and production speed.

SUMMARY

An adhesive formulation for paper is disclosed, comprising a first polymer obtained by polymerization of monomers including (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35; and a second polymer obtained by polymerization of monomers including at least 50% by weight of a vinyl formamide monomer. The formulation can be an aqueous composition comprising the first polymer and the second polymer. In some

embodiments, the second polymer is a vinyl formamide homopolymer. In some embodiments, the monomers polymerized to form the second polymer also include a vinylamine monomer. In some embodiments, the formulation includes from 0.5 to 5% by weight of the second polymer, based on the total dry weight of the first polymer and the second polymer. In some embodiments, (a) can include styrene and (b) can include butadiene. In some embodiments, (a) can include styrene and (b) can include a

(meth)acrylate monomer. The monomers in the first polymer can further include (meth)acrylamide, (meth)acrylonitrile, or mixtures thereof. In some embodiments, the carbohydrate derived compound can have a molecular weight of about 3000 to about 20,000 and can be selected from the group consisting of dextrins, maltodextrins, and mixtures thereof. The copolymer can be a pure acrylic copolymer, a styrene acrylic copolymer, a styrene butadiene copolymer, or a vinyl acrylic copolymer. The copolymer can be derived from about 1 to about 33 parts by weight of the carbohydrate derived compound based on the total monomer weight. The formulation can be substantially free of polyvinyl alcohol, carboxylmethylcellulose, polyvinylpyrrolidone and water-insoluble starches.

A method of preparing a paper adhesive formulation is disclosed, comprising mixing an aqueous dispersion of a first polymer obtained by polymerizing a mixture of (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35 with a second polymer obtained by polymerizing monomers including at least 50% by weight vinylformamide monomer. In some embodiments, the aqueous dispersion is prepared by polymerizing a mixture of (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35, in an aqueous medium. The second polymer can also be provided in an aqueous composition. The first polymer and the second polymer can be as described above.

A method of adhering a first paper substrate to a second paper substrate is also disclosed; comprising applying an adhesive formulation as described above to a first paper surface from a first paper substrate; and contacting a second paper surface from a second paper substrate with the first paper surface and adhering the first paper surface to the second paper surface via the adhesive formulation. In some embodiments, at least one of the first paper substrate and the second paper substrate are paperboard or cardboard, or the first paper substrate and the second paper substrate can both be paperboard or cardboard. In some embodiments, the applying and contacting steps are repeated to form a multilayered paper product.

A product is also disclosed, comprising a first paper surface bonded to a second paper surface using an adhesive formulation as described above. The product can be, for example, corrugated cardboard. The details of one or more embodiments are set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute part of this specification, illustrate several aspects described below.

Figure 1 displays the effects of total substitution of starch with a thickener and either Polymer Dispersion A or Polymer Dispersion B on dry pin adhesion.

Figure 2 displays the effects of total substitution of starch with a thickener and either Polymer Dispersion A or Polymer Dispersion B on wet pin adhesion.

DETAILED DESCRIPTION

The term "comprising" and variations thereof as used herein are open, non- limiting terms. The term "including" and variations thereof as used herein mean

"comprising" and variations thereof. The term "paper" as used herein includes free sheet, paperboard, cardboard, and the like. The term "(meth)acryl..." includes "acryl...," "methacryl...," or mixtures thereof.

A paper adhesive formulation comprises a first polymer and a second polymer. The first polymer is obtained by polymerization of monomers including (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound. The vinyl aromatic monomer (a) can include styrene, a-methylstyrene, o-chlorostyrene, vinyltoluenes, or mixtures thereof. In some embodiments, the (a) includes styrene. The diene monomer (b) can include 1,2- butadiene (i.e. butadiene); conjugated dienes (e.g. 1,3-butadiene and isoprene), or mixtures thereof. In some embodiments, (b) includes butadiene. The (meth)acrylate monomer (b) can include an ester of α,β-monoethylenically unsaturated mono- and dicarboxylic acids having 3 to 6 carbon atoms with alkanols having 1 to 12 carbon atoms (e.g. esters of acrylic acid, methacrylic acid, maleic acid, fumaric acid, or itaconic acid, with CI -C12, CI -C8, or CI -C4 alkanols such as ethyl, n-butyl, isobutyl and 2- ethylhexyl acrylates and methacrylates, dimethyl maleate and n-butyl maleate). In some embodiments, (b) includes ethylhexyl acrylate, n-butyl acrylate, or combinations thereof.

In addition to the vinyl aromatic and diene/(meth)acrylate monomers, the copolymer is formed from a carbohydrate derived compound. The carbohydrate derived compound can have a dextrose equivalent (DE) of about 10 to about 35, about 12.5 to about 25, or about 15 to about 20. The DE value can be determined in accordance with the Lane and Eynon test method (International Standard ISO 5377: 1981). The weight average molecular weight (M_w) of the carbohydrate derived compound can be about 3000 to about 20,000, about 5000 to about 17,000, or about 8000 to about 14,000. The carbohydrate derived compound can be soluble in water at room temperature in an amount of greater than about 40%, greater than about 50%, or greater than about 60% by weight, or can even be completely soluble in water at room temperature. Solutions of the carbohydrate derived compound in an amount of 50% by weight in water at room temperature can have a viscosity of 100 to 1000 cp, or 200 to 500 cp.

In some embodiments, the carbohydrate derived compound can include dextrins, maltodextrins, or mixtures thereof. The dextrins, maltodextrins, or mixtures thereof can have the DE's, molecular weights, water solubilities, and viscosities described above. The dextrins and maltodextrins are generally degraded starches whose degradation is effected by heating with or without addition of chemicals, it being possible to recombine degradation fragments under the degradation conditions to form new bonds which were not present in this form in the original starch. Roast dextrins such as white and yellow dextrins that are prepared by heating moist-dry starch, usually in the presence of small amounts of acid, are less preferred. The carbohydrate derived compound can be prepared as described in Guinther Tegge, Starke und Starkederivate, Behr's Verlag, Hamburg 1984, p. 173 and p. 220 ff. and in EP 441 197.

The carbohydrate derived compound can be can be prepared from any native starches, such as cereal starches (e.g. corn, wheat, rice or barley), tuber and root starches (e.g. potatoes, tapioca roots or arrowroot) or sago starches. The carbohydrate derived compound can also have a bimodal molecular weight distribution and can have a weight average molecular weight as described above. The carbohydrate derived compound can have a nonuniformity U (defined as the ratio between the weight average weight M_w and the number average molecular weight M_n) that characterizes the molecular weight distribution in the range from 6 to 12, from 7 to 11 or from 8 to 10. The proportion by weight of carbohydrate derived compound having a molecular weight of below 1000 can be from 10%> to 70%> by weight, or 20 to 40%> by weight. In some embodiments, the carbohydrate derived compound in a 40%> strength by weight aqueous solution can have a dynamic viscosity η⁴⁰ [Pa-s], determined in accordance with DIN 53 019 at 25 °C and a shear gradient of 75 s^"1, of from 0.01 to 0.06, 0.015 to 0.04, or 0.02 to 0.035. In some embodiments, the carbohydrate derived compound can be chemically modified such as by etherification or esterification. The chemical modification can also be carried out in advance on a starting starch before its degradation. Esterifications are possible using both inorganic and organic acids, or anhydrides or chlorides thereof.

Phosphated and acetylated degraded starches can also be used. The most common method of etherification is treatment with organohalogen compounds, epoxides or sulfates in aqueous alkaline solution. The ethers can be alkyl ethers, hydroxyalkyl ethers, carboxy alkyl ethers and allylethers.

The first polymer can be formed from one or more additional monomers. Suitable monomers include α,β-monoethylenically unsaturated mono- and dicarboxylic acids or anhydrides thereof (e.g. acrylic acid, methacrylic acid, crotonic acid, dimethacrylic acid, ethylacrylic acid, allylacetic acid, vinylacetic acid maleic acid, fumaric acid, itaconic acid, mesaconic acid, methylenemalonic acid, citraconic acid, maleic anhydride, itaconic anhydride, and methylmalonic anhydride); acrylamides and alkyl-substituted acrylamides (e.g. (meth)acrylamide, N-tert-butylacrylamide, and N-methyl(meth)acrylamide);

(meth)acrylonitrile; vinyl and vinylidene halides (e.g. vinyl chloride and vinylidene chloride); vinyl esters of CI -CI 8 mono- or dicarboxylic acids (e.g. vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate); C1-C4 hydroxyalkyl esters of C3-C6 mono- or dicarboxylic acids, especially of acrylic acid, methacrylic acid or maleic acid, or their derivatives alkoxylated with from 2 to 50 moles of ethylene oxide, propylene oxide, butylene oxide or mixtures thereof, or esters of these acids with CI - C18 alcohols alkoxylated with from 2 to 50 mol of ethylene oxide, propylene oxide, butylene oxide or mixtures thereof (e.g. hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and methylpolyglycol acrylate); and monomers containing glycidyl groups (e.g. glycidyl methacrylate).

Other additional monomers that can be used include linear 1 -olefins, branched- chain 1 -olefins or cyclic olefins (e.g., ethene, propene, butene, isobutene, pentene, cyclopentene, hexene, and cyclohexene); vinyl and allyl alkyl ethers having 1 to 40 carbon atoms in the alkyl radical, wherein the alkyl radical can possibly carry further substituents such as a hydroxyl group, an amino or dialkylamino group, or one or more alkoxylated groups (e.g. methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2-(diethylamino)ethyl vinyl ether, 2-(di-n-butylamino)ethyl vinyl ether, methyldiglycol vinyl ether, and the corresponding allyl ethers); sulfo- functional monomers (e.g. allylsulfonic acid, methallylsulfonic acid, styrenesulfonate, vinylsulfonic acid, allyloxybenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their corresponding alkali metal or ammonium salts, sulfopropyl acrylate and sulfopropyl methacrylate); vinylphosphonic acid, dimethyl vinylphosphonate, and other phosphorus monomers; alkylaminoalkyl (meth)acrylates or alkylaminoalkyl(meth)acrylamides or quaternization products thereof (e.g. 2-(N,N-dimethylamino)ethyl (meth)acrylate, 3-(N,N-dimethylamino)propyl (meth)acrylate, 2-(N,N,N-trimethylammonium)ethyl (meth)acrylate chloride, 2- dimethylaminoethyl(meth)acrylamide, 3-dimethylaminopropyl(meth)acrylamide, and 3- trimethylammoniumpropyl(meth)acrylamide chloride); allyl esters of CI -C30 monocarboxylic acids; N- Vinyl compounds (e.g. N-vinylformamide, N-vinyl-N- methylformamide, N-vinylpyrrolidone, N-vinylimidazole, l-vinyl-2-methylimidazole, 1- vinyl-2-methylimidazoline, N-vinylcaprolactam, vinylcarbazole, 2-vinylpyridine, and 4- vinylpyridine); monomers containing 1,3-diketo groups (e.g.

acetoacetoxyethyl(meth)acrylate or diacetonacrylamide; monomers containing urea groups (e.g. ureidoethyl (meth)acrylate, acrylamidogly colic acid, and

methacrylamidoglycolate methyl ether); and monomers containing silyl groups (e.g. trimethoxy sily lpropy 1 methacrylate) .

The monomers can also include one or more crosslinkers such as N-alkylolamides of α,β-monoethylenically unsaturated carboxylic acids having 3 to 10 carbon atoms and esters thereof with alcohols having 1 to 4 carbon atoms (e.g. N-methylolacrylamide and N-methylolmethacrylamide); glyoxal based crosslinkers; monomers containing two vinyl radicals; monomers containing two vinylidene radicals; and monomers containing two alkenyl radicals. Exemplary crosslinking monomers include diesters of dihydric alcohols with α,β-monoethylenically unsaturated monocarboxylic acids, of which in turn acrylic acid and methacrylic acid can be employed. Examples of such monomers containing two non-conjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate and propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate and methylenebisacrylamide. In some embodiments, the crosslinking monomers include alkylene glycol diacrylates and dimethacrylates, and/or

divinylbenzene. The crosslinking monomers when used in the copolymer can be present in an amount of from 0.2% to 5% by weight based on the weight of the total monomer and are considered part of the total amount of monomers used in the copolymer.

In addition to the crosslinking monomers, small amounts (e.g. from 0.01 to 4% by weight based on the total monomer weight) of molecular weight regulators, such as tert- dodecyl mercaptan. Such substances are preferably added to the polymerization zone in a mixture with the monomers to be polymerized and are considered part of the total amount of unsaturated monomers used in the copolymer.

In some embodiments, the first polymer can be a styrene butadiene copolymer derived from monomers including styrene, butadiene, the carbohydrate derived compound, and optionally (meth)acrylamide, (meth)acrylonitrile, or an acrylic acid such as itaconic acid, (meth)acrylic acid, or mixtures thereof. The styrene butadiene copolymer can include from 40 to 75 parts by weight of styrene, from 25 to 60 parts by weight of butadiene, from greater than 0 to less than 50 parts by weight of the

carbohydrate derived compound, 0 to 10 parts by weight (e.g., 1 to 8, or 2 to 6 parts by weight) of itaconic and/or (meth)acrylic acid, 0 to 3 parts by weight of (meth)acrylamide, and 0 to 20 parts by weight (e.g., 0 to 10 parts by weight) (meth)acrylonitrile. The styrene butadiene copolymer can also include from 0 to 5 parts by weight of one or more crosslinking monomers as described above such as divinylbenzene. In some

embodiments, the first polymer is derived from 45 to 70 parts, 50 to 65 parts, or 55 to 60 parts by weight, styrene. In some embodiments, the first polymer is derived from 30 to 50 parts, 32 to 45 parts, or 35 to 42 parts by weight, of butadiene. In some embodiments, the first polymer is derived from 5 to 45 parts, 8 to 40 parts, or 15 to 35 parts by weight, of the carbohydrate derived compound. Alternatively, the styrene butadiene copolymer can include from 30 to 70%> (e.g., 40-60%>) by weight of styrene, from 18 to 55% (e.g., 20-45%) by weight of butadiene, from greater than 0 to 33% (e.g., 3-31% or 5-29%) by weight of the carbohydrate derived compound, 0 to 8% by weight (e.g., 1-7% or 2-6% by weight) of itaconic and/or (meth)acrylic acid, 0 to 3% (e.g., 0-2% by weight) by weight of (meth)acrylamide, and 0 to 15% by weight (e.g., 0-8% by weight) (meth)acrylonitrile.

In some embodiments, the copolymer can be a styrene acrylic copolymer derived from monomers including styrene, (meth)acrylic acid esters, the carbohydrate derived compound, and optionally (meth)acrylic acid, (meth)acrylamide, (meth)acrylonitrile, and mixtures thereof. For example, the styrene acrylic copolymer can include styrene, the carbohydrate derived compound, and at least one of (meth)acrylic acid, itaconic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate. The styrene acrylic copolymer can include from 30 to 60 parts by weight of styrene, from 39 to 69 parts by weight of

(meth)acrylates, from greater than 0 to less than 50 parts by weight of the carbohydrate derived compound, 0 to 10 parts by weight (e.g., 1 to 8, or 2 to 6 parts by weight) of itaconic and/or (meth)acrylic acid, 0 to 3 parts by weight of (meth)acrylamide, and 0 to 10 parts by weight (e.g., 0 to 5 parts by weight) (meth)acrylonitrile. In some embodiments, the first polymer is derived from 35 to 55 parts, or 40 to 50 parts by weight, styrene. In some embodiments, the first polymer is derived from 45 to 65 parts, or 50 to 60 parts by weight, of (meth)acrylates. In some embodiments, the first polymer is derived from 5 to 45 parts, 8 to 40 parts, or 15 to 35 parts by weight, of the carbohydrate derived compound. The styrene acrylic copolymer can also include from 0 to 5 parts by weight of one or more crosslinking monomers as described above such as alkylene glycol diacrylates and dimethacrylates. Alternatively, the styrene acrylic copolymer can include from 20 to 50% (e.g., 23-48%) or 25-45%) by weight of styrene, from 25 to 55% by weight of

(meth)acrylates (e.g., 30-53% or 35-50%), from greater than 0 to 33% (e.g., 3-31% or 5- 29%) by weight of the carbohydrate derived compound, 0 to 8% by weight (e.g., 1-7% or 2-6%o by weight) of itaconic and/or (meth)acrylic acid, 0 to 3% (e.g., 0-2% by weight) by weight of (meth)acrylamide, and 0 to 8% by weight (e.g., 0-5% by weight)

(meth)acrylonitrile, and from 0 to 4% by weight of one or more crosslinking monomers as described above such as alkylene glycol diacrylates and dimethacrylates.

In some embodiments, the first polymer can be a blend of a styrene butadiene copolymer and a styrene acrylic copolymer.

The first polymer can be provided as an aqueous polymer dispersion. The aqueous polymer dispersion can include, as the disperse phase, particles of the first polymer including the carbohydrate derived compound dispersed in an aqueous dispersion medium or aqueous phase. The aqueous polymer dispersion can include the first polymer in an amount of 40-75% solids.

The aqueous polymer dispersions can be prepared by polymerizing the

unsaturated monomers using free-radical aqueous emulsion polymerization in the presence of the carbohydrate derived compound. Suitable methods are described in U.S. Patent No. 6,080,813, which is hereby incorporated by reference in its entirety. The emulsion polymerization temperature is generally from 30 to 95 °C or from 75 to 90°C. The polymerization medium can include water alone or a mixture of water and water- miscible liquids, such as methanol. In some embodiments, water is used alone. The emulsion polymerization can be carried out either as a batch process or in the form of a feed process, including a step or gradient procedure. In some embodiments, a feed process is used in which part of the polymerization batch is heated to the polymerization temperature and partially polymerized, and the remainder of the polymerization batch is subsequently fed to the polymerization zone continuously, in steps or with superposition of a concentration gradient, usually via a plurality of spatially separate feed streams, of which one or more contain the monomers in pure or emulsified form, while maintaining the polymerization. The initially introduced mixture and/or the monomer feed stream can contain small amounts of emulsifiers, generally less than 0.5% by weight, based on the total amount of monomers to be polymerized. The monomers can be frequently fed to the polymerization zone after pre-emulsification with these assistant emulsifiers. The feed process can be designed by initially introducing all of the carbohydrate derived compound to be used in dissolved form in an aqueous mixture. This means that the aqueous solution produced on partial hydrolysis of the starting starch can, after the hydrolysis has been terminated to form the carbohydrate derived compound, for example by neutralization of the catalytic acid and cooling, be further used directly for the aqueous emulsion polymerization. Prior isolation of the carbohydrate derived compound, for example by spray drying, is unnecessary but can also be used.

The free-radical emulsion polymerization can be carried out in the presence of a free-radical polymerization initiator. The free-radical polymerization initiators that can be used in the process are all those which are capable of initiating a free-radical aqueous emulsion polymerization including alkali metal peroxydisulfates and H2O2, or azo compounds. Combined systems can also be used comprising at least one organic reducing agent and at least one peroxide and/or hydroperoxide, e.g., tert-butyl

hydroperoxide and the sodium metal salt of hydro xymethanesulfmic acid or hydrogen peroxide and ascorbic acid. Combined systems can also be used additionally containing a small amount of a metal compound which is soluble in the polymerization medium and whose metallic component can exist in more than one oxidation state, e.g., ascorbic acid/iron(II) sulfate/hydrogen peroxide, where ascorbic acid can be replaced by the sodium metal salt of hydroxymethanesulfinic acid, sodium sulfite, sodium hydrogen sulfite or sodium metal bisulfite and hydrogen peroxide can be replaced by tert-butyl hydroperoxide or alkali metal peroxydisulfates and/or ammonium peroxydisulfates. In the combined systems, the carbohydrate derived compound can also be used as the reducing component. In general, the amount of free-radical initiator systems employed is from 0.1 to 2% by weight, based on the total amount of the monomers to be polymerized. In some embodiments, the initiators are ammonium and/or alkali metal peroxydisulfates (e.g. sodium peroxydisulfates), alone or as a constituent of combined systems.

The manner in which the free-radical initiator system is added to the

polymerization reactor during the free-radical aqueous emulsion polymerization is not critical. It can either all be introduced into the polymerization reactor at the beginning, or added continuously or stepwise as it is consumed during the free-radical aqueous emulsion polymerization. In detail, this depends in a manner known to an average person skilled in the art both from the chemical nature of the initiator system and on the polymerization temperature. In some embodiments, some is introduced at the beginning and the remainder is added to the polymerization zone as it is consumed. It is also possible to carry out the free-radical aqueous emulsion polymerization under

superatmospheric or reduced pressure.

The paper adhesive formulation includes a second polymer. The second polymer can be obtained by polymerization of monomers including at least 50% by weight of a vinyl formamide monomer. For example, the second polymer can be polymerized from 50% or greater, 55% or greater, 60% or greater, 65 % or greater, 70% or greater, 75% or greater, 80% or greater, 85% or greater, 90% or greater, or 95% or greater, by weight of vinyl formamide monomer. In some embodiments, the second polymer can be either anionic or nonionic. In some embodiments, the second polymer is a vinyl formamide homopolymer. A suitable vinyl formamide homopolymer is LUPAMIN 4500, an aqueous solution having 36% solids and commercially available from BASF Corporation. In some embodiments, the monomers polymerized to form the second polymer also include a second monomer such as a vinylamine monomer. Suitable vinyl formamide copolymers are commercially available from BASF Corporation under the LUPAMIN trademark. The second polymer can have a molecular weight of from 2000 to 8000, e.g., from 4000 to 6000. The second polymer can be provided in an aqueous composition such as an aqueous solution of the second polymer.

The paper adhesive formulation can include from 0.5 to 5% by weight of the second polymer, based on the total dry weight of the first polymer and the second polymer. For example, the paper adhesive formulation can include 0.6 to 4% by weight, 0.7 to 3%) by weight, 0.8 to 2.5% by weight, 0.9 to 2% by weight, of the second polymer, based on the total dry weight of the first polymer and the second polymer. The adhesive formulation can include a thickener. Suitable thickeners include (meth)acrylic acid/alkyl (meth)acrylate copolymers, hydroxy ethyl cellulose, guar gum, jaguar, carrageenan, xanthan, acetan, konjac mannan, xyloglucan, urethanes and mixtures thereof. The thickener can be added to the formulation as an aqueous dispersion or emulsion, or as a solid powder.

In some embodiments, the adhesive formulation can include one or more additional additives. The additives can include any additives that can be generally included in an adhesive binding formulation for paper. Suitable additives include fillers, pigments, dyes, surfactants, leveling aids (e.g. polyvinylpyrrolidone), wetting agents, protective colloids, biocides, dispersing agents, thixotropic agents, freeze store stability additives, pH adjusting agents, corrosion inhibitors, ultraviolet light stabilizers, solubilizers (e.g., if the first polymer is a styrene acrylic based copolymer), crosslinkers, crosslinking promoters, and lubricants.

In some embodiments, the formulation can be substantially free of or free of polyvinyl alcohol, carboxylmethylcellulose, polyvinylpyrrolidone and water-insoluble starches. In some embodiments, the formulation can be substantially free of or free of water-insoluble starches. The formulation can be "substantially free" of a particular compound by including, for example, less than 0.5% or less than 0.1% by weight of the compound.

The paper adhesive or coating composition can include about 30-60%) solids, for example 30%, 35%, 40%, 45%, 50%, 55%, or 60% solids by weight.

The adhesive formulation can be applied to the paper substrate as a coating. Typically, the coating is applied at locations on the paper substrate that are to be adhered to another substrate such as another paper substrate. The formulation can be applied using any known method in the art. The adhesive can be applied at a viscosity of from 200-800 cp at 25°C and a thickness of from 0.001 to 0.005 inches. Once the coating is applied to a first surface of the first paper substrate, a second paper substrate can be contacted with the first paper surface along a second paper surface thereby adhering the first paper surface to the second paper surface using the adhesive formulation. The adhesive formulation can then be dried by using heat (e.g., at a temperature of from 85- 120°C). The adhesive formulation can be applied at a cardboard line speed of 150-950 meters per minute and can be applied at 500 meters per minute or greater, or 600 meters per minute or greater. In some embodiments, at least one of the first paper substrate and the second paper substrate are paperboard or cardboard, or the first paper substrate and the second paper substrate can both be paperboard or cardboard. In some embodiments, the applying and contacting steps are repeated to form a multilayered paper product.

The adhesive formulation provides sufficient adhesive strength and can be dried with less energy requirements than known formulations based on starch. Thus, a laminating machine can dry the adhesive with a lower energy requirement or can be run at higher line speeds, depending on the particular need. The wet-shear numbers for the formulation when used to bond cardboard substrates can exceed 10,000 seconds (with a 1 kg weight) as described in TAPPI UM 807 (1991).

The resulting paper product comprises a first paper surface bonded to a second paper surface using an adhesive formulation as described above. The product can be, for example, corrugated cardboard.

EXAMPLES

Example 1

A carboxylated styrene -butadiene aqueous polymer (first polymer) dispersion was prepared by polymerizing 58 parts by weight styrene, 38 parts by weight butadiene, 30 parts by weight of a maltodextrin compound, and 4 parts by weight acrylic acid. The maltodextrin compound had a DE=18 and a M_w of 11 ,000. The aqueous dispersion had a solid percentage of about 68%. The aqueous dispersion was combined with sufficient LUPAMIN 4500 to produce 1% by weight of the second polymer, based on the total dry monomer weight of the first polymer and second polymer.

The resulting dispersion was applied to a cardboard substrate and tested. The wet- shear numbers for the formulation when used to bond a cardboard substrate exceeded 10,000 seconds (with a 1 kg weight) using the procedure described in TAPPI UM 807 (1991).

Example 2

The performance characteristics of a maltodextrin-based polymer dispersion and Lupimen 4500 were assessed when used in an adhesive.

The corrugator machine used a liner and medium. Starch adhesive was from Harper Love (27% solids, 14 seconds Love Cup viscosity). Glue loading was controlled by glue gap at the single facer - the standard setting was 0.012" and 0.007" for the reduced loading setting. An ISO Bar glue applicator roll was utilized at the double backer. The glue film was controlled by a metering rod and the applicator roll speed. A #20 metering rod was used and applicator roll speed was varied from 60% to 75% to control glue loading (the higher the roll speed, the lower the glue loading). The corrugator machine speed was between 100 and 150 fpm. Two glue loading conditions were run for each condition. Samples were evaluated for wet and dry pin adhesion, edge crush and glue weight. The glue weight was determined gravimetrically using untreated samples of both the liner and medium.

Lupimen 4500 and Sterocoll FS (an aqueous, anionic dispersion of an ethyl acrylate-carboxylic acid copolymer) were assessed as thickeners with two Polymer Dispersions: Polymer Dispersion A, a copolymer prepared by polymerizing styrene, acrylonitrile, butyl acrylate, and acrylic acid, and having 50%> solids, a pH of 7.5, an average particle size of 200 nm, and a T_g of 4°C; and Polymer Dispersion B, a copolymer prepared by polymerizing styrene, butadiene, itaconic acid, acrylic acid, and 30%> by weight maltodextrin, and having 50%> solids, a pH of 7, an average particle size of 125 nm, and a T_g of 15°C.

Thickener addition levels and resultant viscosity are summarized in Table 1. Two glue addition levels were run for each condition, and the results for each are shown in Table 2. The effects of total substitution of starch with a thickener and either Polymer Dispersion A or Polymer Dispersion B on dry and wet pin adhesion are shown in Figure 1 and Figure 2, respectively. The performance of both products is better when thickened with Lupimen 4500, compared to with Sterocoll FS, and Polymer Dispersion B had better overall dry and wet pin performance, particularly at a 25% reduction, over Polymer Dispersion A.

Table 1. Effects of thickeners on viscosity

Table 2. Polymer Dispersions in combination with thickeners

*Experimental conditions resulted in a very low signal to noise ratio for glue weight determinations, leading to unreliable glue weight measurements.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Further, while only certain representative combinations of the formulations, methods, or products are disclosed herein are specifically described, other combinations of the method steps or combinations of elements of a composition or product are intended to fall within the scope of the appended claims. Thus a combination of steps, elements, or components may be explicitly mentioned herein; however, all other combinations of steps, elements, and components are included, even though not explicitly stated.

Claims

CLAIMS What is claimed is:

1. An adhesive formulation for paper, comprising:

a first polymer obtained by polymerization of monomers including (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35; and

a second polymer obtained by polymerization of monomers including at least 50% by weight of a vinyl formamide monomer.

2. The formulation according to claim 1, wherein the formulation is an aqueous composition comprising the first polymer and the second polymer.

3. The formulation according to any of the claims 1-2, wherein the second polymer is a vinyl formamide homopolymer.

4. The formulation according to any of the claims 1-2, wherein the monomers polymerized to form the second polymer also include a vinylamine monomer.

5. The formulation according to any of the claims 1-4, wherein the formulation includes from 0.5 to 5% by weight of the second polymer, based on the total dry weight of the first polymer and the second polymer.

6. The formulation according to any of the claims 1-5, wherein (a) includes styrene and (b) includes butadiene.

7. The formulation according to any of the claims 1-5, wherein (a) includes styrene and (b) includes a (meth)acrylate monomer.

8. The formulation according to any of the claims 1-7, wherein the monomers in the first polymer further include (meth)acrylamide, (meth)acrylonitrile, or mixtures thereof.

9. The formulation according to any of the claims 1-8, wherein the carbohydrate derived compound is selected from the group consisting of dextrins, maltodextrins, and mixtures thereof.

10. The formulation according to any of the claims 1-9, wherein the DE of the carbohydrate derived compound is from about 12.5 to about 25.

11. The formulation according to any of the claims 1-9, wherein the DE of the carbohydrate derived compound is from about 15 to about 20.

12. The formulation according to any of the claims 1-1 1, wherein the molecular weight of the carbohydrate derived compound is from about 3000 to about 20,000.

13. The formulation according to any of the claims 1-1 1, wherein the molecular weight of the carbohydrate derived compound is from about 5000 to about 17,000.

14. The formulation according to any of the claims 1-13, wherein the carbohydrate derived compound is soluble in water at room temperature in an amount of greater than about 40% by weight.

15. The formulation according to any of the claims 1-14, wherein the copolymer is derived from about 1 to about 33 percent by weight of the carbohydrate derived compound based on the total monomer weight.

16. The formulation according to any of the claims 1-14, wherein the copolymer is derived from about 5 to about 29 percent by weight of the carbohydrate derived compound based on the total monomer weight.

17. The formulation according to any of the claims 1-16, wherein the aqueous polymer dispersion comprises a disperse phase and an aqueous phase and the carbohydrate derived compound provided in the copolymer is present in the disperse phase.

18. The formulation according to any of the claims 1-17, wherein the formulation is substantially free of water-insoluble starches.

19. The formulation according to any of the claims 1-17, wherein the formulation is substantially free of polyvinyl alcohol, carboxylmethylcellulose, polyvinylpyrrolidone and water-insoluble starches.

20. A method of preparing a paper adhesive formulation, comprising:

mixing an aqueous dispersion of a first polymer obtained by polymerizing a mixture of (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35, with a second polymer obtained by polymerizing monomers including at least 50% by weight vinylformamide monomer.

21. The method according to claim 20, further comprising the step of polymerizing a mixture of (a) a vinyl aromatic monomer, (b) a diene monomer, a (meth)acrylate monomer, or a combination thereof, and (c) a carbohydrate derived compound having a dextrose equivalent (DE) of about 10 to about 35, in an aqueous medium to produce the aqueous dispersion.

22. The method according to any of the claims 20-21, wherein the mixing step comprises mixing an aqueous composition comprising the second polymer with an aqueous dispersion of the first polymer.

23. The method according to any of the claims 20-22, wherein the second polymer is a vinyl formamide homopolymer.

24. The method according to any of the claims 20-23, wherein the monomers polymerized to form the second polymer also include a vinylamine monomer.

25. The formulation according to any of the claims 20-24, wherein the formulation includes from 0.5 to 5% by weight of the second polymer, based on the total dry weight of the first polymer and the second polymer.

26. The formulation according to any of the claims 20-25, wherein (a) includes styrene and (b) includes butadiene.

27. The formulation according to any of the claims 20-25, wherein (a) includes styrene and (b) includes a (meth)acrylate monomer.

28. The formulation according to any of the claims 20-27, wherein the monomers in the first polymer further include (meth)acrylamide, (meth)acrylonitrile, or mixtures thereof.

29. The method according to any of the claims 20-28, wherein the carbohydrate derived compound is selected from the group consisting of dextrins, maltodextrins, and mixtures thereof.

30. The method according to any of the claims 20-29, wherein the DE of the carbohydrate derived compound is from about 12.5 to about 25.

31. The method according to any of the claims 20-30, wherein the molecular weight of the carbohydrate derived compound is from about 3000 to about 20,000.

32. The method according to any of the claims 20-31 , wherein said polymerizing step comprising first mixing an aqueous solution of a carbohydrate derived compound at room temperature comprising greater than about 40% by weight of the carbohydrate derived compound with the unsaturated monomer and polymerizing the mixture to form the copolymer.

33. The method according to any of the claims 20-32, wherein the copolymer is derived from about 1 to about 33 percent by weight of the carbohydrate derived compound based on the total monomer weight.

34. The method according to any of the claims 20-33, wherein the formulation is substantially free of water-insoluble starches.

35. The method according to any of the claims 20-33, wherein the formulation is substantially free of polyvinyl alcohol, carboxylmethylcellulose, polyvinylpyrrolidone and water-insoluble starches.

36. A method of adhering a first paper substrate to a second paper substrate;

comprising:

applying the adhesive formulation of any of claims 1-19 or the formulation prepared by the method of any of claims 20-35 to a first paper surface from a first paper substrate; and

contacting a second paper surface from a second paper substrate with the first paper surface and adhering the first paper surface to the second paper surface via the adhesive formulation.

37. The method according to claim 36, wherein at least one of the first paper substrate and the second paper substrate are paperboard or cardboard.

38. The method according to claim 36, wherein the first paper substrate and the second paper substrate are paperboard or cardboard.

39. The method according to any of the claims 36-38, wherein the applying and contacting steps are repeated to form a multilayered paper product.

40. A product, comprising a first paper surface bonded to a second paper surface using an adhesive formulation of any of claims 1-19 or the formulation prepared by the method of any of claims 20-35.

41. The product according to claim 40, where the product is corrugated cardboard.