Paper making and fiber liberation – Processes and products – Multi-layer waterlaid webs or sheets
Reexamination Certificate
2001-01-03
2004-03-16
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
Multi-layer waterlaid webs or sheets
C137S164000, C137S175000, C137S184000, C137S186000, C106S205600, C106S205720, C106S214100, C106S215500, C427S411000, C427S421100, C156S302000, C156S307300, C156S307700, C156S324000
Reexamination Certificate
active
06706145
ABSTRACT:
The invention relates to aqueous adhesive dispersions and to a process for producing multilayered paper, cardboard and carton having improved layer and ply strength, using said adhesive dispersions.
Multilayered papers are obtained from paper pulp mixtures of same or different composition by compressing (couching) the wet paper webs. Essentially, the quality of multilayered packaging papers or cartons is determined by the internal strength of these materials, the cohesion in the interface region between the individual plies of paper representing a weak point, however. Therefore, adhesive starch or starch derivatives are frequently used to improve the layer and ply strength. When exposed to major shear forces, heat or increased moisture during storage and further processing, however, stability may be lost even in products produced in this fashion, and the material may undergo breaking.
To date, native or modified starch in the form of an aqueous dispersion is sprayed as adhesive onto or between the paper plies, undergoing gelatinization in the drying section of the paper machine, thereby effecting bonding of the plies. Frequently, however, the layer and ply strength achieved in this manner is limited, particularly in those cases where the starch bonding undergoes complete or partial irreversible embrittlement during subsequent heat exposure. According to F. Andruchovici and R. Wilken, PTS-Verlag Munich, 1994, PTS-Forschungsbericht, PTS-FB 09/93, p. 19, the use of native starch is disadvantageous in that native starch can be employed with only low solids content due to its rheological characteristics (high viscosity), while the exclusive use of cationic starch is disadvantageous for cost reasons.
According to EP-B-310,078, an adhesive composition of stable viscosity on the basis of gelled particulate starch is used in the production of corrugated cardboard, which starch is employed together with a polymeric thickening agent of basic reaction, such as an acetone-formaldehyde resin, in the form of an aqueous dispersion.
A concentrated starch glue for the production of corrugated cardboard is known from DE-A-44 01 529, which includes an ionic surfactant to reduce its viscosity.
According to EP-B-415,385, surface and web strength and tear resistance of paper and cardboard are achieved by spraying the wet paper webs with a slurry of non-gelled starch grains having a gel temperature of 35-55° C., previously obtained by heating a mixture of crude starch, urea, phosphoric acid or a phosphate at a temperature of 80-150° C. for a period of from 0.5 to 5 hours.
Other paper sizing agents are known from EP-A-742,316, which agents include cationized starch preferably esterified with unsaturated dicarboxylic acids or anhydrides.
These well-known adhesives can only be produced with high technical input and have an adhesive effect that is insufficient for many applications.
Likewise, the use of polyacrylamide instead of starch as strengthening agent in spray coating, as described by K. Sato in Japan Tappi Journal 49, 318-323 (1995), No. 2, is inappropriate. Alternatively, the product is employed in the form of a solution which, however, not only remains on the surface of the paper web after spraying, but rather, penetrates therein.
Furthermore, a process for producing an abrasion-resistant decorative laminate is known from EP-B-555,093, wherein an aqueous slurry of aluminum oxide particles and a high molecular weight cationic retention agent such as polyacrylamide is coated on the uppermost wet layer of paper material and then subjected to further conventional paper manufacturing.
EP-B-606,431 describes a composition for coating cardboard, containing cationic starch and a vinyl acetate polymerization product which are also coated together with pigments. As is well-known, however, laminating of paper sheet materials involves other requirements as compared to the production of multilayered paper per se.
It was therefore the object to provide an adhesive dispersion that would enable easy production of multilayered paper with improved properties, particularly with enhanced layer and ply strength.
Said object is accomplished by providing the aqueous adhesive dispersions according to the invention, containing
A) 0.1-10 wt.-%, preferably 2-6 wt.-%, relative to the overall weight of the dispersion, of an adhesive polymer in dispersed form,
B) 0.1-100 parts by weight, preferably 0.1-20 parts by weight, more preferably 0.1-10 parts by weight, relative to 100 parts by weight of component A), of at least one anionic or cationic polyelectrolyte, and
C) 0-50 parts by weight, preferably 0.1-30 parts by weight, more preferably 0.1-20 parts by weight, relative to 100 parts by weight of component A), of at least one polyalkylene glycol having a molar mass ranging from 200 to 100,000 g/mol.
At least one natural or synthetic adhesive polymer, preferably a polysaccharide, an optionally modified polysaccharide, a protein, and/or a polyvinyl alcohol is used as component A), which polymer is present in dispersed form in said dispersion, i.e., has not been heated above its gelatinization temperature.
It is particularly preferred to use starch, modified starch, cellulose ethers such as carboxymethylcellulose, polyvinyl alcohols, alginates, proteins such as glutin, casein, and/or guar meal as adhesive polymers. However, starch and/or starch derivatives are preferred for economic reasons.
In this context, native starch, such as potato starch, wheat starch, corn starch, rice starch, pea starch and/or mixtures thereof, modified starches such as starch degradation products, particularly dextrins, chemically modified starches such as substituted starch derivatives and especially anionic starches such as dialdehyde starch, carboxystarch, and starch degraded by persulfate, anionic starch esters such as starch phosphoric acid mono- or di-esters, starch acetates and starch citrates, anionic starch ethers such as carboxymethylstarch, carboxymethyl-2-hydroxyethylstarch, and carboxymethyl-3-hydroxypropylstarch, and cationic starch derivatives such as N-containing starch ethers, particularly starches having primary or secondary amino or imino groups, and tertiary amino groups positively charged by protonation with acids, and quaternary ammonium groups are used.
The cationic or anionic polyelectrolytes to be used as component B) according to the invention are selected from the group of synthetic or optionally modified natural polymer products. Preferably, they are water-soluble or water-swellable cationic or anionic synthetic homo- or co-polymers of monoethylenically unsaturated monomers with acid groups which at least partially are present as salts, or their esters with di(C
1
-C
2
)alkylamino(C
2
-C
6
)alkylalcohols, or their amides with di(C
1
-C
2
)alkylamino(C
2
-C
6
)alkylamines as reported in EP-A-0,013,416 or in EP-A-0,113,038, each one being used in protonated or quaternized form, and optionally other monoethylenically unsaturated monomers.
These polyelectrolytes are remarkable in that they do not act as a flocculant for component A) below the gelatinization temperature thereof, but rather, form stable aqueous dispersions with A).
Preferably, homopolymers or copolymers of water-soluble, monoethylenically unsaturated vinyl compounds, such as acrylic acid and methacrylic acid esters of dialkylaminoalkylalcohols in protonated or quaternized form, such as dimethylaminoethyl acrylate, acrylic acid and methacrylic acid amides of dialkylaminoalkylamines, in protonated or quaternized form, such as acrylamidopropyltrimethylammonium chloride and/or acrylamidopropyltrimethylammonium methyl methosulfate can be used as cationically active polyelectrolytes.
Furthermore, Mannich bases of polymers containing acrylamide, polyvinylamines, polyamines such as diethyleneamine, dipropylenetriamine, triethylenetetramine, and polyalkylenepolyamines (polyethyleneimines) with molar masses of from 450 to 100,000 g/mol, preferably liquid polyalkylenepolyamines with molar masses of from 450 to 20,000 g/mol or solutions thereof in water are suitable as ca
Reinhardt Bernd
Rienaecker Klaus
Werres Joachim
Ahlstrom GmbH
Griffin Steven P.
Hug Eric
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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