Abstract: Decorated sheets on the basis of cellulose non-woven fabrics, such as paper, for the production of decorated laminates are impregnated with synthetic resins. Consequently, their sizes are changed, they become brittle and are not water-resistant in the laminate. In the method according to the invention the printed or unprinted non-woven fabrics are impregnated with an aqueous dispersion of a polymer which is cross-linkable by UV radiation, dried and optionally printed and finally irradiated with UV radiation. The decorated sheets thus obtained are water-resistant in the laminate and can be coiled up and stored after each process step.

Abstract: Methods for making phenolic resins modified with one or more monosaccharides and methods for making composite products therewith are provided. In at least one specific embodiment, a method for making a composite product can include contacting a plurality of cellulosic sheets with a resin composition that includes a phenolic resin and a monosaccharide. The resin composition can include about 0.5 wt % to about 30 wt % of the monosaccharide, based on a combined weight of the phenolic resin and the monosaccharide. The method can also include at least partially curing the resin composition to produce a composite product.

Abstract: A fire retardant intumescent coating composition is disclosed, which includes expandable graphite, an aromatic polyamine resin, and a phosphorous-containing compound. An overlay for applying to a wood substrate is also disclosed, which includes a core layer comprising a substrate and a resin composition, a top layer on one side of the core layer comprising the fire retardant intumescent coating composition, and an optional bottom layer on the opposite side of the core layer from the top layer. A process of forming the overlay is also disclosed, which includes applying the resin composition to the core layer substrate to form a resinated core layer, and applying a coating composition on the resinated core layer, directly or indirectly, to form the top layer; wherein the coating composition comprises expandable graphite, an aromatic polyamine resin, and a phosphorous-containing compound.

Abstract: Resin systems and methods for making and using same are provided. The resin system can include a first aqueous resin comprising at least two polymerized monomers and a second aqueous resin comprising at least two polymerized monomers. The first aqueous resin can be present in an amount of about 5 wt % to about 95 wt %, based on the total weight the resin system. The second aqueous resin can be present in an amount of about 5 wt % to about 95 wt %, based on the total weight the resin system. The at least two polymerized monomers of the first and second aqueous resins can be the same monomers.

Abstract: A fire retardant intumescent coating composition is disclosed, which includes expandable graphite, an aromatic polyamine resin, and a phosphorous-containing compound. An overlay for applying to a wood substrate is also disclosed, which includes a core layer comprising a substrate and a resin composition, a top layer on one side of the core layer comprising the fire retardant intumescent coating composition, and an optional bottom layer on the opposite side of the core layer from the top layer. A process of forming the overlay is also disclosed, which includes applying the resin composition to the core layer substrate to form a resinated core layer, and applying a coating composition on the resinated core layer, directly or indirectly, to form the top layer; wherein the coating composition comprises expandable graphite, an aromatic polyamine resin, and a phosphorous-containing compound.

Abstract: Preservative composition for lignocellulosic-based composites providing rapid and long-lasting protection against insect and fungal attack, in both low and high moisture environments, through the use of a combination of higher solubility and lower solubility borates. Pesticidal amounts of a lower solubility borate and a higher solubility borate are combined before or during their incorporation into a lignocellulosic-based composite. Useful low solubility borates include copper borate, zinc borate and barium metaborate. Useful high solubility borates include boric acid, boric oxide, ammonium borate and alkali metal borates such as sodium borate. Some alkaline earth metal borates, including calcium borates, calcium magnesium borates, magnesium borates and calcium sodium borates, are of intermediate solubility and may be used effectively as either a low soluble or high soluble borate depending on the combination used.

Abstract: A derived timber board with a surface coating applied at least in parts is characterized in that at least one coating of a synthetic resin reinforced with fibers is applied as a surface coating. A method for applying the coating is also described.

Abstract: A sheet of cellulose based material having enhanced strength, particularly the dry strength, substantially unaffected repulpability is disclosed. The sheet of cellulose based materials generally includes a first cellulose based material connected with a second cellulose base material element. The first cellulose based material is formed by separating a portion of the fiber from a furnish, treating the separated portion with a cationic wet strength resin which is allowed to bond to the fiber. The treated fiber is them mixed with the untreated balance of the fiber at some point before the paper machine. The fiber that is separated may be secondary fiber, virgin fiber or combinations thereof. The second cellulose base material element is substantially free from any treatment. The second cellulose base material element may be include substantially all untreated fibers.

Abstract: A dope solution in which a cellulose acylate and a cycloolefin compound having a mass-average molecular mass of from 200 to 20,000 are dissolved in admixture is subjected to solution film forming to obtain a hybrid film. Further, an optically anisotropic layer having retardation Re of from 0 nm to 200 nm is provided on the hybrid film to prepare an optically compensatory film. The optically compensatory film and a polarizer are stuck to each other to prepare a polarizing plate which is then used to obtain a liquid crystal display device.

Abstract: Preservative composition for lignocellulosic-based composites providing rapid and long-lasting protection against insect and fungal attack, in both low and high moisture environments, through the use of a combination of higher solubility and lower solubility borates. Pesticidal amounts of a lower solubility borate and a higher solubility borate are combined before or during their incorporation into a lignocellulosic-based composite. Useful low solubility borates includes copper borate, zinc borate and barium metaborate. Useful high solubility borates includes boric acid, boric oxide, ammonium borate and alkali metal borates such as sodium borate. Some alkaline earth metal borates, including calcium borates, are of intermediate solubility and may be used effectively as either a low soluble or high soluble borate depending on the combination used.

Abstract: The process described herein presents a unique method and means of manufacturing medium density fibreboard (MDF) using agricultural plant stalks. The plant stalks are first depithed. The stalks are then broken down into fiber-like threads and made into fiber bundles. These fiber bundles are then combined with a resin component and a wax component, and the resulting mixture is cured. The MDF is economical to manufacture than prior art fibreboard in that it does not necessitate the use of expensive MDI resin. Further, the fibreboard is environmentally friendly in that it provides a beneficial use for agricultural waste.

Abstract: The present invention relates to the use for coating three-dimensionally structured surfaces and/or moldings of melamine resin sheets and/or films produced from cellulosic fiber materials post- or pre- and post-impregnated with an aqueous solution comprising (i) a melamine-formaldehyde condensate, (ii) an etherified melamine-formaldehyde condensate, and (iii) a polymer dispersion.

Abstract: Curable urea formaldehyde binder compositions are provided which are useful in coated abrasive and wood engineering applications, in a time released fashion. The time released curable binder compositions include a urea formaldehyde resin and an aryl phosphite in varying concentrations. The curable binder compositions of the present invention provide desirable working times and faster curing times tinder ambient or near ambient conditions.

Abstract: Compositions of high and low performance elastomer are formed using a process that chemically reacts some of the high and low performance elastomers together to form a graft copolymer. The elastomeric compositions provide intimately mixed elastomeric compositions which are thermodynamically stable and do not phase separate. The elastomeric compositions exhibit a variety of improved properties compared to simple blends of the same high and low performance elastomers in the same weight proportions. The elastomeric compositions are useful for producing films, fabrics, and laminates for use in a wide variety of personal care and medical articles.

Abstract: Laminated board for exterior cladding formed from a core (13) of kraft paper impregnated with phenolic resin, at least one layer of natural wood (14) and at least one surface covering layer (15) including a coating film (17) and a substrate film (16). The coating film (17) is a single-layer film based on polymethyl methacrylate (PMMA), a two-layer film with its lower layer based on polymethyl methacrylate and its upper layer based on polyvinylidine fluoride (PVDF), or a PMMA/PVDF single-layer film. The substrate film (16) consists of a paper impregnated with a compound formed from 80-95% by weight of a phenolic resin and 5-20% by weight of a polymer promoting adhesion of the coating film (17), such as an acrylic, melamine or urea polymer or a combination thereof.

Abstract: A component such as a siding panel comprised of a PVC/wood flour composite. Another embodiment is a component such as a siding panel that is made from a PVC/CPE/wood flour composite. The cellulosic composite may be extruded through a die and then bent into the shape of the component. Optionally, a reinforcement backer (e.g., an expanded polystyrene foam panel) may be adhered to the cellulosic composite siding.

Abstract: A thin abrasion resistant decorative thermosetting laminate of postforming quality is glued to a longitudinal carrier. The carrier preferably consists of a fibre board or a particle board with a rectangular cross section and at least two opposite rounded-off edges. One or more floor strips with the same or different cross section is machined from the laminate clad carrier.

Abstract: A prepreg can be obtained by impregnating a base paper with a heat-curing resin free from formaldehyde, the prepreg exhibiting a residual moisture content of 2 to 4% by weight after drying, the resin of the prepreg being non-crosslinked and exhibiting a degree of crosslinking of maximum about 85 in the case of thermal treatment of the prepreg over a period of about 40 seconds at about 132° C.

Abstract: A direct drawing type lithographic printing plate precursor comprising a water-resistant support and an image-receiving layer, the image-receiving layer comprising a filler and a binder resin, wherein the filler comprises a porous filler, and the binder resin comprises a complex comprising a resin containing a bond in which a metal atom is connected with an oxygen atom and an organic polymer containing a group capable of forming a hydrogen bond with the resin.

Abstract: A wood product is made from treating wood with two solutions, in series, including a penetrating solution and a topcoat composition. The penetrating solution is made up of boric acid, a metallocene catalyst, a free radical initiator, a first film-forming polymer and an adhesion promoter. The topcoat includes a continuous film-forming polymer. Application of the penetrating solution to the wood gets the solution into the wood to cross-link boric acid with cellulose fibers, then the topcoat forms the continuous film. The film seals in the penetrating solution so that it does not leach out during subsequent exposure to water and weather, allowing soluble salts such as borax to migrate and infiltrate deeper into the wood. Microbiological growth is prevented by several mechanisms.

Abstract: At first, a brazing filler metal sheet is prepared (step S1). The brazing filler metal sheet comprises a brazing filler metal layer, a sticking material layer, and a released paper. The brazing filler metal layer comprises a brazing filler metal. A coating material layer is laminated on the brazing filler metal layer (step S2). The coating material layer comprises a mixture of coating material particles and a binder. As the coating material particles, MCrAlY particles and abrasive particles (cubic boron nitride particles or the like) are used. The coating material layer is then dried (step S3), and the brazing filler metal sheet is cut (step S4), and adhered to a rotor blade (step S5). The rotor blade is heated (step S6), to melt the brazing filler metal. The brazing filler metal gets wet as a liquid phase around the MCrAlY particles, and diffuses due to the heat treatment holding process. A solidified layer is then formed by cooling (step S7).

Abstract: Disclosed is a floor-covering material, in which a phenol composite resin comprising phenol resin of resorcinol-formaline and polyurethane resin is incorporated with paper and dried, to form a prepreg, which is then thermally compressed to the upper side of a PVC base or a waterproof plywood layer, yielding a transparent protective layer and a shaping layer. In the flooring material, the transparent layer and the shaping layer are made of phenol composite resin, and thus low in heat- and moisture-distortion, with no curling. Further, since a surface layer of the floor-covering material is hardly distorted by heat, a balance layer for the suppression of such distortion is not additionally required.

Abstract: A method for reducing the migration of aldehyde compounds present in packaging material the interior of a package formed by said packaging material, said method comprising: (a) selecting an initial packaging sheet stock used for forming a package having an interior in which an aldehyde sensitive product can be contained, wherein said initial packaging sheet stock has a first surface that forms the interior wall of said formed package, wherein said initial packaging sheet stock has a second surface that forms the exterior wall of said formed package, and wherein said initial packaging sheet stock contains one or more aldehyde compounds that are capable of migrating from said initial packaging sheet stock to said package interior or exterior; (b) preparing an amine-containing composition comprising an amine that chemically reacts with said aldehyde compounds to form a substantially non-migrating compound; and (c) applying said amine-containing composition onto said first surface of said initial packaging sheet

Abstract: A laminate panel having desired characteristics even though the materials having these desired characteristics are not compatible in at least one aspect is disclosed. One of the substances having the desired characteristics may be adapted to be compatible with the other substance, and the two substances placed adjacent to each other. For example, the laminate panel includes a liquid impermeable layer that substantially prevents the penetration of moisture. The panel also includes a layer of a balancing substance disposed adjacent to the liquid impermeable layer to balance another layer of the laminate panel. The balancing substance is adapted to provide a desired bonding between the liquid impermeable layer and the layer of the balancing substance.

Abstract: Aqueous melamine resin dispersions comprise as discontinuous phase a melamine resin stabilized with a combination of a cationic protective colloid and an anionic protective colloid.

Abstract: A thin abrasion resistant decorative thermosetting laminate of postforming quality is glued to a longitudinal carrier. The carrier preferably consists of a fiberboard or a particle board with a rectangular cross section and at least two opposite rounded-off edges. One or more floor strips with the same or different cross section is machined from the laminate clad carrier.

Abstract: A packaged article, especially a respiring foodstuff such as cheese which generates or releases gas during storage, and a permeable multilayer biaxially oriented film suitable for allowing escape of such gas while minimizing transfer of oxygen across the film which has a thin layer of a blend of EVOH and nylon. In a preferred embodiment the low cost film having a high permeability to CO2 and low O2 permeability is used to package cheese.

Abstract: A composition for impregnation of a lignocellulosic material such as wood or wood particles, comprises a high boiling point tar acid or a pitch derived from coal; a solvent for the tar acid or pitch selected from a low carbon alcohol, an aceotrope of a low carbon alcohol and another solvent, and a mixture of a lower carbon alcohol and water; a phenol formaldehyde resole resin; an acid catalyst for the phenol formaldehyde resole resin; and preferably a formaldehyde donor or a precursor thereof. There is also disclosed a method of preparing a finished product from a lignocellulosic material by using the impregnating composition.

Abstract: The present invention related to a recyclable image-recording medium comprising a base layer, an intermediate layer and a water-swelling surface layer; a manufacturing method of the recyclable image-recording medium; and a printed material-removing method that uses such an image-recording medium.

Abstract: A decorative sheet or a molding, in particular suitable for indoor or outdoor applications on buildings, is in each case composed of a single- or multi-layer core, monolaterally or bilaterally laminated with decorative layer(s) The core layer(s) comprise(s) wood fibers, cellulose fibers, or timber sawdust products and also an organic or inorganic filler material, and a hot-curing resin. The particle size of the filler material is smaller than the thickness of the fibers or of the timber sawdust products in the core layer(s). These core layer(s) are composed of from 15 to 80% by weight of fibers or of timber sawdust products, from 10 to 75% by weight of filler material, and from 10 to 50% by weight of resin, based in each case on the total weight of the core layer(s).

Abstract: A method is provided for forming a durable, smooth-sided, multi-layer integral, composite engineered panel. The method typically is directed to first forming a mat comprising a plurality of layers of lignocellulosic strands or wafers. The plurality of layers of lignocellulosic strands or wafers are bonded together by an adhesive material. Then, at least one layer of smaller particles of lignocellulosic material is formed on the mat. This layer of smaller particles is blended together with an adhesive material thereby joining the layer of smaller particles to at least one outer surface of the mat. Next, at least one sheet of paper is joined to an outer layer of smaller particles of lignocellulosic material. This step takes place during the formation of the multi-layer integral, composite engineered panel. Finally, a substantially smooth outer surface is formed, upon pressing, in at least one surfaces of the multi-layer integral, composite engineered panel.

Abstract: A decorative laminate is provided which is comprised of a one or more cellulosic core sheets, one or more decor sheets and optional overlay sheets. In one embodiment, one or more of the overlay sheets and/or decor sheets are impregnated prior to lamination with a mixture of a transparent resin and a photoluminescent material. As a result, the entire upper surface of the laminate visibly luminesces in the presence of exciting radiation. In another embodiment, an image or pattern is printed on one or more of the decor sheets with a ink including an organic photoluminescent material to provide an visibly luminescent image or pattern therein. It is envisioned that the invention could be used to provide a unique and appealing appearance when used as the surfacing for a wide variety of applications, including bowling lanes, game tables, counter-tops, dance floors, and signs such as “exit” signs.

Abstract: The invention pertains to compositions which can be coated onto substrates. These compositions include a combination of a resin blend comprising a first polyester resin and a second polyester resin, wherein the first polyester is different from the second polyester, an aminoplast crosslinking resin, an acid catalyst, and a urea-aldehyde resin. Films prepared from coating compositions made in accordance with the present invention having improved stain resistance. In many instances, films prepared from coating compositions made in accordance with the present invention not only have improved stain resistance, but also have low temperature flexibility.

Abstract: The present invention provides a jet ink composition suitable for application onto a substrate comprising an ink carrier, a colorant, a polyol, an aldehyde-based cross-linking agent, and a catalyst that promotes a reaction between the cross-linking agent, the polyol, and the substrate. The present invention further provides a process of jet ink printing onto a substrate comprising projecting a stream of ink droplets to said substrate, controlling the direction of the droplets so that the droplets form the desired printed image on the substrate, and heating the image to obtain a cured printed image. Examples of preferred cross-linking agents are modified melamine formaldehyde resin and modified urea formaldehyde resin. The substrates preferably possess carboxyl, hydroxyl, amide, or sulfhydryl groups. An example of a preferred substrate is cellulose. The cross-linking reaction is carried out at relatively moderate temperatures and at high speeds.

Abstract: This invention relates to an economical coating composition for porous substrates that provides extremely glossy surfaces, is capable of supporting holographic images, provides good oxygen barrier properties as well as good oil, grease, solvent and water resistance. Said coatings on paper substrates are printable, biodegradable, recyclable, and repulpable. They are also suitable for use in conjunction with food products. This invention also relates to a process for applying said coatings onto porous substrates as well as a process for the economical production of inexpensive holographic images on substrates such as paper and cardboard containers.

Abstract: Modified melamine-formaldehyde resins are made of a condensate of formaldehyde, urea, melamine and modifying agents which contains: (a) a combination of 5 to 25 wt %, with respect to melamine, of dicyanodiamide and 8 to 30 wt %, with respect to melamine, of water-soluble polyalcohol with at least two hydroxyalkyl groups, and/or (b) 1.5 to 20 wt % amines having the formulas (Ia)NR.sub.4 R.sub.5 --R.sub.1 --X (Ia)and/or (Ib),NR.sub.4 R.sub.5 --R.sub.2 --Y--R.sub.3 --X (Ib)in which R.sub.1 and R.sub.3 are the same or different and depending on the meaning of X stand for a linear, branched or cyclic C.sub.1 -C.sub.12 alkyl or alkylene radical and R.sub.2 stands for a linear, branched or cyclic C.sub.1 -C.sub.12 alkylene radical; R.sub.4 and R.sub.5 can be the same or different and can stand for H or for a linear or branched C.sub.1 -C.sub.12 alkyl radical; and X can stand for hydrogen, OH or NR.sub.4 R.sub.5 and Y can stand for --O-- or --NH--. The molar ratio of melamine to formaldehyde ranges from 1:1.

Abstract: There is disclosed a resin-coated overlay for bonding to solid substrates, and which imparts improved waterproofing and chemical resistance to the resulting resin-coated overlaid solid substrate. Depending upon the desired end use of resin-coated overlaid solid substrate, the resin-coating may be modified to impart desirable surface features and/or characteristics. For example, additives such as waxes, oils, silicones, fluorocarbons and fatty acid compounds may be used to promote the release of concrete from forms made of solid substrates overlaid with the resin-coated overlays of the present invention. Moreover, resin-coated overlaid solid substrates may be produced having a surface which is suitable for painting and which accepts application of various tape products. Other modifications are disclosed which can be used to gain desirable cure speed, cost, and chemical/mechanical properties in the resin-coating.

Abstract: An improved oxazolidine-based hardener to be used with a resorcinol resin or a tannin resin as the adhesive for the bonding of wood articles. Preferably, an oxazolidine is combined with a base such as NaOH and a powdered absorbent such as wheat flour. The adhesive based on the improved hardener can be used to glue wood particles to pass wet strength requirements after the glue is cured at room temperature for under 24 hours. The improved hardener composition is storage stable; it can be prepared anytime before its use, thus eliminating the need to prepare a hardener immediately prior to the glue use. Since it is formaldehyde-free; it eliminates the safety issues associated with handling formaldehyde or paraformaldehyde. Also, the hardener provides flexible gel time or working time. Since the resins can be cured at room temperature, heating in an oven is not needed but could be used to reduce curing time. If radio frequencies are used to cure the resins, the exposure time can be reduced.

Abstract: A decorative, high-pressure laminate produced with a sorbitol-modified melamine-formaldehyde resin and methods of making high-pressure laminates.

Abstract: A recyclable double-faced liner bard, the board having a top layer, a medium corrugated layer, and a bottom layer, the top layer having a coating formed from an aqueous composition comprising (A) an emulsion of a curable butadience-styrene copolymer and (B) TiO.sub.2, the medium layer having a coating formed from an aqueous composition containing an emulsion of wax particles and a binder (preferably sodium alginate); and the bottom layer having a coating formed from an aqueous composition comprising about 10 to 85 percent by weight of a liquid curable styrene-butadiene copolymer (or a carboxylated copolymer) and wax.

Abstract: A unitary laminated bathtub wall covering having a back panel and at least one side panel comprises a formable core, such as phenolic resin impregnated layers of kraft paper, laminated between front and back layers of finishing resin such as melamine. The laminated bathtub wall has a reduced co-efficient of expansion the nature of which is linear to reduce buckling and delamination. A bathtub wall covering may be custom cut and shaped, i.e. post-formed, according to the method described from precise measurements of the bathtub enclosure area for easy installation with a single, mastic type adhesive.

Abstract: A film suitable for continuous application to particle boards in the making of laminated particle board is disclosed, which film is stem penetrable and impregnated with semi-cured impregnating resins and provided with a partially cured layer of glue on one side and a fully cured lacquer layer on the other side, which film is permeable to gases generated during production of laminated particle board. A process for producing such a film is also disclosed and also a method for producing a laminated particle board by means of a continuous direct lamination process.

Abstract: A two component adhesive comprising a natural or synthetic rubber first component and a second component capable of destabilizing the natural or synthetic rubber first component slowly can be utilized in conventional application equipment designed for applying single component adhesives is provided.

Abstract: A decor sheet for use in decorative laminates wherein the sheet is treated with a sizing agent to reduce its capacity for a laminating resin and enhance its opacity; in a preferred embodiment, the resin-impregnated decor sheet exhibits a resin gradient in the thickness direction to provide a decor sheet having a resin-rich top layer and a resin-starved bottom layer; in accordance with a preferred embodiment, the resin gradient is achieved by differentially sizing the bottom versus the top surface of the decor sheet; a decorative laminate employing such decor sheets are described.

Abstract: A friction lining (5) for a device which is cooled with fluid or lubricant and is intended for transferring torque, in particular a friction clutch, synchronizing element or brake, the friction lining being fastened on a carrier body (2) in order to form a friction surface (6) and the torque being transferred to a counter-surface, is constructed from at least two different layers, and in particular from at least one porous substrate (11, 11') which is fastened on the carrier body (2) and which is constructed like a composite material from a cellulose base with synthetic fibers and filler, and from a porous friction layer (12) which is fastened on the substrate (11,11') and is made of synthetic fibers, preferably carbon, which are bonded with a thermoset resin.

Abstract: A composite board which includes a core and inner and outer surface layers, said core and surface layers each including cellulose material and a cured resin binding said cellulose material together, wherein the resin in the core of the composite is an acid setting resin and the core includes a low steam volatile weak acid in an amount of between 2 to 8% by weight to the dry weight of the cellulose material in the core.

Abstract: This invention refers to a wood substitute with lignocellulosic and mineral material particles which are molded in sheet, e.g. plates and/or panels in different thicknesses or forms in stencil at choice, using in principal natural and artificial, and vegetal cellulosic material components, e.g. dried leaves, sawdust, rotten wood particles splinters, paperwastes, roots and mineral materials as limestone from sulphates type carbonates or calcium oxides, with synthetic binders from different chemical structures, with or without dyes, in these proportions: 35-60 by weight lignocellulosic components particles, 5-35 by weight limestone types, 5-30 by weight synthetic binders from different harmless chemical structures, with or without synthetic dyes from varied chemical structures and with or without requested additions.

Abstract: Low-density press board material is prepared by particulate kenaf core raw material and a cold-set, thermosetting or thermoplastic binder. The compressed and cured material exhibits dimensional stability, acoustical and thermal insulative properties and related characteristics roughly equivalent to some currently available wood and wood-substitute materials. The surfaces of the kenaf core board can be upgraded with the addition of overlays.

Abstract: A fire and chemical resistant fabric having anti-static properties which comprises at least one laminate formed by coextruding a pair of polymeric sheets with an intermediate layer of a polar resin or hydrophilic polymer which is adhered to a fabric scrim comprising a blend of polyester and cellulosic fibers, the fabric scrim containing an effective amount of an anti-static and fire resistant agent.

Abstract: Cationic urea/formaldehyde resins are obtainable by condensing urea and formaldehyde in a molar ratio of from 1:1.5 to 1:3 in the presence of polymers which contain not less than 1 mol % of polymerized vinylamine units and have Fikentscher K values of from 5 to 300, in an amount of from 5 to 50 g per mole of urea in the end product, where the mixture is first a) precondensed at a pH of from 8 to 14, then acidified and b) condensed at a pH of from 1 to 5 until gel formation begins, c) then from 0.3 to 1.5 moles of formaldehyde are added per mole of urea used, d) post-condensation is carried out and e) the resin solution is subsequently neutralized. The resins thus obtained are used in papermaking as assistants for increasing the dry and wet strength of paper and result in less dulling of the whiteness of the paper.