Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-10-26
2003-04-22
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S327000, C428S524000, C428S526000, C428S532000, C428S537500, C528S232000, C525S398000
Reexamination Certificate
active
06551702
ABSTRACT:
The present invention relates to aqueous melamine resin dispersions comprising as discontinuous phase a melamine resin stabilized by a combination of a cationic protective colloid and an anionic protective colloid.
The invention further relates to formulations comprising these dispersions, to decorative sheets coated with these formulations, to woodbase materials coated with these decorative sheets, and to processes for preparing or producing the melamine resin dispersions, decorative sheets and coated woodbase materials.
Melamine resin solutions comprising melamine and formaldehyde are general knowledge from, for example, Kunststoff Handbuch, 2nd Edition 1988, Volume 10, pp. 41 to 49.
From these solutions it is common, by impregnating and coating paper, to produce melamine resin sheets which are used inter alia for coating woodbase materials in the furniture industry.
The processing industry and the end users impose various requirements on the melamine resins and the products produced from them regarding the processing properties and end properties of the melamine resins and products produced from them.
According to the prior art, a sheet of a decorative paper is impregnated with a melamine resin condensate in a one- or two-stage process, dried and subsequently laminated under pressure and with heating onto a support plate. In the one-stage process, the resin filling the paper and the resin forming the sealing surface are identical. In the two-stage impregnating process, the decorative paper is first filled with 50-100% of solid resin (based on the paper weight) and, directly or after initial drying, further resin is applied to the top and/or bottom of the paper sheet by dipping, knife coating or brushing. This makes it possible to use different grades of impregnating resin in the two impregnating stages. The paper sheet is preferably filled using relatively inexpensive urea-formaldehyde impregnating resins or mixtures of urea-formaldehyde and melamine-formaldehyde impregnating resins. The top layer, which is critical to the properties of the product, consists preferably of pure melamine resin.
As far as the processability of the melamine resins is concerned, a particular desire is that the melamine resins are readily dilutable in water even after prolonged storage; in other words, on dilution with water they should not form any tacky coagulum. Good dilutability in water is important because this property is a precondition for easy cleaning of transportation vessels and processing machines. Further, it is desired that the melamine resins do not form a skin during the drying of the impregnated paper sheet. Premature filming of the resin surface, or formation of a skin, is disadvantageous since it hinders the subsequent drying process and reduces the rate of drying, whereas the processor is particularly interested in very rapid drying and thus high productivity.
As far as the service properties of the sheets produced with the melamine resins is concerned, these sheets are intended to possess a certain degree of elasticity so that they can also be used to coat structured and profiled surfaces of woodbase material parts without cracking in the pressed-on sheets. Furthermore, the elasticity should be sufficient to ensure that swelling and shrinkage in the woodbase material, as may occur, for example, with a change in the ambient climate, again do not result in surface cracking. In addition to cracking resistance of this kind, the pressed-on melamine resin sheets should in addition be insensitive to humidity and, in particular, to water vapor.
Moreover, the surface coatings are intended to impart an impression of color which is as brilliant as possible. This is often countered, however, by the fact that the resins used to impregnate the decorative papers gray on curing and tend to develop white efflorescence, and thus attenuate the color effect of color-printed or colored decorative papers. This phenomenon occurs particularly with black decorative papers, which then in many cases no longer have the desired “blackness”.
A further requirement made by furniture producers is that the impregnated products produced with the melamine resins form high-gloss surfaces when pressed onto furniture parts.
The melamine resin solutions known from the prior art are generally already well able to meet this profile of requirements. However, as far as their water dilutability following storage is concerned, these resin solutions appear to be still in need of improvement. It is also regarded as disadvantageous that following application to the decorative paper which is to be coated the resin solutions form films prematurely, which may impair the drying process by forming bubbles or dust and/or may lead to reduced machine speeds and defects in the sheet surfaces.
Also known from the prior art are aqueous dispersions of melamine resins which are already in a fully or partly cured state.
A similar process for preparing benzoguanamine-melamine-formaldehyde particles is described in U.S. Pat No. 3,945,980. The amino resin precondensate there is diluted until its water compatibility limit is exceeded, with the addition of polyvinyl alcohol, and is cured by means of heat and acidity.
Moreover, the preparation of melamine resin particles is described in European Patents EP 0 415 273 and EP 0 363 752. The starting material used in this case is a methanol-etherified melamine resin which is crosslinked by means of acidity and heat in the presence of a sulfonic acid polymer at concentrations of about 7%. These melamine resins are in practice unsuitable for producing decorative sheets since in the course of the production of the sheets or of the coated woodbase materials they give off methanol, which is unacceptable from the industrial hygiene standpoint.
Processes similar to the above are described in DD 224 602, JP 11021355, SU 441 272, JP 62068811, DD 248803 and DE 3 628 244. The products in all cases are fully cured, unmeltable and insoluble thermoset powders with a wide variety of particle sizes, which are recommended for use as calibration material, pigment, rheology modifier, filler, flame retardant, and flatting agent. The space-time yields are unsatisfactory in every case and the particle sizes, owing to the use of the protective colloid systems described, are in some cases severely scattered.
The preparation of melamine resin particles is known, furthermore, from U.S. Pat. No. 3,428,607. The preparation is described of cured melamine resin particles by stirring a M/F precondensate into an aqueous solution of protective colloids such as carboxymethylcellulose, gelatine, agar-agar, starch or alginates at melamine resin concentrations of 0.01%-10% and carrying out reaction at a pH of 6-8 and at the boiling temperature of the solvent.
U.S. Pat. No. 5,344,704 discloses aqueous mixtures containing precured melamine resin particles and an additional binder (e.g., sodium alginate or microcrystalline cellulose). Decorative papers are impregnated or coated with this mixture, dried, impregnated with melamine resin solutions and then cured to produce sheets used for surface coating. Said mixtures are prepared by fully or partly curing a melamine resin and subsequently grinding it to an average particle size of about 50 &mgr;m and dispersing it together with a protective colloid in water or a melamine resin solution. A particular disadvantage of this process is that the dispersions coagulate rapidly owing to the size of the resin particles. Furthermore, the grinding of the partly cured resin is technically complex.
WO 97/07152 describes a process for preparing aqueous dispersions containing fully or partly cured melamine resins. For this purpose an aqueous melamine resin solution is admixed with an aqueous suspension of a water-insoluble protective colloid, such as microcrystalline cellulose, the melamine resin precipitating as a result of exceeding its solubility limit, and forming a stable dispersion. This mixture is subsequently reacted further, if desired, so that the melamine resin attains the desired degree of
Andre Valerie
Biedermann Norbert
Decher Jakob
Hennig Ingolf
Jäckh Christof
BASF - Aktiengesellschaft
Kiliman Leszek
LandOfFree
Melamine resin dispersions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Melamine resin dispersions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Melamine resin dispersions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3056575