Stock material or miscellaneous articles – Composite – Of carbohydrate
Reexamination Certificate
1999-10-01
2004-03-23
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of carbohydrate
C428S511000, C428S194000, C427S393000
Reexamination Certificate
active
06709764
ABSTRACT:
The invention relates to a decorative paper sheet made impregnable by a thermosetting resin. This sheet is used in the manufacture of laminated decorative panels or moulded section. The invention also relates to the decorative sheets impregnated with a thermosetting resin as well as to the laminated decorative panels or moulded section which include it, and to the processes for manufacturing the sheets.
Laminated decorative panels or moulded section (also called “laminates”) have been used for many years as materials in dwellings and in commercial and industrial premises. Typical applications of such laminates are coverings for furniture, tabletops, chairs and other articles or floor coverings such as, in particular, coverings imitating a parquet floor.
There are two main types of decorative “laminates”, namely so-called high-pressure “laminates” and so-called low-pressure “laminates”.
The so-called high-pressure decorative laminates are produced from a core consisting of resin-impregnated sheets. These sheets are generally made of kraft paper and have been impregnated with a thermosetting resin, usually a phenolic resin.
After the sheets have been impregnated with resin, they are dried, cut and then stacked on top of one another. The number of sheets in the stack depends on the applications and varies between three and nine, but may be greater than this.
Next, the stack of sheets forming the core is placed on a decorative sheet. In general, a protective covering sheet, called an “overlay”, devoid of any pattern and transparent in the final laminate, is placed on top of the decorative sheet in order to improve the abrasion resistance of the laminate.
Next, the impregnated sheets are placed in a laminating press, the platens of which are provided with a metal sheet giving the laminate its surface finish. The stack is then densified by heating, at a temperature of about 110° C. to 170° C., and by pressing, at a pressure of about 5.5 MPa to 11 MPa, for approximately 25 to 60 minutes in order to obtain a unitary structure.
Next, this structure is fixed to a base support, for example by adhesively bonding it to the said support, such as a particleboard, especially a wood chipboard.
The so-called low-pressure decorative laminates are produced using only a decorative sheet impregnated with thermosetting resin, and optionally an overlay sheet, which are laminated directly to the base support such as a board during a short cycle, the temperature being about 160 to 170° C. and the pressure 1.25 MPa to 3 MPa.
The impregnable decorative sheet used for the manufacture of laminates is generally a sheet of paper produced on a papermaking machine and which includes cellulose fibres and optionally synthetic fibres, the cellulose fibres being split between from 40 to 100%, preferably from 80 to 100%, by weight of short fibres and from 0 to 60%, preferably from 0 to 20%, by weight of long fibres, from 0.2 to 1%, preferably from 0.4 to 0.5%, by dry weight with respect to the sheet of a wet-strength agent and from 5 to 50% by dry weight with respect to the sheet of decorative particles, for example iridescent pigments, and/or of pigmentary colorants or organic dyes, and/or of opacifying fillers such as titanium dioxide, especially of the rutile type, the said opacifying filler such as titanium dioxide being in quantities of preferably at least 15% and generally between approximately 15 and 40% with respect to the weight of the sheet. It may also contain other additives usually employed in papermaking and, in particular, retention agents or specific agents such as alkaline products allowing characteristics such as post-forming to be controlled.
These decorative sheets do not include a sizing agent, nor are subjected to any surface treatment, as they must be highly absorbent with respect to the thermosetting resin with which they will be impregnated.
Moreover, a decoration may be printed on this sheet, for example a decoration imitating wood or any other fancy decoration.
Next, this sheet is impregnated with a thermosetting, but thermally stable (non-yellowing), resin, usually with melamine-formaldehyde resins or urea-formaldehyde resins, or sometimes with benzoguanamine-formaldehyde resins or unsaturated polyester resins. In a second step, the impregnated sheet is heated and the resin is partially crosslinked (thermally cured) so that the resin is no longer in a tacky state and the sheet can be handled. Such a decorative sheet impregnated with partially cured resin is called, in the art, “decoration film” or “decorative film” or “melamine-resin film”.
This second step is generally carried out by heating the sheet at temperatures of approximately 110 to 140° C. and is controlled, so that the resin during the final lamination of the decoration film flows correctly into the sheet, by measuring the content of volatiles remaining in the decoration film since the latter then includes a certain percentage—about 5 to 8%—of volatile products (water, being the solvent for the resin, water resulting from the chemical condensation of the resin, residual formaldehyde, other residual products, etc). These volatiles represent compounds which will be removed during the complete curing of the resin, during the lamination of the decoration film.
The resin, once it has been thermally cured completely, will provide, after lamination, the surface resistance of the final laminate (abrasion resistance, resistance to soiling, to steam and to chemicals, such as solvents, acids and bases, etc).
Moreover, this sheet, once laminated, must have a very high degree of lightfastness since it is exposed almost permanently to light radiation because of its use as a surface covering; the compounds of which it is composed must therefore be selected so as to obtain this lightfastness, which is preferably greater than or equal to 6 on the scale of blues according to the ISO 4586-2.16 standard.
In addition, this sheet must allow an opaque decoration film to be obtained after lamination since it is important not to be able to see, through the said sheet, the base support and/or the sheets of kraft paper on which the impregnated decorative sheet has been laminated, so that there is no interference with the decoration of the sheet. It is therefore necessary to have a decorative sheet which is as opaque as possible.
In the case of a white decoration, for which a very white opacifying filler such as titanium dioxide is used, one is then forced to use large quantities (approximately 40% by weight with respect to the sheet) of fillers such as titanium dioxide in order to obtain this opacity. In fact, after impregnation and lamination, it is only the titanium dioxide which provides the opacity since, because cellulose has a refractive index close to that of the resin, the cellulose fibres are rendered transparent, this being all the more so the greater the amount of resin.
It is therefore necessary to incorporate as much filler, such as titanium dioxide, as possible, but this is expensive and degrades the mechanical properties of the sheet.
In order to reduce the cost of the decoration film, it is sought to minimize the amount of resin absorbed by the sheet while still maintaining the mechanical and surface-resistance properties of the decorative laminate that the thermally cured resin gives it.
This problem is especially important in the case of low-pressure laminated decorative panels or moulded section since the impregnated decorative sheet is directly laminated to the support board.
In Patent Application EP 677,401, these problems were dealt with by proposing a decorative sheet which includes a sizing agent and by preferably creating a thermosetting-resin absorption gradient so that the upper part of the sheet is richer in resin than the lower part internal to the laminate. The sizing agent, because of its hydrophobic effect, prevents the impregnation resin from completely penetrating into the sheet. The sizing agent is added in the bulk or to the surface, and in a differential manner, or by forming two plies, the lower ply having the sizi
Godet Jean-Yves
Perrin Claude
Bacon & Thomas
Ferguson L.
Kelly Cynthia H.
Wiggins Arjo
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