Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-04-13
2001-11-06
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S474400, C428S513000, C428S514000, C524S521000
Reexamination Certificate
active
06312827
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacture of a pre-impregnated product, to the pre-impregnated product obtained with the method, including its employment in the fabrication of decorative compound structures. The invention also relates to the impregnation solution used for impregnating the pre-impregnated product.
BACKGROUND OF THE INVENTION
It is known that decorative laminates and pieces of furniture can be produced by coating particle boards with impregnated decorative papers. A crucial role is played by the impregnated paper, which is obtained by impregnating a basic paper with a specific impregnation solution or an impregnation resin. The impregnated paper is identified in this instance as pre-impregnated product and serves also as decoration-carrying component in the named applications.
A method of the initially described type is apparent from EP 0 223 922. This patent describes method for manufacture of widths of paper impregnated with synthetic resins in the form of solutions and dispersions. As impregnation fluid, a mixture is used of watery anionic copolymer dispersions on basis of acrylic acid, acrylic acid ester, acrylic nitrile, vinyl acetate and/or styrol and of watery anionic solutions of copolymerisates on basis of maleic anhydride or maleic acid with styrol, acrylic acid and acrylic acid esters.
WO 94/00523 discloses a watery impregnation solution, with which papers are impregnated, which are then used to manufacture laminated boards. The watery impregnation solution contains 5 to 90 parts by weight of polyvinyl alcohol on 10 to 95 parts by weight of a dispersion of an ethyl-styrol/acrylate/butyl-acrylate-copolymer.
According to the state of the art, since the end of the eighties, a pre-impregnated product has been known, from marketing efforts, which is obtained by impregnating a basic paper of a cellulose mixture of long- and short fibers with an impregnation solution known according to internal identification R20. The impregnated solution contains 15% of a glyoxal/urea-precondensate or -resin in watery solution, 57% of a 50% watery dispersion of a copolymer on basis of n-butylacrylate and styrol and 28% water. The pre-impregnate has various desirable properties, such as for example, high resistance toward hardening and abrasion, high temperature resistance, color-fast property, neutral natural color, excellent resistance to water, as well as excellent resistance to chemicals, high degree of flame-resistance, high optical transparency, is devoid of odor and taste, as well as toxicologically completely harmless. Specifically involved is a low formaldehyde pre-impregnate. However, when unfavorable temperatures and varnish systems are combined, it is not sufficiently stable with respect to turning yellow.
The term “turning yellow” shall not mean, in this case, insufficient light resistance, but the chemical reaction which occurs based on the employed impregnation solution. The known pre-impregnate finds little application in the so-called “white” sector due to said yellowing. The skilled person understands by “white” sector, light-colored laminates or pieces of furniture, where turning yellow has a particularly detrimental effect.
SUMMARY OF THE INVENTION
The invention was, therefore, based on the object to provide a pre-impregnate that has all the desirable properties of the above-described pre-impregnate, but, at the same time, shows no tendency toward turning yellow.
According to the invention, said object is solved with a method which is characterized in that a base paper is impregnated with an impregnation solution, which contains a) a watery dispersion on basis of an acrylic acid ester/styrol copolymer, b) a dry-hardener on basis of a copolymerisate of (meth-)acrylamide and (meth-)acrylic acid and c) water, whereby per dry weight part of dry copolymerisate from (methacrylamide and (meth-)acrylic acid, approximately 0.3 to 13 parts by weight of dry acrylic acid ester/styrol-copolymer are used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The designation “pre-impregnate” involves a technical term known to the expert. The pre-impregnate is obtained, as mentioned above, by impregnation of basic paper with an impregnation solution. It is subsequently dried. It is then present in the form of resin-soaked fiber material - in the language of trade also called “foil” - and is sold in this form on the market. Depending upon required end use, it may be further modified.
It is preferred, within the scope of the invention, that per weight part of copolymerisate from (meth-)acrylamide and (meth-)acrylic acid, approximately 1 to 9 parts by weight, specifically approximately 3 to 7 parts by weight are used of acrylic acid ester/styrol-copolymer. The last named sector has the advantage that a product is obtained which is low in formaldehyde, flexible and resistant with respect to turning yellow.
The pH value of the employed impregnation solution lies preferably within the range of approximately 4.5 to 8.0, specifically within the range of approximately 5.0 to 5.5. Adjustment of desired pH value can be done with soda lye and sulphuric acid or hydrochloric acid. Too high a pH value may lead to instability of the dispersion, too low a pH value may result in potential fiber damage.
The viscosity (measured according to DIN 53211) of the impregnation solution should amount to approximately 10 to 18 seconds, specifically approximately 11 to 14 seconds.
The solid matter contents of the impregnation solution lies, depending upon the application product, in the range of approximately 15 to 50 percent by weight. A solid matter contents of approximately 30 percent by weight is preferred, since this will achieve a desirable impregnation degree of the fibrous fabric.
With respect to the acrylic acid ester of the acrylic acid ester/styrol-copolymer, this may involve ethyl-, n-butyl-, i-butyl- and 2-ethylhexylester, with employment of n-butylacrylate being preferred.
The commercial product Acronal S 305 D
R
from BASF Aktiengesellschaft has proven itself as particularly suitable. Acronal S 305 D
R
is a 50% watery dispersion of a copolymer on basis of a n-butylacrylate and styrol.
In the pre-impregnate, the acrylic acid ester/styrol copolymer is present in form of a film. The minimum film forming temperature lies preferably within the range of approximately 5 to 70° C., specifically within the range of approximately 10 to 30° C.
The dry hardener preferably involves a copolymerisate of acrylamide and acrylic acid with anionic charge. In comparison with a dry hardener on the basis of a copolymersate of methacrylamide and methacrylic acid with anionic charge, the use of a copolymerisate on the basis of acrylamide and acrylic acid leads to less brittle products.
The dry hardener itself has a solid matter content of approximately 15 to 30%, specifically of approximately 20 to 22%, a pH value in the range of approximately 6.0 to 9.0, a viscosity of approximately 100 to 300 mpa.s (Brookfield; 20° C.), and also a density of approximately 1.0 g/rl at 20° C.
In conformity with the analysis, the dry hardener is to be introduced into the paper mass in order to develop the hereinafter described properties. Since the dry hardener forms polymer bridges, it hardens the paper structure without interfering with the sheet forming or affecting the porosity. That means that all firmness properties of the paper are improved. Depending upon application volume and type of paper, one achieves improvements in the breaking length and points per pound as well as in the tear growth resistance and the interlaminar strength of the paper. This permits, depending upon the requirements with respect to quality, the use of cost-effective raw materials, higher ash contents of the basic paper and savings in auxiliaries. Significant improvement in retention is a further side effect.
Long and short cellulose fibers may be employed as basic fibrous materials. The material texture of the base paper before impregnation does not significantly differ from that of the decoration papers. Lo
Fay Sharpe Fagan Minnich & McKee LLP
Koehler decor GmbH & Co. KG
Pyon Harold
Tsoy Elena
LandOfFree
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