Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2000-12-21
2002-09-24
Boykin, Terressa M. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
Reexamination Certificate
active
06455162
ABSTRACT:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
The present patent application claims the right of priority under 35 U.S.C. §119 (a)-(d) and 35 U.S.C. §365 of International Application No. PCT/EP99/04179, filed 17 June 1999, which was published in German as International Patent Publication No. WO 00/00554 on 6 January 2000, which is entitled to the right of priority of German Patent Application No. 198 29 163.9, filed Jun. 30, 1998.
FIELD OF THE INVENTION
The present invention relates to coating agents and to their use for the preparation of transparent water-spreading coatings on thermoplastic or glass mouldings.
BACKGROUND OF THE INVENTION
The term “water-spreading” is understood as meaning the property of a surface to form a contact angle of less than 20 degrees with a drop of water placed thereon. Accordingly, a water-spreading coating is a coating which confers this property on a surface.
Mouldings with a water-spreading surface have the property whereby water which comes into contact with its surface does not contract to mutually separate drops on said surface, but the drops spread and, when touched, coalesce to a continuous film. This gives rise to an improved luminous reflectance on the water-wetted surface and a better transparency in the case of translucent mouldings. Also, water cannot so easily drip from the underside of the moulding. These properties of inhibiting drop formation, or so-called antidrop properties, are in demand especially for various glazing materials made of inorganic glasses (hereafter abbreviated to glass) or thermoplastics. It is desirable in these cases that the condensation water or rain water deposited thereon should not fall off in drops, but that, following the slope of the material, it should run off at the lower edge in a continuous film or at least in coherent streaks.
The opposite behaviour to that of a water-spreading surface is shown by a water-repellent surface. On water-repellent surfaces, water which comes into contact with such a surface contracts to mutually separate drops.
Numerous attempts to provide water-repellent plastic surfaces with water-spreading layers have been reported in the literature. According to DE-A 21 61 645, such coatings are produced from a copolymer of alkyl esters, hydroxyalkyl esters and quaternary aminoalkyl esters of acrylic or methacrylic acid and methylol ethers of methacrylamide as crosslinking agents. They initially take up water, with swelling, and gradually change to a water-spreading state. As a result of the swelling, however, the coating becomes soft and sensitive to mechanical damage.
To improve the mechanical strength of water-spreading coatings, inorganic constituents such as colloidal metal oxides, especially aluminium oxide, or colloidal silicon dioxide were incorporated into the coating compounds (EP-A 7 681 877 or EP-A 7 606 193).
To achieve a higher mechanical resistance, coatings were developed with hydrophilic inorganic constituents in a hydrophilic binder. According to JP-A 76 81 877, polyvinyl chloride sheets or polymethyl methacrylate sheets are covered with a coating of colloidal aluminium oxide as a hard ingredient for conferring hydrophilicity and polyvinyl alcohol and ammonium polyacrylate as binders. Again, however, this coating is sensitive to mechanical stresses in the water-swollen state.
Attempts have even been made to incorporate wetting agents into the plastic material from which the moulding is produced. Thus, according to DE-A 2 017 002, water-spreading coverings for greenhouses and similar moist enclosures are made of a plastic containing surface-active agents like polyalkylene glycol. The water-spreading action of this additive is inadequate and the weather resistance of the plastic is also impaired.
JP-A 76 06 193 has proposed, as glazing means, polymethacrylate panels with a coating of 95 parts of colloidal silicon dioxide and 5 parts of a dispersion of a hydrophobic acrylic resin. However, the adhesion of this coating is wholly unsatisfactory, especially in the wet state.
According to EP-A 51 405, the adhesion of a water-spreading coating on plastic mouldings is improved with a coating made up of two layers, both layers containing colloidal silicon dioxide, a partially hydrolyzed polysiloxane and polyvinyl alcohol as a binder. The ratio of silicon to carbon is greater in the bottom layer than in the top layer.
It can be established in general terms that although a coating with good water spreading can usually be obtained with strongly hydrophilic coating materials, the coating is normally too soft in the swollen state. If one wants to counteract this disadvantage through stronger crosslinking or lower hydrophilicity, the water-spreading action is impaired along with the mechanical sensitivity. Although silicon dioxide and various other metal or semimetal oxides combine the advantages of high hardness and good wettability by water without swelling, they have the disadvantage of not adhering at all.
The greater the amount of binder used to anchor the oxides to the plastic surface, the more the wettability of the oxides and the hence the water-spreading action of the coating are impaired and the more the disadvantages of the binders become apparent: mechanical sensitivity in the case of hydrophilic binders and inadequate water spreading in the case of hydrophobic binders.
DE-A 34 00 079 has proposed creating a strong adhesive bond between the water-repellent surface of a plastic moulding and a water-spreading layer essentially consisting entirely of silicon dioxide or other metal oxides of colloidal particle size, which itself has an inadequate adhesive strength on the plastic layer, by means of a coupling layer of a water-insoluble and essentially non-swellable organic polymer with polar groups.
The use of this coupling layer or other so-called primer layers in order to improve the bond between the water-spreading layer and the plastic surface requires an additional step in the coating process, making the manufacture of coated mouldings more complicated and more expensive.
SUMMARY OF THE INVENTION
All the coating agents mentioned have the disadvantage that they have to be applied from organic solvents.
The object of the present invention is to provide coating agents which are suitable for the preparation of transparent water-spreading coatings on mouldings and which have an excellent adhesive strength without a coupling layer, together with a high mechanical strength.
According to the invention, this object is achieved by the provision of a coating agent containing
A) 0.005 to 2 parts by weight of a compound represented by general formula (1):
wherein
R
1
is a hydrocarbon radical having 1 to 30 C atoms,
R
2
is hydrogen or a hydrocarbon radical having 1 to 6 C atoms,
A is a single bond or a divalent hydrocarbon radical having 1 to 30 C atoms.
B is a single bond or a divalent hydrocarbon radical having 1 to 30 C atoms,
n is 1,2,3 or 4 and
M
n+
is a cation with n positive charges,
B) 1 to 20 parts by weight of a water-insoluble oxide or several water-insoluble oxides of a metal or semimetal, and
C) 80 to 100 parts by weight of an acid/water mixture comprising more than 90% of water,
with the proviso that the pH of the coating agent is below 6, said coating agent being a subject of the invention.
The present invention also provides the use of the coating agents according to the invention for the preparation of transparent water-spreading coatings on mouldings of any kind, preferably on thermoplastic or glass mouldings.
DETAILED DESCRIPTION OF THE INVENTION
Transparent water-spreading coatings can be prepared on mouldings from the coating agents according to the invention. The coatings have an excellent adhesive strength together with a high mechanical strength. Coupling layers are not required. A further advantage of the coating agents according to the invention is that they contain predominantly water and hence only small amounts of organic solvents, thereby affording economic and ecological advantages.
The compounds represented by general formula (1), w
Bayer Aktiengesellschaft
Boykin Terressa M.
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