Patent Application
20110020656
Particles have great economic significance, in particular when they are used in surface coatings, which need to create abrasion-resistant surfaces for the most varying materials. As a rule, the particles are thereby mixed into polymerizable surface coatings, which, after curing, form a matrix made of synthetic resins on the surface to be coated. The surface coatings are usually adapted to the respective surface and to the application process.
Hard material particles include e.g. corundum, carbides, in particular silicon carbide and wolfram carbide, boron nitride, diamonds and silicates. Corundum is frequently referred to below. It is expressly noted that corundum is then also representative for other hard material particles.
Corundum is used for example on a large scale in the coating of wood and/or wood material surfaces, in particular in the coating of flooring elements with heat-curing, thermosetting synthetic resins. Corundum also contributes here to a significant degree to improving the abrasion resistance of the surface coating. It is known in this connection that the transparency of the coating is improved when silanized corundum is used. Corundum is silanized in order to adjust the polarity of the corundum surface better to the polarity of the respective synthetic resin so that the mixability of the corundum with the synthetic resin is improved. As a result, the transparency of the surface coating is then thereby improved.
However, besides thermosetting surface coatings for flooring elements, e.g. based on melamine resin, the lacquering of the surfaces is also gaining in significance. A thin layer of radiation-curing lacquers are applied to the surface of workpieces, here e.g. wood materials, in order to create abrasion-resistant coatings using hard material particles.
However, the permanent, secure inclusion of hard material particles in the lacquer of the surface coating is problematic. The abrasion resistance of the surface coating is highly impaired through the early breaking out of the hard material particles from the synthetic resin matrix. This phenomenon is independent of respectively selected synthetic resin, hard material or the type of surface to be coated.
Thus, the object of the invention is to suggest polymerizable hard-material-particle-containing surface coatings, which have permanently high abrasion resistance.
This object is solved with a process for functionalizing hard material particles according to claim 1, with functionalized hard material particles according to claim 14, with coating materials, which contain functionalized hard material particles (claim 16) and with workpieces, in particular flooring panels, which are provided at least in sections with such surface coatings (claims 18, 19).
The process according to the invention for the production of functionalized hard material particles takes place through the reaction of at least one hard material particle with at least one anchor molecule, wherein an anchor molecule has at least one silane bonding group and at least one polymerizable group. Silane bonding group and polymerizable group are connected via a bridge group, which consists in the simplest case of one carbon atom.
In connection with this invention, the term anchor molecule is used for a molecule, which has at least one, preferably two or three silane bonding groups, which form a chemical bond with the surface of the hard material particle, and which has at least one polymerizable group, which preferably forms a cross-linking reaction with the polymerizable coating material of the surface coating. The hard material particle, typically corundum, is thereby permanently integrated into the matrix of the synthetic resin by means of chemical bonds and a breaking out of the particles from the cured surface coating as a result of use is largely prevented.
It results from the above that the polymerizable group behaves inertly under the reaction conditions, which lead to the adsorption of the silane bonding group to the surface of the hard material particle. The polymerizable group preferably reacts under the reaction conditions, e.g. heat or radiation, which lead to the curing of the polymerizable coating material of the surface coating.
According to the invention, an important error, which was shown during use of hard-material-containing surface coatings, is thus resolved. The efficiency of the used hard material in the abrasion behavior of the surface coating is considerably reduced in that the hard material particles (also silanized hard material particles) are not optimally integrated into the polymer matrix of a surface coating. They are broken out of the lacquer surface relatively quickly under the influence of abrasive wear. The solution according to the invention solves this problem. The functionalized hard material according to the invention is permanently integrated into the surface coating of a material, e.g. a wood material, of wood, abrasive medium or coupling disks, through the “integration” of selected polymerizable groups.
Corundum is a frequently used hard material. According to the invention, all other hard materials are also suitable, in particular the aforementioned carbides, nitrides, oxides and silicates and diamond. Hard materials with a density of more than 1.5 g/cm3, advantageously with a density of 1.75 g/cm3 to 4.5 g/cm3, are preferred.
In accordance with a preferred embodiment, the functionalization of hard material particles takes place in an inert solvent under the reaction conditions of hydrolysis. In this connection, inert means that the solvent under the conditions of the hydrolysis reacts neither with the silane bonding group nor with the polymerizable group. Water is not used as a solvent due to its strongly hydrolyzing properties. Inert, non-aqueous solvents are thus preferably used.
Typical inert solvents are alcohols, ester or ether solutions. Preferred solvents are aqueous, polymerizable monomers, which react with the coating material of the later surface coating. Mixtures of the aforementioned solvents can also be used. During selection of the polymerizable monomer(s) that can be used as solvent, it is preferred if the monomers have no reactive OH groups. The undesired condensation reactions between silane and solvent described above are thereby avoided. Preferred polymerizable monomers are among other things alkenes (e.g. butadiene), dicarbon acids and dicarbon acid derivates, diols, acrylic acid esters, acrylates, methacrylates, alkyl methacrylates, phthalic acid esters and/or diamines.
The integration of the silane bonding groups into the surface of the hard material particle takes place as a rule in the presence of slightly substoichiometric amounts of water, which enable a targeted reaction of the silane bonding groups with the hard material surface. The molar ratio between the hydrolyzable groups of the silane and water (expressed as the ROR value) should be set under 0.8, preferably under 0.6, advantageously under 0.4, especially preferably under 0.2.
A catalyst, which simplifies the hydrolysis of the silane bonding groups, is usually already added to the solvent. Typically, a base or an acid (organic or mineral) is used, for example hydrochloric acid, phosphoric acid, sulfuric acid, formic or acetic acid and sodium hydroxide, ammonia or ammonium hydroxide. Since diluted bases or acids are generally used, the water quantity added with the catalyst is used to set the desired ROR value.
As explained above, each anchor molecule requires at least one silane bonding group and at least one polymerizable group for the chemical cross-linking of the hard material particles with the polymer matrix of the surface coating. However, anchor molecules are preferably used, which have two, three or more silane bonding groups and two or more polymerizable groups. According to an advantageous embodiment of the invention, mixtures of different anchor molecules can also be used.
The polymerizable groups of the anchor molecule are preferably adapted for the polymerizable groups of the coating means and react with these groups so that a polymer matrix is created, into which the hard material particles are much better integrated than previously due to chemical bonds.
In order to realize the invention, one or more anchor molecules of the general formula
Ra(SiX)4-a Formula 1
are generally suitable, wherein in Formula 1,
In general Formula I, the hydrolyzable groups X (silane bonding groups), which can be the same or different from each other, are for example hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably C1-6 alkoxy, such as e.g. methoxy, ethoxy, n-propoxy and butoxy), aryloxy (preferably C6-10-aryloxy, such as e.g. phenoxy), acyloxy (preferably C2-7 acyloxy, such as e.g. acetoxy or propionoxy), alkylcarbonyl (preferably C2-7-alkylcarbonyl, such as e.g. acetyl), amino, monoalkyl amino or dialkyl amino with preferably 1 to 12, in particular 1 to 6, carbon atoms. Preferable hydrolyzable remainders are halogens, alkoxy groups and acyloxy groups. Especially preferable hydrolyzable groups are C1-4 alkoxy groups, in particular methoxy and ethoxy groups.
The polymerizable under the reaction conditions of hydrolysis, non-hydrolyzable remainders R, which can be the same or different, are non-hydrolyzable remainders R with a functional group, via which a cross-linking with the polymer matrix of a surface coating is possible. The remainders R are inert under the reaction conditions, under which the silane bonding groups attach to the surface of the hard material particles.
The non-hydrolyzable remainder R with a functional group, via which a cross-linking is possible, can e.g. be selected from a group, which as a functional group comprises an epoxide (e.g.: glycidyl or glycidyloxy), hydroxy, ether, amino, monoalkyl amino, dialkyl amino, if applicable substituted anilino, amide, carboxy, alkinyl, acryl, acryloxy, methacryl, methacryloxy, mercapto, cyano, alkoxy, isocyanato, aldehyde, alkylcarbonyl, acid anhydride and/or phosphoric acid, group. Preferred examples for the preferably polymerizable, non-hydrolyzable remainders R with functional groups, via which a cross-linking is possible, are a gycidyl or a glycidyloxy-(C1-20)-alkylene remainder, an acryloxy-(C1-6)-alkylene remainder, such as e.g. an acryloxymethyl, an acryloxyethyl or an acryloxypropyl remainder or a methacryloxy-(C1-6)-alkylene remainder, such as e.g. a metacryloxymethyl, a metacryloxyethyl or a methacryloxypropyl remainder. Especially preferred remainders are y-gylcidyloxypropyl and acryloxypropyl and methacryloxypropyl.
These functional groups are bonded to the silicon atom via alkyl, alkylene, alkenylene or arylene bridge groups, which can be broken by oxygen or NH groups. The bridge groups preferably contain 1 to 8 and in particular 1 to 6 carbon atoms. Examples for non-hydrolyzable remainders R with alkenyl or alkinyl groups are C2-6-alkenyl, such as e.g. vinyl, 1-propenyl, 2-propenyl and butenyl and C2-6-alkinyl such as e.g. acetylenyl and propargyl.
Concrete examples for corresponding anchor molecules are
The “polymerizable” groups named in connection with the invention are in particular polymerizable, polyaddable and/or polycondensable groups. According to the invention, polymerization reactions are all reactions via which a cross-linking with the polymerizable coating material of the surface coating is possible. The polymerizable groups are preferably selected such that an organic cross-linking and integration of the hard material particles into the polymer matrix of the surface coating can be executed via if applicable catalyzed polymerization, addition and/or condensation reactions.
In order to perform the process described above, corundum is most frequently used as the main component among the generally known and available hard material particles. During the production of a dispersion, the solvent: hard material ratio is advantageously 1:1.5 to 1:3, preferably 1:2.0 to 1:2.5, respectively expressed in wt-%.
With respect to the hard material used, only a small portion of anchor molecules are required to better integrate the hard material particles into polymerizable coatings. With respect to the hard material used, only up to 0.001 wt-% of anchor molecules are used, preferably up to 0.01 wt-%, especially preferably up to 0.1 wt-%, advantageously up to 1.0 wt-% of the hard material. Thus, only a small amount of anchor molecules is required in order to enable a significant improvement in the adhesive strength or integration of the hard material into polymerizable coating materials or surface coatings respectively in that the bonding groups attach to the surface of the hard material. It should be considered a particular advantage of the invention that, as a result of the improved integration of hard material, usually from corundum into the polymer matrix of surface coatings, larger hard material particles can also be used. Larger hard material particles are much less expensive than highly reduced particles.
A stabilizer can be added in order to prevent the sedimentation of the functionalized hard material in the liquid medium, e.g. in a solvent made of liquid, polymerizable monomers, during transport and storage or also to prevent unwanted reactions of solvents and/or anchor molecules during transport and storage.
The object of the invention is the functionalized hard material as process product but the object of the invention are also polymerizable coating materials, which also have hard material particles in addition to polymerizable monomers and/or oligomers, which are connected with at least one anchor molecule, the at least one silane bonding group of which is connected with the surface of the hard material particle, and which have at least one polymerizable group, which polymerize with the monomers and/or oligomers of the coating material via addition or condensation. These can e.g. be both heat-curing as well as radiation-curing surface coatings.
The object of the invention is also a workpiece, in particular a wood material panel, which is at least in sections coated with a polymerized coating material, which contains hard material particles, in particular corundum, wherein the hard material particles are connected with an anchor molecule, which have at least one bonding group of a silane, which is chemically bonded with the surface of the hard material, and wherein the anchor molecule has at least one polymerized group, which is chemically bonded with the coating material via a preceding addition, condensation or polymerization reaction. Typical areas of application for surfaces coated according to the invention are workbenches, workstations or floors.
The object of the invention is also abrasive mediums and coupling disks, which are provided with a coating in the manner described above, which contains functionalized hard material particles according to the invention.
Details of the invention are described in greater detail based on the following exemplary embodiments:
A dispersion of corundum is first produced in the solvent. For this, 60 wt-% corundum is stirred in using a dispersion agitator for 15 minutes in 40 wt-% 3,4 epoxycyclohexylmethyl-3-4-epoxycyclohexane. The 3,4-epoxycyclohexylmethyl-3-4-epoxycyclohexane serves as an inert solvent.
Then, 1 wt-% (with respect to the corundum used) of an anchor molecule, here y-gylcidyloxypropyltriethoxysilane, is added to this dispersion and also stirred for 15 minutes. The anchor molecule named above has three silane bonding groups and an epoxy group as a polymerizable group.
0.1 molar hydrochloric acid is then added in an amount that sets an ROR value of 0.8. After addition of the hydrochloric acid, the dispersion is stirred again for 30 minutes, whereby the temperature does not exceed 50° C.
The dispersion, containing functionalized corundum, can be stored for at least one month. Instead of corundum, other hard material particles can also be used, in particular those with a density of over 1.5 g/cm3 such as e.g. boron nitride, silicon carbide or diamonds.
The dispersion described above containing functionalized corundum is mixed with a liquid, UV-curing epoxide lacquer, e.g. Uvacure 1533 by Cytec, at weight ratio of 3:2. The weight ratio between epoxide lacquer and corundum dispersion can be selected in a broad range depending on how many corundum particles are required for the respective surface coating.
This surface material can be stored for at least one month.
3. Coating of a Workpiece with a Surface Coating Containing Functionalized Corundum
2% of a cationic photo starter (e.g. Additol PCPK by Cytec) is added to the coating material described above in order to ensure an even and fast curing of the epoxide lacquer. By means of roller application, 60 g/m2 of this coating material is applied to MDF plates and then cured into an abrasion-resistant surface coating through the impact of UV light.
MDF plates coated according to the invention were subjected to an abrasion test. MDF plates coated with the same UV-curing epoxide lacquer, containing the same amount of corundum but only silanized and not functionalized, and cured under the same conditions as the MDF plates coated according to the invention, were used for comparison.
The abrasion test as per EN 13329 showed that all coated plates achieved abrasion class AC3. However, for the plates coated with functionalized corundum according to the invention, the test results were at least 15% better. Thus, either more overall abrasion-resistant surfaces or specified abrasion values with a smaller amount of corundum can be achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 060 376.4 | Dec 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/010581 | 12/12/2008 | WO | 00 | 9/27/2010 |
