HK1061663B - Method for producing a coating on porous and/or absorbent materials - Google Patents

Description

Method for producing a coating on a porous or absorbent material

Technical Field

The present invention relates to a method for producing coatings on porous or absorbent materials by radiation-induced polymerization of liquid coating agents.

Background

Radiation-curable coating compositions based on low-viscosity (meth) acrylates are known, for example, from DE-A3706355. Such coating agents, which typically have a dynamic viscosity of less than 1000mpa.s, are applied to the substrate to be coated by various methods, such as roll coating, without the use of solvents but with the addition of photoinitiators and optionally additives, and are then hardened by the action of uv radiation.

The low viscosity of the coating agent is critical for the application of thin layers, but is disadvantageous if the substrate to be coated is a material with porosity and/or absorption properties. For example, liquid, low-viscosity coating agents penetrate into the substrate, with the result that, when subsequently irradiated, the portion of the coating agent which has penetrated will not be irradiated with radiation or insufficiently irradiated and will therefore not harden or harden incompletely. This unhardened, still liquid component will then have a negative effect on the quality of the coating. In particular, the so-called "sweating" phenomenon of the person skilled in the art will occur, in which the liquid component exudes through the hardened film and is visible on the surface of the coating. This effect can occur even after a very short time, e.g. hours, or only after a longer time, e.g. months.

Disclosure of Invention

The object of the present invention is to provide a process for producing a coating on a porous or absorbent material by applying a coating agent and then hardening it with uv radiation, which process prevents the unhardened components from sweating.

It has now been found that this object is achieved by means of certain additives which are polyamide or oligomeric or polymeric fatty acid amides and are generally used as thixotropic agents.

The invention relates to a method for producing a coating on a porous and/or absorbent material by applying a liquid coating agent comprising at least one component having a dynamic viscosity of less than 2000mPa.s and a (meth) acryloyl group and subsequently polymerizing by radiation induction, characterized in that the coating agent comprises 0.1 to 10 wt.%, relative to its non-volatile components, of an additive selected from the group consisting of polyamides and/or oligomeric or polymeric fatty acid amides.

Liquid coating compositions which can be hardened by radiation are known, for example, from the description of P.K.T.Oldring (eds.), "chemistry and technology of UV and electron beam formulations for coatings, inks and paints", Vol.2, 1991, SITA technology, London, p.31 to 235. Mention may be made, by way of example, of epoxy acrylates, urethane acrylates, polyester acrylates and amine-modified and unmodified polyether acrylates. These products are commercially available and, depending on the composition, vary in viscosity from about 100mpa.s to about 100,000 mpa.s. They may be used alone or as a blend.

The high-viscosity coating agents are usually mixed with diluents which also participate in the (co) polymerization during UV-curing. Such diluents are described in p.k.t.oldring (eds.), "chemistry and technology for uv and electron beam formulations of coatings, inks and paints", volume 2, 1991, SITA technology, london, p.237 to 285. Esters of acrylic acid and methacrylic acid are given as examples, with the acrylic esters of the following alcohols being preferred. Monohydric alcohols are the various isomeric butanols, pentanols, hexanols, heptanols, octanols, nonanols and decanols, but also cycloaliphatic alcohols, such as isobornyl alcohol, cyclohexanol and alkylated cyclohexanols, dicyclopentanol, arylaliphatic alcohols, such as phenoxyethanol and nonylphenylethanol, and also tetrahydrofurfuryl alcohol. Alkoxylated derivatives of these alcohols may also be used. Diols are, for example, alcohols such as ethylene glycol, propylene glycol-1, 2, propylene glycol-1, 3, diethylene glycol, dipropylene glycol, the isomeric butanediols, neopentyl glycol, hexanediol-1, 6, 2-ethylhexanediol and tripropylene glycol, or alkoxylated derivatives of these alcohols. Preferred diols are hexanediol-1, 6, dipropylene glycol and tripropylene glycol. The triol is glycerol or trimethylolpropane or an alkoxylated derivative thereof. Propoxylated glycerol is preferred. Alcohols such as pentaerythritol or ditrimethylolpropane or alkoxylated derivatives thereof may be used as the polyol.

The coating agents used in the process of the invention comprise at least one such component having a (meth) acryloyl group, the dynamic viscosity of which is less than 2000mpa.s, preferably less than 1000mpa.s, particularly preferably less than 500 mpa.s.

The coating agents used in the process of the invention contain known initiators which are capable of initiating free-radical polymerization after irradiation with high-energy radiation, such as ultraviolet light. Such photoinitiators are described, for example, in P.K.T.Oldring (eds.), "chemistry and technology for UV and electron beam formulations for coatings, inks and paints", Vol.3, 1991, SITA technology, London, p.61-325. They are used in an amount of 0.1 to 10 parts by weight, preferably 2 to 7 parts by weight, particularly preferably 3 to 4 parts by weight, based on the liquid coating agent.

The coating agent also contains, relative to its non-volatile component content, 0.1 to 10 wt.%, preferably 0.3 to 5 wt.%, particularly preferably 0.5 to 2 wt.% of an additive selected from the group consisting of polyamides or oligomeric or polymeric fatty acid amides. The polyamides of the invention are, for example, waxy polyamide polymers and/or fatty acid-modified polyamides, commercially available, for example, under the trade name CrayvallacSuper^*(Lubrizol Coating Additives, Ritterhue, Germany) or Disparlon^*6200. 6500 or 6600(c.h. erbsl * h, Krefeld, germany); fatty acid amides are described, for example, in DE-A3135183. Oligomeric or polymeric fatty acid amides are also commercially available, for example, Crayvallac^*MT and Crayvallac^*SF (amide-modified, hydrogenated castor oil product, Lubrizol Coating Additives, Ritterhue, Germany). The effects observed with these products according to the invention are surprising, since many other thixotropic agents do not have any effect in the process according to the invention and are therefore unsuitable.

The coating compositions prepared according to the invention can also be used in admixture with a wide variety of auxiliaries and additives. These include fillers, pigments, dyes, smoothing agents, matting agents or levelling agents, which may be used in conventional amounts. Solvents inert to free-radical polymerization can also be used. The method according to the invention therefore comprises, between the coating and the hardening process, ventilation or evaporation of the solvent from the liquid coating.

The process of the invention is suitable for producing high-quality coatings on absorbent and/or porous substrates, for example paper, cardboard, leather, textiles, wood-based materials such as medium-density fibreboard, ceramic or mineral materials and also on porous plastics.

Application of the coating composition to the material to be coated can be carried out by conventional and known methods for lacquer technology, such as, for example, spray coating, knife coating, roll coating, flow coating, dip coating, spin coating and spraying (vaccumate). The liquid coating agent is hardened by irradiation with ultraviolet light. For this purpose, the coated material is passed under a mercury medium-pressure radiator. Hardening with UV-radiation is carried out in a known manner and is described in P.K.T.Oldring (eds.), "chemistry and technology of UV and electron beam formulations for coatings, inks and paints", Vol.1, 1991, SITA technology, London, p.167 to 269.

Detailed Description

Examples

The coating compositions are formulated according to the following table (numbers in parts by weight) and homogenized by dispersion. The coating was applied to oak plywood with a hand knife in a layer thickness of about 30 μm. The sheet was then passed under a mercury high-pressure radiator with an output of 80 watts per cm of lamp length. In each case a hard, solvent resistant film was formed (test using 50 double rubs with cotton balls soaked in butyl acetate). To test the sweating performance, the paint film was sanded and the sanded powder was allowed to remain on the paint film or panel overnight. The next morning, the degree of wetness of the sanding powder was evaluated and used as a measure of sweating. A completely dry sanding powder was rated 0 and a very wet sanding powder was rated 5.

Formulation (parts by weight)]	Reference to				The invention
											Examples	1	2	3	4	5	6	7	8	9	10
Roskydal*UA VP LS2299	84		84	84	84	84	84	84	84
											Laromer*PO 84F		100								100
TPGDA	16		16	16	16	16	16	16
											DPGDA									16
Esacure*TZT	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5
											Byk*410			2
Aerosil*300				2
											Crayvallac*MT					2
Crayvallac*SF						2
											Crayvallac*Super							2		2
Disparlon*6500								2		2
											Test [ Scoring]

Formulation (parts by weight)]	Reference to				The invention
											Sweating 10.0m/min	3	5	4	3	0	0	0	1	0	0
Sweating 20.0m/min	5	5	5	3	0	0	0	1	0	0
											Sweating is 30.0m/min	5	5	5	3	1	1	0	1	0	0
Sweating 40.0m/min	5	5	5	4	1	2	0	2	0	0

The formula is as follows: number in parts by weight

Roskydal^*UA VP LS 2299 (bayer, Leverkusen, germany) -amine modified polyether acrylates with a viscosity of about 800 mpa.s.

Laromer^*PO84F (BASF, Ludwigshafen, Germany) amine-modified oligoether acrylate having a viscosity of about 1000mPa.s

Diacrylate esters of TPGDA-tripropylene glycol

Diacrylate of DPGDA-dipropylene glycol

Esacure^*TZT (Lamberti, Aldizzate, Italy), photoinitiator (modified benzophenone)

Byk^*410(Byk-Chemie, Wesel, Germany) solution of modified urea

Aerosil^*300 (Degussa-Huls, Frankfurt, Germany) -pyrogenic silicic acid

Crayvallac^*MT and Crayvallac^*SF (Lubrizol coating additives Co., Ritterhue, Germany) -amide-modified hydrogenated castor oil

Crayvallac^*Super (Lubrizol Coating Additives, Ritterhupe, Germany) -Polyamide wax

Disparlon^*6500(C.H.Erbsl * h, Krefeld, Germany) -fatty acid-modified polyamides

The various panels were cured at different belt speeds (10, 20, 30, 40m/min) and then tested for their sweating performance: 0 is the best score and 5 is the worst score.

These examples clearly show that the process of the invention (examples 5 to 10) significantly reduces, often completely prevents, sweating compared to the reference process (examples 1 to 4).

Claims (10)

1. A process for producing a coating on a porous and/or absorbent material by applying a liquid coating agent comprising at least one component having a dynamic viscosity of less than 2000mpa.s and having (meth) acryloyl groups and subsequently radiation induced polymerization, characterized in that the coating agent comprises 0.1 to 10 wt.%, relative to its non-volatile components, of an additive selected from polyamides and/or oligomeric or polymeric fatty acid amides.

2. The method according to claim 1, characterized in that paper is used as porous and/or absorbent material.

3. The method according to claim 1, characterized in that cardboard is used as porous and/or absorbent material.

4. The method according to claim 1, characterized in that a fabric is used as the porous and/or absorbent material.

5. A method according to claim 1, characterized in that wood is used as porous and/or absorbent material.

6. The method as claimed in claim 1, characterized in that a wood material is used as the porous and/or absorbent material.

7. The method according to claim 1, characterized in that a fibre board is used as the porous and/or absorbent material.

8. A method according to claim 1, characterized in that ceramic material is used as porous and/or absorbent material.

9. The method according to claim 1, characterized in that mineral material is used as porous and/or absorbent material.

10. The method as claimed in claim 1, characterized in that porous plastic is used as the porous and/or absorbent material.