EP1290091A2

EP1290091A2 - Coating agents which can be hardened by means of uv radiation, method for producing coatings from said coating agents and use thereof

Info

Publication number: EP1290091A2
Application number: EP01940531A
Authority: EP
Inventors: Dietmar Votteler; Siegfried Fabriz; Jörg SENTKO
Original assignee: Votteler Lackfabrik GmbH and Co KG
Current assignee: Votteler Lackfabrik GmbH and Co KG
Priority date: 2000-06-03
Filing date: 2001-05-26
Publication date: 2003-03-12
Also published as: AU2001274072A1; DE10027670A1; WO2001094478A2; WO2001094478A3; US20030176527A1

Abstract

The invention relates to acrylate-based coating agents which can be hardened by means of UV radiation, and used to coat wood components. Said coating agent contains 5 to 80 wt. % of acrylate resin, 5 to 75 wt. % of a reactive diluting agent, 0.1 to 5 wt. % of a thixotropic agent, 0.1 to 10 wt. % of a photo-initiator and 0.05 to 20 wt. % of an additive. The invention also relates to the method for producing coatings, whereby 4 to 8 layers are hot-sprayed onto pre-fabricated wooden elements and hardened by means of UV radiation. The invention is characterised in that the coated components have low emissions after the final hardening and have VOC values (volatile organic compounds) of < 100 ppm. Said values are far below the standard values of known polyester lacquers.

Description

Coating agents curable by UV radiation, processes for producing coatings from these coating agents and their use

description

The invention relates to coating compositions curable by UV radiation, processes for producing coatings from these coating compositions and their use.

So far, for the surface coating of wooden parts, foils, tapes and the like. Or of three-dimensional objects, such as. B. kitchen furniture, peroxidically curable polyester paints, for example paraffin-containing paints based on phthalic anhydride or paraffin-free paints with a glossy surface based on allyl ether. The layers were applied using customary paint application methods such as rolling, pouring or spraying.

Peroxidically curable polyester paints based on unsaturated polyester, diluted with styrene or with compounds with a vinyl function, have also hitherto been used for the coating of wooden components intended for the interior of motor vehicles. The viscosities of these polyester paints are adjusted to a viscosity in the range from about 150 to 250 mPa.s at 21 ° C. so that they are sprayable. The polyester lacquers can be applied by compressed air spraying, with the polyester and peroxide components being mixed using the intermixing method and sprayed from a pot. It is also possible to run the two-component spray process, the peroxide component and the polyester component separately to the gun and mix in there in the spray jet. The wooden base is used for spray painting by pickling, priming, if necessary patinating and Isolate prepared. After drying, the polyester lacquer layer is sprayed onto the substrate prepared in this way.

Usually, several layers, preferably 4 to 8 layers, are applied one above the other in thicknesses of approximately 150 to 240 μm, so that layer thicknesses are obtained which enable the entire layer to be reworked, for example by grinding and polishing. It is necessary that the sprayed polyester paints thixotropize so that they also adhere to vertical surfaces. To adjust the thixotropy, they contain inorganic and / or organic thixotropic agents. The individual layers are gelled and UV-cured by UV radiation. The intermediate gelation and intermediate curing takes place through the radicals released from the peroxide component by UV radiation and, depending on the setting of the radiation, takes about 10 to 30 minutes for each individual layer. The final hardening of the entire layer is carried out by additional radiation with a high-pressure or medium-pressure mercury vapor lamp.

After the irradiation, the parts must be stored for three to four days in order to achieve the final hardness required for post-processing. When hardening, a volume decrease of about 12 to 17% is obtained. The weight loss is of the same order of magnitude. The shrinking parts that are released into the atmosphere in polyester / styrene systems consist predominantly of monostyrene or of styrene oxide, which is formed from monostyrene during the polymerization. Both substances are volatile organic compounds (VOC), which are undesirable in the sense of VOC regulations. Cyclohexanone, which arises from the cyclohexanone peroxide used for the polymerization, is also undesirable. Depending on the course of the polymerization, the polyester layer contains more or less volatile constituents, which are also gradually released. In addition to the substances mentioned above, these are phthalates and solvent residues. The VOC value, as a measure of the volatile constituents, is around 1,500 ppm for the above-mentioned gloss coating systems and around 1,700 to 2,200 ppm for polyester coatings containing paraffin.

However, environmental regulations will in future require VOC values of less than 100 ppm, which cannot be achieved with polyester paints.

It is therefore necessary to look for another paint system that meets these conditions. As such, a UV-curable acrylic lacquer system lends itself. So far, radiation-curable acrylate lacquers have been applied by customary lacquer application methods, for example by thin-layer application by means of rollers, the layer thicknesses of the applied layers being 5 to 15 μm. These thin layers are also applied in several layers, gelled and sometimes even sanded. The intermediate gelling, which is necessary for the adhesion of the next layer, is achieved by UV radiation. When applying thin layers by rolling, viscosities of about 300 to 800 mPa.s have been set.

For the lacquer application process by spraying, lower viscosities in the range of approximately 150 to 250 mPa.s at 21 ° C. are required. Acrylics with the addition of solvents were used for spraying in order to achieve the desired course, to keep the layer thickness correspondingly low, to obtain bubble-free layers and, if desired, to be able to adjust the matting. Until now, solvents that are less harmful to health have been used in the processing of radiation-curable paints by spraying. Reactive thinners, which are much more problematic in this regard, have generally not been used. Proceeding from this, the object of the invention is to develop a liquid coating composition curable by means of UV light which has good sprayability, good film properties in the end result and a low VOC value.

The object is achieved according to the invention by a liquid coating agent which can be hardened by UV radiation and which contains the following constituents:

5 to 80% by weight of a mixture of monomeric, oligomeric and polymeric multifunctional, crosslinkable acrylates and / or methacrylates;

5 - 75% by weight of a reactive diluent;

0.1-5% by weight of a thixotropic agent;

0.1-10% by weight of a photoinitiator and 0.05-20% by weight of additives.

Advantageous embodiments of the invention result from subclaims 2 to 11.

The invention further relates to a method for producing a coating on a prefabricated wooden surface, in which the coating agent is applied by hot spraying at 35 to 80 ° C in several layers with a layer thickness of 50 to 800 microns and applied in each layer by UV radiation.

With the measures according to the invention it is achieved that the painted, hardened wooden component can be milled, sanded, polished and light-resistant, chemical-resistant and moisture-resistant. As far as moisture resistance is concerned, a 500h condensation storage (at 40 ° C and 95% relative humidity) is required. The main characteristic is that the coating agent according to the invention is low in emissions, ie has a low VOC value of <100 ppm.

The invention is explained in more detail below on the basis of the specific description.

The invention relates to coating compositions curable by UV light, which use acrylic resins as coating raw materials. The importance of the invention is based in particular in the fact that solvent-free and low-emission paints are used which lead to a variety of desired properties.

The coating composition contains about 5 to 80% by weight, preferably about 10 to 60% by weight, of polyfunctional crosslinkable acrylates or methacrylates. Starting materials are, depending on the structural structure, polyether, polyester, epoxy, urethane, melamine, silicone acrylates and / or methacrylates and acrylated and / or methacrylated polyacrylates. According to the invention, preference is given to an epoxy acrylate in an amount of 50 to 80 parts by weight, which is a diglycidyl ether of bisphenol A, reacted with two molar parts of acrylic acid. The materials include all molecular weight ranges between monomers, oligomers and polymers and may contain other functional groups in addition to the acrylate group. The molecular weights (weight average) are in a range from about 500 to 6,000, the composition being selected so that application by spraying is ensured and enough low molecular weight components are present so that a total viscosity of 150 to 250 mPa.s at 21 ° C results. On the other hand, to ensure good film properties of the end product, high-molecular components must also be present. The coating composition contains about 5 to 75% by weight of a reactive diluent. The reactive diluents are monomers or also low-viscosity oligomers that replace volatile organic solvents. They have molecular weights in the range from about 50 to 500. The reactive diluents, which contain radical-polymerizable radicals, are selected from the group of acrylic esters of simple alcohols, hexanediol diacrylate, hydroxymethylethylacrylate, hydroxypropyl acrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, dipropylene glycol diacrylate or mixtures of the same, tripropylene glycol. Styrene-free unsaturated acrylate and polyester acrylate resins are available, for example, from BASF under the trade names Laromer® and Sartomer®.

To adjust the thixotropy of the coating agent, about 0.1 to 30% by weight of a thixotropic agent based on silicon dioxide is added. According to the invention, fumed silica is preferred in an amount of 0.5 to 1.5% by weight. The thixotropic agent is combined with the resins or resin components of Van der Waals bonds, which bring about a reduction in viscosity under the action of mechanical forces during processing. After the mechanical stress has ceased, the thixotropy is reset, thereby preventing vertical surfaces from running off.

Other constituents of the coating agent are photoinitiators, which are added in an amount of about 0.01 to 10% by weight, preferably 1 to 3% by weight. These are compounds which, under the action of high-energy radiation, form start radicals which trigger the polymerization of the coating composition. UV initiators which can be used in the context of the present invention are, for example, benzoin ether, benzil dimethyl ketal, diethoxyacetophenone, hydroxy ketones, aminoketones, benzophenones, a mixture of benzophenone and 1-hydroxy-cyclohexyl-phenyl ketone (trade name Irgacure® from Ciba Specialty Chemicals, Basel), 2-hydroxy 2-methyl-1-phenyl-propan-1-one (trade name Darocur® from Ciba Specialty Chemicals, Basel), monoacylphosphine oxides and bisacylphosphine oxides, or mixtures thereof (trade name Lucirin® from BASF).

Conventional additives are also added to the coating agent. Among such z. B. understood additives to increase the scratch resistance, heat resistance and light fastness. They can optionally be contained in amounts of approximately 0 to 20% by weight. To regulate the surface tension of the coating composition and to set good application properties, surface-active substances are added in concentrations of 0.0001 to 2% by weight, for example organic silicone compounds of the polymethylsiloxane type (trade name Baysilone® from Bayer).

Other common additives are stabilizers or inhibitors, which intercept potential start radicals. The amounts used are of the order of about 0 to 20% by weight, preferably from 0 to 8% by weight. Stabilizers or inhibitors which can be used in the context of the present invention can include hydroquinone, hydroquinone monomethyl ether, p-benzoquinone, p-tertiary-butylcatechol, phenothiazine, 2,6-di-tertiary-butylhydroxytoluene, sterically hindered amines and benzotriazole (trade name Tinuvin® from Ciba Specialty Chemicals , Basel).

The coating agent of the present invention is a material that has no short-life pot life. The polymerisation is only triggered by the action of UV radiation by UV initiators. The consequence of this is that sprayed material, which for example reaches the conveyor belt, is recyclable and can be recycled by appropriate devices. Due to the use of functional reactive thinners instead of organic solvents, there is no weight loss during the polymerization process. This means that the recovered materials can be reused without much effort can be supplied, and on the other hand that the hardened acrylate varnish remains dimensionally stable and later releases no volatile products. The latter is an essential prerequisite for low VOC values. The functionality of the reactive diluents and thus their crosslinking action is, in addition to the viscosity, the dilution action and volatility, an important selection criterion when using the same. If stabilizers remain in the product during manufacture, the paint properties must not be impaired. At most UV initiators are emitted from the product.

To prevent the release of volatile constituents, the reaction conditions with regard to temperature, mixing etc., as well as the stabilizer and UV initiator system, must be carefully coordinated. Temperatures of the reaction system of about 110 to 130 ° C should not be exceeded.

The use of functional reactive thinners is an essential prerequisite for low values of volatile organic compounds (VOC).

embodiments

Example 1 :

A coating batch is made by simply mixing the components below with heating (to about 40 ° C) to ensure the dissolution of these components. The mixture has a viscosity of about 550 mPa.s (measured at 21 ° C). 60 parts by weight of epoxy acrylate, MW: 2,500;

20 parts by weight of reactive diluent 1,6-hexanediol diacrylate

1 part by weight of fumed silica;

2 parts by weight of UV initiator consisting of a mixture of monoacylphosphine oxide and bisacylphosphine oxide;

0.1 part by weight of polymethylsiloxane; 1 part by weight of benzotriazole.

Example 2:

The components of Example 1 are used, with the exception that a mixture of 20 parts by weight of hexanediol diacrylate and 15 parts by weight of tripropylene glycol diacrylate is used instead of the reactive diluent. Instead of the UV initiator, 1 part by weight of a mixture of benzophenone and 1-hydroxycyclohexylphenyl ketone is used. The coating batch is prepared as indicated in Example 1. The mixture has a viscosity of about 600 mPa.s (measured at 21 ° C).

Example 3:

The components of Example 1 are used, with the exception that 35 parts by weight of a mixture of hydroxymethyl ethyl acrylate and hydroxypropyl acrylate are used instead of the reactive diluent. UV initiator is 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur®).

The coating batch is prepared as indicated in Example 1. The mixture has a viscosity of about 580 mPa.s (measured at 21 ° C). Example 4:

The components of Example 1 are used, with the exception that 20 parts by weight of polyester acrylate (Laromer®), MW: 2,100, are used instead of the reactive diluent.

In addition to spraying, suitable application methods for the coating compositions of the invention are also pouring, flooding, dipping or rolling. According to the invention, preference is given to a hot spraying process at a paint temperature of approximately 35 to 60 ° C. The total number of paint jobs is 4 to 8 jobs. 50 to 500 g / m ² , preferably 150 to 250 g / m ^{2, are} sprayed on per application.

After the coating film has been applied to the substrate, the polymerization is carried out by means of UV radiation. It can advantageously also be carried out in an inert gas atmosphere, for example under nitrogen gas, to exclude the polymerization-inhibiting atmospheric oxygen. Since various additives are considered hazardous substances, for example there are risks of skin contact, it is advantageous to apply the layers of paint in a closed chamber.

The UV irradiation time required for gelling and / or curing depends on the temperature and the chemical composition of the coating agent, on the type and power of the UV source, on its distance from the coating agent and on any inert gas atmosphere that may be present. Guideline values for the radiation duration are a few seconds to a few minutes. The UV radiation source should emit radiation in the range from about 150 to 600 nm, preferably from 200 to 400 nm wavelength. The radiated energy is in a range from about 5 to 2,000 mJ / cm ² . Guide values for the distance between the UV source and the lacquer layer are in the range of approximately 20 to 1,000 mm. The four coating agents described above are used in a coating process as described below.

An interior fine wood veneer for motor vehicles is chosen as the substrate.

The wood is cemented with a spatula and hardener and hardened for about 2 hours at 20 to 28 ° C at 50 to 60% relative humidity.

After sanding, hydrogen peroxide (35%) with bleaching additive is sprayed onto the wooden substrate for bleaching. This is followed by drying for at least 48 hours under the conditions specified for the kitten.

The wood substrate is then pickled by spraying a dye solution and dried under the conditions specified for the kitten for 4 hours and cooled back to room temperature.

A two-component polyurethane system is sprayed on for priming. The application quantity is 20 to 40 g / m ² , depending on the part and type of wood, with 1 or 2 applications and ventilation between the applications.

Hardening: 3 to 16h at 20 to 23 ° C at 50 to 60% relative humidity.

For the insulation, a colorless insulating base (two-component polyurethane system) and hardener are sprayed on with an application amount of 20 to 40 g / m ² . Hardening: 3 to 16h at 20 to 23 ° C at 50 to 60% relative humidity.

For painting, one of the previously described paint systems is applied by hot spraying. The paint temperature is 35 to 60 ° C. Application quantity: 4 to 8 X 150 to 180 g / m ² . After flashing off, the polymerization is carried out by means of UV radiation. For this purpose cold light, ie two spotlights with different wavelength and power. Duration: 1 to 2 minutes at 20 to 35 ° C with 5 W / cm light output. Gelling, hardening: V = 1.5 to 3 m / min. with 80 W / cm light output.

Post-curing is carried out at 50 ° C for 16 hours.

VOC determination is carried out according to the applicable standards using two methods:

1. Head space method (GC-MS = gas chromatography mass spectrometry) and

2. TDS-GC method (thermal desorption gas chromatography).

Both processes work at elevated temperatures in a range from 90 to 120 ° C. the TDS-GC method e.g. B. at 120 ° C. The entire material is loaded at this temperature. What evaporates is determined as VOC.

With the Head-Space-GC-MS, VOC values of around 1,500 ppm were measured up to 90 ° C in so-called polyester gloss coating systems and VOC values of around 1,700 to 2,200 ppm in polyester coatings containing paraffin. In contrast, VOC values of approximately 40 to 60 ppm are measured in the above exemplary embodiments according to the invention.

In summary, the following can be stated: The invention relates to acrylate-based coating compositions which are curable by UV radiation and which are suitable for coating wooden components. The coating composition contains 5 to 80% by weight of acrylic resins; 5 to 75% by weight of a reactive diluent; 0.1 to 5% by weight of a thixotropic agent; 0.1 to 10% by weight of a photoinitiator and 0.05 to 20% by weight of additives. The process for the production of coatings is also protected. In this 4 to 8 layers applied to pre-assembled wooden parts in a hot spraying process and hardened using UV radiation.

It is essential that the coated components have low emissions after the final hardening and VOC values have volatile organic compounds of <100 ppm. These are far below the usual values for the known polyester coatings.

Claims

claims

1. Liquid coating composition curable by means of UV radiation, which contains the following constituents: 5 to 80% by weight of a mixture of monomeric, oligomeric and polymeric multifunctional, crosslinkable acrylates and / or methacrylates;

5 to 75% by weight of a reactive diluent; 0.1 to 5% by weight of a thixotropic agent; 0.1 to 10% by weight of a photoinitiator and

0.05 to 20 wt% additives.

2. Coating composition according to claim 1, characterized in that it contains the following constituents: 20-80% by weight of a mixture of monomeric, oligomeric and polymeric multifunctional, crosslinkable acrylates and / or methacrylates;

5 to 25% by weight of a reactive diluent; 2 to 4% by weight of a thixotropic agent; 2 to 5% by weight of a photoinitiator and

0.05 to 10% by weight of additives.

3. Coating composition according to claim 1 or 2, characterized in that the polyfunctional acrylates are selected from the group of polyether, polyester, epoxy, urethane, melamine, silicone acrylate and / or acrylated polyacrylates; Polyether, polyester, epoxy, urethane, melamine, silicone methacrylate and / or methacrylated polyacrylates.

4. Coating composition according to one of claims 1 to 3, characterized in that the polyfunctional acrylates and / or methacrylate have molecular weights in the range from 500 to 6,000.

5. Coating composition according to one of claims 1 to 4, characterized in that the reactive diluent contains radical-polymerizable radicals and is selected from the group of acrylic esters of simple alcohols, hexanediol diacrylate, hydroxymethyl ethyl acrylate, hydroxypropyl acrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, triphylene glycol, triphylene glycol, triphylene glycol, triphylene glycol, di-propylene glycol mixtures, di-propylene glycol mixtures, di-propylene glycol mixtures, di-propylene glycol mixtures, di-propylene glycol mixtures thereof, and polyester acrylates.

6. Coating composition according to one of claims 1 and 5, characterized in that the reactive diluents have molecular weights in the range from 50 to 500.

7. Coating agent according to one of claims 1 to 6, characterized in that a thixotropic agent, preferably based on SiO ₂ , is added.

8. Coating agent according to one of claims 1 to 7, characterized in that the photoinitiator is a UV initiator and is selected from the group of benzoin ether, benzil dimethyl ketal, diethoxyacetophenone, hydroxy ketones, aminoketones, benzophenones, a mixture of benzophenone and 1-hydroxy-cyclohexyl-phenyl ketone, 2-

Hydroxy-2-methyl-1-phenyl-propan-1-one, monoacylphosphine oxide and bisacylphosphine oxide or mixtures thereof.

9. Coating composition according to one of claims 1 to 8, characterized in that it is an additive, a surface-active substance, preferably contains an organic silicone compound of the polymethylsiloxane type with a proportion of less than 2% by weight.

10. Coating composition according to one of claims 1 to 9, characterized in that it contains as an additive at least one stabilizer and / or inhibitor which is selected from the group of hydroquinone, hydroquinone monomethyl ether, p-benzoquinone, p- Tertiary-butyl-catechol, phenothiazine, 2,6-di-tertiary-butylhydroxytoluene, sterically hindered amines and benzotriazole with a proportion less than 8% by weight.

11. Coating composition according to one of claims 1 to 10, characterized in that the components are chosen in their weight composition so that there is a processing viscosity of 150 to 250 mPa.s at 35 to 60 ° C.

12. A method for producing a coating on a prefabricated wooden surface, characterized in that a coating agent according to one of claims 1 to 11 applied in several layers to the wooden surface with a layer thickness of 50 to 500 microns by hot spraying at 35 to 80 ° C. and that each layer after its application is gelled by UV radiation.

13. The method according to claim 12, characterized in that each layer is sprayed with a layer thickness of 150 to 250 microns.

14. The method according to claim 12 or 13, characterized in that the coating agent has a viscosity of 150 to 250 mPa.s when sprayed.

15. The method according to any one of claims 12 to 14, characterized in that a photo radiation in the wavelength range of 150 to 600 nm is used for the gelation of the layers.

16. The method according to any one of claims 12 to 15, characterized in that the gelation of each layer is carried out in three-dimensional wooden components in an inert gas atmosphere.

17. The method according to any one of claims 12 to 16, characterized in that after spraying and gelling of all layers, post-curing with UV radiation is carried out.

18. The method according to any one of claims 12 to 17, characterized in that a total of 4 to 8 layers are sprayed on.

19. The method according to any one of claims 12 to 18, characterized in that the spraying and gelling of the layers is carried out in a closed chamber.

20. Use of the coating agent prepared according to one of claims 1 to 11 for coating wooden components which are intended for the interior of motor vehicles.