WATERBORNE RADIATION CURABLE LACQUERS BASED ON CELLULOSE AND THEIR PREPARATION

Abstract: The application relates to a radiation curable lacquer composition comprising a radiation curable resin and a cellulose ester. This lacquer composition shows improved properties in comparison with known lacquer compositions. The lacquer composition is obtainable by mixing a dispersion comprising a cellulose ester, which dispersion is substantially free of radiation curable components, with a dispersion comprising a radiation curable resin.

Description: WATERBORNE RADIATION CURABLE LACQUERS BASED ON CELLULOSE AND THEIR PREPARATION The present invention relates to a process for the preparation of a waterborne radiation curable lacquer composition comprising a radiation curable resin and a cellulose ester, and the lacquer composition thus obtained. In EP 0 154 241 a UV curable coating composition is disclosed based on cellulose nitrate and at least one UV curable unsaturated resin. Optionally other components are present in the composition. The composition is prepared by dissolving the cellulose nitrate, the unsaturated resin, and the optional components in a suitable organic solvent or a mixture of solvents. The thus obtained high-viscous cellulose nitrate-containing paste is then emulsified at elevated temperature under high shear forces by the addition of water and optionally a dispersant. A drawback of this method is the need to use a substantial amount of organic solvent in the preparation of the paste containing the cellulose nitrate and the unsaturated resin. After the dispersion of these components in water, the organic solvent is still present and will evaporate during cure of the coating composition. The emission of most organic solvents contributes to the VOC level of the coating composition. The VOC level is restricted by present day legislation. Such restriction is expected to increase in the near future. In normal use, the water is evaporated from the coating composition and the components in the composition are cured. A drawback of this known method is tackiness of the coated surface after evaporation of the water. To prevent sticking of particles to the tacky surface of a freshly coated object, special care is needed to place the object in a dust-free area. In particular in industrial coating processes this presents a major problem, e.g., when the object is a GONRΠUXΠON COPY WO 01/16239 PCTYEPOO/08492 wooden object which is coated in the same environment where the wood is also cut into pieces or sanded. Further, it was found that the unsaturated resin(s) present in the compositions prepared according to these known processes show(s) a relatively low cure response upon radiation. This leads to a prolonged application process. Further, the lacquer compositions of EP 0 154 241 show insufficient water, coffee, and ethanol resistance. In US 5,254,603 UV curable cellulose based lacquers are disclosed. These compositions contain a relatively large amount of reactive diluents. A problem with these coatings on porous substrates is the penetration of the coating composition into the pores. Since the radiation does not reach these areas, uncured coating material is the result. This can give health, safety, and environmental problems, e.g., when the substrate is cut or sanded. These problems occur even years after the lacquer has been applied. The same problems can be found in other substrates comprising shadow areas, e.g. in 3- D substrates, or when a pigmented lacquer is used. In EP 426085 a solvent borne radiation curable coating composition is disclosed comprising a cellulose ester. These compositions all contain a relatively large amount of solvent that has to be evaporated before curing of the composition. In DE 2436614 water containing radiation curable coating compositions are disclosed comprising a cellulose ester. A mixture comprising a radiation curable resin and the cellulose ester is dispersed in water in a way comparable to the process disclosed in EP 0 154 241. In US3,615,792 a method is disclosed for the preparation of cellulose containing coating compositions. The preparation of water borne radiation curable lacquer compositions comprising cellulose and a radiation curable resin is not disclosed in this document. The invention relates to a process for the preparation of waterborne lacquer compositions which contain a substantially lower amount of organic solvents than known lacquer compositions based on cellulose esters and show improved properties upon application, i.e. which are not tacky after evaporation of the water from the dispersion, and after curing show, e.g., an improved resistance to various liquids. Surprisingly, a very simple process was found for the preparation of a radiation curable lacquer. This process comprises the following steps: preparation of a dispersion which is substantially free of radiation curable components comprising cellulose ester and water, by dissolving the cellulose ester in an appropriate solvent and emulsifying the thus obtained solution by the addition of water and optionally a dispersant, mixing said cellulose-containing dispersion with a radiation curable resin until a homogeneous dispersion is obtained. The process according to the present invention offers a high degree of freedom with regard to the formulation of coating compositions. The cellulose ester- comprising dispersion can be mixed with virtually any radiation curable resin. This mixing can be done at any stage of the preparation of the lacquer composition. The type of radiation curable resin can be adjusted to the requirements of the substrate and/or the desired coating. The present invention further relates to a radiation curable lacquer composition which shows improved behaviour over known radiation curable lacquer compositions based on cellulose esters, in particular with respect to cure speed, water, coffee, and ethanol resistance. It was found that, in comparison with known non-radiation curable cellulose ester-based lacquers, the lacquer composition according to the present invention also shows improved chemical resistance, scratch resistance, and pendulum hardness. Further, this new lacquer composition shows no yellowing after curing. Within the framework of the present invention, the following definitions are used - a dispersion is a distribution of finely divided particles (solid or liquid) in a (liquid) medium, a dispersion which is not curable by radiation, other than infrared radiation, is considered to be a dispersion which is substantially free of radiation curable components, - a radiation curable resin or dispersion comprising a radiation curable resin is a compound which can be cured by radiation having a wavelength λ < 500 nm, optionally after the addition of a small amount of radiation sensitive compound, a radiation curable lacquer composition is a lacquer which is cured by using electromagnetic radiation having a wavelength λ < 500 nm. Examples of electromagnetic radiation having a wavelength λ < 500 nm are, e.g., UV radiation or electron beam radiation. Among the cellulose esters eligible for use according to the invention are the known nitrate esters, as well as esters based on acetobutyrate and acetopropionate. Preference is given to the use of cellulose nitrate, cellulose acetobutyrate, cellulose acetopropionate, or cellulose acetate, as well as mixtures thereof. In DE 27 02 986 a process for the preparation of a dispersion comprising a cellulose ester is disclosed. In this process, a cellulose ester-comprising dispersion is prepared by dissolving a cellulose ester in an appropriate organic solvent and dispersing the thus obtained solution by the addition of water and optionally a dispersant. The organic solvent can be (partially) removed after the dispersion has been obtained, e.g., by distillation. In the process according to the present invention, the dispersion comprising the cellulose ester can further comprise other resins which are compatible with the cellulose ester employed to improve the properties of the coating composition. Without being limitative in any way, examples of these other resins are: alkyd/polyester resins, epoxy resins, polyethers, polyurethanes, amino resins, and acrylic or vinyl polymers, or mixtures thereof. Optionally, portions of these other resins can be functionalised with reactive groups. These other resins can be incorporated into the cellulose ester-comprising dispersion at any moment in time. They can be mixed in prior to dispersion or when the dispersion is prepared. However, it is also possible to add these other resins after the preparation of the cellulose ester-comprising dispersion. Further, it is possible to add the other resins to the cellulose ester-comprising dispersion at or after the mixing with the radiation curable resin. According to the present invention, the waterborne radiation curable lacquer composition is obtainable by mixing a dispersion comprising a cellulose ester and a radiation curable resin. In this process any water dispersible or water dilutable radiation curable resin known to the man skilled in the art can be used. However, the addition of such resins to the cellulose ester-comprising dispersion can result in a change in the viscosity of the lacquer composition. In a subsequent step, the viscosity then has to be adjusted for the proper application of the lacquer composition. To circumvent this, it is preferred to mix the cellulose ester-comprising dispersion with a dispersion or an aqueous solution comprising the radiation curable resin. The dispersion comprising the radiation curable resin can be prepared by using any dispersible radiation curable resin known to the man skilled in the art. Examples of such dispersions are all acrylate dispersions, polyester acrylate dispersions, aliphatic polyurethane dispersions, epoxy acrylate dispersions, urethane acrylate dispersions, urethane epoxy acrylate dispersions, aromatic urethane acrylate dispersions, and aliphatic urethane acrylate dispersions. Suitable dispersions are commercially available under the following tradenames: Alberdingk LUX 11 , Alberdingk LUX 22, Alberdingk LUX 33 (all ex Alberdingk Boley), UV-Link SA 01 , UV-Link AP 03 (both ex ADD APT), Halwedrol UV 14, Halwedrol UV 20, Halwedrol UV 74, Halwedrol UV 94, Halwedrol TN 6306/40W (all ex Hϋttenes- Albertus), Primal E 3120 (ex Rohm & Haas), Laromer LR 8895, Laromer LR 8983, Laromer LR 8949 (all ex BASF), Daotan VTW 1236, Viaktin VTE 6155W, Viaktin VTE 6166W, Viaktin VTE 6165W, Viaktin VTE 5972W, Viaktin VTE 6169/45W (all ex Vianova), NeoRad R 440, NeoRad R 441 (both ex Zeneca) and Uretanacrylat 98-283W (ex Rahn). Good results are found if the dispersion comprising the radiation curable resin has a solids content (based on the total weight of the dispersion) of 20 - 80%, preferably 30 - 60%. Normally 3 - 40 pbw, preferably 5 - 30 pbw, of the dispersion comprising the radiation curable resin are mixed with 100 pbw of the dispersion comprising the cellulose ester. Optionally, a photoinitiator is added to the lacquer composition. Suitable photoinitiators for use in the lacquer composition according to the present invention are Irgacure 500, Irgacure 1000, Irgacure 2959, and Darocure 1173 (all ex Ciba) or Esacure KTO 46 and KIP EM (both ex Lamberti). The photoinitiator can be added to the radiation curable resin, i.e. before the mixing of the dispersion comprising the cellulose ester and the radiation curable resin. It is also possible to add the photoinitiator after the mixing of the dispersion comprising the cellulose ester and the radiation curable resin. Additives and fillers that are known to those skilled in the art can be added to the lacquer compositions according to the present invention, e.g., co-solvents, defoamers, levelling agents, antisettling agents, rheology modifiers, and pigments. The lacquer compositions according to the present invention can be cured in a comparatively short time and at ambient temperature. Therefore, these coating compositions are in particular suited for industrial coating processes. The compositions can be used to coat heat sensitive substrates, e.g., wooden or plastic substrates. However, they can also be used on other substrates, e.g., they can be used as a clear coat or a pigmented coat on any substrate to get an aesthetic effect, taking advantage of the rapid cure of these lacquer compositions. Due to their excellent properties the lacquer compositions of the present invention are very suited to be used as a clear coat on wooden substrates, e.g., as a clear coat on wooden furniture. The invention will be elucidated with reference to the following examples. These are intended to illustrate the invention but are not to be construed as limiting in any manner the scope thereof. Examples Examples 1 - 19 Unless otherwise indicated, "pbw" stands for "parts by weight". The ethanol resistance and the resistance to other chemicals were measured in accordance with European Standard EN 12720. Several of the tests from EN 12720 are also used in the "Mδbelfakta" test. "Mobelfakta" is a well-known and accepted test used for testing furniture coatings. The results of these tests are given on a 5-point scale, wherein 1 indicates "poor" and 5 indicates "excellent" performance. Preparation of hvdroxyl-functional alkvd resin 32,2 parts of tall oil fatty acid, 18,5 parts of trimethylol propane, 16,3 parts of pentaerythritol, and 32,6 parts of phthalic anhydride were mixed and heated for 50 minutes at 185°C with continuous stirring. At 240°C xylene was added, and the water of reaction was removed with refluxing until an acid value of < 7 was reached. Next, the product was diluted with butyl acetate to a solids content of 70 ± 1 ,5%. An oil-in-water dispersion was prepared by mixing the following components: 34,5 pbw of the hydroxyl-functional alkyd resin solution 3,0 pbw of dibutyl phthalate 2,5 pbw of methoxypropyl acetate 4,5 pbw of dispersants/emulsifiers 27,0 pbw of nitro-cellulose (Standard 24 E (65 wt.% dry solids) The mixture was homogenised at 45°C and with slow stirring 28,5 pbw of water were added dropwise. The obtained oil-in-water dispersion had an alkyd resin to nitro-cellulose ratio based on solids of 1:1. Samples were prepared by mixing 100 pbw of the dispersion comprising nitrocellulose and the alkyd resin (NC/AR) with a dispersion comprising a radiation curable resin and optionally 2 pbw of a photoinitiator (Irgacure 500, ex Ciba). In the examples the following commercially available dispersions comprising a radiation curable resin were used: R1 Primal E 3120 all acrylate dispersion ex Rohm & Haas R2 Viaktin VTE 6165W urethane acrylate dispersion ex Vianova R3 UA 98-283W urethane acrylate dispersion ex Rahn R4 Laromer LR 8983 aromatic urethane acrylate dispersion ex BASF R5 Laromer LR 8949 aliphatic urethane acrylate dispersion ex BASF R6 Viaktin VTE 6169 urethane acrylate dispersion ex Vianova To prepare lacquers from the thus obtained dispersions, 100 parts of each dispersion were mixed at room temperature with 5 parts of a non-ionic wax dispersion, 0.7 parts of silica, 6.5 part of 3-Metoxi-n-butylacetat (or Butoxyl), 0.5 parts of additives , and 5 parts of water. The lacquer samples were applied on wooden panels using an airmix spraygun. Two layers were applied at 70 g/m 2 . Water was evaporated at 50°C for 10 minutes. Then the panels were mounted on a drive belt and passed under a 80 W/cm 2 Hg Lamp at a speed of 5 m/min. Example 1 was cured by using IR radiation only. It was noted that after evaporation of the water, the coated surfaces were not tacky. In Table 1 the results for pendulum hardness and ethanol resistance of the lacquer samples are presented. Table 1 * Comparative example - not measured Example 20 (comparative) A waterborne cellulose ester containing lacquer composition according to EP 0 154 241 was prepared. In a first step at 50°C a solution was prepared comprising a polyesteracrylate resin (Roskydal 850 W ® ), cellulose nitrate Norm 27E, and n-butylacetate. From this solution, in a second step, a dispersion was prepared by the slow addition of water under constant mixing. A photoinitiator was added to the dispersion. A lacquer was prepared from this dispersion in the same way as was done for the other samples. The lacquer was applied on a wooden panel and cured as described before. It was noted that after evaporation of the water, the coated surface was still tacky. In Table 2 the results of the Mδbelfakta test for some of the samples are presented. Table 2, results of Mδbelfakta tests "Comparative example

Claims: Claims 1. A process for the preparation of a radiation curable lacquer composition comprising a radiation curable resin and a cellulose ester, characterised in that in a first step a dispersion comprising a cellulose ester and water is prepared, said dispersion being substantially free of radiation curable components, by dissolving a cellulose ester in an appropriate solvent and emulsifying the thus obtained solution by the addition of water and optionally a dispersant, and that in a subsequent step said dispersion is mixed with a radiation curable resin, to obtain a radiation curable lacquer composition. 2. The process of claim 1 , characterised in that the dispersion comprising a cellulose ester and water is mixed with a dispersion comprising the radiation curable resin. 3. The process according to either of the preceding claims, characterised in that the dispersion comprising the cellulose ester further comprises an alkyd resin. 4. Radiation curable lacquer composition comprising a radiation curable resin and a cellulose ester, obtainable by mixing A) a dispersion comprising a cellulose ester, which dispersion is substantially free of radiation curable components, with B) a radiation curable resin. 5. Radiation curable lacquer composition according to claim 4, characterised in that the dispersion comprising a cellulose ester further comprises an alkyd resin. 6. Radiation curable lacquer compositions according to claim 4 or 5, characterised in that the dispersion comprising a cellulose ester and water is mixed with a dispersion comprising the radiation curable resin. 7. Radiation curable lacquer composition according to claim 4 or 5, characterised in that the dispersion comprising the radiation curable resin further comprises a photoinitiator. 8. Use of the radiation curable lacquer composition comprising a radiation curable resin and a cellulose ester of claims 4-7 for the coating of heat sensitive substrates.

Inventors: KJELLQVIST LINDELL ANN KERSTIN, KRUITHOF KLAAS JAN HENDRIK, KJELLQVIST LINDELL, ANN, KERSTIN, BIRGITTA, KRUITHOF, KLAAS, JAN, HENDRIK
Applicants: AKZO NOBEL NV, KJELLQVIST LINDELL ANN KERSTIN, KRUITHOF KLAAS JAN HENDRIK, AKZO NOBEL N.V., KJELLQVIST LINDELL, ANN, KERSTIN, BIRGITTA, KRUITHOF, KLAAS, JAN, HENDRIK
Application year: 2000
Main classification: C09D101
IPC codes: C09D101