CS210407B1 - Unsaturated UV-curable polyester paints - Google Patents

Abstract

The invention relates to new types of coatings based on unsaturated polyester resins, which are cured by UV radiation and are particularly suitable for the surface treatment of wooden furniture. The coatings contain 0.005 to 1 wt. % of acrylic polymers or copolymers with a molecular weight of 15,000 to 150,000 and optionally other additives affecting the properties of the coating films or the cured coating, e.g. paraffin, silicone oil, colloidal silica, zinc and cobalt soaps, etc.

Description

The present invention relates to novel types of unsaturated polyester paints which are UV curing. These coatings are particularly suitable for surface treatment of wood and cellulosic materials.

In the furniture industry, a wide range of coatings, lacquers and enamels are commonly used for surface treatment of wooden substrates. In particular, they are applied to veneer boards, wood-fiber boards with glued cellulose foil containing amino resin as binder. These substrates are surface treated with shiny to matt paints, most often nitro-cellulosic, acrylate, polyurethane, saturated polyesters or epoxyesters containing amino resins, etc. To achieve a perfect homogeneous appearance of the final surface, the substrate is usually pretreated, eg by cementing, pore filler, or by applying several layers of the same paint. The number of layers to be applied depends on the dry substance of the paint. This base layer mainly eliminates the uneven absorbency of the substrate and is usually ground to remove protruding wood fibers from the surface or to even out the unevenness of the substrate. The substrate treated in this way can then be finished with substantially less paint than the non-uniformly absorbent substrate.

When using paints with a low dry matter content, it is necessary to pre-dry the individual layers, which is time and energy consuming. * το base layer can be applied eg unsaturated polyester sealant cured chemically or UV-radiation, which, however, only suits under opaque coatings, not under varnishes, where it optically interferes. In other cases chemically curable, unsaturated polyester paraffinic polyester varnishes can also be used, which can be applied by pouring and whose surface is finished after grinding with the desired varnish or enamel. However, this process has the disadvantage that the layers become too thick and the curing process is time and energy consuming. It is preferable to use UV-cured unsaturated polyester lacquers which are applied by roller in thinner layers and whose curing time is shorter. These are special types of unsaturated polyester varnishes that do not inhibit during air oxygen curing and produce non-sticky hard surfaces. These lacquers are usually modified with allyl ethers and may contain acrylic acid esters of glycols or saturated polyesters terminated with acrylic groups instead of styrene. However, it is also possible to use unsaturated polyester varnishes of the paraffinic type with the addition of photoinitiators, which, however, have to be cured in succession by low-pressure UV-emitters and reinforced by medium- or high-pressure emitters. If only high-pressure emitters are used, the ecrch remains soft and overcoating with some types of coating reduces adhesion of the system or surface defects.

A variety of additives are used for chemically curable unsaturated polyester varnishes of the paraffinic type in order to eliminate solid defects, in particular the formation of craters, bubbles, etc., and to improve their flow. For example, organic solvents (ketones, toluene, propyl alcohol, acrylic acid, etc.) as well as esters of acrylic acid with a carbon number in the alkyl group of 1 to 8 (especially 2-ethylhexyl acrylate) or their polymers (most commonly polybutyl acrylate or poly-2- ethylhexyl acrylate) of mol. weight to? 000.

These polymers only act as flowing agents, but they themselves do not have film-forming properties because they produce a soft and permanently sticky film. In unsaturated polyester varnishes curable chemically by the redox system, the formation of the paraffinic layer increases its gloss and reduces the hardness. In larger quantities the hardened coating becomes cloudy. When curing the unsaturated polyester varnishes of the air-inhibiting type of paraffin and adding a photoinitiator using low-pressure emitters at a temperature of up to 33 ° C, the paraffin layer is evenly output, which has separating properties for further coatings and must therefore be abraded. When curing with medium-pressure or high-pressure or pulsed UV-emitters (so-called IST-emitters), the temperature in the curing space is usually above 30 ° C.

Under these conditions, the surface of the coating remains soft and grinds the sanding paper when sanding. When applied in a thin layer to absorbent wood, the coating may then remain insufficiently cured due to air inhibition, which will have a beneficial effect on the properties of the entire coating system, especially after application (other grids containing ketones or aromatic solvents).

These drawbacks have no coating compositions according to the present invention which consist of unsaturated polyester resins, bleaching monomers, photoinitiators, organic solvents and additives and which are particularly suitable for surface treatment of wood and cellulosic materials. The essence of the invention is that these coatings comprise

0.003 to 1 wt. polymers and / or copolymers of alkyl esters of acrylic and / or methacrylic acid having a number of carbon atoms in the alkyl group of 1 to 8, preferably 1 to 4, or copolymers of these esters with other acrylic monomers and / or Sestyrene, by mol. from 13,000 to 130,000 and optionally from the group comprising alkyl esters of phosphoric acid having a carbon number of 1 to 3, silicone oil, paraffin having a softening point of 40 to 60 ° C, colloidal silica, zinc and cobalt soaps, preferably octoates, organic solvents such as aliphatic monovalent alcohols having a carbon number of 1 to 3 and aliphatic ketones having a carbon number of 3 to 3, acrylic and methacrylic acid and soluble dyes, in individual amounts up to 2% by weight;

The unsaturated polyester paints according to the invention can be UV-cured even at temperatures above 50 ° C. The cured coating film is glossy and non-sticky. Its hardness depends on the degree of unsaturation of the polyester resin used and reaches up to No. 13, measured in pencil. Sandability and recoatability with unsaturated polyester or other coatings are satisfactory. The adhesion of the topcoats is excellent and their resistance to the action of chemicals and solvents is the same as that of the coatings formed from the respective paint itself at a suitable layer thickness. The base cured coating has a very thin layer on the surface of a different composition, which whitishes in the presence of water, but its wiping or polishing no longer bleaches the surfaces. This layer, like the polyacrylate component used, is soluble in organic solvents, such as acetone, acetic acid esters and the like, and when overcoated with paints, these solvent-containing solvents are largely dissolved in the coating layer. This ensures the necessary adhesion of the individual layers of the coating system.

For the preparation of the coating compositions according to the invention, conventional unsaturated redox-cured polyester lacquers containing styrene and paraffin or other barrier waxy substances protecting the surface against air inhibition during curing can be used. Addition of these

However, 210 407 barriers are not necessary. The resin base of the lacquers is usually unsaturated polyesters based on un-learned dicarboxylic acids (maleic, fumaric) and saturated dicarboxylic acids (phthalic, etc.), used in moles relative to each other. ratio of 0.5 to 1: 3: 1, and glycols. In order to increase the temperature resistance of the system, it is preferable to combine these types of polyesters with plasticizing unsaturated polyesters prepared, for example, using adipic acid in addition to conventional starting materials.

The acrylic component of the coating compositions according to the invention are polymers and / or copolymers of alkyl esters of acrylic acid and / or methacrylic acid, the alkyl groups of which contain 1 to 8 carbon atoms, preferably 1 to 4, or copolymers of these esters with other acrylic monomers, i.e. free acrylic acid. , methacrylic and their nitriles and amides. Suitable examples are polybutyl methacrylate, butyl methacrylate copolymer with methyl methacrylate, butyl acrylate with methyl methacrylate, ethyl acrylate β 2-ethylhexyl acrylate, and others. Due to the desired molecular weight of 15,000 to 150,000, they are film-forming polymers and copolymers which, in combination with unsaturated polyesters, increase the hardness of the coating films, as opposed to the low molecular weight types which serve as flow agents and do not have film-forming properties per se. They are added to the unsaturated polyester lacquers in the form of solutions in organic solvents such as xylene, toluene, ethyl acetate, styrene and the like. The dry weight of these solutions depends on the molecular weight of the acrylic polymer or copolymer.

The total acrylic content of the coating composition is also dependent on this weight, which decreases with increasing molecular weight.

Suitable photoinitiators are benzain and its derivatives, e.g. benzoin butyl ether, benzoinisopropyl ether, benzoin chloroacetate and in particular benzildimethyl ketal, furthermore furoin and its derivatives, ketones such as benzophenone and butylacetophenone, sulfides, e.g. dibenzyl disulfide, sulfochlorides and the like. for ease of dosing and rapid dissolution as a solution in organic solvents, preferably toluene, ethyl acetate or triethyl phosphate. The amount of photoinitiator should be selected according to the type of UV-light source, its distance from the surface of the cured coating, the desired time of curing layer passage through the curing medium and possibly the thickness of the coating. Combinations of different types of photoinitiators can also be used for larger thicknesses (above 150 µm).

In addition to these components, the coating compositions of the present invention may contain, if desired, other substances (additives) which are added in individual amounts of not more than 2% by weight in order to influence or achieve some desired properties of the coating composition or cured coating. These flights include colloidal silicon dioxide, alkyl esters of phosphoric acid (even partial) of 1 to 5 carbon atoms in alkyl groups, naphthenates and octoates of zinc and cobalt, silicone oil, especially containing methyl and phenyl groups, paraffin with a softening temperature of 40 to 60 ° C and organic solvents such as aliphatic monovalent alcohols having a carbon number of 1 to 3, aliphatic ketones having a carbon number of 3 to 5, and optionally acidic to acrylic and methacrylic acid. Certain soluble dyes may also be added to suppress unwanted color shades, which may partially replace stains.

Optimum choice and ratio of the components of unsaturated polyester paints

210 407 according to the invention, in relation to UV radiation, controls the desired properties of the cured coating, e.g. hardness, adhesion, impact resistance or temperature variation, etc. The most advantageous formulation in relation to the substrate and its moisture in terms of suppressing surface defects can be to achieve a different combination of said additives.

Paints of this type can be applied by application rollers, by pouring or spraying,

Low-pressure to high-pressure UV irradiators as well as IST-emitters (pulsed) can be used for the curing of the coatings over a temperature range in the curing space of 30 to 90 ° C. The heating of the surface of the substrate material can then be controlled by the rate of its passage through the curing environment.

The basic type of coating composition according to the invention is suitable for the formation of single-layer and multi-layer coatings. Said surface part of the final layer can be removed if necessary, for example by polishing with a fine abrasive paste.

Tlm achieves the surface resistance to water Si of other liquids required by coating testing, eg for minor or interior visible surfaces of furniture. This type of unsaturated polyester paints can therefore be replaced with paints with a high proportion of organic solvents, which is of great importance for the environment environment in furniture surface treatment plants.

Example 1

Paint components:

Unsaturated polyester resin of mol. ratio of saturated and unsaturated dicarboxylic acids 1: 1.9 as a 60% solution in styrene

Copolymer of methyl methacrylate with butyl methacrylate (molar ratio: 1) of mol. weight 20,000 as a J > 0% solution in xylene

Styren

Paraffin with a softening point of 52-54 ° C

50% benzoin solution in ethyl acetate / triethyl phosphate (10: 1 weight ratio)

Silicone oil

Koloidnl SiOg

85.0 wt. parts

1.0 wt. parts 15.0 kmet. parts

0.05 wt. parts

1.0 wt. parts 0.01 wt. parts 0.1 wt. parts • o.

The lacquer applied to the substrate by a roller at 50 g / m < 2 > was cured by medium pressure UV radiation at a curing temperature of 50 [deg.] C. for 3 minutes. The coating obtained after curing is smooth, shiny, slightly opalescent, free of craters and milky bubbles. It is immediately overcoatable with other base coatings. After polishing with a polishing paste, it is satisfactory! water resistance.

210 407

Example 2

Paint components:

The unsaturated polyester resin of Example 1

Unsaturated polyester resin containing adipic acid in mol. ratio to unsaturated acids 4: 1, in the form of a 65½ solution in a mixture of styrene and ethyl acrylate (weight ratio 10 s 1)

Polybutyl methacrylate of mol. weight 38,000 as a 40® solution in xylene / toluene (2: 1 weight ratio)

Styren

Triethyl phosphate

Zn-octoate

Benzoinisopropyláteř

80.0 wt. parts

15.0 wt. parts

0.8 wt. parts

15.0 wt. 1.0 wt. parts 0.01 wt. 3.0 wt. parts

The lacquer layer applied at 30 g / m is cured by a system of high-pressure radiators for 30 s.

Example 3

The varnish components are the same as in Example 1, except that the acrylic component is a copolymer of methyl acrylate, butyl acrylate and acrylic acid in moles. monomer ratio of 1: 3, 0.1 mol%. weight 80 000.

Claims (1)

UV-curable unsaturated polyester coatings consisting of unsaturated polyester resins, crosslinking monomers, photoinitiators, organic solvents and additives, and particularly suitable for the treatment of wood and cellulosic materials, characterized in that they contain from 0.005 to 1% by weight of wood. polymers and / or copolymers of alkyl esters of acrylic and / or methacrylic acid having a number of carbon atoms in the alkyl group of 1 to 8, preferably 1 to 4, or copolymers of these esters with other acrylic monomers and / or styrene having a molecular weight of 15000 to 150,000 and optionally the group includes alkyl phosphoric esters of carbon atoms in alkyl groups of 1 to 5, silicone oil, paraffin at a softening point of 40 to 60 ° C, colloidal silicon dioxide, zinc and cobalt soaps, preferably octoates, organic solvents % of aliphatic monovalent alcohols having a carbon number of 1 to 3 and aliphatic ketones having a carbon number of 3 to 5, acrylic acid and methacrylic acid and soluble dyes, in individual amounts up to 2% by weight;