WO2001027207A1 - Method for the production of coatings by uv-hardening - Google Patents

Abstract

The invention relates to a method for the production of adhesive-free, reduced-migration and reduced-yellowing coatings, in particular Foliendeckstrichen. Inventive coating materials containing less than 0.1 weight % of a photoinitiator and even in the absence of a photoinitiator can be hardened by exposure to UV-radiation, if the coating materials contain (meth)acrylate groups (A) and >CH-O-ether structure units (B) in certain minimum amounts, whereby (A) and (B) can also be accommodated in one molecule or in different molecules. The method exhibits many economic, technical and toxicological advantages due to said reduction of the amount of photoinitiators or the absence of photoinitiators.

Description

Process for the production of coatings by UV curing

The invention relates to the production of tack-free coatings by UV curing thin photoinitiator-poor or photoinitiator-free coating compositions which contain acrylate and / or methacrylate esters and an ether component.

It is known to carry out coatings by radiation hardening of coating compositions which contain olefinically unsaturated monomers and / or oligomers, optionally photoinitiators and possibly other customary additives. Radiation types for the technical production of coatings by radiation hardening are primarily electron beams and UV rays. The hardening of unsaturated coating compositions with electron beams has the disadvantage that the systems or corresponding painting lines required for this purpose are technically complex due to the need for high current voltages, a vacuum, inert gas and the necessary shielding against an uncontrolled escape of electron beams and a larger one Require space. In addition, hardening with the aid of electron beams often leads to yellowing, particularly in the case of light-colored carrier materials. For this reason, when curing unsaturated coating compositions, it is usually preferable to harden them with UV rays. While the presence of photoinitiators is not necessary for the curing of coating compositions with electron beams, photoinitiators which absorb the UV radiation, form radicals or protons and photopolymerization or photocrosslinking are added to the mixtures for curing the photosensitive mixtures start. The amount of photoinitiators added is more than 1% by weight of the hardenable unsaturated compounds, generally even more than 3% by weight, the more precise amount required, inter alia, depending on the type of application of the UV-hardenable mixtures. UV curing under an inert gas atmosphere allows a certain reduction in the amount of photoinitiator required. It is known that a photocurable coating composition containing a photoimtiator is often more unstable than a corresponding composition without a photoimtiator. Since photoinitiators are among the expensive components of a UV-hardenable coating material, UV-hardenable coating materials that contain no photoinitiators or only a small amount of them are advantageous. Also, photoinitiators or their fragments resulting from the irradiation with UV light often lead to yellowing or even odor pollution of the coating materials used. Finally, in some cases, the coating compositions may contain photoinitiators or their decomposition processes that occur during curing. products lead to toxic concerns when used.

EP-A 618 237 describes curing without photoinitiators by means of photochemically initiating donor-acceptor complex-forming monomers which polymerize after UV exposure. A disadvantage is the sensitivity to hydrolysis of the vinyl compounds used, which can easily lead to odor-intensive acetaldehyde. Resin mixtures, in particular with additives, pigments and other additives which have an acidic character, are generally not stable in storage.

There is therefore a justified need for additional UV-curable coating compositions which can be cured with only very small amounts of photoinitiators or even in the absence of photoinitiators with UV radiation and which have the aforementioned disadvantages of the coating compositions containing photoinitiator to a reduced extent or not at all.

It was an object of the present invention to find photo-polymerizable coating compositions which can be cured to a large extent to scratch-resistant coatings in thin layers with UV radiation, even in the presence of very small amounts of photoinitiators and preferably even in the absence of photoinitiators. An additional task was to achieve this with materials that are commercially available and suitable for the production of coatings.

It has now been found that coating compositions which contain (meth) acrylic acid esters based on at least dihydric and preferably trihydric to tetravalent aliphatic alcohols can be cured with UV rays in the presence of very small amounts and even in the absence of photoinitiators, if they contain a minimum amount of C = C double bonds and additionally in the same or an added compound a minimum amount of aliphatic> CHO ether structural units.

The invention thus relates to a process for the production of tack-free, low-migration coatings by UV curing of a coating composition containing at least one olefinically unsaturated compound, optionally a photoinitiator and possibly conventional additives, which is characterized in that the coating composition contains

a) at least one (meth) acrylate group (A) of an at least dihydric aliphatic alcohol in an amount such that its C = C structural units (molecular weight = 24) amount to at least 5 and preferably at least 15% by weight, and

b) at least one compound with aliphatic> CHO ether structure units (B) in an amount such that the amount by weight

Hydrogen atoms H (M = 1) of the units (B) amount to at least 0.5 and preferably at least 2% by weight,

wherein the structural units (A) and (B) can be contained in different compounds and / or together in at least one compound of the coating composition, and the curing of the coating composition with UV rays in the presence of less than 0.1% by weight of a Photoinitiators or in the absence of a photoinitiator, the percentages each refer to the total amount of UV-hardenable olefinically unsaturated compounds contained in the coating composition.

It is thus a characteristic of the process according to the invention that the coating compositions used contain compounds with acrylic ester and / or methacrylic ester units (A) of aliphatic at least dihydric alcohols in such a minimum amount that their C = C structure units, calculated with a molecular weight of M = 24, in an amount of at least 5 and preferably at least 15 percent by weight of the total amount of the UV-hardenable olefinically unsaturated compounds contained in the coating composition and preferably of the (meth) acrylate compounds. A further characteristic of the method according to the invention is that the coating composition contains aliphatic> CH-0 ether structure units (B) in an amount such that the amount of H atoms (M = 1) of the> CH-0 ether structure units contains at least 0.5 and preferably at least 2% by weight of the total amount of the olefinically unsaturated compounds which can be hardened with UV rays and preferably the (meth) acrylic compounds contained in the coating composition.

The structural units (A) and (B) are preferably contained together in at least one hardenable acrylate and / or methacrylate compound, preferably in an acrylic ester compound. Compounds of this type which contain both acrylic ester and / or methacrylic ester groups and> CH-0-Structural units as aliphatic ether components are, for example, commercially available (meth) acrylic acid esters of ethoxylated and / or propoxylated polyalcohols and methacrylic acid esters and preferably acrylic acid esters of hydroxyl group-containing polyethers, such as those obtained by adding ethylene oxide and / or propylene oxide or mixtures thereof to aliphatic hydroxyl compounds can. Examples of compounds with structural units (A) and (B) in the same compound are, for example, ether (meth) acrylates such as tripropylene glycol di (meth) acrylate, but preferably methacrylates and in particular acrylates, which are obtained by alkoxylation, in particular ethoxylation and / or propoxylation, of polyalcohols , preferably from those having 2 to 8 carbon atoms and 2 to 6 hydroxyl groups, and subsequent esterification or partial esterification with methacrylic acid or, in particular, acrylic acid to give poly (meth) acrylates. Examples of polyalcohols with 2 to 6 hydroxyl groups are pentaerythritol, dipentaerythritol, trimethylolpropane, ditrimethylolpropane, sorbitol, glycerol, ethylene glycol, propylene glycol, hexanediol, neopentyl glycol and the like. Very suitable polyalcohols or polyalcohol mixtures are those which contain more than 2, in particular at least 3.5 and particularly preferably at least 4, hydroxyl groups. The then alkoxylated polyalcohols in particular contain on average 1 to 5 alkoxy groups and preferably 1 to 3 alkoxy groups per hydroxyl group of the polyalcohol, ethoxy and propoxy groups being preferred as alkoxy groups. The alkoxylated polyalcohols are then reacted in a manner known per se with methacrylic acid, acrylic acid or mixtures thereof, preferably with acrylic acid, to give the corresponding esters or partial esters.

Suitable further compounds used according to the invention with the structural units (A) and (B) in the same unsaturated compound are polyether (meth) acrylates, polyester (meth) acrylates modified with ether groups and epoxyacrylates modified in such a way as they are e.g. in P. Oldring, Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints, J.Wiley and Sons, New York, and Sita Technology Ltd., London, 1991, especially in

Volume II (prepolymers and reactive diluents) are described. Of these, the compounds described are relevant, which contain the structural units in the amounts mentioned.

As indicated above, the (meth) acrylate and> CH-0 ether structural units need not be bound in the same chemical molecule in the amounts indicated, but can also be present in different compounds. It is thus possible for the coating compositions to contain (meth) acrylates, to which ether compounds having the> CH-0 ether structural units have been mixed in the stated amounts. For example, (meth) acrylate compounds with in particular 2 and preferably at least 3.5 (meth) acrylate structural units in the molecule, such as a hexanediol diacrylate or pentaerythritol tetraacrylate, can be admixed with compounds which have the> CH-0 structural units in the required amount Contain amount, such as block copolymers of propylene oxide and ethylene oxide or other polyether compounds such as polyether acrylates with a sufficient proportion of> CH-0 ether structure elements.

Photoinitiators for the coating compositions of the inventive method are used in amounts of less than 0.1% by weight, i.e. 0 to 0.099% by weight, added, in particular in an amount of less than 0.01% by weight, the percentages relating to the total amount of the olefin-unsaturated compounds which can be hardened with UV rays and are contained in the coating composition. It is particularly advantageous to harden the coating compositions in the absence of photoinitiators with UV rays. Suitable photoinitiators are the known photoinitiators, in particular those of the benzophenone, thioxanthone, α-hydroxyketone, α-dicarbonyl compound, acylphosphmoxide, bis-acylphosph oxide and acylphosphate sulfide type. Examples of suitable photoinitiators are benzophenone, hydroxycyclohexylphenyl ketone, 4-methylbenzophenone, 2, 4-dimethylbenzophenone, 2-chlorobenzophenone, 4-methoxybenzophenone, anthrachmon, 2-ethylanthrachmon, thioxanthone, 1- and 2-isopropylthiooxanthone -Dιmethylbenzoyldιphenylphos- phmoxid. More detailed information on photoinitiators can be found in volume III with the title "Photoinitiators for Free Radical, Catiomc, Anionic Polymerization", 2nd edition, from the series of P.Oldrmg, "Chemistry and Technology of UV & EB Formulation for Coatmgs, Inks." & Paints ", J. Wiley and Sons, New York and Sita Technology Ltd., London.

The usual UV lamps which emit radiation components of less than 300 nm, such as excimer lamps, pulsed emitters, lasers and high-pressure mercury lamps, are preferred as UV light sources for UV curing in accordance with the method according to the invention, preference being given to high-pressure mercury lamps are. The UV curing of the coating compositions can be carried out in the presence of air, but is preferably carried out under an inert gas atmosphere such as under nitrogen, with generally higher reactivity being achieved and it being possible to cure faster.

In addition to the photoinitiators, the coating compositions used according to the invention can contain additives in customary amounts, such as leveling agents, defoamers, matting agents, pigments, dispersing agents, solvents or water, but also additional binders and reactive thinners. Coating compositions with a solids content of 100% by weight are preferred. If the coating compositions contain solvents and / or water, it is advisable to dry them before the UV radiation at relatively low temperatures, for example at 50 to 80 ° C. for 15 to 50 minutes. The coating compositions can be applied to the substrates using customary coating methods, such as by rolling, knife coating, spraying, pouring, dipping, etc., to match the desired layer thickness. The suitable layer thickness for clear lacquer layers is 5 - 15 μm, in general the layer thickness naturally depends on the components and the application of the coating material. The suitable hardenable layer thickness can easily be determined by a few preliminary tests. The layer thickness for curing clearcoats should not exceed 15 μm in the practical absence of photoinitiators.

Coating compositions used according to the invention are particularly suitable for lacquers, printing inks, photoresists and printing plates. The coatings according to the invention are particularly suitable for the production of film top coats.

The following examples, including the comparative experiments, are intended to explain the invention further, but not to limit it. Unless otherwise stated, parts and percentages are by weight.

In systems containing 100% by weight of solids, the tape speed (m / min) during UV curing was determined as a measure of the reactivity, with which a liquid lacquer film of 8 μm thickness, applied with a box squeegee on white paper, under an undoped high-pressure mercury lamp ( Power 120 W / cm lamp length, lamp distance to the substrate 12 cm) can be passed through in order to obtain a scratch-resistant and adhesive coating against the fingernail.

In the case of aqueous systems which were physically dried at 60 ° C. for 20-30 minutes, the dried coating compositions were UV-cured at a belt speed of 10 m / min. (Total UV dose 640 mJ / cm ² ) on an approx. 100 μm thick film on glass the degree of hardness was determined using pendulum damping measurements in accordance with DIN 53157.

The measurements were carried out in air and under nitrogen.

To calculate the double bond content, the amount of C = C structural units contained in the coating composition (based on the molecular weight M = 24) was determined as% by weight of the total amount of the olefinically unsaturated compounds curable with UV rays in the coating composition. The total amount of H atoms was used as a measure of the content of aliphatic> CHO ether structural units (B) in the coating composition (Molecular weight = 1) of the number of> CHO ether structural units present in the coating composition calculated as% by weight of the total amount of the UV-radiation-curable olefinically unsaturated compounds contained in the coating composition.

Examples 1-4

With mixtures of an acrylic ester of ethoxylated pentaerythritol (PEA) (content of C = C (M = 24) structural units: 18.8%; content of H (M = 1) of the> CH-0 ether structural units: 3.3%, in each case based on the total amount of monomers) and different amounts of hydroxycyclohexylphenyl ketone as photoinitiator (PI), 8 μm thick films were produced in each case and, as stated above, their reactivities in air and under nitrogen were determined. The results are shown in Table 1, in which Example 1 represents a comparison test (W).

Table 1: Reactivities in air or below N (m / min) with different amounts of photoinitiator

Ex. 1 (W) Ex. 2 Ex. 3 Ex. 4

Monomeric PEA PEA PEA PEA (parts) 100 100 100 100

Pl (parts) 4 0.09 0.009 without

Reactive. Air 5 not tack-free at 2 m / min

Reactive. N> 150 50 25 20

Examples 5-

The procedure was as in Examples 1-4, but tripropylene glycol diacrylate (TPGDA) was used as the monomer (content of C = c (M = 24) structural units: 15.19%; content of H (M = 1) der> CH-0 ether structural units: 1.90%). The results are shown in Table 2, in which Example 5 represents a comparison test (W). Table 2: Reactivities in air or under N ₂ (m / mm) with different amounts of photoinitiator

Example 5 (W) Example 6 Example 7 Example

5

Monomeric TPGDA TPGDA TPGDA TPGDA (parts) 100 100 100 100

PI (parts) 4 0.09 0.009 without 0

Reactive. Air not tack-free at 2 m / mm

Reactive. N ₂ 130 10 10 10 5

Examples 9 to 12

The procedure was as in Examples 1 to 4, but with a mixture of 90 parts of 1,6-hexanediol-acrylate (HDDA) as component 0 1 and 10 parts of a block copolymer (POPEBC) (molecular weight 5600) made of 60% polypropylene oxide (PO) and 40 % Of polyethylene oxide as component 2 (content of C = C (M = 24) structural units: 19.12%; content of H (M = 1) of the> CH-0 ether structure units 0.68%, in each case based on the total amount 1, 6-Hexandιoldιacrylat in the 5 mass) with different amounts of Photoimtiator (PI) used for film production. The results are shown in Table 3, in which Example 9 represents a comparative test (W).

Table 3 Reactivities in air or under N ₂ (m / mm) 0 with different amounts of photoinitiator

Example 9 (W) Example 10 Example 11 Example 12

Comp. 1 HDDA HDDA HDDA HDDA 5 (parts) 90 90 90 90

Comp. 2 POPEBC POPEBC POPEBC POPEBC (parts) 10 10 10 10

40 PΙ (parts) 4 0.09 0.009 without

Reactive. Air does not sticky at 2m / min

Reactive. .N ₂ 120 10 5 5

Λ R Examples 13-15

Mixtures of different amounts of hydroxycyclohexylphenyl ketone as photoimtiator (PI), each with 25 parts of a commercially available polyether acrylate (Laromer ® PO 43F) as component 1 (P0 43F) and 75 parts (based on the solids content) of an aqueous polyurethane dispersion ( PUR) as component 2 (content of the mixture of C = C (M = 24) structural units: 6.05%; content of H (M = 1) of the> CH-0 ether structure units: 1.13%) were on glass physically at 60 ° C 20 mm. long dried to a coating. UV curing was carried out using a high-pressure mercury lamp (power 120 W / cm, lamp distance from the substrate 12 cm) at a belt speed of 10 m / mm (total UV dose 640 mJ / cm ² ) in air and under nitrogen. The degrees of hardness of the resulting approximately 100 μm thick films were assessed using pendulum vapor measurements according to Konig (according to DIN 53157). The results are shown in Table 4, in which Example 13 represents a comparative test (W).

Table 4 Hardening of films hardened with different amounts of photoinitiator

Ex. 13 (W) Ex. 14 Ex. 15

Comp. 1 PO 43F PO 43F PO 43F (parts; 25 25 25

Comp. 2 PUR PUR PUR (parts' 75 75 75

Parts 0.09 0.009

Pendulum steaming (sec) after curing lOm / min 119 104 90 in air

Pendulum steaming (sec) after hardening lOrn / mm 119 95 under nitrogen

Examples 16 and 17

A mixture of 25 parts of a commercially available polyether acrylate (Laromer® PO 43F) and 75 parts (based on the solids content) of an aqueous polyurethane dispersion (content of the mixture an C = C (M = 24) structural units: 6.05%; H (M = 1) content of the> CH-0 ether structure units: 1.13%) was in the case of Example 16 with a photoinitiator mixture of 1.5 parts of hydroxycyclohexylphenyl ketone (PI 1) and 1.5 parts of benzophenone (PI 2) 5 mixed while in the case of Example 17 there was no photoinitiator additive. As in Examples 13-15, the mixtures were applied in layers to glass, dried and cured under UV light. As in Examples 13-15, pendulum vapor measurements were carried out on the coatings, but in addition 10 measurements were also carried out on the dried but not yet UV-cured coatings. The results are shown in Table 5, in which Example 16 represents a comparative test (W).

Table 5 Film hardening after drying or subsequent UV-15 hardening in air or under a nitrogen atmosphere

Ex. 16 (W) Ex. 17

Comp. L PO 43F PO 43F

20 (parts) 25 25

Comp. 2 PUR PUR

(Parts) 75 75

25 PI 1 (parts) 1.5 without

PI 2 (parts) 1.5 without

Pendulum damping (sec) 30 after drying, but 59 92 before UV curing

Pendulum damping (sec) after UV curing 115 119

35 10 m / min in air

Pendulum damping (sec) after UV curing 118 125 lOm / min under N ₂ 40

45

Claims

claims 1. A process for the production of tack-free, low-migration and low-yellowing coatings by UV curing a coating composition which contains at least one olefinically unsaturated compound which can be polymerized with UV light, optionally a photoinitiator and, if appropriate, customary additives, characterized in that the coating composition contains a) at least one connection with at least one (Meth) acrylate grouping (A) of an at least dihydric aliphatic alcohol in an amount such that its C = C structural units (molecular weight = 24) at least 5% by weight, and b) at least one compound with aliphatic> CH-0 ether structural units (B) in an amount such that the amount by weight of hydrogen atoms H (M = 1) of the Structural units (B) is at least 0.5% by weight, wherein the structural units (A) and (B) can be contained in different compounds and / or together in at least one compound of the coating composition, and the UV curing of the coating composition in the presence of less than 0.1% by weight of a photoinitiator or in the absence a photoinitiator is carried out, the percentages based in each case on the total amount of the UV-curable olefinically unsaturated compounds contained in the coating composition. 2. The method according to claim 1, characterized in that the UV curing of the coating composition in the absence of Photoiniators takes place. 3. The method according to claim 1, characterized in that the coating composition in the UV curing contains less than 0.01 wt.% Of a photoinitiator, based on the total amount of UV-curable olefinically unsaturated compounds. 4. The method according to any one of claims 1 to 3, characterized in that the UV curing of the coating composition is carried out under an inert gas atmosphere. 5 5. The method according to any one of claims 1 to 4, characterized in that the UV curing is carried out with a high-pressure mercury lamp as a UV light source. 6. The method according to any one of claims 1 to 5, characterized in 0 that clear coat with a Layer thickness of not more than 15 microns can be cured with UV light. 7. The method according to any one of claims 1 to 6, characterized in that the coating composition contains C = C (M = 24) structural units of the (meth) acrylate groups (A) in an amount of at least 15% by weight, based on the total amount of UV-curable olefinically unsaturated compounds contained in the coating composition. 0 8. The method according to any one of claims 1 to 7, characterized in that the coating composition contains hydrogen atoms H (M = 1) of the aliphatic> CH-0 ether structural units (B) in an amount of at least 2% by weight, based on the Ge - 5 total amount of the UV-curable olefinically unsaturated compounds contained in the coating composition. 9. The method according to any one of claims 1 to 8, characterized in that the coating composition contains as compounds with the 0 structural units (A) and (B) (meth) acrylic esters of ethoxylated and / or propoxylated polyalcohols. 10. The method according to any one of claims 1 to 8, characterized in that the coating composition as compounds having 5 the structural units (A) and (B) simultaneously, Contains (meth) acrylic acid esters of polyethylene and / or polypropylene glycols. 11. The method according to any one of claims 1 to 10, characterized in that the coating composition as compounds with the Structural units (A) and (B) contains mixtures of (meth) acrylic acid esters of polyalcohols and polyethers made from ethylene oxide and / or propylene oxide. 45 12. A process for the production of film top coats by the process according to one of claims 1 to 11.