UV lacquer for direct metal application

Abstract

We have developed a UV-curing lacquer that exhibits improved adhesion to metal substrates. This lacquer composition contains the following components: (a) A mixture of several different epoxy resins, (b) Acrylate compounds, (c) Photoinitiator, (d) Polycaprolactone triol, (e) Cellulose acetate butyrate.

Description

Technical Field

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[0001] The present invention relates to a UV-curable lacquer composition, particularly a UV-curable lacquer composition suitable for use on plasma-treated substrates such as tin-free steel, tin-plated steel, or aluminum. These substrates can be used as packaging materials for industry, food, or beverages.

Background Art

[0002] For many years, metal packaging materials have been coated using thermosetting coating compositions. Such coatings contain volatile organic solvents and consume a great deal of energy. In order to reduce or even eliminate the amount of such organic solvents and to reduce the energy consumption required for complete curing of the coating, the applicant has developed various types of UV-curable coating systems. By using these UV-curable coatings, the amount of solvent released during curing can be reduced by more than 40% compared to thermosetting systems. Since UV curing is a high-speed process (complete curing in less than 20 seconds), the use of UV-curable coatings leads to a relatively low-cost and relatively rapid production process.

[0003] Using these UV-curable lacquers on tinplate or tin-free steel has been found to show some variation in performance, partly due to the adhesion performance of these coatings. In the technical field, it is known that the aforementioned substrates need to be treated before a protective coating can be applied, because the surfaces of these substrates are often contaminated. This contamination reduces the adhesion of the lacquer applied to such surfaces.

[0004] It was found that by using plasma pretreatment, the surface of such substrates exhibited improved adhesion of the applied lacquer compared to untreated surfaces. However, defects causing poor adhesion were still observed with available UV-curable lacquers, which proved to make these coated substrates relatively unsuitable for use as packaging materials for industrial, food, or beverage applications. [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention provides a UV lacquer composition that exhibits relatively excellent adhesion to substrates typically used as packaging materials for food or beverages, such as tin-free steel, tin-plated steel, or aluminum. [Means for solving the problem]

[0006] The present invention relates to a UV-curable lacquer composition comprising the following components. (a) A mixture of several different epoxy resins, (b) Acrylate compounds, (c) Photoinitiator, (d) Polycaprolactone triol, and (e) Cellulose acetate butyrate.

[0007] Tin-free steel (TFS) is widely used as a packaging material for food and beverages, for example, as a food container. TFS consists of a steel base on which thin layers of chromium and chromium oxide are deposited. This material has a metallic luster and good corrosion resistance.

[0008] Tinplate or tin-plated steel consists of a steel base on which layers of tin-iron alloy, tin, tin oxide, and passivation are deposited. This material has good corrosion resistance and good formability, and is easy to weld. [Modes for carrying out the invention]

[0009] Coating composition

[0010] The coating composition according to the present invention comprises the following components:

[0011] epoxy resin

[0012] The composition according to the present invention comprises a mixture of several different epoxy resins. In one embodiment, the mixture comprises an aliphatic epoxy resin and an aromatic epoxy resin. In a further embodiment, the mixture of several different epoxy resins comprises at least 85% by weight of one or more aliphatic epoxy resins, the weight percentage of which is calculated based on the total weight of epoxy resins present in the lacquer composition.

[0013] Suitable aliphatic epoxy resins that can be used in the compositions of the present invention include epoxy resins that are conventional in epoxy resin technology. Examples of such epoxy resins include:

[0014] (I) Polyglycidyl ether or poly-(p-methylglycidyl) ether. These are obtained by reacting a compound having at least one, preferably two, free alcoholic hydroxyl groups with epichlorohydrin or β-methylepichlorohydrin under alkaline conditions or in the presence of an acidic catalyst, followed by alkaline treatment. This type of glycidyl ether is derived from, for example, acyclic alcohols, such as ethylene glycol, diethylene glycol or high molecular weight poly(oxyethylene) glycol, propane-1,2-diol or poly(oxypropylene) glycol, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene) glycol, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol, C12-14OH (Araldit® DY-E), 1,1,1-trimethylolpropane, pentaerythritol, sorbitol, and polyepichlorohydrin. Other types of glycidyl ethers are derived from alicyclic alcohols, such as 1,4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)-propane, or tricyclodecanedimethanol.

[0015] (II) Alicyclic epoxy resins. 3,4-Epoxycyclohexylmethyl-3,4-Epoxycyclohexylcarboxylate is an alicyclic epoxy that can be synthesized by the reaction of 3-cyclohexenylmethyl-3-cyclohexenecarboxylate with peracetic acid. These aliphatic resins exhibit many useful properties in the compositions of the present invention, such as thermal stability.

[0016] Suitable aromatic epoxy resins that can be used in the compositions according to the present invention include glycidyl ethers produced by a reaction of epichlorohydrin with an aromatic compound having at least one hydroxyl group, carried out under alkaline conditions. Other suitable epoxy resins can be produced by reacting epichlorohydrin with certain polynuclear polyhydroxyphenol compounds, such as bis(p-hydroxyphenyl)methane and 4,4-dihydroxybiphenyl, such as mononuclear divalent and trivalent hydroxyphenol compounds, such as resorcinol and phloroglucinol. Epoxy resins suitable for the compositions of the present invention generally have a molecular weight in the range of 86 to 10000, preferably 200 to 1500. The commercially available epoxy resin 2,2-bis(4-hydroxyphenylpropane) (bisphenol A) has a molecular weight of 400, an epoxy equivalent (ASTM D-1652) of 185 to 192, and an n value (calculated from the above formula) of 0.2, and is currently a preferred epoxy resin because it is low viscosity and commercially available.

[0017] Generally, the compositions of the present invention contain 30 to 60% by weight of epoxy resin, based on the total weight of the composition.

[0018] Acrylate compounds

[0019] The composition according to the present invention comprises an acrylate compound. This acrylate compound must have at least two unsaturated carbon-carbon bonds. Such unsaturated bonds can be cleaved under the influence of UV light in the presence of a photoinitiator.

[0020] Suitable acrylate compounds that can be used in the composition according to the present invention include ethoxylated (3) trimethylolpropane triacrylate, glycerylpropoxy triacrylate, or trimethylolpropane triacrylate.

[0021] Generally, the compositions of the present invention contain 25% to 35% by weight of an acrylate compound, based on the total weight of the composition.

[0022] Photoinitiator

[0023] The composition according to the present invention contains an effective amount of a photoinitiator or a mixture of a plurality of different photoinitiators, thereby effectively photocuring the composition by UV exposure. Generally, this amount is about 0.01% to about 10% by weight based on the total weight of the composition. Examples of photoinitiators that can be used in the composition according to the present invention include hydroxycyclohexyl phenyl ketone, benzophenone, triarylsulfonium hexafluorophosphonium in propylene carbonate, and the like.

[0024] Polycaprolactone triol

[0025] Polycaprolactone triol is present in the composition according to the present invention and greatly enhances the strength of the cured coating film. Generally, the composition contains 5 to 10% by weight of polycaprolactone triol based on the total weight of the composition.

[0026] Cellulose acetate butyrate

[0027] Cellulose acetate butyrate is present in the composition according to the present invention, thereby improving the adhesion of the composition to various (metal) substrates. Generally, the composition contains 10% to 15% by weight of cellulose acetate butyrate based on the total weight of the composition.

[0028] Application process

[0029] The present invention also relates to the application process of the above coating composition. This process includes the following steps: · Before applying the coating composition, perform plasma treatment on the surface of the substrate. · After plasma treatment, apply the coating composition to the surface of the plasma-treated substrate. · Cure the substrate obtained in step (ii) by exposing it to UV irradiation.

[0030] In this process, tinplate, tin-free steel, or aluminum is preferably used as the base material.

[0031] Plasma treatment of metal substrates can be performed, for example, using the Openair-Plasma® process developed by Plasmatreat. [Examples]

[0032] Different types of lacquers were applied to plasma-treated and non-plasma-treated substrates. Various tests were then performed to evaluate the adhesion of the lacquers to the substrates as follows: Test results score 1 Does not peel off Partially peeling off 2 Completely peels off 3

[0033] The following lacquers were used: Lacquer # Description Lacquer 1 Lacquer according to the present invention Lacquer 2: Conventional UV-curing lacquer supplied by ACTEGA.

[0034] The following substrates were used: Base material # Description Base material 1: Untreated tin-free steel Base material 2: Plasma-treated tin-free steel Base material 3: Tinplate Base material 4: Plasma-treated tinplate

[0035] The evaluation results are shown in Tables 1 and 2 below.

[0036] [Table 1]

Claims

1. A UV-curable lacquer composition comprising the following components: (a) A mixture of several different epoxy resins, (b) Acrylate compounds, (c) Photoinitiator, (d) Polycaprolactone triol, (e) Cellulose acetate butyrate, A UV-curable lacquer composition containing the following.

2. The UV-curable lacquer composition according to claim 1, wherein the mixture of the various different epoxy resins comprises an aliphatic epoxy resin and an aromatic epoxy resin.

3. The UV-curable lacquer composition according to claim 1 or 2, wherein the mixture of the different epoxy resins contains at least 85% by weight of one or more aliphatic epoxy resins, the weight percentage of which is calculated based on the total weight of epoxy resins present in the lacquer composition.

4. The UV-curable lacquer composition according to claim 2 or 3, wherein the epoxy resin mixture comprises a bisphenol A type epoxy resin.

5. The following ingredients: (a) A mixture of several different epoxy resins in an amount of 30 to 60% by weight, (b) 25-35% by weight of an acrylate compound or a mixture of several different acrylate compounds, (c) 0.1 to 10% by weight of a photoinitiator or a mixture of several different photoinitiators, (d) 5 to 10% by weight of polycaprolactone triol or a mixture of several different polycaprolactone triols, (e) 10-15% by weight of cellulose acetate butyrate, The UV-curable lacquer composition according to claim 1, comprising, wherein the weight percentage of the component is based on the total weight of the composition.

6. A process for applying a coating to a metal substrate, comprising the following steps: i. Plasma treatment of the surface of the substrate before applying the coating composition. ii. After the plasma treatment, the coating composition is applied to the surface of the plasma-treated substrate. iii. The coating composition is cured by exposing the substrate obtained in step (ii) to UV irradiation. A process comprising, wherein the coating composition applied in step (ii) is the UV-curable lacquer composition according to any one of claims 1 to 5.

7. The process according to claim 6, wherein the metal substrate is selected from the group consisting of tinplate, tin-free steel, and aluminum.

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