DE4414589A1 - Improving adhesion of coating materials to plastic substrates - Google Patents

Abstract

The coating of plastic substrates (I) with a film-forming coating material (II) comprises (a) directly coating the surface of (I) with low-mol. wt. cpd(s). (III) which form radicals when subjected to high-energy radiation, (b) irradiating the treated surface with high-energy radiation, (c) opt. cleaning the surface mechanically and/or chemically, and (d) applying material (II) to the treated surface and drying or hardening the coating obtd..

Description

The invention relates to a method for coating plastic sub particularly strate polyolefin substrates.

Plastic moldings are widely used in the manufacture of automo bilen or components thereof or used as components of machines. The molded plastic parts can be made from different polymers consist. Examples of suitable polymers are polyolefins, such as polypropy len polyethylene polystyrene, acrylonitrile-butadiene-styrene copolymers Polyurethanes, polyamides, polyesters such as polyethylene terephthalate and Polycarbonates. These plastics can also by inserting suitable fibers e.g. B. glass fibers are mechanically reinforced. These Molded parts made of plastic have favorable mechanical properties and have a low specific weight. In particular polyolefin However, plastics have the disadvantage that they are difficult to paint are, because the usual paint binders on the plastic moldings have insufficient liability. This liability also has to occur mechanical loads such. B. mechanical shocks or expansion due to increased temperature. No one is allowed to do so Cracks, flaking or extensive delamination occur.

To improve the adhesion of paints to molded polyolefin parts Various processes have already been described. On the one hand it is possible by pretreating these plastic molded parts, e.g. B. by Beflam men, plasma treatment of the surface or by dissolving the surface with special organic solvents or with a corona treatment the surface before the actual coating process is better to be liable. However, these processes are sometimes very complex, such as B. the corona treatment, they do not work with physiologically harmless solvents or lose theirs after a short time  liability-improving effect. Because of this, it is necessary to have such To improve pretreatment types.

Furthermore, the use of special adhesive primers has already been described ben. These are aqueous adhesive primers or those on the Basis of organic solvents. These generally contain Polyolefins with polar groups, especially chlorinated polyolefins (CPO). These chlorinated polyolefins are given with the primer and if proportions of binders on the cleaned and to be coated Applied substrate and then dried at elevated temperature. The actual adhesion agent layer is then applied to the layer Coating agent applied.

Such aqueous coating compositions are described, for example, in DE-A-39 10 901 described. It is an aqueous coating composition tongues containing a film-forming resin, pigments, water and a fine particle current dispersion of chlorinated polyolefins with a degree of chlorination of Contain polyolefins from 20 to 35 wt .-%. The dispersions are made by Distillation of solvent-containing dispersions of CPO and if appropriate, prepares suitable binders.

EP-A-0 487 323 describes adhesion promoters for plastic substrates described. The procedure is such that special plastic sub strate a conventional primer based on organic solvents, the high molecular weight polyolefins with polar groups, especially CPO contains, is applied, before or after application of the primer irradiation with UV light of a wavelength up to 300 nm during is performed for more than 60 seconds. As plastic substrates special polypropylene copolymers described with unsaturated Carboxyl groups are modified.

These processes have the disadvantage that they have coating agents with larger ones Use shares in CPO. These are relatively high molecular weight compounds gen (number average molecular weight, Mn 10000-50000), either by Solvent or by heating in a good flowable form to Benet tion of the substrate must be brought. The use of  larger amounts of chlorinated components in a later Vernich tung, z. B. Burning of the coated substrates from negative Influence. In addition, these coating agents do not work on all substrates, e.g. B. in polyolefins.

The object of the present invention is therefore to provide a Process for coating plastic substrates, especially poly olefin substrates that do not require major technical pretreatments, such as e.g. B. Corona treatment, requires and easy and simple activation tion of the plastic surface, the subsequent painting also can be applied after a long period of time without losing their good adhesive properties to lose. The coated substrates thus obtained are said to good adhesion of the coatings even in the cold and excellent Have low-temperature impact strength.

It has been shown that this problem can be solved by one The present invention is a method for coating art material substrates by applying a film-forming coating agent, if necessary after mechanical or chemical cleaning of the surface and drying or hardening the coating obtained thereby characterized is that one

• a) first directly on the surface of the plastic substrate or more that form radicals under high-energy radiation molecular compounds,
• b) the surface treated in this way with high-energy radiation Radiation,
• c) optionally a mechanical and / or chemical cleaning agent surface and
• d) the film-forming coating agent on the surface treated in this way applies and dries or hardens.

According to the optionally pre-cleaned surface of the  coating plastic substrate with one or more under energy rich radiation radical forming low molecular weight compounds treated. These compounds can be solid, liquid or gaseous. Examples of such substances are compounds containing halogen atoms, e.g. B. Chlorine atoms, can split off, peroxides, which can form OH radicals, Azo compounds that can form nitrogen radicals; Nitro compounds, Oxygen, as well as the usual ones used for radical reactions known photoinitiators. Examples of such photoinitiators are chlorine-containing aromatic compounds, such as in US-A-4 089 815, aromatic ketones, such as, for example, in EP-A-0 161 463, hydroxyalkylphenones, such as in US-A-4 347 111 and / or phosphine oxides, as described, for example, in EP A-0 413 657.

They are monomeric compounds, that is, low-molecular compounds Compounds and not polymeric, such as chlorinated Polyolefins (CPO).

The radical-forming compounds can either as such, or in aqueous and / or organic solvent medium to the surface of the treating substrate are applied. You can after treatment evaporate or remain on the substrate surface. It is also possible to use them together with one or more binders, which form a coating on the substrate.

A gaseous compound that can be used as a low molecular radical generator For example, oxygen is dissolved in a solvent can be applied. It is possible that after the fiction According to the method, no coating remains on the substrate and only one activated surface is obtained. Examples of liquid substances are peroxides such as peracids, e.g. B. peracetic acid, performic acid; Cumene hydroperoxide, hydrogen peroxide; halogenated substances, in particular those with more than one halogen atom on the carbon atom, such as trichlor methanesulfonic acid chloride, thionychloride, trihaloethane. This substance Zen can also evaporate with the solvent or they  remain as a coating together with the binder used Substrate.

Examples of solid compounds are low molecular weight halogenated Compounds those up to a molecular weight of less than 1000, the chlorato contain me, such as chloronaphthalene, chlorosuccinimide. Examples of halo Gene-free compounds are azo compounds such as azoisobutyronitrile; Nitro compounds such as dinitrophenylacetic acid or known photoinitia goals.

These compounds can be dissolved in organic solvents. If necessary, they can swell and as finely divided gel-like Dispersions are used.

If aqueous systems are used, the radical-forming compounds either in the water phase or in the Water phase emulsified. That can e.g. B. by ionic or non-ionic Emulsifiers are supported, they are used along with the proportions of the emulsified organic solvent or they own the water dilutability-supporting ionic groups.

The proportions are chosen, for example, so that the amount the radical-forming compound in the solution or dispersion below 25 % By weight. However, other conditions are also possible, in particular especially for dissolved gases that are only used in smaller quantities are, or, less preferably, liquid compounds in highly concentrated ter form, e.g. B. also in 100%. Aqueous systems can e.g. B. additionally organic solvents and only small amounts of the radical-forming Connection included.

It is inexpensive and represents a preferred embodiment of the invention represents when to be applied to the plastic surface to be treated Systems containing radical formers contain one or more organic solvents contain the surface of the plastic substrate to be treated can dissolve or swell. These are in particular: aromatic hydrocarbons, ketones and / or pyrrolidones, as well  may be present in the binders suitable according to the invention.

According to a further preferred embodiment of the invention however, radical-generating compounds are also used which themselves have a certain affinity for the plastic substrate. In one in this case, dissolving solvents can be used; however, such compounds are preferred without such solvents used. Examples of such radical formers are e.g. B. hydrophobic Free radical formers, such as halogenated aromatic hydrocarbons, such as Chloronaphthalene, and chlorinated, e.g. B. perchlorinated aliphatic compound with functional groups, such as acid groups, hydroxyl groups, Imide functions and their derivatives. Examples are trichloroacetic acid ethyl ester, trichloromethanesulfonic acid chloride, 2,2,2-trichloroethanol, N- chlorosuccinimide.

In the method according to the invention, however, it is also possible to use the radical forming compounds within one or more binders containing coating agent on the surface of the plastic substrate to apply.

Aqueous and / or solvent-containing coating agents are suitable as coating agents suitable that contain one or more film-forming binders. The Coating agents which can be used according to the invention can also have one or several organic solvents, water and common paint additives exhibit.

If organic solvents are used, especially solvents are suitable, which can evaporate in the drying conditions. Become Formulated aqueous systems, the content of organic solvents is for example up to 50% by weight, in particular above 1 and below 25 % By weight. In this case the organic solvents are in the water phase se miscible or they can be emulsified stably in the water phase.

As organic solvents such. B. aromatic solvents such as toluene or xylene, esters such as ethyl acetate or butyl acetate, ketones such as acetone or methyl ethyl ketone, alcohols, such as ethanol, butanol or isopropanol,  aliphatic hydrocarbons, ethers such as methoxypropanol, butoxypropa nol, ethyl glycol or N-methylpyrrolidone are suitable. The solvents can be used individually or in a mixture. It can be at room temperature applicable systems are obtained, or systems are obtained that must be dried at elevated temperature. Preferred solvents are aromatic hydrocarbons and ketones. Are also preferred Solvents with a low boiling point below 150 ° C.

The solvents should give the surface good wetting. she additionally stabilize the resulting radicals.

The binders or additives should be added in the solvents if not, the radical-forming substances should be readily soluble.

The solvents are used for conventional systems containing binders for example in amounts of 10 to 90% by weight, in particular 30 to 60%, used. The coating agents should be thin-viscosity.

The paint additives contained in the coating agent are usual additives. You can, for example, application technology Influencing properties, such as leveling agents, or manufacturing technology cal properties, e.g. B. anti-foaming agents, emulsifiers, wetting agents. If necessary, it is also possible to use catalysts, sensitizers, Use accelerators or dyes. The amount of additives is based on the coating agent, for example up to 10% by weight.

The known film can be used as a binder in the coating agent forming resins are used. This is for example resins based on polyesters, polyacrylates, epoxy resins, polyure than resins or alkyd resins. These binders are in the literature known and already described. You can network, that is, either self-network or with third-party networkers or you can only physically be drying.

About the choice of binders z. B. the usage property the plastic can be affected. It is preferred to use good wetting properties  Binder used. The binders are either organic Solvent soluble or it is a binder in water are dispersed or dissolved. It is possible that they form a film the resins carry hydrophilic groups. Examples of such groups are Polyether groups, in particular based on polyethylene oxide, OH groups or ionic groups or substitutes which can be converted into ionic groups ten. Examples of such substituents are primary, secondary or tertiary amines, sulfonic acids, carboxylic acids or phosphoric acid derivatives.

Suitable binders of this type are, for example, conventional polyurethane resins as in DE-A-40 00 889 or DE-A-36 28 124, customary epoxy resins, such as in DE-A-36 43 751 or in each case customary polyesters, alkyd resins and Acrylic resins.

The amount of the film-forming resins is, for example, 1 to 40% by weight based on the total coating agent. The coating agent contains in generally no inorganic or organic pigments or fillers fe, but it can be useful for special purposes, fillers and / or adding pigments, for example to treat the treatment optically make visible.

Processes for producing the coating compositions are known. Organic Coating agents are e.g. B. manufactured in that the individual sub punch dissolved or dispersed in the organic solution with good stirring be greeded. Thereafter, if necessary, for. B. with solid additives Grinding step can be interposed. About the content of solution means or the addition of additives, e.g. B. thickening, it is possible adjust the viscosity of the coating agent. A warehouse is created stable thin-viscosity coating agent. Methods are also known, gases dissolve in liquids. This can be done directly before the application or the gaseous solutions are in a stable form, e.g. B. under pressure, transported to the user.

If aqueous coating compositions are produced, for example in the water phase, if appropriate, using emulsifiers which dispersed organic components. Furthermore, insoluble be  components, e.g. B. higher molecular weight compounds, disper in the water phase yaws. For the dispersion of the additives in water, the film-forming organic resins can be added. These will either used as a water-soluble resin or it becomes an aqueous binder Oil dispersion added. The coating agents are made after mixing homogenized thoroughly. Stable emulsions and dispersion are formed nen.

The liquid systems containing the radical formers can by Brushing, dipping, flooding, spraying or rolling can be applied. If radical-forming substances are used that can evaporate the wet coating of radiation with high-energy radiation exposed. It may be necessary in a protection to work in a gas atmosphere. Here or after, the substrates of volatile components dried.

If film-forming coating agents are applied, they are applied at room temperature or the coatings are dried or hardened at elevated temperature. Here a homogeneous continuous film of the over forms on the substrate traction means. The coated substrate is filled with high-energy radiation irradiated.

According to the invention it is generally sufficient if only a thin layer of the the system containing the free radical generator onto the substrate surface is applied. For example, especially in the case of Binder containing coating agents dry layer thicknesses up to 20 µm, preferably up to 10 microns, in particular from 1 to 5 microns are applied. However, it can also be applied with little or no remaining layer gene, especially in the case of the use of aqueous and / or binder-free systems containing organic solvents. Important is in any case that even wetting of the plastic surface area entry.

The substrate surface treated in this way then becomes more energy-rich Radiation irradiated. This can be done with electron beams, with UV rays tion, especially at a wavelength of 200 to 400 nm or with  visible light, e.g. B. with a wavelength of 400 to 800 nm be tested. In particular, it is possible to use radiation of wavelengths to work over 300 nm.

The radiation can be adapted to the radical-forming compound used become, so that a breakdown into radicals occurs. By radiation Free radicals form, which adhere well to the plastic surface produce. The radiation can be coated on the still wet Substrate take place, or the coating or the coating agent is only dried or optionally crosslinked and then irradiated. The irradiated can also be done continuously. The duration is usually less than 60 s, especially under 30 and over 5 s.

It is advantageous to warm up before or in parallel or after the irradiation to carry out, preferably simultaneously with the irradiation. This can the adhesion to the substrate can be improved or, if necessary, the Irradiation time can be reduced.

According to the invention, it is possible to add sensitizers. These are supposed to increase the reactivity of the system. They are used in amounts up to 5% by weight, based on the overall system (solvent, initiator, sensitizer and optionally binder) incorporated into the system. Here it is preferably organic aromatic compounds without or with heteroatoms. Examples include anthracene, benzophenones, Thioxanthones and derivatives, e.g. B. C₁-₇-alkyl or C₁-₇-alkoxy substituent ized connections.

The surface of the substrate treated in this way becomes reactive for Subsequent layers or they are liable to be created by the radiation Reaction products. They can be treated in this way before further processing substrates for mechanical or chemical cleaning of the surface be subjected. The chemical cleaning can, for example, with Solvents, with aqueous cleaners or by dry processes happen.

The substrates treated according to the invention can easily be followed  layers, e.g. B. primers, basecoats or topcoats be layered. The coating agent of the subsequent layer is not one subject to special restrictions. This coating can be done directly happen after the treatment according to the invention or the workpieces are stored before further processing. In the case of direct processing If necessary, pre-treatment and subsequent shift may be necessary harden together.

According to the invention, the surfaces of a wide variety of plastic substrates be treated. There are any substrates, for. B. on the Based on polystyrene, acrylonitrile butadiene, styrene copolymers, poly urethanes, polyamides, polyesters, polycarbonates or polyolefins. Polyolefins, for example polypropylene or, are particularly suitable Polypropylene copolymers. From such polymers, for example Molded parts are produced as substrates to be coated. they draw outstanding mechanical stability and flexibility even at low temperatures.

The procedure according to the invention makes it possible in a simple manner Way to activate the surfaces of plastic substrates, thereby Subsequent varnishes good adhesive properties are imparted. these can also applied after a long period after the activation treatment become. The coatings obtained show a good one even in the cold Adhesion and excellent impact resistance.

The following examples serve to illustrate the invention. Parts and Unless otherwise stated, percentages relate to the Weight.

example 1

A mixture is prepared from 95 g of xylene, 2.5 g of benzophenone and 2.5 g of 2-hydroxy-2-methyl-1-phenylpropan-1-one. This mix is going on a degreased substrate (Hostalen® PPR 8008 from Hoechst AG) gen. The coated substrate is at a distance of 15 cm with a  Speed of 2 m / min past 2 spotlights (100 watts / cm). The substrate is then dried at 80 ° C.

A commercially available 2-component primer is applied to the substrate treated in this way applied and cross-linked at 50-60 ° C.

The substrate coated in this way shows good adhesion to the coating agent.

Example 2

A mixture is prepared from 97 g of xylene, 1 g of benzophenone and 2 g Chloronaphthalene. This mixture is applied to a degreased substrate (Hosta len® PPR 8008 from Hoechst AG). The substrate coated in this way is at a distance of 5 cm in an ESH system (electron beam System) irradiated with 100 kGy.

Example 3

An emulsion is prepared from 2 g emulsifier, 75 g water, 1 g additives, 2 g 1-chloronaphthalene, 1 g benzophenone, 19 g Solvesso 100 (aromatic solvent mixture). This mixture is degreased Substrate (Hostalen® PPR 8008 from Hoechst AG) applied. The radiation takes place as indicated in Example 1.

Claims (12)

1. A method for coating plastic substrates by applying a film-forming coating agent and drying or curing the coating obtained, characterized in that

• a) first applies one or more low-molecular compounds which form free radicals to the surface of the plastic substrate under high-energy radiation,
• b) subjecting the surface treated in this way to radiation with high-energy radiation,
• c) if necessary, then carries out a mechanical and / or chemical cleaning of the surface and
• d) the film-forming coating agent is applied to the surface treated in this way and dries or hardens.

2. The method according to claim 1, characterized in that one Radical forming compound dissolved or dispersed in water and / or one or more organic solvents and the radiation before or after the removal of the water and / or organic solvent. 3. The method according to claim 1, characterized in that the Radical compound in a water and / or solvent and one containing one or more film-forming binders applies traction means and the radiation before or during the Drying or hardening of the coating agent. 4. The method according to any one of claims 1 to 3, characterized in  that in step a) the radical-forming compound with pigments and / or dyes. 5. The method according to any one of the preceding claims, characterized records that one under radicals under high-energy radiation forming monomeric compound halogens releasing compounds, Peroxides, azo compounds, nitro compounds, oxygen and / or Usual photoinitiators used. 6. The method according to any one of the preceding claims, characterized records that the radical-forming compound in aqueous Medium together with one or more solvents that the upper surface of the plastic substrate can be used. 7. The method according to any one of claims 1 to 5, characterized in that that radical-forming compounds with a hydrophobic portion in an aqueous medium without the addition of the plastic substrate Solvents used. 8. The method according to any one of the preceding claims, characterized records that the radical-forming compound together with one or more sensitizers used. 9. The method according to any one of the preceding claims, characterized records that heat is applied before, during or after the irradiation becomes. 10. The method according to any one of the preceding claims, characterized records that UV radiation and / or as high-energy radiation uses visible light or electron radiation. 11. The method according to any one of claims 1 to 9, characterized in that one is irradiation with actinic light with a wavelength performs over 300 nm.   12. The method according to any one of the preceding claims, characterized records that one with an irradiation time of less than 60 seconds is working.