EP2598561A1

EP2598561A1 - Process for scratch- and abrasion-resistant coating and physical matting of plastics substrates, more particularly polymethyl methacrylate, with nanocomposite coating material

Info

Publication number: EP2598561A1
Application number: EP11712805.8A
Authority: EP
Inventors: Dieter Meinhard; Rolf Schubert; Evelin Bilz; Sandra Reemers
Original assignee: Evonik Roehm GmbH
Current assignee: Roehm GmbH Darmstadt
Priority date: 2010-07-29
Filing date: 2011-03-28
Publication date: 2013-06-05
Also published as: TW201211177A; CN102985469A; WO2012013364A1; US20130129980A1; CA2806968A1; AU2011285153A1; MX2013001052A; BR112013001922A2; ZA201300728B

Abstract

The invention relates to a process for the surface-finishing of plastics substrates, preferably polymethyl methacrylate (abbreviated hereinafter to PMMA), by coating with a clear coating material comprising nanoparticles (hereinafter nanocomposite coating material) and irradiating the same with vacuum UV light of wavelength 172 nm from an Xe* excimer lamp. This process leads to excellent adhesion of the coating substance on the substrate. It is moreover possible to give the coating surface a topography. The mechanical and chemical properties and performance characteristics of uncoated substrate are substantially exceeded when a substrate is coated in this way.

Description

Process for the scratch and abrasion resistant coating and physical matting of plastic substrates, in particular polymethyl methacrylate, with nanocomposite paint

Field of the invention

The invention relates to a method for

Surface refinement of plastic substrates,

in particular polymethyl methacrylate (hereinafter abbreviated

PMMA), by coating with a nanoparticle-containing paint, preferably a clearcoat, (hereinafter

Nanocomposite lacquer) and irradiation thereof with vacuum UV light of wavelength 172 nm of a Xe * excimer lamp. This process leads to excellent adhesion of the

Coating material on the substrate. In addition, the production of a topography with a matte appearance and a pleasant feel of the coating surface

allows. The mechanical, chemical and

Application properties of uncoated substrate are significantly exceeded by such a coated substrate.

State of the art

Like other thermoplastics, PMMA, with its inherent properties, can not meet all requirements. It is susceptible to stress cracking, especially after prior contact with solvents, e.g. Acetone or aliphatic alcohols. It comes to crackle, so Plexiglas surfaces are not allowed with alcohol or

Solvents are cleaned. PMMA is indeed compared to other mass plastics relatively scratch-resistant, for many

Applications, the scratch resistance is not enough.

By a surface finish, e.g. in form of a

Coating the surface of the PMMA may be deficiencies

largely resolved and property improvements are achieved. These coatings are respecting the

optical properties mainly related to the increase in scratch resistance in conjunction with

Self-cleaning properties, weather resistance,

Anti-reflective and anti-graffiti effect. The improved scratch resistance is either directly by application of a hard layer of double bond-containing, multifunctional radically polymerizing and crosslinkable mono- and oligomers such as (fluoro) alkyl (meth) acrylates or silica SiO _x , melamine resin produced or a pseudo effect due to better sliding on the

Surface achieved by using acrylated polysiloxanes or waxes as an additive in the coating material. The type of coating comes from painting - also with UV curing and with peroxide-initiated thermal treatment

Curing, plasma coating, calendering (EP 313979) and high pressure rolling process (WO 9929766). According to EP 180129, the anti-reflection coating is formed by porous silica particles in organosilicone polymers in (meth) acrylates or melamine resin of 1 to 40 μm

Coating thickness realized, whereby u.a. a rough matt surface arises. To produce a matt surface by a rough coating is according to WO

2008/059157 also the use of microparticles

different sizes and concentrations

Methacrylatbasis proposed. With all known coatings and

Application method is not yet

Property combination of deep matt PMMA surface with good transparency, with very high abrasion and

Scratch resistance, excellent chemical, weathering and UV resistance ^¬, good wettability and a pleasant feel achievable. This surface refinement can be achieved over a large area by means of

Coating can be achieved with a clearcoat. For this purpose, according to DE 10207401 a particular suitable

ultraviolet or electron beam polymerizable and crosslinkable with SiO x nanoparticles reinforced acrylate (nanocomposite), which gives its surface high abrasion and scratch resistance of its surface without substantial change in the optical properties of the PMMA base material, makes it resistant to solvents and its UV and

Weather resistance at least receives. This

solvent-free nanocomposite also has the

Advantage that the surface of a coating thereof by irradiation with short-wave UV light or

Electron radiation can be microstructured, creating a dull appearance of this surface with significantly increased mechanical and chemical resistances and wherein a good transparency is maintained because the SiOx nanoparticles with their refractive index of 1.45 corresponds approximately to the paint matrix and the organophilic particles covalently into the paint matrix are involved.

To generate this topography by the so-called

"Photochemical micromolding", the planar PMMA product coated with a liquid nanocomposite coating layer passes through the beam path of a 172 nm excimer VUV Lamp under nitrogen atmosphere. The VUV photons penetrating only a few 100 nm deep into the lacquer layer produce by photochemical polymerization or crosslinking, wherein no photoinitiator is required, because acrylates absorb very well in this short-wave UV range and the photon energy (7.2 eV) is very high , a thin skin that is due to polymerisation

Shrinkage stresses curls (DE 19842510). After the completion of the micro-folding process, this skin still floats on a still-liquid lacquer layer, which is subsequently exposed to UV light in the presence of longer-wave UV light in the presence of

Photo-initiator or by means of electron beam radiation, whereby the folding skin is fixed and the entire coating is brought to the substrate for adhesion. The degree of gloss resulting from the microplating depends on the resulting topography. This is essentially determined by the paint formulation and can be varied within certain limits by the technological parameters (DE 102006042063). In addition to this matte finish, the high efficiency in double bond conversion and the additional generation of radicals by the 172 nm

Photons, creating a higher degree of crosslinking compared to the classic polychromatic UV curing, of great advantage. A significant increase in microhardness in the near-surface area of the coating with positive

Impact on the abrasion and scratch resistance and on improved barrier properties is the result. The round pleat combs provide a pleasant feel and the vacuum UV light (VUV) produces polar groups that improve the hydrophilicity. A good substrate adhesion of a solvent-free

to be applied and fully curable (meth) Acrylatlbeschichtung on PMMA is achieved according to EP 245728 and DE 2928512 on a warm substrate.

Issue

The object of the present invention was to provide a method by means of which a semifinished product which is evenly matted can be produced on the basis of PMMA or other plastic substrates.

In addition, the task was by means of this

Processes to provide semi-finished, the improved mechanical properties, such as improved scratch and abrasion resistance, and increased chemical resistance at the same time good UV and

Have weather resistance.

In addition, there has been a demand for coatings which fulfill the foregoing objectives and, moreover, have very good substrate adhesion. In addition, the task was to provide this by a low-energy, fast and easy to implement method.

Further tasks which are not explicitly mentioned emerge from the overall context of the following description, claims and examples. solution

The objects are achieved by a novel process for coating plastic substrates, in particular polymethyl (meth) acrylate surfaces. In particular, this method can be used to coat transparent

Polymethyl (meth) acrylate surfaces are used. The process according to the invention is a coating process using special nanocomposite paints. The nanocomposite lacquer contains silicon oxide (SiO _x ) nanoparticles, at least one crosslinkable one

Acrylate- or methacrylate-based binders, at least one reactive diluent and optionally at least one

Thickener.

Surprisingly, it was found that the use of the

inventive method using the

likewise SiO x nanoparticle-containing nanocomposite UV varnishes according to the invention, the production of transparent semi-finished products with high abrasion and scratch resistance, with improved chemical, UV and weathering resistance compared with the prior art while at the same time being very good

Substrate adhesion of the coating and good mechanical properties allows.

In the process according to the invention, the nanocomposite lacquer has a viscosity between 500 mPas and 20 Pas, preferably between 6 Pas and 20 Pas, and more preferably between 10 Pas and 18 Pas during application. The polymer surface to be coated simultaneously has a

Temperature of at least 40 ° C, better of at least 60 ° C, but not higher than the melting or glass transition temperature of the polymer to be coated. In the case of PMMA as Substrate temperatures between 35 ° C and 120 ° C, preferably between 40 ° C and 90 ° C apply. The paint can be applied both at room temperature and preheated, for example, to the respective substrate temperature.

In a second process step after coating, a thin skin is produced by irradiation with short-wave UV light on the surface of the liquid lacquer layer, which after microfolding in a subsequent third process step by curing the entire nanocomposite coating by means of a second,

long-wavelength light-emitting UV lamp is fixed on the substrate.

In particular, the first UV radiation is monochromatic 172 nm excimer VUV radiation. A

preferred radiation dose is below 20 mJ.cm ^-2 . In this only with a very small depth in the

Lackmatrix penetrating short-wave UV radiation receives the coating due to microfilming the surface of a matte appearance, ie analog gloss values and haptics to the state of the art. At the second radiation source,

preferably UV radiation source may be, for example, a medium-pressure mercury lamp, for example with a power of 160 W. cm ^"1 and an irradiation dose of 800 mJ.cm ^-2 , or an electron accelerator After this final curing, the coating has excellent adhesion to the substrate, or in particular the semifinished product.

In the crosslinkable binder (meth) acrylate of Nanokompositlackes, it is preferably a tri or multifunctional ^¬ Urethanacrylateoligomer or a mixture of various urethane acrylate oligomers containing at least one tri- or multi-functional urethane acrylate oligomer. It is preferably a multifunctional urethane acrylate oligomer. Multifunctional in this context means that the number of

Carbon double bond end groups per monomer unit is greater than or equal to 4, preferably greater than or equal to 6. The advantage of these urethane acrylate oligomers is that they scarcely yellow under UV light exposure and have a high scratch resistance, for example characterized by the pencil hardness, when cured.

Alternatively and preferably, the crosslinkable binder can also be used as a mixture of the described multifunctional urethane acrylate oligomers with a lower proportion

Lower functionality urethane acrylate oligomers, especially a 2 to 3 urethane acrylate oligomer

Carbon double bond end groups are present. Such a mixture shows improved flexibility and

Impact strength.

The reactive diluents used according to the invention, which are capable of reacting with the crosslinkable binder, may preferably be acrylates.

It is particularly preferred that

Reactive thinner to 1, 6-hexanediol diacrylate (HDDA).

The SiO _x nanoparticles are silicon oxides with an x value between 1.6 and 2.0, preferably between 1.9 and 2.0. The silicon oxide nanoparticles can be present individually or as mixed oxides. The particle size of these oxide particles should be in the nanometer range due to the transparency of the product. Preferably, the particles have at most a size of 300 nm, in particular in a range of 1 to 200 nm, preferably 1 to 50 nm.

The thickening additives optionally containing are preferably (meth) acrylic functional

Polyetherdimethylsiloxane such as BYK ^® UV 3500th The nanocomposite lacquer preferably contains the

Thickening additive in a concentration between 0.1 and 5.0% by weight, preferably between 0.5 and 2.0% by weight.

The nanocomposite lacquers used according to the invention are additionally concomitant despite the already increased viscosity

Thickening additives added to give the paint a pasty consistency. This ensures that after application of the coating material by means of a

structure-giving application method, for example with a screen printing technology, the micro-structure produced remains stable even at temperatures up to 90 ° C.

The method according to the invention can preferably be carried out in direct connection to an extrusion process for the production of the substrate to be coated, in particular semifinished product.

Most preferably, the process is in-line in the

Integrated plant for the production of the substrate to be coated. Thus, the

Production of the substrate or semi-finished product and the method for coating the same can be carried out continuously.

The nanocomposite lacquer may be screen printed, roll coater technology or other suitable

structuring methods are applied. The nanocomposite lacquer is preferably applied to the substrate surface by means of rotary screen printing. In another, preferred embodiment is in a

Roller application method for coating with the

Nanocomposite lacquer worked with a profiled applicator roll or the application with a smooth roller is followed by a profiled roller for structuring.

With these preferred embodiments of

Applying a high viscosity varnish can be applied, whereby it is given a Vorstruktur which remains stable even at the higher temperatures, and which receives after irradiation with the first radiation source, a superstructure, which to the

optical matting and a haptic pleasant

Surface with anti-fingerprint effect leads.

In addition to the process described, the nanocomposite lacquer which can be used in this process and whose binder matrix is 30.0 to 60.0% by weight, preferably 35.0 to 55.0% by weight, of a multifunctional urethane acrylate oligomer having> 6 carbon double bonds per component is part of the present invention Monomer unit, which hardly yellows under UV light exposure and has a high scratch resistance (scratch resistance). Furthermore, the binder matrix contains 2.0 to 20.0% by weight, preferably 5.0 to 15.0% by weight of a likewise UV-stable urethane acrylate oligomer of lower functionality having 2 to 3 carbon double bonds per monomer unit for the purposes of flexibilization and increase in impact strength. In addition, the binder matrix has a

Reactive diluent portion - preferably 1.6-

Hexanediol diacrylate (HDDA) for outdoor use - from 10 to 50% by weight, preferably from 20 to 40% by weight. This paint formulation is used in an in situ process analogous to DE 10207401, in which silica nanoparticles in a proportion of 1.0 to 15.0% by weight, preferably from 3.0 to 12.0% by weight and particularly preferably of 5, 0% by weight of a hydrolysis of a silane, for example Dynasylan VTMO ^® from Evonik Degussa GmbH be covalently bonded to 10.0, modified. The silane, preferably one

(meth) acryl-functional silane may be between 1.0 and 10.0% by weight, preferably between 2.5 and 7.5% by weight. For a final hardening of the coating after the excimer-VUV-initiated microplating, a maximum of 5.0% by weight, preferably not more than 3.5% by weight, of a mixture of non-yellowing to slightly yellowing photoinitiators is added, and the lacquer in addition to UV protection with 1.0 to 3.0% by weight of a UV absorber and 0.5 to 2.5% by weight of a HALS additive

(Hindered amine light stabilizer) provided. In addition, a thickening additive, e.g. BYK-UV 3500, with a proportion between 0.1 and 5.0% by weight, preferably between 0.2 and 2.5% by weight, to the final pasty

To achieve rheology. This results in the coating of the substrate by means of a structuring

Application method, such. B. with a

Screen printing technology, that the generated

Micro Vorstruktur remains stable even at temperatures up to 90 ° C. By subsequent irradiation of this

pre-structured PMMA coating with 172 nm excimer VUV radiation with an irradiation dose <20 mJ.cm ^-2 gives the surface due to superimposed Mikrofaltung a matte appearance, ie gloss values and a feel that of a commercially available frosted PMMA semi-finished, such as PLEXIGLAS Satinice ^® from Evonik Röhm GmbH. After final hardening with a

Mercury medium pressure lamp with adequate Irradiation dose, the coating with excellent adhesion according to ISO 2409: 1992 (GT 0) has a very high pencil hardness and also the

Abrasion resistance, tested with the TABER 5151 ABRASER according to ASTM D-1003 and D-1044 with CS10 F and judged by the Hazeänderung, is after 100 revolutions at 500 g

Load with a very small change in the Haze

excellent. The chemical resistance, UV resistance and weathering resistance are correspondingly good.

Is a higher flexibility of the coating for a thermoplastic deformation of the rigid PMMA semi-finished products, which suffers only an expansion or compression,

required, then this can be achieved at the expense of scratch and abrasion resistance by changing the Oligomeranteile.

In addition, the means of the invention

Produced process, preferably produced

coated semi-finished part of the present

Invention. Such coated semi-finished products can

For example, use in store, trade fair or furniture, cover as bulbs, as picture glazing, in billboards or street signs or surfaces of touch screens or photovoltaic modules, without this listing would be in any form suitable to limit the present invention.

Among semi-finished products are in the sense of this invention

understood ready-made raw material forms. These may be, for example, rods, tubes, plates or in particular foils. Examples

The examples which follow serve to clarify and to better understand the present invention, but in no way limit it in terms of their scope or scope.

The following is a with an inventive

Nanokompositlack coated semi-finished product with a PLEXIGLAS ^® Satinice sample of the Fa. Evonik Röhm GmbH as

Comparison example. Here are the

Composition of the PMMA semifinished product and their dimensions identical. The application of the paint was carried out by screen printing.

Two nanocomposite coatings with the same matrix composition as shown in Table 1, which differ only in the proportion of the thickening additive, were heated to 60 ° C. or 90 ° C. by means of a sieve 120-34Y with an average layer thickness of 7 to 9 μπι to give a sample plate Applied to the preliminary structure. After a maximum of one minute residence time then the surface of the

Coatings with the inventive method according to Figure 1 in the inerted irradiation channel - with a

Residual oxygen content less than 70 ppm - microinflated initiated by a 172 nm excimer VUV dose of 4.5 mJ.cm-2, and then the final coating was finally cured with a UV dose of 800 mJ.cm-2 of a medium pressure mercury lamp. The surface properties of the two examples and a comparative example (PLEXIGLAS Satinice) are shown in Table 2 and in FIG. Table 2 clearly shows that, despite the different topography of the

Microfolding and the obtained by impression

Surface texture of PLEXIGLAS Satinice in good

Approximate same gloss values with significant improvement of the mechanical load values and the UV and

Weathering resistance can be achieved by the coating. From Figure 2 it can be seen that the

Surface friction coefficients and the resulting trends of both structures are about the same, which can be considered as a criterion for an analog haptic. The comparison of

On the other hand, both approaches illustrate the big one

Significance of the thickening additive, here BYK UV 3500, when coating a warm substrate.

Although a higher additive concentration reduces the risk of the preliminary structure passing between the application and the beginning of the microfolding process at elevated temperature (90 ° C.), this results in approximately constant gloss values at 85 °

Measuring geometry reflects, but it comes through the larger proportion to a decrease in the scratch resistance.

Table 1: Composition Examples

Example 1 Example 2

Substance Name Weight Shares Weight Shares

(Trade name) [wt. -%] [wt. -%] multi functional DM 5812 39, 72 39.30

urethane

the functional DM 570 7, 95 7.86

urethane acrylate

Reactive thinner HDDA 31,78 31,44

Silane Dynasilan VTMO 4.49 4.44

Excipients for maleic anhydride 1, 87 * 10 ^{~ z} 1, 85 * 10 ^{~ z}

silanization

4-Metoxy anisole 1, 87xl0 ^_1 1, 85xl0 ^_1

SiO _x nanoparticles Aerosil A380 9, 35 9,25

Photoinitiator mixture ^* Darocure 1173 2.00 3.00 Irgacure 184 1.00

UV absorber Tinuvin 400 2.00 2.00

HALS Tinuvin 123 1.00 1.00

Thickening additive BYK UV 3500 0,50 1,5

Referred to by the company Cetelon Nanotechnik GmbH Table 2: Comparison of the optical and mechanical

Surface self-shadowing

GT = adhesion test by means of cross-cut and tesa test in accordance with DIN EN ISO 2409: 2007 with values between 0 (total adhesion) and 5 (complete release) Gloss values in highlights measured at 20 °, 60 ° and 85 ° angles to the vertical according to DIN 67 530: 1982, DIN ISO 2813: 1999, ASTM D 523-08 and D 2457-08. The gloss values were determined by means of a Haze Guard plus (Byk Gardner).

The abrasion resistance was determined by means of TABER 5151

ABRASER based on the standards ASTM D 1044-7 and

1003-7 with the specification CS10F with a weighting of 500 g after 100 revolutions as Hazeänderung with the

BYK Gardner haze-gard plus spectrometer intended.

The scratch resistance was determined by means of Erichsen 413 Scratch stronger according to DIN EN 438-2: 2005.

The UV and weather resistance is in one

QSUN / 1000 Xenon tester according to DIN EN ISO 11341: been in a long-term test of 3 ^'000 tested h in 2004, using as

Criterion the color change was measured.

The results show that this invention

produced semi-finished products compared to the best known prior art in analog, if desired variable

Matt gloss and also good feel and lasting good transparency increased scratching and

Abrasion resistance and significantly improved

Chemical resistance at comparable

Weather resistance.

This is followed by 1 sheet with 2 drawings Fig. 1: Technological scheme of photochemical

micro fold

The inscription numbers mean the following:

1: 172 nm excimer lamp

2: Mercury medium pressure lamp

3: substrate (or semi-finished product to be coated)

4: Liquid coating

5: folding skin (surface-crosslinked coating with micro-folding)

6: Hardened coating

7: shielding gas (N ₂ -) supply line

Figure 2: Behavior of the surface friction of two identical structures of the comparative example and of

Example 1 as a criterion for the comparison of haptics 1: Comparative Example

2: Example 1

Claims

1. Process for coating plastic surfaces, preferably surfaces more transparent or not

transparent thermoplastics, such as

Polymethyl (meth) acrylate surfaces, with a

Nanocomposite lacquer, characterized in that the

Nanocomposite lacquer SiO _x nanoparticles, at least one

hochvernet zbares binder and at least one

Contains reactive diluent,

that the nanocomposite paint during application a

Viscosity between 6 Pas and 20 Pas,

the substrate surface has a temperature between 35 ° C and 120 ° C during application,

that the nanocomposite lacquer after application with

hardened shortwave UV light at the surface and is made to the microfolding,

and that the paint is then completely cured with a second UV lamp.

2. The method according to claim 1, characterized in that the coating contains at least one thickener.

3. The method according to claim 1 or 2, characterized

characterized in that the first UV radiation is a monochromatic 172 nm excimer VUV radiation.

4. The method according to any one of claims 1 to 3, characterized in that it is in the

Reactive thinner to an acrylate, preferably 1,6-hexanediol diacrylate (HDDA) is.

5. The method according to any one of claims 1 to 4, characterized in that it is in the

hochvernet tenable binder to a tri- or

multifunctional urethane acrylate oligomer or a

Mixture of various urethane acrylate oligomers containing at least one tri- or multifunctional

Urethanacrylatoligomer, where multifunctional in this context means that the number of

Carbon double bond end groups per monomer unit is greater than or equal to 4, preferably greater than or equal to 6.

6. The method according to any one of claims 1 to 5, characterized in that it is in the

Thickening additive around a (meth) acrylfunktionelles

Polyetherdimethylsiloxan acts.

7. The method according to claim 6, characterized in that the nanocomposite lacquer, the thickening additive in a

Concentration between 0.1 and 5.0 wt%, preferably between 0.5 and 2.0 wt%.

8. The method according to any one of claims 1 to 7, characterized in that the substrate surface during the coating has a temperature between 40 ° C and 90 ° C.

9. The method according to any one of claims 1 to 8, characterized in that the method is carried out in direct connection to an extrusion process for the production of the substrate to be coated.

10. The method according to claim 9, characterized in that the plant for performing the method is integrated in-line in the plant for the production of the substrate to be coated, and that the production of the substrate and the method for coating are carried out continuously.

11. The method according to any one of claims 1 to 10, characterized in that the nanocomposite lacquer by means of a structuring endless

Coating method such as rotary screen printing or a roll coater method is applied.

12. The method according to claim 11, characterized in that the coating roller is profiled for the nanocomposite lacquer or an application by means of a smooth roller follows a profiled roller for pre-lacquering.

13. Nanocomposite coating for coating

Polymethyl (meth) acrylate surfaces, characterized

in that the nanocomposite lacquer comprises 0.1% to 5.0% by weight of a thickening additive, 35.0% to 55.0% by weight of a multifunctional urethane acrylate oligomer, 5.0% to 15.0% by weight of a difunctional or trifunctional

Urethane acrylate oligomer, 3.0 wt% to 12.0 wt% SiO _x nanoparticles and 20 wt% to 40 wt% reactive diluents, where multifunctional in this context means that the number of

14. nanocomposite paint according to claim 13, characterized in that this according to a method according to any one of claims 1 to 12 to a

Polymethyl (meth) acrylate semifinished product is applicable.

15. Coated semi-finished product, characterized in that it can be produced by a method according to at least one of claims 1 to 12.