Improved one-component anti-reflective coatings, their manufacture and use on components and devices

Abstract

The invention relates to one-component, water-dilutable coating materials for producing antireflective coatings on substrate surfaces. The coating materials contain one or more water-dilutable, aliphatic polyurethane resin dispersions, black plastic spheres with sphere diameters d50 in the range of 9 to 17 µm, and black pigments. The invention further relates to methods for producing the antireflective coatings and their use in components and devices whose functions are impaired by the reflection of electromagnetic radiation, in particular by the reflection of light.

Description

[0001] The invention relates to antireflective coatings, coating materials, and methods for producing antireflective coatings on substrate surfaces. It further relates to the use of the antireflective coatings for components and devices whose functions are impaired by the reflection of electromagnetic radiation, in particular by the reflection of light.

[0002] Different coatings and coating systems are used to coat surfaces, depending on the technical requirements. In addition to the usual protective and decorative properties, the technical properties of the coated surface are also important. For example, anti-reflective coatings are used for optical or electronic devices to suppress or at least significantly reduce light reflection. In the following, the term anti-reflective coating refers to coatings that suppress the reflection of electromagnetic radiation from surfaces.

[0003] The coating materials known to date produce antireflective coatings that suppress reflection, but exhibit insufficient mechanical stability and packaging strength. Furthermore, these known coating materials cannot be processed using the standard processes employed for mass production coating.

[0004] From WO 2019 / 073210 A1, methods for producing antireflective coatings are known in which suspensions of black pigments in a binder solution are sprayed onto a substrate surface and subsequently dried by evaporating the solvent. However, the coatings obtained in this way exhibit only low resistance to mechanical stress and significant abrasion. Abrasion refers to the removal of coating material by external influences. Abrasion occurs, for example, during friction and grinding, cleaning processes, and also during the handling of the coated objects, such as packaging. The resistance of a coating during the packaging process is referred to as packaging strength.

[0005] It is therefore an object of the present invention to provide improved antireflective coatings that overcome the known disadvantages. This object is achieved by coating materials according to the main claim. It is also achieved by coatings made from coating materials according to the invention and their use on components and devices. Furthermore, it is achieved by methods for coating substrate surfaces.

[0006] The coating materials according to the invention contain at least - Containing 20 to 88 wt% of one or more water-dilutable, aliphatic polyurethane resin dispersions with solids contents in the range of 30 to 50%. - Containing 10 to 40 wt.% black plastic spheres with a sphere diameter d50 in the range of 9 to 17 µm, as well as - 0.5 to 2 wt.% black pigments, based on the total weight of the coating material.

[0007] In a preferred embodiment, the coating materials have pigment volume concentrations of at least 70%, preferably at least 73%. The pigment volume concentration (PVC) of a coating material is defined as the ratio of the total volume of its solid particles that do not participate in film formation to the total volume of its non-volatile components. In addition to pigments and fillers, the solid particles also include other particles such as the plastic spheres used according to the invention.

[0008] According to the invention, water-dilutable, aliphatic polyurethane resin dispersions are preferably used in amounts of 40 to 70 wt.%, preferably 50 to 60 wt.%, and particularly preferably 53 to 57 wt.%, in each case based on the total weight of the coating material. Suitable dispersions are polyurethane resins comprising one or more, identical or different, functional groups selected from ester, ether, acrylate, methacrylate, and carbonate groups. Polyacrylate-polyurethane resin dispersions, polyester-polyurethane resin dispersions, polyether-polyurethane resin dispersions, polycarbonate-polyurethane resin dispersions, and mixtures thereof, particularly polycarbonate-polyurethane resin dispersions, are preferred.

[0009] In further preferred embodiments, the water-dilutable, aliphatic polyurethane resin dispersions have solids contents in the range of 35 to 45%, particularly preferably in the range of 37 to 42%. Solids contents below the lower limit of this range result in coatings with significantly reduced resistance. Solids contents above the upper limit of this range result in coatings with undesirably increased gloss. Hereinafter, the solids content of the binder is understood to be the mass fraction that remains as residue after evaporation under specified conditions. To determine this, approximately 1 g of substance is evaporated in an aluminum dish with a diameter of 8 cm at 105 °C in a drying oven or convection oven for 30 minutes. After cooling, the weight of the residue is determined. The solids content is the quotient of the weight of the residue and the amount of substance used.It is given as a percentage.

[0010] In further preferred embodiments, the water-dilutable aliphatic polyurethane resin dispersions have minimum film formation temperatures in the range of 0°C to 20°C, preferably from 0°C to 15°C, particularly preferably from 0°C to 10°C, and most preferably from 0°C to 5°C. The minimum film formation temperature (abbreviated: MFT) is understood below to be the temperature above which a water-dilutable binder dispersion forms a continuous film. Below the minimum film formation temperature, film formation is impaired or incomplete. To determine the minimum film formation temperature, the dispersion is applied to a plate which is heated at one end and cooled at the other. The minimum film formation temperature of the dispersion can be determined by temperature sensors which are placed at close intervals along the plate.

[0011] According to the invention, the black plastic spheres are preferably used in amounts of 20 to 40 wt.%, particularly preferably 30 to 40 wt.%, and most preferably 33 to 37 wt.%, in each case based on the total weight of the coating material. Suitable plastic spheres are made of black-colored polyurethanes (PU), polycarbonates (PC), polymethyl methacrylates (PMMA), and polyamides (PA). Polyurethane spheres are preferred.

[0012] The black plastic spheres have a sphere diameter d50 in the range of 10 to 16 µm, preferably from 11 to 15 µm. The value d50 denotes the equivalent particle diameter below which 50 percent by volume of the plastic spheres lie. This value can be determined using standard methods for determining particle size, such as sieve analysis.

[0013] In further embodiments, a proportion of the black plastic spheres is replaced by smaller, transparent plastic spheres. These are used in amounts of 5 to 25 wt.%, preferably 10 to 25 wt.%, particularly preferably 15 to 20 wt.%, and most preferably 16 to 19 wt.%, in each case based on the total weight of the coating material. The total amount of all plastic spheres used remains unchanged in the range of 10 to 40 wt.% based on the total weight of the composition. Suitable transparent plastic spheres according to the invention are made of polyurethanes (PU), polycarbonates (PC), polymethyl methacrylates (PMMA), and polyamides (PA). Polyurethane spheres are preferred.

[0014] In further embodiments, the coating materials according to the invention comprise black plastic spheres having a sphere diameter d50 in the range of 9 to 17 µm and transparent plastic spheres having a sphere diameter d50 in the range of 3 to 10 µm, preferably black plastic spheres having a sphere diameter d50 in the range of 10 to 16 µm and transparent plastic spheres having a sphere diameter d50 in the range of 4 to 9 µm, particularly preferably black plastic spheres having a sphere diameter d50 in the range of 11 to 15 µm and transparent plastic spheres having a sphere diameter d50 in the range of 5 to 8 µm.

[0015] According to the invention, the coating materials preferably contain black pigments in amounts of 0.5 to 1.5 wt.%, particularly preferably 0.6 to 1.3 wt.%, in each case based on the total weight of the coating material. Suitable black pigments are carbon blacks such as flame soot, gas or sewer soot, furnace soot, crack soot and acetylene soot, spinel black, perylene black, iron oxide, manganese oxide, mixed metal oxides and mixtures thereof. Preferred black pigments are iron oxide and carbon blacks, in particular flame soot, gas or sewer soot, furnace soot, crack soot, acetylene soot and mixtures thereof.

[0016] Furthermore, the coating materials according to the invention can include the usual auxiliary materials and additives known to those skilled in the art, such as defoamers, pH modifiers, thickeners, surface additives, wetting and dispersing additives.

[0017] The coating materials according to the invention form black coatings with a closed, rough surface during drying, exhibiting minimal gloss and low reflectivity. Gloss refers to the optical property of a surface to reflect light wholly or partially specularly. The degree of gloss is expressed as the quotient of the specularly reflected component and the diffusely reflected component of a luminous flux incident on a surface. Specular gloss has a diffusely reflected component close to zero, ideally zero. In contrast, matte gloss or dullness has a specularly reflected component close to zero, ideally zero. The gloss of surface coatings such as varnishes and paints is usually determined using a reflectometer or gloss meter. For this purpose, directed light is shone onto the sample surface at a defined angle.A detector records the light radiation reflected from the sample surface at the same angle. The results obtained are expressed in gloss units (GU). The angle at which the measurement is taken is selected according to the material and the expected gloss to best utilize the detector's sensitivity. In contrast to previously known antireflective coatings, the coatings according to the invention, with their rough, black surfaces, exhibit a very low gloss in the range of 0 to 0.1 GU across the entire angular range.

[0018] Reflectance refers to the optical property of a surface to reflect light completely or partially specularly. The THR value (Total Hemispherical Reflectance) describes the reflectance of a surface over the wavelength range between 360 and 740 nm. The higher the value, the more radiation is reflected. The coatings according to the invention exhibit THR values ​​of less than 1.2. These values ​​are determined using a conventional measurement method in which the sample is diffusely illuminated with an Ulbrich sphere, and the reflected and remitted radiation is measured at an angle of 8° to the sample.

[0019] The coatings according to the invention are weather-resistant and exhibit typical resistance to mechanical, thermal, and chemical stresses. Furthermore, they are abrasion- and packaging-resistant. Despite their high PVK values, they are surprisingly not brittle. This makes handling components coated accordingly, e.g., during installation in devices, significantly easier than with known antireflective coatings. In addition, the coatings according to the invention exhibit low outgassing of volatile components, which prevents undesirable condensation or fogging. Therefore, they are particularly well-suited for use on devices and components for vehicles, especially for vehicle interiors.

[0020] The coatings according to the invention are used as antireflective coatings. They are preferably used as coatings on devices and components where reflection of electromagnetic radiation, particularly in the visible light range, is undesirable or disruptive. They are especially preferably used as coatings on optical and electronic devices.

[0021] Another aspect of the present invention is a method for producing an antireflective coating on a substrate surface, comprising the following steps: (a) Providing a coating material according to the invention (b) Applying a coating material according to the invention to the substrate surface by means of spray application, (c) Allowing the applied coating film to evaporate at room temperature and then (d) Drying the film at elevated temperature

[0022] To improve their processability, the coating materials according to the invention can be diluted with water-miscible solvents before application. Suitable solvents include, for example, water, acetone, ethanol, methanol, butanone, and mixtures thereof. Mixtures of water and acetone are preferred.

[0023] Due to their mechanical stability, the coating materials according to the invention can be applied to a substrate surface using conventional spraying and atomizing methods familiar to those skilled in the art. Airless and compressed air spraying methods are preferred, in which liquid coating materials are applied as a film to the surface of a substrate to be coated using spray guns.

[0024] The coating materials according to the invention are applied to the surface of a substrate to be coated using a commercially available compressed air spray gun. Preferably, a spray nozzle size in the range of 1.2 to 1.6 mm and an atomizing pressure between 3.0 and 4.0 bar are used.

[0025] The coatings according to the invention preferably have dry film thicknesses of at least 100 µm, more preferably 100 to 180 µm, and particularly preferably 130 to 160 µm. Dry film thickness refers to the thickness of the cured coating. To achieve these dry film thicknesses, the coating materials according to the invention are applied very dry in at least two, more preferably at least three, and particularly preferably at least four spray passes. This means that the spray gun is moved at least twice over the surface to be sprayed at a large distance of at least 20 cm, more preferably 25 cm, and particularly preferably 30 cm, from the surface of the substrate. Repeating the spray passes results in a thick application of the coating materials, whereby, due to the large distance of the spray nozzle, some of the solvents evaporate before reaching the surface.

[0026] To form the coating, the assembly consisting of the substrate and applied coating material is first allowed to evaporate for approximately 15 minutes at room temperature in the range of 20 to 35°C. Subsequently, the assembly is cured for approximately 30 minutes at temperatures in the range of 60 to 120°C, preferably in the range of 70 to 90°C, and particularly preferably in the range of 75 to 85°C.

[0027] Due to their improved processing properties and simplified handling, the antireflective coatings according to the invention can be used in conventional series painting processes. Furthermore, with their low gloss and reflectivity, the antireflective coatings according to the invention are particularly suitable for use on components and devices whose function is impaired by light reflection, such as dashboards, camera housings, measuring and display devices, e.g., head-up displays. Examples of coating materials Example 1 ingredient Quantity [Wt.%] Aliphatic polycarbonate-polyurethane resin dispersion (MFT: 5°C, solids content: 40%) 55,3 black plastic spheres (d50: 12 µm) 36,4 Black pigment (flame soot) 0,7 Defoamer 0,4 Wetting agent 1, 2 sunscreen 1,5 Water 4,5 Example 2 ingredient Quantity [Wt.%] Aliphatic polycarbonate-polyurethane resin dispersion (MFT: 5°C, solids content: 40%) 55,3 black plastic spheres (d50: 12 µm) 21, 8 transparent plastic spheres (d50: 7 µm) 15, 6 Black pigment (flame soot) 0,7 Defoamer 0,4 Wetting agent 1, 2 sunscreen 1,5 Water 3,5 Example 3 ingredient Quantity [Wt.%] Aliphatic polycarbonate-polyurethane resin dispersion (MFT: 17°C, solids content: 42%) 54,8 black plastic spheres (d50: 15 µm) 36,8 Black pigment (flame soot) 1,3 Defoamer 0,4 Wetting agent 0,9 sunscreen 1,5 Water 4,3 Example 4 ingredient Quantity [Wt.%] Aliphatic polycarbonate-polyurethane resin dispersion (MFT: 11°C, solids content: 40%) 55,1 black plastic spheres (d50: 12 µm) 36,3 Black pigment (iron oxide) 0,7 Defoamer 0,4 Wetting agent 1,2 sunscreen 1,5 Water 4,8 Test methods

[0028] To determine the coating properties, test specimens are prepared. First, the coating material is prepared by mixing the components according to the example and applied to plastic plates by spraying. The plates are allowed to flash off for 15 minutes and then dried for 30 minutes at 80 °C in a convection oven. The coated, dried plates are then tested. Determination of dry film thickness

[0029] The dry film thickness is determined using the Bykotest 4500 measuring device from Byk-Gardner GmbH. For this purpose, an aluminum plate is glued to the surface of the test specimen before painting. Gloss measurement

[0030] The micro-TRIgloss gloss meter from BYK-Gardener GmbH is used to determine the gloss level. Measurements are taken at an angle of 60° and at an angle of 85°. Determination of the THR value

[0031] The measurement is performed using the CM-3700A measuring device from Konica Minolta. Cross-cut test

[0032] The adhesion of the coatings is tested using a cross-cut test. For this purpose, two strips of six cuts each are applied to the coating on the test specimen at right angles to each other. The cuts extend to the substrate surface. After the cuts are made, the cut area is brushed in a controlled manner, and then, under defined conditions, the adhesive tape is abruptly pulled off. Beiersdorf Tesa-Band 4657 is used as the adhesive tape. The results of the cross-cut test are visually assessed as follows: GT 0 Smooth cut edges, no chipping. GT 1 Up to 5% of the sections have chipped off. GT2 Between 5 and 15% of the sections have chipped off. GT3 Between 15% and 35% of the sections have chipped off. GT 4 Between 35 and 65% of the sections have chipped off. GT 5 Over 65% of the sections have chipped off. Hydrolysis resistance testing

[0033] After preconditioning (48 hours storage at 60 °C), the coated specimens are stored in a climate chamber at 90 °C and ≥ 93% relative humidity for 72 hours. The specimens are then conditioned at room temperature for 60 minutes. Finally, the adhesion of the coating is determined using the cross-cut test. Condensation constant climate test

[0034] After preconditioning (48 hours at 60 °C or 7 days at room temperature), the coated specimens are stored in a climate chamber for 240 hours at 40 °C and ≥ 98% relative humidity. The specimens are then conditioned for 60 minutes at room temperature. Finally, the adhesion of the coating is determined using the cross-cut test. Abrasion test

[0035] The SDL Atlas Electronic Crockmeter M238BB is used to determine the colorfastness of the coating to rubbing. A rubbing finger with an attached rubbing cloth is used for the measurement. Under controlled conditions, the rubbing cloth is rubbed in a straight motion against the surface being tested. The color change of the rubbing cloth due to dye uptake from the sample is then visually assessed using a gray scale. The standard gray scale used here has nine pairs of matte gray and white plates with varying contrast levels. The plate pairs are assigned grades of 1, 1 / 5, 2, 2 / 5, 3, 3 / 5, 4, 4 / 5, and 5. Grade 1 indicates strong abrasion, while grade 5 indicates no or barely visible abrasion. Results

[0036] Table 1, Table 2 and Table 3 show the results of the tests. Table 1: Gloss and Reflection Example 1 2 3 4 Dry film thickness [µm] 131 143 138 135 Gloss level angle 60° 0,0 0,0 0,1 0,0 Gloss level angle 85° 0,0 0,1 0,0 0,1 THR value [%] 1,07 1, 19 1,09 1,12 Table 2: Adhesion (cross-cut test) Example 1 2 3 4 Initial liability [Gt] 0 0 0 0 Liability according - Hydrolysis [Gt] 0 0 0 0 - Condensation constant climate test [Gt] 0 0 0 0 Table 3: Abrasion Example 1 2 3 4 Comparison* abrasion 4 / 5 4 / 5 4 / 5 4 / 5 1 * a standard anti-reflective coating QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2019 / 073210 A1

[0004]

Claims

[1] containing coating material - Containing 20 to 88 wt% of one or more water-dilutable, aliphatic polyurethane resin dispersions with solids contents in the range of 30 to 50%. - Containing 10 to 40 wt% black plastic spheres with a sphere diameter d50 in the range of 9 to 17 µm, as well as - 0.5 to 2 wt.% black pigments, based on the total weight of the coating material. [2] Coating material according to claim 1, characterized by that the coating material has pigment volume concentrations of at least 70%. [3] Coating material according to claim 1 or 2, characterized by , that the coating material continues to contain transparent plastic spheres with sphere diameters d50 in the range of 3 to 10 µm. [4] Coating material according to claim 3, characterized by, that the transparent plastic spheres are contained in quantities of 5 to 20 wt.% based on the total weight of the coating material, whereby the total amount of plastic spheres used remains unchanged in the range of 20 to 40 wt.% based on the total weight of the coating material. [5] Coating material according to any one of the preceding claims, characterized by that the water-dilutable, aliphatic polyurethane resin dispersions have minimum film formation temperatures in the range of 0°C to 20°C. [6] Coating material according to any one of the preceding claims, characterized by that the water-dilutable, aliphatic polyurethane resin dispersions are used in quantities of 40 to 70 wt.% based on the total weight of the coating material. [7] Coating material according to any one of the preceding claims, characterized by, that water-dilutable, aliphatic polyurethane resin dispersions have solids contents in the range of 35 to 45%. [8] Coating material according to any one of the preceding claims, characterized by , that water-dilutable, aliphatic polyurethane resin dispersions are selected from polyurethane resins which have one or more, identical or different, functional groups selected from ester, ether, acrylate, methacrylate and carbonate groups. [9] Coating material according to any one of the preceding claims, characterized by that the black pigments are selected from the group containing carbon black, spinel black, perylene black, iron oxide, manganese oxide, mixed metal oxides and mixtures thereof. [10] Coating material according to claim 9, characterized by that the black pigments are iron oxide, soot, or mixtures thereof. [11] Use of the coating material according to any one of claims 1 to 10 for the production of antireflective coatings on components and devices. [12] Use according to claim 11, characterized by that the anti-reflective coatings are used for optical and electronic devices. [13] Method for producing antireflective coatings on a substrate surface comprising the steps (a) Providing a coating material according to any one of claims 1 to 10, (b) Applying the coating material to the substrate surface by spray application, (c) Allowing the resulting film to air dry at room temperature in the range of 20 to 35°C, (d) Drying at temperatures in the range of 60 to 120°C. [14] Method according to claim 13, characterized by , that in step (a) the coating material is diluted by adding one or more water-miscible solvents. [15] Component coated with an anti-reflective coating made from a coating material according to any one of claims 1 to 10.