MXPA98008852A - Multilayer interference pigment with absorbent central layer - Google Patents

Abstract

The invention concerns a multilayer interference pigment consisting of a central absorbent layer and alternating layers of a material with a low refraction coefficient and a metal or material with a high refraction coefficient on both sides of the central layer. The material with a low refraction coefficient is preferably acrylate and the metal is aluminium or chromium. The absorbent layer consists of a paint system which contains carbon black or chromophoric absorption pigments.

Description

DmrapSRENCTA PIGMENT IN MULTICAPS WITH AN ABSORBENT INTERMEDIATE LAYER DESCRIPTION OF THE INVENTION The invention relates to multilayer interference pigments consisting of alternating layers of a material of low refractive index and of a metal or a material of high refractive index, the core layer is formed from an absorbent material. Multilayer pigments having alternating layers of a high refractive index material and a material of low refractive index are known. They consist predominantly of metal oxides. However, the high refractive index material can also be replaced by a semitransparent metal layer. The metal oxide layers are produced either by a wet method, by precipitation of metal oxide hydrates from a metal salt solution on a substrate material, or by vapor deposition or vacuum bombardment. For example, U.S. Patent 4,434,010 discloses a multilayer interference pigment consisting of a central layer of a reflective material (aluminum) and alternating layers of two transparent materials, dielectrics, of high and low refractive index, e.g. titanium and silicon dioxide, either on one side or the other of the central aluminum layer. In an additional mode of the pigment, REF .: 28555 the layers that follow the central aluminum layer are formed by magnesium fluoride and chromium. This pigment is used for the printing of titles. JP H7-759 (A) discloses a multilayer interference pigment with a metallic luster. It consists of a substrate that is coated with alternating layers of titanium dioxide and silicon dioxide. The substrate is formed from platelets of aluminum, gold or silver or from platelets of mica or glass, which are coated with metals. All types of pigment having a metal layer as the central layer have the disadvantage that each wavelength is reflected from this reflection layer, with the effect that, although a high luster is obtained, the actual interference color it is at the same time masked. The object of the invention is to provide an interference pigment having strong interference colors, a narrow angular dependence of the interference colors and a high hiding power. This object is obtained according to the invention by means of a multilayer interference pigment consisting of a central layer of an absorbent material and alternating layers of a material of low refractive index and of a metal or of a material of high refractive index. , either on one side or the other of the central layer.

This object is also obtained, according to the invention, by a process for preparing the new pigment comprising the steps of: applying a release layer comprising a water-soluble or solvent-soluble material, to a substrate, depositing a Layer system comprising alternating layers of a low refractive index material and of a metal or a high refractive index material, on the release layer, the applied central layer consists of a layer of an absorbent material, - separate the layer system formed of the substrate upon dissolving the release layer and washing and drying the resultant platelet-shaped interference pigment, - heat treating the pigment in a stream of nitrogen at a temperature of 100 to 300 ° C and grinding or milling and classify the treated pigment. The invention also provides for the use of the new pigments for pigment paints, printing inks, plastics and cosmetics and for producing films. The high refractive index material is a metal oxide or mixtures of metal oxides with or without absorbing properties, for example, Ti02, Zr02, Fe203, Fe304, Cr203 or ZnO or a compound of high refractive index, for example, iron titanates, iron oxide hydrates or aluminum suboxides or mixtures and / or mixed phases of these compounds with each other or with other metal oxides. The metal is preferably aluminum, chromium, nickel, a chromium-nickel alloy or silver. Chromium and aluminum are preferred in this context, since they are easy to deposit. In addition, the layers in the present have a reflectivity which is easy to control and a high resistance to corrosion. The metal layers are preferred with respect to the layers of a high refractive index material. The low refractive index material is MgF2 or a metal oxide such as Si02, A1203 or a mixture thereof and may also have absorbent or non-absorbent properties. If desired, the low refractive index material may include alkali metal oxides and alkaline earth metal oxides as constituents. As the material of low refractive index, however, the use of polymers, for example acrylates, is preferred. The monomers used have a molecular weight of 200 to 100 and are available as mono-, di- or triacrylates. In terms of functional groups, they are available as hydrocarbons, polyols, polyethers, silicones or as fluorinated Teflon-like monomers.

These monomers can be polymerized by means of electron beams or UV radiation. The resulting layers have stability at a temperature of up to 250 ° C. The refractive indices of the acrylate layers are in the range of 1.35 to 1.60. Additional details can be found in David G. Shaw and Marc G. Langlois: Use of a new high speed acrylate deposition process to make novel multilayer structures, MRS Conference in San Francisco in 1995; A new high speed process for vapour depositing fluoro and silicone acrylates for reléase coating applications, Conference of the Society of Vacuum Coaters in Chicago, Illinois, 1995. The absorbent intermediate layer consists of a conventional coating system comprising carbon black or absorbent pigments that impart color or mixtures thereof. A preferred coating system, which adheres well to the metal layers, is an acrylate-melamine resin. Alternatively, the absorbent intermediate layer may consist of materials of high or low refractive index containing metals. Examples of these are magnesium fluoride or silicon monoxide containing chromium or titanium monoxide, which likewise contain chromium. These layers are produced by vapor deposition or vacuum bombardment and are of the state of the art.

The density of the absorption layer is between 50 nm and 2 μm. The difference in refractive indexes between a high refractive index layer and a low refractive index layer must be at least 0.1. The layer thickness of the layers of low refractive index is adjusted to values between 20 nm and 700 nm, preferably between 60 nm and 500 nm. The layer thickness of the metal layers is adjusted to a thickness of 5 to 20 nm in order to provide semitransparency. The maximum obtainable reflection that is possible with a multilayer system depends on the number of layers and the refractive indices of the layers: In this formula, nH is the refractive index of the high refractive index layer, nL is the refractive index of the low refractive index layer and p is the number of layers (layer count). This equation is valid for a layer count of 2p + 1. The layer thickness for the maximum reflection is in each case d =? / 4n or a multiple thereof with the wavelength?. The thickness and number of layers depends on the desired effect in terms of interference color and angular dependence of the interference color,? varies within the range of between 400 nm (violet light) to approximately 750 nm (red region). In order to obtain appropriate colors, the layer thickness must be adjusted according to the refractive index of the optically thinner medium. In addition, the new pigments can also be used to produce appropriate pigments, which selectively reflect in regions of attached wavelength (infrared ultraviolet). In precision optical components, for example in the production of mirror layers, beam splitters or filters, layer counts of up to 100 or more are employed. Layer counts of this magnitude are not necessary for the preparation of pigments. The number of layers is usually less than 10. The individual layers are produced according to known techniques by sputtering metals, for example aluminum or chromium or alloys, for example Cr-Ni alloys and metal oxides, for example , titanium oxide, silicon oxide or indium-tin oxide or by thermal vaporization of metals, metal oxides or acrylates. In order to prepare the new pigments preference is given to coating in vacuum strips, as described in U.S. Patent 5,440,446, for the production of high voltage capacitors and in EP 0 733 919 for the production of interference color filters. The substrate used for the interference layer system is a flexible strip of polyethylene terephthalate (PET), other polyesters, polyacrylates, polyethylene (PE) or polypropylene (PP). The release layer that is applied to the substrate in order to allow the interference layer system to separate from the flexible strip after the deposition has been carried out, consists of a water-soluble or solvent-soluble material, example, polyethylene glycol, wax or silicone. The solvent used is water or acetone. In the text below, the application of the interference layers by vapor deposition is described in more detail: In the vapor deposition technique, the substances to be vaporized are heated in a vacuum and vaporized. The vapors are condensed on the cold surfaces of the substrate, to provide the desired thin layers. The vaporization is carried out either in metal containers (tungsten canisters, molybdenum or tantalum metal sheet), which are heated directly by the passage of a current or by bombardment with electron beams. The interference layer system can be prepared by employing a conventional strip vapor deposition unit. The vapor deposition unit consists of customary components, such as vacuum boiler, vacuum pump system, pressure measurement and control units, vaporizer devices, such as resistance vaporizers (cans) or vaporizers electrons, a layer thickness measurement and control system, a device for establishing the defined pressure conditions and a gas entry and regulation system for oxygen. The technique of high vacuum vapor deposition is described in detail in Vacuum-Beschichtung, volumes 1-5; Editors Frey, Kienel and Lóbl, VDI Verlag 1995. The application of the layers by the technique of sputtering is as follows: In the case of the technique of sputtering or in the case of atomization of the cathode, a gas discharge (plasma) is ignited between the substrate and the coating material (target) which is in the form of plates. The coating material is bombarded with high energy ions from the plasma, for example argon ions and by this it is subjected to abrasion or atomization. The atoms and molecules of the atomized coating material are deposited on the substrate and form the desired thin layer. Metals or alloys are particularly suitable for sputtering techniques. They can be atomized at comparatively high speeds, especially in the process called DC Magnetron.

Compounds such as oxides or sub-oxides or mixtures of oxides can also be atomized by employing high-frequency sputtering. The chemical composition of the layers is determined by the composition of the coating material (objective). However, it can also be influenced by the addition of substances to the gas that forms the plasma. Layers of oxide or nitride, in particular, are produced by the addition of oxygen or nitrogen to the gas space. The structure of the layers can be influenced by appropriate measures, such as bombardment of the culture layer or growth by plasma ions. The technique of sputtering is also described in Vacuum-Beschichtung, volumes 1-5; Editors Frey, Kienel and Lóbl, VDI Verlag 1995. The principle of the technique of applying metal and polymeric layers is described in U.S. Patent No. 5,440,446 and EP 0 733 and is carried out as follows: The entire coating unit is located inside a conventional vacuum chamber 1. A strip 3 of polyester is wound onto an assortment roll 2 and already has a release layer on one side. The polyester strip 3 is guided via a rotating drum 4 and wound on the acceptor roller 5. The rollers 6 and 7 serve as tension and guide rollers. The strip passes through the metallization station 8, where a semitransparent metal layer is deposited by vacuum vapor deposition or sputtering. Then, the strip passes through the high-speed vaporizer 9. In the vaporizer there is a gaseous acrylate monomer which deposits as a thin layer on the metal layer which is located on the strip of the substrate. Then, the strip passes through an irradiation station 10, where it is irradiated with electrons or with ultraviolet light. The irradiation initiates the polymerization of the acrylate monomer. Subsequently, the strip passes through the second metallization station 11. Thereafter the strip, which is coated with two semitransparent metal layers and an acrylate layer therebetween and after passing through the tension roller 7, is rolled up and the absorbent metal layer is applied in a coating unit by conventional strips to the outside of the vacuum unit.

The absorbent intermediate layer is applied, for example, by the application of a conventional coating system comprising carbon black or absorption pigments that impart color or mixtures thereof, by means of a roll with geometric figures or by spraying or coating with blade or spatula. Other transfer and printing techniques are also appropriate for this stage of the process. By adjusting the thickness of the intermediate layer and the concentration of the printing ink, it is also possible to make a distinction between the intermediate low-transfer layers and the intermediate layers which are completely absorbent. The strip subsequently passes through the vacuum unit for a second time, where the metal layers and the acrylate layer are deposited in the same manner as during the first step. For a 7-layer system consisting of a central absorption layer and two layers of metal and an acrylate layer on either side of the central layer, two steps are required through the vacuum coating unit, the absorbent intermediate layer is applied after the first step. After the coating operation, the multiple coating is separated by dissolving the release layer in a water bath, possibly at a relatively high temperature or in a solvent, possibly at a relatively high temperature, by brushing, scraping or preferably by washing. Where acrylates are used as the low refractive index material, it is necessary to grind the pigment at relatively low temperatures in the range of 90 to 273 ° K. The following examples are intended to illustrate the invention.

Example 1 An interference pigment consisting of 7 layers, is produced by alternative vapor deposition of chromium or aluminum and acrylate on a polyester strip in a vacuum vapor deposition unit according to Figure 1. The polyester strip It is coated with a release layer of stearin. Following the application of a layer of chromium, an acrylate layer and an aluminum layer, the strip is separated from the unit and the absorbent intermediate layer is applied to the aluminum layer by coating with a knife or spatula in a coating unit by conventional stripes. This central layer consists of an acrylate-melamine resin curable by ultraviolet light containing carbon black in dispersed form. Then, the strip passes a second time through the vacuum unit, where the metal layers and the acrylate layer are deposited in the same manner as during the first step. Layer structure of pigment Layer no. Material Layer thickness, nm 1 chromium 12 2 acrylate 275 3 aluminum 15 4 resin layer with 1500 carbon black 5 aluminum 15 6 acrylate 275 7 chromium 12 The layer system is separated from the substrate strip by using acetone, washed with acetone and dried. Subsequently, the resulting pigment is heated to a temperature of 300 ° C, in a stream of nitrogen, for 90 minutes and then crushed to a particle size of 20 to 40 μm in a Netsch mortar mill for 30 minutes, mixed with dry ice of carbon dioxide at a temperature of -5 to -10 ° C.

Example 2 An interference pigment consisting of 7 layers is produced by alternating vapor deposition of chromium and acrylate on a strip of polyethylene terephthalate (PET) in a vacuum vapor deposition unit according to Figure 1. The strip of PET is coated with a release layer of stearin. Following the application of two layers of chromium and an acrylate layer, the strip is separated from the unit and the absorbent intermediate layer is applied to the second chrome layer by knife or spatula coating in a conventional strip coating unit. This central layer consists of an acrylate-melamine resin curable by UV light, which contains red pigment in dispersed form. Then, the strip passes through the vacuum unit for a second time, where the metal layers and the acrylate layer are deposited in the same manner as during the first step.

Structures of pigment layers No. layer material Layer thickness, nm 1 chrome 10 2 acrylate 350 3 chrome 11 4 resin layer with 950 pigment red chrome 10 6 acrylate 350 7 chrome 10 The layer system is separated from the substrate strip when acetone is used, it is leached with acetone and dried. Subsequently, the resulting pigment is heated to a temperature of 300 ° C in a stream of nitrogen for 90 minutes and then crushed to a particle size of 20 to 40 μm, in a Netsch mortar mill for 30 minutes, mixed with dry ice of carbon dioxide at a temperature of -5 to -10 ° C.

Example 3 An interference pigment consisting of 7 layers is produced by alternative vapor deposition of chromium and aluminum and magnesium fluoride on a polyethylene terephthalate film. The central layer (absorption layer), which consists of a black material, is produced by vapor deposition of a mixture of chromium and silicon dioxide. The starting material used is a mixture of silicon dioxide and chromium, which is marketed under the trade designation Schwarz A Pulverpatinal® by the company Merck KGaA.

The vapor deposition is carried out in a high vacuum steam deposition unit A 700 Q from the company Leybold AG.

Structure of pigment layers No. layer material Layer thickness, nm 1 Cr 5 2 MgF2 453 3 Al 10 4 Si02 / Cr 90 5 Al 10 6 MgF2 453 7 Cr 5 The layer system is separated with acetone from the film, washed with acetone and dried and ground or ground in a Netsch mortar mill for 30 minutes. A pigment having an average particle size of 40 μm is obtained. The reflection spectrum is shown in Figure 2.

Example 4 An interference pigment consisting of five layers is produced by alternative vapor deposition of chromium and magnesium fluoride on a polyethylene terephthalate film. The central layer (absorption layer), which consists of a black material, is produced by vapor deposition of a mixture of chromium and silicon dioxide. The starting material used is a mixture of silicon dioxide and chromium which is marketed under the trade designation Schwarz A Pulverpatinal® by the company Merck KGaA. The vapor deposition is carried out in a high vacuum steam deposition unit A 700 Q from the company Leybold AG.

Structure of pigment layers No. layer material Layer thickness, nm 1 Cr 5 2 MgF2 453 3 Si02 / Cr 90 4 MgF2 453 5 Cr 5 The layer system is separated with acetone from the film, washed with acetone and dried and ground in a Netsch mortar mill for 30 minutes. A pigment having an average particle size of 40 μm is obtained.

The reflection spectrum is shown in Figure 3.

It is noted that, in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (17)

1. Claims 1. A multilayer interference pigment, characterized in that it consists of a central absorbent layer and alternating layers of a material of low refractive index and of a metal or a material of high refractive index either on one side or the other of the central layer.
2. 2. The interference pigment according to claim 1, characterized in that the material of low refractive index is MgF2, a metal oxide or a polymer.
3. 3. The interference pigment according to claim 2, characterized in that the polymer is an acrylate.
4. 4. The interference pigment according to claim 2, characterized in that the metal oxide is Si0, A1203 or a mixture thereof.
5. 5. The interference pigment according to claim 1, characterized in that the metal is aluminum, chromium, nickel, a Ni-Cr alloy or silver.
6. 6. The interference pigment according to claim 1, characterized in that the high refractive index material is Ti02, Zr02, Fe203, Cr03, ZnO or a mixture of these oxides or is an iron titanate, a titanium suboxide or a mixture or mixed phase of these compounds.
7. 7. The interference pigment according to claim 1, characterized in that the central absorbent layer consists of a coating system comprising carbon black, absorption pigments that impart color or mixtures thereof.
8. 8. A process for the preparation of the interference pigment according to claims 1 to 7, characterized in that: a release layer comprising a water-soluble or solvent-soluble material is applied to a substrate, a layer system that it comprises alternating layers of a low refractive index material and a metal or a high refractive index material is deposited on the release layer, the central layer deposited is a layer of an absorbent material, the layer system formed is it separates from the substrate by dissolving the release layer and the resultant platelet-shaped interference pigment is washed and dried, the pigment is subjected to heat treatment at a temperature of 100 to 300 ° C, in a stream of nitrogen and - the treated pigment is ground and sorted.
9. 9. The process according to claim 8, characterized in that the material of low refractive index is MgF2, a metal oxide or a polymer.
10. 10. The process according to claim 9, characterized in that the polymer is an acrylate.
11. 11. The process according to claim 9, characterized in that the metal oxide is SiO2, A1203 or a mixture thereof.
12. 12. The process according to claim 8, characterized in that the metal is aluminum, chromium, nickel, a Ni-Cr alloy or silver. The process according to claim 8, characterized in that the high refractive index material is Ti02, Zr02, Fe203, Cr203, ZnO or a mixture of these oxides or is an iron titanate, a titanium suboxide or a mixture or mixed phase of these compounds. The process according to claim 8, characterized in that the central absorbent layer consists of a coating system comprising carbon black, absorption pigments that impart color or mixtures thereof. 15. The pigments according to claims 1 to 7, characterized in that they are used in pigment paints, printing inks, plastics and cosmetics. 16. The pigments according to claim 15, characterized in that they are used as mixtures with conventional pigments and with other special effect pigments. 17. The pigment according to claims 1 to 7, characterized in that it is used in paints, printing inks, plastics and cosmetics, which have been pigmented therewith.