JP2013018987A - Interference pigment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new interference pigment.SOLUTION: The interference pigment is based on low-refractive-index transparent flake-type substrates having a high-refractive-index coating that comprises TiOhaving a thickness of 20 to 200 nm and an optional outer protective layer. The present invention also relates to the use of the pigment in paints, coatings, printing ink, printing ink for securities, plastics, button pastes, ceramic materials and glass, for coloring seeds, or as dopants for laser marking on plastics and paper sheets, as additives for laser welding on plastics, as additives for coloring in a field of foods and pharmaceutical drugs, for use in cosmetic formulations, or for preparation of pigment compositions and dry preparations. The standard deviation of the thickness of the base material is equal to or less than 15% with respect to the average thickness. The substrates are formed of SiO, AlO, natural or synthetic mica, or glass.

Description

  The invention relates to interference pigments with strong color shifts based on flaky transparent low refractive index substrates and their laser marking of plastics and paper, especially in paints, coatings, printing inks, plastics It relates to use as a dopant, as an additive in the food and pharmaceutical fields, and in cosmetic formulations.

  Glossy or effect pigments are used in many areas of the industry, especially in automotive finishes, decorative coatings, plastics, paints, printing ink areas and cosmetic formulations.

  Because of its color function, luster pigments that exhibit a viewing angle dependent color change between multiple interference colors are of particular interest for automotive finishing and forgery prevention of securities.

  Mineral-based pearl luster pigments are particularly important. Pearl luster pigments are made by coating an inorganic flaky support with a high refractive index, usually oxide layer. These pigment colors are caused by wavelength selective partial reflection and interference of light reflected or transmitted at the medium / oxide or oxide / substrate interface.

  The interference color of these pigments is determined by the thickness of the oxide layer, for example, the hue of green pigment (in the optical sense) has a maximum reflection at an optical thickness of about 500 nm in the visible wavelength range. Generated by the resulting single high refractive index layer. This wavelength is perceived as green by the human eye. However, in the case of the first order maximum value, the intensity curve is so wide that too much light is reflected over the entire visible light region, giving the human eye a very bright, rather colorless impression.

According to the known rules of the optical properties of the thin layer, in particular from the coating of the optical components, the arrangement of several layers with alternating high and low refractive indices gives a simple reflected light intensity. Significant increase compared to one layer. Therefore, when the TiO ₂ —SiO ₂ —TiO ₂ layer system is applied to the mica particles, the intensity of the reflected light is increased by about 60% compared to the TiO ₂ single layer system. Therefore, since the profile of light reflected by interference is significantly stronger, a high density and bright reflected color is expected for this type of multilayer system. This type of pigment is described in German Offenlegungsschrift 19 196 569 A1.

  According to the prior art, green interference pigments are disclosed, for example based on mica flakes. Mica flakes generally have a very wide scattering of layer thickness and thus have a neutral behavior with respect to interference colors. Pearl luster pigments with a single high refractive index coating of mica thus represent single layer optics, ie the interference color is determined solely by the layer thickness of the high refractive index metal oxide layer. Therefore, mica / metal oxide green pigments have very limited color design tolerances. Furthermore, the mica particles are uneven on the surface due to the structure of these layers, which causes scattering, thereby reducing the transparency and color quality of the product. In addition, mica exhibits a somewhat strong gray / brown mass tone. This property further reduces transparency and adversely affects the color absorbed by the adaptive medium.

  The object of the present invention is therefore interference pigments, in particular green interference pigments, in particular high transparency and pure white masstone, and strong color flops with excellent special color effects such as green, blue, etc. An interference pigment is provided.

Examples of interference pigments, their production and use, pigment compositions containing interference pigments and dry preparations include:
1) An interference pigment based on a low refractive index transparent flaky substrate, characterized by having a high refractive index coating consisting of TiO ₂ with a layer thickness of 20 to 200 nm and optionally an external protective layer.
2) The interference pigment according to 1), wherein the standard deviation of the thickness of the substrate flakes is ≦ 15% with respect to the average thickness.
3) The interference pigment according to 1) or 2), wherein the transparent flakes are SiO ₂ flakes, Al ₂ O ₃ flakes, natural or synthetic mica flakes or glass flakes.
4) The interference pigment according to 3), wherein the transparent flakes are SiO ₂ flakes.
5) The interference pigment according to any one of 1) to 4), wherein TiO ₂ is a rutile modification.
6) The coating of the substrate is carried out by a wet chemical method by hydrolytic decomposition of a metal salt in an aqueous medium, or by thermal decomposition by a CVD method or a PVD method. ) A method for producing the interference pigment according to any one of the above.
7) Paints, button pastes, coatings, printing inks, securities printing inks, printing inks for secure printing, plastics, ceramic materials, dopants for laser marking of plastics and paper for coating of seeds in glass, plastics Use of the interference pigments according to 1) for the preparation of pigment compositions and dry preparations in cosmetic formulations as additives for laser welding, as coloring additives in the food and pharmaceutical fields.
8) A pigment composition comprising one or more binders, optionally one or more additives and one or more interference pigments according to 1).
9) Dry preparations such as pellets, granules, chips, briquettes and the like comprising the interference pigment according to 1).

Surprisingly, certain transparent low index flakes such as SiO ₂ flakes coated with a thin TiO ₂ layer give a strong, eg green color impression, and at the same time an exceptionally strong color flop It was found to show. As always in the case of interference colors, the color shift does not necessarily occur from a long wavelength color to a short wavelength color, but may occur in the opposite direction, for example from a relatively short wavelength green to a relatively long wavelength red. . This is achieved by coating a thin flake, for example a SiO ₂ flake, with a TiO ₂ layer whose thickness closely matches the thickness of the flake.

  Compared to a single coated pigment, for example of green pigment, based on mica, the pigment according to the invention exhibits the following properties:

Excellent transparency in media Pure white masstone Strong, e.g. green interference color Very bright luster Strong color shift If the substrate and coating layer thicknesses are matched properly, flat wavelengths are flattened out of long wavelength at steep viewing angles It is possible to realize a color shift from green to red, especially for green interference pigments, to short wavelength colors at a reasonable viewing angle.

  In addition to these properties, the pigments according to the invention are superior to known interference pigments due to the following characteristics:

Strong shine effect Green adjustable yellow / blue shades The shades interfere by matching the TiO ₂ layer thickness and by selecting transparent flakes of varying thickness, eg SiO ₂ flakes It can be changed over a wide range without losing the impression of the pigment.

Accordingly, the present invention provides a highly chromatic, especially green flake-like transparent low refractive index substrate having a high refractive index coating comprising TiO ₂ having a layer thickness of 20-200 nm and optionally an external protective layer. The present invention relates to an interference pigment as a base.

  The invention further relates to plastic laser welding additives, plastics and paper for coating of seeds of interference pigments according to the invention in paints, coatings, printing inks, plastics, button pastes, ceramic materials, glass. For use as a dopant in laser marking or laser welding, as a coloring additive in the food and pharmaceutical fields and in particular in cosmetic formulations. The pigments according to the invention are furthermore suitable for the preparation of pigment compositions and for the preparation of dry preparations such as granules, chips, pellets, briquettes and the like. The dry preparation is particularly suitable for printing inks and cosmetic formulations.

Suitable base substrates for the interference pigments according to the invention are substrates having a refractive index of <1.9, for example flaky SiO ₂ flakes as described in WO 93/08237. In addition to the SiO ₂ flakes, any flaky transparent substrate known to those skilled in the art is suitable, for example Al ₂ O ₃ flakes and glass flakes, natural or synthetic mica, and flaky plastic particles. ing. A particularly preferred substrate is SiO ₂ flake. Certain properties, such as adjustable hue and in particular its angular dependence, are critically influenced by a defined average thickness with a narrow thickness distribution.

  Therefore, the standard deviation of the substrate flake thickness should be ≦ 15%, preferably ≦ 10%, particularly preferably ≦ 6% with respect to its average thickness.

  In the present invention, the average thickness and standard deviation are defined as follows.

Average thickness (calculated value) = (sum of all thickness values) / (number of measurements)
The standard deviation is a 66% percent deviation of all individual measurements relative to the calculated average thickness.

  The dimensions of the base substrate are not critical per se and can be adapted to the particular application. In general, the flaky transparent substrate has an average thickness between 0.02 and 2 μm, preferably between 0.1 and 1 μm, in particular between 0.2 and 0.8 μm. The other two dimensions are usually between 1 and 450 μm, preferably between 2 and 200 μm, in particular between 5 and 500 μm, most preferably between 5 and 60 μm.

  Again, in order to achieve a high density color effect, for example a green or blue effect, with an angle-dependent hue, it is important that the average thickness of the individual flakes is within a standard deviation of ≦ 15%. is there.

  The aspect ratio (diameter / thickness ratio) of the substrate is preferably 1-1000, in particular 3-500, particularly preferably 5-200.

The thickness of the TiO ₂ layer and the substrate is critical to the optical properties of the pigment. The layer thickness must be set accurately and matched to the average thickness of the substrate flakes. The thickness of the TiO ₂ layer is 20 to 200 nm, preferably 50 to 180 nm, in particular 70 to 160 nm.

The pigments according to the invention can be more easily produced by producing a high refractive index TiO ₂ interference layer having a precisely defined thickness and a smooth surface on a finely ground flaky substrate. . TiO ₂ can be either rutile or anatase. TiO ₂ is preferably a rutile modification. SiO ₂ flakes coated with a rutile layer are particularly preferred.

Suitable low refractive index substrates are all inorganic and organic transparent materials that can be produced in the form of finely ground flakes with a narrow thickness distribution and have a refractive index of ≦ 1.8. Suitable organic substrates are, inter alia, polymers such as polyester (eg PET), polycarbonate, polyimide, polymethacrylate and the like. Particularly preferred inorganic substrates are interference pigments based in particular on SiO ₂ , Al ₂ O ₃ , flaky single crystals and glass flakes, which may also be coated with a thin SiO ₂ layer.

  The metal oxide layer is preferably applied by a wet chemical method, and it is possible to use a wet chemical coating method developed for the production of pearlescent pigments. This type of process is described, for example, in German Patent Publication No. 1467468, German Patent Publication No. 1959988, German Patent Publication No. 20007566, German Patent Publication No. 2214545, German Patent Publication No. 2215191, German Patent Publication No. 2244298, Germany Patent Publication No. 2313331, German Patent Publication No. 2522572, German Patent Publication No. 3137808, German Patent Publication No. 3137809, German Patent Publication No. 3151343, German Patent Publication No. 3151354, German Patent Publication No. 3151355, German Patent It is described in the publication 3211602, the German patent publication 3230517 or even in the patent literature and other literature known to those skilled in the art.

  In the case of wet coating, the substrate particles were suspended in water and the metal oxide or metal oxide hydrate was selected to precipitate directly on the flakes without causing a significant second precipitation. Species or hydrolyzable titanium salts are added at a pH suitable for hydrolysis. Usually the pH is kept constant by simultaneous metering of base and / or acid. The pigment can then be separated, washed, dried at 50-150 ° C., calcined for 0.1-3 hours if desired, and the calcination temperature can be optimized for the individual coatings present. In general, the calcination temperature is between 250 and 1000 ° C, preferably between 350 and 950 ° C.

  Furthermore, the coating can also be carried out by gas phase coating in a fluidized bed reactor, for example similarly using the methods proposed in EP 0045851 A1 and EP 0106235 A1 for the production of pearlescent pigments. Is possible.

  The hue of the pigment can be varied within very wide limits while maintaining the interference effect, for example the green interference effect, by variously selecting the coating amount or the layer thickness obtained therefrom. An angle-dependent color shift, for example from green with steep vision to red with flat viewing angle, is substantially maintained in this case. In particular, the hue variation is related to the yellow and / or blue component. Fine adjustment for a hue can be obtained by bringing it closer to the desired color with the naked eye or under the control of the measurement technique, rather than selecting a pure amount.

In order to increase light, water and climate stability, it is often desirable to topcoat or post-treat the finished pigment depending on the application area. Suitable topcoats or post-treatments are, for example, the methods described in German Patent No. 2215191, German Patent Publication No. A3151354, German Patent Publication No. A32335017 or German Patent Publication No. A3334598. This overcoat further increases the chemical stability and simplifies the handling of the pigment, especially the mixing into various media. In order to increase the wettability, dispersibility and / or compatibility with the medium used, a functional coating of Al ₂ O ₃ or ZrO ₂ or mixtures or mixed phases thereof can be applied to the pigment surface. Also, for example, European Patent No. 0090259, European Patent No. 063459, International Publication No. 99/57204, International Publication No. 96/32446, International Publication No. 99/57204, US Pat. No. 5,759,255, US Pat. No. 5,571,851. International Publication No. WO 01/92425, or J. Org. J. et al. Ponjee, Philips Technical Review, Vol. 44, No. 3, p. 81 et seq. H. Harding, J.H. C. Berg, J. et al. Adhesion Sci. Technol. 11, Vol. 4, No. 4, pages 471 to 493, for example, an organic material or an organic / inorganic mixture with silane can be coated.

  The interference pigments according to the invention are simple and easy to handle. The pigment can be incorporated into the application system by simple stirring injection. Complex grinding and dispersion of the pigment is not necessary.

  The interference pigments according to the invention combine high gloss, high transparency and pure white masstone, so that they are particularly effective in media for various applications without significantly affecting the color to be absorbed. An effect can be obtained.

Needless to say, interference pigments for various applications also include, for example, transparent and opaque, organic dyes such as white, colored and black pigments, organic pigments or other pigments, and flaky iron oxides, organic pigments, holography It can also be used advantageously in the form of a mixture with conventional transparent colored and black luster pigments based on pigments, LCP (liquid crystal polymers), mica coated with metal oxides and SiO ₂ flakes. The interference pigment can be mixed in any ratio with commercially available pigments and fillers.

  In various applications, the pigments according to the invention can also be used, for example, Timiron (R), Scopearl (R) (BASF AG), Chroma-Flair (R) (Flex Products Inc.), BiOCl pigments, e.g. from Eckert It can also be combined with any other type of colorant, such as pearl essences or metal pigments, for example organic and / or inorganic absorbing pigments and dyes, multilayer interference pigments. There are no restrictions on the mixing ratio and concentration.

  The pigments according to the invention are compatible with various, preferably color systems from the areas of paints, coatings and printing inks. For example, for the production of printing inks for gravure printing, flexographic printing, offset printing, offset overprint varnishing, a variety of binders such as BASF, Marabu, Proll, Sericol, Hartmann, Gebr. Particularly suitable are water-soluble grades sold by Schmidt, Sicpa, Aarberg, Siegberg, GSB-Wahl, Fallmann, Ruco or Coates Screen INKS GmbH. The printing ink may be water based or solvent based. The pigments are furthermore suitable for laser marking of paper or plastics and for the coloring of agricultural fields such as greenhouse sheets and tent awnings.

  The interference pigments according to the present invention are surface coatings, printing inks, plastics, agricultural sheets, seed coatings, food colorings, button pastes, drug coatings or lipsticks, nail varnishes, compact powders, shampoos, soaps, loose powders. And can be used for coloring cosmetic formulations such as gels. The concentration of the pigment mixture in the application system to be colored is generally between 0.1 and 70% by weight, preferably between 0.1 and 50% by weight, in particular between 0.5 and 0.5%, based on the total solids content of the system. Between 10% by weight. This generally depends on the particular application. In the plastic containing the green interference pigment according to the invention, a particularly strong sparkling effect is obtained, preferably in an amount of 0.01 to 50% by weight, in particular 0.1 to 7% by weight.

  In the surface coating field, interference pigments are also used in 3-coat systems in amounts of 0.1 to 20% by weight, preferably 1 to 10% by weight, especially in automotive finishes.

  For surface coatings, the interference pigments according to the invention have the advantage that the target gloss is achieved with a one-coat finish (primary or two-coat primer). For example, a finish comprising a pigment according to the invention compared to a finish containing a mica-based multilayer pigment or a conventional pearlescent pigment based on a substrate having a wide distribution of thickness instead of the pigment according to the invention Shows a brighter and deeper effect and a stronger gloss effect.

The interference pigments according to the invention can also be used advantageously in decorative and care cosmetics. Use concentrations range from 0.01% by weight in shampoo to 100% by weight in the case of loose powder. Interference pigments and spherical fillers, in the case of a mixture of SiO ₂ for example, the concentration in the formulation may be 0.01 to 70 wt%. For cosmetic products such as nail varnishes, compact powders, shampoos, loose powders and gels, they are characterized by particularly interesting color effects and strong color shifts. The color flop effect in nail polish can be significantly increased with the pigments according to the invention compared to conventional nail polish.

  In addition, the pigments according to the invention can be used in bath additives, toothpastes, and in food finishes, for example in the mass coloring and / or coating of boiled confectionery, for example in wine gums, confections such as jelly babies, pralines, licorice candy. It can be used for sticks, candies, bramanges, effervescent soft drinks, soda, etc. or for example as a coating on standard and coated tablets in the pharmaceutical field.

  The pigments according to the invention can furthermore be mixed with commercially available fillers. Fillers that may be mentioned are, for example, natural and synthetic mica, nylon powder, pure or filled melamine resin, talc, glass, kaolin, aluminum, magnesium, calcium, zinc oxide or hydroxide, BiOCl, sulfuric acid Barium, calcium sulfate, calcium carbonate, magnesium carbonate, carbon, and physical or chemical combinations of these materials. There is no restriction on the particle shape of the filler. It can be, for example, flaky, spherical or acicular according to the requirements.

  The pigments according to the invention can of course be combined in the formulation with cosmetic raw materials and any type of auxiliaries. These include, among others, oils, fats, waxes, film formers, preservatives, and, for example, thickeners, bentonite, hectorite, silicon dioxide, Ca silicate, gelatin, high molecular weight carbohydrates and / or surfactants. There are generally auxiliaries that determine the technical properties such as rheological additives such as auxiliaries.

  Formulations comprising interference pigments according to the invention can belong to the lipophilic, hydrophilic or hydrophobic type. In the case of heterogeneous formulations with separated aqueous and non-aqueous phases, the pigments according to the invention may be present in each case only in one of the two phases or distributed over both phases. .

  The pH value of the formulation can be between 1 and 14, preferably between 2 and 11, particularly preferably between 5 and 8.

  No limit is set for the concentration in the formulation of interference pigments according to the invention. They can be between 0.001 (rinse product, eg, shower gel) and 100% (eg, glossy articles for a particular application), depending on the application. The pigments according to the invention may also be combined with cosmetic active ingredients. Suitable active ingredients are, for example, insect repellents, UV A / BC protection filters (eg OMC, B3 and MBC), anti-aging active ingredients, vitamins and their derivatives (eg vitamins A, C, E etc.), self-tanning agents ( For example, DHA, erythrulose, among others), and other cosmetic active ingredients such as bisabolol, LPO, ectoine, Emblica, allantoin, bioflavonoids, and derivatives thereof.

  In binder-based coloring, for example for printing inks for surface coating and gravure printing, offset printing or screen printing, or as precursors for printing inks, in the form of highly colored pastes, granules, pellets, etc. The use of interference pigments according to the invention has proven particularly suitable. This pigment is generally incorporated into the printing ink in an amount of 2 to 35% by weight, preferably 5 to 25% by weight and in particular 8 to 20% by weight. The offset printing ink may contain up to 40% by weight of this pigment. The precursor of the printing ink contains, for example in the form of granules, as pellets, briquettes etc., up to 98% by weight of the pigment according to the invention in addition to binders and additives. Printing inks containing pigments according to the present invention exhibit a purer hue, in particular a green hue, than those containing conventional effect pigments. The thickness of the particles of the interference pigments according to the invention is relatively small and thus provides particularly good printability.

  The interference pigments according to the invention further comprise the preparation of flowable pigment compositions and dry preparations, in particular printing inks, comprising one or more pigments according to the invention, binders and optionally one or more additives. Suitable for The invention therefore relates to a formulation comprising an interference pigment according to the invention.

  In particular, the present invention includes an interference pigment according to the present invention, an absorbent, an astringent, an antibacterial substance, an antioxidant, an antiperspirant, an antifoaming agent, an anti-dandruff active ingredient, an antistatic agent, a binder, a biological Additive, bleaching agent, chelating agent, deodorant, emollient, emulsifier, emulsion stabilizer, dye, wetting agent, film forming agent, odor substance, flavor substance, insect repellent, antiseptic, anticorrosive, cosmetic oil, At least one component selected from a solvent, an oxidizing agent, a vegetable ingredient, a buffer substance, a reducing agent, a surfactant, a high-pressure gas, an opacifier, an ultraviolet filter and an ultraviolet absorber, a denaturing agent, a viscosity modifier, a fragrance, and a vitamin Contain formulation.

  The following examples are intended to illustrate the invention without, however, limiting it.

Example 1
Interference pigment whose color changes from green to red with high concentration 100 g of SiO ₂ flakes (particle size 5 to 50 μm, average thickness 450 nm, thickness standard deviation: about 5%) are suspended in 2 l of deionized water. And heat to 80 ° C. with vigorous stirring. A solution of 12 g SnCl ₄ × 5H ₂ O and 40 ml hydrochloric acid (37%) in 360 ml deionized water is metered into this mixture at pH 1.6. Subsequently, a volume of 460 ml of TiCl ₄ solution (400 g of TiCl ₄ / l) is metered in at a pH of 1.6. During the addition of SnCl ₄ × 5H ₂ O solution and TiCl ₄ solution, the pH is kept constant with NaOH solution (32%). The pH is subsequently adjusted to 5.0 using sodium hydroxide solution (32%) and the mixture is stirred for a further 15 minutes.

  For post-treatment, the pigment is filtered off, washed with 20 l of deionized water, dried at 110 ° C. and calcined at 850 ° C. for 30 minutes to give a high concentration of bright green, strong gloss and high transparency. Get. When changed to a flat viewing angle, the pigment exhibits a red interference color.

Examples of use Example A: Shower gel Phase A

  Phase B

  Phase C

Preparation For phase A, the interference pigment is stirred in water. Disperse gradually in Keltrol T with stirring and stir until it dissolves. Add phases B and C in order and stir slowly until everything is evenly dispersed. Adjust the pH to 6.0-6.4.

  Example B: nail polish

Preparation The interference pigment is weighed together with the varnish base, mixed thoroughly manually with a spatula and subsequently stirred at 1000 rpm for 10 minutes.

Example C: Surface coating system 90% by weight Hydrogla BG / S Colorless (aqueous varnish from Ernst Diego GmbH)
10% by weight of green interference pigment from Example 1 coated by spraying at 80 ° C. 5 minutes pre-drying at 80 ° C. 20 minutes baking at 180 ° C. Example D: 5 g of polystyrene granules of 1 kg plastic in a rotary mixer Wet uniformly with the agent. Then 42 g of green interference pigment from Example 1 is added and mixed for 2 minutes. These granules are converted into stepped plates having dimensions of 4 × 3 × 0.5 cm under normal conditions in an injection molding machine. This stepped plate is characterized by its strong shine effect.

Example E: Confectionery Colored Raw Product: Effervescent White Sweet Spray Solution:
Spray 94% Kaul shellac alcohol solution 6% green interference pigment effervescent sweetness from Example 1 with interference pigment / shellac solution until the desired color deposition is achieved. Subsequently, drying using cold air is possible.

Claims (9)

An interference pigment based on a low refractive index transparent flaky substrate with a high refractive index coating of TiO ₂ having a layer thickness of 20-200 nm,
The standard deviation of the thickness of the transparent flaky substrate is ≦ 15% with respect to its average thickness,
An interference pigment, wherein the transparent flaky substrate is made of SiO ₂ , Al ₂ O ₃ , natural or synthetic mica, or glass.   The interference pigment according to claim 1, further comprising an external protective layer. The interference pigment according to claim 1, wherein the transparent flaky substrate is made of SiO ₂ . The interference pigment according to claim 1, wherein TiO ₂ is a rutile modification.   5. The substrate according to claim 1, wherein the coating of the substrate is performed by a wet chemical method by hydrolytic decomposition of a metal salt in an aqueous medium, or by thermal decomposition by a CVD method or a PVD method. A method for producing the interference pigment according to any one of the above.   Paints, button pastes, coatings, printing inks, securities printing inks, printing inks for secure printing, plastics, ceramic materials, dopants for laser marking of plastics and paper in glass, seeds for plastics, plastic lasers 5. A pigment composition and a dry preparation according to any one of claims 1 to 4 for the preparation of pigment compositions and dry preparations in cosmetic formulations as welding additives, food and pharmaceutical coloring additives. Use of interference pigments.   A pigment composition comprising one or more binders and one or more interference pigments according to any one of claims 1 to 4.   The pigment composition according to claim 7, further comprising one or more additives.   A dry preparation selected from the group consisting of pellets, granules, chips and briquettes, comprising the interference pigment according to any one of claims 1 to 4.