WO1998022539A1

WO1998022539A1 - Uv light absorber, a matrix containing said absorber, method for filtering out ultraviolet radiation and use of uv light absorbers

Info

Publication number: WO1998022539A1
Application number: PCT/EP1997/006066
Authority: WO
Inventors: Werner Hoheisel; Reimer Holm
Original assignee: Bayer Aktiengesellschaft
Priority date: 1996-11-15
Filing date: 1997-11-03
Publication date: 1998-05-28
Also published as: EP0946651A1; JP2001510496A; AU7301498A

Abstract

The present invention relates to a novel, substantially improved UV radiation absorber, which can be used in a wide ultraviolet spectral region (UVA and UVB, that is, a wavelength of approximately 250 nm to 400 nm), a matrix containing said UV light absorber, a method for protection against UV radiation and the use of UV light absorbers to reduce UV radiation harming synthetic materials, contents in transparent containers and sun protective agents in the field of cosmetics.

Description

UV light absorber, a matrix containing this UV light absorber, a method for filtering out ultraviolet radiation and the use of UV light absorbers

The present invention relates to a new, significantly improved UV light absorber, which acts for a broad ultraviolet spectral range (UVA and UVB, ie a wavelength of about 250 nm to 400 nm), a matrix containing this UV light absorber, a method for Protection against ultraviolet radiation and the use of UV light absorbers to mitigate harmful UV radiation for plastics, for the contents of transparent containers and for sunscreens in the cosmetics sector

It is known that UV radiation, even at an intensity such as that which reaches the surface of the earth from sunlight, has a damaging effect on many substances. In the case of plastics such as polycarbonate, polyurethane, etc., UV radiation is used

Radicals formed, which decompose the material.This manifests itself in an increasing yellowing and brittleness of the material.This process decreases sharply with increasing wavelength, but due to the simultaneously increasing spectral density of sunlight on the earth's surface, it can reach a wavelength of around 400 nm not to be neglected But other materials such as wood, paints and coatings can also be sensitive to UV radiation and must be protected accordingly. When stored in sunlight, many foods must be stored in containers that do not allow UV radiation to pass through Finally, UV light absorbers are required for sunscreens in the cosmetics sector, which also have a high sun protection factor in the UVA range in order to optimally protect the skin from the UV radiation which is harmful to them. In all the applications described here, there is a high absorption capacity of the UV to be used Light absorbers in the entire UV range, that is to say a wavelength of approximately 250 nm to 400 nm with a simultaneous high transparency which is as neutral as possible, is desirable

A UV-light absorber, such as is needed in the above examples, in exterior applications, its surface can be achieved in particular with a coating of poly by incorporating a UV light absorber in the volume of the _j square end Whether ect or by a UV hchtabsorbierende coating ^¬ materials such as polycarbonate, the shielding of the UVA Light should be almost complete, since otherwise degradation products of the polymer can accumulate in the boundary layer between the coating and the polymer, and this coating is prematurely detached and destroyed

Up to now, organic compounds have mostly been used as UV light absorbers, which have a molecular absorption band in the relevant wavelength range and do not absorb in the visible spectral range

A disadvantage of these compounds is their relatively low weather resistance, that is, they can evaporate, wash out and / or fade from the substrate when weathered. To achieve a high sun protection factor, relatively high concentrations of UV

Light absorbers are used which can trigger an allergic reaction or cause other intolerances in an increasing number of people

However, UV light absorbers are also proposed which contain inorganic solid materials in particulate form and are applied or incorporated in the form of a suspension as a layer on the material to be protected or incorporated in the same. These inorganic particles can, depending on their size and choice of material, cause areas of damage Absorbing and / or scattering UV light It is preferable to absorb the scattering of light, since photons that are scattered into the material to be protected can still damage it, particularly when the particles are incorporated. Furthermore, too much scattering of the light leads to clouding of the material to be protected Materials From Absorption and Scattering of Light by Small Particles, CF Bohren, D R. Huffman, S 93 to 104 and 130 to 141, 1983 it is known that with decreasing size of the particles their absorption capacity of light is higher than their ability to transmit light sprinkle For a transparent UV light absorber So only very small particles are suitable To ensure that the UV light absorber is also colorless, the material of the particles must have an absorption edge in the wavelength range between approximately 300 nm and 400 nm. According to WO 93/06164, materials with a band gap between 2 are suitable for such an effect , 8 eV and 4.1 eV, which corresponds to a wavelength range between 303 nm and 445 nm. From this class of materials, TiO ₂ , ZnO, CeO ₂ , SiC are already used for this purpose, see, for example, WO 93/06164, WO 95/09895 and WO 92/21315 However, UV light absorbers that contain particles from the above-mentioned inorganic compounds have the disadvantage that high particle concentrations are necessary due to an absorption edge extending over large parts of the UVA range (320 nm to 400 nm) and / or a relatively small absolute absorption cross section are sufficient to absorb light in the entire UVA range. However, the high particle concentrations required as a result result in greater turbidity and harbor the risk of a lower mechanical strength of the polymer matrix TiO ₂ than the best known UV light-absorbing particle to date is also photocatalytically active , so that these must be encased in order not to be protected by the medium to be protected

Damaging radical formation that is initiated by the particle itself

From WO 96/16114, however, fine-particle silicon is also known as a UV light absorber. The particles described there have the disadvantage that their UV-absorbing properties decrease as a result of agglomeration taking place

The object of the present invention was therefore to provide UV light absorbers which do not have the disadvantages known in the prior art

It has been found that UV light absorbers, containing predominantly particles of silicon and / or of solid compounds in which silicon is present in a stochiometric excess, have an average diameter of less than 120 nm, these particles additionally comprising an oxide layer with a Thickness from 1 nm to 300 nm are surrounded by advantageous properties, such as high transparency in the visible spectral range at lower particle concentrations, high stability in air, high environmental and biocompatibility and complete absence of photocatalytic activities and filtering out light in UVA and UVB range with high efficiency, grouting They are suitable for incorporation in polymer materials, in coating materials, in paints, in cosmetics and similar materials. They are particularly useful when these materials are exposed to sunlight and they protect themselves or other substances underneath should be

The invention therefore relates to UV light absorbers which contain particles of silicon and / or solid compounds in which silicon is present in a stoichiometric excess with an average diameter of less than 120 nm. hold, these particles are additionally surrounded by an oxide layer with a thickness of 1 nm to 300 nm

The mean diameter is the maximum of the number distribution

Elemental silicon is amorphous or crystalline silicon, preferably crystalline silicon. The size of the silicon particles is preferably between 1 nm and 120 nm, particularly preferably between 1 nm and 70 nm, very particularly preferably between 10 nm and 50 nm Particles with a large distribution with a maximum half-width of 40 nm on silicon particles with this average diameter are preferably produced by means of a gas phase reaction (CVR) according to the method described in US Pat. No. 5,472,477. Production according to J Phys Chem, 97, p 1224 to 1230 (1993), J Vac. Sei Technol A10, S 1048 (1992) and Int J Heat Mass Transfer 31, S 2236 (1988)

The term solid compounds includes compounds which are solid at room temperature, such as, for example, silicides, CaSi ₂ and / or BaSi _2. The term compounds in which silicon is present in a stochiometric excess preferably includes compounds of the formula Si _λ Z _jx with 0.5 <x ≤l, preferably x> 0.7 and Z = C, N, O, Ge, Ca, Ba and Sr The presence of other materials shifts the energetic position of the absorption edge within certain limits and modifies the shape of the edge here Si _λ C, _.x or

Si _χ Ge, _ _λ preferred

In a preferred embodiment of the invention, the solid compounds in which silicon is present in a stochiometric excess have a core-shell structure. The average diameter of the particles is preferably less than 120 nm, particularly preferably less than 100 nm, very particularly preferably smaller Is 50 nm. These preferably have a particle size distribution with a maximum half-width of 40 nm. It is preferred that this consists of a core made of titanium nitride and a shell made of silicon, the silicon volume fraction being at least 30% per particle

In a further preferred embodiment of the invention, the UV

Light absorber shell particles in the form of a solid compound consisting of silicon and such materials in the red spectral range (600 nm <λ <700 nm) are more absorbent than those in the blue-green (400 nm <λ <550 nm) spectral range

The solid compounds, including those with a core-shell structure, can be prepared, for example, by thermal decomposition of a silicon-containing gas, such as, for example, silanes, organosilanes or SiCl ₄ , so that a

Aerosol is formed (see J Phys Chem, 97, S 1224 to 1230 (1973), J Vac Sei Technol A10, S 1048 (1992). The admixture of further gases, which contain, for example, germanium or carbon, results in correspondingly stochiometric compounds in the case of solid compounds with a core-shell structure, the core is first produced by means of the previously described method and then the shell is applied by means of decomposition or reaction in the gas phase of appropriately composed gases, such as, for example, S ₄ or S ₄ together with H ₂ Thermal decomposition can be carried out in a gas phase reactor, preferably in a CVR (Chemical Vapor Reaction) reactor, or also by laser absorption (see Int J Heat Mass Transfer, 31,

S 2239 (1988) take place The thermal decomposition of gases is particularly suitable for the production of crystalline particles. It is also possible to use a PECVD (Plasma Enhanced Chemical Vapor Deposition) process (see J Vac Sei Technol, A10, S 1048 (1992)) In the last process, amorphous particles are formed, which can be stabilized by a thermal aftertreatment (see Nanostructured Materials, Vol 6, S 493 to 496 (1995))

In a preferred embodiment, the particles are spherical. Particles with a size of less than 100 nm are known to tend to agglomeration in practice. As a result, the advantageous optical properties of the isolated individual particles, such as low light scattering and / or position, correspond

Absorption bands not calculated in advance. It has now been found that the particles of the UV light absorber according to the invention act optically like non-agglomerated individual particles. In this case, the particles are then electromagnetically decoupled. Thus, despite the agglomeration of the coated particle particles, the optical properties of isolated particles are retained The in

Silicon particles containing UV light absorbers are preferably surrounded by an oxide layer with a thickness of 1 nm to 300 nm, particularly preferably from 10 nm to 100 nm. Another advantage of a silicon oxide layer is that the refractive index in the visible spectral range is very similar like the media to be protected against UV radiation, such as polycarbonate, polyurethane, Water / oil emulsions etc. This reduces the light-scattering effect and the matrix remains transparent. This oxide layer can be done, for example, by adding oxygen to the CVR reactor after the particles have been produced

In a preferred embodiment, the UV light absorber according to the invention additionally contains particles of oxides and / or nitrides of metals which are in the red

Absorb spectral range of 600 nm <λ <700 nm more strongly than in the blue-green spectral range of 400 nm <λ <550 nm. Such additives are particles of titanium nit with an average diameter of 1 nm to 400 nm, preferably 10 nm to 120 nm or agglomerates of these titanium nitride particles can be considered. Their manufacture can be carried out, for example, according to US Pat. No. 5,472,477. In a preferred embodiment, the UV light absorber contains not only silicon particles but also TiN particles with an average diameter of 10 to 120 nm -Light absorber works very effectively in the UVA range and at the same time ensures color neutrality with high transparency. Also preferred are additives in the form of particles made of aluminum-sodium-silicates (Ultramarine

Pigments), for example available from Nubiola SA, under the name Nubix ⁸¹ pigments. They can also contain blue inorganic pigments, for example made of iron (III) hexacyanoferrate (II)

In a further embodiment of the invention, the UV light absorber preferably consists of a mixture of the silicon-containing particles and

Particles from the following group of silicon carbide and / or oxides of the metals titanium, cerium, tungsten, zinc, tin and iron. Such mixtures allow the absorption edge, in particular the steepness thereof, to be manipulated. The particle size of the mixed particles is preferably between 1 nm and 200 nm obtainable by the process described in US Pat. No. 5,472,477

The UV light absorber according to the invention can be uniformly dispersed in the matrix to be protected, incorporated there (matrix modification), enriched on the surface or applied to it, for example, as a varnish. The invention also relates to a matrix containing 0.001 to 30 atom%. At least one UV light absorber according to the invention The matrix is plastics, coatings, lacquers, paints, wood, cosmetics and / or glass. The UV light absorber according to the invention is preferably present in proportions of 0.01% to 10% in the matrix to be protected. before All% figures refer to atomic percent The invention also relates to a method for protecting against ultraviolet radiation, according to which at least one UV light absorber according to the invention has been incorporated into the material to be protected or applied to it as a protective layer. Suitable incorporation methods are, for example, stirring or dispersing. The application of the protective layer can likewise by conventional methods by means of vapor deposition or brushing on. The materials to be protected (matrix) are, for example, plastics, coatings, lacquers, paints or wood. Plastics can be, for example, polycarbonate, polyurethane, polyester, polyimide, polyamide and / or polyacrylonitrile By incorporating in or by applying a coating to the above-mentioned materials, but also by incorporating in or applying a coating to materials that are insensitive to UV light, such as, for example, glasses, the content of containers made from these materials s ind, are protected from harmful UV radiation. The UV light absorbers according to the invention are moreover particularly useful in cosmetics in order to

Protect skin from the harmful effects of the UV component in solar radiation

In order to demonstrate the advantageous effect of the invention, the extinction of preferred UV light absorbers was calculated. To this end, the optical density OD was calculated as a function of the particle diameter d and the light wavelength λ. It is defined as follows

I _{0 is} the incident light intensity, I is the light intensity transmitted in 180 °, C _ext is the extinction cross section, which is composed of the sum of the absorption cross section C _scatter , c is the concentration of the particles in the medium, z is the layer thickness and r is the density of the particle material Der

The extinction cross section C _ext for individual particles not interacting with each other was calculated using the well-known formalism of the Mie theory (see e.g. Absorption and Scanningπng of Light by Small Particles, pp. 93 to 104 (1983)). To calculate C _ext as a function of the wavelength of Particles with a small distance between them, ie taking into account a particle-particle interaction, a generalized Mie Theoπe was used (see eg Applied Optics 32, 6173 (1993)) Die in this Calculations for material-dependent parameters are the complex refractive index of the material under consideration and the refractive index of the surrounding medium. A typical value for plastics and glasses of n _med = 1.55 was used for the surrounding medium. The dependence of the complex refractive indices on the wavelength can vary depending on the one used

Literature source differ from one another Therefore, for the example calculations presented here, various literature sources were first compared with one another and those that appeared to be the most reliable were used. The following literature sources were used in detail: Absorption and Scanningπng of Light by Small Particles, S 93 to 104, 1983, WO 93/06164, WO 95 / 09895, WO 92/21315, Phys

Rev B 27, 985 (1983), for Sι _{0 8} Ge _{0 2} E Schmidt, Phys Stat Sol, 27 57 (1968) for TιO ₂ (Rutil) in "Handbook of Optical Constants of Sohds I" by ED Palik Academic Press, 1985, S 795, and for TiN Surface Science 251, 200 (1991) The layer thickness z is z = 1 mm for all calculations carried out

Fig. 1 gives an example of the UV protection properties of crystalline isolated

Silicon particles again (comparison) The optical density of a UV light absorber consisting of crystalline silicon as a function of the wavelength was calculated for particle diameters of 20 nm (4), 30 nm (3), 40 nm (2) and 50 nm (1) The particle concentration was c = 0.25 g / L. It can be seen that, in principle, all particles with a size of less than 50 nm shield UV light. In particular with particle sizes from 30 nm to 50 nm, even low concentrations will also be in addition to the light of the UVB range that of the UVA range is absorbed very effectively, so that the underlying material is effectively protected. For example, the transmission of 40 nm particles at a wavelength of λ = 400 nm at 70% and at λ = 350 nm at 1.5% by increasing Concentration makes it very easy to achieve very high light protection factors, even for particles with a smaller mean diameter, in order to further reduce minor scatter components e also calculated the extinction spectrum of rutιl-TιO ₂ particles with a diameter of 20 nm in the same concentration

TiA remains in the UVA range, well behind the light-absorbing properties of silicon. In order to achieve the same protective effect, the concentration of TιO ₂ particles must be increased many times over

FIG. 2 shows the cross sections Q normalized to a single particle for absorption (1) and scattering (2) as a function of the wavelength of an agglomerate from pure silicon particles, which consists of 55 primary particles (Si) with a diameter of 20 nm, which are arranged in two shells (again made of pure silicon) around a central particle (made of Si). The following equations were used for the standardized cross section Q.

in the case of absorption ((1) and (3))

Q = ^C abs π d ²

4 in the case of childcare ((2) and (4))

Q = ° scatter π d ²

4

the measure would be that C _eχt = = c _abs + C _scatter and C _ext according to Absorption and Scanningπng of Light by Small Particles, S 93-104 (1983) and Applied Optics 32

6173 (1993) The cross sections for absorption (from Si) (3) and scattering (4) of an inventive UV light absorber of the same geometric shape are also shown in FIG. 2. The Si particles calculated here have a diameter of 20 nm and a shell with a thickness of 25 nm. It can clearly be seen that the light scattering is far more dominant than the absorption in the case of the uncoated particles than in the case of the coated particles. The UV light absorber according to the invention thus results in a significantly reduced clouding of the matrix

The invention therefore also relates to the use of the UV light absorbers according to the invention for UV light protection in plastics, paints, varnishes,

Glass or coatings, as self-protection or for protecting an underlying or still UV-sensitive material, in wood preservatives and / or in cosmetics

Incorporation or application to the material to be protected can be carried out using conventional methods (see WO 95/09 895, WO 92/21 315 and EP

A 628 303)

Claims

claims

1 UV light absorber, characterized in that these predominantly contain particles of silicon and / or solid compounds, in which silicon is present in a stochiometric excess, with an average diameter of less than 120 nm, these particles additionally having a

Oxide layer with a thickness of 1 nm to 300 nm are surrounded

2 UV light absorber according to claim 1, characterized in that the solid compounds in which silicon in the stochiometπ see excess is present, compounds of the formula Sι _λ Z, _χ with 0.5 <x ≤ \ and Z = C, N, O, Are Ge, Ca, Ba and / or Sr

3 UV light absorber according to one of claims 1 or 2, characterized in that the particles are spherical

4 UV light absorber according to one or more of claims 1 to 3, characterized in that the solid compounds in which silicon is present in a stochiometric excess have a core-shell structure

5 UV light absorber according to claim 4, characterized in that it consists of a core of titanium nitride and a shell of silicon, the silicon volume fraction being at least 30% per particle

6 UV light absorber according to one or more of claims 1 to 5, characterized in that these particles have a size distribution with a maximum half width of 40 nm

7 UV light absorber according to one or more of claims 1 to 6, characterized in that it additionally contains particles of oxides and / or nitrides of metals which in the red spectral range of

Absorb 600 nm <λ <700 nm more than in the blue-green spectral range of 400 nm <λ <550 nm

8 UV light absorber according to claim 7, characterized in that the additional particles made of Titanmtπd, with an average particle diameter exist from 1 nm to 400 nm or are agglomerates of these titanium nitride primary particles

9 UV light absorber according to claim 7, characterized in that the additional particles are aluminum-sodium silicates

5 10 UV light absorber according to one or more of claims 1 to 9, characterized in that it additionally contains oxides of iron, titanium, cerium, tungsten, tin and / or zinc

1 1 matrix of plastics, coatings, paints, paints, wood, cosmetics and / or glass, containing 0.001 to 30 atom% of at least one of the UV

) Light absorber according to one or more of claims 1 to 10

12 A method of protecting against ultraviolet radiation, characterized in that at least one UV light absorber according to one or more of claims 1 to 11 is incorporated into the material to be protected or applied to it as a protective layer

5 13 Use of UV light absorbers according to one or more of claims 1 to 1 1 for UV light protection in plastics, paints, varnishes, glass or coatings, as self-protection or to protect the UV light-sensitive material underneath in wood preservatives and / or in cosmetics.