Patent Description:
Recycling of plastics demands a fast and cost-efficient method of sorting the various plastics from municipal waste. Since about <NUM> years NIR (Near Infrared) spectroscopy is used in automatically sorting systems. Plastics can be detected by specific vibrations absorption bands in the NIR region.

To embellish the look of plastic articles effect pigments like flaky metal pigments, particularly aluminium effect pigments or pearlescent pigments may be added to the plastic. Usually, the effect pigments are mixed with the thermoplastic melt by an extrusion process. Aluminum pigments add a silvery metallic appearance to the plastic article. As these pigments are opaque to visible wavelength' they exhibit an extremely high hiding power. The plane-parallel orientation of the flaky pigments in a plastic, however, is much less distinct compared to wet-coatings and therefore properties like flip-flop or high gloss as known from wet-coating applications or from printing inks are not as high here.

It has been recognized that the pigmentation of plastics with metal effect pigments diminishes the ability of the plastic material to be detected and identified by means of NIR spectroscopy. Apparently, the high reflection also of infrared rays of aluminum is the reason to this behavior.

<CIT> discloses an effect pigment mixture of a platy aluminum effect pigment with silvery pearlescent pigments and coating formulations containing this mixture. Applications in plastics are not mentioned therein.

<CIT> discloses a blend of at least one effect pigment with a small amount of an aluminum metal pigment having a mirror-like appearance. This effect pigment mixture has a high hiding power and applications are focussed on coating formulations, especially automotive topcoat compositions. The automized sorting of plastics by NIR spectroscopy is not mentioned therein.

It is therefore an object of this invention to make available an inexpensive plastic part having a metallic effect look like especially a high hiding powder and being capable to be detected reliably in an automized sorting system by NIR spectroscopy.

This object is solved by providing a plastic part having a mean thickness tpl containing a mixture of effect pigments comprising flaky aluminum pigments obtained by milling of aluminum or aluminum-based alloy powder in a concentration cAl and silvery, absorbing pearlescent pigments in a concentration cP,
wherein.

The plastic parts of this invention have a distinct metallic appearance. Such metallic appearance especially refers to opacity, a rather high brightness and a certain metallic flip-flop. Flop and brightness of mass-colored plastics are not as high as obtained from wet-coatings of lacquers or printing inks containing flaky aluminum effect pigments as the orientation of the flakes in a resin is less pronounced, but still they do apply. The plastic parts have a pronounced opacity as aluminum effect pigments are opaque for visible light. Especially IR radiation is reflected almost completely by aluminum which causes the problem of being detected in an automatic sorting device. In such sorting devices the plastic articles are first separated such that they essentially do not overlap and they are transported on a band at high speed. The specific types of plastics are detected by NIR spectrometers in reflection and apparently aluminum flakes increase the reflection but do not allow the IR radiation to penetrate deeply into the plastic part and therefore the IR spectra of the resin are not detected with sufficient intensity and accuracy. The aluminum pigments exhibit a masking effect of the plastic part against IR radiation penetration.

The plastic part can have several forms like e.g. films, foils, bottles, trays, containers, flip-tops, and closures etc.. When located on a sorting band the plastic parts will be placed in a somewhat statistical or random manner. The area contacting the band will be a rather large area for static reasons. The thickness perpendicular to the band of such area of the plastic part is the thickness tPl. If this thickness is not uniform a mean thickness may be defined. Should the plastic part be hollow the thickness of the area opposing the contacting area is the part of the plastic which is detected by IR beam and therefore tPl, the mean thickness of this area.

The mean thickness tpl of the plastic part is preferably in a range of <NUM> to <NUM>.

The opaqueness of the plastic part depends on the concentration of effect pigments and on the mean thickness tPl. Therefore, based on the Lambert-Beer law the opaqueness may be well represented by the product of the aluminum effect pigment concentration cAl or the pearlescent pigments concentration cP with the mean thickness tpl.

The flaky aluminum pigments can be divided into two categories: a first category of type i) which moderate to low hiding power in a mass-colored plastic and to a type ii) having a high hiding power in a mass-colored plastic. The hiding power of flaky aluminum pigments are mainly determined by their thickness and the particle size distribution. For aluminum pigments obtained by milling these parameters are correlated in the sense that small pigments are usually also thin because of extensive milling.

For the flaky aluminum pigments of type i) the D<NUM> ≥ <NUM>.

For the flaky aluminum pigments of type ii) the D<NUM> < <NUM>.

The pigment particle size distribution is typically indicated using D values which denote to quantile values of the volume averaged particle size distribution in frequency representation.

Here, the number indicates the percentage of particles smaller than a specified size contained in a volume-averaged particle size distribution. For example, the D<NUM> value indicates the size wherein <NUM>% of the particles are smaller or equal to this value and the D<NUM> indicates the size wherein <NUM>% of the particles are smaller or equal to this value. These measurements are conducted e.g. by means of laser granulometry using a particle size analyzer manufactured by Sympatec GmbH (model: Helos/ BR). The measurements are conducted according to indications from the manufacturer. The sizes are determined using Fraunhofer approximation and volume averaged equivalent spheres.

The span ΔD is defined by the well-known formula (I) <MAT> and is a measure of the relative width of a particle size distribution.

One can roughly state, that the effect pigments of type i) are so-called silver dollar aluminum pigments. These effect pigments are obtained by essentially deformation milling of essentially sphere-like aluminium powder.

The aluminum pigments of type ii) are so-called cornflake pigments. They are obtained essentially comminution milling of non-sphere-like aluminium powder. A milling process of aluminum powder under conditions with high energy impact will lead to a large number of small particles by crushing small parts from the edge of a flake and therefore the D<NUM> will have rather low values. On the other hand the aluminum particles obtained by milling may be sieved in different manners and therefore also the span of the particle size distribution is important.

In a further embodiment the flaky aluminum pigments of type i) have a <NUM> ≤ D<NUM> ≤ <NUM> and in a preferred further embodiment the flaky aluminum pigments of type i) have a D<NUM> value in the range of <NUM> to <NUM> and even more preferred in a range of <NUM> to <NUM>. In most cases flaky aluminum pigments with a D<NUM> value in a range of <NUM> to <NUM> do not have the problem of NIR detection of the plastic in automized sorting apparatuses.

In a further embodiment the flaky aluminum pigments of type i) have a span ΔD < <NUM>.

In a further embodiment the flaky aluminum pigments of type ii) have a D<NUM> < <NUM>. Preferably the flaky aluminum pigments of type ii) have a span equal to or larger than <NUM> and more preferably larger than <NUM> and most preferably larger than <NUM>.

The product of the concentration of cAl and tpl is for flaky aluminium pigments of type i) is in a range of <NUM> to <NUM> wt. % cm, and for aluminium pigments of type ii) is in a range of <NUM> to <NUM> wt.

"Flaky aluminum pigments" are used interchangeable to the expression "aluminum effect pigments" within this document.

When the concentrations and are expressed in "%" always "wt. %", referred to the total plastic part is meant in this document, if not indicated otherwise.

Usually the flaky aluminum pigments of type i) exhibit a much lower hiding power compared to flaky aluminum pigments of type ii) and therefore much more aluminum pigments can be used. The type ii) pigments are more sensitive with respect to the masking effect of IR radiation and therefore much lower concentrations are tolerable.

In some embodiments the aluminum effect pigment may be completely exchanged by pearlescent pigments as demonstrated in the experimental section. As aluminum pigments are usually less expensive compared to the silvery, absorbing pearlescent pigments it is, however, preferred to use a certain minimum amount of aluminum pigments. Therefore, in a more preferred embodiments the product of the concentration of the aluminum effect pigments cAl in wt. % and tpl is for flaky aluminium pigments of type i) cAl * tpl s in a range of <NUM> to <NUM> wt. % cm, and for aluminium effect pigments of type ii) cAl * tpl is in a range of <NUM> to <NUM> wt. % cm, each concentration referred to the total plastic part.

In further preferred embodiments of the product of the concentration of the flaky aluminum pigments cAl and tpl is for flaky aluminum pigments of type i) are in a range of <NUM> to <NUM> wt. % cm, more further preferred in a range of <NUM> to <NUM> wt. % cm and most preferred in a range of <NUM> to <NUM> wt.

For the flaky aluminum pigments of type ii) in further preferred embodiments the product of the concentration of the flaky aluminum pigments cAl and tpl is in a range of <NUM> to <NUM> wt. % cm, more further preferred in a range of <NUM> to <NUM> wt. % cm and most preferred in a range of <NUM> to <NUM> wt.

In these respective concentration regimes an optimum may be achieved with respect to precise sorting properties by NIR detection of the plastic, costs and process stability.

The flaky aluminum pigments contained in the plastic part preferably has a d<NUM> in a range of <NUM> to <NUM>, more preferably in a range of <NUM> to <NUM> and most preferably in a range of <NUM> to <NUM>.

The flaky aluminum pigments of type i) preferably have a mean thickness hAl in a range of <NUM> to <NUM> and more preferably in a range of <NUM> to <NUM>. The flaky aluminum pigments of type ii) preferably have a mean thickness hAl in a range of <NUM> to <NUM>, more preferably in a range of <NUM> to <NUM> and most preferably in a range of <NUM> to < <NUM>.

The mean thickness may be determined by SEM based on the procedure described in <CIT> on page <NUM>, lines <NUM> to <NUM> and further detailed in the experimental section.

In further embodiments the flaky aluminum pigment is coated with a metal oxide which is preferably selected from the group consisting of SiO<NUM>, Ce-oxide, Mo-oxide, V-oxide, Cr-oxide and mixtures or combinations thereof. Most preferably the aluminium effect pigment is coated with SiO<NUM>. The coatings with such metal oxides impart mechanical stability to the aluminum pigment and improve their corrosion stability against humidity or other chemicals and weather stability.

The pearlescent pigments used in the effect pigment mixture of the plastic parts are silvery, absorbing pearlescent pigments with optical properties reflecting a metallic look. These pearlescent pigments usually have optical properties such that the resulting color in reflection is essentially a neutral silver tone or a slightly colored tone and cover a region from absorbing grey to anthracite shades. With respect to pearlescent pigments generally the color tone "anthracite" is also often referred to as "black". In this invention the term "silvery, absorbing pearlescent pigments" is used for pearlescent pigments which have a combination of neutral silver or slightly colored reflection color and grey to anthracite absorption color tones providing a metallic-like characteristic.

In preferred embodiments the silvery, absorbing pearlescent pigments are selected from the following types:.

and mixtures or combinations of the pearlescent pigments a) to e) or pearlescent pigments with mixtures or combinations of the various coating layers mentioned in the pearlescent pigments a) to e).

The optical properties of the silvery, absorbing pearlescent pigments useable for the effect pigment mixture can be evaluated by making a drawdown of a colorless lacquer (preferably BASF farblos ZM <NUM>- <NUM>) with a pigmentation height of <NUM> wt. % of the pearlescent pigment using a <NUM> doctor <NUM> blade on a black/white cartoon paper. The total content of non-volatile components in the lacquer should be <NUM> wt. The optical properties of the dried drawdowns are measured with a BYK-Mac instrument. Preferably, the chroma C*<NUM>∘ of such a drawdown of the silvery pearlescent pigments measured on black background is ≤ <NUM>, more preferably ≤ <NUM> and most preferably ≤ <NUM>. The hiding power of the silvery pearlescent pigment in such drawdowns can be defined as the ratio of the L*<NUM>°,black/L*<NUM>°,white-values measured on the black to white background, respectively. This ratio is preferably higher than <NUM>%. This high hiding power is mainly achieved by the absorbing layer of the pearlescent pigments. The lightness is represented by the L*<NUM>∘ value which is close to the angle of reflection and preferably this value measured on the drawdowns on black background is above <NUM> and more preferably above <NUM> for the pearlescent pigments of the effect pigment mixture in this particular application.

In a first preferred embodiment a) the silvery pearlescent pigments used in the effect pigment mixture are pearlescent pigments comprising a transparent substrate which is coated with a high-refractive index layer with n > <NUM>, which comprises or consists of an iron-oxide with Fe(II)- ions. In a further preferred embodiment the silvery pearlescent pigment a) has a coating comprising a metal oxide layer comprising Ti and Fe, wherein the iron is mainly Fe(II) ions, which is preferably an ilmenite (FeTiO<NUM>) layer or a magnetite (Fe<NUM>O<NUM>) layer or mixtures thereof. In a further preferred embodiment the pearlescent pigment has a coating comprising a first layer of TiO<NUM> followed by a metal oxide layer containing Fe(II)-ions, preferably consisting of ilmenite. Pearlescent pigments with a coating comprising a homogeneously distributed ilmenite (FeTiO<NUM>) have been described in <CIT>. Pearlescent pigments with a coating comprising first a TiO<NUM> layer followed by an inhomogeneously distributed ilmenite layer have been described in <CIT>. Further examples of such pearlescent pigments are disclosed in <CIT>, <CIT> (with an Al<NUM>O<NUM> substrate) or <CIT> (with a further high-refractive index coating). Pearlescent pigments with a single layer of ilmenite on a TiO<NUM> platelet substrate have been described in <CIT>. The thicknesses of the layers disclosed in these documents need to be reduced in order to achieve the silvery to grey shaded pearlescent pigments in reflection as demanded in the effect pigment mixture.

In further preferred embodiments the silvery pearlescent pigment comprises the following structure: (a1) a transparent platelet-shaped synthetic substrate, (a2) a titanium oxide layer, followed by (a3) a metal oxide layer comprising Ti- and Fe-ions, wherein the Fe-ions are mainly Fe(II)-ions. In a further preferred embodiment the silvery pearlescent pigment has a layer of ilmenite (FeTiO<NUM>). In further preferred embodiments the pearlescent pigment has an iron(III) oxide content of less than <NUM>% by weight, based on the total weight of the pigment. All other amounts of Fe-ions in iron oxides are in the reduced Fe(II) oxidation state. A higher amount of remaining Fe(III)-ions would lead to an undesired brownish absorption color. The amounts of Fe(II) or Fe(III) can be determined with Mößbauer spectroscopy or with XPS analysis, possibly combined with sputter profiles. In further embodiments the total amount of iron compounds, calculated as elemental iron, in the silvery, absorbing pearlescent pigment according to the invention is less than <NUM>% by weight, preferably in a range from <NUM>% by weight to <NUM>% by weight, particularly preferably in a range from <NUM>% by weight to <NUM>% by weight and very particularly preferably in a range from <NUM>% by weight to <NUM>% by weight, based in each case on the total weight of the pearlescent pigment. With such low amounts of Fe a silvery color can be well developed. Higher amounts than <NUM> wt. % lead to pearlescent pigments with a too strong absorption color. In further preferred embodiments the pearlescent pigment of type a) has an iron/titanium weight ratio as a function of the coating, in accordance with formula (II): <MAT> is in a range from <NUM> to <NUM>. Herein "iron content" stands for the amount of iron compounds, calculated as elemental iron, and "titanium content" stands for the amount of titanium compounds, calculated as elemental titanium, in each case in the pearlescent pigment and based on the total weight of the pearlescent pigment, and where the "fraction of the coating (% by weight)" stands for the weight fraction, based on the total weight of the pearlescent pigment, of the overall coating applied to the substrate. In other embodiments this parameter is in a range from <NUM> to <NUM>, preferably in a range from <NUM> to <NUM>, particularly preferably in a range from <NUM> to <NUM>, and very particularly preferably in a range from <NUM> to <NUM>. This parameter especially ensures that the pearlescent pigment has a silvery color as demanded in the effect pigment mixture.

In another embodiment b) the silvery, absorbing pearlescent pigments comprise a transparent substrate which is coated with a high-refractive index layer with n > <NUM> which comprises or consists of a titanium suboxide or a substrate with a high-refractive index n > <NUM> layer comprising or consisting of a titanium suboxide that is optionally coated with a high-refractive index layer with n > <NUM>. The high-refractive coating layer with n > <NUM> of the second kind of pigment is made from a different material than the substrate's titanium suboxide and is preferably TiO<NUM>. The coated titanium suboxide layer or the titanium suboxide substrate denote to titanium oxides wherein the formal oxidation number of titanium is below <NUM>. They can be represented by the formula:.

wherein n in an integer of <NUM> to <NUM>, preferably n = <NUM> to <NUM>. Typical examples of such compounds are TiO, Ti<NUM>O<NUM>, Ti<NUM>O<NUM>, Ti<NUM>O<NUM>. Mixtures of any such species may be also included. In further embodiments the titanium suboxide content can be less than <NUM>% based on the total pigment and the main component of said titanium suboxide is Ti<NUM>O<NUM>. An example of a commercially available pearlescent pigment with titanium suboxide is Iriodin® <NUM> (Merck).

In another embodiment c) the silvery pearlescent pigments comprise a transparent substrate which is coated with a high-refractive index layer with n > <NUM>, which comprises or consists of titanium oxynitride. The titanium oxynitrides can be expressed by the general formula:.

wherein x is <NUM> to <NUM>, y is <NUM> to <NUM> and z is <NUM> to <NUM>, which comprises a solid solution of <NUM> nitrogen in titanium monoxide. Such pearlescent pigments have been described in <CIT>. Pearlescent pigments with intense blue color or a bluish fade have been described in <CIT> or in <CIT>. Herein a first TiO<NUM> layer is reduced with ammonia at temperatures in the range of <NUM> to <NUM>. If the optical thickness of the TiO<NUM> layer deposited in a first step is in the range of <NUM> to <NUM><NUM> silvery effect pigments are obtained. In <CIT> pearlescent pigments are described were a flakyTiO<NUM> substrate is first formed by solidification of a hydrolysable aqueous solution of a titanium compound on an endless band. These substrates can be coated with further TiO<NUM> or other metal oxides and calcined under reducing conditions.

Examples of such pearlescent pigments are Paliocrom Blausilber L6000 and L6001, which have been earlier manufactured by BASF Colors and Effects GmbH.

In a further embodiment d) the pearlescent pigment of the effect pigment mixture comprises a transparent substrate which is coated with a layer comprising carbon, wherein the carbon is enclosed in a particulate form in another metal oxide layer or is formed as a separate, individual layer on at least one high-refractive index layer. In <CIT> pearlescent pigments were disclosed, wherein pearlescent substrates or TiO<NUM> coated pearlescent pigments were coated with organofunctional silanes and calcined or pyrolyzed under inert gas atmosphere yielding a pearlescent pigment containing carbon in silica matrix and having a darker color. Similar pearlescent pigments were disclosed in <CIT>. In <CIT> a pearlescent pigment with metallic silvery look was disclosed where on top of a high-refractive index coating like TiO<NUM> a very thin pure carbon layer is coated via a fluidized bed apparatus.

In a further embodiment e) the pearlescent pigment of the effect pigment mixture comprises a transparent substrate platelet coated with a first layer comprising or consisting of a mixture of the oxides of titanium, iron and at least one of cobalt and chromium and a second layer on the first layer, wherein the second layer comprises an oxide of titanium. Such pearlescent pigments have a black absorption color and are described in <CIT> and <CIT>. Commercially available Products are Vegetable Black Olive (Sun Colors and Effects).

In further embodiments mixtures or combinations of the pearlescent pigments a) to e) itself or pearlescent pigments with mixtures or combinations of the various coating layers mentioned in the pearlescent pigments a) to e) can be used. For example, pearlescent pigments comprising a coating of mixtures or combinations of titanium suboxide and titanium oxynitride may be used.

In preferred embodiments the silvery, absorbing pearlescent pigments are taken from the following group:.

The transparent substrates used for all variants of the silvery, absorbing pearlescent pigments are typically natural or synthetic mica, glass flakes, SiO<NUM>-flakes, Al<NUM>O<NUM>-flakes or mixtures thereof. Preferred substrates are glass flakes, natural synthetic mica as these substrates provide pearlescent pigments with pure silvery color tones and high gloss. Furthermore, the more expensive substrates SiO<NUM> or Al<NUM>O<NUM> are rarely used in plastic industry as they are the costliest ones. Especially Al<NUM>O<NUM> substrates may have further disadvantages in the sense that pearlescent pigments which are mass-molded into a plastic, for example by extrusion exhibit strong shear forces which peel off part of the coating of high-refractive index layers. Due to its high hardness the thus exposed Al<NUM>O<NUM> flakes can act as undesired abrasion aid which may impart an unpleasant touch feeling.

The high-refractive index layers of the silvery pearlescent pigments of type a), b) or c) preferably have an index of refraction n of > <NUM> and more preferably n > <NUM>.

In preferred embodiments the silvery pearlescent pigments according to the invention may be provided with at least one external protective layer. This protective layer further enhances the light stability, weather stability and/or chemical stability of the pearlescent pigment. Especially the photoactivity of any TiO<NUM> layers and the concomitant destroying of organic resins in coatings may be effectively reduced by these protective layers. The external protective layer of the silver-colored pigments according to the invention can comprise, or preferably consist of, one or two metal oxide layers and/or metal hydroxide layers and/or metal oxide hydrate layers of the elements Si, Al, Zr or Ce. In one variant, a silicon oxide layer, preferably SiO<NUM> layer, is applied as the outermost metal oxide layer.

After these protective layer organofunctional coupling agents may be coated on the outermost protective layer as described above in the section dealing with aluminum effect pigments. In principle, the same kind of organofunctional coupling agents can be used as well for the silvery pearlescent pigments. Such weather stable external protective layer are described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT> or <CIT>, for example.

As the silvery, absorbing pearlescent pigments itself do not affect the detection and identification of the of the plastic parts in automated sorting devices and, on the other hand, have a rather metallic look with a high hiding power compared to conventional pearlescent pigments they can surprisingly replace at least part of the flaky aluminum pigments in a plastic part. The improve the flop and their use open up a great process stability for the automated sorting of plastic parts with metallic look.

The silvery, absorbing pearlescent pigments are preferably used together with flaky aluminum pigments in such amounts that cP * cPl is in a range of <NUM> to <NUM> wt. %, more preferred in a range of <NUM> to <NUM> wt. % and most preferred in a range of <NUM> to <NUM> wt. Within these ranges the concentrations of pearlescent pigments are relatively low and inexpensive plastic parts with a great variability of processing with respect to their sorting behavior can be provided.

For embodiments without flaky aluminum pigments the concentrations of pearlescent pigments should be chosen such that cP * cPl is in a range of <NUM> to <NUM> wt. %, more preferred in a range of <NUM> to <NUM> wt. % and most preferred in a range of <NUM> to <NUM> wt.

The plastic material for the plastic parts is preferably selected from the group consisting of polypropylene (PP high density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyethylene terephthalate (PET), polystyrene (PS), polyurethane (PUR), polyacrylate, polyamide (PA) or nylons, polyvinylchloride (PVC), polycarbonate (PC) and ABS / MABS.

Examples for nylons are PA6 (nylon <NUM>), PA66 (nylon <NUM>/<NUM>), PA12 nylon <NUM>, PA11 (nylon <NUM>) (PA), PA <NUM> (nylon <NUM>/<NUM>), PA610 (nylon <NUM>/<NUM>), PA612 (nylon <NUM>/<NUM>) PA46 (nylon <NUM>), PA6, PA66, PA610, PA11, PA12, PA1010, PA612 and PA46.

Examples for aromatic polyamides are, PA6T, PA9T, for semi-aromatic polyamides are PA6T/<NUM>, PA6T/<NUM>, PA9T, and for polyphthalamides is PA6T/6I.

These kinds of polymers are widely used in the plastic industry and are automatically detectable and sortable using NIR spectroscopy. Most preferred are polypropylene, polyethylene, polystyrene and polyethylene terephthalate.

The plastic part is most preferably opaque for visible light. In preferred embodiments, the optical density OD of the plastic part is ≥ <NUM> when measured along the mean thickness tpl as defined above.

In certain embodiments the metallic pigments can be completely resigned (cAl * tPl, = <NUM> %). For this case I the product of tPl with the concentration of silvery, absorbing pearlescent pigment cP is preferably <NUM> wt. %≤ cP * tpl < about <NUM> wt. % and more preferably %, <NUM> wt. %≤ cP * tpl < about <NUM> wt.

As these embodiments might be more costly, it is preferred to use flaky aluminum pigments in the plastic parts. When differentiating certain ranges of the product of tPl, with cAl the following ranges of tPl * cp for the silvery, absorbing pearlescent pigments are preferred:.

Especially when using flaky aluminum pigments of type ii) which have a great impact on the sorting behavior the amount of silvery, absorbing pearlescent pigments may be carefully adjusted to the (low) concentrations of the flaky metal pigments in order not to risk an insufficient sorting behavior. Already rather small additions of silvery, absorbing pearlescent pigments can improve the flop. In case of flaky aluminum pigments of type ii) (cornflake type) the addition of pearlescent pigments also improve the brightness of the plastic part.

In further embodiments of the plastic parts predetermined ranges of the product of tPl, with cAl impart the following ranges of the product of tPl with cp for the silvery, absorbing pearlescent pigments:.

The plastic parts comprising the effect pigment mixture can further contain at least one of additives, UV absorbers, antioxidants, fillers, conventional color pigments and additional pearlescent pigments, which are no silvery absorbing pearlescent pigments.

As conventional pigments inorganic or organic pigments can be used. With conventional pigments it is meant that these pigments do not have an angle dependency (either the angle of incidence or of observation) in their optical properties which is just contrary to effect pigments.

These conventional pigments are used to impart color to the Resin mold, if demanded. The conventional pigment may be an organic pigment, an inorganic pigment or a mixture thereof.

Accordingly, in a preferred aspect, the conventional pigment is a transparent pigment, especially selected from the group consisting of an organic pigment, an inorganic pigment or a mixture thereof.

Organic colored absorption pigments suitable for the present coating formulation include, for example, a pigment selected from the group consisting of a monoazo, disazo, disazo condensation, anthanthrone, anthraquinone, anthrapyrimidine, benzimidazolone, quinacridone, quinophthalone, diketopyrrolopyrrole, dithioketopyrrolopyrrole, dioxazine, flavanthrone, isoindoline, isoindolinone, isoviolanthrone, metal complex, perinone, perylene, pyranthrone, pyrazoloquinazolone, indigo, thioindigo, triarylcarbonium pigment and a mixture thereof.

In further embodiments the coating formulation contains additional pearlescent pigments. The additional pearlescent pigments are none of the ones used in the effect pigment mixture described above. The additional pearlescent pigments are characterized therein, that they are based on a transparent substrate and the layers contributing to the color consist of one or two high-refractive index layers consisting of TiO<NUM>, Fe<NUM>O<NUM> or mixtures thereof, and optionally one or more low refractive layers with n < <NUM>.

Preferably, these additional pearlescent pigments have one layer consisting of TiO<NUM> or Fe<NUM>O<NUM>, most preferably one layer consisting of TiO<NUM>. "Consisting of TiO<NUM>" means in this case, that small amounts of SnO<NUM> may be present which may have been used to rutilize the TiO<NUM> in well-known manner.

These additional pearlescent pigments do have mainly coloristic properties. They may be used to adjust color tones or to improve the flop. Usually they do not have the opacity and the metallic appearance of the pearlescent pigments used for claim <NUM> of the plastic part containing the therein claimed effect pigment mixture.

It is preferred that the total amount of the effect pigments of the effect pigment mixture, optionally additional pearlescent pigments and optionally additional conventional pigments is equal to or less than <NUM> wt. %, based on the plastic part, more preferably is in a range of <NUM> to <NUM> wt. %, and most preferred in a range of <NUM> to <NUM> wt. %, based on the total amount of the plastic part.

Above <NUM> wt. % the effect pigment and optionally conventional pigments the mechanical properties of the plastic parts are strongly affected adversely such as tensile strength, elongation at break, impact strength, etc..

The plastic parts of this invention are typically used in applications such as electrical & electronic equipment's, computers, communication & consumer electronics (3C), household & home appliances, lifestyle articles, construction & building industry, sports & leisure goods, consumer goods, foils & films, automotive applications, cosmetic & food packaging, toys and so-called flip-tops.

The plastic parts containing the effect pigments are typically manufactured by methods such as extrusion, calendaring, cast-film, blown-film, blow molding, roto molding, injection molding, injection blow molding, injection stretch blow molding (ISBM)) for containers and packaging, preform stretch blow molding (SBM), pressing, thermoforming, fused deposition modeling (FDM) or fused filament fabrication (FFF), fluidized bed coating, and laser sintering.

A further embodiment is directed to a method of separation of waste plastic parts comprising the steps of:.

The waste mixture is transported on a band at velocities of several m/s. Previous to these steps the plastic waste is preferably separated in a sorting device such that each plastic part lying on the transportation band is not covered by another piece. Prior to this separation method there are usually other steps involved like particle size separation of the waste pieces or magnetically separation of magnetic waste pieces like tinplate.

The detected NIR signals are processed by a software which compares the spectra using a database to identify the plastic of a certain piece of waste and then activating compressed air nozzles in order to separate the identified plastic part from the band. In this way different kinds of plastics are separated successively. The detection of a certain plastics is usually made according to characteristic vibration bands in the spectral region of about <NUM> to <NUM>.

A further embodiment is directed to the use of the plastic part in a method of separation of waste plastics comprising the steps of:.

Several samples were prepared by extruding masterbatches of metal effect pigments (comparative examples) or absorbing, silvery pearlescent pigments or mixtures thereof in varying concentrations with polypropylene. As aluminum effect pigments a commercially available silver dollar pigment (originally Metalux (abbrev. MEX) <NUM>, Eckart GmbH) and a commercially available cornflake type (STAPA WM Chromal V/<NUM>, Eckart GmbH) were used. The silver dollar pigment paste was first pelletized with a polyolefin to a pellet with <NUM> wt. % metal pigment and <NUM> wt. % of the binder (commercially available as MASTERSAFE MP <NUM>-20B, Eckart GmbH). In all references to the pure aluminum pigments these types are abbreviated "<NUM>" and "Chromal V" hereinafter.

As silvery, absorbing pearlescent pigments the commercially available products Symic C604, Symic B604 and Symic A <NUM> (all from Eckart GmbH) were used. These pearlescent pigments were based on synthetic mica and had a coating of TiO<NUM> and Fe<NUM>O<NUM> which were calcined under reducing conditions forming a mixed oxide of TiO<NUM> and Fe-oxide which includes Fe(II) ions.

The effect pigments were mixed with polypropylene and extruded to form a masterbatch of <NUM> wt. % effect pigment concentration. To produce the respective masterbatches of these effect pigments, the process was as follows:.

The thus obtained masterbatch granular materials were further diluted with the polypropylene to the desired final pigment contents relative to the proportion by weight of the plate. The final concentrations of the effect pigments are depicted in tables <NUM> (pure effect pigments) and table <NUM> (effect pigment mixtures). These masterbatch granular materials were then processed to form plates with a surface area of <NUM> ×<NUM> and a thickness of <NUM> by means of the injection-molding machine (Arburg <NUM>-<NUM>-<NUM>) at a processing temperature of <NUM>° C.

Comparative Example series <NUM>: Various concentrations of Metalux <NUM> (processed as Mastersafe mp <NUM>-20b) without pearlescent pigments. This aluminium effect pigment is of "silver dollar" type. Its particle size parameters as measured with a Helios /BR are: D<NUM>: <NUM>, D<NUM> = <NUM> and D<NUM> = <NUM>.

Comparative Example series <NUM>: Various concentrations of STAPA WM Chromal V/<NUM> without pearlescent pigments. This aluminium effect pigment is of "cornflake" type. Its particle size parameters as measured with a Helios/BR are: D<NUM>: <NUM>, D<NUM> = <NUM> and D<NUM> = <NUM>.

Example series <NUM>: Various concentrations of Symic C604. This is a silvery absorbing pearlescent pigment comprising a high-refractive index layer comprising Fe(II)-ions. The median particle size d<NUM>,p is <NUM>.

Example series <NUM>: Various concentrations of Symic B604. This is a silvery absorbing pearlescent pigment comprising a high-refractive index layer comprising Fe(II)-ions. The median particle size d<NUM>,p is <NUM>.

Example series <NUM>: Various concentrations of Symic A604. This is a silvery absorbing pearlescent pigment comprising a high-refractive index layer comprising Fe(II)-ions. The median particle size d<NUM>,p is <NUM>.

Examples series <NUM>: Mixtures of MASTERSAFE MP <NUM>-20B with aluminum pigment content of <NUM>% and various amounts of Symic B604.

Examples series <NUM>: Mixtures of STAPA WM Chromal V/<NUM> with <NUM>% aluminum pigment content various amounts of Symic A604.

Examples series <NUM>: Mixtures of STAPA WM Chromal V/<NUM> with <NUM>% aluminum pigment content and various amounts of Symic A604.

B1 Determination of average thickness of aluminum effect pigments by SEM:
The aluminum pigments were originally present in the form of a paste and were each first washed with acetone and then dried.

The aluminum powder than was poured onto a conductive adhesive label (Spectro tabs from Plano GmbH, Germany). By this procedure, a certain amount of the flaky aluminium pigments become fixed into an upright position. Under the SEM these particles can be well identified and their thickness at the pigments edge was determined. For each sample <NUM> particles were counted and the average thickness tAl was determined.

B2: The specific surface was measured with the BET method using a three-point method.

B3: Particles size distribution measurements:
These measurements are conducted e.g. by means of laser granulometry using a particle size analyzer manufactured by Sympatec GmbH (model: Helos/ BR). The measurements are conducted according to data from the manufacturer. With this apparatus powdered samples as well as pastes can be measured.

Table <NUM> summarises the different samples with respect to the effect pigments used and the respective concentrations.

Rectangular test sheets having a length of <NUM>, a width of <NUM> and a thickness of <NUM> were obtained.

B4: The optical densities of these test sheets were determined using a SW-densitometer (Heiland electronic GmbH TRD <NUM>, Wetzlar, Germany) using a blend with diameter of <NUM>. This apparatus can measure the optical density until a maximum value of <NUM> log. D in transmission mode. After this value, a saturation region is reached (overload).

B5: L*-values were measured at different angles of observation (-<NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>° and <NUM>°) using a Byk-Mac in the CILAB system. The conditions used were D65 (light source) and <NUM>° for the standard photometric observer; the angle of incidence was <NUM>°. L*<NUM>∘was used as measure of the brightness and the flop was calculated to the well-known formula (V): <MAT>.

Underneath of the sample plates black and white papers were deposited and the L*-values were measured. For the ratio L*<NUM>∘,black /L*<NUM>°,white it was found that the OD was at <NUM> if this ratio was less than <NUM>%.

B6: Furthermore the NIR separating behavior of the samples was evaluated by the following tests developed and conducted by cyclos-HTP for the NIR detection and sorting performance of packaging samples.

The test equipment was a setup by Steinert UniSort (Germany) and included a high-resolution operational NIR camera with a full-spectral analysis. The samples were placed on an accelerator belt with <NUM> width and a speed of <NUM>/s. This accelerator belt passed a valve block with <NUM> nozzle distance and <NUM> bar air pressure and included nineteen operational classifiers. The measured data were read out by a software and visualized for the NIR image. Each kind of detectable plastic was highlighted by a predetermined color. <NUM> Sample preparation:
For a statistical evaluation of measurable surfaces the probability of different positions) of the samples were evaluated.

Also all relevant components of the test samples were evaluated.

As specimen size <NUM> pieces per article were used.

This first test was passed when at least <NUM>% of the pixels generated from the sample were attributable to a certain kind of plastic.

The sorting test was passed when the discharge behavior is ≥ <NUM>%.

A limited sorting behavior is attributed to a discharge behavior of > <NUM>% to < <NUM>% (test failed) and the sorting test is definitely failed when the discharge behavior is ≤ <NUM>%.

In table <NUM> the results characterizing the metal effect pigments are summarized:.

The hiding behavior of the two different aluminum effect pigments is strikingly different: for Chromal V the sorting tests ale fulfilled only at extremely low concentrations (<NUM>%) , whereas for the <NUM> samples the concentration can be up to <NUM> wt. % to pass the sorting tests. The Chromal samples are much smaller and thinner yielding a larger number of particles per gram metal pigment. Also, they exhibit a broad particle size distribution (span) yielding a better hiding power compared to the other sample.

The three pearlescent effect pigments have no effect on the discharge behavior irrespective of their concentrations. The hiding power is largest for Symic A604 (Example <NUM> series), followed by the Symic B604 series (Example <NUM> series) and the Symic C604 (Example <NUM> series). This behavior can be attributed to the smaller particle sizes (the D<NUM>-values increases within this series).

As smaller synthetic mica is obtained by milling also fractions of smaller particle sizes yield thinner particles. As the layer thickness of TiO<NUM> is the same (about <NUM>) for all samples the smallest and thinnest particles (A-series) will exhibit the highest TiO<NUM> content. As this high-refractive index layer is mainly responsible for the hiding power the smallest fractions have a high hiding power.

From these tests the possible highest concentrations for each aluminum pigment can be estimated. To work with these high concentrations, however, may lower the process stability as the plastic bodies may behave different in different shapes and also the sorting behavior may in reality differ from device to device. Therefore mixtures of the metal pigments with the pearlescent pigments are more favourable.

Claim 1:
Plastic part having a mean thickness tpl containing a mixture of effect pigments comprising flaky aluminum pigments obtained by milling of aluminum or aluminum-based alloy powder in a concentration cAl and silvery, absorbing pearlescent pigments in a concentration cP,
wherein
i) for flaky aluminium pigments having a D<NUM> ≥ <NUM>: cAl * tpl is in a range of <NUM> to <NUM> wt.% cm, or
ii) for flaky aluminium pigments having a D<NUM> < <NUM>: cAl * tpl is in a range of <NUM> to <NUM> wt.% cm, wherein each concentration refers in wt.% to the total plastic part.