Polycarbonate article

Abstract

The invention relates to an article comprising a surface layer portion consisting of a polycarbonate composition, wherein the surface layer portion comprises a foamed portion and a non-foamed portion.

Description

POLYCARBONATE ARTICLEThe present invention relates to an article comprising a polycarbonate composition and a process for making such article. The invention further relates to use of such article.Polycarbonate is well known as a transparent material. It is known to employ white pigments such as TiO2 to convert transparent polycarbonate into white color by compounding TiC>2 with a polycarbonate in an extruder. It is also known to add to polycarbonate light diffusing particles, typically cross-linked acrylate or silicone particles, in order to impart light diffusing properties while maintaining a relatively high light transmission.US2014 / 0226342 describes a reflector comprising a polycarbonate composition, wherein the polycarbonate composition comprising 10 wt % to 20 wt % titanium dioxide based upon a total weight of the polycarbonate composition. A plaque formed from the polycarbonate composition has a reflectance of greater than or equal to 95%. A molded article of the polycarbonate has transmission level greater than or equal to 90.0% at 2.5 mm thickness as measured by ASTM D1003-00 and a yellow index (Yl) less than or equal to 1.5 as measured by ASTM D1925.The addition of pigments such as TiC>2 results in changes of properties other than the color such as the mechanical properties. Such unavoidable changes in the mechanical properties may not be necessary or desirable for the intended application. Alternatively, paint coating process is sometimes utilized to make the transparent polycarbonate into white opaque. However, the chemicals in paint can cause a variety of environmental issues when they are manufactured, applied and used. Further to the foregoing, addition of light-diffusing particles adds complexity in terms of manufacturing and / or logistics and moreover will add cost to the final product.L. Monnereau et al., Polymer 59 (2015) 117-123 discloses gradient foaming of polycarbonate / carbon nanotube based nanocomposites with supercritical carbon dioxide and their EMI shielding performances. Foams were prepared from nanocomposites filled with 1 wt% or 2 wt% of carbon nanotube by the solid-statefoaming process by saturating polymer slices with CO2 at 75 bar and 100 °C and subsequently by placing the saturated PC samples at 190 °C in a hot press for 90 s.EP4132762B1 discloses a method for making a foamed article by partially infusing a foamable article with carbon dioxide in a liquid form. The foamable article comprises a thermoplastic elastomeric material.US2013 / 075944A1 discloses a method for producing a polycarbonate resin hollow foamed molded article. The foamed molded article may have a multilayer structure composed of a foamed resin layer and a non-foamed resin layer.WO2023 / 190679A1 discloses an extrusion foam molded sheet comprising a core layer made of a foamed resin and a second skin layer made of a non-foamed layer. The skin layer is extruded from the die outlet in an unfoamed state by a coextrusion method, and is laminated integrally with the core layer.It is an object of the invention to provide an opaque or translucent article in which the above-mentioned and / or other problems are solved at least in part.The present invention provides an article comprising a surface layer portion consisting of a polycarbonate composition, wherein the surface layer portion comprises a foamed portion and a non-foamed portion.The present invention provides an article comprising a surface layer portion consisting of a polycarbonate composition, wherein the surface layer portion comprises a foamed portion and a non-foamed portion, wherein the foamed portion and the non-foamed portion are non-laminated.The present invention provides an article comprising a surface layer portion consisting of a polycarbonate composition, wherein the surface layer portion comprises a foamed portion and a non-foamed portion, wherein the foamed portion and the non-foamed portion are non-laminated, wherein the foamed portion is present at an outer surface of the surface layer portion and the non-foamed portion is adjacent to the foamed portion and is further away from the outer surface of the surface layer portion than the foamedportion. Thus, the foamed portion defines the outer surface of the article and the nonfoamed portion is beneath the foamed portion of the article.The article according to the invention is a partly foamed article. Part or all of the surfaces of the article according to the invention is foamed and has a cellular structure. Observation of the surface of the article according to the invention e.g. by (electron) microscope can reveal the presence of cells. The cells are present for a certain thickness from the surface. This part of the surface layer portion having a cellular structure is referred as a foamed portion. After a certain thickness from the surface, the surface layer portion has a part which is free of cells or substantially free of cells. This part of the surface layer portion further away from the surface than the foamed portion is referred as the non-foamed portion. Observation of the cross section of the surface layer portion e.g. by (electron) microscope can reveal the presence of the foamed portion and the non-foamed portion. The skilled person will understand that the difference between the foamed portion and the non-foamed portion is the density. The foamed portion has a density that is lower than the density of the non-foamed portion. From a composition, i.e. chemical perspective however both portions do not differ.The foamed portion and the non-foamed portion are non-laminated and thus the article according to the invention is different from a laminate of a non-foamed molded article and a layer of a foamed material provided thereon.The foamed portion of the surface layer portion gives the article an opaque or translucent appearance while the non-foamed portion gives the article properties close to those of a non-foamed article. Accordingly, the article according to the invention achieves the desired light diffusion while maintaining similar mechanical properties as those of a non-foamed article. The shape of the article according to the invention can also be similar to the shape before foaming.When the article is described to have an opaque appearance, it is understood that when the article is placed on an object without a light source, the object is not visible through the article. If the object has a light source, it may be possible for at least a portion of the light from the light source to travel through the surface layer portion of the article.The degree of light diffusion can advantageously be controlled by adjusting the thickness of the foamed portion. Further, less time is needed for partial foaming than for complete foaming.The foamed portion has cells due to foaming. The cells can be open or closed, but generally are closed. The cells can have an aspect ratio of less than or equal to 10, specifically, less than or equal to 7.5, more specifically, less than or equal to 5, even more specifically, less than or equal to 3. The cells can have a size of less than or equal to 500 micrometers (pm), specifically, less than or equal to 250 micrometers, more specifically, less than or equal to 200 micrometers, even more specifically, less than or equal to 100 micrometers, still more specifically, less than or equal to 50 micrometers, and yet more specifically, less than or equal to 20 micrometers.Preferably, the foamed portion has a density of less than 0.90 g / cm3, for example 0.30 to 0.80 g / cm3.Preferably, the non-foamed portion has a density of at least 1.00 g / cm3, for example 1.10 to 1.25 g / cm3.Preferably, the article according to the invention has a density of 0.85 to 1.25 g / cm3, for example 1.10 to 1.25 g / cm3.Preferably, the density of the foamed portion with respect to the density of the nonfoamed portion is less than 90.0 wt%, for example 30.0 to 80.0 wt%.Preferably, the density of the article according to the invention with respect to the density of the non-foamed portion is 50.0 to 99.9 wt%, for example 70.0 to 99.7 wt% or 90.0 to 99.5 wt%.The density of the article according to the invention may be determined according to ISO1183-1 :2019.The density of the non-foamed portion may be determined according to ISO1183- 1 :2019.The density of the foamed portion may be determined according to IS0845:2006.Preferably, the foamed portion has a thickness of 0.01 to 1.5 mm. In some embodiments, the thickness is 0.5 to 1.5 mm, preferably 0.8 to 1.2 mm. In some embodiments, the thickness is at least 0.01 mm and less than 0.5 mm, preferably 0.03 to 0.1 mm. A higher thickness of the foamed portion results in an opaque appearance of the article and a lower thickness of the foamed portion results in a translucent appearance.Preferably, the surface layer portion according to the invention has a thickness of 1.0 to 10.0 mm, for example 1.5 to 5.0 mm.Preferably, the article according to the invention has a thickness of 1.0 to 10.0 mm, for example 1.5 to 5.0 mm.The ratio between the thickness of the foamed portion and the thickness of the nonfoamed portion can be 5:95 to 95:5, for example 20:80 to 80:20 or 30:70 to 70:30, or 5:95 to 50:50 or 10:90 to 40:60, or 50:50 to 95:5 or 60:40 to 90: 10.The ratio between the volume of the foamed portion and the volume of the non-foamed portion can be 5:95 to 95:5, for example 20:80 to 80:20 or 30:70 to 70:30, or 5:95 to 50:50 or 10:90 to 40:60, or 50:50 to 95:5 or 60:40 to 90:10.Preferably, the article according to the invention has a CIE L* value of at least 70, for example 75 to 95, measured with Xrite™ Ci7862 in reflection SCI mode, 10-degree observation angle.Preferably, the article according to the invention has a Tristimulus Value Y of Transmission of at most 50, for example 0.1 to 50, 1.0 to 40 or 3.0 to 35, or at most 5.0, as determined by ASTM E805 on XriteTM color spectrometer Ci7862 using transmission mode with D65 light source and a 10° observer.The article according to the invention may e.g. be a non-curved sheet or a curved sheet. The article according to the invention may e.g. shaped to at least partially enclose e.g. a light source.In some preferred embodiments, the article according to the invention is an injection molded article, i.e. an article obtained by injection molding of a polycarbonate composition and subsequent foaming.In some preferred embodiments, the article according to the invention is an extruded sheet, i.e. an article obtained by forming a sheet by extrusion of a polycarbonate composition and subsequent foaming. The extrusion may be a co-extrusion of the polycarbonate composition and a different polymer composition.The article according to the invention can consist of the surface layer portion. The article according to the invention can consist of the foamed portion and the non-foamed portion. Alternatively, the article according to the invention can also be a laminate of a layer of the surface layer portion and a further layer laminated on the non-foamed portion of the surface layer portion.Preferably, the article according to the invention is a light diffusing article, for example selected from the group consisting of a light bar, a light guide, a light cover (e.g. for covering a logo or for use on a music box), an LED lightbulb and an LED tube.The invention further relates to a system comprising a light-source and the article according to the invention, wherein the light source, when in use, is positioned such that at least a portion of the light from the light source travels through the surface layer portion of the article.In some embodiments, all or substantially all surfaces of the article according to the invention are foamed. For example, the article is a sheet and both sides of the sheet are foamed. In other embodiments, the article has a non-foamed surface layer portion in addition to a foamed surface layer portion. For example, the article according to the invention is a sheet wherein one side is foamed and the other side is not foamed, or a sheet having one side which has a non-foamed section and a foamed section.ProcessThe article according to the invention is obtained by partial foaming of a shaped article.The invention further provides a process for making the article according to the invention, comprising the steps of a) forming a polycarbonate composition to obtain a shaped article, b) impregnating the shaped article with a supercritical gas and c) degassing the impregnated article of step b).According to the invention, steps b) and c) are performed such that the shaped article is foamed only to a certain depth from a surface of the shaped article. It was observed that the thickness of the foamed portion can be controlled by selecting process conditions such as temperature, pressure and duration of steps b) and c).The step for obtaining a shaped article may be performed by any known method, such as injection molding and extrusion.In some preferred embodiments, the shaped article is a sheet. The sheet may have a thickness of 1.0 to 10.0 mm, for example 1.5 to 5.0 m.The shaped article subjected to steps b) and c) preferably has a high transparency. Preferably, the shaped article, for example a sheet, has Tristimulus Value Y of Transmission of at least 50 according to ASTM E805.The process according to the invention comprises the step of impregnating the shaped article with a supercritical gas. An impregnated article impregnated with the supercritical gas is obtained. A supercritical gas has a state that shows intermediate properties between gas state and liquid state. A gas reaches a supercritical state when its pressure and temperature go beyond a given point (critical point) that is specific for the gas.Any gas can be used for impregnation as long as the gas can penetrate into the polycarbonate composition in its supercritical state. For example, the supercritical gas can e.g. be gases of carbon dioxide, nitrogen, air, oxygen, hydrogen or inert gas like helium. Preferably, the supercritical gas is carbon dioxide gas.Generally, higher temperature, higher pressure and longer duration lead to the thickness of the foamed portion becoming greater.Preferably, step b) is performed at a temperature of 70 to 120 °C, more preferably 90 to 110 °C.Preferably, step b) is performed at a pressure of 10 to 18 MPa, more preferably 14 to 16 MPa.Preferably, step b) is performed for a duration of 20 minutes to 8 hours, more preferably 30 minutes to 120 minutes.In some embodiments, step b) is performed such that substantially all surfaces of the shaped article are exposed to the superficial gas. This results in substantially all surfaces of the shaped article are foamed and the thickness of the foamed section being relatively homogeneous over the whole surface.In some embodiments, step b) is performed such that part of surfaces of the shaped article is covered to prevent being exposed to the superficial gas. The part of the surfaces which has been covered is prevented from being foamed and the thickness of the foamed section of that part is substantially none.The process according to the invention comprises the step of degassing the impregnated molded article to obtain the partly-foamed article according to the invention.In this step, the pressure is reduced to a pressure below the critical pressure of the impregnated gas, typically to ambient pressure.Preferably, step c) is performed at a pressure release rate of 1.0 to 10 MPa / s, more preferably 2.0 to 6.0 MPa / s. Such pressure release rate results in uniform closed cells.Preferably, the partly-foamed article according to the invention has a thickness of at least 101%, for example 103 to 130%, of the thickness of the shaped article of step a).Preferably, step b) is performed in a container to obtain the impregnated article and step c) is performed by reducing the pressure in said container. Performing step b) and step c) in the same container allows a simple process.Preferably, step c) is started at the same temperature as in step b). For example, if the impregnated article has a temperature of 100 °C at end of step b), step c) is started by degassing the impregnated article at 100 °C. During step c), the temperature of the impregnated article can decrease e.g. to room temperature.The polycarbonate composition used for obtaining the article according to the invention comprises polycarbonate. The amount of polycarbonate in the composition may be at least 60 wt%, for example at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt.% or 100 wt% on the basis of the total amount of polymers in the polycarbonate composition.The polycarbonate in the polycarbonate composition can be a mixture of at least two polycarbonates which each may be a homopolymer or a copolymer. A specific example of a mixture consists of bisphenol A polycarbonate homopolymer and a polycarbonatepolysiloxane copolymer. It is preferred that the polycarbonate is a polycarbonate homopolymer obtained by reacting a bisphenol, such as bisphenol A, with a carbonate source such as phosgene or a diarylcarbonate such as diphenyl carbonate.Accordingly the polycarbonate of the composition according to the invention may be prepared using the so called interfacial process, wherein BPA reacts with phosgene, or may be prepared by means of the so-called melt or direct transesterification process, wherein BPA reacts with diphenyl carbonate. These two types of polycarbonate are known to the skilled person and may be further referred to herein as interfacial polycarbonate and melt polycarbonate. The skilled person knows that these two typesof polycarbonate differ in amount of Fries branching, which only exists in melt polycarbonate and further in the terminal hydroxyl content, which is typically much lower for interfacial polycarbonate.It is preferred that the polycarbonate is obtained via the interfacial process for the reason that said process, compared to the melt process, typically provides polycarbonate with a low number of hydroxyl chain ends. A low amount of hydroxyl chain ends is advantageous for heat stability and color retention of the polycarbonate. Nonetheless, polycarbonate obtained via the melt process, i.e. melt polycarbonate, is not excluded from being used in the present invention. In an embodiment the polycarbonate is a mixture of at least one polycarbonate obtained via the interfacial process and at least one polycarbonate obtained with the melt process. In such an embodiment the amount of melt polycarbonate may be from 30 - 70 wt.% and the amount of interfacial polycarbonate from 70 - 30 wt.%, based on the combined weight of the melt polycarbonate and the interfacial polycarbonate.It is preferred that the polycarbonate comprises or consists of interfacial polycarbonate. It is further preferred that the polycarbonate is an interfacial polycarbonate prepared by reacting bisphenol A and phosgene. Accordingly it is preferred that the polycarbonate is a bisphenol A polycarbonate or a bisphenol A polycarbonate homopolymer.Preferably, the polycarbonate, or mixture of polycarbonates, preferably has a melt flow rate according to ISO1133-1 :2011 at 300 °C and 1.2 kg of from 3 to 35 g / 10min, preferably from 6 to 25 g / 10min, more preferably from 14 to 21 g / 10min.In some preferred embodiments, the polycarbonate composition comprises a first polycarbonate having a melt flow rate according to ISO1133-1 :2011 at 300 °C and 1.2 kg of 3 to 15 g / 10min and a second polycarbonate having a melt flow rate according to ISO1133-1 :2011 at 300 °C and 1 .2 kg of 20 to 35 g / 1 Omin.Preferably, the polycarbonate composition preferably has a melt flow rate according to ISO1133-1 :2011 at 300 °C and 1 .2 kg of from 3 to 35 g / 1 Omin, preferably from 6 to 25 g / 10min, more preferably from 14 to 21 g / 10min.Polycarbonate and its production methods are per se well-known and is further described in detail e.g. in WO2014130751 ,

[0037] -

[0082] , incorporate herein by reference.Preferably, the polycarbonate composition comprises bisphenol A polycarbonate homopolymer, wherein the amount of bisphenol A polycarbonate homopolymer with respect to polycarbonate in the polycarbonate composition is at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt% or the polycarbonate in the polycarbonate composition is bisphenol A polycarbonate homopolymer.Preferably, polycarbonate in the polycarbonate composition used in the present invention does not comprise an elastomeric polycarbonate homopolymers or copolymers.The polycarbonate composition may comprise further polymers, for example polybutylene terephthalate, polyethylene terephthalate and / or acrylonitrile butadiene styrene (ABS) copolymers. The amount of further polymers may e.g. be 1.0 to 40 wt%, for example 1 .0 to 10 wt% with respect to the total composition.AdditivesThe polycarbonate composition of the present invention may optionally include additives which do not interfere with the previously mentioned desirable properties but enhance other favorable properties.Optional additives that may be compounded or blended into the composition of the invention in customary amounts include lubricants, release agents, UV absorbers, UV stabilizers, anti-oxidants, anti-ozonants, stabilizers, stain-proofing agents, anti-static additives, anti-microbial agents, melt viscosity enhancers, impact modifiers, quenchers, processing aids, and the like. The different additives that can be incorporated in the compositions are commonly used and known to one skilled in the art. Illustrative descriptions of such additives may be found in R. Gachter and H. Muller, Plastics Additives Handbook, 6th edition, 2009.The amount of the additives may e.g. be 0.0 to 5.0 wt%, for example 0.1 to 1.0 wt%. Preferably, the total amount of polymer and the additives is 100 wt% of the total composition. Preferably, the total amount of polycarbonate and the additives is 100 wt% of the total composition.Preferably, the polycarbonate composition is free of or substantially free of titanium dioxide and zinc oxide. Preferably, the total amount of titanium dioxide and zinc oxide in the composition is 0.0 wt% or more than 0.0 wt% and less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, more preferably less than 0.01 wt%.Preferably, the polycarbonate composition is free of or substantially free of inorganic pigments. Preferably, the amount of inorganic pigments in the composition is 0.0 wt% or more than 0.0 wt% and less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, more preferably less than 0.01 wt%.Preferably, the polycarbonate composition is free of or substantially free of carbon nanotubes. Preferably, the amount of carbon nanotubes in the composition is 0.0 wt% or more than 0.0 wt% and less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, more preferably less than 0.01 wt%.In some preferred embodiments, the polycarbonate composition comprises at least 60 wt% of the polycarbonate, 0 to 40 wt% of a further polymer selected from polybutylene terephthalate, polyethylene terephthalate and acrylonitrile butadiene styrene (ABS) copolymer and combinations thereof and 0 to 5.0 wt% of additives.In some preferred embodiments, the polycarbonate composition comprises at least 90 wt% of the polycarbonate, 0 to 10 wt% of a further polymer selected from polybutylene terephthalate, polyethylene terephthalate and acrylonitrile butadiene styrene (ABS) copolymer and combinations thereof and 0 to 5.0 wt% of additives.In particularly preferred embodiments, the polycarbonate composition comprises at least 60 wt% of polycarbonate, 0 to 40 wt% of a further polymer selected from polybutylene terephthalate, polyethylene terephthalate and acrylonitrile butadienestyrene (ABS) copolymer and combinations thereof and 0 to 5.0 wt% of additives, with respect to the total polycarbonate composition, wherein the total of the polycarbonate and the further polymer is 95 to 100 wt% with respect to the total polycarbonate composition, wherein the amount of bisphenol A polycarbonate homopolymer with respect to polycarbonate in the polycarbonate composition is at least 90 wt%, at least 95 wt%, at least 99 wt% or the polycarbonate in the polycarbonate composition is bisphenol A polycarbonate homopolymer.It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.The invention is now elucidated by way of the following examples, without however being limited thereto.Compounding:Components as shown in Table 2 were melt-mixed in a twin-screw extruder under the conditions shown in Table 1 to obtain pellets. Table 1. Extrusion profileInjection moldingThe obtained pellets were dried for 4-6hr at 120°C and injection molded by a 110 tonFanuc injection molding machine with barrel temperature setting at 280-300 °C and mold temperature 75 °C. Plaques having a thickness of 2 mm were obtained.Superficial CO2 foamingThe obtained plaques were placed in a foaming equipment such that substantially all surfaces of the plaques were exposed to the surrounding gas. The plaques were heated up to the desired temperature, and maintained at selected pressure for CO2 foaming under set dwelling time as shown in Table 2. Partly foamed plaques were obtained wherein both faces of the plaques are foamed.Figure 1 shows the cross section of a partly foamed plaque obtained according to the invention.PC1 : polycarbonate obtained by interfacial process having a melt flow index of 7 dg / min according to ISO1133-1:2011 at 300 °C and 1.2 kg;PC2: linear high flow polycarbonate having a melt flow index of 27 dg / min according to ISO1133-1 :2011 at 300 °C and 1.2 kgCIE L*, a*, b* were measured with Xrite™ Ci7862 in reflection SCI mode, 10-degree observation angle.T ristimulus Value Y of T ransmission was measured at the indicated thickness on Xrite™ color spectrometer Ci7862 using transmission mode with D65 light source and a 10° observer according to ASTM E805 “Standard Practice for Identification of Instrumental Methods of Color or Color-Difference Measurement of Materials”.Table 2A plaque made of a composition without TiO2 and without foaming is transparent (CEx 1). The addition of TiC>2 results in a plaque with a white diffusive appearance (CEx 2) or white opaque appearance (CEx 3).A partly-foamed plaque made by partial foaming of a plaque made of a composition without TiO2 has a white diffusive appearance (Ex 4 and 5) or white opaque appearance (Ex 6). Increase in dwelling time and increase in dwelling pressure decreases the transmission.

Claims

CLAIMS1. An article comprising a surface layer portion consisting of a polycarbonate composition, wherein the surface layer portion comprises a foamed portion and a non-foamed portion.

2. The article according to claim 1 , wherein the foamed portion has a density of less than 0.90 g / cm3and the non-foamed portion has a density of at least 1.00 g / cm3.

3. The article according to any one of the preceding claims, wherein the foamed portion has a thickness of 0.01 to 1.5 mm, for example 0.5 to 1.5 mm or at least 0.01 mm and less than 0.5 mm.

4. The article according to any one of the preceding claims, wherein the article has a T ristimulus Value Y of T ransmission of at most 50, for example 0.1 to 50, 1.0 to 40 or 3.0 to 35, as determined according to ASTM E805.

5. The article according to any one of the preceding claims, wherein the polycarbonate composition comprises at least 60 wt% of polycarbonate, 0 to 40 wt% of a further polymer selected from polybutylene terephthalate, polyethylene terephthalate and acrylonitrile butadiene styrene (ABS) copolymer and combinations thereof and 0 to 5.0 wt% of additives, with respect to the total polycarbonate composition.

6. The article according to any one of the preceding claims, wherein the polycarbonate composition comprises bisphenol A polycarbonate homopolymer, wherein the amount of bisphenol A polycarbonate homopolymer with respect to polycarbonate in the polycarbonate composition is at least 50 wt%, at least 75 wt%, at least 90 wt%, at least 95 wt%, at least 99 wt% or the polycarbonate in the polycarbonate composition is bisphenol A polycarbonate.

7. The article according to any one of the preceding claims, wherein the total amount of titanium dioxide and zinc oxide in the polycarbonate composition is 0.0 wt% ormore than 0.0 wt% and less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, more preferably less than 0.01 wt%.

8. The article according to any one of the preceding claims, wherein the amount of carbon nanotubes in the composition is 0.0 wt% or more than 0.0 wt% and less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, more preferably less than 0.01 wt%.

9. The article according to any one of the preceding claims, wherein the article has a thickness of 1.0 to 10.0 mm, for example 1.5 to 5.0 m.

10. The article according to any one of the preceding claims, wherein the article is an injection molded article or an extruded sheet.11 . The article according to any one of the preceding claims, wherein the article is a light diffusing article, for example selected from the group consisting of a light bar, a light guide, a light cover (e.g. for covering a logo or for use on a music box), an LED lightbulb and an LED tube.

12. A system comprising a light source and the article according to any one of claims 1 to 11 , wherein the light source, when in use, is positioned such that at least a portion of the light from the light source travels through the surface layer portion of the article.

13. A process for making the article according to any one of claims 1 to 11 , comprising the steps of a) forming a polycarbonate composition to obtain a shaped article, b) impregnating the shaped article with a supercritical gas and c) degassing the impregnated article of step b), preferably wherein steps b) and c) are performed in the same container.

14. The process according to claim 13, wherein the supercritical gas is CO2, step b) is performed at a temperature of 70 to 120 °C and a pressure of 10 to 18 Mpa for a period of 20 minutes to 8 hours andstep c) is performed at a pressure release rate of 1 to 10 MPa / s.

15. The process according to any one of claims 13-14, wherein the article obtained by step c) has a thickness of at least 101% of the thickness of the shaped article of step a).

16. The process according to any one of claims 13-15, wherein step b) is performed in a container to obtain the impregnated article and step c) is performed by reducing the pressure in said container17. The process according to any one of claims 13-16, wherein step b) is performed such that substantially all surfaces of the shaped article is exposed to the superficial gas.

18. The process according to any one of claims 13-16, wherein step b) is performed such that part of surfaces of the shaped article is covered to prevent being exposed to the superficial gas.

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