Light-shielding polymer composition

Abstract

Disclosed herein is polymer composition comprising, based on the total weight of the composition (A) from 65 - 90 wt.% of aromatic polycarbonate (B) from 5 - 25 wt.% of an additive composition comprising titanium dioxide (B1) and at least one second component (B2), selected from the group consisting of zinc sulfide, zinc oxide, calcium carbonate and barium sulfate, wherein the weight ratio between the B1 and B2 is from 95:5 to 40:60. (C) from 0.0001 to 0.1 wt.% of carbon black (D) from 1 to 10 wt.% of further components wherein, the combined amounts of (A) to (D) is 100 wt. %.

Description

[0001] LIGHT-SHIELDING POLYMER COMPOSITION

[0002] The present invention relates to a polymer composition suitable for the manufacture of articles having light-shielding properties. More in particular, the present invention relates to compositions comprising polycarbonate which have a white color, are opaque and light-shielding, along with exhibiting good mechanical properties. The present invention further relates to articles comprising or consisting of such compositions.

[0003] Plastic parts comprising polycarbonate are used in a variety of applications such as in particular in the automotive and electronics industry. Especially, with the wide application of LED light source, new requirements have been put forward for such plastic parts comprising polycarbonate. In some applications like consumer electronics and auto lighting bezel, light-shielding performance is an industry challenge for white polycarbonate. TiO2is considered as an effective white pigment in polycarbonate, due to its high refractive index. However, at high loading of TiO2(such as 20% or more) sufficient light-shielding power is not obtained, in order to shield the LED spot, especially in thin wall applications (thickness up to 2 mm). Additionally, at very high loading of TiO2the polycarbonate material is easily degraded. On the other hand, colorants with high absorption coefficient like carbon black is very powerful for light-shielding. However, adding even tiny loading of carbon black makes the plastic part appear dark, which is not desirable. Accordingly there is a need for polymer compositions demonstrating high- whiteness in combination with good light-shielding performance.

[0004] CN114231004A discloses white PC material comprising the following components in parts by weight: 90.96-94.69 parts of polycarbonate resin; 4-6 parts of titanium dioxide; 0.5-1.5 parts of zinc sulfide; 0.01-0.04 parts of a whitening agent; 0.8-1.5 parts of functional auxiliary agent. The whitening agent is 2.5-bis (5-tert-butyl-2-benzoxazole) thiophene.

[0005] CN111978699B discloses high-shading thin-wall flame-retardant PC material, comprising, 70-90% of PC resin, 5-20% of shading filler, 2-4% of toughening agent, 0.2- 0.5% of antioxidant, 0.2-0.5% of lubricant, 0.1 -0.3% of ultraviolet absorbent, 0.1-1% of flame retardant A, 1-10% of flame retardant B, 0.1 -0.5% of anti-dripping agent and 0.2- US7928168B2, corresponding to US 2008 / 230751 , discloses a polymer composition, which is white and opaque comprising a blend of (i) a silicon-free polycarbonate polymer and (ii) a polycarbonate-polysiloxane copolymer; a whitener such as titanium dioxide; and (iii) a non-white colorant such as carbon black. The composition also has good impact strength at low temperatures and good stability during processing.

[0006] US20050085580A1 discloses light-colored polycarbonate compositions comprising polycarbonate-siloxane copolymer in an amount sufficient to provide an amount of siloxane of at least 3% by weight of the total composition; and a colorant composition comprising titanium dioxide having an organic coating. The composition can be used to prepare shaped articles, particularly those with thin wall region that has both light color and good flame-retardance.

[0007] In at least some of the prior white polycarbonate compositions based on the use of TiO2are disclosed, which however require the use of polycarbonate-siloxane copolymer or silicone additives. Such additives add cost to the composition and more complexity with regards to their manufacture. Also mere use of Whiteners such TiO2and / or ZnO does not help to achieve good light-shielding, especially as the part thickness decreases. Even at high loadings, for example 15 wt.% to 20 wt.% TiO2, cannot provide sufficient hiding power to shield the LED spot in thin wall applications. Furthermore, properties such as stability of the polymer during processing and mechanical properties such as impact strength are adversely affected by such a high loading of whitener.

[0008] Accordingly, there is a need for white polycarbonate compositions with good lightshielding performance, in particular for articles having wall thicknesses of 1 millimeter or less.

[0009] It is an object of the invention to provide for a polymer composition having a white color, have good light-shielding properties at low thickness, and exhibit good mechanical properties.

[0010] This object is met in accordance with the invention disclosed herein which is directed at a polymer composition comprising, based on the total weight of the composition A. from 65 - 90 wt.% of aromatic polycarbonate

[0011] B. from 5 - 25 wt.% of a composition comprising titanium dioxide (B1) and at least one second component (B2), selected from the group consisting of zinc sulfide, zinc oxide, calcium carbonate and barium sulfate, wherein preferably the weight ratio between the B1 and B2 is from 95:5 to 40:60.

[0012] C. from 0.0001 to 0.1 wt.% of carbon black

[0013] D. from 1 to 10 wt.% of further components wherein, the combined amounts of (A) to (D) is 100 wt. %.

[0014] The invention will now be described in more detail.

[0015] (A) Polycarbonate

[0016] Aromatic polycarbonates are generally manufactured using two different technologies. In a first technology, known as the interfacial technology or interfacial process, phosgene is reacted with a bisphenol, typically bisphenol A (BPA) in a liquid phase. Another well- known technology is the so-called melt technology, sometimes also referred to as melt transesterification or melt polycondensation technology. In the melt technology, or melt process, a bisphenol, typically BPA, is reacted with a carbonate, typically diphenyl carbonate (DPC), in the melt phase. Aromatic polycarbonate obtained by the melt transesterification process is known to be structurally different from aromatic polycarbonate obtained by the interfacial process. In that respect it is noted that in particular the so called “melt polycarbonate” typically has a minimum amount of Fries branching, which is generally absent in “interfacial polycarbonate”. Apart from that melt polycarbonate typically has a higher number of phenolic hydroxy end groups while polycarbonate obtained by the interfacial process is typically end-capped and has at most 150 ppm, preferably at most 50 ppm, more preferably at most 10 ppm of phenol hydroxyl end-groups.

[0017] In accordance with the invention, it is preferred that the aromatic polycarbonate comprises or consists of bisphenol A polycarbonate homopolymer (also referred to herein as bisphenol A polycarbonate). Preferably, the aromatic polycarbonate of the invention disclosed herein comprises at least 70 wt. %, preferably at least 90 wt.% of bisphenol A polycarbonate homopolymer based on the total amount of aromatic polycarbonate. More preferably, the aromatic polycarbonate in the composition essentially consists or consists of bisphenol A polycarbonate homopolymer, essentially consisting meaning that the aromatic polycarbonate comprises at least 98 wt.% of bisphenol A polycarbonate homopolymer. It is preferred that the aromatic polycarbonate has a weight average molecular weight (Mw) of 15,000 to 60,000 g / mol determined using gel permeation chromatography with polycarbonate standards. Preferably, the Mw of the aromatic polycarbonate is from 30,000 - 65,000 g / mol.

[0018] In an aspect, the polycarbonate is an interfacial polycarbonate.

[0019] In another aspect, the polycarbonate is a melt polycarbonate, preferably a melt polycarbonate essentially consisting or consisting of bisphenol A polycarbonate homopolymer.

[0020] In yet another aspect the polycarbonate is a mixture of from 20 - 80 wt.% or 40 - 60 wt.% of interfacial polycarbonate and from 80 - 20 wt.% or 60 - 40 wt.% of melt polycarbonate, based on the weight of the aromatic polycarbonate.

[0021] The polycarbonate may be a mixture of two or more polycarbonates differing in melt volume rate (i.e. in molecular weight). The polycarbonates of the mixture may both be a bisphenol A polycarbonate homopolymer.

[0022] In another aspect the aromatic polycarbonate comprises a polycarbonate copolymer comprising structural units of bisphenol A and structural units from another bisphenol.

[0023] The aromatic polycarbonate (A) preferably has a melt volume rate of from 5 - 30 cm3 / 1 Omin as determined in accordance with ISO 1 133 (300 °C, 1 .2 kg). The melt volume rate of the polycarbonate (A) may be from 6 - 27 cm3 / 10 min. In case the polycarbonate (A) is a mixture of two or more polycarbonates then this requirement applies to the mixture and accordingly does not limit the melt volume rates of the individual polycarbonates. It is however preferred that each individual polycarbonate in such a mixture has a melt volume rate of 5 - 30 cm3 / 1 Omin, preferably from 6 - 27 cm3 / 1 Omin.

[0024] It is preferred that the aromatic polycarbonate (A) does not comprise a polycarbonate - polysiloxane copolymer and / or a polysiloxane. Component B

[0025] Component B gives the polymer composition a white color. Incident light on an article manufactured from the composition disclosed herein is reflected.

[0026] In accordance with the invention, the polymer composition comprises from 5 - 25 wt.% of a composition comprising titanium dioxide (B1) and at least one second component (B2), selected from the group consisting of zinc sulfide, zinc oxide, calcium carbonate and barium sulfate, wherein the weight ratio between the B1 and B2 preferably is from 95:5 to 40:60. Preferably, the weight ratio between B1 and B2 is from 90:10 to 60:40, preferably from 80:20 to 65:35. Within this range, the impact resistance, rigidity and whiteness of the polymer composition is found to be satisfactory.

[0027] In an aspect component (B) comprises or consists of titanium dioxide (B1) and zinc sulfide (B2). The titanium dioxide is not particularly limited, but may include, for example, rutile type stable at high temperature, anatase type stable at low temperature, and brookite type titanium dioxide stable at intermediate temperature. Titanium dioxide particles may further comprise an organic coating to reduce surface reactivity and improve handling characteristics. Preferably, at least part of the titanium dioxide is coated with alumina or polysiloxane. Coated titanium dioxides are commercially available from many suppliers, such as E.l. du Pont de Nemours, Inc., Kronos Worldwide International, Inc. and Millennium Chemicals, and in many different grades. Examples of commercially available titanium dioxides suitable for use include, but are not limited to, Kronos® 2233, Kronos®2450 (both available from Kronos Worldwide, Inc.) and Tiona® RL-91 (Millennium Chemicals). The coated titanium dioxide has a bulk density of 700 g / m2, an oil absorption of 13 as measured using ISO 787 / 5 and a titanium dioxide content of greater than or equal to 96%. The zinc sulfide is not particularly limited. The zinc sulfide may work in combination with titanium dioxide to further improve the light-shielding property of the polymer composition, and may implement a synergistic effect of increasing whiteness.

[0028] (C) Carbon Black

[0029] In accordance with the invention, the polymer composition comprises from 0.0001 to 0.1 wt.% of carbon black based on the total weight of the composition, preferably, the carbon black is present in the amount of from 0.0005 to about 0.01 wt.%, more preferably from 0.001 to 0.01 wt.%. For the purpose of manufacturing the polymer composition of the present, the carbon black may be in the form of a powder or in the form of a masterbatch. In some aspects, the carbon black may be surface treated with a predetermined sizing material to prevent the reaction with the resin and improve the degree of impregnation. The surface treatment may be performed at the time of preparing the carbon black particles or in a later step. The sizing material is not particularly limited, but may be, for example, an epoxy compound. In this case, compatibility with the polycarbonate resin may be excellent. For the purpose of the invention, i.e. the provision of a light-shielding yet white polycarbonate composition, the type of carbon black is of less relevance.

[0030] (D) Further components

[0031] Further components that are used in the composition can comprise one or more of impact modifiers, flame-retardants, anti-dripping agents, flame retardant synergists, lubricants, dispersants, and mold release, nucleating agents, stabilizers, UV stabilizers, heat stabilizers, antioxidants, colorants, and optical brighteners.

[0032] Composition

[0033] The combination of specific types and amounts materials constituting the polymer composition allows for a desired property profile in terms of in particular light-shielding and mechanical properties. The examples and comparative examples disclosed herein provide the skilled person with materials that fall inside and outside the scope of the invention respectively, and thereby constitute a basis for the development of further embodiments according to the invention without undue burden.

[0034] It is preferred that the composition does not comprise a polycarbonate - polysiloxane copolymer and / or a polysiloxane.

[0035] For the avoidance of doubt the skilled person will understand that the total weight of the composition will be 100 wt.% and that any combination of materials which would not form 100 wt.% in total is unrealistic and not according to the invention.

[0036] In accordance with the invention, the polymer composition has or is selected to have a L* value of 90 or greater, preferably at least 95 as measured according to the International Lighting Commission (CIE) Lab on a specimen chip having a thickness of 2 mm.

[0037] Preferably, the polymer composition has or is selected to have less than 0.5% transmission of white light when molded and measured in a specimen, having a thickness of at least 2.0 mm, preferably, at least 1 .5 mm, more preferably at least 1 .0 mm, yet more preferably at least 0.3 mm in accordance with the method set out in the description.

[0038] Preferably, the polymer composition has or is selected to have a notched Izod impact resistance determined in accordance with ASTM D-256 at a temperature of 23°C of at least 300 J / m, preferably from 300 - 900 J / m.

[0039] Preferably, the polymer composition has or is selected to have a melt volume rate of the composition is from 5 - 20 cm3 / 10 min., preferably from 8 - 18 cm3 / 10 min measured in accordance with ISO 1133 (300°C, 1.2 kg).

[0040] Preferred ranges for the amount of the components and preferred ranges for the properties of the composition may be combined without limitation, provided of course that these fall within the scope of the invention as defined herein in its broadest form. That is to say, a preferred range for one or more of the amounts and / or types of the components constituting the polymer composition may be combined with a preferred range for one or more of the properties of the polymer composition and all such combinations are considered as disclosed herein.

[0041] Use / Article

[0042] The polymer composition of the present invention may be used for the manufacture of white-colored articles having thin walls which must still have high opacity, i.e. no, or very low visible light transmission. Shaped, formed, or molded articles comprising the polymer compositions are also provided. The polymer compositions can be molded into useful shaped articles by a variety of means such as injection molding, extrusion, rotational molding, blow molding and thermoforming to form articles such as, for example, computer and business machine housings such as housings for monitors, handheld electronic device housings such as housings for cell phones and digital cameras, fixed electrical enclosures such as exit signs, humidifier housings and H AC (heat ventilation and air conditioning) housings, electrical connectors, and components of lighting fixtures, ornaments, home appliances, roofs, greenhouses, sun rooms, swimming pool enclosures, and the like.

[0043] In a particular aspect the article is an injection molded article having a thickness of from 0.1 - 3.0 mm, preferably from 0.3 - 2.0 mm such as from 0.5 - 1.5mm and having a L* value of 90 or greater as measured according to the International Lighting Commission (CIE) Lab on a specimen chip having a thickness of 2 mm.

[0044] Furthermore, the invention is directed at the use of the polymer composition disclosed herein for the manufacture of articles for in the LED illumination-shielding field, preferably in consumer electronics and automotive lighting bezel.

[0045] Accordingly, the present invention is further directed at a device comprising an article manufactured at least in part from the polymer composition as disclosed herein and a light source, preferably an LED light source, configured such that the light source, in use, radiates light towards said article.

[0046] The invention as presented herein will now be further elucidated on the basis of the following non-limiting examples.

[0047] The present examples and comparative examples together with the description provided herein is considered to provide the skilled person sufficient guidance to manufacture further compositions meeting the required properties. In that respect, it is further noted that the invention as presented herein in some preferred embodiments, requires a composition, which is selected to have certain properties. The properties and their method of determination are well known as such so that accordingly the skilled person is not faced with an undue burden to establish whether or not a further composition meets the requirements of the invention as defined and disclosed herein.

[0048] Measurement methods able 1 : Components of the compositions and their source

[0049] The amounts in Table 2 are in weight percent based on the total weight of the composition. In all the examples, the total amount of components, equals 100 weight percent.

[0050] Table 2: Formulations and properties for the polymer compositions

[0051]

[0052] 5 NM - Not measured

[0053] From the results of Table 2, it can be seen CE1 , PC compositions with 15% TiO2was able to achieve ultra-white color with L* of 98.0. However, the light-shielding performance was found to be poor. With the increase of carbon black loading, the light-shielding performance was found to effectively improve (CE2, CE3, CE4) however at the expense of the whiteness (L* value) which significantly drops with an increased carbon black loading. The color performance of compositions were also experimented incorporating tinting colorants (CE5). When the blue and violet dyes are added, they were found to help in improving the light-shielding performance, however, the L* and b* value drops dramatically, indicating dark and blue color shift. Carbon black was introduced to further improve the light-shielding performance (CE6) along with optical brightener in CE7 in order to maintain the brightness.

[0054] CE8, E1 and E2 depicts the properties of the polymer composition comprising TiO2and ZnS together as inorganic additive. Surprisingly it is found that combinations of TiO2and ZnS gives even better light-shielding performance than TiO2or ZnS used individually, indicating the synergistic effect between TiO2and ZnS in improving light-shielding performance. It is also observed that an optimum ratio between TiO2and ZnS is important to achieve the desired balance of properties.

[0055] Figure 1 shows the % Transmission curve of specimens molded from the polymer composition of Exp. 9, having thickness of 3 mm thickness, 2 mm thickness, 1 mm thickness and 0.3 mm thickness against the wavelength of light source, measured in accordance with the method provided in the description. It was found that the %T value of the specimens showed was less than 0.1 % in all the cases, in accordance with the invention.

[0056] It is thus demonstrated that, a polymer resin composition in accordance with the present invention shows excellent whiteness properties along with light-shielding, impact resistance and balance of these properties. Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims

CLAIMS1 . A polymer composition comprising, based on the total weight of the composition(A) from 65 - 90 wt.% of aromatic polycarbonate(B) from 5 - 25 wt.% of a composition comprising titanium dioxide (B1) and at least one second component (B2), selected from the group consisting of zinc sulfide, zinc oxide, calcium carbonate and barium sulfate, wherein preferably the weight ratio between the B1 and B2 is from 95:5 to 40:60.(C) from 0.0001 to 0.1 wt.% of carbon black(D) from 1 to 10 wt.% of further components wherein, the combined amounts of (A) to (D) is 100 wt. %.

2. The polymer composition of claim 1 , having or selected to have a L* value of at least 90, preferably at least 95 as measured according to the International Lighting Commission (CIE) Lab on a specimen chip having a thickness of 2 mm .

3. The polymer composition of any one or more of claims 1 - 2, wherein component (B) comprises or consists of titanium dioxide (B1) and zinc sulfide (B2).

4. The polymer composition of any one or more of claims 1 - 3, wherein at least part of the titanium dioxide is coated with alumina or polysiloxane.

5. The polymer composition of any one or more of claims 1 - 4, wherein the polycarbonate (A) has a melt volume rate from 5 - 30 cm3 / 10 min. measured in accordance with ISO 1133 (300°C, 1.2 kg).

6. The polymer composition of any one or more of claims 1 - 5, wherein the polycarbonate (A) comprises at least 90 wt.% of bisphenol A polycarbonate homopolymer based on the total amount of polycarbonate (A).

7. The polymer composition of any one or more of claims 1 - 6, wherein the composition does not comprise a polycarbonate - polysiloxane copolymer and / or a polysiloxane.

8. The polymer composition of any one or more of claims 1 - 7, wherein the amount of carbon black is from 0.001 to 0.05 wt.%, preferably from 0.0005 to 0.01 wt.%.

9. The polymer composition of any one or more of claims 1 - 8, wherein the further components comprises one or more of impact modifiers, flame retardants, antidripping agents, flame retardant synergists, lubricants, dispersants, mold release agents, nucleating agents, stabilizers, UV stabilizers, heat stabilizers, antioxidants, colorants, and optical brighteners.

10. The polymer composition of any one or more of claims 1 - 9, having, or further selected to have, less than 0.5% transmission of white light when measured on a molded specimen, having a thickness of at least 2.0 mm, preferably, at least 1 .5 mm, more preferably at least 1.0 mm, yet more preferably at least 0.3 mm in accordance with the method set out in the description.

11. The polymer composition of any one or more of claims 1 - 10, having, or further selected to have a notched Izod impact resistance determined in accordance with ASTM D-256 at a temperature of 23°C of at least 300 J / m, preferably from 300 - 900 J / m.

12. The polymer composition of any one or more of claims 1 - 11 , wherein the melt volume rate of the composition is from 5 - 20 cm3 / 10 min., preferably from 8 - 18 cm3 / 10 min measured in accordance with ISO 1133 (300°C, 1.2 kg).

13. Article comprising or consisting of the polymer composition of any one or more of claims 1-12.

14. Use of the polymer composition of any one or more of claims 1 - 13 for the manufacture of light-shielding articles preferably having a thickness of of from 0.1 - 3.0 mm, preferably from 0.3 - 2.0 mm such as from 0.5 - 1 ,5mm, or at most 1 .0mm15. A device comprising an article manufactured at least in part from the polymer composition according to any one or more of claims 1 - 12 and a light source, preferably a LED light source, configured such that the light source, in use, radiates light towards the article.

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