Light shielding polymer composition

Abstract

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

Description

[0001] This invention relates to polymer compositions suitable for manufacturing articles with light-shielding properties. More specifically, this invention relates to compositions comprising polycarbonate, which are white, opaque, and light-shielding, and exhibit good mechanical properties. The invention also relates to articles comprising or composed of such compositions.

[0002] Polycarbonate-containing plastic parts are used in a variety of applications, particularly in the automotive and electronics industries. In particular, the widespread use of LED light sources has placed new demands on these polycarbonate-containing plastic parts. In some applications (such as consumer electronics and automotive headlight bezels), light-shielding performance is an industry challenge for white polycarbonate. TiO2 is considered an effective white pigment in polycarbonate due to its high refractive index. However, at high TiO2 loadings (e.g., 20% or more), sufficient light-shielding ability is not achieved to shield LED spots, especially in thin-walled applications (thickness up to 2 mm). Furthermore, polycarbonate materials are prone to degradation at very high TiO2 loadings. On the other hand, colorants with high absorption coefficients (such as carbon black) are very effective at light shielding. However, even adding trace amounts of carbon black can make plastic parts appear dull, which is undesirable. Therefore, there is a need for polymer compositions that combine high whiteness with good light-shielding performance.

[0003] CN114231004A discloses a white PC material comprising the following components by weight: 90.96-94.69 parts polycarbonate resin; 4-6 parts titanium dioxide; 0.5-1.5 parts zinc sulfide; 0.01-0.04 parts whitening agent; and 0.8-1.5 parts functional additives. The whitening agent is 2,5-bis(5-tert-butyl-2-benzoxazole)thiophene.

[0004] CN111978699B discloses a high-light-shielding, thin-walled, flame-retardant PC material, comprising 70-90% PC resin, 5-20% light-shielding filler, 2-4% toughening agent, 0.2-0.5% antioxidant, 0.2-0.5% lubricant, 0.1-0.3% ultraviolet absorber, 0.1-1% flame retardant A, 1-10% flame retardant B, 0.1-0.5% anti-dripping agent, and 0.2-0.5% silicone masterbatch. The silicone masterbatch is used as a dispersant.

[0005] US7928168B2, corresponding to US2008 / 230751, discloses a polymer composition that is white and opaque, comprising (i) a silicone-free polycarbonate polymer and (ii) a blend of a polycarbonate-polysiloxane copolymer; a whitening agent, such as titanium dioxide; and (iii) a non-white colorant, such as carbon black. The composition also exhibits good low-temperature impact strength and good processing stability.

[0006] US20050085580A1 discloses a light-colored polycarbonate composition comprising a polycarbonate-siloxane copolymer containing at least 3% by weight of a siloxane to provide the total composition; and a colorant composition comprising titanium dioxide with an organic coating. This composition can be used to prepare molded articles, particularly those having thin-walled regions that are light-colored and have good flame retardancy.

[0007] At least some prior art discloses white polycarbonate compositions based on the use of TiO2, but these require the use of polycarbonate-siloxane copolymers or silicone additives. These additives increase the cost of the composition and make its manufacture more complex. Moreover, using only whitening agents such as TiO2 and / or ZnO does not contribute to achieving good light-shielding effects, especially when the part thickness is reduced. Even at high loadings, such as 15% to 20% by weight of TiO2, it is not possible to provide sufficient hiding power to shield LED spots in thin-walled applications. Furthermore, properties such as stability during polymer processing and mechanical properties such as impact strength are adversely affected by such high loadings of whitening agents.

[0008] Therefore, there is a need for white polycarbonate compositions with good light-blocking properties, especially for articles with a wall thickness of 1 mm or less.

[0009] The purpose of this invention is to provide a polymer composition that is white, has good light-blocking properties when it is thin, and exhibits good mechanical properties.

[0010] This objective is achieved according to the invention disclosed herein, which relates to a polymer composition comprising, based on the total weight of the composition:

[0011] A. 65-90% by weight of aromatic polycarbonate,

[0012] B. A composition comprising 5-25% by weight of titanium dioxide (B1) and at least one second component (B2), the second component being selected from zinc sulfide, zinc oxide, calcium carbonate, and barium sulfate, wherein preferably the weight ratio of B1 to B2 is from 95:5 to 40:60.

[0013] C. 0.0001-0.1% by weight of carbon black,

[0014] D. 1-10% by weight of other components,

[0015] The total weight of (A) to (D) is 100%.

[0016] The invention will now be described in more detail.

[0017] (A) Polycarbonate

[0018] Aromatic polycarbonates are typically manufactured using two different techniques. In the first technique, known as interfacial technology or interfacial process, phosgene reacts with bisphenol (usually bisphenol A (BPA)) in a liquid phase. The other well-known technique is the so-called melt technique, sometimes also called melt transesterification or melt polycondensation. In the melt technique or melt process, bisphenol (usually BPA) reacts with a carbonate (usually diphenyl carbonate (DPC)) in a molten phase. Aromatic polycarbonates prepared by melt transesterification are known to differ structurally from those prepared by the interfacial process. In this respect, it is important to note that, in particular, so-called “melt polycarbonates” typically have a minimal amount of Fries branching, which is generally not present in “interfacial polycarbonates.” Furthermore, melt polycarbonates typically have a higher number of phenolic hydroxyl end groups, while polycarbonates prepared by the interfacial process are typically capped and have up to 150 ppm, preferably up to 50 ppm, more preferably up to 10 ppm of phenolic hydroxyl end groups.

[0019] According to the invention, preferably, the aromatic polycarbonate comprises or consists of a 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% by weight, preferably at least 90% by weight, of a bisphenol A polycarbonate homopolymer, based on the total amount of aromatic polycarbonate. More preferably, the aromatic polycarbonate in the composition consists substantially of or consists of a bisphenol A polycarbonate homopolymer, meaning that the aromatic polycarbonate comprises at least 98% by weight of a bisphenol A polycarbonate homopolymer. Preferably, the aromatic polycarbonate has a weight-average molecular weight (Mw) of 15,000-60,000 g / mol, determined using gel permeation chromatography of polycarbonate standards. Preferably, the Mw of the aromatic polycarbonate is 30,000-65,000 g / mol.

[0020] In one respect, polycarbonate is interfacial polycarbonate.

[0021] In another aspect, the polycarbonate is a molten polycarbonate, preferably a molten polycarbonate consisting essentially of or composed of bisphenol A polycarbonate homopolymer.

[0022] In another aspect, the polycarbonate is a mixture of 20-80 wt% or 40-60 wt% interfacial polycarbonate and 80-20 wt% or 60-40 wt% molten polycarbonate, based on the weight of aromatic polycarbonate.

[0023] Polycarbonate can be a mixture of two or more polycarbonates with different melt volume rates (i.e., molecular weights). The polycarbonates in this mixture can all be bisphenol A polycarbonate homopolymers.

[0024] In another aspect, aromatic polycarbonates comprise polycarbonate copolymers containing structural units of bisphenol A and structural units from another bisphenol.

[0025] Aromatic polycarbonate (A) preferably has a thickness of 5-30 cm. 3 The melt volume rate was measured per 10 min according to ISO 1133 (300 °C, 1.2 kg). The melt volume rate of polycarbonate (A) can be 6-27 cm⁻¹. 3 / 10min. If polycarbonate (A) is a mixture of two or more polycarbonates, this requirement applies to the mixture and therefore does not limit the melt volume rate of individual polycarbonates. However, preferably, each individual polycarbonate in such a mixture has a melt volume rate of 5-30cm. 3 / 10min, preferably 6-27cm 3 Melt volume rate per 10 min.

[0026] Preferably, the aromatic polycarbonate (A) does not contain polycarbonate-polysiloxane copolymers and / or polysiloxanes.

[0027] Component B

[0028] Component B gives the polymer composition a white color. Incident light is reflected onto articles made from the compositions disclosed herein.

[0029] According to the present invention, the polymer composition comprises 5-25% by weight of a composition comprising titanium dioxide (B1) and at least one second component (B2) selected from zinc sulfide, zinc oxide, calcium carbonate, and barium sulfate, wherein the weight ratio of B1 to B2 is preferably 95:5 to 40:60. Preferably, the weight ratio of B1 to B2 is 90:10 to 60:40, more preferably 80:20 to 65:35. Within this range, the polymer composition is found to have satisfactory impact resistance, rigidity, and whiteness.

[0030] In one aspect, component (B) comprises titanium dioxide (B1) and zinc sulfide (B2) or is composed thereof. There are no particular limitations on the titanium dioxide, but it may include, for example, high-temperature stable rutile, low-temperature stable anatase, and medium-temperature stable brookite titanium dioxide. The titanium dioxide particles may also contain an organic coating to reduce surface reactivity and improve processing properties. Preferably, at least a portion of the titanium dioxide is coated with alumina or polysiloxane. Coated titanium dioxide is commercially available from many suppliers, such as EI du Pont de Nemours, Inc., Kronos Worldwide International, Inc., and Millennium Chemicals, and is available in many different grades. Examples of commercially available titanium dioxide suitable for use include, but are not limited to, Kronos. ® 2233, Kronos ® 2450 (both from Kronos Worldwide, Inc.) and Tiona ® RL-91 (Millennium Chemicals). The coated titanium dioxide has a strength of 700 g / m³. 2 The bulk density, oil absorption of 13% (measured using ISO 787 / 5), and titanium dioxide content greater than or equal to 96% are all acceptable. There are no particular limitations on zinc sulfide. Zinc sulfide can be used in combination with titanium dioxide to further improve the opacity of the polymer composition and achieve a synergistic effect in improving whiteness.

[0031] (C) Carbon black

[0032] According to the present invention, the polymer composition comprises 0.0001-0.1% by weight of carbon black, preferably present in an amount of 0.0005-about 0.01% by weight, more preferably 0.001-0.01% by weight, based on the total weight of the composition. For the manufacture of the polymer composition of the present invention, the carbon black may be present in powder form or in masterbatch form. In some aspects, the carbon black may be surface-treated with a predetermined sizing material to prevent reaction with the resin and to improve the degree of impregnation. Surface treatment may be performed during the preparation of carbon black granules or in a subsequent 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 purposes of the present invention, namely to provide a light-shielding but white polycarbonate composition, the type of carbon black is less critical.

[0033] (D) Other components

[0034] Other components used in the composition may include one or more of the following: impact modifiers, flame retardants, anti-drip agents, flame retardant synergists, lubricants, dispersants and release agents, nucleating agents, stabilizers, UV stabilizers, heat stabilizers, antioxidants, colorants, and fluorescent whitening agents.

[0035] Composition

[0036] The specific types and amounts of materials constituting the polymer composition allow for the attainment of desired property distributions in terms of particular light-shielding properties and mechanical properties. The examples and comparative examples disclosed herein provide those skilled in the art with materials that fall within and outside the scope of the invention, thereby forming a basis for developing further embodiments according to the invention without undue burden.

[0037] Preferably, the composition does not contain polycarbonate-polysiloxane copolymers and / or polysiloxanes.

[0038] To avoid any doubt, those skilled in the art will understand that the total weight of the composition will be 100% by weight and that any combination that does not form a total of 100% by weight of material is impractical and does not conform to the present invention.

[0039] According to the present invention, the polymer composition has, or is selected to have, an L of 90 or greater, preferably at least 95, as determined by the International Commission on Illumination (CIE) Lab on a sample sheet having a thickness of 2 mm. value.

[0040] Preferably, the polymer composition has, or is selected to have, a white light transmittance of less than 0.5% when molded and measured in a sample having a thickness of at least 2.0 mm, preferably at least 1.5 mm, more preferably at least 1.0 mm, and even more preferably at least 0.3 mm, according to the method described in the specification.

[0041] Preferably, the polymer composition has or is selected to have a notched Izod impact resistance of at least 300 J / m, preferably 300-900 J / m, as determined by ASTM D-256 at 23°C.

[0042] Preferably, the polymer composition has, or is selected to have, a thickness of 5-20 cm as determined according to ISO 1133 (300°C, 1.2 kg). 3 / 10min, preferably 8-18cm 3 Melt volume rate per 10 min.

[0043] Preferred ranges for the amounts of components and preferred ranges for the properties of the composition can be combined without limitation, provided that these fall within the scope of the invention as defined herein in its broadest form. That is, preferred ranges for one or more amounts and / or types of components constituting a polymer composition can be combined with one or more preferred ranges for the properties of the polymer composition, and all such combinations are considered to be disclosed herein.

[0044] Uses / Products

[0045] The polymer compositions of the present invention can be used to manufacture white articles with thin walls, which must still have high opacity, i.e., no or very low visible light transmission. Articles comprising the polymer compositions are also provided. The polymer compositions can be molded into useful molded articles by various methods such as injection molding, extrusion, rotational molding, blow molding, and thermoforming to form articles such as computer and office machine housings (e.g., monitor housings), handheld electronic device housings (e.g., mobile phone and digital camera housings), fixed electrical housings (e.g., exit signs, humidifier housings, and HVAC (heating, ventilation, and air conditioning) housings), electrical connectors and lighting fixtures, decorative items, components for household appliances, roofs, greenhouses, sunrooms, swimming pool enclosures, etc.

[0046] In certain aspects, the article is an injection-molded article having a thickness of 0.1-3.0 mm, preferably 0.3-2.0 mm, for example 0.5-1.5 mm, and having an L of 90 or greater as determined by the International Commission on Illumination (CIE) Lab on a sample sheet with a thickness of 2 mm. value.

[0047] Furthermore, this invention relates to the use of the polymer compositions disclosed herein in the manufacture of articles for LED lighting shielding, preferably articles for consumer electronics and automotive headlight bezels.

[0048] Therefore, the present invention also relates to an apparatus comprising an article made at least in part from the polymer compositions disclosed herein and a light source, preferably an LED light source, the apparatus being configured such that the light source radiates light onto the article during use.

[0049] The invention presented herein will now be further illustrated based on the following non-limiting embodiments.

[0050] The examples and comparative examples provided herein, together with the description, are intended to provide sufficient guidance to those skilled in the art to manufacture other compositions that meet the desired properties. In this regard, it should also be noted that in some preferred embodiments, such as the invention presented herein, a composition is selected to have certain properties. The properties and methods for their determination are known in themselves, and therefore those skilled in the art do not face an undue burden to establish whether other compositions meet the requirements of the invention as defined and disclosed herein.

[0051] Measurement methods

[0052]

[0053] Table 1: Components of the composition and their sources

[0054]

[0055] The quantities in Table 2 are expressed as a weight percentage based on the total weight of the composition. In all examples, the total amount of the components is equal to 100% by weight.

[0056] Table 2: Formulations and properties of polymer compositions

[0057]

[0058]

[0059] NM - Not measured

[0060] As can be seen from the results in Table 2, CE1, a PC composition containing 15% TiO2, can achieve L The light-blocking performance was found to be 98.0% ultra-white. However, poor light-blocking properties were observed. With increasing carbon black loading, the light-blocking performance was effectively improved (CE2, CE3, CE4), but at the cost of whiteness (L). At the cost of (value), it decreased significantly with increasing carbon black loading. The color properties of the composition incorporating coloring pigments (CE5) were also tested. When blue and purple dyes were added, they were found to improve the opacity; however, L... and b A sharp drop in value indicates that the color has darkened and a blue shift has occurred. Carbon black is introduced to further improve the light-blocking performance (CE6), and a fluorescent whitening agent is introduced in CE7 to maintain brightness.

[0061] CE8, E1, and E2 represent the properties of polymer compositions containing TiO2 and ZnS as inorganic additives. Surprisingly, the combination of TiO2 and ZnS was found to have even better light-blocking properties than TiO2 or ZnS used alone, indicating a synergistic effect between TiO2 and ZnS to improve light-blocking performance. It was also observed that the optimal ratio between TiO2 and ZnS is important for achieving the desired performance balance.

[0062] Figure 1 The % transmittance curves relative to the light source wavelength of specimens molded from the polymer composition of Example 9 with thicknesses of 3 mm, 2 mm, 1 mm, and 0.3 mm, as determined according to the method provided in the specification, are shown. It was found that the %T value of the specimens shown was less than 0.1% in all cases conforming to the present invention.

[0063] Therefore, it has been demonstrated that the polymer resin compositions according to the present invention exhibit excellent whiteness properties, as well as light-blocking properties, impact resistance, and a balance between these properties. Those skilled in the art can readily make simple modifications or alterations to the present invention, and all such modifications or alterations are considered to be included within the scope of the present invention.

Claims

1. A polymer composition comprising, based on the total weight of the composition: (A) 65-90% by weight of aromatic polycarbonate, (B) A composition comprising 5-25% by weight of titanium dioxide (B1) and at least one second component (B2), the second component being selected from zinc sulfide, zinc oxide, calcium carbonate, and barium sulfate, wherein preferably the weight ratio of B1 to B2 is from 95:5 to 40:

60. (C) 0.0001-0.1% by weight of carbon black, (D) 1-10% by weight of other components, The total weight of (A) to (D) is 100%.

2. The polymer composition according to claim 1, wherein it has or is selected to have an L of at least 90, preferably at least 95, as determined by the International Commission on Illumination (CIE) Lab on a 2 mm thick sample sheet. value.

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

5. The polymer composition according to any one or more of claims 1-4, wherein the polycarbonate (A) has a thickness of 5-30 cm² as determined according to ISO 1133 (300°C, 1.2 kg). 3 Melt volume rate per 10 min.

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

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

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

9. The polymer composition according to any one or more of claims 1-8, wherein the other component comprises one or more of impact modifiers, flame retardants, anti-drip agents, flame retardant synergists, lubricants, dispersants, release agents, nucleating agents, stabilizers, UV stabilizers, heat stabilizers, antioxidants, colorants, and fluorescent whitening agents.

10. The polymer composition according to any one or more of claims 1-9, having or further being selected to have a white light transmittance of less than 0.5% when measured on a molded specimen with a thickness of at least 2.0 mm, preferably at least 1.5 mm, more preferably at least 1.0 mm, or even more preferably at least 0.3 mm, according to the method described in the specification.

11. The polymer composition according to any one or more of claims 1-10, having or further preferably having a notched Izod impact strength of at least 300 J / m, preferably 300-900 J / m, as determined according to ASTM D-256 at 23°C.

12. The polymer composition according to any one or more of claims 1-11, wherein the melt volume rate of the composition is 5-20 cm⁻¹ as determined according to ISO 1133 (300°C, 1.2 kg). 3 / 10min, preferably 8-18cm 3 / 10min.

13. An article comprising or consisting of the polymer composition according to any one or more of claims 1-12.

14. Use of the polymer composition according to any one or more of claims 1-13 for manufacturing a light-shielding article, wherein the light-shielding article preferably has a thickness of 0.1-3.0 mm, preferably 0.3-2.0 mm, for example 0.5-1.5 mm, or up to 1.0 mm.

15. An apparatus comprising an article of at least part made of a polymer composition according to any one or more of claims 1-12 and a light source, preferably an LED light source, the apparatus being configured such that the light source radiates light onto the article of use.

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