WO2017076770A1

WO2017076770A1 - Light diffusing article

Info

Publication number: WO2017076770A1
Application number: PCT/EP2016/076095
Authority: WO
Inventors: Ting Huang; Guangming WU; Yang FU; Liang Wen; Chaodong LIANG
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-11-02
Filing date: 2016-10-28
Publication date: 2017-05-11
Also published as: CN108350223A

Abstract

The invention relates to a light diffusing article, preferably a sheet, a tube or a light bulb, comprising a polypropylene composition comprising (A) a propylene-based polymer, wherein the propylene-based polymer consists of (a1) a propylene homopolymer or (a2) a propylene random copolymer consisting of at least 96 wt% of propylene and at most 4 wt% of an α-olefin having 2 or 4-10 carbon atoms based on the total weight of the propylene-based polymer and (B) crosslinked silicone particles.

Description

LIGHT DIFFUSING ARTICLE

The present invention relates to a light diffusing article and a lighting device comprising such light diffusing article.

Materials prepared by dispersing an organic or inorganic light diffusing agent in a transparent resin have been widely used in application fields in which light diffusion property is required. The application fields include lighting covers, displays, car meters and face plates. Typical transparent resins are aromatic polycarbonate resin, acrylic resin and styrene resin. Among these transparent resins, aromatic polycarbonate resins are widely used as they have good mechanical properties, heat resistance and weatherability and high light transmittance. For example, EP2829574 discloses a light- diffusing resin composition comprising a polycarbonate.

It is known to use organic particles having a crosslinked structure as a light diffusing agent, and examples thereof include crosslinked acrylic particles, crosslinked silicone- based particles and crosslinked styrene-based particles. Further, inorganic particles such as calcium carbonate, barium sulfate, aluminum hydroxide, silicon dioxide, titanium oxide and calcium fluoride, and inorganic fibers such as glass short fibers are also used.

Use of polypropylene for making a light diffusion plate is also known. For example, WO2010074312 discloses a light diffusion plate comprising a polypropylene resin and a hindered amine light stabilizer having a specific chemical structure. WO2010074312 mentions that the light diffusion plate preferably further comprises light diffusing particles and/or a nucleating agent The nucleating agent is sorbitol-based nucleating agents, organic phosphate-based nucleating agents, nucleating agents of metal salts of carboxylic acid and rosin-based nucleating agents.

It is desirable for light diffusing sheets and tubes to have good optical properties as well as good mechanical properties such as impact strength especially when they are used in outdoor lighting applications. There is a need in the industry for a light diffusing article which has a high diffusing property and a high light transmittance and has good mechanical properties. Further, it is desirable that the manufacturing of the light diffusing article is simple. It is an objective of the present invention to solve the above-mentioned and/or other needs.

Accordingly, the invention provides a light diffusing article, preferably a sheet, a tube or a light bulb, comprising a polypropylene composition comprising (A) a propylene-based polymer and (B) crosslinked silicone particles, wherein (A) the propylene-based polymer consists of (a1) a propylene homopolymer or (a2) a propylene random copolymer consisting of at least 96 wt% of propylene and at most 4 wt% of a-olefin having 2 or 4-10 carbon atoms based on the total weight of the propylene-based polymer.

For the purpose of the present invention ethylene is considered as an a-olefin.

It was surprisingly found that the crosslinked silicone particles improve the impact strength while providing a very high diffusing function with little decrease in the transmittance. The improvement in the impact strength allows using only a propylene homopolymer or only a propylene copolymer for making the light diffusing article, without the addition of other propylene polymers for increasing impact strength.

For increasing the impact strength of articles made of polypropylene compositions, it is customary to use so-called heterophasic propylene copolymers, also known as impact propylene copolymers or propylene block copolymers. Heterophasic propylene copolymers are generally prepared in two or more than two reactors in series, by polymerization of propylene (or propylene and a-olefin) in the presence of a catalyst and subsequent polymerization of an ethyiene-a-olefin mixture. The resulting polymeric materials consist of a propylene-based matrix and (b) a dispersed ethyiene-a-olefin copolymer. Heterophasic propylene copolymers are described e.g. in WO2014044680.

According to the present invention, the propylene composition does not comprise such a heterophasic propylene copolymer but the propylene-based polymer in the propylene composition consists of only a propylene homopolymer or a random copolymer. This leads to a simpler process as well as a lower cost. Even without the use of the heterophasic propylene copolymer, the impact strength surprisingly reaches an acceptable level by the use of the crosslinked silicone particles. The absence of the heterophasic propylene copolymer results in a high transmittance of the light diffusing article according to the invention.

The present invention provides a light diffusing article using cost-efficient materials in a simple manner. proDvlene-based polymer

In some preferred embodiments, the propylene-based polymer is a propylene homopolymer. The light diffusing article according to the invention wherein the propylene-based polymer is a propylene homopolymer was found to have an extremely high light diffusion property. Preferably, the propylene homopolymer has a melt flow rate as measured according to IS0 1133, 230°C, 2.16 kg of 0.1 - 100 dg/min, preferably 0.1 -75 dg/min such as 0.1- 50 dg/min. The minimum melt flow rate is preferably at least 0.5 dg/min, or at least 1 dg/min, or at least 5 dg/min or at least 10 dg/min. The maximum melt flow rate may be at most 40 dg/min, at most 30 dg/min, at most 20 dg/min, at most 15 dg/min.

Preferably, the propylene homopolymer has a melt flow rate of 1-10 dg/min as measured according to ISO 1133 (230°C, 2.16 kg).

In some other embodiments, the propylene-based polymer is a propylene random copolymer. The copolymer may consist of at least 96 wt% of propylene and up to 4 wt% of a-olefin, based on the total weight of the propylene-based polymer. Preferably, the a-olefin in the propylene-a-olefin copolymer is selected from the group of a-olefins having 2 or 4-10 carbon atoms, for example ethylene, 1-butene, 1-pentene, 4-methyl-1- pentene, 1-hexen, 1-heptene or 1-octene, preferably ethylene. The amount of the α-olefin in the propylene a-olefin copolymer is preferably 0.1-3.5 wt%, for example 0.5-3 wt% or 1-2 wt%.

Preferably, the propylene α-olefin copolymer is a propylene-ethylene random copolymer wherein the amount of ethylene is 0.1-3.5 wt%, for example 0.5-3 wt% or 1- 2 wt% based on the total weight of the propylene-based polymer. The light diffusing article according to the invention wherein the propylene-based polymer is a propylene random copolymer was found to have a particularly high light transmittance. Preferably, the propylene random copolymer has a melt flow rate as measured according to IS0 1133, 230°C, 2.16 kg of 0.1 - 100 dg/min, preferably 0.1 - 75 dg/min such as 0.1-50 dg/min. The minimum melt flow rate is preferably at least 0.5 dg/min, or at least 1 dg/min, or at least 5 dg/min or at least 10 dg/min. The maximum melt flow rate may be at most 40 dg/min, at most 30 dg/min, at most 20 dg/min, at most 15 dg/min. Preferably, the propylene random copolymer has a melt flow rate of 1 -10 dg/min as measured according to ISO 1133 (230°C, 2.16 kg).

Preferably, the propylene-based polymer has a haze of at least 50%, preferably at least 60%, for example 60-95%, according to ASTM D1003 measured as a sheet having a thickness of 1 mm. When the propylene-based polymer is a propylene homopolymer, the propylene-based polymer preferably has a haze of at least 50%, preferably at least 60%, for example 60-95%, according to ASTM D1003 measured as a sheet having a thickness of 1 mm. When the propylene-based polymer is a propylene random copolymer, the propylene-based polymer preferably has a haze of at least 80%, preferably at least 85%, for example 85-95%, according to ASTM D1003 measured as a sheet having a thickness of 1 mm. crosslinked silicone particles

Preferably, the amount of the crosslinked silicone particles is 0.05-10.0 wt%, more preferably 0.1-5.0 wt%, more preferably 0.1-2.0 wt% and more preferably 0.1-1.0 wt% with respect to the total composition. Preferably, the amount of the crosslinked silicone particles is at least 0.8 wt% or at least 0.9 wt% with respect to the total composition. A higher amount of the crosslinked silicone particles leads to a higher light diffusing property but a lower total light transmittance.

Silicone particles comprise a three-dimensional polymer chain of the formula

RxSi0₂Kx/2) (I)

wherein x is a positive number greater than or equal to 1, and each R is independently an aliphatic hydrocarbon group, an aromatic hydrocarbon or an unsaturated group

Preferably, x is a positive number greater than or equal to 1, specifically, 1 to 1.9, more specifically, 1 to 1.5, and even more specifically, 1 to 1.2; and each R is independently an organic group, such as an aliphatic hydrocarbon group, e.g., methyl, ethyl, or butyl; or an aromatic hydrocarbon, e.g., phenyl, and can comprise an unsaturated group, e.g., vinyl.

In exemplary embodiments, R is a hydrocarbon group having 1 to 8, specifically, 1 to 5, carbon atoms, more specifically, methyl. Specifically mentioned silicon resin particles comprise methyisilsequioxane. The crosslinked silicone particles have an average particle diameter of preferably 0.01 to 50 μιτι, more preferably 1 to 30 Mm, more preferably 1.8 to 10 pm. When the average particle diameter is smaller than 0.01 pm or larger than 50 μνη, light diffusion property may become unsatisfactory. The average particle diameter indicates a 50 % value (D50) of an integral particle size distribution obtained by a laser diffraction/scattering method. The number of particle size distributions may be single or plural. That is, it is possible to combine two or more different kinds of crosslinked silicone particles which differ in average particle diameter. However, preferably, the crosslinked silicone particles have a narrow particle size distribution. It is preferred that the crosslinked silicone particles have a distribution in which at least 70 wt% of all particles are included in an average particle diameter range of 1.8 to 2.2 pm. The shape of the light diffusing agent is preferably almost globular from the viewpoint of light diffusion property and more preferably almost spherical. The globular shape includes an elliptical shape. The bulk specific gravity of the silicone particles may be 0.35 to 0.67 kilograms per liter.

The refractive index of the light diffusing agent is preferably 1.30 to 1.80, more preferably 1.33 to 1.70 and much more preferably 1.35 to 1.65. When it is contained in the resin composition, it exhibits a satisfactory light diffusing function.

Preferably, the specific surface area of the crosslinked silicone particles is at least 10 m²/g, preferably at least 20 m²/g, preferably at least 30 m²/g as determined by BET nitrogen absorption technique according ISO 9277-2010. Commercially available silicone-based light diffusing fine particles suitable for use in the present invention include the TOSPEARL series of Toshiba Silicone Co., Ltd., the TORAYFIL series of Dow Coming Toray Co., Ltd. and the silicone powders of Shin- Etsu Chemical Co., Ltd.

Additives

The composition according to the invention may optionally comprise at least one further component such as additives. The amount of the optional component is typically 0 to 30 wt% of the total of the composition.

It will be appreciated that the optional components are used to the extent that they do not interfere with obtaining the desired properties of the light diffusion film or tube.

The additives may include stabilisers, e.g. heat stabilisers, anti-oxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants;

flame-retardants; mould-release agents; flow improving agents; plasticizers; anti-static agents; external elastomeric impact modifiers; blowing agents; inorganic fillers and reinforcing agents; and/or components that enhance interfacial bonding between polymer and filler, such as a maleated polypropylene.

The skilled person can readily select any suitable combination of additives and additive amounts without undue experimentation. The amount of the additives depends on their type and function and typically is of from 0 to about 30 wt%. The amount of the additives may e.g. be from about 1 to about 20 wt%; from about 2 to about 10 wt% or of from 3 to about 5 wt% based on the total composition. The sum of all components added in the process of the invention to form the composition comprising the propylene-based polymer, the crosslinked silicone particles and the optional components should add up to 100% by weight.

Preferably, the total of the propylene-based polymer and the crosslinked silicone particles is at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 97 wt%, at least 98 wt%, at least 99 wt%, at least 99.5 wt%, at least 99.9 wt% or 100 wt% of the total composition.

It is preferred that the composition according to the invention is substantially free of other fillers including but not limited to inorganic fillers like talc, glass fibres and glass beads or organic fillers, such as organic fibres. In this context the term substantially free means that such optional fillers are present in an amount of at most 1 wt.%, preferably at most 0.5 wt.% more preferably at most 0.1 wt.% such as 0.01 wt.%. It is most preferred that the composition is free of other fillers. Light diffusing article

The light diffusing article according to the invention is not a porous article. Accordingly, the density does not substantially change during the formation of the light diffusing article from the polypropylene composition. In contrast, a porous film such as made by biaxial stretching of a polymer composition has a substantially lower density than the polymer composition.

Preferably, the light diffusing article according to the invention is an injection molded article. Injection molding does not result in a porous article. Preferably, the light diffusing article according to the invention has the light diffusing article has a density d_a and the propylene-based polymer has a density dp and |d_p-d_a|/d_p is at most 1%, for example at most 0.5%, wherein d_a and d_p are measured according to IS01183-1:2012. Preferably, the light diffusing article according to the invention has a density of 0.8900- 0.9100 g/cm³, e.g. 0.8960-0.9040 g/cm³ as measured according to IS01183-1:2012.

Preferably, the polypropylene composition of the light diffusing article according to the invention has a density of 0.8900-0.9100 g/cm³, e.g. 0.8960-0.9040 g/cm³ as measured according to IS01183-1:2012.

Preferably, the propylene-based polymer of the polypropylene composition of the light diffusing article according to the invention has a density of 0.8900-0.9100 g/cm³, e.g. 0.8960-0.9040 g/cm³ as measured according to IS01183-1:2012.

The light diffusing article according to the invention has a small thickness for transmitting the light from the light source, as generally understood In the art. The light diffusing article according to the invention may have any shape, but typical examples include a light diffusing sheet, a light diffusing tube and a light diffusing lightbulb. Typically, the thickness of article is 0.2 - 10 mm, for example 0.2-5 mm, 0.5 - 5 mm or 0.8 - 3 mm.

The term 'sheet' is herein understood to mean an article having a small thickness and extending in two dimensions perpendicular to the thickness direction. When the thickness of the sheet is small, e.g. smaller than 0.25 mm, the sheet may also be called a film.

The term 'tube' is herein understood to mean an article having a shape of a hollow cylinder, having a small thickness perpendicular to the axis direction.

The term 'lightbulb^* is generally understood In the art, i.e. a housing of a light source such as an LED lamp. The invention further provides a process for the preparation of the light diffusion article according to the invention, comprising melt mixing the polypropylene-based polymer and the crosslinked silicone particles to obtain the composition and forming the composition into the light diffusion article. Properties

Preferably, the polypropylene composition in the light diffusion article according to the invention has a melt flow rate of at most 50 dg/min, at most 40 dg/min, at most 30 dg/min, at most 20 dg/min or at most 15 dg/min (IS0 1133, 230°C, 2.16 kg). Preferably, the melt flow rate of the composition according to the invention is at least 0.1 dg/min, at least 0.5 dg/min, at least 1 dg/min, at least 5 dg/min or at least 10 dg/min (IS0 1133, 230°C, 2.16 kg). Preferably, the composition according to the invention has a melt flow rate of 5-50 dg/min (IS0 1133, 230°C, 2.16 kg).

In the context of the present invention, the light diffusion property is represented by a degree of light dispersion (DLD), wherein the DLD is defined as the receiving angle that obtains a luminous intensity which equals to the half of a luminous intensity of the vertically transmitted light. The luminous intensity may be measured by a

goniophotometer, for example GP200 in transmission mode. In the context of the present invention, the light transmittance and the haze are measured according to ASTM D1003. In the context of the present invention, the mold shrinkage is determined by preparing a plaque having a dimension of 60 mm *60 mm*2 mm by transfer molding, demolding the plaque and allowing the plaque to cool down to room temperature and measuring the dimension of the plaque in flow and cross flow direction at 25 °C.

Preferably, the polypropylene composition in the light diffusion article according to the invention has a degree of light dispersion (DLD) of at least 10, more preferably at least 15, at least 20, more preferably at least 25, more preferably at least 30, more preferably at least 40 measured as a sheet having a thickness of 1 mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention has a light transmittance of at least 70%, more preferably at least 75%, more preferably at least 80%, more preferably at least 85%, as a sheet having a thickness of 1mm.

Preferably, polypropylene composition in the light diffusion article according to the invention has a haze of at least 75%, at least 90% or at least 98% measured as a sheet having a thickness of 1mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention has an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², preferably at least 4.1 kJ/m², more preferably at least 4.2 kJ/m², more preferably at least 4.5 kJ/m², more preferably at least 5.0 kJ/m².

Preferably, the polypropylene composition in the light diffusion article according to the invention has a mold shrinkage gap of at most 0.2%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross-flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction. Preferably, the shrinkage gap is at most 0.15%, more preferably at most 0.1%, more preferably at most 0.08%, even more preferably at most 0.05%.

Preferably, the properties of the propylene composition fulfil the following equation:

wherein S is the specific surface area of cross-linked silicon resins, D is the ratio of the DLD of the light diffusing article at a thickness of 1 mm to the DLD of a sheet having a thickness of 1 mm made of the propylene-based polymer, wherein the DLD is defined as the receiving angle that obtains a value which equals to the half of a value of the vertically transmitted light,

T is the ratio of the light transmittance of the light diffusing article at a thickness of 1 mm to the light transmittance of a sheet having a thickness of 1 mm made of the propylene-based polymer, wherein light transmittance is measured according to ASTM D1003,

C is the amount of the crosslinked silicone particles based on the total weight of the composition. More preferably, the value of F is at least 75, more preferably at least 200. propylene homopolvmer

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene homopolymer has a degree of light dispersion (DLD) of at least 20 degrees, more preferably at least 25 degrees, more preferably at least 30 degrees, more preferably at least 40 degrees measured as a sheet having a thickness of 1 mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene homopolymer has a light transmittance of at least 70%, more preferably at least 75%, more preferably at least 80%, more preferably at least 85% as a sheet having a thickness of mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene homopolymer has an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², preferably at least 4.1 kJ/m², more preferably at least 4.5 kJ/m², more preferably at least 5.0 kJ/m².

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene homopolymer has a mold shrinkage gap of at most 0.2%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction. Preferably, the shrinkage gap is at most 0.15%, more preferably at most 0.1%, even more preferably at most 0.05%.

Preferably, the polypropylene composition according to the invention wherein the propylene-based polymer is a propylene homopolymer has

a degree of light dispersion (DLD) of at least 20 degrees measured as a sheet having a thickness of 1 mm and

a light transmittance of at least 70% as a sheet having a thickness of 1mm and optionally an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m².

a degree of light dispersion (DLD) of at least 20 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 70% as a sheet having a thickness of 1mm and an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², and optionally

a mold shrinkage gap of at most 0.2%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage In cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction.

Preferably, the polypropylene composition according to the invention wherein the propylene-based polymer is a propylene homopolymer and the amount of the crosslinked silicone particles is 0.2-0.8 wt% with respect to the polypropylene composition has

a degree of light dispersion (DLD) of at least 25 degrees measured as a sheet having a thickness of 1 mm and

a light transmittance of at least 80% as a sheet having a thickness of 1 mm and optionally an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 5 kJ/m².

a degree of light dispersion (DLD) of at least 25 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 80% as a sheet having a thickness of 1 mm and an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 5 kJ/m², and optionally

a mold shrinkage gap of at most 0.1%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction. random copolymer

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has a degree of light dispersion (DLD) of at least 10 degrees, more preferably at least 15 degrees, more preferably at least 20 degrees, more preferably at least 30 degrees measured as a sheet having a thickness of 1 mm. Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has a light transmittance of at least 75%, more preferably at least 80%, more preferably at least 85%, as a sheet having a thickness of 1mm. Preferably, the propylene random copolymer in the light diffusion article according to the invention has a light transmittance of at least 85% measured as a sheet having a thickness of 1 mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², preferably at least 4.1 kJ/m², more preferably at least 4.2 kJ/m², more preferably at least 4.5 kJ/m². Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has a mold shrinkage gap of at most 0.1%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction. Preferably, the shrinkage gap is at most O.OB %, more preferably at most 0.05%.

Preferably, the polypropylene composition In the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has a degree of light dispersion (DLD) of at least 10 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 75% as a sheet having a thickness of 1mm and optionally an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m². Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer has a degree of light dispersion (DLD) of at least 10 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 75% as a sheet having a thickness of 1mm and an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², and optionally

a mold shrinkage gap of at most 0.1%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene random copolymer and the amount of the crosslinked silicone particles with respect to the polypropylene composition is 1.2-2.5 wt% with respect to the polypropylene composition has a degree of light dispersion (DLD) of at least 20 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 80% as a sheet having a thickness of 1mm and an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², and optionally a mold shrinkage gap of at most 0.1%, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a mold shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propyiene-based polymer is a propylene random copolymer and the amount of the crosslinked silicone particles with respect to the polypropylene composition is 1.2-2.5 wt% with respect to the polypropylene composition has a degree of light dispersion (DLD) of at least 20 degrees measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 80% as a sheet having a thickness of 1mm and an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², and optionally

a mold shrinkage gap of at most 0.1 %, wherein the shrinkage gap is defined as the difference between a mold shrinkage in flow direction and a moid shrinkage in cross- flow direction and wherein the mold shrinkage in flow direction and the mold shrinkage in cross-flow direction. The invention further relates to use of a polypropylene composition comprising (A) a propyiene-based polymer and (B) crosslinked silicone particles, wherein (A) the propyiene-based polymer consists of (a1 ) a propylene homopolymer or (a2) a propylene random copolymer consisting of a propylene copolymer consisting of at least 96 wt% of propylene and at most 4 wt% of a-olefin having 2 or 4-10 carbon atoms based on the total weight of the propyiene-based polymer, for making a light diffusing article.

The invention further relates to use of the sheet, a tube or a light bulb according to the invention for diffusing light.

The invention further relates to use of crosslinked silicone particles for increasing impact strength of a light diffusing article comprising a polypropylene composition comprising a propyiene-based polymer, wherein the propyiene-based polymer consists of (a1) a propylene homopolymer or (a2) a propylene random copolymer consisting of at least 96 wt% of propylene and at most 4 wt% of a-olefin having 2 or 4-10 carbon atoms based on the total weight of the propyiene-based polymer. The invention further relates to a lighting device comprising a housing containing a light source and the light diffusing article according to the invention, said article being positioned relative to the light source such that it diffuses at least part of the light coming from said light source. Preferably, the light source is a LED lamp.

Although the invention has been described in detail for purposes of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the claims.

It is further noted that the invention relates to all 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. The invention is now elucidated by way of the following examples, without however being limited thereto.

Materials

propylene-based polymer

Polymer 1 1s a propylene homopolymer

Polymer 2 is a propylene-ethylene copolymer. Polymer 3 is a heterophasic propylene copolymer comprising a matrix phase of a propylene homopolymer and a dispersed phase of propylene-ethylene copolymer. Each composition comprises an additive package comprising anti-static agent, antioxidant in total of 4000 ppm.

MFR is measured according to IS0 1133, 230°C, 2.16 kg.

Additives:

Crosslinked silicone particles: Tospeari 120 from Momentive, particle size D50: 2 pm. The specific surface area as measured as determined by BET nitrogen absorption technique according ISO 9277-2010 is 15-35 m²/g

The propyiene-based polymer was pre-blended with the crosslinked silicone particles and other additives. Subsequently the pre-blended powder was extruded using a twin extruder. The pellets were dried at 100 °C for 2 h and injection molded using FANUC injection molding machine (S-2000Q to prepare the parts for test.

Equipment and Procedures

For the optical properties measurements, transmittance data were obtained on a

Hazegard II with standard D65 lamp following ASTM D1003 protocol (uncompensated mode). Degree of light dispersion (DLD) was measured by Goniophotometer GP-200 in transmission mode. The maximum DLD is 60 degree based on Lambert's law. The compositions and test results are shown in Tables 1-3. The polymer compositions did not contain any additional fillers.

Table 1: polymer 1 (homopolymer)

It can be understood that the DLD dramatically increases by the addition of a small amount of silicone particles, at as low as 0.5 wt%. Further, the impact strength increase by the addition of a small amount of silicone particles. The transmittance decreases as the amount of the silicone particles increases, but is maintained at an acceptable level. The combination of desirable properties at a very low amount such as 0.5 wt% of silicone particles is extraordinary.

Table 2: polymer 2 (random copolymer)

It can be understood that the DLD dramatically increases by the addition of a small amount of silicone particles, between 0.5 wt% and 1.0 wt%. Further, the impact strength increase by the addition of a small amount of silicone particles. The transmittance decreases as the amount of the silicone particles increases, but is maintained at an acceptable level. In particular, the decrease in the transmittance is very small in this set of experiments. The molt shrinkage is decreased as the silicone particles are added.

Table 3: polymer 3 (heterophasic propylene copolymer)

An increase in DLD is visible, but the transmittance is much lower compared to the samples in Tables 1 and 2. The composition is not suitable for light diffusing article used in various environments. The addition of silicone particles leads to little increase in the impact strength or decrease.

Claims

1. A light diffusing article, preferably a sheet, a tube or a light bulb, comprising a

polypropylene composition comprising (A) a propylene-based polymer, wherein the propylene-based polymer consists of (a1 ) a propylene homopolymer or (a2) a propylene random copolymer consisting of at least 96 wt% of propylene and at most 4wt% of an a-olefln having 2 or 4-10 carbon atoms based on the total weight of the propylene-based polymer and (B) crosslinked silicone particles.

2. The light diffusing article of claim 1 , wherein the light diffusing article is an injection molded article.

3. The light diffusing article of any one of the preceding claims, wherein the light

diffusing article has a density d_a and the propylene-based polymer has a density d_p and |d_p-d_a|/d_p is at most 1 %, wherein d. and d_p are measured according to

IS01183-1:2012.

4. The light diffusing article of any one of the preceding claims, wherein the

propylene-based polymer has a haze of at least 50%, preferably at least 60%, for example 60-95%, according to ASTM D1003 measured as a sheet having a thickness of 1 mm.

5. The light diffusing article of any one of the preceding claims, wherein the amount of the crosslinked silicone particles is 0.05-10.0 wt%, more preferably 0.1-5.0 wt%, more preferably 0.1-2.0 wt% and more preferably 0.1-1.0 wt% with respect to the total composition.

6. The light diffusing article of any one of the preceding claims, wherein the

crosslinked silicone particles have the formula (I)

RxSiO*<x/2) (I)

wherein x is a positive number greater than or equal to 1, and each R is

independently an aliphatic hydrocarbon group, an aromatic hydrocarbon or an unsaturated group.

7. The light diffusing article of any one of the preceding claims, wherein the

crosslinked silicone particle comprises methylsilsequioxane.

8. The light diffusing article any one of the preceding claims, wherein the specific surface area of cross-linked silicon resins is at least 10 m²/g, preferably at least 20 m²/g, preferably at least 30 m²/g as determined by BET nitrogen absorption technique according ISO 9277-2010.

9. The light article of any one of the preceding claims having a thickness of 0.2-10 mm.

10. The light diffusing article of any one of the preceding claims, wherein the

polypropylene composition has a degree of light dispersion (DLD) of at least 10, more preferably at least 15, at least 20, more preferably at least 25, more preferably at least 30, more preferably at least 40 measured as a sheet having a thickness of 1 mm.

11. The light diffusing article of any one of the preceding claims, wherein the

polypropylene composition has a light transmittance of at least 70%, more preferably at least 75%, more preferably at least 80%, more preferably at least 85%, as a sheet having a thickness of 1mm, wherein the light transmittance is measured according to ASTM D1003.

12. The light diffusing sheet of any one of the preceding claims, wherein the

polypropylene composition has an (zod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m², preferably at least 4.1 kJ/m², more preferably at least 4.2 kJ/m², more preferably at least 4.5 kJ/m², more preferably at least 5.0 kJ/m².

13. The light diffusing sheet of any one of claims 1-12, wherein the propylene-based polymer is a propylene homopolymer and the amount of the crosslinked silicone particles is 0.2-0.8 wt% with respect to the polypropylene composition and the polypropylene composition has

a degree of light dispersion (DLD) of at least 25 measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 80% measured as a sheet having a thickness of 1 mm and optionally an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 5 kJ/m²,

14. The light diffusing sheet of any one of claims 1-12, wherein the propylene-based polymer is a propylene random copolymer and the amount of the crosslinked silicone particles with respect to the polypropylene composition is 1.2-2.5 wt% with respect to the polypropylene composition and the polypropylene composition has a degree of light dispersion (DLD) of at least 20 measured as a sheet having a thickness of 1 mm,

a light transmittance of at least 80% measured as a sheet having a thickness of 1mm and

optionally an Izod notched impact (23 °C, parallel) measured in accordance with ISO 180/4A of at least 4 kJ/m²,

15. The light diffusing sheet of any one of the preceding claims, wherein the properties of the propylene composition fulfil the following equation:

F=S "* ln (2^) > 150

wherein S Is the specific surface area of cross-linked silicon resins in m^z/g,

D is the ratio of the DLD of the light diffusing article at a thickness of 1 mm to the DLD of a sheet having a thickness of 1 mm made of the propylene-based polymer, wherein the DLD is defined as the receiving angle that obtains a value which equals to the half of a value of the vertically transmitted light,

C is the amount of the crosslinked silicone particles based on the total weight of the composition.

16. Use of a polypropylene composition comprising (A) a propylene-based polymer and (B) crosslinked silicone particles, wherein (A) the propylene-based polymer consists of (a1) a propylene homopolymer or (a2) a propylene random copolymer consisting of a propylene copolymer consisting of at least 96 wt% of propylene and at most 4 wt% of a-olefin having 2 or 4-10 carbon atoms based on the total weight of the propylene-based polymer, for making a light diffusing article.

17. A lighting device comprising a housing containing a light source and the light diffusing sheet according to any one of claims 1 - 15, said sheet being positioned relative to the light source such that it diffuses at least part of the light coming from said light source.

18. The lighting device of claim 17, wherein the light source is a LED lamp