WO2017076772A1

WO2017076772A1 - Light diffusing article

Info

Publication number: WO2017076772A1
Application number: PCT/EP2016/076100
Authority: WO
Inventors: Liang Wen; Chaodong JIANG; Ting Huang; Shan QIN; Wesley LI
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: CN108350213A

Abstract

The invention relates to a light diffusing article, preferably a sheet, a tube or a light bulb, comprising a polypropylene composition comprising a propylene-based polymer, wherein the polypropylene composition is β-nucleated. 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.

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 such as an aromatic polycarbonate resin, acrylic resin or styrene 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. Among these transparent resins, aromatic polycarbonate resins are widely used as resins having 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.

JP5887024 discloses a polypropylene expanded film comprising a nucleating agent of sorbitol derivative, having a light scattering index of less than 6% and a haze of less than 1%. JP5887024 uses a-nucleation of the polypropylene to obtain a low diffusion contrary to providing a light diffusion sheet For obtaining a high degree of light dispersion, a high loading of diffusing agents is required. However, this leads to increase in the cost and decreases the light transmittance. It is an objective of the present invention to solve the above-mentioned and/or other problems.

Accordingly, the invention provides a light diffusing article, preferably a sheet, a tube or a light bulb, comprising a polypropylene composition comprising a propylene-based polymer, wherein the propylene composition is B-nucleated.

The polypropylene composition used according to the invention is β-nucleated. It was surprisingly found that the β-nucleated polypropylene itself acts as a light diffuser. In contrast, ct-nucleated polypropylene does not act as a light diffuser and therefore a light diffusion sheet made of a-nucleated polypropylene requires an additional light diffusing agent. According to the invention, due to the presence of the β-nucleated PP which acts as a light diffuser, an article can be obtained with a high light diffusing function without a further light diffusing agent or with a less amount of further light diffusing agent.

It is noted that US2010285251 discloses a polypropylene composition comprising (a) a propylene homopolymer and (b) a random propylene-butene copolymer or a random propylene-ethylene copolymer with an ethylene content not exceeding 3.0 wt.~%, wherein the polypropylene composition is β-nucleated. According to US2010285251, the polypropylene composition enables the manufacture of pipes with an excellent pressure test performance by keeping the stiffness as well as the impact strength on high levels. US2010285251 does not relate to light diffusion.

B-nucleation

The polypropylene composition according to the invention is B-nucleated, i.e. the polypropylene composition must be partially crystallized in the B-modification. It Is preferred that the amount of β-modification of the polypropylene composition is at least 10%, more preferably at least 20%₇ still more preferably at least 30%, still more preferably at least 40% still more preferably at least at least 50%, still more preferably at least 60%, still more preferably at least 70% determined by Differential Scanning Calorimetry (DSC). The amount of B-modification is determined by Differential Scanning Calorimetry (DSC). DSC is run according to ISO 3146/part 3/method C2 with a scan rate of 10° C/min. The amount of β-modification is calculated from the second heat by the following formula:

B-area/(a-area+S-area)

Since the thermodynamical B-modification starts to be changed into the more stable ct- modification at temperatures above 150° C, a part of the β-modification is transferred within the heating process of DSC-measurement. Therefore, the amount of B- polypropylene determined by DSC is lower as when measured according to the method of Turner-Jones by WAXS (A. Turner-Jones et. al., Makromol. Chem 75 (1964) 134).

"Second heat" means that the sample is heated according to ISO 3146/part 3/method C2 for a first time and then cooled to room temperature at a rate of 10° C/min. The sample is then heated a second time, also according to ISO 3146/part 3/method C2. This second heat is relevant for measurement and calculation.

During the first heat" all thermal history of the sample giving rise to different crystalline structure, which typically comes from different processing conditions and/or methods, is destroyed. Using the second heat for determination of B-crystallinity, it is possible to compare samples regardless of the way the samples were originally manufactured. polypropylene-based oolvmer

homoDolvmer and homogeneous copolymer

The polypropylene-based polymer may be a propylene homopolymer or a propylene a- olefin copolymer including random copolymers and (multi)block copolymers. The copolymer is preferably a random copolymer. The copolymer may consist of at least 70 wt% of propylene and up to 30 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.

Thus, for the purpose of the present invention ethylene is considered as an a-olefin. The amount of the a-olefin in the propylene a-olefin copolymer is preferably 1-15 wt%, more preferably 1-10 wt%, more preferably 1-6 wt%, more preferably 1-4 wt%.

Preferably, the propylene a-olefin copolymer is a propylene-ethylene random copolymer wherein the amount of ethylene is 1-15 wt%, more preferably 1-10 wt%, more preferably 1-6 wt%, more preferably 1-4 wt% based on the total weight of the propylene-based polymer.

Preferably, the propylene homopolymer or the propylene α-olefin copolymer 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. heterophasic propylene copolymer

Preferably, the polypropylene-based polymer is a heterophasic propylene copolymer. It was found that the presence of both the matrix phase and the dispersed phase led to a higher diffusion performance. Although not wishing to be bound by theory, the difference in the reflective index between the matrix phase and the dispersed phase leads to a higher diffusion property. Heterophasic propylene copolymers, also known as impact propylene copolymers or propylene block copolymers, are an important class of polymers due to their attractive combination of mechanical properties, such as impact strength over a wide

temperature range and their low cost. These copolymers find a wide range of applications ranging from the consumer industry (for example packaging and housewares), the automotive industry to electrical applications.

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 are heterophasic, but the specific morphology usually depends on the preparation method and monomer ratios used.

The heterophasic propylene copolymers employed in the process according to present invention can be produced using any conventional technique known to the skilled person, for example multistage process polymerization, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combinations thereof. Any conventional catalyst systems, for example, Ziegler-Natta or metallocene may be used. Such techniques and catalysts are described, for example, In WO06/010414; Polypropylene and other Pdyolefins, by Ser van der Ven, Studies in Polymer Science 7, Elsevier 1990; WO06/010414, US4399054 and US4472524.

Preferably, the heterophasic propylene copolymer is made using Ziegler-Natta catalyst.

The heterophasic propylene copolymer may be prepared by the process comprising

- polymerizing propylene and optionally α-olefin in the presence of a catalyst system to obtain the propylene-based matrix and

- subsequently polymerizing ethylene and a-olefin in the propylene-based matrix in the presence of a catalyst system to obtain the dispersed ethylene-a olefin copolymer.

These steps are preferably performed in different reactors. The catalyst systems for the first step and for the second step may be different or same.

The heterophasic propylene copolymer consists of a propylene-based matrix and a dispersed ethylene-a-olefin copolymer. The propylene-based matrix typically forms the continuous phase in the heterophasic propylene copolymer. The amounts of the propylene-based matrix and the dispersed ethylene-a-olefin copolymer may be determined by ¹³C-NMR, as well known in the art. The heterophasic propylene copolymer consists of

(a) a propylene-based matrix,

wherein the propylene-based matrix consists of a propylene homopolymer and/or a propviene-a-olefin copolymer consisting of at least 70 wt% of propylene and at most 30 wt% of σ-olefin, based on the total weight of the propylene-based matrix and wherein the propylene-based matrix is present in an amount of 60 to 95 wt% based on the total heterophasic propylene copolymer and

(b) a dispersed ethylene-a-olefin copolymer,

wherein the dispersed ethylene-a-olefin copolymer is present in an amount of 40 to 5 wt% based on the total heterophasic propylene copolymer and

wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-a-olefin copolymer in the heterophasic propylene copolymer is 100 wt%.

The propylene-based matrix consists of a propylene homopolymer and/or a propylene- a-olefin copolymer consisting of at least 70 wt% of propylene and up to 30 wt% of a- olefin, for example ethylene, for example consisting of at least 80 wt% of propylene and up to 20 wt% of α-olefin, for example consisting of at least 90 wt% of propylene and up to 10 wt% of α-olefin, based on the total weight of the propylene-based matrix.

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-hexene, 1-heptene or 1-octene, and is preferably ethylene.

Preferably, the propylene-based matrix consists of a propylene homopolymer. The propylene-based matrix is present in an amount of 60 to 95 wt%, for example 65 to 85 wt%, for example 70 to 85 wt%, for example 70 to 80 wt%, for example 65 to 75 wt% or 75 to 85 wt% based on the total heterophasic propylene copolymer.

The propylene-based matrix is preferably semi-crystalline, that means it is not 100% amorphous, nor 100% crystalline. For example, the propylene-based matrix is at least 30%, for example at least 40% crystalline, for example at least 50%, for example at least 60% crystalline and/or for example at most 80% crystalline, for example at most 70% crystalline. For example, the propylene-based matrix has a crystallinity of 60 to 70%. For purpose of the invention, the degree of crystallinity of the propylene-based matrix is measured using differential scanning calorimetry (DSC) according to

IS011357-1 and IS011357-3 of 1997, using a scan rate of 10°C/min, a sample of 5mg and the second heating curve using as a theoretical standard for a 100% crystalline material 207.1 J/g. [Besides the propylene-based matrix, the heterophasic propylene copolymer also comprises a dispersed ethylene-a-olefin copolymer. The dispersed ethylene-a-olefin copolymer is also referred to herein as the 'dispersed phase'. The dispersed phase is embedded in the heterophasic propylene copolymer in a discontinuous form. The particle size of the dispersed phase is typically in the range of 0.05 to 5.0 microns, more typically 0.05 to 2.0 microns, as may be determined by transmission electron microscopy (TEM).

The dispersed ethylene-a-olefin copolymer is present in an amount of 40 to 5 wt%. Preferably, the dispersed ethylene-a-olefin copolymer is present in an amount of at least 10 wt%, for example at least 15 wt% or at least 17 wt%, and/or at most 35 wt%, for example at most 30 wt% or 25 wt%, based on the total heterophasic propylene copolymer. These ranges lead to a higher light diffusion property. In the heterophasic propylene copolymer in the composition of the invention, the sum of the total weight of the propylene-based matrix and the total weight of the dispersed ethylene-a-olefin copolymer is 100 wt%.

Preferably, the amount of ethylene in the ethylene- α-olefin copolymer is In the range of 20 to 65wt%, for example in the range of 40 to 60wt% based on the ethylene- a-olefin copolymer, for example the amount of ethylene in the ethylene- α-olefin copolymer is at least 30 wt% and/or for example at most 55wt% based on the ethylene- a-olefin copolymer. A higher amount of ethylene in the dispersed phase leads to a larger difference in the reflective index between the matrix phase and the dispersed phase, which in turn leads to a higher light diffusion property.

The σ-olefin in the ethylene-a-olefin copolymer is preferably chosen from the group of a-olefins having 3 to 8 carbon atoms and any mixtures thereof, preferably the a-olefin in the ethylene-a-olefin copolymer is chosen from the group of a-olefins having 3 to 4 carbon atoms and any mixture thereof, more preferably the α-olefin is propylene, in which case the ethylene-a-olefin copolymer is ethylene-propylene copolymer.

Examples of suitable α-olefins having 3 to 8 carbon atoms, which may be employed as ethylene comonomers to form the ethylene α-olefin copolymer include but are not limited to propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexen, 1-heptene and

1-octene.

Preferably, the amount of ethylene in the heterophasic propylene copolymer is 3-40 wt%, for example at least 5 wt%, based on the heterophasic propylene copolymer. More preferably, the the amount of ethylene in the heterophasic propylene copolymer is at least 6 wt%, more preferably at least 8 wt%.

Preferably, the propylene-based matrix has a melt flow rate (before it is mixed with other components of the composition of the invention; MFIPP) of at most 70 dg/min, preferably at most 50 dg/min, preferably at most 30 dg/min, most preferably at most 20 dg/min (ISO 1133, 230°C. 2.16 kg). Preferably, the propylene-based matrix has a melt flow rate of 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 (ISO 1133, 230°C, 2.16 kg).

Preferably, the dispersed ethylene α-olefin copolymer has a melt flow rate (before it is mixed with other components of the composition of the invention; MFIEPR) of at least 0.001 dg/min, at least 0.01 dg/min, at least 0.1 dg/min, at least 0.3 dg/min, at least 0.7 dg/min, at least 1 dg/min, and/or for example at most 20 dg/min, at most 15 dg/min at most 10 dg/min, at most 5 dg/min or at most 3 dg/min. The MFI of the dispersed ethylene a-olefin copolymer (MFIEPR) is calculated taking into account the MFI of the propylene-based matrix (MFIPP), the MFI of the heterophasic propylene copolymer (MFIheterophasic) and the amount of the propylene-based matrix in the heterophasic propylene copolymer (matrix content) and the amount of the dispersed phase in the heterophasic propylene copolymer (rubber content (RC)) according to the following formula:

Preferably, the heterophasic propylene copolymer has a melt flow rate

(MFIheterophasic) 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 (ISO 1133, 230°C, 2.16 kg). Preferably, the melt flow rate of the heterophasic propylene copolymer 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 (ISO 1133, 230°C, 2.16 kg). The values of the MFI of the propylene-based matrix (MFIPP) and the MFI of the dispersed ethylene-a-olefin elastomer (MFIEPR) mentioned herein are understood as the values before the heterophasic propylene copolymer is mixed with the nucleating agents and optional components to obtain the composition according to the invention. The value of the MFI of the heterophasic propylene copolymer (MFIheterophasic) refers to the final MFI of the heterophasic propylene copolymer. To exemplify this: In case the heterophasic propylene copolymer is not subjected to vis-breaking or shifting by melt-mixing with a peroxide, the MFIheterophasic is the original MFI value of the heterophasic propylene copolymer. In case the heterophasic propylene copolymer is subjected to vis-breaking or shifting by melt-mixing with a peroxide, the

MFIheterophasic is the value of the heterophasic propylene copolymer after such vis- breaking or shifting.

It has been recognized that the β-nucleation takes in particular place in the propylene- based matrix (a) than the dispersed phase (b). Thus as a further preferred requirement the propylene-based matrix (a) is more β-crystaliised than the dispersed phase (b). Preferably, the heterophasic propylene copolymer has a density of 0.8900-0.9100 g/cm³, e.g. 0.6960-0.9040 g/cm³ as measured according to IS01183-1:2012.

The propylene-based polymer may also be a combination of any of the propylene- based polymer mentioned above, e.g. a mixture of a propylene homopolymer and a heterophasic propylene copolymer at a weight ratio of 1:99-99:1 or 50:50 or a mixture of a propylene homopolymer and a random propylene-ethylene copolymer at a weight ratio of 1:99-99:1 or 50:50. nucleating aaent

The amount of the β-nucleating agent In the composition is preferably 0.0001 to 2.0 wt%, for example at least 0.001 wt%, at least 0.002 wt% or at least 0.005 wt%, for example at least 0.025 wt%, for example at least 0.05wt%, and/or for example at most 2.0 wt%, for example at most 1.5 wt%, for example at most 1.0 wt%, at most 0.5 wt%, at most 0.1 wt%, based on the total composition.

Suitable examples of B-nucleating agent are described e.g. in US2010285251 and US8637625, incorporated herein by reference.

Suitable types of β-nucleating agents include

dicyclohexyl-2,6-naphthalene dicarboxamide and N,N'-dicyclooctyl-2,6-naphthalene dicarboxamide,

cyclopentanedicarboxamide,

Further suitable of β-nucleating agents are

quinacridone type compounds, e.g.

- quinacridone, dimethylquinacridone and dimethoxyquinacridone,

quinacridonequinone type compounds, e.g.

- quinacridonequinone, a mixed crystal of 5, 12-dihydro(2,3b)acridine-7, 14-dione with quino(2,3b)acridine-6,7,13,14-(5H, 12H)-tetrone and dimethoxyquinacridonequinone and

dihydroquinacridone type compounds, e.g.

- dihydroquinacridone, dimethoxydihydroquinacridone and

dibenzodihydroquinacridone.

Still further suitable β-nucleating agents are

dicarboxylic acid salts of metals from group Ha of periodic system, e.g. calcium salt of cis-A4-tetrahydrophthalic acid, pimelic acid calcium salt and suberic acid calcium salt; and mixtures of dicarboxylic acids and salts of metals from group Ha of periodic system. Still further suitable β-nucleating agents are

salts of metals from group lla of periodic system and imido acids of the formula

- calcium salts of phthaloylglycine, hexahydrophthaloyiglycine, N-phthaloylalanine and/or N-4-methylphthaloylglycine. The examples of β-nucleating agents described in US2010285251 and US8637625 are incorporated herein by reference.

Preferably, the β-nucleating agent comprises dicarboxylic acid salts of calcium, most preferably a calcium salt of cls-A4-tetrahydrophthalic acid (also known as cis-4- cyclohexene-1 ,2-dicarboxyiic acid).

A nucleating composition comprising a calcium salt of cis-A4-tetrahydrophthalic acid is commercially available from GCH Technology Co.,Ltd. as NAB-82, which consists of cis-A4-tetrahydrophthalic acid and calcium stearate (molar ratio 1:2, i.e. 25.7 wt% of NAB-82 is calcium salt of cis-A4-tetrahydrophthalic acid).

The B-nucleating agent may be any combination of the above. light diffusing aaent

In some embodiments, the polypropylene composition comprises little or no light diffusing agent. For example, the polypropylene composition comprises less than 0.05 wt%, less than 0.01 wt%, or less than 0.001 wt% or 0 wt% of the light diffusing agent with respect to the total composition.

In some embodiments, the polypropylene composition further comprises a light diffusing agent. Preferably, when present, the amount of the light diffusing agent 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. A higher amount of the light diffusing agent leads to a higher light diffusing property but a lower total light transmittance.

Any known types of the light diffusing agent may be used and it may be either organic particles or inorganic particles. Typical examples of organic particles are polymers which include crosslinked particles obtained by polymerizing a non-crosslinkable monomer and a crosslinkable monomer.

Polymer particles are preferred, and crosslinked particles may be particularly preferably used. Examples of the monomer used as the non-crosslinkable monomer in the crosslinked particles include non-crosslinkable vinyl-based monomers such as acrylic monomers, styrene-based monomers and acryionitrile-based monomers, and olefin- based monomers. The acrylic monomers include methyl acryiate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethyihexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethyihexyl methacrylate and phenyl methacrylate, all of which may be used alone or in combination. Out of these, methyl methacrylate is particularly preferred.

The styrene-based monomers include styrene, alkyl styrenes such as a-methyl styrene, methyl styrene (vinyl toluene) and ethyl styrene, and halogenated styrenes such as brominated styrene, out of which styrene is particularly preferred. The acryionitrile- based monomers include acrylonitrile and methacrylonitrile.

The olefin-based monomers include ethylene and norbornene compounds. Further, examples of the other copolymerizable monomer include glycidyl methacrylate, N- methylmaleimide and maleic anhydride. The organic crosslinked particles may have a unit such as N-ethyl glutarimide.

Examples of the crosslinkable monomer to be used in combination with the non- crosslinkable vinyl-based monomer include divinyl benzene, ally! methacrylate, triallyl cyanurate, triallyl isocyanate, ethylene glycol di(meth)acrylate, diethyiene glycol di(meth)acrylate, propylene glycol (meth)acryiate, 1 ,6-hexanediol di(meth)acrylate, trimethylolpropane (methjacrylate, pentaerythritol tetra(meth)acrylate, bisphenol A di(meth)acryiate, dicyclopentanyl di(meth)acrylate, dicyclopentenyl di(meth)acryiate and N-methylol (meth)acrylamide. Preferably, the light diffusing agent Is crosslinked silicone particles.

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

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 methylsilsequioxane.

The crosslinked silicone particles have an average particle diameter of preferably 0.01 to 50 pm, more preferably 1 to 30 μm, more preferably 1.8 to 10 pm. When the average particle diameter is smaller than 0.01 pm or larger than 50 pm, 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 Corning Toray Co., Ltd. and the silicone powders of Shin- Etsu Chemical Co., Ltd.

Other optional components

The composition according to the invention may optionally comprise at least one further component. Examples of the optional components are peroxides and other 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. For example, additives which serve as a-nucleating agents should not be utilized in accordance with the present invention.

Peroxides

In some embodiments, the composition according to the invention can be obtained by melt-mixing a peroxide with the propylene-based polymer and the nucleating agents. The composition obtained by the addition of a peroxide has a different (higher) MFI from the MFI of the propylene-based polymer (in particular heterophasic copolymer) used in preparing the composition. This step is also known in the art as vis-breaking or shifting. The term "visbreaking" is well known in the field of the invention. For example methods of visbreaking polypropylene have been disclosed in US 4,282,076 and EP 0063654. It is also possible to first melt-mix a peroxide with the propylene-based polymer, which changes the melt flow index of the heterophasic propylene copolymer, and then mix with the nucleating agents.

Examples of organic peroxides are well known and include dialkyl peroxides, e.g.

dicumvi peroxides, peroxyketals, peroxycarbonates, diacyl peroxides, peroxyesters and peroxydicarbonates. Specific examples of these include benzoyl peroxide,

sec-octoate, tert-butyl perpivalate, cumyl perpivalate.

It can easily be determined by the person skilled in the art through routine

experimentation how much peroxide should be used to obtain a composition having the desired melt flow index. This also depends on the half-life of the peroxide and on the conditions used for the melt-mixing, which in turn depend on the exact composition of the heterophasic propylene copolymer. When a peroxide is used, the amount of peroxide will typically lie in the range of 0.02 to 0.5 wt% based on the heterophasic propylene copolymer.

In some embodiments, the composition according to the invention is prepared without using a peroxide.

Additives

The composition according to the invention may further comprise additives. The additives may include β-nucleating agents and light diffusing agents as described elsewhere. 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 nucleating agents and the optional components should add up to 100% by weight Preferably, the total of the propylene-based polymer and the nucleating agents is at ieast 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 97 wt%, at least 98 wt%, at Ieast 99 wt%, at Ieast 99.5 wt%, at least 99.9 wt% or 100 wt% of the total composition. Preferably, the composition according to the invention comprises an acid scavenger. The acid scavenger may be added to the composition according to the invention separately from the β-nucleating agent. Additionally or alternatively, the acid scavenger may be added to the composition as a composition comprising the β-nucleating agent and the acid scavenger. Preferably, the amount of the acid scavenger in the composition is 0.01- 1 wt% with respect to the total composition. Any known acid scavenger is suitable and may e.g. be selected from the group consisting of hydrotalcite, calcium stearate, sodium stearate, zinc stearate, magnesium stearate and combinations thereof. The invention further relates to a composition comprising no or little amount of a inorganic filler. The amount of the inorganic filler in the composition according to the invention may be at most 5 wt%, at most 3 wt%, at most 1 wt%, at most 0.5 wt%, at most 0.1 wt% or 0 wt%. The invention further relates to a composition comprising no or little amount of a polypropylene homopolymer as an additional component to the propylene-based polymer and the nucleating agents. The amount of the polypropylene homopolymer in the composition according to the invention may be at most 5 wt%, at most 3 wt%, at most 1 wt%, at most 0.5 wt%, at most 0.1 wt% or 0 wt%.

In some embodiments, the composition according to the invention comprises inorganic fillers or glass fibers as an additional component to the propylene-based polymer and the nucleating agents. The amount of the inorganic fillers or glass fibers may e.g. be 5 to 30 wt%, e.g. 10 to 25 wt%, e.g. 15 to 20 wt%. The invention further relates to a composition comprising no or little amount of inorganic fillers or glass fibers as an additional component to the propylene-based polymer and the nucleating agents. The amount of the inorganic fillers or glass fibers may e.g. be at most 5 wt%, at most 3 wt%, at most 1 wt%, at most 0.5 wt%, at most 0.1 wt% or 0 wt%.

In some embodiments, the composition according to the invention comprises impact modifiers such as ethylene-a-olefin copolymer as an additional component to the propylene-based polymer and the nucleating agents. The amount of the impact modifiers may e.g. be 5 to 30 wt%, e.g. 10 to 25 wt%, e.g. 15 to 20 wt%. The invention further relates to a composition comprising no or little amount of impact modifiers such as ethylene-a-olefin copolymer as an additional component to the propylene-based polymer and the nucleating agents. The amount of the impact modifiers such as ethylene-a-olefin copolymer in the composition according to the invention may be at most 5 wt%, at most 3 wt%, at most 1 wt%, at most 0.5 wt%, at most 0.1 wt% or 0 wt%.

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 d_p 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 IS01 183-1 :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 fightbulb. 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 β-nucleating agent 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 (ISO 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 (ISO 1133, 230°C, 2.16 kg). Preferably, the composition according to the invention has a melt flow rate of 5-50 dg/min (ISO 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 transparency and the haze are measured according to ASTM D1003. Preferably, the polypropylene composition in the light diffusion article according to the invention has a degree of light dispersion (DLD) of at least 10 degrees , at least 15 degrees, at least 20 degrees, at least 25 degrees, at least 30 degrees, at least 35 degrees, at least 40 degrees, at least 44 degrees, at least 45 degrees, at least 47.5 degrees or at least 50 degrees measured as a sheet having a thickness of 1 mm and/or a DLD of at least 10 degrees, at least 15 degrees, at least 20 degrees, at least 30 degrees, at least 40 degrees, at least 50 degrees, at least 56 degrees or at least 57 degrees measured as a sheet having a thickness of 1.5 mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention has a light transmittance of at least 55% or at least 65% measured as a sheet having a thickness of 1mm and/or a light transmittance of at least 45% or at least 55% measured as a sheet having a thickness of 1.5 mm.

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 1 mm and/or a haze of at least 85%, at least 90% or at least 98% measured as a sheet having a thickness of 1.5 mm. heterophasic propylene copolymer

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a heterophasic propylene copolymer as described herein has a degree of light dispersion (DLD) of at least 44 degrees, at least 45 degrees, at least 47.5 degrees or at least 50 degrees measured as a sheet having a thickness of 1 mm and/or a DLD of at least 56 degrees or at least 57 degrees measured as a sheet having a thickness of 1.5 mm. Such compositions may however also have a lower minimum degree of fight dispersion, such as at least 10, 15, 20, 25, 30, 35 or 40 degrees as set out above. Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a heterophasic propylene copolymer as described herein has a light transmittance of at least 65% measured as a sheet having a thickness of 1mm and/or a light transmittance of at least 55% measured as a sheet having a thickness of 1.5 mm.

Preferably, polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a heterophasic propylene copolymer as described herein has a haze of at least 98% measured as a sheet having a thickness of 1mm and/or a haze of at least 98% measured as a sheet having a thickness of 1.5 mm.

In particularly preferred embodiments, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a heterophasic propylene copolymer as described herein has a degree of light dispersion (DLD) of at least 44 degrees measured as a sheet having a thickness of 1 mm, a light transmittance of at least 65% measured as a sheet having a thickness of 1mm and a haze of at least 98% measured as a sheet having a thickness of 1mm. propylene a-olefin copolymer

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene a-olefin copolymer as described herein has a degree of light dispersion (DLD) of at least 10 degrees or at least 15 degrees measured as a sheet having a thickness of 1 mm and/or a DLD of at least 10 degrees or of at least 15 degrees measured as a sheet having a thickness of 1.5 mm.

Preferably, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene α-olefin copolymer as described herein has a light transmittance of at least 65% measured as a sheet having a thickness of 1mm and/or a light transmittance of at least 55% measured as a sheet having a thickness of 1.5 mm. Preferably, polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene α-olefin copolymer as described herein has a haze of at least 75% or at least 90% measured as a sheet having a thickness of 1mm and/or a haze of at least 85%, at least 90% or at least 98% measured as a sheet having a thickness of 1.5 mm.

In particularly preferred embodiments, the polypropylene composition in the light diffusion article according to the invention wherein the propylene-based polymer is a propylene a-olefin copolymer as described herein has a degree of light dispersion (DLD) of at least 15 degrees measured as a sheet having a thickness of 1.5 mm, a light transmittance of at least 65% measured as a sheet having a thickness of 1mm and a haze of at least 85% measured as a sheet having a thickness of 1 mm.

The invention further relates to use of a polypropylene composition comprising a propylene-based polymer, wherein the polypropylene composition is β-nucleated, for making a light diffusing article, preferably a sheet, a tube or a light bulb. 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 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 is a heterophasic propylene copolymer comprising a matrix phase of a propylene homopolymer and a dispersed phase of propylene-ethylene copolymer. Polymer 2 is a propylene-ethylene copolymer.

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

Density was measured according to IS01183-1 :2012.

Additives:

sodium benzoate

a-nucleating agent composition 1 : Bis(4-(tert-butyl)benzoato-0)hydroxyaluminium, GCH TECHNOLOGY CO., LTD.;

a-nucleating agent composition 2: Zinc stearate 34 wt%, Ca HHPA 66 wt%, Milliken; β-nucleating agent composition: calcium salt of stearic acid and calcium salt of cis-A4- tetrahydrophthalic acid, molar ratio is approximately 2:1 (25.7 wt% is calcium salt of cis-A4-tetrahydrophthalic acid), GCH TECHNOLOGY CO., LTD. In addition, anti-static agent, antioxidant 1 and antioxidant 2 were used as indicated in the below tables. The propylene-based polymer was pre-blended with the additives. Subsequently the pre-blended powder was extruded using a twin extruder. The pellets were dried at 100 °C for 3 h and injection molded using FANUC injection molding machine (S-2000I) 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 degrees based on Lambert's law.

The amount of B-modification was determined by Differential Scanning Calorimetry (DSC). DSC is run according to ISO 3146/part 3/method C2 with a scan rate of 10° C/min. The amount of B-modification is calculated from the second heat by the following formula:

|3-area/(a-area+B-area)

The density was tested according to IS0 1183-1 :2012.

The compositions and test results are shown in Tables 1-4.

Table 1: polymer 1 with sodium benzoate

Sodium benzoate was used as an α-nucleating agent, and its effect on diffusion performance is shown in Table 1. It can be seen that DLD did not improve by the addition of sodium benzoate. Table 2: polymer 1 with a-nucleating composition

In the experiments of Table 2, two types of other α-nucleating agents were used. In both cases, it can be seen that DLD did not improve by the addition of a-nucleating agent.

Table 3: polymer 1 with β-nucleating composition

It can be seen from Table 3 that the addition of the β-nucleating agent resulted in increase in DLD. Especially with a thin sheet of 1 mm, the increase in the DLD is particularly large. The level of DLD increased to a level comparable to that of a polycarbonate with a light diffusing agent (see Table 5). The transparency is maintained at a constant level.

Table 4: polymer 2 with various nucleating agents

Instead of a heterophasic propylene copolymer as in Tables 1-3, the propylene-based polymer was an ethylene-propylene random copolymer in the experiments of Table 4. As in the experiments with the heterophasic propylene copolymer, the use of a- nucleating agent did not lead to an increase in DLD. In comparison, the formation of β- morphology led to an increase in DLD at a thickness of 1.5 mm. The formation of β- morphology further led to an increase in the impact strength and a decrease in the flexural modulus.

The MFR was measured according to IS01133 (2.16 kg, 230 °C).

The Charpy impact strength was measured according to IS0 179 at 23 °C.

The flexural modulus was measured according to IS0178 at 23 °C.

Further, the optical properties of a light diffusing sheet of polycarbonate are shown in Table 5.

Table 5

Claims

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

polypropylene composition comprising a propylene-based polymer, wherein the polypropylene composition is β-nucleated.

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 |dp-d_a|/dp is at most 1%, wherein d_a and d_p are measured according to

IS01183-1 :2012.

4. The light diffusing article of any one of the preceding claims, wherein the amount of β-modification of the polypropylene composition is at least 10% determined by Differential Scanning Calorimetry.

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

polypropylene composition comprises a β-nucleating agent, wherein preferably the amount of the β-nucleating agent is 0.0001 to 2.0 wt%, preferably 0.001 to 2.0 wt%, for example at least 0.002 wt%, at least 0.005 wt%, at least 0.025 wt% or at least 0.05wt%, and/or for example at most 1.5 wt%, for example at most 1.0 wt%, at most 0.5 wt% or at most 0.1 wt%, with respect to the total composition.

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

polypropylene composition further comprises a light diffusing agent, wherein preferably the amount of the light diffusing agent is 0.05-10.0 wt% with respect to the total composition.

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

polypropylene composition comprises little or no light diffusing agent, wherein preferably the polypropylene composition comprises less than 0.05 wt% of the light diffusing agent with respect to the total composition.

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

9. The light diffusing article of any one of claims 1-8, wherein the propylene-based polymer is a heterophasic propylene copolymer which consists of

(a) a propylene-based matrix wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene-a-olefin copolymer consisting of at least 70 wt% of propylene and at most 30 wt% of a-olefin, based on the total weight of the propylene-based matrix and

wherein the propylene-based matrix is present in an amount of 60 to 95 wt% based on the total heterophasic propylene copolymer and

(b) a dispersed ethylene-a-olefin copolymer, wherein the dispersed ethylene-a- olefin copolymer is present in an amount of 40 to 5 wt% based on the total heterophasic propylene copolymer and

wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-a-olefin copolymer in the heterophasic propylene copolymer is 100 wt%,

preferably wherein the propylene-based polymer 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 and/or wherein the polypropylene composition 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.

10. The light diffusing article of claim 9, wherein the amount of ethylene in the

ethylene- a-olefin copolymer is in the range of 20 to 65wt% based on the ethylene- a-olefin copolymer.

11. The light diffusing article of claim 9 or 10, wherein the polypropylene composition has a degree of light dispersion (DLD) of at least 44 degrees, at least 45 degrees, at least 47.5 degrees or at least 50 degrees measured as a sheet having a thickness of 1 mm and/or a DLD of at least 56 degrees or at least 57 degrees measured as a sheet having a thickness of 1.5 mm, 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.

12. The light diffusing article of any one of claims 9-11 , wherein the polypropylene composition has a light transmittance of at least 55% measured as a sheet having a thickness of 1 mm and/or a light transmittance of at least 45% measured as a sheet having a thickness of 1.5 mm, wherein the light transmittance is measured according to ASTM D1003.

13. The light diffusing article of any one of claims 9-12, wherein the polypropylene composition has a haze of at least 75% measured as a sheet having a thickness of 1 mm and/or a haze of at least 85% measured as a sheet having a thickness of 1.5 mm, wherein the haze is measured according to ASTM D1003.

14. The light diffusing article of any one of claims 1-8, wherein the propylene-based polymer is a propylene a-olefin copolymer and wherein the polypropylene composition has a degree of light dispersion (DLD) of at least 15 degrees measured as a sheet having a thickness of 1.5 mm, a light transmittance of at least 55% measured as a sheet having a thickness of 1 mm and a haze of at least 75% measured as a sheet having a thickness of 1mm, preferably wherein the propylene- based polymer 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 and/or wherein the polypropylene composition 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.

15. Use of a polypropylene composition comprising a propylene-based polymer,

wherein the polypropylene composition is β-nucleated, for making a light diffusing article, preferably a sheet, a tube or a light bulb.

16. A lighting device comprising a housing containing a light source and the light

diffusing article according to any one of claims 1 - 14, said article being positioned relative to the light source such that it diffuses at least part of the light coming from said light source.

17. The lighting device of claim 16, wherein the light source is a LED lamp.