Polyolefin compositions with improved properties

ES 2 348 383 T3

POLYOLEFIN COMPOSITIONS WITH IMPROVED PROPERTIES

Description

The invention relates to polyolefin compositions with improved impact resistance and improved optical properties. More particularly, the invention relates to polyolefin compositions, especially polypropylene compositions with improved impact resistance at temperatures below room temperature, especially at temperatures below 0 ° C, which have improved optical properties, especially higher transparency and lower turbidity.

The compositions of the invention are particularly useful for packaging applications, especially food packaging for deep freeze application.

Background of the invention

Polypropylene homopolymers are widely used in packaging applications. Polypropylene homopolymers show balanced properties and are cheap polymers, which decompose easily, but show poor transparency and poor impact resistance.

It was suggested to improve the poor optical properties and impact resistance of polypropylene homopolymers by adding nucleating and / or clarifying agents. Suitable nucleating agents are, for example, talc, disorbitol, organic phosphates, and the like.

Regardless, the desired properties of propylene homopolymers cannot be improved to the desired degree, in particular to show high impact strength at low temperatures.

Compositions with improved impact resistance and improved optical properties are, for example, propylene / α-olefin random copolymers, where the α-olefin is ethylene or an α-olefin with 4-10 carbon atoms. Although the transparency is higher and the impact resistance improves considerably at room temperature, the impact resistance at lower temperature, ie 0 ° C and below, is still not satisfactory. Random propylene / α-olefin copolymers have a ductile to brittle transition temperature between -5 ° C and 5 ° C, depending on the monomer content and therefore impact resistance at lower temperatures is still very poor .

ES 2 348 383 T3

To improve impact resistance at lower temperatures, heterophasic polymer compositions have been suggested. Heterophasic polymers are polymers that have a matrix phase (phase 1) and a second phase. The matrix phase is normally a polypropylene homopolymer or polypropylene / α-olefin copolymer phase and the second phase is normally a propylene rubber / α-olefin polymer.

Second phase polymers have low glass transition temperatures, typically below -30 ° C. Therefore, the impact resistance of such heterophasic systems is quite satisfactory, even for deep freezing applications. A major drawback is poor transparency, mainly due to large gum particles in the heterophasic system.

Various attempts have been made to improve the transparency of heterophasic polymer systems.

EP-B 0 373 660 describes heterophasic polymer systems with improved impact resistance and improved transparency, of an elastomeric propylene / ethylene as matrix phase and a phase 2 which is propylene rubber / α-olefin, in which the Intrinsic viscosity ratio between phase 1 and phase 2 has to be a defined value, specifically 0.2. Therefore, the heterophasic system of the description of EP B 0 373 660 is restricted to very special combinations of phase 1 polymers and

2.

EP-A 0 814 127 describes cracking resistant polyolefin compositions and flexible articles thereof based on propylene homopolymers or propylene / α-olefin copolymers and elastomeric copolymers of ethylene with propylene or butane-1. Elastomeric copolymers enhance flexibility without affecting the transparency of the polymer composition, which is not even satisfactory for packaging applications, although these compositions are claimed for use in the production of medical articles and food packaging material.

EP B 0 593 221 describes polypropylene resin compositions comprising polypropylenes of defined MFR and ethylene / α-olefin copolymers with a good balance between impact resistance and stiffness and high formability, useful for automotive parts. These compositions do not

ES 2 348 383 T3 have good optical properties, especially low transparency and high haze.

EP-A-844281 describes blends of 100 parts of block polymer of 85-94% polypropylene, 5-15% ethylenepropylene copolymer with 30-60% ethylene content (MFR 70 g / 10 min ( description 50-500 g / 10 min) and 29 parts of VLDPE (20-50% octene, d = 0.86-0.89, MFR <2 g / 10 min).

Document US-A-5331047 describes, in example 4, a composition of LLDPE at 25% (octene, d = 0.92, MI = 0.1 g / 10 min) and a 75% heterophasic polymer of 37% of polypropylene and 63% of a mixture of ethylene-propylene copolymers (9.37% 57% ethylene, 57.6% 27% ethylene, MFR 30 g / 10 min (description 5-400 g / 10 min )).

Similar compositions are described in EP-A-714923. Object of the invention

An object of the invention is to provide polypropylene compositions for packaging applications with improved impact resistance at room temperature and low temperatures, which have improved optical properties, especially good transparency and low haze.

A further object of the invention is a process for producing polypropylene compositions for packaging applications, with improved impact resistance at low temperatures and good optical properties.

A further object of the invention is to provide articles made of these polypropylene compositions useful for packaging applications, especially for food packaging for deep freezing applications.

Brief description of the invention

The object of the invention has been solved by providing heterophasic polymer systems which are modified by a modifier, which show improved impact resistance, as well as improved optical properties.

The invention, therefore, relates to polyolefin compositions with good impact resistance and transparency, comprising

a) 85-98% by weight, based on the total weight of the composition, of a heterophasic propylene / α-olefin copolymer, comprising a polymer or

ES 2 348 383 T3 copolymer of propylene and an α-olefin with 0-15% mol of an α-olefin as matrix polymer and a copolymer of propylene rubber / α-olefin comprising 20-80% mol of a-olefin

b) 15-2% by weight, based on the total weight of the composition, of an ethylene homopolymer or an ethylene / α-olefin copolymer, the aolefin in the ethylene copolymer having 4-10 carbon atoms, the ethylene homoo copolymer with a density less than 0.925 g / m³, in which the melt index of component b), determined at a temperature of 190 ° C and a load of 2.16 kg, is at least two times greater than the melt index of component a) determined at a temperature of 230 ° C and a load of 2.16 kg.

Detailed description of the invention

Component a) is preferably a propylene / α-olefin heterophasic copolymer comprising a propylene polymer or copolymer with 0-15 mol% of an α-olefin as matrix polymer (phase 1 polymer) and u n propylene rubber / α-olefin copolymer comprising 2080% by mole of the α-olefin.

Preferably, the molecular weight of the propylene / α-olefin gum is equal to or less than the molecular weight of the propylene homopolymer relative to the polypropylene / α-olefin copolymer.

The heterophasic polymer of component a) can be produced by a multistage process polymerization of polypropylene or polypropylene and α-olefin, such as bulk polymerization, gas phase polymerization, suspension polymerization, solution polymerization or combinations thereof, using conventional catalysts. These processes are well known to a person skilled in the art.

A preferred process is a combination of a bulk slurry loop reactor (s) and a gas phase reactor (s). The matrix polymer can be prepared in loop reactors or in a combination of loop reactor and gas phase.

The polymer produced in this way is transferred to another reactor and the propylene / α-olefin rubber is polymerized. Preferably, this polymerization step is carried out in a gas phase polymerization.

A suitable catalyst for the polymerization of the heterophasic copolymer is any stereospecific catalyst for the polymerization of propylene that

ES 2 348 383 T3 is capable of polymerizing and copolymerizing propylene and comonomers at a temperature of 40 to 110 ° C and a pressure of 10 to 100 bar. Ziegler-Natta catalysts as well as metallocene catalysts are suitable catalysts.

One skilled in the art is aware of the various possibilities for producing such heterophasic systems and will simply find a suitable process to produce the suitable heterophasic polymer systems used in the present invention.

The matrix polymers of the heterophasic polymers of component a) may have a ratio of matrix polymer (phase 1 polymer) to phase 2 polymer of about 97: 3 to 80:20, preferably 95: 5 to 90:10 .

The heterophasic polymer exhibits a melt index of about 0.1 to 200 g / 10 min, preferably 0.2 to 50 g / 10 min, more preferably 0.3 to 20 g / 10 min according to ISO 1133. The ethylene content of the matrix polymer can be up to 7% by mole and the overall ethylene content of the heterophasic polymer of component a) can be up to 30% by mole, preferably up to 15% by mole.

The polymer of component a) preferably has a flexural modulus greater than 500 mPa (DIN 53457).

Component b) is an ethylene homopolymer or an ethylene / α-olefin copolymer, the α-olefin having 4-10 carbon atoms.

For example, component b) can be a low density ethylene homopolymer or a copolymer of ethylene with, for example, vinyl acetate or butyl acetate or the like. The amount of component b) is 2-15% by weight, based on the total weight of the composition, preferably 3-10% by weight, more preferably 4-7% by weight.

Preferably, the density of the low density ethylene homo- or copolymer (component b)) is less than 0.925 g / cm³ according to ISO 1183. More preferably, the density of the low density ethylene homo- or copolymer is less than 0.920 g / cm³. More preferably, the density is 0.8900.920 g / cm³.

The ethylene homo- or copolymer (component b)) has a melt index (MFR) at least two times, more preferably at least five times greater than the melt index of component a). The MFR of component b)

ES 2 348 383 T3 are determined at a temperature of 190 ° C and a load of 2.15 kg. The MFRs of component a) are determined at a temperature of 230 ° C and a load of 2.16 kg. Those homo- or copolymers of ethylene can be produced in a high pressure tubular process or in a high pressure autoclave process. Alternatively, a linear low density type ethylene copolymer can be produced in a low pressure process, typically with a Ziegler type catalyst. Additionally, the polymers of component b) can be produced using a metallocene catalyst. The polymers of component b) produced using metallocene catalysts are typically elastic copolymers of ethylene or butene or octane, having a density of preferably 0.890-0.915 g / cm³.

The compositions of the present invention may additionally comprise conventional additives, such as antioxidants, stabilizers, acid acceptors, clarifying agents, coloring agents, anti UV agents, nucleating agents, antistatic agents, slip / mold release agents, fillers. , such as nano-fillers etc. Typically, these additives may be present at least 2% by weight each, more preferably at least 0.5% by weight, relative to the total weight of the composition.

Examples of such conventional additives include Irganox 1010 and Irgafos 168 (stabilizers commercially available from Ciba Specialty Chemicals), calcium stearate, and synthetic hydrotalcite (for example, DHT-4A from Kyowa Chemical Industry) and 1,2: 3,4 -di (ethylbenzylidene) sorbitol-EBDS (eg NC-4 from Mitsui Toatsu and 1,3: 2,4 bis (3,4-dimethylbenzylidene) sorbitolDMBDS (eg Millad 3988 from Milliken Chemicals).

The polypropylene composition of the present invention is preferably clarified. Clarified propylenes can be produced, for example, by adding clarifying or nucleating agents, for example sorbitol derivatives such as EDBS, MOBS (1,3: 2,7-di (methylbenzylidene) sorbitol and DMDBS, phosphate salts, such as, for example, 2,2'-methylene-bis (4,6-di-tert-butylphenyl) phosphate sodium, polyvinylcyclohexane etc. Typically such clarifying or nucleating agents can result in haze levels, after injection molding, less than 60%, preferably less than 40%, in 2mm injection molding sheets.

The polyolefin compositions of the present invention are produced

ES 2 348 383 T3 mixing the heterophasic polymer of component a) with component b) optionally adding conventional additives and / or stabilizers and / or fillers.

Preferably the mixing is done by melt blending, in an extruder or other melt blending unit, preferably in a twin screw extruder, usually followed by granulation.

The components can be melt mixed, as is, or the melt mixing can be performed in the presence of a peroxide component to increase the melt flow rate of the composition. Then the peroxide, preferably an organic peroxide, which is suitable for degradation of polypropylene (viscosity reduction) is supplied to the mixing unit together with components a) and b), or the peroxide can be supplied separately in the mixing unit. melt mixture.

The compositions of the present invention show improved impact resistance, especially at temperatures below 0 ° C, and improved optical properties, especially high transparency and low haze.

The polypropylene composition of this invention can be further converted into a final product using normal conversion techniques, such as injection molding, compression molding, blow molding (extrusion or injection stretch blow molding), extrusion (film extrusion , sheet, pipe, tube, profile), blown film, thermoforming and the like. Preferably, the final products are packaging containers prepared by injection molding, blow molding or thermoforming, or packaging films made by film extrusion.

The products are particularly suitable for food packaging applications, especially deep freeze applications.

Yet another object of the invention is to provide new articles with good impact resistance and good optical properties, especially good transparency and low haze.

This object is achieved by using a polyolefin composition comprising

a) 85-98% by weight, based on the total weight of the composition, of a heterophasic propylene / α-olefin copolymer, comprising a polymer or

ES 2 348 383 T3 copolymer of propylene and an α-olefin with 0-15% mol of the α-olefin as matrix polymer and a copolymer of propylene rubber / α-olefin comprising 20-80% mol of a-olefin and

b) 15-2% by weight, based on the total weight of the composition, of an ethylene homopolymer or an ethylene / α-olefin copolymer, the aolefin having 4-10 carbon atoms in the ethylene copolymer, having the homoo copolymer of ethylene with a density of less than 0.925 g / m³, for the production of articles with good impact resistance and good transparency, in which the melt index of component b), determined at a temperature of 190 ° C and a load of 2.16 kg, is at least two times higher than the melt index of component a), determined at a temperature of 230 ° C and a load of 2.16 kg, for the production of an article with good impact resistance and good transparency.

Examples

Heterophasic polymers:

Heterophasic polymers were produced in a two-stage process. In the first stage, a random propylene / ethylene copolymer was polymerized (polymerization in liquid propylene), and in the second stage, a propylene / ethylene rubber was polymerized. The ratio of propylene / ethylene random copolymer to propylene / ethylene rubber was 92: 8.

For the viscosity reduction from the basic melt index to a melt index of about 10-15 g / 10 min, di-tert-butyl peroxide was used.

The compositions and additives were combined in a twin screw extruder at a temperature of 250 ° C. The strands were quenched in cold water and granulated.

The characteristics of the heterophasic polymers are given in table 1.

Table 1

<td></td><td>MFR2</td><td>XCS</td><td>C2</td><td>MFR2</td><td>XCS</td><td>C2</td><td>i..V.</td><td>C3 / XCS</td>

<td></td><td>matrix</td><td>matrix</td><td>matrix</td><td>total</td><td>total</td><td>total</td><td>XCS</td><td></td>

<td>polymer</td><td>[g / 10 ']</td><td>[% p]</td><td>[% mol]</td><td>[g / 10 ']</td><td>[% p]</td><td>[% mol]</td><td>[ml / g]</td><td>[% p]</td>

<td>polymer 1</td><td> 1,09</td><td> 7,2</td><td> 5,6</td><td> 1,22</td><td> 12,2</td><td> 8,5</td><td> 1,38</td><td> 66,0</td>

<td>polymer 2</td><td> 1,13</td><td> 6,7</td><td> 6,3</td><td> 1,27</td><td> 12,0</td><td> 9,8</td><td> 1,65</td><td> 65,0</td>

<td>polymer 3</td><td> 1,13</td><td> 6,7</td><td> 6,3</td><td> 1,19</td><td> 12,1</td><td> 9,2</td><td> 1,59</td><td> 66,0</td>

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<td>polymer 4</td><td> 1,05</td><td> 6,6</td><td> 6,0</td><td> 1,12</td><td> 13,3</td><td> 8,4</td><td> 1,70</td><td> 68,5</td>

<td colspan="9">Matrix MFR2: flow index acc. ISO 1133 phase (1) XCS matrix: xylene cold soluble fraction of phase (1) Matrix C2: ethylene content (randomly incorporated) of phase (1) Total MFR2: flow index acc. ISO 1133 of the heterophasic system (phase 1 + 2) Total XCS: fraction cold soluble in xylene of the hydrophase system (phase 1 + 2) Total C2: total ethylene content of the heterophasic system (phase 1 + 2) IV / XCS: intrinsic viscosity of fraction cold soluble in xylene (indication of molecular weight of propylene / ethylene rubber - phase 2) C3 / XCS: propylene content of the fraction cold soluble in xylene</td>

The polymers were mixed with conventional additives (0.05% Irgafos 168, 0.05% Irganox 1010, 0.1% Ca stearate, 0.06% glycerol monostearate, 0.18% Millad 3988) in an intensive mixer (Henschel mixer) for 20 seconds.

Examples 1-4:

Polymers 1-4 from Table 1 (Component a)) were mixed with 5% Exact 2M048, and a commercial metallocene catalyst based on a polyethylene grade with MFR (190 ° C, 2.16 kg) was added. 10 g / 10 min, density 902 g / cm³; DexPlastomers (component b)).

For the viscosity reduction from the basic melt index to a melt index of about 10-15 g / 10 min, di-tert-butyl peroxide was used. The compositions and additives were combined in a twin screw extruder at a temperature of 250 ° C. The strands were quenched in cold water and granulated.

Injection molded test bars were produced and notches for impact resistance were measured in accordance with ISO 179.

In order to determine the optical properties, especially transparency and haze, injection molded plates (60 * 60 * 2mm) were produced. Optical properties were measured according to ASTM D-1003-92.

Comparative Examples 1-4:

Heterophasic polymers from Table 1 were used as comparative compounds.

Impact resistance and optical properties were determined as described.

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The results are given in Table 2.

Table 2

<td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td></td><td></td><td>MFR</td><td>NIS / + 23 ° C</td><td>IS / -20 ° C</td><td>haze</td>

<td>example</td><td>polymer</td><td>modifier</td><td>[g / 10 ']</td><td>179 1eA / + 23 ° C</td><td>179 1eU / -20 ° C</td><td> [%]</td>

<td></td><td></td><td></td><td></td><td>[kJ / m²]</td><td>[kJ / m²]</td><td></td>

<td>Example 1</td><td>polymer 1</td><td>5% of Exact 2M048</td><td> 12,7</td><td> 11,6</td><td> 77,5</td><td> 28,0</td>

<td>example 2</td><td>polymer 2</td><td>5% of Exact 2M048</td><td> 12,4</td><td> 13,2</td><td> 131,7</td><td> 39,4</td>

<td>example 3</td><td>polymer 3</td><td>5% of Exact 2M048</td><td> 12,5</td><td> 11,8</td><td> 125,9</td><td> 38,5</td>

<td>Example 4</td><td>polymer 4</td><td>5% of Exact 2M048</td><td> 12,0</td><td> 11,1</td><td> 130,3</td><td> 43,5</td>

<td>Example comp. 1</td><td>polymer 1</td><td></td><td> 13,8</td><td> 9,4</td><td> 62,9</td><td> 36,0</td>

<td>Example comp. 2</td><td>polymer 2</td><td></td><td> 13,6</td><td> 10,5</td><td> 88,9</td><td> 54,0</td>

<td>Example comp. 3</td><td>polymer 3</td><td></td><td> 13,4</td><td> 9,3</td><td> 75,8</td><td> 53,6</td>

<td>Example comp. 4</td><td>polymer 4</td><td></td><td> 13,0</td><td> 8,8</td><td> 70,4</td><td> 60,6</td>

Examples 5-6:

The heterophasic polymers selected from Table 1 (component a)) were mixed with 5% Borealis CA9150 (LDPE grade commercially available with MFR (190 ° C, 2.16 kg) 15 g / 10 min, density 915 g / cm³, (component b)).

Comparative Examples 5 and 6 were prepared without adding component b).

The compositions were processed as described above, the impact resistance and optical properties were determined as described above.

The results are given in Table 3.

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Table 3

MFR NIS / + 23 ° C IS / -20 ° C Turbidity example polymer modifier [g / 10 '] 1791eA / + 23 ° C 179 1eU / -20 ° C [%] [kJ / m

2

] [kJ / m

2

] example 5 polymer 2 5 of Borealis CA 9150 13.5 10.5 108.3 40.8 example 6 polymer 4 5 of Borealis CA 9150 12.5 10.0 115.8 44.2