WO2011144486A1

WO2011144486A1 - Polypropylene tub for washing machine

Info

Publication number: WO2011144486A1
Application number: PCT/EP2011/057471
Authority: WO
Inventors: Marco Ciarafoni; Manikandan Rathinakumar; Paola Massari; Jackie Tong
Original assignee: Basell Poliolefine Italia SRL
Current assignee: Basell Poliolefine Italia SRL
Priority date: 2010-05-19
Filing date: 2011-05-10
Publication date: 2011-11-24
Anticipated expiration: 2012-11-19
Also published as: CN102884123B; CN102884123A

Abstract

A process for producing a fixed tub of a washing machine comprising the step of injection molding a polypropylene resin in the form of the tub; wherein the polypropylene resin comprises (percent by weight): A) from 50% to 90%; of a propylene polymer propylene containing from 0 to 5% by weight of ethylene derived units, having a polydispersity (PI) ranging from 4.5 to 8.0; B) from 50% to 10% of a propylene ethylene copolymer containing from 25% by weight to 60% by weight of ethylene derived units.

Description

TITLE:

Polypropylene tub for washing machine

The present invention relates to the use of a particular polypropylene resin for obtaining tubs for washing machines, more specifically dishwashers and clothes washing machines.

Tubs for washing machines can be divided in two categories, tubs rotating through the horizontal axis and fixed tubs having an opening in the bottom for the agitator or pulsator rotating through the vertical axis. The two type of tubs have different characteristics since they are stressed in a different way.

The present invention is limited to washing machines having a fixed tub wherein the agitator rotates on a vertical axis.

US 6,716,383 relates to a washing tub formed by a reinforcing body made from a non-metallic material, such as plastic or fiberglass, and a thin interior liner portion constituted by a metallic material. The reinforcing body is formed from plastic, such as polypropylene. This document is silent about the type of polypropylene resin that can be used.

US 2006/0086379 relates to a method for improving stain resistance of a plastic washing machine component arranged within a wash chamber of a washing machine. Also this document relates generally to polypropylene without specifying its features.

Thus there is the need of tubs having improved features and that can be produced in an easy way. An object of the present invention is therefore a process for producing a fixed tub of a washing machine comprising the step of injection molding a polypropylene resin in the form of the tub; wherein the polypropylene resin comprises (percent by weight):

A) from 50% to 90%; preferably from 70% to 85%, more preferably from 75% from 85% of a propylene polymer containing from 0 to 5% by weight of ethylene derived units, having a polydispersity (PI) ranging from 4.5 to 8.0; preferably from 4.6 to 7.0; more preferably from 4.8 to 6.0 and

B) from 10% to 50%; preferably from 30% to 10%; more preferably from 15% to 25% of a propylene ethylene copolymer containing from 25% by weight to 60% by weight preferably from 30% by weight to 49% by weight; more preferably from 38% by weight to 48% by weight of ethylene derived units.

Preferably the polypropylene resin to be used in the process of the present invention has an intrinsic viscosity of the fraction soluble in xylene at 25 °C comprised between 2.0 and 5.0 dl/g; preferably between 2.5 and 4.0 dl/g more preferably between 2.9 and 3.5 dl/g and a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) from 30 to 100 g/10 min preferably from 40 to 90 g/10 min more preferably from 50 to 80 g/10 min; even more preferably from 55 to 70 g/10 min.

From the above definitions it is evident that the term "copolymer" includes polymers containing only two kinds of comonomers.

Preferably component A) is a propylene homopolymer

Another preferred features for the polypropylene resin to be used in the process of the present invention are:

The Flexural Modulus preferably comprised between 1000 MPa and 2000 MPa, more preferably comprised between 1100 and 1800 MPa; even more preferably comprised between 1200 and 1700 MPa

The propylene polymer compositions of the present invention can be prepared by sequential polymerization in at least two stages, with each subsequent polymerization stage being conducted in the presence of the polymeric material formed in the immediately preceding polymerization reaction, wherein the polymer (A) is normally prepared in at least one first polymerization stage and the copolymer (B) is normally prepared in at least one second polymerization stage.

Preferably, each polymerization stage is carried out in presence of a highly stereospecific heterogeneous Ziegler-Natta catalyst. The Ziegler-Natta catalysts suitable for producing the propylene polymer compositions of the invention comprise a solid catalyst component comprising at least one titanium compound having at least one titanium-halogen bond and at least an electron-donor compound (internal donor), both supported on magnesium chloride. The Ziegler-Natta catalysts systems further comprise an organo-aluminum compound as essential co- catalyst and optionally an external electron-donor compound.

Suitable catalysts systems are described in the European patents EP45977, EP361494, EP728769, EP 1272533 and in the international patent application W000163261.

Preferably, the solid catalyst component comprises Mg, Ti, halogen and an electron donor.

The electron donor can be selected from succinates of formula (I):

1 2 ·

wherein the radicals R and R , equal to or different from each other, are a C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms belonging to groups 15-17 of the periodic table; the radicals R³ to R⁶ equal to or different from each other, are hydrogen or a C₁-C₂ linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms, and the radicals R³ to R⁶ which are joined to the same carbon atom can be linked together to form a cycle.

R¹ and R² are preferably Ci-Cs alkyl, cycloalkyl, aryl, arylalkyl and alkylaryl groups.

1 2

Particularly preferred are the compounds in which R and R are selected from primary alkyls and in particular branched primary alkyls. Examples of suitable R¹ and R² groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, neopentyl, 2-ethylhexyl. Particularly preferred are ethyl, isobutyl, and neopentyl.

One of the preferred groups of compounds described by the formula (I) is that in which R³ to R⁵ are hydrogen and R⁶ is a branched alkyl, cycloalkyl, aryl, arylalkyl and alkylaryl radical having from 3 to 10 carbon atoms. Another preferred group of compounds within those of formula (I) is that in which at least two radicals from R³ to R⁶ are different from hydrogen and are selected from C₁-C₂₀ linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms belonging to groups.

Particularly preferred are the compounds in which the two radicals different from hydrogen are linked to the same carbon atom. Furthermore, also the compounds in which at least two radicals different from hydrogen are linked to different carbon atoms, that is R³ and R⁵ or R⁴ and R⁶ are particularly preferred.

In a alternative embodiment the electron donor can be of the type described in EP 09163192.9. According to a preferred method, the solid catalyst component can be prepared by reacting a titanium compound of formula Ti(OR)_n__yX_y where n is the valence of titanium and y is a number between 1 and n, preferably TiC4, with a magnesium chloride deriving from an adduct of formula MgCl₂ pROH, where p is a number between 0.1 and 6, preferably from 2 to 3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared in spherical form by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct (100-130 "C). Then, the emulsion is quickly quenched, thereby causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in US 4,399,054 and US 4,469,648. The so obtained adduct can be directly reacted with the Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130 °C) so as to obtain an adduct in which the number of moles of alcohol is generally lower than 3, preferably between 0.1 and 2.5. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold TiCU (generally 0 °C); the mixture is heated up to 80-130 °C and kept at this temperature for 0.5-2 hours. The treatment with Tic4 can be carried out one or more times. The internal donor can be added during the treatment with T1CI₄ and the treatment with the electron donor compound can be repeated one or more times. Generally, the succinate of formula (I) is used in molar ratio with respect to the MgC12 of from 0.01 to 1 preferably from 0.05 to 0.5. The preparation of catalyst components in spherical form is described for example in European patent application EP-A-395083 and in the International patent application W098144001. The solid catalyst components obtained according to the above method show a surface area (by B.E.T. method) generally between 20 and 500 m21g and preferably between 50 and 400 m21g, and a total porosity (by B.E.T. method) higher than 0.2 cm31 g preferably between 0.2 and 0.6 cm31g. The porosity (Hg method) due to pores with radius up to 10.000A generally ranges from 0.3 to 1.5 cm31g, preferably from 0.45 to 1 cm31g.

The organo -aluminum compound is preferably an alkyl-Al selected from the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri- n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum's with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as

Preferred external electron-donor compounds include silicon compounds, ethers, esters such as ethyl 4-ethoxybenzoate, amines, heterocyclic compounds and particularly 2,2,6,6-tetramethyl piperidine, ketones and the 1,3-diethers. Another class of preferred external donor compounds is that of silicon compounds of formula R_a ⁵Rt,⁶Si(OR⁷)_c where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R⁵, R⁶, and R⁷, are alkyl, cycloalkyl or aryl radicals with 1 -18 carbon atoms optionally containing heteroatoms. Particularly preferred are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1 ,1 ,trifiuoropropyl-2-ethylpiperidinyl-dimethoxysilane and 1,1,1 ,trifluoropropyl- metildimethoxysilane. The external electron donor compound is used in such an amount to give a molar ratio between the organo-aluminum compound and said electron donor compound of from 0.1 to 500.

The polymerization process can be carried out in gas phase and/or in liquid phase, in continuous or batch reactors, such as fiuidized bed or slurry reactors. For example, it is possible to carry out the polymerization of the propylene polymer (A) in liquid phase, using liquid propylene as diluent, while the copolymerization stage to obtain the propylene copolymer fraction (B) is carried out in gas phase, without intermediate stages except for the partial degassing of the monomers. Alternatively, all the sequential polymerization stages can be carried out in gas phase. The reaction time, temperature and pressure of the polymerization steps are not critical, however the temperature for the preparation of fraction (A) and (B), that can be the same or different, is usually from 50°C to 120°C. The polymerization pressure preferably ranges from 0.5 to 12 MPa if the polymerization is carried out in gas-phase. The catalytic system can be pre-contacted (pre- polymerized) with small amounts of olefins. The molecular weight of the propylene polymer composition is regulated by using known regulators, such as hydrogen.

In the second stage of the particularly preferred polymerization process, the propylene/ethylene copolymer (B) is produced in a conventional fluidized-bed gas-phase reactor in the presence of the polymeric material and the catalyst system coming from the preceding polymerization step. The propylene polymer compositions of the present invention can also be obtained by separately preparing the said copolymers (A) and (B), operating with the same catalysts and substantially under the same polymerization conditions as previously illustrated and subsequently mechanically blending said copolymers in the molten state using conventional mixing apparatuses, like twin-screw extruders.

The polypropylene resin to be used in the process of the present invention may further comprise additives commonly employed in the polyolefin field, such as antioxidants, light stabilizers, nucleating agents, antiacids, colorants and fillers. The polypropylene resin can be molded and injected according to the process of the present invention with processes commonly know in the art.

A further object of the present invention is the use of the polypropylene resin comprising component A) and component B) as described above for the production of fixed tubs for washing machines.

A further object of the present invention is a fixed tub for washing machines characterized by being made of polypropylene resin comprising component A) and component B) as described above.

Preferably the fixed tub has a cylindrical or parallelepipedal shape and at least one opening in the bottom part.

More preferably the fixed tub is divided in two chambers one used as washing chamber and presenting the opening in the bottom part, the second being used as drying chamber.

A still further object of the present invention is a washing machine comprising a fixed tub as described above.

Figure 1 shows a partially broken elevational sectional view of a clothes washing machine wherein the tub is made of polypropylene resin in accordance with the present invention, the washing machine comprises a washing tub 1 arranged at a side inside the housing 2 and a dryer tub 3 arranged at the other side, which washing tub 1 is provided with an opening 6 for the roller type agitator on the bottom and a driving mechanism 5 equipped under the bottom thereof.

Figure 2 shows the partially broken elevational sectional view described in figure 1 wherein the tub made in polypropylene resin according to the present invention is divided in two chambers, a washing chamber 11 and a drying chamber 13, by a dividing plate 17 that can be a fixed plate so that the whole tub divided in two chambers is directly obtained by injection moulding as a whole shape, or a removable plate.

Figure 3 describes a dishwasher tub 21 obtained with the process according to the present invention. In general, dishwasher tub 21 includes an outer body portion 22 and an inner liner portion 23. More specifically, dishwasher tub 21 includes opposing sides 24 and 25, a top 26 and a bottom 27. Furthermore, dishwasher tub 22 is provided with a substantially central opening 28 formed in bottom 27.

Figure 4 describes the load test carried out to evaluate the stiffness of the tub of the present invention. The tub 31 comprises a washing chamber 32 having an opening on the bottom part 36 and a drying chamber 33, the washing chamber and the drying chamber are created by a divisor plate 34. During the test the height 37 with or without the load 35 put on points A, B, C and D has been measured in several tubs.

The following examples are given to illustrate and not to limit the present invention.

Examples

The data of the propylene polymer materials were obtained according to the following methods: Xylene-soluble faction

2.5 g of polymer and 250 rnL of o-xylene are introduced in a glass flask equipped with a refrigerator and a magnetical stirrer. The temperature is raised in 30 minutes up to the boiling pint of the solvent. The so obtained solution is then kept under reflux and stirring for further 30 minutes. The closed flask is then kept for 30 minutes in a bath of ice and water and in thermostatic water bath at 25°C for 30 minutes as well. The solid thus obtained is filtered on quick filtering paper and the filtered liquid is divided into two 100 ml aliquots. One 100 ml aliquots of the filtered liquid is poured in a previously weighed aluminum container, which is heated on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80°C under vacuum until constant weight is obtained. The residue is weighed to determine the percentage of xylene-soluble polymer.

Ethylene (C2) content

By IR spectroscopy.

The comonomer content of the Component B is determined on the precipitated "amorphous" fraction of the polymer. The precipitated "amorphous" fraction is obtained as follows: to one 100 ml aliquot of the filtered liquid obtained as described above (procedure for the Xylene-soluble faction) 200 ml of acetone are added under vigorous stirring. Precipitation must be complete as evidenced by a clear solid-solution separation. The solid thus obtained is filtered on a tared metallic screen and dried in a vacuum oven at 70°C until a constant weight is reached.

Molar ratio of feed gasses

Determined by gas-chromatography

Melt flow rate (MFR)

Determined according to ISO 1133 (230°C, 2.16 Kg)

Intrinsic viscosity

Determined in tetrahydronaphthalene at 135°C Flexural modulus

Determined according to ISO 178

Stress at yield and at break

Determined according to ISO 527

Elongation at yield and break

Determined according to ISO 527

IZOD Impact Strength

Determined according to ISO 18011 A

Melting temperature, melting enthalpy and crystallization temperature

Determined by DSC with a temperature variation of 20°C per minute

Polydispersity Index (PI): measurement of molecular weight distribution of the polymer. To determine the PI value, the modulus separation at low modulus value, e.g. 500 Pa, is determined at a temperature of 200 °C by using a RMS-800 parallel plates rheometer model marketed by Pvheometrics (USA), operating at an oscillation frequency which increases from 0.01 rad/second to 100 rad/second. From the modulus separation value, the PI can be derived using the following equation:

PI = 54.6 x (modulus separation)^{"1 76}

wherein the modulus separation (MS) is defined as:

MS = (frequency at G' = 500 Pa)/(frequency at G" = 500 Pa)

wherein G' is the storage modulus and G" is the loss modulus.

Example 1 production of the polypropylene resin

Preparation of the solid catalyst component

Into a 500 mL four-necked round flask, purged with nitrogen, 250 mL of TiCU were introduced at 0 °C. While stirring, 10.0 g of microspheroidal MgCl₂*2.8C₂H₅OH (prepared according to the method described in ex.2 of USP 4,399,054 but operating at 3000 rpm instead of 10000 rpm) and 7.4 mmol of diethyl 2,3-diisopropylsuccinate were added. The temperature was raised to 100 °C and maintained for 120 min. Then, the stirring was discontinued, the solid product was allowed to settle and the supernatant liquid was siphoned off. Then 250 mL of fresh TiC were added. The mixture was reacted at 120 °C for 60 min and, then, the supernatant liquid was siphoned off. The solid was washed six times with anhydrous hexane (6 x 100 mL) at 60 °C. Catalyst system and prepolymerization treatment

Before introducing it into the polymerization reactors, the solid catalyst component described above is contacted at 12 °C for 24 minutes with aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS). The weight ratio of TEAL to the solid catalyst component in indicated in table 1 , the weight ratio TEAL/DCPMS is indicated in table 1.

The catalyst system is then subjected to prepolymerization by maintaining it in suspension in liquid propylene at 20 °C for about 5 minutes before introducing it into the first polymerization reactor.

Polymerization

The propylene polymer compositions of the examples were prepared in a two-step polymerization process, wherein the copolymer (A) was prepared in the first polymerization step by feeing the monomers and the catalyst system to a gas-phase polymerization reactor comprising two interconnected polymerization zones, a riser and a downcomer, as described in the European Patent EP1012195. The polymerization mixture was discharged from said reactor, conveyed to a gas-solid separator and the polymerized material was sent into a conventional gas-phase fluidized-bed reactor where the ethylene/propylene copolymer (B) was produced. The operative conditions are indicated in Table 1.

Table 1

PI 5-5.5

Component B (gas phase reactor)

Temperature °C 80

Pressure MPa 2

Split * % 18

c₂vc₂-+c₃- mol/mol 0.34

H₂/C₂ ^" mol/mol 0.037

C2= ethylene C3 = propylene

XS = xylene solubles

Comparative example 1

Into a 500 ml four-necked round flask, purged with nitrogen, 225 ml of TiCU were introduced at 0

°C. While stirring, 6.8 g of microspheroidal MgCl₂»2.7C₂H₅OH (prepared as described in Ex. 2 of

USP 4,399,054 but operating at 3,000 rpm instead of 10,000 rpm) were added.

The flask was heated to 40°C and 4.4 mmoles of diisobutylphthalate were thereupon added. The temperature was raised to 100 °C and maintained for two hours, then the stirring was discontinued, the solid product was allowed to settle and the supernatant liquid was siphoned off.

200 ml of fresh TiCU were added, the mixture was reacted at 120 °C for one hour then the supernatant liquid was siphoned off.

200 ml of fresh TiCU were added, the mixture was reacted at 120 °C for one hour then the supernatant liquid was siphoned off and the solid obtained was washed six times with anhydrous hexane (6 x 100 ml) at 60 °C and then dried under vacuum. The catalyst component contained 2.8 wt% of Ti and 12.3 wt% of phthalate.

The catalyst system is then subjected to prepolymerization by maintaining it in suspension in liquid propylene at 20 °C for about 5 minutes before introducing it into the first polymerization reactor. Polymerization

The polymerization run is conducted in continuous mode in a series of three reactors equipped with devices to transfer the product from one reactor to the one immediately next to it. The first two reactors are liquid phase reactors, and the third is a fluid bed gas phase reactor. Component (A) is prepared in the first and second reactor, while component (B) is prepared in the third. Hydrogen is used as molecular weight regulator.

The gas phase (propylene, ethylene and hydrogen) is continuously analyzed via gas- chromatography.

At the end of the run the powder is discharged and dried under a nitrogen flow.

The main polymerization conditions are reported in Table2.

Table 2

On Table 3 are reported the characterization data measured on the compositions obtained by mixing the polymer powders of the example 1 and comparative example 1 with the additives rerted on table 3 extruded in a twin-screw extruder Berstorff (L/D=33) under the following operating conditions:

Temperature of the feeding section: 190-210°C

Melt temperature: 240°C

Temperature of the die section: 230°C

Flow rate: 16 Kg/h

Rotational speed: 250 rpm Table 3

The polypropylene resin of example 2 and of comparative example 1 were injection molded to form a tub similar to that one described in figure 2. A load test with a load of 4,5 kg to evaluate the stiffness of the product has been carried out. As described in figure 4, the test has been carried out by measuring the height 37 with or without the load 35 put on points A-D. several tubs haven been tested the results are show in table 4.

Table 4

Measures are in mm

The results of the test show that the tub made according to the invention has an improved stiffness.

Claims

1. A process for producing a fixed tub of a washing machine comprising the step of injection molding a polypropylene resin in the form of the tub;

wherein the polypropylene resin comprises (percent by weight):

A) from 50% to 90%; of a propylene polymer propylene containing from 0 to 5% by weight of ethylene derived units, having a polydispersity (PI) ranging from 4.5 to 8.0;

B) from 50% to 10% of a propylene ethylene copolymer containing from 25% by weight to 60% by weight of ethylene derived units.

2. The process according to claim 1 wherein the polypropylene resin comprises (percent by weight) from 70% to 85% of component A) and from 15 to 30% of component B)

3. The process according to claims 1 or 2 wherein the polydispersity of component A) ranges from 4.6 to 7.0.

4. The process according to anyone of claims 1 to 3 wherein the ethylene content of component B) ranges from 30% by weight to 50% by weight.

5. The process according to anyone of claims 1 to 4 component B) is a propylene homopolymer.

6 A fixed tub for washing machines characterized by being made of polypropylene resin comprising component A) and component B) as described in claims 1 -5.

7. The fixed tub according to claim 6 having a cylindrical or rettangular box shape and at least one opening in the bottom part.

8. The fixed tub according to claims 7 or 8 divided in two chambers one used as washing chamber and having the opening in the bottom part, the second being used as drying chamber

9. The fixed tub according to anyone of claims 6-8 being a dishwasher tub, comprising two chambers, a washing chamber 11 and a drying chamber 13, separated by a fixed or removable plate 17.

10. A washing machine comprising a fixed tub of claims 6-9.