Dish support rack for dishwasher

Abstract

The invention pertains to a dish support rack having outstanding resistance to chemically harsh environments, and possessing improved mechanical properties, said dish support rack comprising a metal wire frame coated with a polyamide composition [composition (C)] comprising: more than 50% wt of a polyamide [polyamide (A), herein after], more than 50% moles of recurring units of said polyamide complying with formula: HN(CH.sub.2).sub.6NHC(O)(CH.sub.2).sub.8C(O) [recurring units (R.sub.6,10)], and, optionally: up to 10% wt of conventional filler(s) and/or additive(s), and to a method for its manufacture.

Claims

1. A dish support rack, comprising: a metal wire frame coated with a polyamide composition, said composition comprising: more than 50 weight % of a polyamide, that comprises recurring units, wherein more than 50 mole % of the recurring units are first recurring units according to the formula: HN(CH.sub.2).sub.6NHC(O)(CH.sub.2).sub.8C(O), and said polyamide exhibits a relative viscosity of at least 2.5 and of at most 4.2, when measured in formic acid, according to ISO 307 standard.

2. The dish support rack of claim 1, wherein the polyamide is a co-polyamide, wherein the recurring units, further comprise second recurring units according to formula (I) or (II), provided that the second recurring units are different from the first recurring units:
NHR.sup.1CO(I),
NHR.sup.2NHCOR.sup.3CO(II), wherein: R.sup.1, equal to or different from each other at each occurrence, is a divalent hydrocarbon group having from 3 to 17 carbon atoms; R.sup.2, equal to or different from each other at each occurrence, is a divalent hydrocarbon group having from 2 to 18 carbon atoms; and R.sup.3, equal to or different from each other at each occurrence, is a bond or a divalent hydrocarbon group having from 1 to 16 carbon atoms.

3. The dish support rack of claim 2, wherein the polyamide is an aliphatic polyamide.

4. The dish support rack of claim 2, wherein the second recurring units are selected from the group consisting of:
NH(CH.sub.2).sub.5CO,(j)
NH(CH.sub.2).sub.8CO,(jj)
NH(CH.sub.2).sub.9CO,(jjj)
NH(CH.sub.2).sub.10CO,(jv)
NH(CH.sub.2).sub.11CO,(v)
NH(CH.sub.2).sub.6NHCO(CH.sub.2).sub.4CO,(vj)
NH(CH.sub.2).sub.6NHCO(CH.sub.2).sub.10CO,(vjj)
NH(CH.sub.2).sub.6NHCO(CH.sub.2).sub.12CO,(vjjj)
NH(CH.sub.2).sub.10NHCO(CH.sub.2).sub.10CO(jx)
NH(CH.sub.2).sub.6NHCO(CH.sub.2).sub.7CO,(x)
NH(CH.sub.2).sub.12NHCO(CH.sub.2).sub.10CO,(xj)
NH(CH.sub.2).sub.10NHCO(CH.sub.2).sub.8CO,(xjj)
NH(CH.sub.2).sub.4NHCO(CH.sub.2).sub.4CO, and(xjjj)
NH(CH.sub.2).sub.4NHCO(CH.sub.2).sub.8CO.(xjv)

5. The dish support rack of claim 1, wherein more than 60 mole % of recurring units of the polyamide are first recurring units.

6. The dish support rack of claim 5, wherein all recurring units of the polyamide are first recurring units.

7. The dish support rack of claim 1, wherein the composition comprises said polyamide in an amount of at least 60 weight % based on the total weight of the composition.

8. The dish support rack of claim 7, wherein the composition comprises, based on the total weight of the composition, at least 90 weight % of the polyamide.

9. The dish support rack of claim 1, wherein the composition further comprises a second polyamide that is different from said polyamide.

10. The dish support rack of claim 1, wherein said composition further comprises at least one opacifying pigment.

11. The dish support rack of claim 10, wherein the opacifying pigment is present in an amount of at least 0.1 weight % and at most 5 weight % each based on the total weight of the composition.

12. The dish support rack of claim 11, wherein the composition comprises, based on the total weight of the composition, at least 0.3 weight % and at most 4 weight % of the at least one opacifying pigment.

13. The dish support rack of claim 11, wherein the composition comprises, based on the total weight of the composition, at least 0.8 weight % and at most 2.5 weight % of the at least one opacifying pigment.

14. The dish support rack of claim 10, wherein said composition further comprises coloured pigment(s) different from the opacifying pigment.

15. The dish support rack of claim 10, wherein the at least one opacifying pigment-is selected from the group consisting of TiO.sub.2, ZnS.sub.2, ZnO, and BaSO.sub.4.

16. The dish support rack of claim 1, wherein said composition comprises at least one stabilizer selected from the group consisting of hindered amine compounds, hindered phenol compounds, phosphorous compounds, and copper-containing stabilizers.

17. The dish support rack of claim 1, wherein the composition consists essentially of: the polyamide, wherein the polyamide is PA 6,10; from 0.1 to 5 weight % of an opacifying pigment; from 0.01 to 3.5 weight % of a hindered phenol compound; from 0.1 to 5 weight % of a coloured pigment different from the opacifying pigment; wherein each weight % is based on the total weight of the composition.

18. A method for manufacturing the dish support rack according to claim 1, comprising applying a coating of the composition to a metal wire frame.

19. The method of claim 18, wherein the step of coating comprises: maintaining the composition, in the form of powder, in a coating chamber in fluidized state, and introducing the metal wire frame, heated at a temperature exceeding melting point of the polyamide, in said coating chamber; and removing, after a residence time in said coating chamber sufficient for achieving target coating thickness, the coated metal wire frame from the coating chamber.

20. The dish support rack of claim 1, wherein the polyamide is a homo-polyaniide PA6.10.

Description

(1) Exemplary embodiments of polyamides (B) are notably polyamide 6, polyamide 6,6, polyamide 4,6, polyamide 12, polyamide 11.

(2) When the composition (C) includes said polyamide (B), the same is comprised in an amount of at most 30% wt, preferably at most 25% wt, more preferably at most 20% wt, even more preferably at most 10% wt, with respect to the total weight of the composition.

(3) Polyamide (A) and, if present, polyamide (B), are provided in the composition (C) generally under the form of solid particles, generally possessing an average particle size (expressed as median diameter d50) of 5 to 1000 m, preferably of 20 to 500 m, more preferably of 50 to 250 m.

(4) Composition (C) may also comprise at least one opacifying pigment.

(5) Said opacifying pigment is generally selected from the group consisting of of TiO.sub.2, ZnS.sub.2, ZnO, and BaSO.sub.4.

(6) The opacifying pigment is advantageously in the form of particles having a weight-average size (equivalent diameter) preferably of below 5 m. Larger sizes may deleteriously affect the properties of the composition. Preferably, the weight-average size of the particles is of below 1 m. Besides, it is preferably above 0.1 m.

(7) The shape of the particles of the opacifying pigment is not particularly limited; they may be notably round, flaky, flat, and so on.

(8) The opacifying pigment is preferably titanium dioxide (TiO.sub.2). The form of titanium dioxide is not particularly limited and a variety of crystalline forms such as the anatase form, the rutile form, and the monoclinic type can be used. However, the rutile form is preferred due to its higher refraction index and its superior light stability. Titanium dioxide may or may not be treated with a surface treatment agent. Preferably the average particle size of the titanium oxide is in the range of 0.15 m to 0.35 m.

(9) The surface of the titanium dioxide particles will preferably be coated. The titanium dioxide will preferably be first coated with an inorganic coating and then an organic coating that is applied over the inorganic coating. The titanium dioxide particles may be coated using any method known in the art. Preferred inorganic coatings include metal oxides. Organic coatings may include one or more of carboxylic acids, polyols, alkanolamines, and/or silicon compounds.

(10) If present, the opacifying pigment is preferably present in the composition (C) in an amount of at least 0.1 wt. %, preferably of at least 0.3 wt. %, more preferably of at least 0.5 wt. %, even more preferably of at least 0.8 wt. %, based on the total weight of the composition (C). Besides, when present, the opacifying pigment is also preferably present in an amount of at most 5 wt. %, preferably of at most 4 wt. %, more preferably of at most 3.5 wt. %, even more preferably of at most 3 wt. %, and most preferably of at most 2.5 wt. %, based on the total weight of the composition (C).

(11) In order to match colour requirements according to the design of the machine to be equipped with the rack of the invention, the composition (C) may additionally comprise coloured pigments (including black pigments) different from opacifying pigment. Selection of coloured pigment(s) and adjustment of relative amount will be effected by one of ordinary skills in the art following routine experiments for colour matching.

(12) Generally, in embodiments wherein colour matching is necessary, the amount of coloured pigment (different from opacifying pigment) will be of advantageously at least 0.1% wt, preferably at least 0.2% wt, more preferably at least 0.5% wt and advantageously at most 5% wt, preferably 3% wt, more preferably 2.5% wt, with respect to the total weight of the composition (C).

(13) The composition (C) may comprise at least one stabilizer selected from the group consisting of hindered amine compounds, hindered phenol compounds, phosphorous compounds and Copper-containing stabilizers.

(14) The expression hindered amine compound is used according to its customary meaning in this field and generally intended to denote derivatives of 2,2,6,6-tetramethyl piperidine well known in the art (see for example: Plastics Additives Handbook, 5th ed., Hanser, 2001). The hindered amine compound of the composition according to the present invention may either be of low or high molecular weight.

(15) The hindered amine compounds of low molecular weight have typically a molecular weight of at most 900, preferably at most 800, more preferably of at most 700, still more preferably at most 600 and most preferably of at most 500 g/mol.

(16) Examples of low molecular weight hindered amine compounds are listed in Table 1 below:

(17) TABLE-US-00001 TABLE 1 Formula (a1) (a2) (a3) (a4) (a5) (a6) (a7) (a8) (a9) (a10) 0 (a11) (a12)

(18) Among those low molecular weight compounds, the hindered amine is preferably selected from the group consisting of the ones corresponding to formula (a1), (a2), (a11) and (a12). More preferably, the hindered amine is selected from the group consisting of the ones corresponding to formula (a1), (a2), and (a12). Still more preferably, the hindered amine is the one corresponding to formula (a2).

(19) The hindered amine compounds of high molecular weight are typically polymeric and have typically a molecular weight of at least 1000, preferably at least 1100, more preferably of at least 1200, still more preferably at least 1300 and most preferably of at least 1400 g/mol.

(20) Examples of high molecular weight hindered amine compounds are listed in Table 2 below:

(21) TABLE-US-00002 TABLE 2 Formula (b1) (b2) (b3) (b4) (b5) (b6)

(22) The n in the formulas (b1) to (b6) of Table 2 indicates the number of repeating units in the polymer and is usually an integral equal or greater than 4.

(23) Among those high molecular weight compounds, the hindered amine is preferably selected from the group consisting of the ones corresponding to formula (b2) and (b5). More preferably, the high molecular weight hindered amine is the one corresponding to formula (b2).

(24) If used, the hindered amine compound is typically present in an amount of advantageously at least 0.01 wt. %, more preferably at least 0.05 wt. %, still more preferably at least 0.1 wt. %, based on the total weight of the composition.

(25) Similarly, when present, the hindered amine compound is also typically present in an amount of advantageously at most 3.5 wt. %, preferably at most 3 wt. %, more preferably at most 2.5 wt. %, still more preferably at most 2.0 wt. %, even more preferably at most 0.8 wt. % and most preferably at most 0.6 wt. %, based on the total weight of the composition.

(26) The expression hindered phenol compound is used according to its customary meaning in this field and generally intended to denote derivatives of ortho-substituted phenol, especially (but not limited to) di-tert-butyl-phenol derivatives, well known in the art

(27) Examples of hindered phenol compounds are listed in Table 3 below:

(28) TABLE-US-00003 TABLE 3 (d1) tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate), commercially available notably as Irganox 1010 stabilizer from BASF (d2) Thiodiethylene bis[3-(3,5-di-tert.-butyl-4- hydroxy-phenyl)propionate], commercially available notably as Irganox 1035 stabilizer from BASF 0 (d3) Octadecyl-3-(3,5-di-tert.butyl-4- hydroxyphenyl)-propionate, commercially available botable as Irganox 1076 stabilizer from BASF (d4) N,N-hexane-1,6-diylbis(3-(3,5-di-tert.-butyl- 4-hydroxyphenylpropionamide)), commercially available notable as Irganox 1098 stabilizer from BASF (d5) 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4- hydroxybenzyl)benzene, commercially available notably as Irganox 1330 stabilizer from BASF (d6) Benzenepropanoic acid, 3,5-bis(1,1- dimethylethyl)-4-hydroxy-,C7-C9 branched alkyl esters, commercially available notably as Irganox 1135 stabilizer from BASF (d7) Hexamethylene bis[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate], commercially available notably as Irganox 259 stabilizer from BASF (d8) Tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanuate, commercially available notably as Irganox 3114 stabilizer from BASF (d9) 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5- triazin-2-ylamino)phenol, commercially available notably as Irganox 565 stabilizer from BASF (d10) commercially available notably as Irganox 1425 stabilizer from BASF (d11) 2-Methyl-4,6- bis(octylsulfanylmethyl)phenol, commercially available notanly as Irganox 1520 stabilizer from BASF (d12) 2,4-Bis(dodecylthiomethyl)-6-methylphenol, commercially available notably as Irganox 1726 stabilizer from BASF 0 (d13) Tirethylene glycol bis(3-tert-butyl-4- hydroxy-5-methylphenyl)propionate, commercially available as Irganox 245 stabilizer from BASF

(29) A hindered phenol compound which has been found particularly effective in the composition (C) of the dish support rack of the invention is N,N-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) of formula (d4), as above specified.

(30) If used, the hindered phenol compound is typically present in an amount of advantageously at least 0.01 wt. %, more preferably at least 0.05 wt. %, still more preferably at least 0.1 wt. %, based on the total weight of the composition.

(31) Similarly, when present, the hindered phenol compound is also typically present in an amount of advantageously at most 3.5 wt. %, preferably at most 3 wt. %, more preferably at most 2.5 wt. %, still more preferably at most 2.0 wt. %, even more preferably at most 0.8 wt. % and most preferably at most 0.6 wt. %, based on the total weight of the composition.

(32) The composition (C) may comprise at least one phosphorous compound selected from the group consisting of an alkali or alkali earth metal hypophosphites, phosphite esters, phosphonites and mixtures thereof.

(33) Sodium and calcium hypophosphites are preferred alkali or alkali earth metal hypophosphites.

(34) A phosphite ester may be represented by the formula P(OR).sub.3, while a phosphonite may be represented by the formula P(OR).sub.2R, wherein each of R, can be the same or different and are typically independently selected from the group consisting of a C.sub.1-20 alkyl, C.sub.3-22 alkenyl, C.sub.6-40 cycloalkyl, C.sub.7-40 cycloalkylene, aryl, alkaryl or arylalkyl moiety.

(35) Examples of phosphite esters are listed in the Table 4 below:

(36) TABLE-US-00004 TABLE 4 Formula (e1) (e2) (e3) (e4) (e5) (e6) (e7) (e8) (e9) 0 (e10) (e11) (e12)

(37) Examples of phosphonites are listed in the table 5 below:

(38) TABLE-US-00005 TABLE 7 Formula Structure (f1) (f2)

(39) When used in the composition (C), the phosphorous compound is preferably present in an amount of at least 0.01 wt. %, more preferably at least 0.05 wt. %, based on the total weight of the composition.

(40) The phosphorous compound is also preferably present in an amount of at most 1 wt. %, more preferably at most 0.5 wt. %, still more preferably at most 0.25 wt. %, based on the total weight of the composition.

(41) Copper-containing stabilizers useful in the practice of the invention may be characterized as comprising a copper compound and an alkali metal halide. More particularly, the copper-containing stabilizer will consist essentially of a copper compound [compound (Cu)] selected from the group consisting of copper (I) oxide, copper (II) oxide, copper (I) salt, for example cuprous acetate, cuprous stearate, a cuprous organic complex compound such as copper acetylacetonate, a cuprous halide or the like; and an alkali metal halide [halide (M)]. Preferably, the copper-containing stabilizer will consist essentially of a copper halide selected from copper iodide and copper bromide and the alkali metal halide will preferably be selected from the iodides and bromides of lithium, sodium and potassium.

(42) A particularly preferred combination is the combination of CuI and KI.

(43) The copper-containing stabilizer will preferably comprise a copper (I) compound [compound (Cu)] and an alkali metal halide [halide (M)] at a weight ratio compound (Cu):halide (M) of 1:99 to 30:70, preferably 5:95 to 20:80, more preferably 10:90 to 15:85. A weight ratio compound (Cu):halide (M) which has been found particularly effective is of about 0.15 (i.e. corresponding to about 13:87).

(44) When present, the combined weight of compound (Cu) and halide (M), i.e. of the copper-containing stabilizer, in the composition (C) will amount to from about 0.01 to about 3 wt %, preferably from about 0.02 to about 2.5% wt, more preferably from about 0.1 to about 1.5 wt %, based on the total weight of composition (C).

(45) The amount of the compound (Cu) in the copper-containing stabilizer, when incorporated in the composition (C) will generally be sufficient to provide a level of from about 25 to about 1000 ppm, preferably of about 50 to about 500 ppm, more preferably of about 75 to about 150 ppm of Copper in the composition (C).

(46) If needed, the composition (C) may additionally comprise one or more than one reinforcing filler.

(47) Reinforcing fillers are well known by the skilled in the art. The reinforcing filler is preferably selected from fibrous and particulate fillers. More preferably, the reinforcing filler is selected from mineral fillers (such as talc, mica, kaolin, calcium carbonate, calcium silicate, magnesium carbonate), glass fiber, carbon fibers, synthetic polymeric fiber, aramid fiber, aluminum fiber, titanium fiber, magnesium fiber, boron carbide fibers, rock wool fiber, steel fiber, wollastonite etc. Still more preferably, it is selected from mica, kaolin, calcium silicate, magnesium carbonate, glass fiber and wollastonite etc.

(48) A particular class of fibrous fillers consists of whiskers, i.e. single crystal fibers made from various raw materials, such as Al.sub.2O.sub.3, SiC, BC, Fe and Ni. Among fibrous fillers, glass fibers are preferred; they include chopped strand A-, E-, C-, D-, S- and R-glass fibers, as described in chapter 5.2.3, p. 43-48 of Additives for Plastics Handbook, 2nd edition, John Murphy, the whole content of which is herein incorporated by reference. Preferably, the filler is chosen from fibrous fillers.

(49) When reinforcement is required, the weight percent of the reinforcing filler in the total weight of the composition (C) is generally of at least 0.5 wt. %, preferably of at least 1 wt. %, more preferably of at least 2 wt. %. Besides, the weight percent of the reinforcing filler in the total weight of the composition (C) is generally of at most 10 wt. %, preferably of at most 5 wt. % and most preferably of at most 3 wt. %.

(50) A composition (C) which has been found particularly suitable in the dish support rack of the invention is a composition consisting essentially of: a polyamide PA6,10, as above detailed; from 0.1 to 5% wt of an opacifying pigment, as above detailed; from 0.01 to 3.5% wt of a hindered phenol compound, as above detailed; from 0.1 to 5% wt of a coloured pigment different from the opacifying pigment, as above detailed.

(51) The dish support rack of the invention generally includes front, rear and opposing side walls interconnected with a bottom portion, and further includes a plurality of tine members to establish dish support zones in the rack, all formed from a plurality of metal wire element coated with composition (C), as above detailed.

(52) The invention further pertains to a method for manufacturing the dish support rack, as above detailed.

(53) This method generally includes providing a metal wire frame and applying thereupon a coating of composition (C).

(54) Techniques for applying such coating are not particularly limited and are well established in the art.

(55) Generally, composition (C) is provided under the form of powder and introduced in a coating chamber wherein is maintained by appropriate fluxing of inert gas (generally air) in fluidized state. The metal wire frame is heated at a temperature exceeding melting point of the polyamide (A) and introduced in said coating chamber. After appropriate residence time, sufficient for achieving target coating thickness, the metal wire frame is removed from the coating chamber and possibly baked in an oven until formation of a uniform coating of composition (C), so as to obtain the dish support rack of the invention.

(56) Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.