METHOD OF APPLYING A COATING OF POLYARYLENE SULPHIDE TO A COOKING UTENSIL

Abstract: A method of applying a coating of polyarylene sulphide to a cooking utensil in which an intimate mixture of a polyarylene sulphide with an aryl ester of an aryl alcohol is applied to the surface of the utensil and subsequently heated to evaporate the ester and cure the coating. The mixture can be a dry powder mixture, a wet powder mixture, a paste, a suspension, a liquid solution or a solid solution. The preferred mixture comprises polyphenylene sulphide and benzyl benzoate.

Description: METHOD OF APPLYING A COATING OF PQLYARYLEHT -SULPHIDE TO " A COOKING UTENSIL The present invention relates, to a method of applyin 5. a coating of polyarylene sulphide to a cooking utensil. Polyarylene sulphides 1 have properties- which, make them suitable for use in various situations- for example as a non-stick coating for cooking utensils, however, the also possess properties- which, make their preparation and 10. application inconvenient and frequently difficult. Available techniques involve the use of toxic chem¬ icals or techniques involving what is essentially powder fusion. The powder fusion techniques limit the roles in which polyarylene sulphides can be used and involve slow 15. processes of low productivity. One of the properties of polyarylene sulphides which limits their use is their high viscosities in the molten state. This renders the distribution of the material difficult in the extreme and makes it difficult there- 20. fore to establish a bond between the polyarylene sulphide and another material. One known method of forming a bond between the polyarylene sulphide and another material is to apply the polyarylene sulphide powder to the other ' material as level and evenly as possible, and then to 25. melt, cure and crosslink the powder. Water based dispersions of PPS .are also known but this is just another form of applying powder since this is what remains after the water has- been evaporated. However, as stated above, using polyarylene 30. sulphide powder involves considerable manufacturing difficulties. Polyphenylene sulphide takes a long time to cure and crosslink, particularly when the powder layer is relatively thick.. Also since the molten powder has a high viscosity and generally does not flow or wet a 5. surface very well, this- results; in voids * and consequently a poor bond between the polyphenylene sulphide and the other material which bond may fail when under load. It is also difficult to achieve a precision thick¬ ness of polyarylene sulphide which is dimensionally stable 10. and even more difficlt to produce very thin, cured layer. It is an object of the present invention to provide polyarylene sulphide in a workable form in order to minimise the above difficulties in providing a non-stick coating. 15. The present invention is. based on the discovery that benzyl benzoate has a plasticizing and, in sufficient quantities, a solvent action on polyphenylene sulphide. According to the present invention a method of applying a coating of polyarylene sulphide to a cooking 20. utensil is characterised by applying a mixture of polyarylene sulphide and an aryl ester of an aryl alcohol to the surface of a backing for forming a cooking utensil, and subsequently heating the mixture to evaporate the ester and to cure the coating. 25. The mixture may be a two phase mixture of resin or a resin rich phase comprising polyarylene sulphide and 5. a solvent or a solvent rich phase comprising an aryl ester of an aryl alcohol preferably benzyl benzoate. Alternatively the mixture may be a single phase r,.y*H*τ*e n * ? ■ "-]-,-- τ>*»«*_ ■*■■ -Υ-* c ** ■ • • < 4- -. <--> • *- • - •* " * ÷- ' j-.e eolVS"* , f**T- vice versa. The resin phase may further include other resins besides polyarylene sulphide in.either a major or minor proportion based on the polyarylene sulphide. Such other resins may include polytetrafluoroethylene, poTyimides and polysulphones. The resin phase may also include fillers, pigments, dyes, surface active additive stabilizers, cross linking agents, coating aids " • such a 5. silica or titanium oxide powders, and bases to enhance bonding. The solvent phase may include or comprise mixtures of aryl .esters of aryl alcohols, for example one or more of benzyl benzoate, benzyl phthalate, benzyl 10. iosphthalate, and benzyl terephthalate, and other materials acting as diluents or extenders or viscosity reducers for the active solvent and having no non-solven action such as to prevent the blend having the necessary plasticiser or solvent action for the resin phase as the 15. case may be. The solvent phase may also include co-solvents whic whilst having no significant solvent action on their own enhance the solvent action of the benzyl benzoate. The solvent phase may also include other solvents 20. for polyphenylene sulphide and when the resin phase includes other resins, solvents for such other resins even if these are not solvents for polyphenylene sulphid though in this case they are preferably miscible with benzyl benzoate to form a single solvent phase. __5. The compositions of the invention may extend from solid particulate matt-rials contain?,£ polyphenylene sulphide plasticized by benzyl benzoate or solid workabl bodies of polyphenylene sulphide p asticized by benzyl benzoate to slurries of polyphenylene sulphide 30. plastici2ed or not by benzyl benzoate in liquid vehicles JU E OMP 4 r W1P which contain benzyl benzoate ' the benzyl benzoate either being in the polyphenylene sulphide or in the liquid, vehicle or in both, to pastes of polyphenylene sulphide plεsticized or not with benzyl benzoate suspended or 5. dissolved in benzyl benzoate or benzyl benzoate contain.ing vehicles or spreadable, dippable- or sprayable solutions of polyphenylene sulphide in benzyl benzoate or benzyl benzoate containing solvents. The polyarylene sulphide resin that can be used in 10, the present invention may be a polymer made by the method disclosed in USP 335*^129 but in general can be represented as a polymer including a recurring unit of the formula in which the ring A may be substituted.. One such form of substitution may be represented Y in which: X represents a fluorine, chlorine, bromine or iodine atom, preferably chlorine or bromine, and Y represents 25. a hydrogen atom, 0 0 O • R 0 - -R, -N(R) 2 , -C-0R, " -8-0M, -3-N(R) 2 , -N-C-R 2> -0-R«, -S-R 1 , -SO^H or -SO^M groups in which: R represents a hydrogen atom, an alkyl, cycloalkyl, 30. aryl,_aralkyl, or alkaryl group containing 1 to 12 carbon atoms and in which: I*, represents an alkali metal atom of a sodium cr potassium atom and in which: p is 0 to 4 and q is 2 to 4. Polyphenylene sulphide in which the repeat ur.it can be represented by the formula The"polyarylene sulphides may be partially oxidized 10. or may have a branched or cross linked structure though non-crcεs linked polymers or ones having a lev degree of cress linking and thus relatively low M.Vf. are preferred e.g. these having K. .'s in the range 17,500 ' to- 5000. More generally polyarylene sulphides having 15. melting points in the range 280 C to 300 C are preferred Also materials having intrinsic viscosities in chloronapthalene at 260°C of at least 0.1, e.g. 0.1 to 0.3 especially 0.13 to 0.23 are preferred. Polyphenylene sulphide has a solubility parameter o 20. 8.5 to 9.5. Uncured PPS sold under the Trade Mark Ryton VI has a melt flow index of lOOOg/min. by the American Society Test Method (ASTM, D1238). Using the same test, part cured PPS sold under the Trade Marks Ryton P2 and P have melt flow indices of 300 and 125g/min. respectively 25. In these compositions including PPS in particulate form the particle size may be in the range 10-200 microns and use of powder of such particle size is convenient as a starting point for the preparation of single phase sys ms in sccorcεnce with the inven ion. 3C. The r-referred solvent cc_r.-Dounds for use in the OM wWiI present invention may be represented by the formula where X, Y, and Z represent a hydrogen atom or a halogen atom e.g. a chlorine atom. The most preferred compound is Compound I, when 10. X, Y, " W and Z are all hydrogen. A less preferred compound is Compound I when V or Z is chlorie and X, Y and Z or V are hydrogen, namely benzyl monochloroben- zoate. Benzyl benzoate has the following properties: 15. melting point 18-20°C boiling point 320°C ' solubility parameter 9.3 Other solvent compounds which may be used in the present invention may comprise phenyl benzoate, di- 20. phenyl phthalate, di-benzyl ether, benzoic anhydride and di-phenyl sulphone. According to preferredaspect of the invention there is provided a method of coating a cooking utensil comprising mixing polyarylene sulphide with an aryl 25. ester of an aryl alcohol, applying the mixture to the utensil, and subsequently evaporating the ester, and at least partly curing the polyarylene sulphide simultaneously to leave the polyarylene sulphide in an at least partly cured state. 30. Preferably the polyarylene sulphide is polyphenylene sulphide and preferably the ester is benzyl benzoate. The resin and ester may both be in the solid state and thus may be in the form of a powder mixture. Alternatively, the ester nay be ir. the liquid state so 5. that the mixture may be a paste or slurry of resin in the ester or may be a solution of the resin in ester. ' The components are preferably heated until they for__ one continuous liquid' phase. The liquid nay be cooled at -this -stage for example in order to promote " 10. precipitation of the resin in the form of fine crystals in the ester. This step is not absolutely necessary in all cases but may be advantageous for example if it is desired to store the formulation for any length.of time.. 15. Preferably the nature of the ester and the resin are such that when the mixture is heated the resin and ester form a single ph--.se and as the ester evaporates, the rosin undergoes curing. Preferably the ester does not evaporate completely until the resin is almost 20. completely cured. Preferably a minimum of ester is employed since this may be lost in evaporation. « The method according to the invention may therefore, render it possible to produce a cured polyarylene sulphide in the form of a thin filr; having a thickness 25. hithc-rto thought to be obt i.naf'e for example as low as 3 x 10 " °c or less, though thicker coatings may also be dbtaii Various methods may be em lo ed in applying the mixture prior to curing. In the case of a dry powder r.ixLure " this :::ay be - zl l .ά fcr -r.-.s le by electro- 30. static spraying, d.--y powder spraying or by fluidised bed methods. In the case of a. paste or wet powder this may be applied for example by wet spraying or spreading while in the case of slurries and solutions these may be applied by wet spraying or by painting or the article 5. to which the resin is to be applied may be dipped into the mixture. The invention may be carried into practice in various " ways and will"be illustrated in the following specific xamples. All percentages in the following 10. examples are by weight. • Examples 1 to 18 are examples of backings for use in the manufacture of cooking utensils coated with polyphenylene sulphide. EXAMPLE 1 8% uncured polyphenylene sulphide sold under the " Trade Mark Ryton VI was mixed with 89% benzyl benzoate 10. and 3% polytetrafluiroethylene. The mixture was heated to a temperature in the range 250° to 290°C by which time the polyphenylene sulphide had dissolved in the benzyl benzoate. A cold backing formed from an aluminium alloy was immersed for 0.5 seconds and withdraw 15. A coating of solution had adhered to the backing. The coated backing was transferred to an air circulatory oven and maintained at a temperature between 300° and 310°C for 5 minutes. The temperature was then increased to a temperature between 370° and 380°C for a further 15 20. minutes after which time the benzyl benzoate had evaporated and the polyphenylene sulphide was fully cured. The layer of polyphenylene sulphide and polytetrafluoroethylene produced was approximately 0.002 cm in thickness. 25. EXAMPLE 2 30% uncured polyphenylene sulphide and 12% polytetrafluoroethylene were heated in a solution 30. comprising 8% di-phenyl phthalate and 50% benzyl OM benzoate and held at a temperature between 250 and 290°C. A backing similar to that used in example 1 was immersed in the solution for 2 minutes thus allowing the backing and solution to reach a thermal equilibrium. 5. The backing, with an adherent coating of solution, was transferred to an oven and heated to a temperature between 300° and 310°C for 5 minutes and then to a temperature between 370° and 380°C fcr a further 15 minutes.. A coating similar to that obtained in Example 1 10. was obtained. ' EXAMPLE 3 A suspension of uncured polyphenylene sulphide and 15. polytetrafluoroethylene was prepared by mixing 30% polyphenylene sulphide with 12% polytetrafluoroethylene and 8% diphenyl phthalate and 50% benzyl benzoate, heating the mixture to a temperature between 250° and 290°C in order to dissolve the polyphenylene sulphide, 20. and subsequently cooling the solution to a room temperature while maintaining a vigorous agitation. A fine cloudy gelatinous suspension was thus formed. The suspension was sprayed on to two backings of an aluminium alloy, one of which was at room temperature 25. and the other of which was heated to about 250°C. The sprayed backings were transferred to an oven where they were held at a temperature between 300° and 310° for 5 minutes and then held at a temperature between 370° and 380 C for a further 15 minutes. An adherent coating 30. of polyphenylene sulphide and polytetrafluoroethylene 0.002 cm thick was produced on each. EXAMPLE 4. 5. A water-based slurry was produced by ball milling together for 24 hours 20% uncured polyphenylene sulphide, 10%"polytetrafluoroethylene, 49% saturated calcium hydroxide solution, 1% o -a nonionic surfactant (as sold under the Trade Mark Triton X 100) and 20% diphenyl * 10. sulphone. This slurry was used to stray coat two backings as described in example 3 a ove and similar coatings were obtained. EXAMPLE ' 5 15. A backing of an aluminium alloy at room temperature, was sprayed with a solution comprising 10% phenyl benzoate in 90% benzyl benzoate until the surface sprayed was fully wet but not dripping. !The wetted surface was 20. sprayed electrostatically with a powder mixture of 66% polyphenylene sulphide, 35% polytetrafluoroethylene and . 1% calcium hydroxide. The backing was placed in an oven and heated to a temperature of between 300°C and 310°C for 5 minutes followed by being heated to a temperature 25. between 370° and 380°C for a further 15 ninutes. As in the previous examples a satisfactory coating was obtaine O EXAMPLE 6. This was carried out in the same way as Example 5 but with diphenyl phthalate replacing phenyl benzoate. 5. Similar results were obtained as those of Example 5. EXAMPLE 7. A water based slurry was produced by ball milling 10. together for 24 hours 30% uncured polyphenylene sulphide, 49% of an aqueous suspension of polytetrafluoroethylene comprising between 15 and 30% polytetrafluoroethylene 1% of a non-ionic surfactant (sold under the Trade Mark Triton X 100) and 20% diphenyl sulphone. This slurry 15. was used to spray coat two backings as described in Example 3 above and similar coatings were obtained. EXAMPLE 8. 20. The following ingredients were mixed intimately in a high speed mixer: 55% uncured polyphenylene sulphide 15 % polytetrafluoroethylene, 20% diphenyl sulphone, 9 % diphenyl phthalate and.1% calcium hydroxide. The mixture was electrostatically sprayed on to a backing 25. of an aluminium alloy at room temperature. The backing was replaced in an oven where it was heated to a temperature between 300 and 310°C, held at that temperature for 5 minutes and subsequently raised to a temperature between 370° and 380°C for 15 minutes. An 30. adherent coating of.polyphenylene sulphide and polytetrafluoroethylene v/as .obtained having a thickness of 0.002 cm approximately. EXAMPLE 9. This was carried out in the same way as example 8 except that the backing was at a temperature between 350° and 370°C prior to its being sprayed with the mixture. Similar results were obtained to those of example 8. " - 0M λvj EXAMPLE 10 This v/as carried out in the same way as example 1 out with the uncured polyphenylene sulphide replaced by 99% part cured polyphenylene sulphide (sold under the Trade Mark Ryton P2) and 1% calcium hydroxide powder. Similar results were obtained to those obtained in example 1 but it v/as found that the curing time was ' shorter than in- example 1. 10. EXAMPLE 11 • Tn±s was carried out in the same way as example 2 but an . uncured polyphenylene sulphide was replaced by a 15, mixture of 99% part cured polyphenylene sulphide and 1% calcium hydroxide, and the diphenyl phthalate/benzyl benzoate mixture was replaced by benzyl benzoate alone. Similar results-were obtained to these of example 2 but it was found that the curing time was shorter than in 20. example 2. EXAI-.^LΞ 12 This v/as carried out in the same way as example 3 25. but* the uncured polyphenylene sulphide was replaced by a mixture of 99% part cured polyphenylene sulphide and 1% calcium hydroxide, and the diphenyl phthallate/ benzyl benzoate mixture was replaced by benzyl benzoate alone. -Similar results w-re obtained to these in example 30. 3 but.it was found that the curing time v/as shorter than in example 3- OMPI EXAMPLE 13. This was carried out in the same way as example 4 but the uncured polyphenylene sulphide was replaced 5. entirely by part cured polyphenylene sulphide. Similar results were obtained to those obtained in example 4 but it was found that the curing time was shorter than in example 4. 10. EXAMPLE 14 This v/as carried put in the same way as example 5 but the uncured polyphenylene sulphide was replaced entirely by part cured polyphenylene sulphide. 15. Similar results were obtained to those obtained in . example 5 but it was found that the curing time was shorter than in example 5. EXAMPLE 15 20. Tiis v/as carried out in the same way as example 6 but the uncured polyphenylene sulphide was replaced entirely by part cured polyphenylene sulphide. Similar results λv τ ere obtained to those obtained in 25. e-.__r.ple 6 but it was found that the curing time v/as shorter than in example 6. EXAMPLE 16 30. This w'-.s carried out in the same way as example 7 'BU OM . r- WIP but the uncured polyphenylene sulphide was replaced by a mixture of 99% part cured polyphenylene sulphide and 1% calcium hydroxide. Similar results were obtained to those obtained in example 7 but it -v/as found that the curing time was shorter than in example 7. EXAMPLE " 17. This v/as carried out in the same way ' s example.8 but the uncured polyphenylene sulphide v/as replaced entirely by part cured polyphenylene sulphide. Similar results were obtained to those- obtained in example 8 but it v/as found that the curing time v/as shorter than in example 8. EXAMPLE 18 This v/as carried out in the same way as example 9 but the uncured polyphenylene sulphide was replaced entirely by part cured polyphenylene sulphide. Similar results were obtained to . those obtained in example 9 but it was found that the curing time was shorter than in example 9. OMPI

Claims: CLAIMS 1. A method of applying a coating of polyarylene sulphide to a cooking utensil characterised by applying a mixture of polyarylene sulphide and an aryl ester of an aryl alcohol to the surface of a backing for forming a cooking utensil, and subsequently heating the mixture to evaporate the ester and to cure the coating. 2. A method as claimed in Claim 1 characterised in that the polyarylene sulphide is. polyphenylene sul¬ phide. ' 3. A method as. claimed in Claim 1 or Claim 2 characterised in that the ester is benzyl Benzoate. •4*. A method as claimed in any of Claims 1 to 3 characterised in that the mixture is a dry powder mixture. 5. A method as claimed in any of Claims 1 to 3 characterised in that the mixture is in the form of a paste. S. A method as claimed in any of Claims 1 to 3 characterised in that the polyarylene sulphide is in suspension in the ester- the ester being in the liquid phase. 7. A method as claimed in any of Claims.. 1 to 3 characterised in that the polyarylene sulphide is dissolved in the ester. 'BVIRE OMPI . . WIPO 8. A method aε claimed in any of Claims 1- to 3 characterised in that the ester is in solid solution in the. polyarylene sulphide. 9L. A method of applying a coating of polyarylene sulphide to a cooking utensil substantially as herein specifically described with reference to any one of the accompanying examples.

Inventors: GLYNDWR J
Applicants: GLACIER METAL CO LTD, GLYNDWR J
Application year: 1981
Main classification: A47J36
IPC codes: A47J36, B05D5, C09D5, C09D181