GB2312901A

GB2312901A - High frequency weldable polyurethane foams

Info

Publication number: GB2312901A
Application number: GB9709310A
Authority: GB
Inventors: Zaki Akhtar; Philip Gatehouse
Original assignee: Caligen Foam Ltd
Current assignee: Caligen Foam Ltd
Priority date: 1996-05-09
Filing date: 1997-05-09
Publication date: 1997-11-12
Also published as: GB9709310D0; GB9609693D0

Abstract

A method of rendering a foamed plastics material high frequency weldable at a desired frequency other than a natural resonant frequency of the material comprises modifying the foam composition to render the desired frequency a resonant frequency of the modified foam. Preferably the foamed plastics material is polyurethane foam and the desired frequency is a resonant frequency of PVC, preferably approximately 27.12mhz. The invention also comprises modified foam formulations for producing this effect, in particular, formulations containing hydroxypivaloyl neopentyl glycol as the radio frequency receptor.

Description

HIGH FREQUENCY WELDABLE FOAMED PLASTICS MATERIALS This invention relates to foamed plastics materials and especially to high frequency weldable polyurethane foam.

It is known to employ high frequency welding (also referred to as radio frequency or RF welding) to weld plastics materials together. High frequency welding is one of the most energy efficient methods of welding and can be readily concentrated in a desired weld area. It is used extensively in a wide range of industries from stationery and automotive products to textile and bedding production. The technique employs electromagnetic radio frequency energy to produce rapid molecular orientation of certain polar materials. This manifests itself as thermal energy which under appropriate pressure conditions results in plastic flow and thereby results in a welding action.

Hitherto the material most commonly employed in high frequency welding is polyvinyl chloride (PVC) in both sheet and foam form. As a result the bulk of industrial high frequency welding equipment is designed to operate at one of the fundamental orientation or resonant frequencies of PVC. The most commonly employed radio frequency within the ISM (Industrial Scientific and Medical) bands is 27.12 MHz and although other frequencies have previously been employed, high frequency welding equipment is currently being standardised on the 27.12 MHz frequency.

In most applications PVC foam is enclosed in an outer skin or sheath of PVC foil or sheet. The resultant material is used in areas where an upholstered or padded effect is required, for example in stationery products and infant bedding. PVC foam is however expensive compared to other polymeric foams such as polyurethane foam but such foams have not hitherto been suitable for dielectric heating as they do not respond satisfactorily to the same frequency as PVC. The use of radio frequencies for industrial purposes is strictly controlled to prevent interference with other equipment operating on the radio frequency band and hence the use of materials other than PVC has effectively been precluded.

It is an object of the present invention to obviate or mitigate this disadvantage.

The invention provides a method of rendering a foamed plastics material high frequency weldable at a desired frequency other than a natural resonant frequency of the material, the method comprising modifying the foam composition to render the desired frequency a resonant frequency of the modified foam.

The invention also provides a foamed plastics material modified to render a desired frequency, different from a natural resonant frequency of the unmodified material, a resonant frequency of the modified material.

Preferably the material is polyurethane foam and the desired frequency is approximately 27.12 MHz.

Thus the invention also provides a polyurethane foam composition having a resonant frequency approximating to a resonant frequency of PVC.

The invention also provides a polyurethane foam composition which will melt under pressure at a frequency approximating to a resonant frequency of PVC.

Preferably the resonant frequency is approximately 27.12 MHz.

The invention further provides a polyurethane foam material comprising the reaction product of a reaction mixture comprising: (a) a polyester diol; (b) a radio frequency receptor capable of generating sufficient thermal energy in response to exposure to radio frequency radiation to melt polyurethane; (c) a diisocyanate; and (d) a blowing agent.

Preferably the reaction mixture also includes a polyether polyol which may itself act as the radio frequency receptor. Preferably said polyester diol and said polyether polyol are present in a ratio of 6:4.

Preferably said diisocyanate is toluene diisocyanate (MIDI) having an 80/20 ratio of 2,4- to 2,6- isomers.. Alternatively two diisocyanates respectively comprising 2,4- and 2,6- isomers in 80/20 ratio and in 65/35 ratio may be used, preferably in a 1:1 ratio. In that event the polyether polyol may be omitted.

The blowing agent is preferably water. The reaction mixture preferably also incorporates a catalyst, preferably a non-pinking amine based catalyst. The reaction mixture preferably also incorporates a surfactant such as a polymethyl siloxane and may include a fire retardant.

Preferably the resultant foam composition has a melting temperature of the order of 160-180"C when subjected to radiation at the desired radio frequency.

Preferably the density (established by BS4443, Part 1, Method 2) of the resultant polyurethane foam composition is in the region of 35 to 47Kg/m3.

Advantageously the foam has a hardness (measured at 4096 compression load deflection to BS4443, Part 1, Method 5A) of 4 to 8 KPa and a minimum of 50% compression set (BS4443, Part 1, Method 3A) of 5-40%. Preferably the cell count of the foam is between 20 and 50, typically 25, cells per inch (BS4443, Part 1, Method 4).

The invention also provides a flexible product comprising a first layer of polyurethane foam and a second layer or skin of polyvinyl chloride (PVC) secured together by high frequency welding.

The product preferably comprises a central core of polyurethane foam contained within an outer envelope of PVC.

Preferably the polyurethane foam comprises a foam composition according to the preceding paragraphs.

Preferably the product is produced by high frequency welding at a frequency of approximately 27.12 MHz.

The invention also provides- a method of producing a composite material comprising placing a sheet of polyurethane foam and a sheet of polyvinyl chloride in surface to surface contact and securing same together by high frequency welding.

Preferably the polyurethane foam comprises a foam composition according to the previous paragraphs.

Welding is preferably carried out at a frequency of approximately 2 z. 12 MHz.

A suitable polyester diol for use in producing polyurethane foam according to the invention is Formez V184-13, having an OHV (hydroxyl value) of 40mg/mgm KOH supplied by Baxenden Chemicals Limited, Applied Chemicals Division, Droitwich, England.

A suitable polyether polyol for use in producing a foam composition according to the invention is Arcol HS100 (a 40% solids acrylonitrile/styrene copolymer dispersion) supplied by Arco, St. Villiers, France.

In one embodiment the polyether polyol may itself act as a radio frequency receptor whereby the foam composition produces sufficient thermal energy to melt it when subjected to the appropriate welding frequency.

Alternatively a separate radio frequency receptor may be employed. This preferably comprises hydroxy pivalyol neopentyl glycol (HPNG). For optimum results the HPNG should be present in an amount of 1-5% by weight of the polyester diol, but preferably in the region of and preferably not greater than 3.5%.

Preferably the composition includes a surfactant selected from polyalkylene oxydimethyl siloxanes, (for example Niax L620LV supplied by Harefield UK or Tegostab B 8234 supplied by Th. Goldschmidt GmbH of Germany). Other suitable surfactants include Tegostab BF2370, Tegostab B3640, Tegostab B8680 or Tegos-tab B5055 supplied by Th. Goldschmidt GmbH, Stabilizer OS15 supplied by Bayer AG or Fomrez M66-82A supplied by Witco Group. The surfactant assists in forming the cell structure of the foam and aids foam stability.

Advantageously one or more catalysts are incorporated to control the blowing and gelling reactions during foaming. Suitable catalysts for the former purpose include amine based catalysts, such as N-ethyl morpholine and for the latter purpose Tegostab CPE (an amine blend containing 1,4 dimethyl piperazine, hexadecyl dimethylamine and an emulsifier type surfactant) from Th. Goldschmidt GmbH. Other suitable catalysts include Polycat U (amine catalyst) supplied by Air Products GmbH, dibutyl tin dilaurate (an organo tin catalyst) supplied by Air Products GmbH, and Kosmos 29 (a tin catalyst) supplied by TH Goldschmidt GmbH Preferably the catalyst comprises a non-pinking catalyst. Certain amine catalysts will migrate from the foam, even when fully cured, and can cause degradation of surrounding material. When foam is encased in a sheath of PVC, this degradation results in a pink discolouration which is generally unacceptable. Non-pinking catalysts do not cause this discolouration.

Suitable flame retardants include halogenated flame retardants, TDCP LV supplied by Alibright & Wilson, Phosflex 41P supplied by Akzo Nobel and DEX OF (a 60% pentabromo diphenyl oxide/40% isopropylated triphenyl phosphate) supplied by Great Lakes Chemical Co.

The following are examples of reaction mixtures for producing high frequency weldable polyurethane foam according to the invention: Example 1 Parts bv wt.

Polyester diol (Fomrez V184-13) 60 Polyether polyol (Arcol HS100) 40 Tegostab CPE (catalyst) 0.3 N-ethyl morpholine (catalyst) 0.8 Silicone surfactants (NIAX L620LV or Tegostab B8234) 1 Flame retardant (DES OF) 5 Tin catalyst (Kosmos 29) .04 Water 2.39 Toluene diisocyanate (TDI) (80% 2,4 isomer, 20% 2,6 isomer) 34.2 Hydroxy pivalyol neopentyl glycol (radio frequency receptor) 2.1 Example 2 Parts bv wt.

Polyester diol (Fomrez V184-13) 96.5 Tegoamin CPE (catalyst) 0.6 N-ethyl morpholine (catalyst) 0.8 Silicone surfactant (Tegostab B8234) 1.0 Flame Retardant (DESOF) 5.0 Tin Catalyst (Kosmos 29) 0.4 Water 2.3 Hydroxy pivaloyl neopentyl glycol 3.5 Toluene diisocyanate 80/20 (80% 2,4 isomer, 20% 2,6 isomer) 20.0 Toluene diisocyanate 65/35 (65% 2,4 isomer, 20% 2,6 isomer) 20.0 The resultant foam compositions were placed within an outer envelope of polyvinyl chloride and subjected to dielectric heating using a Radyne 1.5 KW C-type welding unit operating at a frequency of 70 MHz. The composition was subjected to a weld cycle for 7 seconds and a dwell time of 5 seconds at a power output relating to 4 amps resulting in a clean tearweld with good adhesion of the polyurethane foam core to the surrounding PVC film/foil. Similar satisfactory results were attained at a welding frequency of 27.12 MHz.

The results attained compare favourably with results attained using PVC foam core and improve considerably upon use of conventional polyurethane foam which produces a rough tear weld and poor adhesion to the PVC envelope.

Preferably the weld time and power output are adjusted to produce a welding current of 4-6 amps or lower which has been found to produce good tear and plain welds.

Various modifications may be made without departing from the invention. For example while the invention has been described primarily with reference to a composite material comprising a polyurethane foam core and an outer skin or envelope of PVC, polyurethane or other foamed plastics materials according to the invention may be adhered by welding to themselves or to other materials apart from PVC.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims:

1. A method of rendering a foamed plastics material high frequency weldable at a desired frequency other than a natural resonant frequency of the material, the method comprising modifying the foam composition to render the desired frequency a resonant frequency of the modified foam.

2. A method according to claim 1 wherein the material is a plastics material other than PVC and the desired frequency is a resonant frequency of PVC.

3. A method according to claim 1 or 2 wherein the material is polyurethane foam.

4. A method according to any preceding claim wherein the desired frequency is approximately 27.12 Mhz.

5. A method of rendering a foamed plastics material high frequency weldable at a desired frequency other than a natural resonant frequency of the material substantially as hereinbefore described.

6. A high frequency weldable foamed plastics material produced by the method of any of claims 1 to 5.

7. A foamed plastics material modified to render a desired frequency, different from a natural resonant frequency of the unmodified material, a resonant frequency of the modified material.

8. A material according to claim 7 wherein the material is polyurethane foam.

9. A material according to claim 8 wherein the desired frequency is approximately 27.12 Mhz.

10. A polyurethane foam composition having a resonant frequency approximating to a resonant frequency of PVC.

11. A polyurethane foam composition which will melt under pressure at a frequency approximating to a resonant frequency of PVC.

12. A composition according to claim 10 or 11 wherein the resonant frequency is approximately 27.12 Mhz.

13. A polyurethane foam material comprising the reaction product of a reaction mixture comprising: (a) a polyester diol; (b) a radio frequency receptor capable of generating sufficient thermal energy in response to exposure to radio frequency radiation to melt polyurethane; (c) a diisocyanate; and (d) a blowing agent.

14. A material according to claim 13 wherein the reaction mixture also includes a polyether polyol.

15. A material according to claim 14 wherein said polyether polyol itself acts as said radio frequency receptor.

16. A material according to claim 14 or 15 wherein said polyester diol and said polyether polyol are present in a ratio of 6:4.

17. A material according to any of claims 13 to 16 wherein said diisocyanate is toluene diisocyanate (TDl) having an 80/20 ratio of 2,4- to 2,6- isomers.

18. A material according to any of claims 13 to 16 wherein said reaction mixture incorporates two diisocyanates respectively comprising 2,4- and 2,6 isomers in 80/20 and 65/35 ratios.

19. A material according to claim 18 wherein said diisocyanates are present in a ratio of 1:1.

20. A polyurethane foam material comprising the reaction product of a reaction mixture comprising: (a) a polyester diol; (b) a polyether based polyol; (c) a radio frequency receptor capable of generating sufficient thermal energy in response to exposure to radio frequency radiation to melt polyurethane; (d) toluene diisocyanate having an 80/20 ratio of 2,4- to 2,6- isomers; and (e) a blowing agent.

21. A polyurethane foam material comprising the reaction product of a reaction mixture comprising: (a) a polyester diol; (b) a radio frequency receptor capable of generating sufficient thermal energy in response to exposure to radio frequency radiation to melt polyurethane; (c) toluene diisocyanate having an 80/20 ratio of 2,4- to 2,6- isomers; (d) toluene diisocyanate having a 65/35 ratio of 2,4- to 2,6- isomers; and (e) a blowing agent.

22. A material according to claim 21 in which the 80/20 toluene diisocyanate and the 65/35 toluene diisocyanate are present in the ratio of 1:1.

23. A material according to any of claims 7 to 22 in which the blowing agent is water.

24. A material according to any of claims 7 to 23 wherein the reaction mixture incorporates a catalyst.

25. A material according to claim 24 wherein the catalyst is a non-pinking catalyst.

26. A material according to any of claims 7 to 25 wherein the reaction mixture incorporates a surfactant.

27. A material according to claim 26 wherein the surfactant is polymethyl siloxane.

28. A material according to any of claims 7 to 27 wherein the reaction mixture includes a fire retardant.

29. A material according to any of claims 7 to 28 wherein the resultant foam composition has a melting temperature of the order of 160-180"C when subjected to radiation at the desired radio frequency.

30. A polyurethane foam material produced from a reaction mixture according to Example 1.

31. A polyurethane foam material produced from a reaction mixture according to Example 2.

32. A flexible product comprising a first layer of polyurethane foam and a second layer or skin of polyvinyl chloride (PVC) secured together by high frequency welding.

33. A product according to claim 32 comprising a central core of polyurethane foam contained within an outer envelope of PVC.

34. A product according to claim 32 or 33 wherein the polyurethane foam comprises a foam composition according to any of claims 7 to 30.

35. A product according to any of claims 32 to 34 produced by high frequency welding at a frequency of approximately 27.12 Mhz.

36. A method of producing a composite material comprising placing a sheet of polyurethane foam and a sheet of polyvinyl chloride in surface to surface contact and securing same together by high frequency welding.

37. A method according to claim 36 wherein the polyurethane foam comprises a foam composition according to any of claims 7 to 31.

38. A method according to claim 36 or 37 wherein welding is carried out at a frequency of approximately 27.12 Mhz.

39. A method of producing a composite material substantially as hereinbefore described.

40. A composite product produced by the method according to any of claims 36 to 39.

41. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.