CURING OF RESINS

Abstract: A method of manufacturing a product comprising at least two parts includes the steps of coating one of the parts at least partially with a resin having a trapped catalyst distributed therein, placing the parts together with the resin therebetween and releasing the catalyst into the resin to initiate curing at the desired time. The catalyst may be trapped either by encapsulation or by absorption/adsorption into the structure of a suitable substrate such as almond shell. The catalyst may be an organic peroxide, formic acid or toluene sulphonic acid. An accelerator may be used to accelerate curing.

Description: CURING OF RESINS The present invention relates to a method of controlling the curing of a resin and to a resin modified to provide such control. The invention also includes the application of the method and the use of the resin in the production of articles. In the production of plywood, for example, individual layers of wood are coated with resin, pressed together and subjected to heat in order to cure the resin. The time for which the heat is supplied to obtain a cure can be considerable slowing down the production process. Curing times can be reduced by mixing a catalyst with the resin, but this may interfere with the production process itself as curing may start either before or during the application of the resin. According to one aspect of the present invention, there is provided a method of curing a resin including the steps of trapping a catalyst which when released into the resin initiates curing, mixing the trapped catalyst with the resin and releasing the catalyst into the resin to initiate curing at the desired time. According to another aspect of the present invention, there is provided a method of manufacturing a product comprising at least two parts including the steps of coating one of the parts at least partially with a resin having a trapped catalyst distributed therein, placing the parts together with the resin therebetween and releasing the catalyst into the resin to initiate curing at the desired time. The invention also includes products made by the above method and resins with distributed catalysts for use in the above methods. The catalyst may be trapped either by encapsulation or by adsorption/absorption into the structure of a suitable substrate such as almond shell. The resin may be any of the following Polyester resin. Vinyl esterresin. Phenol formaldehyde resin, Epoxy resin. Acrylic resin, melamine/urea formaldehyde resin. Phenolic resin. The catalyst may be any appropriate catalyst such as:- Organic peroxides for example Di benzoyl peroxide. Methyl ethyl keto- peroxide, Cumene hydroperoxide, Acetylacetone peroxide (sold under trade name Triganox 44B), tert-Butyl peroxybenzoate (sold under trade name Triganox C), tert-Butyl-2-ethyl hexanoate (sold under trade name Triganox 21 ), tert-Butylperoxy-3,5,5, trimethyl hexanoate (sold under trade name Triganox 42s), Cumene hydroperoxide (sold under trade name Triganox K-80), Biz (4-tert-butylcyclohexyi-peroxdicarbonate) (sold under trade name Perkadox 16). Amine Catalysts for example: Diethyltetra amine. Triethylamine Isocyanates, Boron tri fluoride, UV Curing Catalysts, Alkyl Carbonates for example: Propylene and Ethylene carbonate, and mineral and organic acids such as Formic acid, toluene sulphonic acid, or sulphuric acid. The encapsulating material may be any one of the following; gelatine, thermoset resins, fats, waxes, thermoplastics, polymeric compounds, or silane compounds or any of the encapsulation materials disclosed in the applicants copending international application published under publication No. WO 98/26865. Accelerators may also be used such as Colbait octoate (sold under trade name NL-49-P), Diethylaniline (sold under trade name NL-64-10P). Ammonium Sulphate or Ammonium Chloride. The size of the encapsulated or coated particles may lie in the range 0.5 to 1000 microns. Embodiments of the invention will now be described, by way of example. In a first embodiment, which relates to the manufacture of plywood, layers of plies of wood are coated with resin, placed together with the resin sandwiched between adjacent plies and subject to pressure urging them together and/or heat to cure the resin so that the plies adhere strongly together. In the conventional methods of production pressure and heat may have to be applied for a considerable period of time, for example, several minutes, adding to the production time and to the expense of production. In accordance with the invention, a catalyst is distributed through the resin. The catalyst is distributed through the resin. The catalyst which may be propylene carbonate, ethyiene carbonate or any other suitable catalyst initiates curing of the resin to produce a bond between adjacent plies of wood. However, if curing is initiated too early or progresses too quickly, it may be difficult or impossible to carry out the manufacturing process satisfactorily and/or efficiently. For example, if curing is already proceeding when the plies are coated with resin it may not be possible to coat the plies readily and, even if it is, the strength of the bond between plies may be adversely affected. In order to overcome this possible disadvantage, the release of the catalyst into the resin to initiate curing is controlled by encapsulating the catalyst. Encapsulation is achieved by irradiating the catalyst with ultrasound in the presence of an encapsulating material to produce microcapsules of catalyst coated with encapsulating material. The coating isolates the catalyst from the resin even though the encapsulated resin capsules are distributed through the resin. In this state, the resin may be applied to the plies of wood as described previously, but curing will not begin and will therefore not affect this process until the granules are ruptured to release the catalyst into the resin. Rupturing may be effected by irradiating the capsules with ultrasound or by heat or any other suitable method. In an alternative method of encapsulation, catalyst is adsorbed into the surface of granules of an inert substance which are coated with an encapsulating material again by irradiating with ultrasound. In both cases the size of the coated particles would generally lie in the range 0.5 to 1000 microns. The catalyst may be any of the following materials, or any mixture thereof:- Organic peroxides for example Di benzoyl peroxide. Methyl ethyl keto- peroxide, Cumene hydroperoxide, Acetylacetone peroxide (sole under trade name Triganox 44B), tert-Butyi peroxybenzoate (sold under trade name Triganox C, tert-Butyl-2-ethyl hexanoate (sold under trade name Triganox 21), tert-Butylperoxy-3,5,5, trimethyl hexanoate (sold under trade name Triganox 42s), Cumene hydroperoxide (sold under trade name Triganox K-80), Biz (4-tert-butylcyclohexyl-peroxdicarbonate) (sold under trade name Perkadox 16). Amine Catalysts for example: Diethyltetra amine, Triethylamine Isocyanates, Boron tri fluoride, UV Curing Catalysts, Alkyl Carbonates for example: Propylene and Ethylene carbonate and mineral and organic acids such as Formic acid, toluene sulphonic acid, or sulphuric acid. Accelerators may also be used such as Colbalt octoate (sold under trade name NL-49-P), Diethylaniline (sold under trade name NL-64-10P). The encapsulating material may be any one of the following or any mixture thereof:- gelatine, thermoset resins, fats, waxes, thermoplastics, polymeric compounds, or silane compounds or any of the encapsulation materials disclosed in the applicants copending international application published under publication No. WO 98/26865. The resin may be any one of the following or any mixture thereof :- Polyester resin. Vinyl esterresin. Phenol formaldehyde resin, Epoxy resin. Acrylic resin, meiamine/urea formaldehyde resin. Phenolic resin. In a second embodiment, a catalyst is trapped by absorption into a suitable substrate rather than by adsorption as previously described. A suitable substrate is almond shell which has a surface which facilitates absorption/adsorption of catalyst into its porous structure. The catalyst is formic acid and the resin is a melamine/urea formaldehyde resin although other catalysts and resins, for example, as detailed above may be used. The process for making the almond shell formic acid/toluene sulphonic acid catalyst material is as follows. i) The formic acid/toluene sulphonic acid is first dissolved/dispersed in/into acetone. Acetone acts as a carrier solvent for the acid catalyst into the porous structure of the almond shell. ii) almond shell is then added to the acid/acetone mixture. iii) The acid/acetone/almond shell mixture is sonicated using a 20kHz, 400 Watt ultrasonic probe for 3-5 minutes until the acetone/acid has absorbed/adsorbed into the almond shell structure. This process can be easily observed by a significant thickening appearance of the mixture. One of the reasons a solvent is used is in order for ultrasound to work effectively with a high solid almond shell content present. Excess liquid is required (i.e. acetone) in which cavitation can develop. When the cavitation bubbles collapse, a large energy source/shock wave is created and it is this energy which drives the liquid mixture into the almond shell structure. iv) The acetone solvent is removed from the slurry mixture using drying methods leaving just the acid catalyst embedded in the almond shell. The acetone may be removed and re-cycled using condensers. The almond shell/acid catalyst product is a fairly free flowing powder which can be easily dispersed in resin. Acetone is used as a solvent because; a) It has very good dissolving properties. For example, para toluene sulphonic acid catalyst (PTSA) which is a solid powder, needs to be dissolved in the acetone before it can be driven into the almond shell. b) It has a very low boiling point which facilitates its removal during the drying process at low temperature. This is a very important characteristic when formic acid is used because this catalyst has a relatively low boiling point and therefore if high drying temperatures were used, the formic acid would be removed as well. c) The presence of acetone in the sonication process keeps the temperature very low (specific heat capacity characteristic) reducing or eliminating vaporisation problems. When the almond shell/acid catalyst is dispersed with the resin, the molecules of the resin are so large that they cannot access the almond shell structure very easily or quickly and therefore cannot come into contact with the acid catalyst which is embedded in the structure. Curing of the resin will therefore not begin. The acid catalyst can be activated by heat. This will cause the structure to expand and open up allowing the resin to get at the catalyst. It needs to be noted that this is not an encapsulation technology and no coating has been used. However a coating could be applied if the end user/application required much greater pot-life stability. It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention. For example, the method of the invention may be applied to any product manufacture where one or more parts are coated and/or impregnated with a curable resin either to enable the parts to be secured together or as part of the production process. Felts or glass fibre may be impregnated with a curable resin of the invention formed into a desired shape and the resin then cured. Material may be supplied pre-impregnated with resin for use in a downstream production process. These material composites could be employed in the following general areas:- i) Boat construction, ii) Automotive industry - for example interior/exterior components and body panels, iii) Train/Aeorplane construction - for example interior/exterior components and body panels, iv) Off shore marine/oil drilling applications, v) Building construction - wall panels (interior/exterior), roofing vi) House-hold goods, vii) Surface coatings viii) Fire retardent foams/coatings/composites, ix) Binders for the paint and paper industry, x) Binders for use in the foundry industry, xi) Filament windings, xii) Plastic extrusions, xiii) Adhesives, xiv) MDF/Particle Board, xv) Dough Moulding compounds, xvi) Pre-impregnated products, xvii) Binders for concrete applications used in the building/construction industry.

Claims: CLAIMS 1. A method of curing a resin including the steps of trapping a catalyst which when released into the resin initiates curing, mixing the trapped catalyst with the resin and releasing the catalyst into the resin to initiate curing at the desired time. 2. A method of manufacturing a product comprising at least two parts including the steps of coating one of the parts at least partially with a resin having a trapped catalyst distributed therein, placing the parts together with the resin therebetween and releasing the catalyst into the resin to initiate curing at the desired time. 3. A method as claimed in claim 1 or 2, in which the catalyst is trapped by encapsulation. 4. A method as claimed in claim 3, in which the encapsulation material comprises one or more of the following :- gelatine, thermoset resins, fats, waxes, thermoplastics, polymeric compounds, or silane compounds or any of the encapsulation materials disclosed in the applicants copending international application published under publication No. WO 98/26865. 5. A method as claimed in 1 or 2, in which the catalyst is trapped by absorption/adsorption. 6. A method as claimed in claim 5 in which the catalyst is trapped by absorption/adsorption into the surface of almond shell. 7. A method as claimed in any of claims 1 to 6, in which the resin comprises one or more of the following Polyester resin. Vinyl esterresin, Phenol formaldehyde resin, Epoxy resin. Acrylic resin, melamine/urea formaldehyde resin. Phenolic resin. 8. A method as claimed in any preceding claim, in which the catalyst is an organic peroxide. 9. A method as claimed in any of claims 1 to 7, in which the catalyst comprises one or more of the following :- Organic peroxides for example Di benzoyl peroxide. Methyl ethyl keto- peroxide, Cumene hydroperoxide, Acetylacetone peroxide (sold under trade name Triganox 44B), tert-Butyl peroxybenzoate (sold under trade name Triganox C), tert-Butyl-2-ethyl hexanoate (sold under trade name Triganox 21 ), tert-Butylperoxy-3,5,5, trimethyl hexanoate (sold under trade name Triganox 42s), Cumene hydroperoxide (sold under trade name Triganox K-80), Biz (4-tert-butylcyclohexyl-peroxdicarbonate) (sold under trade name Perkadox 16). Amine Catalysts for example: Diethyltetra amine, Triethylamine isocyanates. Boron tri fluoride, UV Curing Catalysts, Alkyl Carbonates for example: Propylene and Ethylene carbonate, and mineral and organic acids such as Formic acid, toluene sulphonic acid, or sulphuric acid. 10. A method of trapping formic acid catalyst in almond shell including the steps of dissolving of dispersing formic acid into acetone, adding almond shell to the acid/acetone mixture and sonicating the mixture until the acetone and mixture has been absorbed/adsorbed into the almond shell structure. 11. A method of trapping toluene sulphonic acid catalyst in almond shell including the steps of dissolving or dispersing toluene sulphonic acid into acetone, adding almond shell to the acid/acetone mixture and sonicating the mixture until the acetone acid mixture has been absorbed/adsorbed into the almond shell structure. 12. A method of trapping as claimed in claim 10 or 11, in which the acid/acetone mixture is sonicated using a 20 KHz 400 watt ultrasonic probe for 3 to 5 minutes. 13. A method of curing a resin including the steps of trapping a catalyst which when released into the resin initiates curing, mixing the trapped catalyst with the resin and releasing the catalyst into the resin to initiate curing at the desired time in which the catalyst is trapped by the method claimed in claim 10, 1 1 or 12. 14. A method as claimed in any of claims 1 to 9 or 13 in which an accelerator is used to accelerate curing. 15. A method as claimed in claim 14, in which the accelerator is Cobalt octoate (sold under trade name NL-49-P), Diethylaniline (sold under trade name NL-64-10P). Ammonium Sulphate or Ammonium Chloride. 16. A product made by the method as claimed in any preceding claim.

Inventors: BATES DARREN MILES, BATES, DARREN, MILES
Applicants: BATES DARREN MILES, CEHMCOLLOIDS LTD, BATES, DARREN, MILES, CHEMCOLLOIDS LIMITED
Application year: 1999
Main classification: C08J3
IPC codes: C08J3, C08K5, C08K9, C08L101, C09J5, C09J11, C09J201