GB2396156A

GB2396156A - Thermosetting powder

Info

Publication number: GB2396156A
Application number: GB0326887A
Authority: GB
Inventors: Roger Walter Britton
Original assignee: WARD AYLIS HAVILAND
Current assignee: WARD AYLIS HAVILAND
Priority date: 2002-11-19
Filing date: 2003-11-19
Publication date: 2004-06-16
Also published as: AU2003286255A1; WO2004046245A1; GB0226917D0; GB0326887D0

Abstract

A thermosetting powder comprising a thermosetting resin comprising a polyester, epoxy resin or a polyester / epoxy copolymer and an additive. The additive is a thermosensitive material, preferably a thermochromic material or a photochromic material, present in an amount sufficient to impart thermosensitive, preferably thermochromic or photochromic, properties to the powder. Also disclosed is a process for the production of a thermosetting powder, in which a polyester, epoxy resin or a polyester / epoxy copolymer is heated at least to its glass transition temperature, an additive in powder form is mixed with the heated resin, the mixture is heated to the extrusion temperature, extruded, cooled, ground and then granulated to the required powder size, wherein the additive is a thermosensitive material, preferably a thermochromic or photochromic material.

Description

2396 1 56

Re: Improved Thermosetting Powder The present invention relates to an improved Thermosetting powder and to a process for its production. Thermosetting powders are known, which comprise a thermosetting resin, either alone or in 5 admixture with one ormore inert additives. Known Thermosetting resins include polyesters, epoxy resins and polyester / epoxy copolymers.

It is known to mix these resins with chemically and thermally inert additives to impart to the finished material a desired texture, colour or other special effect, for example a metallic effect.

The additives can be mixed with the resin as a pure mechanical mixture, and this is acceptable 1 0 where only a low density of additive is required and the overspray powder is not recovered. Where a high density of additive is required and/or it is important to ensure that the mixture is homogeneous, it has been found advantageous to use aprocess in which the thermosetting resin is heated to its glass transition temperature, and the resin is bonded to the additive or additives, enabling the additives to adhere. Alternatively, the resin maybe heated to a temperature at which 15 it melts and the additive or additives in powder form may be combined with the molten resin at elevated temperature. In either case, the mixture is then heated to the extrusion temperature, extruded, cooled, ground and then granulated to the required powder size.

Thermosetting powders ofthis type are used in a wide range of applications, including for example electrostatic powder deposition processes. For many of these applications, either because of further 20 processing considerations orbecause oftheintended final use, itis essentialthat the powder, when cured, is stable at a particular elevated temperature. For example, where the cured powder is to be used as a substrate for dye sublimation printing, it is required that the cured resin be stable above 1 80 C.

This process has heretofore onlybeen used with inert additives, inparticularwith additives which are not affected by the changes in temperature experienced during the process and which do not, in the amounts in which they are added to the thermosetting resin, affect the thermal profile ofthe thermosetting resin. The process has not been used for the manufacture of powders containing a 5 high concentration of additive or for the manufacture of powders containing additives which are themselves affected by the changes in temperature experienced during the process.

[t is an object ofthe present invention to provide a thermosetting powder comprising an additive which is temperature sensitive, which additive may be present in a concentration which affects the thermal profile ofthe basic thermosetting resin, which powder is suitable for use in a sublimation 10 process, and a process for the production of this powder.

The present invention provides a thermosetting powder comprising a polyester, epoxy resin or a polyester/ epoxycopolymer and an additive, characterized in that the additive is athermosensitive material, present in an amount sufficient to impart thermosensitive properties to the powder.

In a preferred embodiment ofthe powder according to the invention, the thermosensitive material 15 is a thermochromic material or a photochromic material.

In a preferred embodiment ofthe powder according to the invention, the thermosetting powder has, in the absence of the additive, a curing temperature higher than the temperature at which the thermosetting powder is to be cured.

The invention further provides a process for the production of a thermosetting powder, in which 20 a polyester, epoxy resin or a polyester / epoxy copolymer is heated at least to its glass transition temperature, an additive in powder form is mixed with the heated resin, the mixture is heated to the extrusion temperature, extruded, cooled, ground and then granulated to the required powder size, characterized in that the additive is a thermosensitive material.

Where the thermosetting powder according to the invention is to be prepared by a process in which

the resin is melted priorto mixing with the additive, the resin may comprise apolyester, epoxyresin or apolyester/ epoxy copolymer which, in the absence ofthe additive, has a curing temperature higher than the temperature at which the thermosetting powder is to be cured, more preferably 10 to20 C higher. Suitable thermosetting resins foruse in this process include polyesters, epoxy resins 5 or polyester / epoxy copolymers, which have been modified by increasing the polymer chain length and/or degree of cross-linking, to increase the curing temperature from 1 80 C to 220 C.

Suitable thermosensitive materials include thermochromic materials such as the thermochromically active ingredients ofthe commercially available liquid thermochromic coating materials described for example in EP-A- 0 677 564.

10 The thermochromic thermosetting powder according to the invention is particularly suitable for use as the coating powder in electrostatic powder deposition processes, in particular for the electrostatic powder deposition process described and claimed in our co-pending UK Patent Application No 0226916.5 The thermochromic thermosetting powder according to the invention preferably comprises less than 15 3% by weight, more preferably from 3 to 25 % by weight, most preferably from 3 to 10 % by weight, based on the total weight of the powder, of the thermochromic material.

The thermochromic thermosetting powder according to the invention and the process for its production will now be described with reference to the following specific Example.

Example

5 g of athermochromic powder haying aparticle size of less than 50micronswas drymixed with 95 g of a powdered thermosetting polyester resin. The mixture was then heated to its glass transition temperature of 60" C, ensuring that the free thermochromic powder adhered to the 5 surface ofthe thermosetting powder. The resultant mixture was then subjected to a conventional powder manufacturing technique, resulting in a graded powder suitable for deposition by an electrostatic process.

Claims

1. A thermosetting powder comprising a thermosetting resin comprising a polyester, epoxy resin or a polyester / epoxy copolymer and an additive, characterised in that the additive is a thermosensitive material, present in an amount sufficient to impart thermosensitive properties to the 5 powder.

2. A thermosetting powder according to claim 1 characterised in that the thermosensitive material is a thermochromic material.

3. A thermosetting powder according to claim 1 characterised in that the thermosensitive material is a photochromic material.

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4. A thermosetting powder according to any of claims 1 to 3 characterised in that, in the absence of the additive, the thermosetting resin has a curing temperature higher than the temperature at which the thermosetting powder is to be cured.

5. A process for the production of a thermosetting powder, in which a polyester, epoxy resin ore polyester/ epoxycopolymeris heated at least to its glass transition temperature, an additive 15 in powder form is mixed with the heated resin, the mixture is heated to the extrusion temperature, extruded, cooled, ground and then granulated to the required powder size, characterised in that the additive is a thermosensitive material.

6. A process according to claim 5 characterised in that the thermosensitive material is a thermochromic material.

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7. A process according to claim 5 characterised in that the thermosensitive material is a photochromic material.

8. A process according to anyofclaims 5 to 7 characterised in that the resin is melted prior

to mixing with the additive and comprises a polyester, epoxy resin or a polyester / epoxy copolymer which, in the absence of the additive, has a curing temperature higher than the temperature at which the thermosetting powder is to be cured.