GB2108037A - Shaping aminoplasts using a hot wire - Google Patents

Abstract

Shaped articles are made from urea/formaldehyde resin foam by hot wire cutting.

Description

SPECIFICATION Improvements in and relating to aminoplast resin foams This invention relates to the production of shaped artefacts from aminoplast resin foams. It has been proposed to mould such artefacts by pouring a foamed aqueous dispersion of resin and hardening agent into a mould. This is satisfactory for some purposes, but obviously requires the manufacture of a mould for each shape of artefact. Where a lot of different shapes are required for use of such a technique is uneconomic. Furthermore, the drying time for the resin is inconveniently long. There is also drying shrinkage.

Recently it has been appreciated that foamed aminoplasts such as urea-formaldehyde are particularly useful for the packing of delicate goods, provided of course that the foam density and hardness are selected appropriately. As a consequence of this recent appreciation, it has become necessary to overcome the deficiencies of the conventional moulding technique described above.

According to the present invention, cured aminoplast resin foam is cut into shaped artefacts by means of a hot wire.

Hitherto, hot wire cutting has been used only for thermoplastics in both foamed and solid forms; aminoplasts such as urea-formaldehyde are thermoset materials. In fact, hot wire cutting is known to be ineffective for other thermosets, such as polyurethane foam; the latter sticks to the hot wire.

In the case of aminoplasts, such as ureaformaldehyde resin foam, the effect of the hot wire is imperfectly understood, because there is no localised melting (as with thermoplastics), nor is there any evident charring of the foam, but the hot wire gives a surprisingly clean cut and enables the rapid production of shaped artefacts. Wire temperatures of up to cherry red heat, ie. from about 1 500C upwards, have been found satisfactory. The hotter the wire the faster the cutting speed. As the wire is normally heated electrically, the temperature may be controlled by adjusting the current through it.

Glycol-plasticised urea-formaldehyde resin foams have been found to cut especially well, leaving a smooth glazed finish.

As in the case of cutting foamed thermoplastics, to cut a block of foam into sheets a taut fine wire (e.g. about 0.25 mm diameter) can be used, and for complex shapes a stiff self supporting wire can be used (e.g. about 4 mm diameter). The wire is generally an appropriate resistance wire to facilitate electric heating.

Claims

1. A method of cutting cured aminoplast resin foam into shaped artefacts, the method comprising cutting the foam by means of a hot wire.

2. A method according to Claim 1 wherein the wire temperature is in the range from about 1 500C to cherry red heat.

3. A method according to Claim 1 or Claim 2 wherein the foam is presented to the wire and caused to follow a path such that a prechosen shape is produced.

4. A method according to Claim 1 or Claim 2 wherein the hot wire is presented to the foam and caused to follow a path therethrough such that a prechosen shape is produced.

5. The method of any preceding claim wherein the aminoplast is urea-formaldehyde.

6. A method according to Claim 5 wherein the resin is plasticised with glycol.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in and relating to aminoplast resin foams This invention relates to the production of shaped artefacts from aminoplast resin foams. It has been proposed to mould such artefacts by pouring a foamed aqueous dispersion of resin and hardening agent into a mould. This is satisfactory for some purposes, but obviously requires the manufacture of a mould for each shape of artefact. Where a lot of different shapes are required for use of such a technique is uneconomic. Furthermore, the drying time for the resin is inconveniently long. There is also drying shrinkage. Recently it has been appreciated that foamed aminoplasts such as urea-formaldehyde are particularly useful for the packing of delicate goods, provided of course that the foam density and hardness are selected appropriately. As a consequence of this recent appreciation, it has become necessary to overcome the deficiencies of the conventional moulding technique described above. According to the present invention, cured aminoplast resin foam is cut into shaped artefacts by means of a hot wire. Hitherto, hot wire cutting has been used only for thermoplastics in both foamed and solid forms; aminoplasts such as urea-formaldehyde are thermoset materials. In fact, hot wire cutting is known to be ineffective for other thermosets, such as polyurethane foam; the latter sticks to the hot wire. In the case of aminoplasts, such as ureaformaldehyde resin foam, the effect of the hot wire is imperfectly understood, because there is no localised melting (as with thermoplastics), nor is there any evident charring of the foam, but the hot wire gives a surprisingly clean cut and enables the rapid production of shaped artefacts. Wire temperatures of up to cherry red heat, ie. from about 1 500C upwards, have been found satisfactory. The hotter the wire the faster the cutting speed. As the wire is normally heated electrically, the temperature may be controlled by adjusting the current through it. Glycol-plasticised urea-formaldehyde resin foams have been found to cut especially well, leaving a smooth glazed finish. As in the case of cutting foamed thermoplastics, to cut a block of foam into sheets a taut fine wire (e.g. about 0.25 mm diameter) can be used, and for complex shapes a stiff self supporting wire can be used (e.g. about 4 mm diameter). The wire is generally an appropriate resistance wire to facilitate electric heating. Claims

1. A method of cutting cured aminoplast resin foam into shaped artefacts, the method comprising cutting the foam by means of a hot wire.

2. A method according to Claim 1 wherein the wire temperature is in the range from about 1 500C to cherry red heat.

3. A method according to Claim 1 or Claim 2 wherein the foam is presented to the wire and caused to follow a path such that a prechosen shape is produced.

4. A method according to Claim 1 or Claim 2 wherein the hot wire is presented to the foam and caused to follow a path therethrough such that a prechosen shape is produced.

5. The method of any preceding claim wherein the aminoplast is urea-formaldehyde.

6. A method according to Claim 5 wherein the resin is plasticised with glycol.