GB1579661A

GB1579661A - Coated chipboard

Info

Publication number: GB1579661A
Application number: GB1791177A
Authority: GB
Original assignee: OESTERR HIAG WERKE AG
Current assignee: OESTERR HIAG WERKE AG
Priority date: 1976-05-03
Filing date: 1977-04-29
Publication date: 1980-11-19
Also published as: FR2350196B1; ATA324676A; PT66501A; AT342872B; DE2718705A1; CH616617A5; FR2350196A1; PT66501B

Abstract

This chipboard panel (1) is provided on at least one side with a covering layer (2) of melamine resin. Said melamine resin is, in the preliminary state, water-soluble and homogeneous. The covering layer interlocks in the fibre structure of the chipboard surface and forms a smooth synthetic resin film on its outer side. The chipboard panel is economical to produce and the covering layer is of high quality. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO COATED CHIPBOARD (71) We, OSTERREICHISCHE HIAG-WERKE AKTIENGESELL SCHAFT, an Austrian Body Corporate, of 2 Gluckgasse, Vienna I, Austria, do hereby declare that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to chipboard having a coating layer of melamine resin on at least one side thereof and to a process for applying the said coating layer.

According to the present invention there is provided chipboard having a coating layer of melamine resin on at least one surface thereof, the said coating layer comprising a homogeneous melamine resin which is water-soluble in the uncured state, the coating layer penetrating into the fibre structure of the chipboard and having a smooth external surface.

Preferably the melamine resin coating layer also contains an inorganic filler.

Further according to the present invention there is provided a process for applying a coating layer of melamine resin onto a surface of chipboard, the process comprising applying an aqueous solution or a water-containing paste of a water-soluble homogeneous melamine resin to the surface of wood chipboard to form a coating, drying the coating and hot-pressing the coating to produce a smooth hardened coating layer.

If desired, boards may be produced having a melamine resin coating layer containing a filler on one surface and an unfilled coating layer of thermosetting synthetic resin on the other surface. This synthetic resin is also water-soluble in its uncured state and so it too can be applied such that it penetrates the fibre structure of the chipboard.

Suitable plastic synthetic resins include amino synthetic resins and phenol synthetic resins. The amino synthetic resin used can be a melamine resin which can be mixed or condensed, with an urea-synthetic resin to improve the polishability of the coating and to reduce the cost of production. If it is not essential for the board to be water-resistant it is preferred in view of the cost of production to use an urea synthetic resin alone as the amino synthetic resin.

In order to obtain a coating of good appearance, the coating layer on at least one surface of the board is preferably pigmented or filled and/or dyed. Preferably the region of the coating layer directly adjacent the woodchip material is rich in filler and pigment, while the region of the coating layer remote from the woodchip material is poor in pigment or filler, or is practically pigment-free or filler-free. This latter region is therefore rich in resin and so is also particularly dense and solid.

This regional concentration variation may be effected by controlling the conditions of the hot-pressing step such that the melamine resin is caused to flow outwards prior to curing. The fillers and pigments, having different flow properties, do not flow outwards to such an extent as the melamine resin.

The drying of the coating layers is preferably effected by means of a current of hot air and/or of heat radiation. Particularly good results can be achieved with a reduced work expenditure if drying is conducted in a hot air channel or furnace through which the boards are passed. In practice, the moisture content of the coating is generally reduced to a value of from 2 to 10 wt. % by the drying step. A reduction to 5 wt.% residual moisture is particularly favourable for the subsequent hardening of the coatings. The drying temperature is preferably kept just below 100"C. The hardening of the coating layers is conducted by hot pressing preferably between hot pressing plates. This results in the production of a smooth surface layer which is substantially free of surface pores.

Chipboard embodying the invention and processes in accordance with the invention will now be particularly described by way of example, with reference to the accompanying diagrammatic drawing, the sole Figure of which is a section through a coated chipboard.

The illustrated board comprises a substrate 1 of chipboard having a coating layer 2 and 3 on each surface thereof. These coating layers 2,3 are produced by applying aqueous solutions or pastes of a thermosetting synthetic resin to the surfaces of the substrate 1 followed by drying and hardening of the resin. In the course of the drying and hardening steps, the synthetic resin penetrates and becomes anchored in the fibre structure of the substrate 1, as illustrated by the extension of some of the hatching lines of the coating layers 2 and 3 into the substrate 1. At least one of the coating layers 2,3 comprise a homogeneous melamine resin, which is optionally provided with an inorganic filler and/or pigment. If only one such melamine resin coating is provided, a coating layer on the opposite face of the board may comprise a thermosetting synthetic resin without a filler. Where both coating layers 2,3 contain filler and pigment, the content of the filler and pigment in the two coating layers 2,3 may be different.

The preparation of various synthetic resins for use in the coating layers will now be described, by way of example.

a) Preparation of an aqueous melamine resin In this preparation 162 g (37% by weight) formaldehyde, 38 g water and 20 g sorbite were mixed together. 126 g melamine were stirred into this mixture. After dissolution the pH was adjusted to 9.0 and maintained at that value by the addition of sodium lye.

The mixture was heated and boiled under reflux until a specimen which had been diluted with water in a ratio of 1:4 and cooled, showed a turbidity temperature of 50"C. Then, 3 g p-toluol sulphonic acid amide were added and the reaction mixture was cooled to 20"C.

b) Preparation of an aqueous urea resin solution.

In this preparation the pH of a mixture containing 60 g urea resin, 170 g (37% by weight) formaldehyde and 20 g sorbite was adjusted with sodium lye to a value of 8.5.

The solution was heated and allowed to boil for 40 minutes. Then, the pH was set to a value of 4.5 with formic acid and the mixture was boiled further until a specimen, which had been diluted with water in the ratio 1:6 and cooled, showed a turbidity temperature of from 3 to 50C. Then, a pH of 8.0 was obtained with sodium lye and the mixture was distilled off until the residue contained a proportion of 65 wt % solid resin.

c) Preparation of a mixed amino synthetic resin In this preparation, 2 ml of HYPERS-AL (Registered Trade Mark), 2.5 ml of 30% hydrogen superoxide and 0.7 ml of formic acid were added to 1000 g melamine resin produced in preparation a The pH of the mixture was adjusted to a value of 7.2 and 500 g urea resin produced in preparation b) was added, together with 5 g ammonium chloride. The resulting mixture was stirred thoroughly.

d) Preparation of a phenol synthetic resin 94 g phenol were mixed with 200 g (37% by weight) of formaldehyde and the mixture was heated to 90 C. At this temperature, 22.5 g sodium lye (33%) were added dropwise over a period of 1 hour, and a further 22.5 g sodium lye (33%) were added. The reaction mixture was kept at a temperature of 90"C until a test specimen had a viscosity of 200 cP. Then, the mixture was cooled abruptly.

e) Preparation of an amino synthetic resin condensed with a phenol synthetic resin The H of a mixture of 60 g urea and 405 g (37c by weight) formaldehyde was adjusted with sodium lye to a value of 8.5. The solution was heated and boiled under reflux for 30 minutes. Acetic acid was used to adjust the pH value to 4.8 and boiling was continued for a further 30 minutes. Then, the pH was further adjusted to a value of 9.0 with sodium lye, and 94 g phenol were added to the solution. After a further 30 minutes boiling the pH value was checked and if necessary adjusted back to 9.0 with sodium lye. The, the temperature was reduced to 90"C and 63 g melamine were stirred in. After the dissolution of the melamine, the reaction mixture was maintained at a temperature of 90"C for a period of 1 hour and then cooled rapidly.

The following examples of the coating of chipboard surface are given by way of illustration only.

Example I 400 g of a melamine resin obtained as described in preparation a) were mixed with 100 g titanium dioxide, 70 g of kaolin, 200 g water and the pH of the mixture brought to a value of 7.2 with formic acid. This resin mixture was applied to the surface of a wood chipboard by spraying or pouring, to form a coating layer in an amount of 300 g of solid per square metre. This coating was then exposed for 12 minutes to infra-red radia tion, after which the residual moisture of the layer amounted to 5 wt %. Then the coated wood chipboard was pressed between pressing plates at a pressure of 20 kp)/cm2 and a temperature of 1500C for 45 seconds. The thus produced wood chipboard had a white coating layer of homogeneous colour. The coating layer did not split or peel off under the influence of mechanical processing.

When both sides of the board are coated, it is possible to apply the resin in succession to the two surfaces of the wood chipboard, and then to subject both surfaces to the drying and pressing treatments at the same time.

Example 2 On one side of a wood chipboard a melamine resin provided with filler as described in Example 1 was applied, and on the other side of the board a melamine resin without a filler was applied. This latter resin had been obtained by adding 2 ml HYP ERS-AL (wetting agent), 2.5 ml 30% hydrogen superperoxide and 0.7 ml formic acid (85%) to 1000 g melamine resin produced as described in preparation a), whereupon the mixture had a pH of 7.2. The application was effected by spraying or painting the resin mixture in an amount of 300 g solid resin per sq.m. The thus formed coatings were dried to a residual moisture level of 5 wt % in ambient air, and then pressing was carried out as described in Example 1.

The filler-free coating layers were produced in similar manner, using synthetic resins produced as described in preparations b), c), d) and e).

Example 3 200 g melamine resin produced as described in preparation a) were mixed with a filler comprising 50 g chalk, 50 g schist flour, 50 g talcum powder, 200 g barium sulphate, 25 g titanium oxide and 10 g Aerosil (Registered Trade Mark). This mixture was applied to a surface of a wood chipboard in an amount of 450 g/m2 by trowelling or by rolling and dried with hot air. Subsequently an amino synthetic resin produced as described in preparation d) was applied to the other surface of the chipboard in an amount of 250 g solid resin per sq.m. The coating produced was dried again, with hot air. The hardening of both coating layers was carried out simultaneously by pressing as described in Example 1.

Example 4 200 g melamine resin produced as de scribed in preparation a) were mixed with 50 g chalk, 50 g schist flour, 100 g talcum powder, 100 g barium sulphate, 100 g titanium dioxide and 50 g furfuryl alcohol, and the resultant mass was aplied to both sides of a chipboard, dried and hardened as described in Example 3.

Example 5 An aqueous solution of urea resin produced as described in preparation b) was applied to one surface of a wood chipboard in an amount of 250 g solid resin per sq. m.

and this coating was dried. A melamine resin provided with filler and pigment similar to that described in Example 1 was then applied to the other surface of the board and this covering layer was dried to a residual moisture of 10 wt %. The coated chipboard was placed in a heated plate press and the synthetic resin layers were hardened. The residual moisture content of the coating layers was higher than in the previous examples, and as a result of this the hot pressing step caused an enrichment of the filler and the pigment in the region of the melamine resin coating layer adjoining the wood chip material. The outer region of the coating layer was particularly rich in resin, dense and solid.

Example 6 A melamine resin solution was obtained as described in preparation a) and 1000 g of this melamine resin was reacted with 2 ml Hypers-al, 2.5 ml 30% hydrogen peroxide and 0.7 ml formic acid (85%). The reaction mixture was applied to a surface of a wood chipboard in an amount of 300 g solid resin per sq. m. by spraying or painting and the resulting coating was dried for 10 minutes.

Then the same amount of melamine resin was applied to the second surface and this second coating was again dried for 10 minutes. Finally pressing was carried out as described in Example 1.

The above described process produced good quality boards which can be manufactured at a lower expenditure than is required using hitherto known coating techniques. The fact that the melamine resin is water-soluble prior to curing means that it can penetrate intimately into the fibre structure of the wood chip board surface during the first stage of the coating process. Thus in the final coating layer there is an intimate interaction between the melamine resin and the surface fibres of the chipboard which overcomes problems of anchoring of the coating which have arisen with hitherto known boards. For instance these boards can be cut without difficulty by means of a saw. Hitherto, sawing of coated boards resulted in a splitting off of the coating at the edge of the saw cuts, and it has required a lot of effort in sawing technology to reduce this splitting off to an acceptable level.

WHAT WE CLAIM IS: 1. Chipboard having a coating layer of melamine resin on at least one surface

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

Claims

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

tion, after which the residual moisture of the layer amounted to 5 wt %. Then the coated wood chipboard was pressed between pressing plates at a pressure of 20 kp)/cm2 and a temperature of 1500C for 45 seconds. The thus produced wood chipboard had a white coating layer of homogeneous colour. The coating layer did not split or peel off under the influence of mechanical processing.

When both sides of the board are coated, it is possible to apply the resin in succession to the two surfaces of the wood chipboard, and then to subject both surfaces to the drying and pressing treatments at the same time.

Example 2 On one side of a wood chipboard a melamine resin provided with filler as described in Example 1 was applied, and on the other side of the board a melamine resin without a filler was applied. This latter resin had been obtained by adding 2 ml HYP ERS-AL (wetting agent), 2.5 ml 30% hydrogen superperoxide and 0.7 ml formic acid (85%) to 1000 g melamine resin produced as described in preparation a), whereupon the mixture had a pH of 7.2. The application was effected by spraying or painting the resin mixture in an amount of 300 g solid resin per sq.m. The thus formed coatings were dried to a residual moisture level of 5 wt % in ambient air, and then pressing was carried out as described in Example 1.

The filler-free coating layers were produced in similar manner, using synthetic resins produced as described in preparations b), c), d) and e).

Example 3

200 g melamine resin produced as described in preparation a) were mixed with a filler comprising 50 g chalk, 50 g schist flour, 50 g talcum powder, 200 g barium sulphate, 25 g titanium oxide and 10 g Aerosil (Registered Trade Mark). This mixture was applied to a surface of a wood chipboard in an amount of 450 g/m2 by trowelling or by rolling and dried with hot air. Subsequently an amino synthetic resin produced as described in preparation d) was applied to the other surface of the chipboard in an amount of 250 g solid resin per sq.m. The coating produced was dried again, with hot air. The hardening of both coating layers was carried out simultaneously by pressing as described in Example 1.

Example 4

200 g melamine resin produced as de scribed in preparation a) were mixed with 50 g chalk, 50 g schist flour, 100 g talcum powder, 100 g barium sulphate, 100 g titanium dioxide and 50 g furfuryl alcohol, and the resultant mass was aplied to both sides of a chipboard, dried and hardened as described in Example 3.

Example 5 An aqueous solution of urea resin produced as described in preparation b) was applied to one surface of a wood chipboard in an amount of 250 g solid resin per sq. m.

and this coating was dried. A melamine resin provided with filler and pigment similar to that described in Example 1 was then applied to the other surface of the board and this covering layer was dried to a residual moisture of 10 wt %. The coated chipboard was placed in a heated plate press and the synthetic resin layers were hardened. The residual moisture content of the coating layers was higher than in the previous examples, and as a result of this the hot pressing step caused an enrichment of the filler and the pigment in the region of the melamine resin coating layer adjoining the wood chip material. The outer region of the coating layer was particularly rich in resin, dense and solid.

Example 6 A melamine resin solution was obtained as described in preparation a) and 1000 g of this melamine resin was reacted with 2 ml Hypers-al, 2.5 ml 30% hydrogen peroxide and 0.7 ml formic acid (85%). The reaction mixture was applied to a surface of a wood chipboard in an amount of 300 g solid resin per sq. m. by spraying or painting and the resulting coating was dried for 10 minutes.

Then the same amount of melamine resin was applied to the second surface and this second coating was again dried for 10 minutes. Finally pressing was carried out as described in Example 1.

The above described process produced good quality boards which can be manufactured at a lower expenditure than is required using hitherto known coating techniques. The fact that the melamine resin is water-soluble prior to curing means that it can penetrate intimately into the fibre structure of the wood chip board surface during the first stage of the coating process. Thus in the final coating layer there is an intimate interaction between the melamine resin and the surface fibres of the chipboard which overcomes problems of anchoring of the coating which have arisen with hitherto known boards. For instance these boards can be cut without difficulty by means of a saw. Hitherto, sawing of coated boards resulted in a splitting off of the coating at the edge of the saw cuts, and it has required a lot of effort in sawing technology to reduce this splitting off to an acceptable level.

WHAT WE CLAIM IS: 1. Chipboard having a coating layer of melamine resin on at least one surface

thereof, the said coating layer comprising a homogeneous melamine resin which is water-soluble in the uncured state, the coating layer penetrating into the fibre structure of the chipboard and having a smooth external surface.
2. Chipboard according to claim 1, wherein the or each melamine resin coating layer also contains an inorganic filler.
3. Chipboard according to claim 2, wherein only one surface of the board is coated with the melamine resin, the other surface is provided with a coating layer of a thermosetting synthetic resin penetrating the fibre structure of the chipboard, the said thermosetting synthetic resin being water soluble in its uncured state.
4. Chipboard according to any one of claims 1 to 3, wherein the or each melamine resin coating layer also contains pigment or dye.
5. Chipboard according to claim 1, wherein the or each melamine resin coating layer contains an inorganic filler and a pigment and the filler and/or the pigment are enriched in the region of the coating layer adjacent to the chipboard, while the region of the coating layer remote from the chipboard is poor in filler and pigment or is practically filler and pigment free.
6. Chipboard according to claim 1, wherein a melamine resin coating layer further containing a filler and a pigment is applied to two opposite surfaces of the chipboard and the filler and pigment content of the coating layer situated on one surface of the chipboard is different from the filler and pigment content of the coating layer on the opposite surface of the board.
7. A process for applying a coating layer of melamine resin onto a surface of chipboard, the process comprising applying an aqueous solution or water-containing paste of a water-soluble homogeneous melamine resin to the surface of wood chipboard to form a coating, drying the coating and hot-pressing the coating to produce a smooth hardened coating layer.
8. A process according to claim 7, wherein the resin solution or resin paste contains an inorganic filler.
9. A process acording to claim 7 or claim 8, wherein the resin solution or resin paste also contains a dye or pigment.
10. A process according to any one of claims 7 to 9, wherein the resin solution or resin paste is applied to the surface of the chipboard by spraying.
11. A process according to any one of claims 7 to 9, wherein the resin solution or resin paste is applied to the surface of the chipboard by rolling or pouring.
12. A process according to any one of the preceding claims, wherein the coating is dried by means of radiant heat.
13. A process according to claim 12, wherein the coating is dried by means of infra-red radiation.
14. A process according to any one of claims 7 to 11, wherein the coating is dried in a hot air furnace or channel.
15. A process according to claim 14, wherein the drying is carried out in association with infra-red radiation.
16. A process according to any one of claims 7 to 15, wherein a further coating is applied to an opposite surface of the chipboard and dried prior to the hot pressing step and the smoothing and hardening of both coating layers is carried out in one heat pressing operation.
17. Chipboard substantially as hereinbefore described with reference to the accompanying drawing.
18. A process substantially as hereinbefore described with reference to the accompanying drawing.
19. A product when produced by a process according to any one of claims 7 to 16 or claim 18.