GB2180545A

GB2180545A - Fast curing condensation product and process for its production

Info

Publication number: GB2180545A
Application number: GB08619389A
Authority: GB
Inventors: Dr Horst Michaud; Dr Josef Seeholzer
Original assignee: SKW Trostberg AG
Current assignee: Evonik Operations GmbH
Priority date: 1985-08-10
Filing date: 1986-08-08
Publication date: 1987-04-01
Also published as: IT8667654A1; GB8619389D0; FR2586023A1; DE3528735A1; IT8667654A0; IT1195821B

Abstract

Condensation products are prepared from a composition which comprises an aminoplastic resin former, formaldehyde, thiourea, and a separating agent. The composition and condensation product may also contain a plasticiser, a guanamine, a wetting agent and/or a curing agent. The condensation products may be used for the production of laminates or laminated derived timber products and require very short pressing times. The separating agent may comprise guanamine or a salt or ester of a fatty acid, e.g. guanidine stearate or palmitate.

Description

SPECIFICATION Fast curing condensation product and process for its production Decorative laminates, such as those used especially for kitchen fittings, especially as work surfaces, have until now been produced only discontinuously in multi-layer presses. Resinimpregnated paper is used for this process: paper impregnated with melamine resin and often dyed or printed is used for the top layer and sodium kraft paper impregnated with phenolic resin is used for the middle and bottom layers, and the whole is pressed to form a laminate under pressures of from 800 to 1000 newtons/cm2 and at temperatures of up to 160 C for up to 40 minutes. This type of laminate production is very expensive in terms of energy as the press has to be cooled before the cured laminated sheet is removed and has to be heated up again once it has been coated again.A further considerable cost factor in the production of such laminates by the high-pressure process is the high cost of investment for the multi-stage presses, the hotwater boiler and the cooling installation, as well as for the numerous metal sheets and the padding required.

A duroplastic resin modified with thiourea is already known from DE-OS 20 27 085: it allows resin-impregnated chipboard to be pressed in from 45 to 120 seconds, recooling before removing the board from the press being unnecessary, and imparts to the resulting product increased acid resistant and dye fastness and improved water resistance in the boiling test.

There has been no lack of attempts to produce such laminates continuously and without recooling using simpler presses. This was first achieved by laminating together resin-impregnated decorative paper and a carrier material on a so-called double band press in a width of approximately 50 cm.

Initially only pressures of from 100 to 200 newtons/cm2 were achieved with such double band presses, which meant that the possible variations in the condensation products to be used were very limited. Only highly free-flowing resins, which consequently could not satisfy all the demands made on them, could be processed on these processes. For that reason the laminates produced in this manner could be used substantially only as edge strips for laminated chipboards.

It was possible eventually to increase the pressures that could be achieved with the double band presses to from 350 to 400 newtons/cm2 and to widen the working width to over a metre. Using suitable resin compositions it was possible to obtain high-quality laminates at passage speeds of approximately 30 seconds or more. The advantages of this process are considerable savings in energy and personnel costs in comparison with discontinuous presses and the avoidance of waste as a result of the continuous format.

The continuous production of laminates becomes more interesting economically the more the passage speed of the material to be pressed can be increased.

As the passage speed was increased further, that is to say at pressing times of less than 30 seconds, blisters began to form in the laminate and the layers began to separate during the boiling test. Attempts to accelerate the curing rate of the melamine resin by increasing the amount of curring agent added were not successful, as the heat radiated from the pressing sheets upstream of the pressing zone was already causing excessive condensation of the resin, as a result of which the resin no longer reacted or flowed completely and the surfaces were therefore no longer unbroken.

There is therefore a need to develop a resin which produces pressed laminates and/or laminated sheets of derived timber products of a quality that satisfies the highest requirements in a very short pressing time in a continuous press.

We have found that a fast curing condensation product based on aminoplastic resin formers, formaldehyde and thiourea and containing a separating agent and, if desired, one or more other additives, for example plasticiser, guanamine, wetting agent and/or curing agent, gives good results.

Although technology has for a long time required faster and faster curing condensation products for producing laminates, laminated chipboards, laminated hardboards and so on, it was surprising that no products have hitherto been found that impart to the end products the required properties as regards surface, shine, hardness, colour fastness and resistance to boiling.

We believe it is only the discovery of the condensation product according to the invention that has allowed such properties to be achieved that make it suitable for use in fast-running band laminating installations.

Accordingly, the present invention provides a composition for preparing a fast curing condensation product which comprises an aminoplastic resin former, formaldehyde, thiourea, and a separating agent.

The invention also provides a fast curing condensation product obtainable from a composition of the invention.

If desired, a guanamine and/or one or more other additives selected, for example, from plasticiser, wetting agent and curing agent, may be present in the composition.

Suitable aminoplastic resin formers are, for example, melamine, urea and thiourea, and also aceto- and benzo-guanamine.

Suitable separating agents present in the condensation product of the invention are, for example, guanamine and salts of long-chain fatty acids having more than 10 carbon atoms and fatty acid esters such as, for example, glycerine stearate. it is preferable to use guanidine salts of long-chain (Cao-C20) fatty acids, guanidine stearate or palmitate being especially preferred. An adequate effect is achieved by adding only relative small amounts.

Preferably the formaldehyde is used in the form of an aqueous solution having a concentration of at least 30% by weight.

If desired, a plasticiser may be used in the condensation product according to the invention, in which case it is present in bound form after the condensation product has been pressed.

Suitable plasticisers are, for example, glycols, e.g. diethylene glycol, dipropylene glycol or dibutylene glycol, and also sugar, sorbitol, caprolactam and toluene sulphonamide; more especially, diethylene glycol is used.

Also if desired, a guanamine, more especially an alkyl-substituted guanamine, may be used in the condensation product of the invention. Suitable guanamines are, for example, caprinoguanamine, dodecyl- or butyro-guanamine, more especially caprinoguanamine. The guanamine may serve both as plasticiser and separating agent.

Thus, for example, the condensation product may consist of formaldehyde, melamine and thiourea and contain a separating agent and optionally a plasticiser. The product may include a small amount of a guanamine having from 1 to 12 carbon atoms in the chain. Before the impregnation princess, if desired a wetting agent and/or a curing agent may also be added to the resin solution.

A preferred fast curing condensation product according to the invention is obtained from the following molar ratios of the constituents: 1.5 to 2.5 mol of formaldehyde 1.0 mol of melamine 0.1 to 1.0 mol of a glycol, e.g.

ethylene or diethylene glycol 0.02 to 1.0 mol of thiourea 0.00005 to 0.005 mol of guanidine stearate 0.00010 to 0.005 mol of aliphatically substituted guanamine One such condensation product, produced from this composition, had a co-efficient of viscosity of from 12 to 25 seconds in a Ford DIN beaker with a 4 mm nozzle at 20"C.

In the condensation product suitable for impregnating backing paper, up to 100 % by weight of the malamine may, if desired, be replaced by urea, the proportion of thiourea being increased at the same time. Thus, a further preferred composition is as follows: 1.5 to 2.5 mol of formaldehyde 0.01 to 0.5 mol of melamine 0.1 to 0.9 mol of urea 0.1 to 0.9 mol of thiourea 0.00005 to 0.005 mol of guanidine stearate All three aminoplastic resin formers taken together require an amount of from 1.5 to 2.5 mol of formaldehyde in order for a correspondingly suitable resin composition to be obtained. A small amount of guanidine stearate serves, in this case also, as a separating agent.

The conditions for condensation should, generally, be maintained in such a manner that clear resin solutions are obtained.

To improve the wetting of the carrier materials (paper sheets) a wetting agent may, if desired, be added to the condensation product of the invention. Suitable wetting agents are non-ionic and anionic wetting agents, preferably non-ionic wetting agents based on ethoxylated phenols, alcohois or amines. Preferably, the wetting agent is added to the prepared resin solution.

Also, if desired, in order to accelerate the curing, a small amount of a latent, commercially available curing agent, such as, for example, an amine salt or p-toluenesulphonic acid, may be added to the condensation product of the invention. The addition is suitably carried out after preparation of the resin and before it is used.

Production of the resin solutions may be effected by adding together all the components in an aqueous medium at a pH in the range of from 6.5 to 10.5, followed by condensation at a temperature in the range of from 80 to 100"C until the whole is from 10 to 50% dilutable with water. It is preferable, however, first to produce a preliminary condensate from formalin, aminoplastic resin former(s) and, if used, part of the plasticiser at a pH in the range of from 8.5 to 10 and for the thiourea to be condensed at a temperature in the range of from 8 to 100"C only once the hydrophobic point has been reached and the pH has been adjusted again. When the condensation is complete the separating agent and the remainder of plasticiser, if used, are added to the cooled resin solution.Subsequent addition of thiourea and plasticiser brings about good storage stability of the resin solution over several weeks.

Resin solutions for impregnating the backing paper may be produced in analogous manner. In order to obtain especially clear and stable resin solutions, in this case a preliminary condensate may first be made from formalin and urea, and thiourea, urea and, if desired, melamine are added thereto, then when the condensation product is from 10 to 50% dilutable, thiourea is added again and after cooling the separating agent, for example methanolic guanidine stearate solution, is added. It is, however, also possible to produce these resins by condensing all the components together.

The plasticiser and guanamine may, to a certain degree, take part in the condensation reaction.

The wetting agent and curing agent do not condense.

Fast curing condensation products according to the invention are outstandingly suitable for impregnating paper sheets for the continuous production of laminates or laminated derived timber products in so-called double band presses. There has been a need for these for many years. Thus, what might appear as relatively small differences in composition and production process from known resins have brought about significant changes in properties: although the pressing time is less than 25 seconds in the double band (twin belt) presses, the surfaces of the products produced from condensation products of the invention by means of such presses have the requisite valuable properties, such as a high shine, completeness of the surface (i.e. unbroken surface), sufficient hardness, high resistance to steam and boiling and excellent properties as regards their ability to be dyed.

The condensation products according to the invention may, of course, also be used to produce laminates, derived timer products or laminated hardboard using discontinuous presses, such as, for example, multistage presses. Especially short pressing cycles can be achieved as a result.

The following Examples illustrate the invention.

Example 1 Resin for surface laminating 654.2 parts by weight of 30% formalin, 40.1 parts by weight of diethylene glycol and 408.9 parts by weight of melamine were introduced at room temperature into a special-steel boiler equipped with stirrer, heating device and cooling device. The pH of the suspension was adjusted to 9.4 by adding 3.545 parts by volume of 1N sodium hydroxide solution and the whole was heated to 90"C in the course of 30 minutes. When the hydrophobic point had been reached (clouding on introduction of a drop of the condensation product into clear water), which established itself after a condensation time of approximately 90 minutes, 0.955 parts by volume of 1N sodium hydroxide solution and 28.6 parts by weight of thiourea were added.Condensation was continued until the precipitation value was 1.6, that is to say until 1 part by volume of resin solution with 1.6 parts by volume of water at 20"C showed clouding. The contents of the boiler were cooled rapidly to 40"C and at this temperature a solution consisting of 0.119 parts by weight of guanidine stearate in 2.261 parts by weight of methanol and 68.2 parts by weight of diethylene glycol was stirred into the resin.

The clear resin solution had a run-out or discharge time of 17 seconds, measured with a Ford beaker with a 4 mm nozzle at 20"C. The viscosity did not change for a period of 3 weeks.

Example 2 Resin for surface laminating 480 parts by weight of 30% formalin were introduced into a special-steel boiler and 2.8 parts by volume of 1N sodium hydroxide solution were added. After the addition of 29.4 parts by weight of diethylene glycol, 1.5 parts by weight of caprinoguanamine and 300 parts by weight of melamine, the pH of the suspension was 9.4. The contents of the boiler were heated to 90"C in the course of 30 minutes and when the hydrophobic point had been reached 0.7 parts by volume of 1N sodium hydroxide solution and 21 parts by weight of thiourea were added.

Condensation was continued at 90"C until the precipitation value was 1.8 and the whole was then cooled rapidly. At 40"C a solution of 0.089 parts by weight of guanidine stearate in 1.681 parts by weight of methanol and 50 parts by weight of diethylene glycol were stirred into the resin.

The resin had a run-out time of 18 seconds, measured with a Ford beaker with a 4 mm nozzle at 200C.

Example 3 Resin for impregnating the backing paper (core layers) 620 parts by weight of 30% formalin and 63 parts by weight of paraformaldehyde (95% strength) were introduced into a special-steel boiler and the pH was adjusted to 6.5 with 0.688 parts by volume of 1N sodium hydroxide solution. After the addition of 165 parts by weight of urea the mixture was heated to 90"C in the course of 40 minutes. The temperature was increased to 95"C and maintained for 40 minutes. After cooling to 900C, 178.7 parts by weight of thiourea and 18.3 parts by weight of urea were added and the whole was condensed further for 10 minutes at 85"C.

52.5 parts by weight of melamine were then added and the whole was condensed further until the precipitation value was 1.2 at 200C, which was achieved after a condensation time of approximately 30 minutes at 85"C. When this degree of condensation was reached, a further 4.6 parts by weight of thiourea were added, the whole was cooled to 40"C and a solution consisting of 0.11 parts by weight of guanidine stearate in 2.09 parts by weight of methanol was stirred into the resin solution.

Example 4 Continuous lamination of derived timber products (chipboard) White decorative paper (i.e. paper base) weighing 100 g/m2 was impregnated with the resin for surface laminating produced according to Example 1. Before the impregnation, the resin was mixed homogeneously with 0.1% by weight of a non-ionic wetting agent (Triton X 114) and 0.1% by weight of a curing agent based on an ammonium salt (Melpers RH 4) (the percentages being based in each case on the liquid resin and the curing agent being used in the form of a 25% aqueous solution). The resin had as a result a clouding time of 5 minutes at 100"C (the clouding time is the time after which a resin sample is completely cloudy after being suspended in boiling water).

The decorative (or decor) paper was impregnated with the resin solution adjusted in this manner in a customary resin-impregnating installation, dried in a downstream suspension dryer and then rolled up. The dried paper film had a weight of 225 g/m2 and its moisture content was 6.0to (determined by drying for 5 minutes at 1600C).

Using these impregnated paper films, 13 mm thick chipboards were laminated on both sides on a Hymmen system double band press. The pressing sheets were at a temperature of 175"C, the paper speed was 8 m/minute and the pressing pressure was 250 newtons/cm2. The pressing table was 2 m in length, producing a pressing time of 15 seconds.

The decorative boards (=laminated chipboards) produced in this manner had outstanding surface properties. The adhesion of the decorative film to the chipboard was excellent. The board surface was completely unbroken. The curing of the board surface was good. In the steam test (action of steam at 100"C on the board surface for 1 hour) no damage to the board surface was detected.The curing test, in which a sulphuric acid-containing rhodamine-B solution (consisting of 200 ml of water, 4 ml of concentrated sulphuric acid and 4 ml of 2% aqueous rhodamine-B solution) was allowed to act on the surface of the board for two hours at room temperature, showed a value of from 1 to 2 with respect to the dyeing, which is described as from very good to good curing Example 5 Continuous laminating of derived timber products (chipboards) The resin solution according to Example 1 was mixed with 0. 1 % by weight of wetting agent (Triton X 114) and 0.15% by weight of curing agent (Melpers RH 4) in the form of the 25% aqueous solutions. The clouding time of the resin solution was 4 minutes. A 100 g/m2 decorative paper was impregnated with this resin solution in a manner analogous to that described in Example 4.The dried paper films then weighed 230 g/m2, with a moisture content of 6.3%.

Using the installation mentioned in Example 4 again 13 mm thick chipboards were laminated under a pressure of 230 newtons/cm2 and at a temperature of 170"C. The belt speed was adjusted to 10 m/minute with the result that the pressing time was only 12.5 seconds. The laminated boards showed no signs of adhering to the pressing sheets. The board surfaces were unbroken. The curing test showed a value of approximately 2, based on dyeing with rhodamine B, which indicates that the curing was good.

Example 6 Continuous production of a laminate 0.1% by weight of wetting agent (Triton X 114) and 0.15% by weight of curing agent (Melpers RH 4) were added to the resin solution prepared according to Example 2, after which the resin solution had a clouding time of 4 minutes at 100"C. After impregnation by machine and drying to a moisture content of 6% the decorative paper, which was originally 100 g/m2, weighed 215 g/m2.

0.4% by weight of curing agent (Melpers RH 4) was added to the resin for the backing paper prepared according to Example 3 and 140 g/m2 of heavy sodium kraft paper was impregnated therewith. After drying to a residual moisture content of 5.4%, the weight of the paper was 250 9lem2.

The rolled-up impregnated papers were drawn into a double band press in such a manner that three backing sheets were pressed with one decorative sheet on top. At a band speed of 8 m/minute and a pressing table length of 2 m the pressing time was 15 seconds. The pressing pressure was 400 newtons/cm2 and the temperature of the pressing sheets 170"C. On leaving the press the individual films had been bonded into a laminate free from blisters. Even the boiling test, in which sample pieces of the laminate were held for two hours in boiling water, did not cause any delamination. In the steam test (the action of steam at 100 C for orje hour), no small blisters were to be seen on the decorative side of the laminate produced according to the invention.The curing test, which was caried out on the basis of the laminate's dyeability with rhodamine-B solution containing sulphuric acid (cf. Example 4), produced values of 1 to 2. The laminate was therefore completely cured even after such a very short pressing time.

Comparative Example A decorative paper weighing 100 g/m2 was impregnated with a resin solution according to DE-OS 20 27 085, dried to a moisture content of 6% and rolled up into a film sheet.

A sodium kraft paper impregnated with commercially available phenolic resin was used as backing paper.

Three sheets of the paper impregnated with phenolic resin were pressed with a sheet of the decorative paper in a double band press under the conditions of Example 6, that is to say for 15 seconds at a temperature of 170 C and under a pressure of 400 newtons/m2. As soon as the laminate left the press, numerous blisters could be seen between the layers. Virtually complete delamination took place during the boiling test and the steam test produced a shabby surface.

Claims

1. A composition which comprises an aminoplastic resin former, formaldehyde, thiourea, and a separating agent.

2. A composition as claimed in claim 1, wherein the aminoplastic resin former comprises melamine.

3. A composition as claimed in claim 1, wherein the aminoplastic resin former comprises urea.

4. A composition as claimed in claim 1, wherein the aminoplastic resin former is urea in combination with thiourea.

5. A composition as claimed in claim 2, wherein formaldehyde, melamine and thiourea are used in a ratio of 1.5 to 2.5 mol of formaldehyde, 0.02 to 1.0 mol of thiourea: 1.0 mol of melamine.

6. A composition as claimed in claim 3, wherein formaldehyde, melamine, urea and thiourea are used in a molar ratio of 0.01 to 0.5 mol of melamine, 0.1 to 0.9 mol of urea, and 0.1 to 0.9 mol of thiourea: 1.5 to 2.5 mol of formaldehyde.

7. A composition as claimed in any one of claims 1 to 6, wherein the separating agent comprises guanamine, a salt of a fatty acid or a fatty acid ester or two or more such compounds.

8. A composition as claimed in claim 7, wherein the separating agent comprises guanidine stearate or guanidine palmitate.

9. A composition as claimed in claim 1, comprising the following compounds in the following specified molar proportions: 1.5 to 2.5 mol of formaldehyde

1.0 mol of melamine 0.1 to 1.0 mol of glycol, 0.02 to 1.0 mol of thiourea 0.00005 to 0.0050 mol of guanidine stearate 0.00010 to 0.0050 mol of guanimine.

10. A composition as claimed in claim 1, comprising the following compounds in the following specified molar proportions: 1.5 to 2.5 mol of formaldehyde 0.01 to 0.5 mol of melamine 0.1 to 0.9 mol of urea 0.1 to 0.9 mol of thiourea 0.00005 to 0.0050 mol of guanidine stearate.

11. A composition as claimed in any one of claims 1 to 10, which includes guanamine and/or one or more other additives selected from plasticiser, wetting agent and curing agent.

12. A composition as claimed in claim 11, wherein the plasticiser comprises dithylene glycol.

13. A composition as claimed in claim 11 or claim 12, wherein the guanamine component comprises caprinoguanamine.

14. A composition as claimed in any one of claims 11 to 13, wherein the wetting agent comprises an ethoxylated phenol, alcohol or amine wetting agent.

15. A composition as claimed in any one of claims 11 to 14, wherein the curing agent comprises an amine salt or p-toluenesulphonic acid.

16. A composition as claimed in claim 1, substantially as described in any one of Examples 1 to 6 herein.

17. A condensation product obtainable from a composition as claimed in any one of claims 1 to 16.

18. A condensation product which is based on an aminoplastic resin former, formaldehyde and thiourea, and containing a separating agent, and, if desired, including a guanamine and/or one or more of the other components selected from plasticiser, wetting agent and curing agent.

19. A condensation product as claimed in claim 18, wherein the aminoplastic resin former is as specified in any one of claims 2 to 6.

20. A condensation product as claimed in claim 18 or claim 19, wherein the separating agent is as specified in claim 7 or claim 8.

21. A condensation product as claimed in claim 18, having molar proportions of constituents as specified in claim 9 or claim 10.

22. A condensation product as claimed in any one of claims 18 to 21, wherein the plasticiser is as specified in claim 12.

23. A condensation product as claimed in any one of claims 18 to 22, wherein the guanamine component is as specified in claim 13.

24. A condensation product as claimed in any one of claims 18 to 23, wherein the wetting agent is as specified in claim 14.

25. A condensation product as claimed in any one of claims 18 to 24, wherein the curing agent is as specified in claim 15.

26. A condensation product as claimed in claim 18, having a composition substantially as described in any one of Examples 1 to 6 herein.

27. A process for the preparation of a condensation product as claimed in claim 17 or claim 18, wherein the condensation reaction is carried out in one or more stages in the presence or absence of the remaining components.

28. A process as claimed in claim 27, which is a one-stage reaction carried out at a pH in the range of from 6.5 to 10.5.

29. A process as claimed in claim 27 or claim 28, which is carried out at a temperature in the range of from 80 to 100"C.

30. A process as claimed in claim 27, which is a two-stage reaction, the thiourea being added in the second stage.

31. A process as claimed in claim 30, wherein plasticiser is added in the first stage and after the second stage.

32. A process as claimed in claim 27, which is a multi-stage reaction including a preliminary condensation of formaldehyde and urea, followed by addition of thiourea, urea and, if desired, melamine, and subsequent addition in the final stage of thiourea.

33. A process for the preparation of a condensation product as claimed in claim 17 or claim 18, which comprises (a) condensing the aminoplastic resin former, formaldehyde and if desired from 1/4 to 1/2 of total plasticiser and/or of the guanamine at a pH in the range of from 6.5 to 10.5 at a temperature in the range of from 80 to 100"C, until the hydrophobic point is reached, (b) adding thiourea, adjusting the pH to a value in the range of from 8.5 to 10 and condensing at a temperature in the range of from 80 to 100"C until the whole is dilutable with water in a ratio such as 1:1.0 to 2.0, (c) cooling to a temperature in the range of from 30 to 50"C and adding the separating agent and if used the remaining amount of plasticiser, and, if desired, (d) adding wetting agent and/or curing agent.

34. A process as claimed in any one of claims 27 to 33, wherein when urea and thiourea are used as aminoplastic resin formers the condensation is carried out at a pH in the range of from 6.5 to 8.0.

35. A process as claimed in any one of claims 27 to 34, wherein the formaldehyde is used in the form of an aqueous solution having a concentration of at least 30%.

36. A process as claimed in claim 27, carried out substantially as described in any one of Examples 1 to 6 herein.

37. A condensation product as claimed in claim 17 or claim 18, whenever prepared by a process as claimed in any one of claims 27 to 36.

38. A process for the production of laminates and/or derived timber products, wherein there is used a condensation product as claimed in any one of claims 17 to 26 and 37.

39. A process as claimed in claim 38, wherein the production of the laminates and/or derived timber products is carried out in a double band press under a pressure of at least 200 newtons/cm2, at a pressing temperature of from 150 to 180"C and for a pressing time of less than 25 seconds.

40. A process as claimed in claim 38, carried out substantially as described in any one of Examples 4 to 6 herein.