CA1062596A

CA1062596A - Resin impregnant containing water soluble sillcate

Info

Publication number: CA1062596A
Application number: CA234,550A
Authority: CA
Inventors: Theodorus H. Linders; Hubertus M.C. Stijnen; Arie Tinkelenberg
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1974-09-06
Filing date: 1975-09-02
Publication date: 1979-09-18
Also published as: JPS5179181A; NO144596C; ES440748A1; FR2283777A1; SE425772B; BE832976A; CH584109A5; FR2283777B1; SE7509796L; ATA683275A; NL7502967A; NO753053L; IL48046A0; BR7505719A; IL48046A; NO144596B; FI752498A; DE2539650A1; GB1516344A

Abstract

ABSTRACT OF THE DISCLOSURE
Aminoplastic laminates and processes for their preparation are disclosed using a novel urea-modified melamine-formaldehyde resin system which resin has a urea content of 4-50%, a molar ratio of formaldehyde per three NH2 groups from the urea or melamine of between 1:1 and 2.5:1. The resin is used in solution and contains 0.2 to 1.4% of SiO2 present as a water soluble silicate. The resin system is impregnated into paper stock and laminated onto a suitable substrate such as particle board with heat and pressure. The resulting laminates arc less costly than melamine-formaldehyde based resins and are useful as decorative panels, countertops or the like.

Description

2764~
~C3 62596 This invention relates to the preparation of a laminate by applying a fibrous sheet material, e.g. paper, impregnated with an aminoplastic resin solution onto a substrate at an elevated temperature and pressure.
Laminates can be prepared by such a process by depositing an impregnated and dried paper on a suitable substrate, generally chipboard, inserting the assembly into a press, and operating the press at a tempera-ture between 125 and 175 C under a pressure between 10 and 50 kg/cm e.g.
for 3 to 6 minutes, after which the laminated assembly is allowed to cool in the press under pressure, According to the recently developed Kurztakt technique the assembly of substrate and impregnated paper is inserted into a heated press and compressed for 0.5 to 2 minutes at 125 to 200 C and 15 to 50 kg/cm pressure, the laminated assembly removed from the press whilst still hot and allowed to cool without pressure being maintained thereon.
The aminoplast resins used in such laminating processes are generally melamine-formaldehyde resins, which may contain one or more modiiiers to improve storage stability of the resin solution and/or the sur-face properties of the finished laminate. The resin solutions may contain if desired a small proportion of a water-soluble inorganic silicate, which serves to improve the stability of the resin solution and when present in sufficient amount, also effects improvement of the surface properties of the laminate, particularly when obtained by the Kurztakt process. It is desirable however that such solutions should be used in the form of a stabilized highly acid silicate solution. Furthermore they should be incorporated in the resin sglution very carefully in order to avoid flaking out of the sili-cate in the resin solution.
A disadvantage of melamine-formaldehyde resins is their high cost.
The less expensive urea-formaldehyde resins and urea melamine formaldehyde resins cannot be used for the preparation of laminates with a high-quality surface, and furthermore the laminates obtained have a low chemical resis-tance.

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The invention provides a process for preparing a laminate comprising impregnating a fibrous sheet material with a urea-modified melamine formal-dehyde resin solution, the said solution (a) having a urea content between 4 % and 50 % by weight based on the weight of urea plus melamine, (b) a molar ratio of formaldehyde to the three NH2 groups originating from urea or melamine of between 1 : 1 and 2.5 : 1, and (c) an inorganic water-soluble silicate in an amount corresponding to 0.2 to 1.4 % by weight of SiO2 based on the total weight of the said solution, and drying the impregnated fibrous sheet and applying the dried sheet to a substrate at an elevated temperature and pressure to form a laminate there-with.
By the practice of the invention laminates having a high-quality surface can be obtained using the relatively inexpensive urea-modified melamine-formaldehyde resin solutions which hitherto have been completely unsuitable for the preparation of laminates.
Furthermore the water-soluble silicate may readily be added to the urea-modified melamine-formaldehyde resin without special precautions.
Thirdly, the storage stability of 'pot-life' of the catalyzed silicate-containing urea-modified resin is greater than that of a silicate-containing pure melamine-formaldehyde resin.
The presence of the silicate in effecting the invention is essential for the production of a laminate having a surface of high quality with the urea-modified melamine-formaldehyde resins used in the process of the invention.
Preferably the fibrous sheet material used is paper.
The said urea-modified melamine-formaldehyde resin solution preferably has a urea content between 25 % and 40 % based on the weight of urea plus melamine and a said molar ratio between 1 : 1 and 2.5 : 1, more preferably between 1.2 : 1 and 2.0 : 1 particularly between 1.5 : 1 and 1.8 : 1 and has said silicate content between 0.4 % and 0~8 % based on the total weight of solution.

1~62596 The pH value of such a non-catalyzed resin solution may lie between ~.5 and 10.0 preferably between 9.0 and 9.5. A resin solution of this kind generally has a storage stability of a few weeks. The calculated solid content is preferably between 53 % and sB % by weight. If desired the resin solution may also contain conventional modifiers e.g. caprolactam, sugars, toluenesulphonamide, glycols and glycol ethers.
Such resin solutions can be obtained by $irst allowing melamine and formaldehyde to react in an aqueous solution in conventional manner, optionally in the presence of one or more modifiers. The formaldehyde to melamine molar ratio should then be smaller than 3.5 : l, preferably between

2 : 1 and 3 : l.
If the condensation has proceeded sufficiently far to a water compatibility between 2 and 6, urea is added, whereupon the condensation reaction is allowed to proceed for a short time or the resin solution cooled.
The pH of the resin solution thus obtained is generally between 9.0 and 9.5.
The resin solution may also be obtained by the mixing of a melamine-formaldehyde resin solution with a urea-formaldehyde resin solution.
The impregnating resin solution used according to the invention may contain between 4 % and 50 % by weight of urea based on the weight of urea plus melamine. At high urea contents the laminates may have a slightly poorer surface. The urea content may be very low at the expense of cost advantage, and thus it is preferable to use a resin solution with a urea content of between 25 % and 40 % by weight.
In some cases, it is desirable that laminates after curing may be reshaped or bent whilst being hsated, without deterioration of the surface properties. If laminates are prepared according to the invention using a resin solution containing between 0.2 and 1.4 % by weight SiO2 based on the total weight of the solution and a F/3 NH3 ratio of between l : 1 and 1.5 : l, reshapeable laminates with satisfactory surface characteristics are obtained.
The silicate is responsible for improving the suriace characteristics both before and after reshaping (post-forming), without diminishing the reshape-ability.
,~, .

-l~;Z596 Since it is difficult to prepare melamine-formaldehyde resin solutions with a formaldehyde/3NH2 ratio which is substantially lower than 1,5, a urea content of at least 4 %, based on uroa plus melamine, is required to bring the formaldehyde/3NH3 ratio below 1,5 : 1, while larger proportions of urea make it possible to commence with a higher formaldehyde/melamine ratio and/or to achieve a lower final value for the formaldehyde/3NH~ ratio, The cost price of the resin decreases and the reshapeability of laminates obtained using said resin solutions increases with increasing urea content, but the surface properties tend to deteriorate at an increasing urea content notwithstanding the presence of the silicate.
A particularly useful urea-modified melamine-formaldehyde impregna-ting resin solution for use according to the invention in the preparation of post-formable laminates comprises a molar ratio of formaldehyde/3N~2 groups originating from urea or melamine of between 1 : 1 and 1,5 : 1, a urea content of 4 to 20 % by weight based on the weight of urea plus melamine, and a water-soluble inorganic silicate content corresponding with an SiO2 content of the solution of between 0.2 and 1.4 % by weight.
~eduction of the formaldehyde/3NH2 iatio improves the reshapeability but causes the surface properties to deteriorate owing to enlargement of the amount of urea used, The optimum formaldehyde/3NH2 ratio lies between 1,2 : 1 and 1,4 : 1, The imprGgnating resin solution is prepared by first condensing melamine and formaldehyde in the usual way at a formaldehyde/3NH2 ratio of between approximately 2 : 1 and 1,5 : 1 and subsequently adding urea, and if desired continuing the condensation for a short time.
Since the silicate-containing resin solution having a silicate content of more than about 0.2 % SiO2 has only a limited storage stability, the silicate is added to the resin solution shortly before the impregnation step is commenced. The silicate may be added in the form of an aqueous solution to the resin solution.

;Z596 If a concentrated silicate solution is used the formation of gel-like flakes may take place, so that preferably a silicate solution is used containing i'rom 10 % to 20 % by weight of SiO2.
The pH value of the resin solution may rise to about 11 when the silicate is added. Before, during or after the addition of silicate the resin solution is usually catalyzed by setting the pH between 7 and 9, particularly between 8.5 and 9Ø These catalyzed resin solutions have a storage stability o~ at least 24 hours at 20 C. The acid catalyst may be added to the resin solution bef'ore, during or after the addition of the silicate solution.
Suitable acidic catalysts are ior instance formic acid, iormamidinesulf'inic acid, toluenesulphonic acid, oxalic acid, acetic acid, phtalic acid, ammonium chloride or diammoniumphosphate.
If silicate is added to a pure melamine-formaldehyde resin solution the risk of flaking-out increases to such an extent that the silicate is added in the ~orm of' a stabilized acid solution. The storage stability of catalyzed silicate-containing pure melamine-f'ormaldehyde resin solutions is significantly less than the storage stability of catalyzed urea modified melamine-formal-dehyde resins with the same silicate content.
Particular inorganic water-soluble silicates incorporated in the resin solution for use according to the invention are lithium silicate, sodium silicates, potassium silicates and quaternary ammonium silicates.
Particularly good results are achieved using aqueous solutions of sodium silicate..Generally, the silicate solution is added in a quantity so that the SiO2 content of the resin solution is between 0.2 % and 1.2 % by weight, preferably between 0.4 % and 1.0 % by weight, and particularly between 0.4 % and 0.8 % by weight.
The resin solutions for use according to the invention are applied f'or impregnation of paper or other fibrous material, followed by drying of the impregnated material and its processing into laminates. The impregnation is e~fected in the usual manner. The resin content of' the dried and impreg-nated material may be between 50 ~ and 60 % by weight. The percentage of volatile material may be between 5 % and 7.5 % by weight, preferably between 6 % and 6.5 % by weight .,, 1~6Z596 The impregnated and dried material may in the usual way be processed to form a laminate, or by the so-called Kurztakt process in which the material is compressed for a short time and cools outsicle the press, or by the con-ventional process according to which the laminate cools in the press.
The following Examples of the invention are provided:

Example I
A urea-modified resin solution was prepared by heating 52.4 kg of 30 % formalin having a pH value of 9.3, 23.6 kg of melamine, 8.7 kg of water and 0.6 kg of aqueous sodium silicate solution (SiO2/Na20 = 3.3) at 95 - 96 C
and by adding 12.8 kg oi' urea at the end oi the condensation reaction.
After cooling, the pH value of the resin solution was brought to approximately 9.5 by addition of dimethylaminoethanol.
Said resin solution was divided into three portions each of which was catalyzed and modified in the way indicated below. With the aid o~ the resin solutions obtained in this manner white decorative paper (90 g/m grade) was then impregnated. When dry, the decorative paper was pressed onto chipboard according to the Kur7takt process, the compression time amounting to 60 seconds and the temperature of the press plate to about 155 C. The surface of the laminates was judged for curing by means of the 'Kiton' colouring test, for surface compactness by the shoe wax test, and for crackle resistance by heating at 100 C in the air for 16 hours. The results are compiled in the table.
A. Starting from the resin solution described above, resin solution A
was prepared by adding 19 g of triethyleneglycolmonoethylether to every kg of the resin solution and by setting the B-time with toluenesulphonic acid at 99 sec. The B-time is an indication of the reactivity of the resin solution and represents the time required by a resin solution in a tube which is seal-melted and heated at 140 C to become turbid. Resin solution A has a total SiO2 content of 0.05 % and is not covered by the invention.
B. Resin solution B was prepared by adding 19 g oi' triethylene-glycolmonoethylether and 40 g of 18 % sodium silicate solution ~62596 (SiO2/Na20 = 3.3) per kg of resin solution, whilst stirring, and by subse-quently setting the B-time at 99 seconds with toluenesulphonic acid. The total SiO2 content amounted to 0.6 %.
C. Resin solution C was prepared by adding, with stirring, an acid, stabilized silicate solution to the resin solution to a total SiO2 content of 0.6 % and by setting the B-time at 95 seconds. The solution added contained toluenesulphonic acid, triethyleneglycolmonoethylether and sodium silicate (SiO2/Na20 = 3.3) and was obtained in the way described in the Netherlands Patent Application 72.10.402.
The properties of the laminates obtained with spplication of the resins A, B and C are listed below:

resin % of volatile 'Kiton' surface crackle solution matter in test compactness resistance impregnated paper A ) 6.7 4 ) 4 _ 5 B 6.9 2 - 3 1 - 2 C 7.2 2 - 3 1 - 2 Scale of judgment: 1 = excellent, 2 = good, 3 = fair~ 4 = poor, 5 = very poor.
)The 'Kiton' test continues to show strong discolouration also at longer compression times; the chemical resistance of the surface is too poor to allow of the curing degree being judged on the basis of this test.
)Not according to the invention.

Laminates obtained by compression in the conventional way have, virtually, the same properties.

Example II
A urea-modified resin solution was prepared by heating 29.1 kg of 30 %
formalin, which had been given a pH value of 9.3 with 0.2 kg of aqueous sodium silicate solution (18 weight % SiO2~ SiO2/Na20 = 3.3), together with 9.0 kg of ~06Z596 water and 25.3 kg of melamine to approximately 95 C until the capability of the formed resin solution of being diluted with water had attained a value of about 2.0 (at 20 C). At the end of the condensation reaction 1.3 kg of urea were added. In this way, resin solution A was obtained, F/3 NH2 = 1.35, containing 4.9 % by weight of urea referred to melamine plus urea.
In the same way a urea-modified melamine-formaldehyde solution was prepared, starting from 22.4 kg of melamine with addition of 3.4 kg of urea.
The solution (solution B) so obtained has an F/3 NH2 ratio of 1.35 and contains 13.1 % by weight of urea.
To each of the solutions A and B 38 g of sodium silicate solution (18 % by weight of SiO2, SiO2/Na20 = 3.3) per kg of resin solution were added with stirring, whereupon the B-time was set at about 100 seconds through addition of toluenesulphonic acid, the pH value then amounting to approximately 7.7 (resin solutions A' and B' respectively). The B-time is an indication of the reactivity of the resin solution and is the time a resin solution, heated at 140 C, in a seal-melted tube requires to become turbid.
For comparison, part of solution B, to which no silicate had been added, was in the same way given a B-time of about 100 sec. (resin solution C) by addition of toluene sulphonic acid.
Again for comparison, also a recipe was followed which is much applied for preparation of resin solutions used for reshapable laminates.
According to this recipe a melamine-formaldehyde resin solution (F/3 NH2 = 1.8), modified with a condensate of toluenesulphonic amide and formaldehyde, was set at B-time of 240 sec. with toluenesulphonic acid (pH = 9.0) (resin solu-tion D).
Each of the catalyzed resin solutions was used for impregnation of white decorative paper (90 gm/m2 grade) which, when having been dried in the usual way, with a laminate temperature of at most 148 C and cooling in the press, was pressed onto 6 layers of standard-quality, reshapable core paper which was impregnated with a phenol resin.
The laminates so obtained were then examined. The degree of curing .md the chemical resistance were examined by application of the well-known 1S36~596 'Kiton' colouring test. The reshapability was examined by locally heating the laminate with infra-red radiation to about 140 C and by bending it to a radius of 9 mm, whereupon the bending-face was judged for crack formation and loss of gloss The results are summarized in the table, in which the scale oi judgment ranges from 1 (excellent, no colouration, no cracks) to 5 (very poor).

resin B-time % of volatile 'Kiton' gloss bending-face solution matter in test crack formation impregnated paper :
A' 100 7.1 2 1 - 2 B' 107 5.5 1 - 2 1 - 2 C ) 96 6.0 3 - 4 2 - 3 D ) 240 5.5 2 1 - 2 2 - 3 -)not according to the invention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preparing a laminate comprising impregnating a, fibrous sheet material with a urea-modified melamine-formaldehyde resin solution, the said solution (a) having an urea content between 4 % and 50 % by weight based on the weight of urea plus melamine, (b) a molar ratio of formaldehyde to the three NH2 groups originating from urea or melamine of between 1 : 1 and 2.5 : 1, and (c) an inorganic water-soluble silicate in an amount correspond-ing to 0.2 to 1.4 % by weight of SiO2 based on the total weight of the said solution, and drying the impregnated fibrous sheet and applying the dried sheet to a substrate at an elevated temperature and pressure to form a laminate therewith.

2. A process according to claim 1, wherein the said inorganic silicate is present in the resin solution in an amount between 0.4 % and 0.8 % by weight of SiO2 based on the total weight of the said solution.

3. A process according to claim 1, wherein the said resin solution has a said molar ratio of formaldehyde/three NH2 groups of between 1 : 1 and 1.5 : 1 and contains from 4 % to 20 % by weight of urea based on the weight of urea and melamine.

4. A process according to claim 3, wherein the said molar ratio is between 1.2 : 1 and 1.4 : 1.

5. A process according to claim 1 wherein the said resin solution has a said molar ratio of formaldehyde/three NH2 groups of between 1.2 : 1 and 2.0 : 1 and contains from 25 % to 40 % by weight of urea based on the weight of urea and melamine.

6. A process according to claim 5, wherein the said molar ratio is between 1.5 : 1 and 1.8 : 1.

7. A process according to claim 1, wherein the said fibrous sheet is a paper sheet.