GB1561909A - Urea formaldehyde resin moulding composition - Google Patents

Description

(54) A UREA FORMALDEHYDE RESIN MOULDING COMPOSITION (71) We, DYNAMIT NOBEL AK TIENGESELLSCHAFT, a German company of 521 Troisdorf, Postfach 1209, Germany (Federal Republic), do hereby declare the invention, for which we pray 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:- This invention relates to urea formaldehyde resin moulding compositions and a hardener therefor.

It is known that urea formaldehyde resin moulding compositions are among the starting materials used for thermosetting plastics. Such compositions are normally produced in the following stages: to begin with, the resin is formed by the condensation of urea and formaldehyde, preferably in aqueous-alkaline medium, followed by the addition of a suitable hardening catalyst. This resin/hardener mixture is then mixed with fillers, such as cellulose or sawdust, lubricants, such as zinc stearate, pigments and optionally plasticisers, such as waxes. The mixture obtained is dried at temperatuers around 80" C and then compacted to form a free-flowing granulate.

Hardening of the urea formaldehyde resin moulding compositions into dimensionally stable plastics articles is normally carried out in heated moulds under pressure at temperatures of from 130 to 1700 C by compression moulding, transfer moulding or injection moulding, compression moulding normally being carried out under pressure of from 300 to 500 kp/cm2 and transfer moulding and injection moulding under pressure of from 1300 to 2000 kp/cm3.

The hardening process, which takes place under the effect of heat and pressure, is based on the crosslinking of the urea formaldehyde resin into a macromolecular structure initiated by the acid reaction of the hardening catalyst used.

The hardening catalysts used by urea formaldehyde moulding compositions are substances which is possible show a basic or neutral reaction at temperatures of around 800 C and which only develop an acid effect at the higher processing temperatures, thereby initiating the crosslinking of the resin. The effect of using hardeners which show an acid reaction, even at relatively low temperatures, is that the resin/ hardener mixtures normally produced at temperatures of from 40 to 500 C are inade quately stable. There is also a danger of premature hardening occurring at the drying tempera tures of approximately 800 C used in bulk production, resulting in an undesirable de crease in the flow properties of the bulk-pro- duced product.In addition, urea formaldehyde resin moulding compositions produced with acid hardeners are unstable in storage, especially at summer temperatures.

There is thus a need for latent hardeners for urea formaldehyde resin moulding compositions which essentially show a basic reaction at temperatures of up to 800 C and only develop a hardening-accelerating effect at the normal processing temperatures through the release of acid.

The hardening accelerators for urea moulding compositions proposed in German Offenlegungsschrift No. 1,933,303 include inter a(ia water-solubel zinc salts of non-reducing acids, preferably zinc nitrate and zinc sulphate.

Their aqueous solutions are known to show an acid reaction. Reference is also made in this document to complex compounds of zinc salts with ammonia, pyridine, dimethyl formamide or formaldehyde, with the qualification that it is not possible to obtain rapid hardening with the neutrally reacting and alkaline reacting substances. Thus, reference is made in the Examples to a 15 0/o solution of zinc chlor- ide in dimethyl formamide which has pH values of 6.6 at 400 C and 5.9 at 800 C.

According to the present invention there is provided a moulding composition comprising a urea formaldehyde resin ard, as hardener therefor, a zinc ammine sulphate.

These zinc sulphate-amine complexes show a basic reaction up to a temperature of approximately 800 C and, accordingly, occupy a special position in relation to the zinc salts hitherto known as aminoplast hardeners. The use of basic zinc amine sulphates as hardeners for urea formaldehyde resins has meant that the moulding compositions according to the invention are generally more resistant to temperature influences during their production and, accordingly, show increased fluidity as end products. They are also generally more resistant to ageing and harden more quickly under normal processing conditions than with conventional hardening accelerators. In addition, the moulding hardened with zince ammine sulphates, especially with zinc tetrammine sulphate, generally show increased elasticity and improved breaking strength.

The zinc ammine sulphates used in compositions of the invention may be characterised by the formula [Zn(NH3)Y]SOt, in which x assumes a value of from 1 to 8. Preferably the zinc ammine sulphate contains from 3 to 6 moles of ammonia per gram atom of zinc.

They are usually obtained by adding the required quantity of ammonia to zinc sulphate.

It is preferred to add an aqueous ammonium hydroxide solution to an aqueous zinc sulphate solution, although it is also possible to introduce gaseous ammonia into an aqueous zinc sulphate solution.

The quantity in which the zinc ammine sulphates are present in compositions according to the invention is preferably from 0.5 and 5.0% by weight, based on the amount of solid resin, and more preferably in a quantity of from 1.0 to 3.5% by weight.

The urea formaldehyde resins used for the production of the compositions are produced in known manner, for example as follows: urea and formaldehyde, preferably in a molar ratio of from 1:1.2 to 1:1.8, are condensed at elevated temperature (for example 40-700 C) in an aqueous-alkaline medium. The water formed is then distilled off in wrcruz until the liquid resin has reached the required density, for example a density of approximately 1.2 g/cc (400 C).

The hardener according to the invention, and any fillers, lubricants, pigments, plasticisers and other additives are added to this liquid resin, followed by drying and grinding.

The powder-form moulding compositions thus obtained are then granulated. The granules obtained may then be processed in known manner into mouldings by compression mould ing or injection moulding. The quantity in.

which the additives are added to the liquid resin is such that the final moulding composition preferably contains from 55 to 70% of solid resin. The filling additives preferably predominantly contain cellulose-containing material. The other additives are preferably only present in quantities of from 0.5 to 5% by weight in each case, based on the moulding composition.

The following Examples illustrate the inven tion. The tests for fluidity, decrease in fluidity under the influence of temperature (ageing resistance), hardening rate and moulding elasticity mentioned therein were carried out by the methods described below.

1. Determining fluidity and resistance to age ing A tablet-form specimen of the moulding composition weighing 1.0 g was moulded in a cylindrical flowduct 3.2 mm in diameter in a standard fluidity tester (manufactured by Zwick & Co.) at a temperature of 1560 C and under a pressure of 75 kp/cm2. The length of the flow rod developed (in mm) and the corresponding flow time (in seconds) give a measure of the fluidity of the composition.

In order to determine resistance to ageing, the fluidity test was repeated with a specimen composition which had been aged by storing for 4 days at a temperature of 50 C. The decrease in flow rate relative to the non-aged composition was measured.

2. Determining the hardening rate Round plaquettes with a wall thickness of 3.2 mm and a diameter of 80 mm were produced at a moulding temperature of 1500 C, under a moulding pressure of 500 kp/cm2 and with moulding times of 60, 90 and 120 seconds. After storage for about 24 hours, the mouldings were boiled for 30 minutes in an aqueous solution of the red dye " Rhodamin B extra" in accordance with DIN 53 499, subsequently removed from the boiling vessel, rinsed with hot water, dried off and cooled to room temperature.

Depending upon their degree of hardening, the mouldings showed different coloration, the intensity of which was graduated on a scale of 1 to 6. On this scale, 1 represents no coloration and very good hardening, whilst 6 represents heavy coloration and inadequate hardening.

Accordingly, the application of this evaluation scale to mouldings in dependence upon their moulding time is a measure of the hardening rate of the particular specimen composition used.

3. Determining moulding elasticity The specimen composition was moulded to form standard beakers in the mould according to DIN 53 465 at a temperature of 1500 C and with hardening times of 45, 90 and 180 seconds.

The beakers, with an orifice 74 mm in diameter, were cooled to room temperature and deformed to fracture in the vicinity of their upper rim zone in a vice-like tester by the application of a uniformly increasing force.

The gap between the jaws of the vice at fracture was a measure of the breaking strength of the moulding.

EXAMPLE 1.

a) A solution of 60 g of ZnSO, 7 H20 in 130 g of water, and b) an aqueous solution of 60 g of ZnSO4 . 7 H2O with different additions of aqueous ammonia, in all six solutions with an integral molar ratio of ammonia to zinc sulphate of from 1:1 to 6:1, were stirred into seven resin samples, each of 5730 parts by weight, of a urea-formaldehyde condensation product produced in known manner with a solid resin content of 47.5% and a pH value of 8.ó.

The seven resin/hardener mixtures obtained were separately mixed in the same way with 1340 parts by weight of cellulose, 48 parts by weight of zinc stearate and 66 parts by weight of pigments, dried at a temperature of approximately 80" C, ground and then granulated.

The granular compositions with moisture contents of approximately 7% by weight were tested for fluidity, resistance to ageing, hardening rate and moulding elasticity by the methods described above. The results are set out in Table 1.

It can be seen from Table 1, that, by comparison with zinc sulphate, the zinc ammine sulphates with a molar ammonia content of > 3 have a more favourable effect as hardeners upon the fluidity and resistance to ageing of the urea formaldehyde resin mould ing compositions. In addition, accelerated hardening of the compositions, surprisingly associated with increased elasticity of the mouldings, is obtained, especially in cases where tri-, tetra- and penta-ammine compounds of zinc sulphate are used.

EXAMPLE 2.

(Comparison Example) For comparison with Example 1, the effect of complex compounds of zinc nitrate and zinc chloride with ammonia and dimethyl formamide as hardener in urea resin moulding compositions was investigated in the test compositions described below.

a) A solution of 55 g of Zn(NO), .6 H20 in 130 g of water, b) an aqueous solution of 55 g of Zn(NOs)2 . 6 H20 with such a quantity of aqueous ammonia added that the molar ratio of ammonia to zinc nitrate amounted to 4:1, and c) 300 ml of a 15% ZnCl2 solution in di methyl formamide, were added to three resin samples, each of 5730 parts by weight, of the urea-formaldehyde condensate of Example 1.

The three resin/hardener mixtures were separately worked up into cellulose-filled granular compositions with moisture contents of approximately 7% by weight under the conditions described in Example 1.

According to the test results set out in Table 2, zinc nitrate and zinc chloride, in contrast to zinc sulphate (Example 1, Table 1), as hardeners in urea resin moulding compositions show no improvement in hardening rate or moulding elasticity where they are present in the form of complex compounds with ammonia or dimethyl formamide. In addition, the resistance to ageing of the urea resin moulding composition is distinctly lower in cases where the zinc chloride/dimethl formamide solution is used as opposed to the zinc ammine sulphates according to the invention. TABLE 1 Fluidity, hardening rate and moulding elasticity of the test compositions according to Example 1

Test Composition No. 1 2 3 4 5 6 7 Hardener: Zn(NH3)x SO4 x = 0 1 2 3 4 5 6 Flow rate of fresh composition (mm/sec) 52/25 55/25 58/23 71/11 74/11 74/20 73/21 Flow rate after 4 days at 50 C (mm/sec) 30/29 33/27 35/25 60/16 65/18 65/24 62/25 Flow rate reduction after 4 days at 50 C (%) 50.29 44.45 44.48 41.89 46.32 26.8 28.65 Moulding hardening (on 1 to 6 scale) for moulding times of 45 secs 4 4.5 3 2 2 3 4 90 secs 2.5 3 2.5 1.5 1 2 2.5 120 secs 1 1.5 1.5 1 1 1 1 (moulding temperature 150 C) Elasticity Test (standard beaker) jaws at fracture (mm) for moulding times of 45 secs 55.0 53.4 53.1 52.0 49.4 52.5 54.2 90 secs 53.8 52.9 52.4 50.5 48.9 50.9 55.4 180 secs 53.4 52.9 52.3 50.7 49.1 50.4 53.6 (moulding temperature 150 C) TABLE 2 Fluidity, hardening rate and moul@ding elasticity of the test compositions according to Example 2

Test No. 1 2 3 Hardener Zn (NO3)2 Zn (NH3)4 (NO3)2 ZnCl2 dissolved in dimethyl formamide Flow rate of fresh composition (mm/sec) 55/26 74/33 72/19 Flow rate after 4 days at 50 C (mm/sec) 32/31 65/35 41/28 Flow rate reduction after 4 days at 50 C (%) 51.2 17.17 61.36 Moulding hardening (on 1 to 6 scale) f@@ moulding times of 45 secs 4 4 4 90 secs 2 2.5 2.5 120 secs 1 1 1 (moulding temperature 150 C) Elasticity Test (standard beaker) jaws gap at fracture (mm) for moulding times of 45 secs 56.7 57.6 59.5 90 secs 55.3 56.3 58.9 180 secs 55.8 57.4 57.8 (moulding temperature 150 C)

Claims (9)

WHAT WE CLAIM IS:-

1. A moulding composition comprising a urea formaldehyde resin and, as hardener therefor, a zinc ammine sulphate.

2. A moulding composition according to claim 1 wherein the zinc ammine sulphate contains from 3 to 6 moles of ammonia per gram atom of zinc.

3. A moulding composition according to claim 1 or 2 which contains from 0.5 to 5.0% by weight of the zinc ammine sulphate, based on the weight of resin.

4. A moulding composition according to claim 3 and containing from 1.0 to 3.5% by weight of the zinc ammine sulphate, based on the weight of resin.

5. A moulding composition according to any one of the preceding claims which comprises urea and formaldehyde condensed in a molar ratio of 1:1.2 to 1:1.8.

6. A moulding composition according to any one of the preceding claims which includes a cellulose-containing material as filler.

7. A moulding composition according to claim 6 comprising from 55 to 70 /O of solid resin.

8. A moulding composition according to claim 1 substantially as hereinbefore described with reference to Example 1.

9. An article when comprising a moulding formed from a moulding composition according to any one of the preceding claims.