IE41929B1 - Moulding of filled synthetic plastics moulding compositions - Google Patents

Abstract

1532626 Injecting filled resin articles BRITISH INDUSTRIAL PLASTICS Ltd 7 Nov 1975 [12 Nov 1974] Heading B5A Filled resin articles are made by injection moulding either a non-homogeneous mixture of dry amino-formaldehyde material with a filler or separate charges of the dry material and filler using a reciprocating screw injection device. The screw is effective to render the components of the working material into a homogeneous blend and the prior art necessity of forming a homogeneous blend before feeding to the injection device is obviated. The filler may be powdered, for example powdered cellulose, woodflour, talc, chalk or powdered glass or may be fibrous for example asbestos, carbon, glass or cellulose fibres. Preferred resins are methylated urea or melamine, alkylated derivatives of them, or urea, or melamine formaldehyde. Mixtures of these with unsaturated polyester resins can be used.

Description

This invention concerns improvements in or relating to the moulding of thermosetting moulding compositions .

An essential feature of the manufacture of thermo5 setting moulding compositions has been the pre-mastication of the thermosetting resinous materials (used as curable matrix) with the filler(s) so that the latter becomes fully compounded with, impregnated by, and coated with, the resinous material. This may be effected under either 1 dry1 conditions where resinous material is essentially solid and is melted or fluxed during the mastication processing, or in the presence of a solvent or other liquid medium optionally followed by drying. _ The resultant moulding compound is subsequently converted, in a separate stage, into cured artefacts by a moulding or extrusion process.

U.S. Patent Specification No. 3746489 discloses a method of manufacturing glass fibre-reinforced mouldings by mixing the fibres and a liquid thermosetting resin material to form a viscous dough-like mixture which is fed continuously fdr direct transfer to an injection device having a nozzle through which the mixture is injected into the cavity of a mould for reaction of the mixture to form cured mouldings. The objects of this prior method are to facilitate handling of the glass 41829 - 3 fibres, to ensure adequate dispersion of the fibres in the resin material, and to maintain fibre length so that no significant loss of properties occurs. To meet these objects a special method of, and apparatus for, mixing the fibres with the resin material are proposed. The dough-like material fed directly from the mixing apparatus to the injection device is, essentially, a homogeneous intimate mixture of the fibres in the resin material, and, as is well known in the art, the compounding action of the injection device must be minimized to prevent fibre degradation.

We have discovered that injection moulding machines can be used to effect final compounding of rough blends of fillers in thermosetting amino-formaldehyde resin materials and to produce cured artefacts directly from such materials without previously forming a homogeneous intimate dispersion of the filler in the resin and without using specially designed mixing apparatus.

In a homogeneous dispersion, the filler (or reinforcing material) particles are intimately mixed with and impregnated or coated with the resin: in a non-homogenous blend of the type used in our process, the filler is not coated or impregnated to any great extent by the resin, but becomes intimately compounded therewith only in the injection or extruding machine.

According to the present invention, we provide a method of injection moulding artefacts from amino-formaldehyde thermosetting material which comprises :(a) providing a dry amino-formaldehyde material which is partly condensed but essentially solid at ambient temperatures (b) introducing said dry material with a filler separately or in a non-homogeneous blend directly into the barrel of an injection moulding machine, said machine having a heated barrel and a rotary screw - 4 which is axially movable in said barrel (c) rotating said screw simultaneously to feed the material and filler along the barrel, further condense the material, plasticize said material and impregnate the filler with the plasticized material to provide a homogeneous blend and effect transfer of homogeneous blend ahead of the screw by screw-back of the screw (d) injecting homogeneous blend from ahead of the screw into a mould and (e) curing the artefact in the mould.

The thermosetting material will comprise a material which is capable of condensing to form a cured matrix {said material hereafter being referred to as a thermosetting substance) in which may be dispersed any of the usual additives such as catalyst, lubricant, stabiliser, or plasticizer, and may be in granular or powder form. The thermosetting substance preferably is an essentially solid product of reaction between formaldehyde and a precursor selected from ureas, and. amino-s-triazines, for example dimethylol urea, dimethylol melamine, or a melamine-formaldehyde resin; a derivative thereof suoh as an alkylated hexamethylol melamine; or a mixture or co-condensate of any of these substances with each other or with another thermosetting substance, such as a solid melamine unsaturated polyester co-condensate. The thermosetting substance preferably is a urea- or melamine-formaldehyde resin, optionally mixed or co-cond<=nsed with other thermosetting material such as an alkyd, diallyl phthalate or epoxy resin.

The thermosetting substance is a thermosetting resin which is partly condensed but essentially solid at ambient temperatures in the absence of solubilizing quantities of water or other solvent. If a liquid - 5 plasticizer, such as water or monocresylglyceryl ether, or other liquid component is used, it should be present in such an amount that the thermosetting material is not liquid, nor (preferably) visibly wet. Preferably, not more than about 10% by weight (of the weight of the thermosetting substance) will be water or other solvent. Any volatile liquid used initially in the non-homogeneous blend, is preferably vented from the barrel during compounding. Since the resins used, or produced in the barrel, are of the condensation type, water or other volatile substance may be evolved during any condensation which may occur under the action of heat, as the filler and thermosetting material are progressed through the barrel. Thus the filler preferably is capable of absorbing the volatile material, or the barrel may be vented.

The more fully but not completely condensed material which issues from the downstream end of the barrel is moulded immediately by direct injection into a mould (or by the so-called injection/compression technique) and is thereby cured.

The non-homogeneous blend may be provided by one of several alternative methods, e.g. (1) by roughly mixing the filler with the thermosetting material in a mixer or blender and transferting the rough mixture to the hopper of the injection machine or extruder; or (2) by introducing the filler and thermosetting material, or the filler and the thermosetting substance and additives, to the hopper and roughly mixing them together in the hopper.

The separate feeding of the filler and thermosetting resin may be achieved by providing the filler in one hopper, and the thermosetting material in another hopper and feeding these materials separately to the interior of the barrel so that the non-homogeneous blend is formed at the upstream end of the barrel.

The thermosetting material may itself be partially filled prior to formation of the non-homogeneous blend with the filler referred to above.

The injection moulding machine preferably has a single screw. It may be necessary to use a machine having a screw housing (barrel) suitably grooved internally, depending on the particle size of the filler Or on the nature of the thermosetting material, particularly for thermosetting materials in finely powdered form, to obtain the desired feed characteristics.

Suitable fillers include powdered cellulose, woodflour, talc, CaCO3, powdered glass, and the like, and the cured particulate aminoplast materials, described in our Belgian Patent Specifications Numbers 796232 and 799052.

The thermosetting materials may also be filled or reinforced, by means of the invention, with fibrous materials, such as cellulose, glass fibres, asbestos fibres, or carbon fibres, and may include any convention al additives or processing aids such as plasticizer, mould lubricant, curing agent or pigment. Pigment may be incorporated, in particular, by roughly blending it with the thermosetting material at the same time as the particulate filler is incorporated.

The following examples illustrate preferred embodiments of the.invention.

Examples 1 and 2.

A BIPEL 155/50 injection moulding machine (BIPEL is a . ' Trade Mark) was used, with two modifications χία) The standard barrel (screw housing) was replaced by one having longitudinal grooving, cireumferen41829 - 7 tially spaced around the interior wall of the barrel and extending through substantially the whole length of the barrel; and (b) The feed hopper was provided with an agitator to effect continuous agitation of the contents of the hopper.

For both the following formulations (Table 1), all the ingredients were charged to a Baker-Perkins Z - blade mixer, before blending commenced, and mixing was effected, from 10 to 30 minutes to produce a nonhomogeneous blend of the aminoformaldehyde material (BL35 - a spray-dried melamine formaldehyde resin produced by our Chemicals Division), the filler, and the other ingredients. The 'rough' blend thus produced was fed to the hopper of the machine, and the machine was operated to agitate the contents of the hopper, feed them to the barrel, compound the non-homogeneous blend in the barrel and to produce test specimen mouldings.

The machine operating conditions and comments on the results are presented in Table 2. 41829 TABLE 1.

Exam- Ingredients Parts by Weight pie BL 35 1956 MCGE^ 148.5 Thermosetting (2) Hexamine ' 14.9 Material Brooksite/M5 55.6 Lubricant 30.0 Woodflour 1000 (Filler) BL 35 2220 Thermosetting Glycerol Material monostearate 10.8 Lubricant 9.0 Blue GLSR(3) 22.0 Blue RS2(4) 9.0 Pigment Black D.C. 7O(5) 1.5 White RH42(6) 1.2 Powdered Cellulose 1000 (Filler) NOTES. (1) (2) (3) Monocresylglyceryl ether Hexamethylene Tetramine Ciba Geigy (U.K.) Ltd. (4) Reckitts Colours Ltd. (5) Blythe Colours Ltd. 25 (6) TiO2~Laporte Industries Ltd.

TABLE 2.

Example 1 2 Barrel Temp (°C) 80 80 Mould Temp (°C) Fixed Part 148 148 Moving Part 148 148 Injection Speed (Sec) 2 2 Injection pressure (psi) 20,000 20,000 Screw Speed (r.p.m.) 60 60 Screw Back Time (secs) 5 6 Screw Stroke (ins) 1.375 1.3 Back Pressure (psig) 700 700 Injection Times (sec) 5 25 Cycle Time (secs) 45 125 COMMENT Consistant mouldings Fair pigment dispersion Examples 3 to 8.

In the following examples, thermosetting materials were made from the thermosetting substances and additives as defined and formed into non-homogeneous blends with the fillers, as defined, in a manner similar to that described in Examples 1 and 2. All parts are by weight. The non-homogenous blend was fed to the stirred hopper of a BIPEL 70/31 screw injection moulding machine, and test mouldings were made, the operating conditions of 41829 - 10 the injection moulding machine being given in Table 3, and the properties of the completed mouldings in Table 4.

Example 3.

BL 35 2220 parts Thermo- setting material Lubricant 20 parts Catalyst 3.2 parts Powdered Cellulose 900 parts Filler BaSO^ 100 parts Example 4, Thermosetting material as in Ex. 3 2543.2 parts Powdered cellulose 700 parts 1/8 glass fibres 300 parts Filler BaSO^ 100 parts Example 5.

Urea-formaldehyde resin 1400 parts Thermo- setting Lubricant 10 parts . Material Plasticizer 40 parts Catalyst 1.4 parts Powdered cellulose 4.76 parts Filler BaSO^ 133 parts The urea-formaldehyde resin was produced by reacting dimethylol urea and urea in a weight ratio of 10:1. - 11 41929 Example 6.

Melamine-urea- formaldehyde resin 1600 parts Thermo- setting Stabilizer 67 parts Material Lubricant 27 parts Woodflour (filler) 1070 parts The melamine-urea-formaldehyde resin was made by blending: Melamine- formaldehyde resin 100 parts Urea-formaldehyde resin 200 parts formaldehyde 165 parts plasticizer 40 parts Example 7.

Solid alkyd as incorporated in BEETLE 4128 polyester resin* 1000 parts BL 35 1000 parts Thermo- setting Diallyl phthalate 100 parts Material Tertiary butyl peroxide 50 Silane coupling agent 13 Lubricant 70 Powdered cellulose 1200 Millicarb CaCOj 1000 Filler China Clay 780 * BEETLE is a Trade Mark. The alkyd and - 12 melamine formaldehyde resin crosslink to produce a mixed resin system in the cured articles.

Example 8.

BL 35 1400 parts Phenolic resin 700 parts Thermosetting Lubricant 20 parts Material Catalyst 2 parts Woodflour 1000 parts Filler Baso4 150 parts TABLE 3.

EXAMPLE 3 4 5 6 7 8 Barrel Temp °C 95 95 90 90 50 100 Mould Temp °C 165 165 150 150 165 165 Injection pressure (p.s.i.) 1750 1750 1750 1750 1750 1750 Held-on Pressure (p.s.i.) 700 700 700 700 700 700 Injection Time (secs) 10 10 10 10 10 10 Total cycle time (secs) ' 40 40 20 20 40 40 TABLE 4. Example Property 3 4 5 6 7 8 Flexural Strength (MN/m2) 77 66 87 95 48 84 Flexural Modulus (GN/m2) 4.8 6.0 4.8 5.5 4.5 5.4 Energy to Break (KJ/m2) 618 363 788 820 256 654 Deflection at break (mm) 1.6 1.1 1.8 1.7 1.1 1.6 Boiling Water Absorption (mg/g) 22 23 25 50 10 17 Insulation resistance (IqIO ohms) 1.3 3.3 27 1.6 43 40 In each of Examples 3 to 8, the mouldings produced were in the form of pingated bars. These showed acceptable surface finish, mechanical strength and physical properties.

The operating conditions of the injection moulding machine can be selected readily by those skilled in the art. For machines of the general type used as described above, preferred conditions are: Barrel temperature 80 to 110°C Mould temperature 140 to 170°C Injection pressure up to 2000 p.s.i.

Total cycle time 15 to 130 seconds 4ΐβ2θ - 14 These may be varied at will depending on the materials being used and the type of mouldings to be produced.

Heretofore, it has been necessary for trade moulders to order from manufacturers moulding compositions containing a suitable amount and type of filler for the particular application which the moulder has in hand. Accordingly it has often been necessary for the moulding composition manufacturers to hold stocks of different moulding compositions, based on the same resinous mater10 ial but incorporating different amounts and/or types of homogeneously dispersed filler, hence space which could be put to better use is often required for storage of such stocks.

By virtue of the present invention, it is now possible for the moulding composition manufacturer to produce only unfilled or partially filled synthetic thermosetting materials for supply to trade moulders who themselves, without much effort or capital expenditure, can roughly mix the thermosetting material with the desired amount and type of filler to produce the nonhomogeneous blend referred to above.

Claims (5)

1. CLAIMS: 1. A method of injection moulding artefacts from aminoformaldehyde thermosetting material which comprises: (a) providing a dry amino-formaldehyde material which is partly condensed but essentially solid at ambient temperatures (b) introducing said dry material with a filler separately or in a non-homogeneous blend directly into the barrel of an injection moulding machine, said machine having a heated barrel and a rotary screw which is axially movable in said barrel (c) rotating said screw simultaneously to feed the material and filler along the barrel, further condense the material, plasticize said material and impregnate the filler with the plasticized material to provide a homogeneous blend and effect transfer of homogeneous blend ahead of the screw by screwback of the screw (d) injecting homogeneous blend from ahead of the screw into a mould and (e) curing the artefact in the mould,

2. A method according to claim 1, wherein the thermosetting material comprises an essentially solid product of reaction between formaldehyde and a precursor selected from ureas, and amino-s-triazines; a derivative of such a product or a mixture or co-condensate of such product or derivative with another such product or with another thermosetting substance.

3. A method according to Claim 2, whereiri the essentially solid product is selected from methylolated urea, methylolated melamine, alkylated derivatives thereof, urea-formaldehyde resins, melamine-formaldehyde resins, and mixtures thereof with unsaturated polyester resins. - 16

4. A method according to any one of the preceding claims, wherein the non-homogeneous blend is provided by roughly mixing the filler with the thermosetting material in a mixer or blender and transferring the rough mixture to the hopper of the injection moulding machine. 5. A method according to any one of claims 1 to 3, wherein the non-homogeneous blend is provided by introducing (a) the filler and thermosetting material, or (b) the filler and components for the thermosetting material, into the hopper of the injection machine or extruder, and forming the non-homogeneous blend into the hopper. 6. A method according to any one of claims 1 to 3, wherein the non-homogeneous blend is provided by separately feeding the filler and the thermosetting material, or the components of the thermosetting material, to the interior of the barrel so that non-homogeneous blend is formed at the upstream end of the barrel. 7. A method according to any one of the preceding claims, wherein the filler is selected from powdered cellulose, woodflour, talc, calcium carbonate, powdered glass, cured particulate aminoplast materials, and fibrous materials. 8. A method according to any one of the preceding claims, wherein the non-homogeneous blend is produced at ambient temperature. 9. A method according to any one of the preceding claims, wherein a mould at the downstream end of the barrel of the injection moulding machine is maintained at a temperature sufficient to initate cure of the homogeneous dispersion. 10. A method of producing mould . synthetic plastics artefacts, substantially as hereinbefore described 418 29 with reference to any one of Examples 1 and 2. 11. A method of producing moulded synthetic plastics artefacts substantially as herein before described with reference to any one of Examples 3 to 8.

5. 12. Moulded synthetic plastics artefacts whenever produced by a method as claimed in any one of the preceding claims.