NO753779L - - Google Patents

Description

Method for the production of objects cast in synthetic plastic.

This invention relates to improvements in or in connection with the casting of thermosetting casting mixtures or masses.

An essential feature in the production of heat-setting molding compounds has been the grinding of the heat-setting resin material (used as curable matrix) with the filler or fillers, so that the latter is completely mixed with, impregnated with and covered by the resin material. This can be carried out either in a "dry" state where the resin material is essentially solid and melted during the grinding process, or in the presence of a solvent or other liquid medium followed by drying if desired. The resulting molding compound is then converted, in a separate step, into hardened objects by a casting or extrusion process.

US Patent No. 3,746,489 discloses a method for producing glass fiber reinforced castings by mixing the fibers and a liquid thermosetting resin material to form a viscous dough-like mixture which is continuously fed for direct transfer to an injection device with a nozzle through which the mixture is injected into a mold cavity where the mixture reacts to form hardened castings. The purpose of this previously known method is to facilitate the handling of the glass fibres, to ensure sufficient dispersion of the fibers in the resin material, as well as to maintain the fiber length so that no essential properties are lost. To achieve these purposes, a special method and device for mixing the fibers and the resin material is proposed. The dough-like material that is fed directly from the mixing device to the spraying device is essentially a homogeneous, intimate mixture of fibers in the resin material, and as is well known in the art, the mixing effect of the spraying device must be minimized to prevent fiber degradation.

We have discovered that the injection molding machines and extruders can be used to produce final mixing of coarse mixtures of fillers in thermosetting resin materials and to produce hardened objects directly from such materials without prior formation of a homogeneous, intimate dispersion

tion of the filler in the resin and without the use of specially designed mixing equipment.

In a homogeneous dispersion are the filler particles

(or the reinforcing material particles) intimately intermingled with and impregnated or coated with the resin; in an inhomogeneous mixture of

the type used in our method, the filler is not coated or impregnated with resin to a significant extent, but is intimately mixed with this only in the injection or extrusion machine.

According to the present invention, a method is provided for the production of molded synthetic plastic objects by a continuous molding or extrusion sequence which comprises: (a) Introducing a non-homogeneous mixture of a filler and a solid, particulate, heat-setting material into a screw injection molding mas-

chin or screw extruder,

(b) operating the injection molding machine or extruder so that

in the non-homogeneous mixture is converted in the cylinder of the machine or extruder into a plasticized, intimately mixed, homogeneous mass and

ii the plasticized mass is fed directly to a molding or extrusion head, and

(c) hardening of the mass transferred to the mold-

or the extrusion head.

The thermosetting material will comprise a material which can condense to form a hardened matrix (hereinafter referred to as hardener) in which any common additive such as catalyst, lubricant, stabilizer or plasticizer can be dispersed, and the material can be present in granulated or powder form. The hardener is preferably a largely solid reaction product between formaldehyde and a precursor selected from urea compounds, amino-s-triazines and phenols, e.g. dimethylolurea, dimethylolmelamine, or a melamine/formaldehyde resin; a derivative thereof such as an alkylated hexamethylol melamine; or a mixture or co-condensate of any of these substances with each other or with other hardeners, such as a solid melamine unsaturated polyester co-condensate. The hardener is preferably a urea, melamine, or phenol formaldehyde resin, optionally mixed with or co-condensed with other curing materials such as an alkyd, diallyl, phthalate or epoxy resin.

The hardener is preferably a hardener which is partly condensed but largely in solid form at ambient temperature in the absence of dissolving amounts of water or other solvent. If a liquid softener, such as water or monocresyl glyceryl ether, or another liquid component is used, it must be present in such an amount that the curing material is not liquid,

(preferably) or not visible, moist. Preferably no more than approx. 10 percent by weight (of the weight of the hardener) is water or other solvent. Any volatile liquid used initially in the inhomogeneous mixture is preferably vented from the cylinder during the mixing process. As the resins used or produced in the cylinder are of the condensation type, water or other volatile matter can develop during any condensation that may occur under the influence of heat, when the filler and curing material are advanced through the cylinder. The filler is therefore preferably able to absorb the volatile material, or the cylinder can be vented.

The additional but not fully condensed material that flows out from the downstream end of the cylinder is cast immediately by direct injection into a mold (or by means of the so-called spray compression technique) or by being fed directly into a heated extrusion head, to then be hardened.

The non-homogeneous mixture can be produced by several alternative methods, e.g.: (1) by coarse mixing of filler and curing material in a mixing device and transfer of the coarse mixture to injection machines or the extruder's hopper, or (2) by introducing the filler and the hardening material, or the filler and the hardening material and additives, to the hopper and rough mixing of the substances in the hopper, or (3) introduction of the filler into one hopper, and hardening material into another hopper and separate delivery of these materials to the interior of the cylinder, as that the inhomogeneous mixture is formed at the upstream end of the cylinder.

The curing material itself may be partially filled before the inhomogeneous mixing with the above-mentioned filler takes place.

The injection molding machine or extruder generally has a single screw. - It may be necessary to use a machine whose screw housing (cylinder) has suitably designed grooves or grooves inside, depending on the particle size of the filler or the properties of the curing material, especially with finely divided curing materials powder form, to achieve the 'desired food characteristics.

Suitable fillers include powdered cellulose, wood flour, talc, cocoa, powdered glass, and the like, and the cured particulate aminoplast materials described in Belgian Patent Nos. 796,232' and 799,052.

The curing materials can also be filled or reinforced, by means of the invention, with fibrous materials, such as cellulose, glass fiber, asbestos fiber, or carbon fiber, and can include any conventional additives or process promoting agents, such as plasticizer, mold lubricant, hardener or pigment . Pigment can in particular be mixed in by rough mixing with the curing material at the same time as the particulate filler is introduced.

The following examples illustrate preferred embodiments of the invention.

Examples 1 and 2

A BIPEL 155/150 injection molding machine (BIPEL is a registered trademark) was used, with two modifications: (a) The standard cylinder (screw housing) was replaced by a cylinder with longitudinal grooves or grooves distributed around the circumference in the inner wall of the cylinder and largely over the entire length of the cylinder length, and (b) the feed hopper was fitted with an agitator to

ensure continuous agitation of the contents, in the funnel.

In both of the following formulations (Table 1), all ingredients were introduced into a Baker-Perkins Z-blade mixer before mixing was started, and mixing was carried out from 10 to 30 minutes to produce a non-homogeneous mixture of the synthetic plastic material (BL 35 - a spray-dried melamine-formaldehyde resin produced by our chemical department), the filler, and the other ingredients. The "coarse" mixture thus prepared was fed to the machine hopper and the machine was put into operation for agitating the contents of the hopper, for feeding the contents to the cylinder, for mixing the non-homogeneous mixture in the cylinder, and for producing test castings.

The machine's operating conditions and comments on the results are given in table 2.

Example 3

A phenolic resin-based casting material was prepared by:

F.enol Novolak resin (m.p. 70°C)

100 parts

Hexamethylenetetramine Curing material

12 parts

Lubricant

2 parts

Brown pigment

2 parts

Wood flour

110 parts (filler)

by mixing the ingredients in a Baker Perkins mixing machine for 10 minutes at ambient temperature, and feeding the coarse mixture to the stirring hopper in a BIPEL 70/31 injection molding machine. The machine worked under the conditions indicated in the table for the production of castings from a DIN rod tool as indicated in the following examples.

Note

(1) Monocresyl glycerol ethers

(2) Hexamethylenetetramine

(3)Ciba Geigy (U.K.) Ltd.

(4) Reckitts Colors Ltd.

(5) Blythe Colors Ltd.

(6) Ti02-Laporte Industries Ltd.

In the following examples, the curing materials were prepared from the curing agents°and additives as indicated, and formed into non-homogeneous mixtures together with the fillers, as indicated,"in the same manner as described in Examples 1 to 3. All parts are parts by weight. Injection Molding Machine Operating Conditions are given in table 3, and the properties of the finished castings are given in table 4.

Example 4

Example 5

Example 6

The urea-formaldehyde resin was produced by reaction between dimethylolurea and urea in a weight ratio of 10:1.

Example 7

The melamine urea formaldehyde resin was prepared by mixing: Example 8

BEETLE is a registered trademark. The alkyd and melamine-formaldehyde resin are cross-linked to produce a mixed resin system in the cured articles.

Example 9

Example 10

In each of examples 4 to 9, the test pieces were produced in the form of pin-gated bars. These showed satisfactory surface, firmness properties and physical properties.

The operating conditions of the injection molding machine (or extruder) can be easily selected by those skilled in the art. For machines of the usual type used as described above, the preferred conditions are as follows:

These can be varied as desired depending on the materials used and the type of castings produced. An extruder will of course be equipped with an extrusion head which can be heated to a sufficiently high temperature to harden the material flowing through it.

Until now, it has been necessary for the foundries to order casting mixtures or compounds from the manufacturers, which contain a suitable amount and type of filler for the particular application relevant to the foundry, and consequently it has often been necessary for the casting compound manufacturers to keep a warehouse of different molding compounds, based on the same resin material, but including different amounts and/or types of homogeneously dispersed filler, and thus often storage rooms that could be used in a better way must be used for the storage of such substances.

As a result of the present invention, it is now possible for the casting compound manufacturers to produce only unfilled or partially filled synthetic hardening materials for delivery to the foundries which, even without great effort or capital outlay, can carry out a rough mixing of the hardening material with the desired amount and type of filler for the production of the non-homogeneous mixture described above.

Claims (8)

Process for producing molded synthetic plastic articles by introducing a filler and a curing material into a screw injection molding machine or a screw extruder, and operating the machine for the direct production of a hardened casting or extrusion object, characterized in that: (a) the curing material is essentially a solid particulate material, (b) the filler and curing material are supplied in the form of a non-homogeneous mixture at the upstream end of the cylinder of the machine, and (c) the machine is operated to convert the inhomogeneous mixture into a homogeneous, intimate mixture in the cylinder. 2. Method as stated in claim 1 where the curing material consists of a curing component and additive components, characterized in that the curing component comprises a substantially solid product of the reaction between formaldehyde and a precursor selected from urea compounds, amino-s-triazines and phenols, a derivative of such a product, or a mixture or a co-condensate of such a product or derivative with another such product or with another hardener. 3. Method as stated in claim 1 or 2, characterized in that the non-homogeneous mixture is produced by coarse mixing of filler and hardening material and feeding the resulting coarsely mixed material to the machine. 4. Method as stated in claim 1 or 2, characterized in that the non-homogeneous mixture is formed in a funnel which is attached to the machine. 5. Method as stated in claim 1 or 2, characterized in that the filler and the hardening material are fed separately to the machine and that the non-homogeneous mixture is formed at the upstream end of the machine's cylinder. 6. Method as stated in one of the preceding claims, characterized in that the filler is selected from powdered cellulose, wood flour, talc, calcium carbonate, powdered glass, hardened, particulate amino plastic materials, and fiber materials. 7. Method as stated in one of the preceding claims, characterized in that the non-homogeneous mixture is prepared at ambient temperature. 8. Method as stated in one of the preceding claims, characterized in that a casting or extrusion head at the downstream end of the cylinder of the injection molding machine or extruder is kept at a temperature sufficient to initiate hardening of the homogeneous mass.