GB2421209A - Moulding an article from a mixture of thermoplastics and filler particles - Google Patents

Abstract

A method of forming a moulded article comprises the steps of grinding a filler material to a mesh size of around 10 to 80 mesh, mixing the filler particles with particles of thermoplastics material, spreading a layer 2 of the mixture on a tray 5 or a belt conveyor 8, applying heat to the layer to melt the thermoplastics particles and form a heated charge, scraping off the heated charge from the trays or conveyor 8 using a scraper knife 3,6 and compressing the heated charge to form the article. An apparatus for forming the article is also claimed, as is an article from the method. A tunnel oven may be used to receive the tray or conveyor. Top and bottom heater elements 2, 7 may heat the mixture. The tray may be made of heat conducting material. Compressing rollers 4 may be used for compressing the mixture. The thermoplastics may be polyethylene or polypropylene. A list of fillers is provided in the text.

Description

TITLE Improved Method for Method of Making a Molded Product according to the Method.

Field of the invention Para 1. The invention relates to, (A) a method of heating and molding a thermoplastic with an organic or inorganic filler material such as wood flour, grain chaff, Kenaf, Water Hyacinth or ground limestone or other material: (B)a machine for doing the method and: (C) a product made according to the method. Para 11. Prior work in the field: In conventional injection molding or extrusion processes a filler material has to be dried to less than 0.5% moisture prior to mixing with a thermoplastic resin. This is a more costly process than effectively kiln drying the filler at the time of using. Other advantages are: reduced machine and mold costs i.e. capital investment, layering of dissimilar materials can be achieved by adaptation of the machine and surface texture and colour can be achieved on one or both sides of a sheet material Para 111. The method is done by: (1) grinding the filler material to a mesh size of around 10 to 80 mesh, by mixing this filler material with a powdered thermoplastic such as polyethylene or polypropylene of any density. (2) to mix these said materials in proportions ranging from 15% to 85% thermoplastic by volume, ( which percentages can vary according to and depending on the properties required by the product) (3) to evenly spread this mix on a tray or belt, that may be coated in P.T.F.E or other non-stick material, to a depth of from about'/4 inch to % of an inch. (4) to heat this tray or belt, for example, in a tunnel oven to the melt temperature of the thermoplastic being used. This would be in the range 130 degrees centigrade to 200 degrees centigrade which will be below the char temperature of the filler material being used and higher than the melt temperature of the thermoplastic. (5) when the entire body of the material has reached the temperature range referred to above, to remove the material from the tray or belt with a scraper blade as per the example shown in Dr. No 1/2 . Fig 2. No 1. (6) To compress the material in a pre-formed mold shape, or compress into sheet of a desired thickness by compression rollers. These rollers can be parallel or have a profiled form such as corrugated. (8) To open the mold and cool the product with cold air or water, or pass the sheet material through a cold air tunnel or cool both sides with water jets. Para.1111. A preferred machine for carrying out the method shown and described in the following drawings and writing. (refer to:- Key to drawing No's. (Page eight of eight) A tunnel oven with heater elements top and bottom heats trays made of heat conducting material which are loaded from a hopper to a depth of between 1/4 to 3/4 of an inch with the premixed composite material. Drl/1. Figl (side elevation) Fig2. (end elevation.) At the desired temperature to move the tray from the conveyor oven and to line it up with the mold cavity. ( The oven temperature will range from 130 degrees centigrade to 200 degrees centigrade depending on the char temperature of the filler material included in the composite) To scrape the tray and deposit the hot composite material into an open mold ( Dr 1/2 . Fig 4 ) To hydraulically, or by other means, close the mold and compress the composite to the mold shape (Drl/1 Fig 2 .7.) As this operation takes place another tray is removed from the oven and lined up with the second mold on the other side of the heater tray. The empty tray is loaded from an overhead hopper (Dr No 1/1 Figl. 4) as it moves from its previous position and re-enters the conveyor oven. (Dr 1/1. Figl. 5.) Dr 1/1 Fig 2 shows the position of the knife (Dr 1/1.Fig 1.) ready to move across to the mold on the other side of the tray. As the first mold opens the lower half moves bringing into position another empty half mold in line with the opposite side of the tray. At the same time the scraper moves across the tray (Dr 1/1 Fig 2) and deposits the composite into the second open mold. (This sequence is shown on Dr 1/2. Fig's 1.2.3.4) As the mold closes another tray is removed from the oven and the process starts again. As the lower half molds moves on the conveyor they pass through a cold air tunnel or water jets. (Dr 1/1. Fig2. 5) The lower half of the mold can also be cooled with water or air to minimize warping or distortion of the molded product. Before the lower mold half returns to the mold position the molded piece is ejected onto a conveyor or into a tank of cold water. The length of the tunnel oven will determine how many feed hoppers can be used to increase the thickness of the composite material on the trays. With a continuous belt, multiple hoppers and multiple belts, one above the other, can give many options as to layer thickness and material type. Dr 1/3 Figl. shows a belt (8) with two hoppers (1). Dr 1/3 Fig2, shows a two tier belt with a reinforcing net (7) being laid between the second and the third layer. Dr 1/4 Figl. shows an example of how different materials and reinforcing net, or the like, can be layered to form a continuous panel. Para v. Organic filler material is potentially hydroscopic, i.e. it can absorb water from the atmosphere. By passing the composite material through an oven the water is driven off as vapor, thus the organic filler material is at 0% moisture content by the time the thermoplastic reaches its melt temperature. The filler material should not enter the oven at more than 10% moisture content or oven heating time will be increased thus reducing production cycle time. Para VI. The method and the machine are adapted to make cost effective molded articles which have and are being made on prior art machines much more complicated as to structure and manner of performing the present method. Para VII. This method will allow the use of co-mingled materials such as plastics, wood, paper and the like recovered from the solid waste stream. Many of these materials are not suitable in conventional molding processes, such as injection and extrusion molding, as their content is inconsistent and contaminated with other waste materials. In many cases the separation of these waste materials is inefficient, unreliable and costly. In this method the outer layer of the material can include fire-retardants, mold inhibitors, U.V protection and others. These additives are difficult to include with prior art machinery as the additives will be dispersed throughout the volume of the material thus being cost prohibitive. Drawings Description. Dr 1/1. Figl. This shows the side elevation of a tunnel oven (1) with heater trays (5) loaded with a thin layer of thermoplastic composite material shown as dark lines on the trays. A scraper knife (Fig 1. 3) is in position to scrape the composite material across the tray ( Fig 2. 3) and to deposit it in the mold on the opposite side. (This sequence is clearly shown in Dr 1/2 Fig's 1,2,3,4.) Figl shows the position of a hopper (4) re-loading a tray as it passes to re-enter the oven. Dr 1/1. Fig 2. The end elevation of the tunnel oven described above. A heater tray (3) loaded with hot composite material (2) is positioned to be scraped by the scraper knife (1) into the open mold (4) Right hand. As this operation takes place the upper mold form closes (7) Left hand, to compress the hot material into the mold form. As soon as the hot material is deposited in the mold, the heater tray moves forward and another tray is lined up with the mold form. When the mold has closed and the upper mold half is on its return stroke the lower mold form moves to line up another mold on the opposite side. Alternate empty lower mold forms will line up as the scraper returns across the plate (6).This cycle is repeated in a continuous operation, the molded parts being cooled by air or water (5) as they are conveyed to an eject mechanism prior to entering the molding position for the next cycle. Dr 1/2. Fig 1. This drawing shows the sequence of the scraper knife (2). The knife starts from its rest position on a stationary plate (4) and moves across the heater plate (3) scraping the hot composite in front. Dr 1/2. Fi'g 2. As the scraper knife moves across the heated plate the hot composite material (1) is moved with the knife and builds up in front of it. Dr 1/2. Fig 3. When the scraper knife (1) reaches the stationary plate (2) on the opposite side, the heater plate moves on and another heated plate covered with hot composite material is brought in line with the mold cavity. Dr 1/2. Fig 4. As soon as the scraper knife (2) reaches the end of its stroke and the hot composite material (3) has been deposited in the mold, the scraper knife swings over ready to return across the next loaded heater plate to fill the mold on the opposite side. Dr 1/3. Fig 1. This shows a continuous belt, rather than individual trays, passing through a tunnel oven. Heater elements top (2) and bottom (7) heat the belt (8). To increase the thickness of the material a second feed hopper is located half way along the belt and deposits another layer of composite material on top of the first layer. The number of hoppers will depend on the length of the belt and each hopper can be loaded with a different mix of composite material. Dr 1/3. Fig 2. This drawing shows how one or more belts can be stacked one above the other. This can greatly increase the thickness of the finished material being produced and also allow many variations of filler material that can be included within the thickness of the final product. Reinforcing net or other material can be introduced anywhere in the thickness (9). Dr 1/4. Fig 1. This shows how by using the method and machine, as described in Dr 1/3, layers of different composite materials and mixes can be incorporated in the production of a final product. Layers such as (2) and (4) could include long wood fibers, or similar other fibers, laid as a random mat or in oriented strands to greatly increase the overall strength of the finished product. A patterned, textured, colored or other finish can be included in the outer surface layers (1) (6) on one or both sides. It will be understood that while a preferred embodiment of the present invention is presented, namely a rectangular tray as seen in elevation , it would be practical, also it provide a circular tray and a companionate scraper that extends radially and, nevertheless, be well within the scope of this disclosed invention.The concept and embodiment disclosed is of a method which teaches the mixture being heated from above and below to a temperature at which it can be formed into an article upon moving the charge on the tray into a forming means such as a "cold" mold form, to be compressed therein when the mold form is closed, which would also be the case if the charge were moved to a cold other means of compressing the heated, scraped molten mixture into another forming means such as pairs of opposed "cold" compression rollers, which are biased to progressively compress the charge to a desired shape, "cold" in this case and as used herein has the meaning at a temperature substantially less than that of the scraped charge of the mixture.Also, the mold disclosed is a compression type which has a mouth or gate at the tray level, however the mold mouth could be differently positioned; and, in general, numerous of the individual elements and functional aspects described may be modified somewhat within the spirit of the invention which therefore should not be limited to the details of this precise disclosure, but rather be awarded the full range implicit in the described invention. To enumerate and draw all possible variations would render this disclosure prolix. Wherefore it will be understood that the structural elements of the apparatus disclosed necessary in describing this embodiment can be replaced by other means which are obvious while still conforming to this invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood be one of ordinary skill in the art to which this invention belongs. Any methods and materials similar or equivalent to those described can be used in the practice or testing of the present invention, and, accordingly , all equivalent disclosure in various publications and patents of elements of this invention are incorporated herein whether by direct reference or not. While the principles of the invention have been made clear in an illustrative embodiment, it will be immediately obvious to those skilled in the art that there are many modifications of structure, arrangement, proportions, the elements, materials and components used in the practice of the invention that are particularly adapted to specific environments and operative requirements without departing from the disclosed invention principles. Key to Dr No's:-

Claims (3)

1. The method of forming a moulded article of composite material comprising the steps of

2. depositing a charge comprising a generally uniform layer of a mixture of small particles of filler material and of thermoplastic sized in a range of about 10 to 80 mesh per inch in a generally uniform layer of a thickness of about '/4 to % inch on a generally flat upper surface of a support tray of heat conductive material, applying heat to the upper surface of the layer without contacting the layer and heating the support tray to warm the particles of the mixture to at temperature at which the thermoplastic is molten, scraping the heated charge of the mixture from the support tray, and compressing and forming the heated charge of the mixture by elements having a temperature less than that of the mixture into a moulded article. 3. A product made according to the process as set forth in claim 1. 4.

3. A machine for making articles comprising a support tray for a layer of granulated or powder type material first heater means to heat the tray second heater means to heat the upper surface of a layer of the material on the tray scraper means to remove the heated layer of material from the tray and means to compress the material into an article of predetermined shape.