NL2006979C2

NL2006979C2 - Molding process.

Info

Publication number: NL2006979C2
Application number: NL2006979A
Authority: NL
Inventors: Rutger Regt
Original assignee: Rutger Regt
Priority date: 2011-06-21
Filing date: 2011-06-21
Publication date: 2012-12-28

Description

MOLDING PROCESS

The present invention relates to a process for the manufacture of a molded article. Further, the present 5 invention relates to the molded article obtainable by the process. Furthermore, the present invention relates to the use of these molded articles.

Nowadays, the plastic industry, specifically, the thermoplastic industry concerns most every day object. Known 10 industrial techniques are for example extrusion molding or injection molding. Plastics extrusion is a high volume manufacturing process in which raw plastic material is melted and formed into a continuous profile. In the extrusion of plastics, raw thermoplastic material in the 15 form of small beads (also designated as resins) is gravity fed from a top mounted hopper into the barrel of the extruder. Additives such as colorants and UV inhibitors (in either liquid or pellet form) are often used and can be mixed into the resin prior to arriving at the hopper. The 20 material enters through a feed throat and comes into contact with the screw. The rotating screw (normally turning at up to 120 rpm) forces the plastic beads forward into the barrel which is heated to the desired melt temperature of the molten plastic (which can range from 200°C to 275°C 25 depending on the polymer). In most processes, a heating profile is set for the barrel in which three or more independent PID controlled heater zones gradually increase the temperature of the barrel from the rear (where the plastic enters) to the front. This allows the plastic beads 30 to melt gradually as they are pushed through the barrel and lowers the risk of overheating which may cause degradation in the polymer. Extra heat is contributed by the intense pressure and friction taking place inside the barrel. In 2 fact, if an extrusion line is running a certain material fast enough, the heaters can be shut off and the melt temperature maintained by pressure and friction alone inside the barrel. In most extruders, cooling fans are present to 5 keep the temperature below a set value if too much heat is generated. If forced air cooling proves insufficient then cast-in heater jackets are employed, and they generally use a closed loop of distilled water in heat exchange with tower or city water.

10 Injection molding is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. The material is fed into a heated barrel, mixed (the material is accordingly in malleable form, or in liquid form), forced into a mold cavity where it cools and 15 hardens to the configuration of the mold cavity. With injection molding, granular plastic is fed by gravity from a hopper into a heated barrel. As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted. As the plunger 20 advances, the melted plastic is forced through a nozzle that rests against the mold, allowing it to enter the mold cavity through a gate and runner system. The mold remains cold so the plastic solidifies almost as soon as the mold is filled. The sequence of events during the injection mold of a 25 plastic part is called the injection molding cycle. The cycle begins when the mold closes, followed by the injection of the polymer into the mold cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. In the next step, the screw turns, 30 feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mold opens and the part is ejected.

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In both industrial techniques, the molds used, even to fabricate the less complex objects, are expensive and complicated to manufacture. These molds are usually only used in mass production where thousands of parts were being 5 produced. The mold consists of two primary components, the injection mold (A plate) and the ejector mold (B plate). Plastic resin enters the mold through a sprue in the injection mold, the sprue bushing is to seal tightly against the nozzle of the injection barrel of the molding machine 10 and to allow molten plastic to flow from the barrel into the mold, also known as the cavity. The sprue bushing directs the molten plastic to the cavity images through channels that are machined into the faces of the A and B plates.

These channels allow plastic to run along them, so they are 15 referred to as runners. The molten plastic flows through the runner and enters one or more specialized gates and into the cavity geometry to form the desired part. The amount of resin required to fill the sprue, runner and cavities of a mold is a shot. Trapped air in the mold can escape through 20 air vents that are ground into the parting line of the mold. If the trapped air is not allowed to escape, it is compressed by the pressure of the incoming material and is squeezed into the corners of the cavity, where it prevents filling and causes other defects as well. The air can become 25 so compressed that it ignites and burns the surrounding plastic material. To allow for removal of the molded part from the mold, the mold features must not overhang one another in the direction that the mold opens, unless parts of the mold are designed to move from between such overhangs 30 when the mold opens (utilizing components called Lifters).

Sides of the part that appear parallel with the direction of draw (The axis of the cored position (hole) or insert is parallel to the up and down movement of the mold as it opens 4 and closes) are typically angled slightly with (draft) to ease release of the part from the mold. Insufficient draft can cause deformation or damage. The draft required for mold release is primarily dependent on the depth of the cavity: 5 the deeper the cavity, the more draft necessary. Shrinkage must also be taken into account when determining the draft required. If the skin is too thin, then the molded part will tend to shrink onto the cores that form them while cooling, and cling to those cores or part may warp, twist, blister or 10 crack when the cavity is pulled away. The mold is usually designed so that the molded part reliably remains on the ejector side of the mold when it opens. The part then falls freely when ejected from the side. Tunnel gates, also known as submarine or mold gate, is located below the parting line 15 or mold surface. The opening is machined into the surface of the mold on the parting line. The molded part is cut (by the mold) from the runner system on ejection from the mold. Ejector pins, also known as knockout pin, is a circular pin placed in either half of the mold (usually the ejector 20 half) , which pushes the finished molded product, or runner system out of a mold.

Both techniques accordingly comprise high pressure processes and therefore require pressure controls and pumps.

The goal of the present invention is to provide a 25 process for the manufacture of a molded article made of molded thermoplastic materials, in particular when one has for goal to manufacture objects, or articles, that are of limited complexity.

Accordingly, the present invention provides a 30 process for the manufacture of a molded article that does not require an expensive mold and which additionally may not be complicated to fabricate. The present invention additionally has the advantage that the process does not 5 require pressure controls and, that further can be carried out in air, at ambient pressure. Further, the present invention provides that the articles fabricated by the process may present irregularities in the form of holes.

5 These goals, among others, are achieved in the present invention by the process for the manufacture of a molded article process for the manufacture of a molded article comprising the steps of: a) introducing granules of a thermoplastic material 10 into a mold having an inner surface and an outer surface, wherein the temperature of the granules is below the melting temperature interval of said thermoplastic material; b) heating at least partially the outer surface of 15 said mold, wherein said heating is carried out at a temperature in the range of, or above, the melting temperature interval of the thermoplastic material, for obtaining melted thermoplastic material; 20 c) cooling the outer surface of said mold below the melting temperature interval of said thermoplastic material, thereby obtaining molded article of thermoplastic material.

In step a), the granules are introduced in a mold. 25 The mold advantageously is a heatable mold and therefore the mold stands the heating of the process. Advantageously in the process according to the present invention, the introduction is carried out at ambient temperature, or room temperature, resulting in that the granules according to the 30 present invention are in solid form. Ambient temperature according to the present invention is generally in the range of 15 C to 30 C. The introduction of the granules into the heatable mold is carried out in absence of heating in step 6 a) of the process according to the present invention. Preferably, the temperature of the mold in step a) is at ambient temperature.

In the context of the present invention, granules 5 of the thermoplastic material are parts such as spheres or pieces of the thermoplastic materials with any other shape. Advantageously, the granules have an average size, i.e. average largest dimension, between 1 millimeter and 2 centimeters, more advantageously between 2 millimeter and 1 10 centimeter, most advantageously between 3 millimeter and 5 millimeter. The granules according to the present invention also be designated as pellets, granulates or beads.

A thermoplastic material is a material made of, composed of, or formed from, a thermoplastic polymer. A 15 polymer in the context of the present invention can be a homopolymer or a copolymer. Homopolymers are the repetition of the same monomer entity. In other words, homopolymers are made by the polymerization of monomers with the same molecular formula. Copolymers comprise more than one type of 20 monomer, in other words they are composed of different monomers. By polymerization is to be understood as any chemical reaction between molecular units, called monomers, to form a polymer. A polymer comprises the multiple repetitions of monomers.

25 The term melting point, when applied to polymers, suggests not a solid-liquid phase transition but a transition from a crystalline or semi-crystalline phase to a solid amorphous phase. Often, the melting point of a polymer occurs within a range, or interval, of temperatures, i.e.

30 starting from the liquid-glass transition temperature until the amorphous state. In the context of the present invention, the melting point of the polymer will be accordingly referred to as a melting temperature interval.

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The melting temperature interval depends on the chemical nature of the thermoplastic material. In step b), the heating is carried out at a temperature in the range of, or above, the melting temperature interval of the thermoplastic 5 material. The expression "in the range of, or above, the melting temperature interval" is to be understood as follows: the heating in step b) is carried out at a temperature being within the melting temperature interval of the thermoplastic polymer (such as any temperature within 10 that range), or above. Accordingly, the heating may also be carried out it may also be above the melting temperature interval. For example, in the case of polyethylene terephtalate (PET), the melting temperature interval is 75°C to 250 C. Thus, the range of melting temperature interval for 15 PET within the context of the present invention is 75°C to

250 C, such as any value within that range, or until 25-50°C

o above 250 C m experimental conditions preventing the decomposition of the polymer. Another example is the polypropylene (PP) which melting temperature interval is 20 130 C to 171 C. Thus, the range of melting temperature interval for PP within the context of the present invention is 130 C to 171 C, such as any value within that range, until o o 25 C above 171 C n experimental conditions preventing the decomposition of the polymer. In particular, the range of 25 melting temperature interval can be from 160 to 166°C for PP. The heating temperature is advantageously not causing any decomposition, or degradation, of the thermoplastic material; accordingly, the heating in step b) is preferably below the decomposition temperature of the thermoplastic 30 material. In the context of the present invention, the values of the melting temperature and of the decomposition temperature depend on the nature of the material, and 8 accordingly the values vary from one material to another. Additionally, in steps a) and c), the expression "below the melting temperature interval of said thermoplastic polymer" is to be understood as a temperature wherein the 5 thermoplastic material does not melt. It can be ambient temperature .

A thermoplastic polymer is a polymer that, when heated undergoes to a liquid-glass transition (i.e. into a semi-liquid or a gel-like state) and solidifies to a glassy 10 state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through Van der Waals forces such as polyethylene, dipole-dipole interactions and hydrogen bonding such as nylon or even stacking of aromatic rings, such as polystyrene. One 15 advantage of thermoplastic polymers is that they can be melted and/or molded several times. Many thermoplastic materials are addition polymers, such as vinyl chain-growth polymers, in particular polyethylene and polypropylene.

Some thermoplastics normally do not crystallize: 20 they are termed "amorphous" plastics. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are polymethylmethacrylate (PMMA), polystyrene (PS) and polycarbonate (PC). Generally, amorphous thermoplastics are 25 less chemically resistant and can be subject to environmental stress cracking. Thermoplastics will crystallize to a certain extent and are called "semicrystalline" for this reason. Typical semi-crystalline thermoplastics are polyethylene (PE), polypropylene (PP), or 30 a terephtalate such as polybutyl terephtalate (PBT), polyethylene terephtalate (PET). The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline 9 thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque.

In the context of the present invention, the 5 following thermoplastics may be used: acrylonitrile butadiene styrene (ABS) polymethylmethacrylate (PMMA), ethylene-vinyl acetate (EVA), ethylene vinyl alcohol (EVOH), polyoxymethylene (POM or Acetal), polyacrylates such as polyacrylonitrile (PAN or Acrylonitrile), polyamide (PA or 10 Nylon), polyamide-imide (PAI), polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene (PB), polybutylene terephthalate (PBT) polycaprolactone (PCL), polychlorotrifluoroethylene (PCTFE), polyethylene terephthalate (PET), polycyclohexylene dimethylene 15 terephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs), polyketone (PK), polyethylene (PE), polyetheretherketone (PEEK), polyetherketoneketone(PEKK), polyetherimide (PEI), polyethersulfone (PES), chlorinated polyethylene (CPE), 20 polyimide (PI), polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene (PP), polystyrene (PS), polysulfone (PSU), polytrimethylene terephthalate (PTT), polyurethane (PU), polyvinyl acetate 25 (PVA), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), styrene-acrylonitrile (SAN). In the context of the present invention, the thermoplastic material can also be a thermoplastic composition, i.e. comprising a thermoplastic polymer and at least one suitable additive. The 30 thermoplastic material according to the present invention is advantageously commercially available.

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The thermoplastics according to the present invention can also be derivatives of the above-mentioned polymers .

According to the present invention, the granules 5 are in solid form in step a). This is to be understood that the granules are not, at the moment of introduction in step a) pre-heated. Advantageously, the granules in the context of the present invention are not in a malleable form, accordingly, the thermoplastic material is not in semi-10 liquid form, and also not in an amorphous form in step a). More advantageously, no heating is provided until the granules are fully introduced in the heatable mold. Preferably, the mold is completely filled with granules after the introduction in step a).

15 In step a), the granules are introduced in the heatable mold. The introduction can be carried out in an automation process or by any other process. Step a) is advantageously directly followed by step b). In step a), no stirring is necessary. Accordingly, in step a) is carried 20 out in the absence of stirring of any form.

In the present invention, the mold is a heatable mold. By "heatable mold" is to be understood that the mold is thermally conductive, or made of a thermally conductive material. A thermally conductive material is a material 25 conducting heat. It can be any conductive material, such as any metal, or any metallic alloy. Examples of heat conducting materials are various types of steel, such as stainless steel or aluminum or aluminum alloys. The mold has an inner surface and an outer surface. The inner surface is 30 in contact with the thermoplastic material and the outer surface in contact with the heat source in order to carry out the heating in step b). The inner surface and outer surface of the mold are not insulated thermally from each 11 other. It means that the heat applied in step b) of the process according to the present invention is transmitted to the inner surface of the mold to allow the melting of the thermoplastic material.

5 The mold used in the process according to the present invention may have any shape. Advantageously, shapes can be hemispherical, cylindrical, cubic, a square-based pyramidal, triangle-based pyramidal, or a triangular prismatic shape.

10 Step b) comprises heating at least partially the outer surface of said mold. The heating can be carried out on the whole outer surface, but also only on pre-determined areas. By heating, or contacting with a heat source is to be understood apply heat. The heat can be applied via any heat 15 source, such as an electrical heat source in contact with the mold, such as an electrical heat source connected to the mold, if the mold is made of a thermally conductive and electrically conductive material. A direct fire heat source may also be used. The heat is advantageously applied on the 20 exterior of the mold, such as on the intersections of the faces of the mold. The intersections of the faces are the edges and angles between the faces. The heating of the last one part of the heatable mold transmits the heat to the thermoplastic material in the mold. The granules of 25 thermoplastic material melt. Accordingly, in step b), the granules of thermoplastic material melt, where the heat is applied. The thicknesses of the material depend on the temperature of the heat and the duration of time that the heat was applied. The thicknesses can be any thicknesses.

30 The structure of the molded articles manufactured by the present invention comprises more than one thickness. Advantageously, the thicknesses are in the range 1 millimeter (mm) to 50 centimeters (cm), such as 1 mm, 2 mm, 12 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, 21 cm, 22 cm, 23 cm, 24 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, 50 5 cm.

Applying the heat on pre-determined areas provides the molded article to have a pre-determined shape which is accordingly defined by the areas of the outer surface of mold in contact with a heat source. Optionally, the whole 10 surface of one face of the mold may be heated. The molded thermostatic material has a shape that is determined by the region(s) of the at least one face of the mold where the heat is applied. Advantageously, the heatable mold comprises at least three faces, to be understood as three faces or 15 more; such as at least four faces, to be understood as four faces or more; such as at least five faces, to be understood as five faces or more; such as at least six faces, to be understood as six faces or more. The top and/or bottom parts may or may not be considered as a face within the context of 20 the present invention, depending on the shape of the mold. The heat may advantageously be applied on the whole surface of every face and/or on the whole surface of the bottom part. Alternatively, it may be applied only along the intersections of the faces (also designated as the angles 25 and corners formed by the faces and/or bottom part). Another alternative is that to heat only on one whole surface of one face and along the intersections formed by the faces, wherein said intersections are extending outwardly from the one whole heated surface of the face.

30 In step c) of the process of the present invention, the at least one heated part of the mold is cooled. The cooling can be carried out by external cooling, or by stopping the heating carried out in step b).

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In the process of the present invention, the thermoplastic material is a semi-crystalline thermoplastic polymer and/or crystalline thermoplastic polymer. A polymer in the context of the present invention is a homopolymers or a copolymer. A 5 copolymer can be made of a polymer comprising crystalline thermoplastic polymer and/or a semi-crystalline thermoplastic polymer, as well of another thermoplastic polymer component that is not crystalline or semicrystalline .

10 According to the process of the present invention, the thermoplastic material comprises at least one thermoplastic polymer, homopolymer or copolymer, chosen from the group polyethylene, polyvinyl chloride, polytetrafluoroethylene, polypropylene, polybutylene 15 terephtalate, polyethylene terephtalate, a polyester-based polyurethane, a polyether-based polyurethane, or derivatives thereof .

Advantageously, the thermoplastic material of the present invention may be such as polyethylene, polyvinyl 20 chloride, polytetrafluoroethylene, polypropylene, polybutylene terephtalate, polyethylene terephtalate, a polyester-based polyurethane, a polyether-based polyurethane, or derivatives thereof.

In the context of the present invention, the 25 derivatives are polymers with the chemical formula and molecular weights of the above-mentioned thermoplastic polymers and containing at least one chemical substitution on the main monomer used in the polymerization.

Polyethylene has the chemical formula (-CH2-CH2-) n-30 Polyvinyl chloride has the chemical formula(-CH2-CHC1-) n.

Polytetrafluoroethylene has the chemical formula(-CF2-CF2-) n-Polypropylene has the chemical formula (-(CH3)CH-CH2-) n-Polybutylene terephtalate has the molecular formula 14 (Ci2Hi204)n. Polyethylene terephtalate has the molecular formula (CioHgO^n. A polyester-based polyurethane can be any polyester-based polyurethane. A polyether-based polyurethane can be any polyether-based polyurethane, such as 5 poly (tetramethylene ether) glycol.

According to the present invention, the thermoplastic material is a thermoplastic polymer comprising polyethylene terephtalate and/or polypropylene. Advantageously, the thermoplastic material is polyethylene 10 terephtalate or polypropylene.

According to the process of the present invention, the mold comprises at least four faces forming an enclosed space. Advantageously, the mold has a hemispherical, cylindrical, a cubic, a square-based pyramidal, triangle-15 based pyramidal, or a triangular prismatic shape. The mold has accordingly the corresponding amount of faces, also designated by sides, or walls, a bottom part and a top part. Advantageously, the top part is provided with an aperture. More advantageously, the aperture allows the removal of the 20 molded thermoplastic material, once steps a) , b) and c) are completed. The top part of the mold may comprise a lid, or a partial lid (not covering the whole surface of the mold. The lid can also be designated as a closing mean. The mold may also have no lid. The lid may be removable. Accordingly, the 25 mold always has a bottom part, but it may, or may not comprise a top part with a lid. The aperture of the mold must allow remove the molded article of thermoplastic material.

A hemisphere is to be understood as half a sphere, 30 and can be designated by a spherical cap. In the context of the present invention, a hemisphere (a spherical cap) is a perfectly round geometrical object in three-dimensional space, or substantially imperfect. Herewith by 15 "hemispherical" is to be understood perfectly hemispherical or substantially hemispherical. In the context of the present invention, the shapes recited can be perfect shapes or can present some geometrical imperfections, giving 5 substantially imprecise geometries. A cylinder, or a mold with a cylindrical shape is to be understood as a curvilinear geometric shape, which surface is formed by the points at a fixed distance from a given line segment, the axis of the cylinder.

10 A cube is to be understood as a three-dimensional solid bounded by six square faces, facets or sides, with three meeting at each vertex. The cubic shape can also be called a regular hexahedron. It is a special kind of square prism, of rectangular parallelepiped and of trigonal 15 trapezohedron. A cuboic shape is to be understood as a shape with six faces, forming a convex polyhedron. There are two competing (but incompatible) definitions of a cuboid in the mathematical literature. In the more general definition of a cuboid, the only additional requirement is that these six 20 faces each be a quadrilateral, and that the undirected graph formed by the vertices and edges of the polyhedron should be isomorphic to the graph of a cube. Alternatively, the word "cuboid" can be used to refer to a shape of this type in which each of the faces is a rectangle (and so each pair of 25 adjacent faces meets in a right angle); this more restrictive type of cuboid is also known as a right cuboid, rectangular box, rectangular hexahedron, right rectangular prism, or rectangular parallelepiped. A square-based pyramidal or a triangle-based pyramidal shape are to be 30 understood as a square pyramid or a triangular pyramid, respectively. In a pyramid having a square base, if the apex is perpendicularly above the center of the square, it will have the C^v symmetry. In a pyramid having a triangular base, 16 if the apex is perpendicularly above the center of the square, it will have the C3V symmetry. The shape of the mold can also be triangular prismatic. A triangular prism is three-sided prism; it is a polyhedron made of a triangular 5 base, a translated copy, and 3 faces joining corresponding sides. Equivalently, it is a pentahedron of which two faces are parallel, while the surface normals of the other three are in the same plane (which is not necessarily parallel to the base planes). These three faces are parallelograms. All 10 cross-sections parallel to the base faces are the same triangle. In the process of the present invention, the thermoplastic material of the present invention, the mold comprises at least four faces, such as four faces, five faces, six faces, seven faces, eight faces, nine faces, ten 15 faces. These faces form an enclosed space, such as one of the above-mentioned tridimensional shape. The mold may or may not have a lid, or top.

In the process according to the present invention, the mold can comprise at least four faces forming an 20 enclosed space, wherein one of the said faces (also designated as the base) is perpendicular to the at least three surfaces. Advantageously, the mold can be a triangular prism, or a cube.

When the mold comprises at least four faces 25 forming an enclosed space, the heating in step b) can be carried out on the whole face that is perpendicular to the at least three faces and along the intersections of the at least three faces at the intersections of the faces.

In molds of other shape, in the context of the present 30 invention, the heating can also be carried out on one whole face of the mold and on intersections extending outwardly from the whole heated face. In this way, it is possible to manufacture any type of articles comprising a flat surface 17 and at least three structures extending outwardly from the surface. Advantageously, the angles between the at least three structures extending outwardly from the face (that can also be designated as the "base" of the mold) can be any 5 angles, advantageously any value between 45° and 90°.

In the process according to the present invention, the mold be a spherical cap. It can be substantially spherical, partially spherical or perfectly spherical. A spherical cap is the region of a sphere which lies above (or 10 below) a given plane. If the plane passes through the center of the sphere, the cap is a called a hemisphere. The mold that is a hemispherical shape and accordingly providing hemispherical shape to the molded article, may be a bag made of aluminum, or of an aluminum alloy that is thermally 15 conductive, but it can be also electrically conductive.

In the process of the present invention, steps b) and c) are carried out in the absence of external pressure. It is to be understood that no mechanical pressure is applied in any of the steps b) and c).

20 According to the present invention, the process is carried out at atmospheric pressure. One advantage of the process according to the present invention is that no particular environmental pressure is required. One other advantage is that the process according to the present 25 invention can be carried out in air, without the need of an inert atmosphere. Yet another advantage of the present invention is that the process is not a high or low pressure process. Accordingly, no complicated apparatus is necessary carry out the process under high or low pressure.

30 Advantageously, the process of the present invention is carried out at atmospheric pressure.

Another aspect of the present invention is a molded article obtainable by the process according to the present invention.

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According to the present invention, the process of 5 the present invention manufactures molded articles with a certain shape and size, defined by the application of the heat in step c) of the process, the temperature and the duration of application of this heat. Additionally, the size of the molded article is also defined by the size of the 10 mold used in step a) of the process.

Additionally, the process according to the present invention maybe part of an automated industrial process to manufacture parts made of molded thermoplastic materials.

The process according to the present invention 15 presents the advantage of not reguiring technically complicated industrial machinery to be carried out.

Additionally, one advantageous characteristic is that the process according to the present invention allows the manufacture of molded articles having one substantially 20 smooth surface, the surface in contact with the mold and composed of the melted granules of thermoplastic material, and the other side of the molded article, a surface that is irregular in thickness and roughness and composed by granules of thermoplastic materials that are partly melted 25 and partly unmelted.

According to the present invention, the molded article manufactured by the process of the present invention is a container, such as a recipient, a jar, a bottle or a box .

30 According to the present invention, the molded article manufactured by the process of the present invention is a tube. The tube can be of any size and diameter. It can be hollow or full.

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According to the present invention, the molded article manufactured by the process of the present invention is a piece of furniture or part of a piece of furniture. The furniture can be such as a seat, for example a chair or a 5 stool, such as a table, for example a coffee-table, a dinner-table or a bedside-table. The molded article manufactured can also be used as a portion of a furniture, such as the structure of a wardrobe, a cupboard, or a bed. The molded article obtainable by the process of the present 10 invention can be used in the packaging industry, such as the food packaging industry, in the medical packaging industry, in the pharmaceutical packaging industry.

The molded article obtainable by the process of the present invention can be used in laboratory/medical 15 equipment.

The molded article obtainable by the process of the present invention can be used in construction, such as in the manufacture of tubing, plates and bars.

Claims

A method for preparing a molded article comprising the steps of: a) introducing granules of a thermoplastic material into a mold having an inner surface and an outer surface, wherein the temperature of the granules is lower than the interval of the melting temperature of the thermoplastic material; B) at least partially heating the outer surface of said mold, said heating being carried out at a temperature in the range of, or above, the melting temperature interval of the thermoplastic material, to obtain molten thermoplastic material; c) cooling the outer surface of the mold below the melting temperature interval of said thermoplastic material, to obtain a molded article of thermoplastic material.

2. A method according to claim 1, wherein the thermoplastic material comprises at least one thermoplastic polymer selected from the group consisting of polyethylene, polyvinyl chloride, polytetrafluoroethylene, polypropylene, polybutylene terephthalate, polyethylene terephthalate, polyester polyurethane, polyether polyurethane, and derivatives thereof.

3. Method according to claim 1 or 2, wherein the thermoplastic material is a thermoplastic polymer comprising polyethylene terephthalate and / or polypropylene.

The method of any one of claims 1 to 3, wherein the mold comprises at least four sides and forms a closed space.

The method of claim 4, wherein one of said sides is perpendicular to at least three sides.

The method of claim 5, wherein the at least partial heating of the mold according to step b) 10 is performed on the entire side that is perpendicular to the at least three sides and to the intersection of the at least three sides.

The method of any one of claims 1 to 3, wherein the shape is a ball cap.

The method of any one of claims 1 to 1, wherein the method is carried out at atmospheric pressure. 20

Shaped article obtainable by a method according to one of claims 1 to 8.

10. Shaped article according to claim 9, wherein the article is a holder.

The shaped article of claim 9, wherein the article is a tube.

The shaped article of claim 9, wherein the article is a piece of furniture or a part of a piece of furniture.

Use of a shaped article as defined in claim 9 in the packaging industry.

Use of a shaped article as defined in claim 9 or 10 in laboratory and / or medical equipment.

Use of a shaped article as defined in claim 9 in the construction.