The invention relates to a method, apparatus and use in manufacturing a product based on thermoplastic according to the preambles of the independent claims .

Today, compression molding is a commonly used method in manufacturing a wide variety of 3D-objects, which is typically based on preheating a manufacturing material into a processing temperature before it is pressed into form in a mold. The benefits of compression molding are its inexpensive mold expenses especially when compared to parallel manufacturing processes, such as e.g. injection molding. As a disadvantage in compression molding is, however, in some cases a nonhomogeneous composition of a manufactured product and controlling of flash being produced in the manufacturing, which is why it is not applicable for manufacturing of certain types of products.

With reference to compression molding, a variety of methods is known, in which in mold arrangements thermosetting plastic and thermoplastic are shaped with both organic and inorganic fibers. Used cellulose based fibers, such as hemp, flax, jute, sisal and kenaf, are used a lot. Correspondingly, from synthetic fibers, viscose, fiberglass and carbon fiber are often used. In addition to these, textile waste is applicable in different compression molding techniques. Thermoplastic is being mixed with other fibers as a fiber-like substance and being carded or being felted with other non-woven techniques. In thermosetting plastic structures felt is only made of fibers and thermosetting plastic is appli- cated or impregnated into the felt before compression molding. In these kinds of fibers, there are often impurities, which present themselves in the end products as unpleasant odors . However, the manufacturing methods of materials based on thermosetting plastics differ significantly from thermoplastic based manufacturing materials and their utilizing purposes differ significantly from one anot- her, which is why methods based on thermosetting plastic and thermoplastic are not comparable with each other .

The main reason for the above mentioned is that the fibers used in connection with thermosetting plastic materials are not able to form chemical bonds between each other, but instead they move freely with respect to each other. This free movement is an advantage when deep forms are created in compression molding, but the form that has been created has, however, to be "locked". This is achieved in two ways in practice, which are by melting the thermosetting plastic and cooling it down into form in the. mold, or by warming up the thermosetting plastic applicated into the felt and crossbridging it into form in the mold. The above mentioned methods are slow from the point of view of process industry, which increases unit costs of the products. As examples of the above mentioned methods, US 2004 / 094867 and US 6695939 may be mentioned. The former is a thermosetting plastic based method and the latter is a two-phase process, in which the material is first being melted by heat in a temperature rising above the melting temperature of plastic (in a plane-type hot press) and thereafter being transferred into a cold press, where it is shaped. A two-phase method like this and problems thereof are explained further in the following .

Today, especially in the manufacturing of products manufactured from composite materials based on thermoplastic, especially GMT (Glass Mat Reinforced Thermoplastic) -manufacturing process has been proven efficient. This process works, with reference to a general operating principle shown e.g. in figure 1, in a way that the plane-like plates or sheets used in the manufacturing of the product are stacked on top of each other, after which the pile is being heated in an oven. After the manufacturing material has reached its melting point, it is being shaped in a pressing mold and furthermore cooled down into a firm end product, by cooling down a steel mold commonly used in that context in a liquid operated manner.

As mentioned before, compression molding is a technically efficient and economically affordable process as such. It is, however, in itself not a recommended manufacturing process especially for processing of thermoplastic based composite materials that contain natural fibers, because natural fibers are very sensitive to high temperatures and degrade easily, which leads to weakening of the mechanical properties of the manufactured product and on the other hand to darkening of color. In this context, a term thermal loading is being commonly used, which is determined as a function of time and temperature, which both have an effect on the degradation or degeneration of the natural fiber. A problem in the processing of materials containing natural fibers is furthermore the fact that the best surface quality, which means a so called closed surface in the manufactured product, is only achieved by using a mold that is hot enough, which is impossible, if the temperature of the mold during shaping of the material is less than the melting point.

From the publication DE 3614533, a method and apparatus for the manufacturing of a thermoplastic product and the use of compression molding in the putting together of a product made of composite material is already known. In the solution according to this publication, the composite structured product being manufactured from a thermoplastic based substance is put together by a compression molding process from a composite material substance containing natural fiber by using a mold arrangement, by means of which the composite material substance having been fed therein is being heated into the thermoplastic's melting temperature and, by means of which the product to be manufactured is cooled down after it has been pressed into form.

The above mentioned solution is based on that that natural fiber substance in the composite material substance is mechanically bonded, which means that it is so called textile structured, thanks to which the compression molding being carried out as cold molding according to the publication is a functional way of manufacturing as such. This is by virtue of the fact that the fibers of the web of the mechanically bonded natural fiber substance, meaning e.g. a textile structure (woven structure) or a felt structure (non-woven) , are able to move with respect to each other when the composite material substance is cold pressed, thus enabling the composite material to be pressed into form.

Instead of the above, when using in the processing a composite material that contains natural fiber substance, in which its plastic substance and possible additional ingredients are inside a chemically bonded 3D-web formed by natural fiber substance, the cold molding based compression molding according to the above mentioned publication is not possible, because a chemically bonded natural fiber substance may not be cold shaped without it getting torn or wrinkled in an uncontrollable manner in the mold. Therefore, if a composite material substance containing a chemically bonded natural fiber web is being set into the mold cold, after which the mold is being closed and, wherein the heating of the composite material substance only takes place after that, the pressed product may be fine externally, but the natural fiber web inside is, however, broken.

The purpose of the method, apparatus and use in manufacturing a product based on thermoplastic according to the present invention is to provide a decisive improvement in terms of the above described problems and thus to substantially upgrade the level of prior art in the field. In order to fulfill this purpose, the method, apparatus and use in manufacturing a product based on thermoplastic according to the invention are principally characterized by what is presented in the characterizing parts of the independent claims related thereto.

The most important benefits gained by the method, apparatus and use in manufacturing a product based on thermoplastic according to the invention notably include the simplicity and efficiency of the technique used in connection with the utilization of the same, especially thanks to the possibility to use in itself technically and economically affordable compression molding also in the manufacturing of products to be put together from a composite material containing natural fiber, when using in the processing especially a composite material substance that contains non-cold-formable natural fiber substance, in which its plastic substance and possible additional ingredients are inside a chemically bonded 3D-web formed by the natural fiber substance. When utilizing the invention, thermal loading of the natural fiber substance in the product being manufactured may be efficiently diminished thanks to the possibility to minimize the length of the heating period of the composite material substance, being carried out by the mold arrangement as a "heating stroke" that lasts as short as possible. Thanks to this, there is no time for an excessive thermal loading to be directed to the natural fiber substance, but optimal mechanical properties and on the other hand _, also good surface quality and, the desired coloring of the product being manufactured are, however, enabled. When diminishing the thermal loading directed to the natural fiber substance, thanks to the invention, a higher than normal compres- sion molding temperature may be used and therefore further advantages in the mechanical properties, among other things, in the product being manufactured may be achieved partly also thanks to the possibility to use plastics that melt in higher temperatures, which is not possible when using traditional manufacturing techniques .

As an advantageous embodiment of the invention, the composite material substance is being heated in the preheating phase at a temperature essentially lower than the melting temperature of the thermoplastic, wherein the duration of the heating at the melting temperature in the mold arrangement can be minimized. In a respective manner, it is also possible to preheat the mold arrangement in a way that also heating of the same at the melting temperature can be performed as fast as possible. In the invention, it is furthermore advantageous to utilize as the natural fiber substance cellulose fiber, such as cellulose or its chemical modifications (derivates) , produced in a water suspension or the like solution, which, as it dries, forms a 3D-web with hydrogen bonds by its OH-groups (hydroxyl group) . When applying the invention, a cellulose that has been ground in a water suspension is able to form a chemical web when water gets removed and thanks to this, it is able to form a firm 3D-web throughout the structure. Thus, the cellulose fibers are no longer able to move with respect to each other without the structure getting broken by tearing. Thermoplastic particles are in this case locked inside the chemically bonded cellulose web, which particles form partial hindrances for the perfect formation of the cellulose web, but, which while melting, add more stretch into the web and, while cooling down, lock the form that has been created in the compression molding. When the invention is applied advantageously, this web, being preheated close to the melting point of the thermoplastic, is being transferred into the mold, wherein the mold is heated typically with hot water or steam or with another heating medium at a temperature above the melting temperature of the plastic in question. When the mold is being closed, the plastic being preheated under pressure melts instantaneously, wherein at the same time cooling water or other medium is being led into the mold, with which the temperature of the mold is decreased below the sof- tening point of the thermoplastic typically in 2-10 seconds depending on the thickness of the product. After this, the mold may immediately be opened and the product removed therefrom. Thus, with the above explained arrangement, a process cycle may be achieved that lasts only 2-10 seconds. This corresponds practically to the cycle times of modern mass production lines, such as injection molding, and significantly elevates the profitability of the process. In addition, a cellulose web formation that has been molded with the arrangement is left intact in the manufactured product. The unbroken, throughout the product existing 3D-web strengthens the end product significantly and thus, thanks to the in- vention, lighter products can be manufactured with respect to traditional compression molding that has been explained earlier. In addition, as an advantage of the invention may be mentioned better deep drawing than with laminated paper, which is often used e.g. in the packages of food industry. Also in this context, deeper forms as well as considering the used plastic, also additional properties, such as different kinds of barrier properties, are achieved. Other advantageous embodiments of the method, apparatus and use in manufacturing a product based on thermoplastic according to the invention are presented in the dependent claims related thereto.

The invention will be discussed in detail in the subsequent specification with reference to the accompanying drawings, in which: in figure 1

is shown in an exemplary manner a general operating principle of a GMT-compression molding process, and in figures 2a-2d

is shown in an exemplary manner a general operating principle of a compression molding process according to the invention.

The invention relates first of all to a method in manufacturing a product based on thermoplastic, wherein a. composite structured product to be manufactured from thermoplastic based material is being put together by a compression molding process from composite material substance comprising natural fiber by using a mold arrangement 2, by means of which composite material substance, being fed thereto, is being heated II at a melting temperature of the thermoplastic and, by means of which the product 1 ' to be produced is being cooled III after pressing P thereof into form. On the principle shown in figures 2a-2d, in the processing a composite material 1" is being used, which contains non- cold-formable natural fiber substance and in which plastic substance and possible additives are inside a chemically bound 3D-web formed of the natural fiber substance, whereby formability of the said 3D-web for performing the compression molding is being achieved by preheating the plastic substance in the natural fiber substance inside the 3D-web prior to performing the compression molding in the stages depicted with figures 2c and 2d.

As an advantageous embodiment of the method according to the invention, particularly with reference to figure 2b, the composite material substance 1" is being preheated la in a separate pretreat ent stage at an essentially lower temperature than the melting temperature of the thermoplastic particularly to minimize thermal loading directed to the natural fiber substance in the composite material substance, in order to soften the plastic substance in the natural fiber substance inside the 3D-web prior to feeding the composite material substance 1" into the mold arrangement 2.

As a furthermore advantageous embodiment of the method according to the invention, the mold arrangement 2 is being heated lb at the melting temperature of the thermoplastic prior to feeding the composite material substance 1" thereto.

With the preheating arrangements described above and by heating of the mold arrangement at the melting temperature of thermoplastic prior to the composite material is being fed therein, such an advantage is achieved that the thermal loading being directed to the composite material substance 1" may be minimized.

As a furthermore advantageous embodiment, in the processing as the natural fiber substance cellulose fiber is being used, the cellulose fiber, such as cellulose or its chemical modifications (derivatives) , being manufactured in a water suspension or the like solution, which when drying forms a 3D-web with hydrogen- bonds by its OH-groups (hydroxyl group) . In this context, in the invention, e.g. a cellulose fiber-plastic (typically 30-70 %) composite material substance is advantageously utilized, which substance has dried at least to some extent and having formed the OH-bonds before compression molding. In the composite material substance, there may, however, still be some humidity left (e.g. 0-25 %) , despite of which the OH- groups are anyhow formed prior to the compression molding.

As a furthermore advantageous embodiment, the heating and cooling stages directed to the composite material substance 1" are being carried out quickly in 2-10, preferably in 5 seconds/material thickness in millimeters of the product to be produced, in which way the thermal loading directed to the natural fiber substance can be further significantly decreased.

Both dry pulpered and so called Never dried- cellulose fibers, being manufactured e.g. in a water suspension or in some other possible solvents, when drying, form a 3D-web as described above, wherein the plastic substance of the composite material substance and possible additional ingredients are left inside this web. When pressing together this type of natural fiber composite material, the fibers do not move between each other, but instead, they preserve the 3D-web. and only get modified. Instead, as mentioned above, the fibers of a 3D-web, e.g. formed of intertwining fibers, slide between each other in the compression molding process. However, when it comes to all natural fibers jointly, they do not melt or thermoform.

The invention relates on the other hand to an apparatus meant for applying the above explained method for manufacturing a product based on thermoplastic and consisting of composite material substance 1 containing natural fiber by using a compression molding process, which apparatus comprises, especially with reference to figures 2c and 2d, a mold arrangement 2 in connection with which is arranged at least a heating arrangement 3 for heating a composite material substance 1 that is fed thereto at a melting temperature of the thermoplastic and on the other hand a cooling arrangement 4 for cooling a product 1' in the mold arrangement 2 after pressing P thereof into form. The apparatus comprises, particularly in order to process a composite material substance 1" containing non-cold-formable natural fiber substance, in which plastic substance and possible additives are inside a chemically bound 3D-web formed by the natural fiber substance, by exploiting compression molding, a preheating arrangement in order to achieve formability of the said 3D-web for performing the compression molding by preheating the plastic substance in the natural fiber substance inside the 3D-web prior to performing the compression molding. As an advantageous embodiment of the apparatus according to the invention, the preheating arrangement comprises with reference to figure 2b a separate preheater 3' for preheating la the composite material substance 1" at a temperature essentially lower than the melting temperature of the thermoplastic particularly in order to minimize thermal loading directed to the natural fiber substance in the composite material substance, for softening the plastic substance in the natural fiber substance inside the 3D-web prior to feeding of the composite material substance 1" into the mold arrangement 2. When melting heat of the plastic substance is avoided at this stage, thermal loading directed to the natural fiber substance can significantly be minimized .

Furthermore, the invention relates to use of a compression molding process, being based on the heating of a manufacturing substance to be used in manufacturing of a product based on thermoplastic and the cooling of a product being pressed into form in a mold arrangement 2, with reference to the general operating principle shown e.g. in figures 2a-2d, in order to put together a composite structured product from a composite material substance 1" particularly containing non-cold-for- mable natural fiber substance, in which its plastic substance and possible additives are inside a chemically bound 3D-web formed by a natural fiber substance, first of all by preheating la the composite material substance, particularly in order to minimize thermal loading directed to the natural fiber substance in the product 1" to be produced preferably at an essentially lower temperature than the melting temperature of the thermoplastic by a preheating arrangement, in order to achieve formability of the natural fiber substance inside the said 3D-web in the natural fiber substance for performing the compression molding, and thereafter especially on the principle shown in figures 2c and 2d' by heating II with the mold arrangement 2 the composite material substance 1" being fed thereto at the melting temperature of the thermoplastic, and furthermore by cooling the same III after pressing P thereof into form.

Thus, as a furthermore advantageous embodiment, the invention relates to use of a compression molding process in the manufacturing process of a product to be manufactured from a composite material substance 1" containing natural fiber, whereby the natural fiber substance being used is cellulose fiber, such as cellulose or its chemical modifications (derivatives) , being manufactured in a water suspension or the like solution, which when drying forms a 3D-web with hydrogen- bonds by its OH-groups (hydroxyl group) , and/or a substance that forms a 3D-web by intertwining, such as cellulose, viscose and/or the like. It is clear that the invention is not limited to the embodiments shown or described above, but instead it may be varied in various ways depending on the composition of the natural fiber composite material at any given time etc. Thus, it is first of all clear that in the manufacturing also other part-ingredients may be used, such as wood, stone, glass-based materials etc. or deviating from what has been shown in figures 2a-2d a mold arrangement with more parts may be used. It is also possible to affect the electricity conducting properties of the product that is manufactured by mixing it with electrically isolating ingredients or ingredients that increase electrical conductivity. The electricity conductivity of the manufacturing material is possible to carry out e.g. by using a plastic material that conducts electricity and/or by mixing metal into one of its ingredients etc. In addition, in the heating and cooling arrangements of the compression molding process, it is possible to use whatever sufficiently effective heating/cooling technique in addition to traditional electrical and/or liquid/steam operated arrangements .