EP0480839A1 - Process for the manufacture of objects formed from paper pulp and device for carrying out the process - Google Patents

Abstract

Process for the manufacture of articles from paper pulp, comprising: 1) a forming stage in which paper pulp is applied to a mould in the shape of the article, and 2) a stage of drying the previously deposited paper pulp, in which heat is applied to the article previously shaped in the mould. According to the invention, during the two stages the mould (1) is stationary and substantially horizontal, the lower part (3) of the mould pointing upwards. In addition, during the shaping stage an overpressure is maintained at room temperature on the outer side (5) of the mould in relation to the inside (3) of the mould (1). Finally, during the drying stage, a reduced pressure is maintained on the outer side (5) of the mould in relation to the inside (3) of the mould (1). <IMAGE>

Description

The present invention relates to a process for manufacturing shaped parts, from paper pulp, and in particular from paper pulp of the quality commonly called "noble pulp" in this industry, the material of these molded parts having substantially the same rigidity. than some cartons.

The invention also relates to a device for implementing this method.

This process makes it possible to manufacture in particular toys, sculptures, decorations of objects, displays and / or packaging for cosmetic products, perfumes, drugs, food products, as well as parts that can be used in jewelry, hygiene or the arts in the form of packaging, boxes or advertising media.

Various devices are known for the production of paper pulp articles.

In particular, patent US-1 697 244 which is relatively old, relates to a machine for forming paper pulp comprising a wheel rotating around a horizontal axis and supporting at its periphery mold holders. At the bottom of this wheel is a container filled with paper pulp. This machine comprises means for maintaining a suction on the molds. Thus, a constant and uniform pressure is maintained on the layer of paper pulp placed in the mold, during the deposition of the paper pulp and the drying thereof. The drying is carried out by the aspiration of hot air through the paper pulp and the mold, during the passage of the latter in the drying chamber. Means are provided for supplying pressurized air to the interior of the mold so as to eject the article when dry.

The patents GB-1,137,761 and FR-1,399,753 are more recent but describe machines for the manufacture of hollow articles of paper pulp comprising similar means and in particular a mold carrier wheel.

It can be seen that, due to their rotation, these machines are complex, in particular as regards the supply systems, for example with compressed air. In addition, changing the molds on the wheel is a relatively long operation.

These machines have large dimensions, because the molds must be fixed on a wheel. Thus, the size of the parts molded by these machines is limited. It is, in particular, not possible to produce parts of a width 2 or 3 meters.

• 1°) appliquer de la pâte à papier dans une empreinte à la forme de la pièce et ménagée dans un support,par aspiration au travers de l'empreinte précitée de ce support, de sorte que la pâte à papier soit mise en forme sur l'empreinte, et
• 2°) sécher la pâte préalablement déposée.

These machines are intended to allow relatively high production rates and they are used for example to produce packaging and packaging for food products such as egg cartons. The known processes for manufacturing cellulose parts produced from paper pulp, implemented in particular by the use of the machines which have just been described, therefore consist in:

• 1 °) apply paper pulp in an impression to the shape of the part and formed in a support, by suction through the aforementioned impression of this support, so that the paper pulp is shaped on the 'imprint, and
• 2) dry the previously deposited dough.

• 1°) Mise en place d'une grille métallique à la forme de la pièce désirée , et définissant l'empreinte , qui est supportée dans une forme analogue en métal plein ou en un autre matériau résistant,destinée à éviter la déformation de la grille ou empreinte, relativement flexible.
  Cette forme en métal est percée d'une multitude de trous pour permettre l'aspiration au travers de cette grille qui la coiffe.
• 2°) Aspiration de la pâte au travers de la grille et de la forme en métal ou autre matériau résistant.
• 3°) Séchage de la pièce moulée par passage dans un four tunnel , dans lequel la pièce est entraînée par une bande transporteuse qui traverse le tunnel, le séchage de la pièce étant assuré par soufflage de jets d'air chaud le long de sa trajectoire dans le four tunnel, l'air chaud étant à une température suffisante pour la transformation du liquide rémanant en vapeur évacuée par un système de ventilation.

These known methods require the use of at least three separate complementary tools and include the following successive steps:

• 1 °) Installation of a metal grid in the shape of the desired part, and defining the imprint, which is supported in an analogous form in solid metal or in another resistant material, intended to avoid deformation of the grid or footprint, relatively flexible.
  This metal shape is pierced with a multitude of holes to allow suction through this grid which covers it.
• 2 °) Suction of the dough through the grid and the metal or other resistant material.
• 3 °) Drying of the molded part by passage in a tunnel oven, in which the part is driven by a conveyor belt which crosses the tunnel, the drying of the part being ensured by blowing jets of hot air along its trajectory in the tunnel oven, the hot air being at a temperature sufficient for the transformation of the residual liquid into vapor evacuated by a ventilation system.

• un premier outillage en métal présentant une empreinte négative de la pièce , et renfermant un ensemble de résistances électriques permettant l'élévation en température de l'outillage à une température comprise entre 260°C et 290°C, l'outillage et l'empreinte étant percés d'une multitude de trous pour laisser s'évacuer la vapeur ,
• un deuxième outillage, similaire au premier en ce qu'il présente une empreinte de la pièce renfermant un ensemble de résistances électriques et chauffantes et est percé d'une multitude de trous , mais tel que son empreinte soit de forme positive, et complémentaire de la forme négative de l'empreinte du premier outillage.

In another embodiment of the drying step, the part is dried using two complementary tools:

• a first metal tool having a negative imprint of the part, and containing a set of electrical resistances allowing the temperature rise of the tool to a temperature between 260 ° C and 290 ° C, the tool and the imprint being drilled with a multitude of holes to let the steam escape,
• a second tool, similar to the first in that it has an imprint of the part containing a set of electrical and heating resistors and is pierced with a multitude of holes, but such that its imprint is of positive shape, and complementary to the negative form of the imprint of the first tool.

Each of the two tools necessary for the implementation of the drying step of the process currently used, is of a complex embodiment and must have a shape corresponding to the part to be dried, which entails considerable cost and time for the manufacture of these devices.

These methods therefore require the use of several tools, several weeks to several months which may be necessary for making these tools, depending on the difficulty resulting from problems of adaptation to the shape of the part to be dried.

Furthermore, these methods are costly to implement, because of their high energy consumption for heating the tools or the tunnel oven.

In addition, the latter is bulky and its upkeep and maintenance complicate production operations.

As for the special drying tools described above, they are very expensive to manufacture and are only suitable for one size and shape of part. It is therefore necessary to produce new tools, with all the resulting production complications, for each different part.

As indicated above, the mold is, in general, constituted by an imprint, made of a metal grid shaped to the desired part and an element of similar shape but made in particular of a solid metal pierced with holes.

It is understood that, in known machines, a large suction must be applied to the mold when the latter is filled with paper pulp. Indeed, the mold is rotated by the wheel and the paper pulp is only held in the mold by the suction applied.

It can be seen that, due to the suction, the paper pulp enters the holes in the grid. This means that only parts having no undercut must be produced. Indeed, a part with an undercut could not be removed from the mold.

This constraint leads to significant drawbacks because it complicates the production of molds. In addition, the presence of undercuts can be advantageous in order to increase the impression of volume of the parts obtained, in particular in the case of production of displays for cosmetic products. It can also be absolutely essential if you want to make sculptures for example.

The present invention aims to remedy these drawbacks, and to provide various advantages, in particular consisting in significantly simplifying the processing device, in proposing a mold which can be executed quickly, generally within 24 hours, in allowing the production of pieces of any dimensions and may have undercuts and allow economical and easy implementation of the drying step, through the use of means in common with those used to shape the parts.

• 1) une étape de mise en forme dans laquelle on applique de la pâte à papier dans un moule à la forme de la pièce et
• 2) une étape de séchage dans laquelle on apporte de la chaleur à la pièce préalablement conformée dans le moule.

To this end, the invention relates to a method of manufacturing parts from paper pulp, comprising:

• 1) a shaping step in which paper pulp is applied in a mold to the shape of the part and
• 2) a drying step in which heat is supplied to the part previously shaped in the mold.

According to the invention, during the two stages, the mold is fixed and substantially horizontal, the internal part of the mold being directed upwards. In addition, during the shaping step, an overpressure on the outside of the mold relative to the inside of the mold is maintained at room temperature.

Finally, during the drying step, a vacuum is maintained on the outside of the mold relative to the inside of the mold.

Advantageously, the intensity of the overpressure maintained during the shaping step is chosen so as to obtain a substantially homogeneous and uniform layer of paper pulp inside the mold.

According to a first embodiment of the invention, during the drying step, heat is added to the room, by infrared radiation.

Preferably, the radiation produces a temperature between 100 ° C and 290 ° C.

According to a second embodiment of the invention, during the drying step, heat is added to the room by heating gases which are drawn through the room due to the vacuum.

In order for the drying of the part to be as short and as complete as possible, the hot gases drawn in during the drying step are at a temperature between 100 ° C and 290 ° C.

While the shaped part is still in the mold, it is dried either by radiation and gas suction, or by suction of gas previously heated through the mold and the support, so that all the stages of the manufacturing process is done until the molded and dried part is removed from the mold, using the same tool for molding, or shaping, and drying.

In order to limit handling and adapt to all shapes of parts, the piece of paper pulp is demolded by injection of compressed air through the mold, after drying.

As a variant, and in order to achieve cost savings, maintenance and handling for the parts, said parts can, in particular when they are large, be removed from the mold by means of a suction device with suction cup, which allows possibly use the same suction source as for the other process steps.

In order to increase the beauty of the part and to give it a better power of communication, the manufacturing process includes an optional additional step of coloring the molded part by depositing pigments on the surface of the part or by adding pigments in pulp. In the latter case, parts dyed in the mass are thus obtained.

In order to increase rigidity and aesthetics, the molded parts can be metallized.

In order for the parts placed outside or stored in damp or unprotected places to withstand the weather, the method of manufacturing the parts includes an optional step of waterproofing by a treatment of resins.

The invention also relates to a device for implementing the method which has just been described.

According to the invention, the mold is made of a porous and non-hydrophilic material.

Preferably, the material resists thermal shocks due to the passage of steam when the drying is obtained by suction of hot gases so that the lifetime of the mold is relatively long. For the same purpose, it is preferable to choose a material which does not oxidize.

This material can be composite.

Various details and advantages of the invention will appear clearly on reading the description which follows, given without limitation, with reference to the appended drawings, in which:

Figures 1 and 2 show, a piece respectively during the shaping step and in the still wet state, then during the suction drying step.

Referring to Figure 1, the device according to the invention for manufacturing parts from paper pulp, essentially comprises a mold 1, placed on a fixed support 2. The mold is arranged substantially horizontally, the inner part 3 of the mold being directed upwards. It is made of a porous gas material.

• on verse , manuellement ou par des moyens automatiques , une quantité appropriée de pâte à papier dans le moule 1,
• et on maintient, à température ambiante,pendant toute l'étape de mise en forme, une surpression ,du côté extérieur 5 du moule 1 par rapport à l'intérieur 3 du moule.

Part 4 is shaped as follows:

• an appropriate quantity of paper pulp is poured into the mold 1 manually or by automatic means,
• and maintaining, at room temperature, throughout the shaping step, an overpressure on the outside 5 of the mold 1 relative to the inside 3 of the mold.

This overpressure, the intensity of which is judiciously chosen, makes it possible to prevent the paper pulp from depositing at the bottom of the mold, due to the gravity, and to maintain a uniform and homogeneous layer of paper pulp on the inner part 3 of the mold.

During the drying step, a depression is established on the outside 5 of the mold 1 relative to the inside 3 of the mold and heat is added to the part previously formed in the mold. This depression can for example be obtained by means of a vacuum pump and a conduit opening at the rear of the mold 1. These devices are not illustrated in the figures.

This heat can be brought to the room by infrared radiation. This radiation is produced by an appropriate device which is not shown in the figures. This device produces in particular a temperature between 100 ° and 290 ° C.

The radiation value can be appropriately determined so that the part is heated without the mold being heated. This effectively protects the mold from thermal shock.

One can also choose to dry the part 4 in the mold 1 by sucking hot gases 6 through the part and the mold, the gas flow being directed from the top to the bottom of the mold, as illustrated by FIG. 2.

This suction 6 of hot gases can for example be obtained by means of a heating device placed above the mold and heating gases which are sucked in due to the vacuum. This device is not shown in FIG. 2. The gases used are preferably made up of ambient air.

Thus, the heating device heats the air to a temperature preferably between 100 ° C and 290 ° C, and the hot air 6 is set in motion through the mold 1 and the part 4, shaped in the mold, by said pump mounted at the end of said suction duct, which dries the shaped part 1 which is still in the impression.

Due to the vacuum, the paper pulp is fixed in the mold. Indeed, the mold, although not hermetic to the pressure, is impermeable to the paper pulp which cannot therefore be carried further by the depression , and this paste takes the form imposed by the mold, while being dried due to the temperature of the radiation or the air sucked in.

• soit par une distribution d'air comprimé, produite par une source d'air comprimé disponible dans l'atelier , cet air comprimé circulant de la même manière que l'air aspiré par la pompe, mais en sens opposé , et expulsant la pièce 4 du moule 1.
• soit un dispositif d'aspiration par ventouse qui est placé sur au moins une surface extérieure de la pièce, et par déplacement de la ou des ventouses sur la pièce 4.

Then the part 1 is removed from the mold in two possible embodiments:

• either by a compressed air distribution, produced by a source of compressed air available in the workshop, this compressed air circulating in the same way as the air sucked by the pump, but in the opposite direction, and expelling the part 4 mold 1.
• either a suction device by suction cup which is placed on at least one external surface of the part, and by displacement of the suction cup (s) on the part 4.

The mold 1 is preferably made of a non-hydrophilic material.

It is subjected to significant thermal shock when drying is ensured by the suction of hot gases and, to increase its service life, it is preferable to make it from a material resistant to thermal shock. For the same purpose, this material does not oxidize. Preferably, the mold 1 can in particular be made of a composite material to be quickly produced.

The process can include an additional step depending on the function assigned to the part, here are some specific examples.

In general, in order to present different aspects according to the different faces of the molded part, so as to modify the communication power of the part used, in particular as a display, the part is colored in an additional step by all types of pigment deposit on the surfaces of said part.

According to another embodiment, the parts obtained have been dyed in the mass by the addition of pigments in the paper pulp, prior to the various stages of the process which have just been described.

According to a specific embodiment, the parts can be metallized.

In order to present a refined appearance necessary in particular for display stands, the shade of the molded part can be obtained by spray painting.

In order to obtain different surface conditions, the process for manufacturing molded parts can include an additional lacquering step with or without baking, which makes it possible to adjust the quality of the surface to the function of the part and to render, in addition, the piece is completely waterproof.

It is clear from the above description that, because the mold is fixed and horizontal, the mold and therefore the part can be of any size.

In addition, the device is very simple compared to known devices. In particular, the mold can be changed very quickly, which is advantageous in the technical field targeted by the invention, when the series are small quantities.

The mold being arranged so that its lower part is directed upwards, the intensity of the gas suction established during the drying step is much lower than that which is necessary in the systems with rotating wheel which do not use not gravity. Thus, the paper pulp penetrates much less into the internal surface of the mold and it is possible to produce parts having undercuts.

Although the invention has been described in connection with a very specific process, it is in no way limited thereto and many variations can be made to it, such as for example all the processes allowing vaporization of residual liquid, in the conformation mold without departing from the scope of the invention.

The reference signs inserted after the technical characteristics mentioned in the claims, have the sole purpose of facilitating the understanding of the latter, and in no way limit their scope.

Claims (16)

Method for manufacturing parts from paper pulp comprising: 1) a shaping step in which paper pulp is applied in a mold to the shape of the part and 2) a drying step, in which heat is supplied to the part previously shaped in the mold, characterized in that, during the two steps, the mold (1) is fixed and substantially horizontal, the inner part (3) of the mold being directed upwards, in that, during the shaping step, an overpressure is maintained at ambient temperature on the outside (5) of the mold relative to the inside (3) of the mold ( 1) and in that, during the drying step, a vacuum is maintained on the outside (5) of the mold relative to the inside (3) of the mold. Method according to claim 1, characterized in that the intensity of the overpressure maintained during the shaping step is chosen so as to obtain a substantially homogeneous and uniform layer of paper pulp inside (3) of the mold (1). Method according to one of claims 1 or 2, characterized in that during the drying step, heat is added to the part (4) by infrared radiation. Method according to claim 3, characterized in that the radiation produces a temperature between 100 ° C and 290 ° C. Method according to one of claims 1 or 2, characterized in that, during the drying step, heat is added to the part (4) by heating gases which are, drawn through the part due to the Depression. Method according to Claim 5, characterized in that the said gases consist of ambient air. Method according to one of claims 5 or 6, characterized in that the hot gases (6) sucked in during the step drying temperatures are between 100 ° C and 290 ° C. Method of manufacturing parts, according to any one of claims 1 to 7, characterized in that after the drying step, the part (4) is released from the mold (1) by injection of compressed air through the mold. Method of manufacturing parts according to one of claims 1 to 7, characterized in that after the drying step, the part (4) is released from the mold (1) by means of a suction device with suction cup . Method for manufacturing parts according to any one of claims 1 to 9, characterized in that it comprises an additional step of coloring the shaped part (4), by depositing pigments on the surface of said part. Method of manufacturing parts according to one of claims 1 to 9, characterized in that it comprises an additional step of coloring in the mass of the part (4), by adding pigments to the paper pulp. Method of manufacturing parts according to any one of claims 1 to 11, characterized in that it comprises an additional step of metallization of the surface of the shaped part (4). Method of manufacturing parts according to one of claims 1 to 12, characterized in that it further comprises a step of waterproofing the parts (4), by a treatment of resins. Device for implementing the method according to one of claims 1 to 13, comprising a mold, characterized in that said mold (1) is made of a non-hydrophilic porous material. Device according to claim 14, characterized in that said material resists thermal shock and does not oxidize. Device according to one of claims 14 or 15, characterized in that said material is composite.

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