EP0158156A1 - Mouldable fibre mat and its manufacturing method - Google Patents

Abstract

A moldable fibrous sheet having a cellulose fiber and textile fiber base, said sheet having a composition comprising from 5 to 95% by weight of cellulose fibers obtained by dry shredding, from about 0.5 to 10% of textile fibers having at least two half-waves per centimeter of length, said sheet being further formed by superimposing fine sheets sewn but not rigidly connected to each other. The sheet may be molded into shaped panels through a molding cycle between 15 seconds and 3 minutes, which panels may be used in automobile construction, furnishing and packing.

Description

The present invention relates to a moldable fibrous mattress based on cellulosic fibers, as well as its manufacturing process, said fibrous mattress being intended for the production of shaped parts finding their application in many fields.

Are already known moldable and / or deformable materials based on wood fibers or wood flour, the presence in the composition of these materials of a vegetable cellulosic compound having for bur, either to lower the cost, or to confer certain mechanical characteristics, or even to combine these two elements. These known materials can be classified into three categories, namely, comprising only cellulosic fibers, a cellulosic powder associated with a thermoplastic material, or else natural fibers and synthetic fibers.

1 - In the first category, a mixture, in the form of a wet paste, consists of cellulose fibers including a small percentage of resin phenolic. The implementation of this material is relatively complicated insofar as it requires a wringing of the mixture in a preform and the conformation in a hot mold where the final drying and densification of the product takes place with a pressure of the order of 40 to 50 kg / cm ² . This results in a fairly long shaping time detrimental to a high yield, as well as costly tooling. Furthermore, the parts cannot receive a covering simultaneously with the molding operation.

2 - Also in the first category, a mattress of resinous wood fibers comprises a phenolic resin as well as rosin. The implementation requires rewetting of the mattress with steam, preforming on a cold mold followed by hot shaping at a temperature above 180 ° C by exerting a pressure of about 50 kg / cm ² . This material, if it gives the finished product good mechanical properties and is suitable for sheathing and painting, however requires very expensive shaping tools. It does not allow significant deformations to be obtained without the obligation to load critical areas with resins and cannot receive a covering during molding. In addition, its conformation cycle is relatively long, of the order of 2 minutes. Furthermore, the absence of porosity of the material in areas heavily loaded with resin implies that a microperforation operation precedes the cladding of the covering.

In the second category, plates are obtained by extrusion of a mixture based on polypropylene and a load of wood flour. The implementation requires preheating between 180 and 200 ° C of the plates using infrared radiation followed by conformation in a mold cooled for one minute at a pressure of 5 to 15 kg / cm ² . This material, if it requires only a low pressure and a short cycle for its conformation, leads to a brittle final product due to the absence of fibrous structure.

4. In the third category, a thermoformable cardboard based on cellulosic fibers and polyethylene fibers is obtained by the papermaking process. Its main drawback is that this cardboard can only be obtained with a grammage between 350 and 700 g / m ² , which requires stacking of several sheets in order to obtain the thickness and the final grammage required generally understood. between 2 and 3 kg / m ² . All of these sheets are preheated between heating plates (170 to 200 ° C) in order to obtain the melting of the polyethylene. The molding is obtained under a pressure of 25 to 50 kg / cm ² in a mold brought to a temperature of 80 ° C.

All the moldable materials based on cellulosic fibers which are currently available or which have been described in the prior art use either a papermaking type manufacturing process, therefore in a humid environment (cf. 4 above), or a process known in the plastics processing industry such as extrusion (cf. 3 above), or even a dry process of the "Rando Wood" type for shaping a fibrous mat from fibers wood of low residual humidity airborne to a modified "Rando" device. In the latter case, we get directly a fibrous mat having the desired final thickness.

The present invention aims to remedy the drawbacks of the above materials, by providing a moldable fibrous mattress, of easy implementation with a view to molding operations, having an excellent aptitude for significant deformations without tearing and thereby leading to shaped parts which are difficult to obtain with known materials.

According to the invention, the mattress has an overall composition comprising in particular from 5 to 95% by weight of cellulosic fibers resulting from dry defibering, and from 0.5 to 10% approximately of synthetic or natural textile fibers having at least two half-undulations per centimeter, said mattress being made up of a superposition of fine needled sheets but not rigidly linked to each other.

According to a first embodiment, the mattress comprises from 5 to 80% by weight approximately of said cellulosic fibers, from 0.5 to 10% approximately of said textile fibers and, moreover, from 5 to 60% by weight approximately of a material thermoplastic.

According to a second embodiment, the mattress comprises up to 95% by weight of said cellulosic fibers and from 0.5 to 10% approximately of said textile fibers, the cellulosic fibers being previously glued using a resin, for example phenolic.

For the manufacture of a mattress of the above type, the mixture of constituents is formed, the mixture thus obtained is carded, a fine sheet of a grammage between 10 and 200 g / m ^{2 is formed} , successive folds of said ply are superimposed by lapping and a needling is carried out to form the mattress, the grammage of which is adjusted to the desired value, up to approximately 2 kg / m ² .

In the particular case of the second embodiment, as defined above, the sizing of the cellulose fibers is carried out before mixing with the textile fibers.

Other characteristics and advantages of the present invention will emerge more clearly from the description which follows, given by way of explanation but in no way limiting.

The cellulose fibers are advantageously of the type obtained thermomechanically from wood and have a low residual humidity, less than 15%, which in no way excludes the possibility of using cellulose fibers obtained by another associated defibering technique. to possible refining according to the various processes well known in the paper or in the fiberboard sector. These fibers may, if necessary, have received a treatment capable of giving them certain properties required depending on the intended application. By way of nonlimiting example, a wax or paraffin can be incorporated in order to obtain a final product that is not very sensitive to water.

The textile fibers having a crimp of several half-undulations per centimeter must have a length such that during the shaping of the mattress by the carding, topping and needling technique, they give a certain mechanical strength to the mattress in order to make it transportable without other form of consolidation.

Furthermore, these fibers will confer a certain deformability on the material without any tearing phenomenon being manifested within the mattress. By way of nonlimiting example, polypropylene or polyester fibers of 38 mm of average length and comprising 3 to 5 half-waves per centimeter have been found to be perfectly suitable.

1 - In the case of the first embodiment mentioned above, the thermoplastic material is an integral part of the mattress, either in the form of fibrils or fibers, or in the form of powder.

In the case of fibrils or fibers, the constituent material is thermoplastic and with a softening point of less than 200 ° C. By way of nonlimiting example, mention may be made of polyethylene or polypropylene fibers.

These thermoplastic fibers, after melting or softening during the subsequent preheating operation, will give better cohesion to the molded product, better mechanical characteristics as well as a certain hydrophobicity in the shaped panel.

Furthermore, the creep in the mold of the thermoplastic material heated beyond its softening point improves the moldability.

It is also possible to envisage, instead of thermoplastic fibers, a thermoplastic polymer in the form of powder or granules of small diameter. This polymer should also have a softening point below 200 ° C.

There are two cases for the operation of mixing the constituents of the mattress:

a) the thermoplastic material is in the form fibers or fibrils:

The three constituents in adequate proportions are mixed in a rotary machine, possibly consisting of a gluing machine. In general, the thermoplastic fibers or fibrils delivered in voluminized form must be separated beforehand in a device of the opener type such as those used in the sector of the textile industry. The same will be true of textile fibers from 10 to 60 mm in length which must receive a similar pretreatment.

b) the thermoplastic material is in the form of powder or granules of small diameter:

Only wood fibers and textile fibers are then mixed in the desired proportions in the rotary machine. The thermoplastic material is subsequently poured in the form of powder or granules of small diameter at the level of the conformation of the mattress using an appropriate device, for information, at the topping stage. In this case, the mattress can be considered to consist in a non-homogeneous manner but more precisely of a succession of alternating layers of small thickness.

The conformation of the mattress calls for textile-type equipment associating a loader, a carding device, a coating machine and a needling machine.

The carding machine must be provided with a carding machine adapted to the treatment of the fibrous mixture previously described so that there is neither jamming in the machine nor segregation between the long fibers and the short fibers, or at least, the least segregation possible.

If necessary, the carding machine will be fitted with a covering designed to constrain the fibers to pass through the carding cylinder or cylinders, as well as a device for recovering short fibers which can be returned to the machine head in the loader.

On leaving the carding machine, the fibrous mixture comprising the wood fibers, the thermoplastic material as well as the very long textile fibers is in the form of a sheet of low grammage (10 to 200 gm ² ) which is possibly maintained by a suitable device of the double canvas type up to the tablecloth.

This layer makes it possible to constitute a mattress of heavy grammage (2 kg / m ² approximately) by successive stacking of layers. The weight of the mattress per square meter can be easily modified by varying, for example, the relative speed between the feeding and exit belts of the coating machine. The number of back and forth movements of the mobile device of the coating machine gives the number of successive stackings in a given time and allows the grammage of the mattress to be adjusted over a wide range. Likewise, the mattress can be obtained in variable widths by simply adjusting the travel of the reciprocating device of the coating machine. The maximum width will only depend on the length of the guide on which the covering element moves. Optionally, an appropriate device associated with the coating machine will make it possible to pour the thermoplastic material in the form of powder or granules of small diameter in order to constitute a material in layers.

This thermoplastic material can thus be inserted, either during each stack of plies coming from the carding machine, or even after a determined number of stacks of plies.

The low density "Mat" is then conveyed by a conveyor belt placed perpendicular to the carding-lapping axis, to a needling machine or possibly a pre-needling machine which will give the final mattress its self-support. At this stage, the mattress has the consistency of a carpet and can therefore be rolled up on itself. It is in this form of rolls or reels that it can be handled with a view to the transformation or molding operation, without however excluding presentation in format if necessary, thanks to an appropriate cutting device.

The density of needles of the needling machine makes it possible to vary to a certain extent the thickness of the mattress that one wishes to obtain as well as its mechanical strength. Thus, a small needling will lead to a sparse but very compressible mattress, while a tighter needling will make it possible to develop a thinner mattress.

However, in all cases, this needling operation, while imparting sufficient mechanical strength to the mattress to be easy to handle, will allow the "mat" to retain excellent deformability in all directions from which it will result in very good ability during molding, the latter resulting in particular from the possible play of the fine plies with respect to each other.

If necessary, it is possible to add at the time of needling to the surface of the mat a surface material which may either participate to the decoration of the finished part after molding, or to facilitate the fusing of the decorative material. By way of nonlimiting example, the mattress emerging from the tablecloth and a synthetic veil of the nonwoven type made of polyethylene, polypropylene or any other thermoplastic material with a softening point of less than 200 ° C. can be needled simultaneously, which, once heated, will allow a better hold of the decorative material by thermofusion or heat-bonding of this nonwoven.

It is essential that the surface material, whether present for decorative purposes or included in order to facilitate the attachment of another support to the finished panel, is itself highly extensible in all directions so as not to interfere unfavorably on the moldability of the fibrous mat.

In the case where the mat contains one or more thermoplastic components, the molding or shaping operation of the mattress is preceded by a stage of preheating the mattress, preferably just before going through the press. However, it cannot be excluded that a suitable device attached to the press very quickly performs this preheating of the mattress.

The purpose of preheating is to bring the thermoplastic material or materials present in the mattress to a temperature above their softening point.

These thermoplastic materials will thus creep during pressure molding and participate, after cooling, in the consolidation of the shaped panel while giving it certain desired physical properties, hydrophobicity for example. In practice, the preheating temperature is between 100 and 200 ° C.

By way of nonlimiting example, preheating may use contact, hot air through and high frequency heating devices.

The apparatus which seems the most suitable in order to have a good homogeneity of cooking of the fibrous mat and a short heating time compatible with the molding cycles, is a heating device by high frequency possibly associated with a heating by contact of the plates. of the device.

After preheating, the mattress is immediately transferred to the press in order to proceed with molding. Optionally, a decorative material constituting a surface "skin" is interposed between the temperature mattress and the mold. The molding can be carried out with a cold mold, or a slightly heated mold. In some cases, in fact, a mold brought to a temperature between 60 and 100 ° C. gives a better surface finish to the finished part.

The molding cycle is between 15 seconds and 3 minutes and the pressure exerted between 20 and 100 kg / cmz. Leaving the press, the material without decorative coating appears as a shaped fibrous panel, with a density between 0.7 and 1.1.

The above moldable mattress makes it possible to obtain parts with strong deformation, free from tears or lack of material, following stretching. The shaped parts thus obtained remain sufficiently porous to carry out a subsequent dressing by suction through the constituent panel.

The nonlimiting example below will better illustrate the manufacture and treatment of a mattress according to the first embodiment according to the invention.

EXAMPLE Basic mixture:

These three constituents are mixed in a gluing machine with rotating fingers adjusted to an appropriate speed of rotation. The mixture is then introduced into a loader which feeds a carding machine in line with a coating machine.

On leaving the coating machine, the mattress weighing between 700 and 2500 g / m ² is needled to form a roll.

If necessary, it is possible to perform a pre-needling on an 800 g / m ² mattress followed by a final needling on a stack of 3 identical mattresses in order to constitute a "mat" with a weight per square meter of 2, 4 kg.

The "mat" is then preheated by means of a high-frequency heating device by dielectric losses, the power of which is between 30 and 50 kw / h and comprising 2 heating plates maintained at a temperature in the region of 140 ° C.

The mattress portion of approximately one square meter is thus brought homogeneously, both to the heart and to the surface, at a temperature of 170 ° C between 30 seconds and one minute depending on the power delivered by the high frequency generator ( frequency 27.12 MHz).

This preheating device is located in the immediate vicinity of the press in order to have a minimum of heat loss during the transfer of the mattress between the preheating station and the press. Optionally, this transfer can be carried out in a thermally insulated tunnel opening at the level of the press plates.

The molding requires between 20 seconds and 2 minutes depending on the type of part, in a cold mold, or at 80 ° C maximum. In general, a cycle of the order of 45 seconds to 1 minute makes it possible to obtain pieces of desired deformation and with an adequate densification of the material.

A pressure of between 40 and 60 kg / cm ² is exerted on the mattress in order to obtain the required properties. Heating the mold to a temperature of 80 ° C. leads to a better surface condition of the finished part without having a fibrous appearance. The surface is then slightly glazed.

After cooling, the shaped material remains sufficiently porous in air to require no other operation of the microperforation type.

II - In the case of the second embodiment mentioned above, the cellulosic fibers and the textile fibers respectively have the same characteristics, but the content of cellulosic fibers can reach 95% by weight while the content of thermoplastic material is zero.

At the level of the manufacture of the mattress, the cellulosic fibers are glued with a thermosetting resin before mixing with the textile fibers, the sequence of operations being identical.

Regarding the molding of the mat according to this second embodiment, the preheating operation is eliminated since no thermoplastic material is to be brought to its melting point, while a steam treatment is carried out just before molding or during molding in a known manner. itself, the molding being carried out in a hot mold at a temperature sufficient for the polymerization of the sizing resin, for example at a temperature above 200 ° C. for a phenolic resin. The molding cycle and conditions are identical for the two embodiments described above.

Thanks to the mattress according to the invention, it is possible to mold parts such as shaped panels for interior trim of automobile doors comprising an integrated armrest, from which a very strong deformation results. No tear initiation is noted, even on the parts with strong stretch.

Tests have also shown that it is possible, at the implementation stage (pressing), to optionally introduce a lining material (carpet, PVC) which remains heat-bonded to the shaped panel.

Cutting and inserting inserts can also take place in the same cycle, resulting in ease of implementation and increased productivity.

It should be noted that at the level of the coating operation, it is also possible to add to the material a compound which generates water vapor during the molding stage, such as an iron alum for example, if the content of cellulosic fibers is high and their humidity less than 15%.

Furthermore, with regard to the packing materials, it is also possible, at the level of the coating operation, to interpose one or more layers with particular properties.

• - construction automobile en tant qu'habillages intérieurs de véhicules : garniture intérieure des portières, tableaux de bord, pied milieu, tablettes arrière, gainages divers, fonds de dossier, pied d'auvent, etc. ;
• - ameublement ;
• - articles de voyage : valises, malles, etc.
• - emballage, conditionnement ;
• - agencement : boîtes à lettres par exemple ;
• - capotages divers en bureautique.

As indicated above, the mattress according to the invention can find various applications involving shaped panels, such as in the following fields:

• - automobile construction as interior trim for vehicles: interior trim for doors, dashboards, center leg, rear shelves, various covers, backrests, awning foot, etc. ;
• - furniture;
• - travel items: suitcases, trunks, etc.
• - packaging, packaging;
• - layout: mailboxes for example;
• - various cowlings in office automation.

It is understood that the present invention has been described for explanatory purposes but is in no way limiting and that any useful modifications may be made to it, in particular in the field of technical equivalences, without going beyond its ambit.

Claims (12)

1. Moldable fibrous mattress, based on cellulosic fibers and synthetic or natural textile fibers, characterized in that it has a composition comprising from 5 to 95% by weight of cellulosic fibers resulting from dry defibration, from 0 , Approximately 5 to 10% of textile fibers having at least two half-corrugations per centimeter in length, said mattress furthermore consisting of a superposition of fine needled plies but not rigidly linked to each other. 2. Fibrous mattress according to claim 1, characterized in that the cellulose fibers are of the type obtained thermomechanically from wood and that they have a residual humidity of less than 15%. 3. fibrous mattress according to one of claims 1 or 2, characterized in that the textile fibers have a length of at least 30 mm, with a crimp of at least two half-undulations per centimeter and that they are made up of polypropylene or polyester. 4. Fibrous mattress according to any one of claims 1 to 3, characterized in that it comprises from 5 to 80% by weight of cellulose fibers, from 0.5 to 10% by weight of textile fibers, and in addition , from 5 to 60% by weight of a thermoplastic material. 5. Fibrous mattress according to claim 4, characterized in that the thermoplastic material consists of fibrils, fibers or a powder made of a material having a softening point below 200 ° C, such as polyethylene or polypropylene. 6. Fibrous mattress according to any one of claims 1 to 3, characterized in that it comprises up to 95% by weight of cellulosic fibers and from 0.5 to 10% by weight of textile fibers, exclusion of thermoplastic material. 7. fibrous mattress according to any one of claims 1 to 6, characterized in that the fine sheets have in themselves a grammage of 10 to 200 g / m ² , for a grammage of said mattress of approximately 2`kg / m2. 8. A method of manufacturing a fibrous mattress according to claim 6, characterized in that the cellulose fibers are glued with a thermosetting resin, the fibers thus glued and the textile fibers previously opened are mixed, the mixture is carded thus obtained in the form of a fine sheet of a grammage of 10 to 20 _U g / m ² , successive folds of said sheet are superimposed by coating to form the mattress whose grammage is adjusted to the desired value up to 2 kg / m ² approximately, then a needling is carried out of said mattress. 9. A method of manufacturing a fibrous mattress according to any one of claims 1 to 5, characterized in that the cellulosic fibers, the textile fibers previously opened and the thermoplastic material are mixed, the mixture thus obtained is carded in the form of a fine sheet of a grammage of 10 to 200 g / m ² , then successive folds of said sheet are superimposed by laying to form the mattress, the grammage of which is adjusted to the desired value up to 2 kg / m ² approximately, then a needling is carried out on said mattress. 10. Application of the moldable fibrous mattress according to any one of claims 1 to 5, for molding shaped panels, characterized in that a molding cycle is carried out between 15 seconds and 3 minutes, at a pressure included between 20 and 100 kg / cm ² , cold or at a temperature between 60 and 100 ° C, with preheating to a temperature above the softening point of the thermoplastic material and which optionally incorporates a surface material immediately before the molding cycle. 11. Application of the moldable fibrous mattress according to claim 6, characterized in that a steam pretreatment is carried out and that a molding cycle is carried out between 15 seconds and 3 minutes, at a pressure between 20 and 100 kg / cm ² in a hot mold, at a temperature sufficient for the polymerization of the thermosetting resin. 12. Shaped panels obtained by means of a moldable fibrous mattress according to any one of claims 1 to 7 and having a density of between 0.7 and 1.1.