GB2053300A - Improved process for impregnating profiled fibrous materials with bitumen, and impregnated materials thus obtained - Google Patents

Abstract

Process for impregnating profiled fibrous materials, in particular cellulosic materials, with hot bitumen. It fundamentally comprises impregnating in vacuo, profiled elements of this material which are advantageously grouped together in a compact load constituting a unit charge, with, if desired, recycling of the hot bitumen for a certain period of time, and, if appropriate, cooling this impregnated charge by immersing it in hot water, this cooling itself being followed, if appropriate, by again subjecting the charge of impregnated profiled elements to a vacuum. Application to the manufacture of improved roofing, boarding or sealing elements.

Description

SPECIFICATION Improved process for impregnating profiled fibrous materials with bitumen and impregnated materials thus obtained The present invention relates to the preparation of profiled fibrous materials, in particular cellulosic materials, impregnated with bitumen; the invention also relates to the preparation of tinted, profiled fibrous materials, in particular cellulosic materials, impregnated in bulk with hot bitumen.

Conventionally, in order to impregnate profiled cellulosic materials with bitumen for the purpose of preparing roofing and boarding materials, the materials, shaped and dried beforehand, are immersed in a hot bitumen bath in either a continuous or discontinuous procedure.

However, this conventional technique has several disadvantages. First of all, impregnation carried out in this way is slow because the hot bitumen does not easily drive out the air and the water which are still present, at this stage, in the bulk of the cellulosic materials subjected to impregnation. This results in substantial deterioration of the cellulosic fibres and, consequently, in a distinct reduction in the mechanical strength (tensile strength, splitting force, impact strength and the like) of the final materials, in particular of the profiled plates or the ridge tiles manufactured in this way, because, at the impregnation temperature, which is above 1 500C, the degradation of the cellulose is rapid and increases with the length of time for which the cellulose is immersed in the hot bitumen.Furthermore, this technique frequently leaves an unattractive bead of bitumen on the lower part of the materials, which emerge from the hot bitumen bath with an approximately vertical orientation, which bead can soil and represents an unnecessary additional consumption of impregnation product, this bead resulting from the excess of bitumen which flows under gravity along the impregnated materials, the cellulose proving incapable of absorbing it.

Furthermore, this technique requires a bulky installation and involves keeping a large amount of bitumen at a high temperature; it therefore demands heavy investments, which take a long time to produce a profit, and high energy consumption, because each element of the material to be impregnated must be clearly separated from the next so that there can be a good contact between the cellulose and the bitumen bath.

Another technique for the impregnation of cellulosic materials is also known, which consists in applying, in an impregnation vat in which the elements of cellulosic material to be impregnated are embedded in hot bitumen and are suitably spaced apart, one or more overpressures, the purpose of which is to force the bitumen to penetrate inside the cellulose system of each element.

Although it makes it possible to reduce the impregnation time, this second known technique nevertheless has several disadvantages.

First of all, since it acts by means of overpressure, it traps a cushion of air and water vapour in the cellulosic material (cardboard), and this makes it very difficult to impregnate to the core; in fact, a "white" central zone, which is unimpregnated and is hence unprotected and can easily rot, is frequently found in elements, in particular profiled or unprofiled plates, of cellulosic material impregnated in accordance with this technique.

Furthermore, this technique does not solve the problem of the sticky bead of bitumen which appears and again constitutes a hindrance. In addition, since it uses an overpressure, a technique of this type involves a discontinuous procedure and makes it necessary to leave, between the successive elements of material to be impregnated, which are grouped together in unit charges, a sufficient space to allow penetration of the hot viscous bitumen, and it consequently requires vats of very large volume (or a very large number of vats), which again demands heavy investments and makes it necessary to keep large amounts of bitumen at a high temperature.

It has now been found, unexpectedly, that it is possible to impregnate profiled fibrous materials with hot bitumen, in a manner which is considerably better in all respects, by means of a process fundamentally comprising the impregnation step in vacuo, advantageously carried out on profiled elements of material to be impregnated, grouped together in a compact load, and, if appropriate, cooling the impregnated elements by immersing them in hot water, this cooling itself being followed, also if appropriate, by again subjecting the impregnated profiled elements, collected after this immersion, to a vacuum.

From the most general point of view, the present invention thus relates to a process for impregnating profiled fibrous materials, in particular cellulosic materials, with hot bitumen, characterised in that it fundamentally comprises impregnating, in vacuo, profiled elements of this material which are advantageously grouped together in a compact load constituting a unit charge, with, if desired, recycling of the hot bitumen for a certain period of time, and, if appropriate (and advantageously), cooling this impregnated charge by immersing it in hot water, this cooling itself being followed, if appropriate, by again subjecting the charge of impregnated profiled elements to a vacuum.

From another essential point of view, the invention relates to profiled elements of cellulosic material, impregnated by means of a process as described above.

It is remarkable and unexpected to find that, by following this procedure, not only are the mechanical characteristics of the resulting impregnated profiled elements distinctly improved, but their presentation is improved and their manufacturing cost is also reduced. In fact, perfect impregnation with the bitumen is thus easily achieved, if desired up to saturation, and the impregnation is remarkably homogeneous, both throughout the bulk of one and the same element and between different elements.

In the present context, the expression "profiled elements of fibrous materials" is understood as meaning any element prepared from a fibrous material, in particular elements of cellulosic material, for example cardboard, which element has been given a simple or complex profile so that it is no longer wholly plane. The elements which are thus in question are, for example, corrugated plates, advantageously single-layer corrugated plates, or advantageously single-layer ridge tile plates; the latter are simply referred to as "ridge tiles" in the following text.

The process according to the invention involves the use of a fairly high vacuum, which preferably leaves a residual pressure of at most 1/3 atmosphere and advantageously of about 1/5 atmosphere (1 atmosphere - 10 Pascals).

The abovementioned impregnation step in vacuo comprises first of all introducing elements to be impregnated into a chamber which can be rendered leaktight and which withstands a reduced pressure, and in which a high vacuum is then created, preferably down to the pressures mentioned above. Once this vacuum has been reached, which has made it possible to remove most of the air present in the fibrous structure, the level of hot bitumen in the chamber is gradually raised, whilst keeping the vacuum in the latter at approximately the same value, and this causes very rapid evaporation of the residual water present in the fibrous elements. It has also been found that the resistance to the penetration of the bitumen inside the fibrous elements is then very low and that the impregnation is very rapid.

An advantageous modification of the impregnation process also comprises a subsequent step involving partial or total breaking of the vacuum, whilst the impregnated fibrous elements are still in the hot bitumen. Even more advantageously, this partial or total breaking of the vacuum, followed by a return to a vacuum having approximately the previous value, itself forms part of a step for recycling the hot bitumen and constitutes an intermediate stage or the final stage of this step; in fact, it has been possible to establish that this produces a further substantial increase in the speed of the impregnation operation.As a variant, it is also possible again to create a vacuum in the chamber, as indicated above, either before or during the discharging of the hot bitumen after the impregnation time which has been fixed (if appropriate after tests for its prior determination in each specific case): according to this very particularly advantageous variant, even if the treated fibrous elements still carry a bead of bitumen after the bitumen has been discharged, the total breaking of the vacuum and the return to atmospheric pressure before the chamber is opened ensure the reabsorption of the bitumen which has sweated onto the surface, and the disappearance of this excess, which is then pumped into the fibrous structure.

Another novel and advantageous characteristic of the process according to the invention, which characteristic is admittedly only optional but which nonetheless produces results of the greatest value, consists in impregnating profiled elements grouped together in a compact load constituting a unit charge.

In fact, in the conventional technique, which comprises impregnation under atmospheric pressure, it is imperative-to keep, between the profiled elements, which in practice are arranged vertically, a space which is sufficient for the bitumen to be able to circulate freely around these elements and for the impregnation not to be hindered by the slow release of the air and the water vapour present in the fibrous system. In contrast, whenever it has been attempted to dispsense with this spacing between fibrous elements in an operation of this type, only very inadequate impregnation, which leaves "white" patches of unimpregnated material, in particular at the top of the approximately vertical fibrous elements, has hitherto been achieved.Now, the production and maintaining of these minimum spacings constitute an obligation which increases the cost of the impregnation operation, complicates its preparation and necessarily makes it longer to carry out. Now, it has been found, totally unexpectedly, that the process according to the invention, comprising impregnation in vacuo, makes it possible, provided that the elements to be treated are not solely plane but are profiled, to group together any number, even a very large number, of unit profiled elements of the fibrous material to be impregnated, one against the other and without any spacing other than that which necessarily arises from the natural, albeit very small, variations, within the specifications, between a given element and the preceding and/or following element in the load formed in this way.

It is even possible in this way to prepare assemblies which, by means of prior bundling, if appropriate with prior palletising, constitute a unit lot representing a unit which can be marketed as such once it has been subjected to the impregnation according to the invention.

Furthermore, it is quite certain that the process as described above is absolutely not limited to the case of a non-pretreated fibrous material and that, on the contrary, it is very particularly applicable to the case of profiled materials, in particular roofing, boarding or sealing materials, which have been coloured or tinted in accordance with the process described in French Patent Application 76/1 6,263 and the Application for a First Certificate of Addition 78/14,039 attached to the said patent, in the name of the same Applicant Company, which applications can advantageously be used for reference purposes, before the said materials have been subjected to the impregnation according to the present invention.

According to an advantageous embodiment of this prior colouring process, the pigment is applied in the form of a pigment formulation containing a thermoplastic or thermosetting binder, in amounts as low as 0.1% and ranging up to 25% of the total weight of the pigment composition, these values being expressed in terms of resin solids in the binder, and preferably of the order of 2 to 3%, also calculated in terms of solids.

The process according to the invention advantageously also comprises, as has been indicated above, a step involving the cooling of the impregnated elements by immersing them in hot water, this step itself being followed, also if appropriate, by again subjecting the impregnated profiled elements, collected after this immersion, to a vacuum.

This cooling in hot water must be such that it very rapidly brings the hot impregnated elements of fibrous material to a temperature of about 1 000C, the hot elements in practice being at a temperature which is still of the order of 1 60-1 800C, before immersion, given that the impregnation is most frequently carried out in practice with bitumen at 1 80-1 900 C.

This step constitutes another novel characteristic of the process according to the invention and it cooperates with the other abovementioned steps to produce impregnated products which are virtually free of defects.

The cooling of grouped elements of fibrous material after the impregnation in vacuo could in fact be the cause of problems which would be difficult to solve industrially. Leaving these hot elements grouped together in fact rapidly leads, if care is not taken, to a self-combustion phenomenon or, at best, to a deterioration in the mechanical properties of these impregnated elements.

Only two solutions would thus appear economically and practically workable, namely cooling in air or cooling in water.

Cooling in air exhibits several disadvantages, the main disadvantage being that it is difficult to control the cooling temperature and that the cooling is hence of poor reproducibility and poor uniformity, both between successive charges and within one unit charge of profiled fibrous elements which are impregnated and hot.

Obvious attention was then turned to cooling in cold water. Now, this resulted in an excessively large uptake of moisture by the elements of fibrous material. The residual moisture represented 10 to 1 5% of the weight of the impregnated elements and was such that storage of the latter produced deformations of the profiles, in particular deformations of the corrugations in corrugated plates of bituminised cardboard, which in that case could even be termed soft plates.

Unexpectedly, it is cooling in hot water, on the contrary, and preferably in water at 92-1 000C, which has proved to be the virtually ideal solution for obtaining undeteriorated impregnated elements.

In practice, a short immersion, for example of the order of about 1 minute or even less, of elements leaving the impregnation step at about 1 60-1 800C, in water at 92-1 000C, is sufficient to ensure that the said elements only take up a reasonable amount of moisture, which is of the order of only about 5 to 7% of the weight of the impregnated elements. The plates are then only at 1 000C or below, after immersion, and there is no longer any risk of their degrading by self-combustion.

Nevertheless, yet another optional variant of the process according to the invention also comprises again subjecting the impregnated profiled elements, collected after this immersion, to a vacuum. In practice, a suitable vacuum in this case is a vacuum of at most about 600 mm of mercury, that is to say a partial vacuum leaving a residual pressure of about 1/5 atmosphere (that is to say 0.2 x 105 Pascals), under which the boiling point of water is then only about 600 C.

Theory indicates that, when subjected to a vacuum of 600 mm of mercury, moist impregnated elements at 1 000C lose 3% of their moist weight by evaporation of water and actually reach a temperature of the order of 600 C. Practice has confirmed that, in this case, they in fact lose 2 to 3% of their weight.

These most advantageous variants of the invention lead to profiled impregnated elements of fibrous material which are "cold" (that is to say at about 600 C) and have a good moisture content (2 to 4% of residual moisture by weight).

The impregnated fibrous elements thus obtained are novel and also form part of the present invention; these are profiled fibrous elements, impregnated with bitumen and, if appropriate, coloured beforehand, which have a normal internal moisture content (about 2 to 4% of residual moisture by weight) as soon as they have been manufactured, and which are capable of being stored or even delivered as such, without subsequently suffering any substantial deterioration.

The invention also relates to assemblies comprising a group of profiled elements of fibrous material, impregnated with bitumen, which elements are juxtaposed so as to form a load without spacing elements, and, if appropriate, are combined by means of prior bundling and, if necessary, prior palletising, so as to constitute a commercial iot which can be stored and even delivered as such, without any operation other than the usual checking and/or identification operations, such as labelling. In contrast to this, profiled impregnated fibrous elements prepared by the known methods conventionally dry in air in the storage areas and, even if they are protected and thus do not take up a marked amount of moisture, they do take up water when in the hands of the users, and this constitutes a substantial disadvantage.

The invention is illustrated in a more concrete manner in the following examples, which in no way imply a limitation.

EXAMPLE 1 To impregnate plates of corrugated single layer cellulosic cardboard having a density of 0.57 and an average unit weight of 3.15 kg and each comprising 10 corrugations, an installation fundamentally composed of the following components was employed: 1 Impregnation vat (capacity 5 m3 and diameter 1.3 m), 1 Melter with walls and bottom (diameter 2.5 m, capacity 12 m3), 1 Bitumen pump with a variable speed motor (1.5 to 6 HP, 500 to 2,000 rpm), 1 Liquid ring vacuum pump delivering 140 m3/hour at 700 mm Hg, 1 Bitumen feed valve with pneumatic control and adjustable operning, 1 Bitumen discharge valve with pneumatic control and adjustable opening, 1 Vacuum-breaking valve with pneumatic control, 1 Valve for separating the vacuum between the vat and the melter, with pneumatic control, 1 Recorder for the feed temperature, the return temperature and the vacuum, 1 Electric level on the overflow of the vat, and 2 Manostats for adjusting the vacuum.

With this installation functioning automatically, the procedure was as follows: the plates, joined side by side and arranged vertically in a metal charging cage, were placed in the vat, and the cover of the vat was then closed and the vacuum pump was started up. Once the vacuum had reached the preset value of 600 mm Hg (that is to say a residual pressure of about 1/5 atmsophere, or 0.2 x 105 Pascals, in the vat), the feed valve opened and the bitumen rose under gravity into the vat up to the overflow, and, at that moment, the bitumen pump and the recycling time-switch started up. Once the preset time had elapsed, the recycling time-switch closed the feed valve and opened the discharge valve and engaged the sweating time-switch. Finally, once the preset sweating time had elapsed, the cycle stopped and the vacuum was broken by hand and the vat opened.

Experiments made it possible to establish that: with 80/100 road bitumen, the temperature of the latter must be at least 1 750C and it is advantageously about 1 800C under the impregnation conditions, and with an automated cycle comprising 5 minutes for creating the vacuum (having a value of about 500 to 600 mm Hg), 5 minutes for filling the vat, 12 minutes for recycling the bitumen, 6 minutes for discharging the bitumen and 10 minutes for allowing the bitumen to sweat out of the plates, the plates obtained all had a comparable degree of impregnation to that of plates, of the same type, impregnated in accordance with the first of the conventional techniques referred to above, but these plates also have perfectly sweated surfaces, their lower edge being perfectly clean to the point that it was no longer possible to distinguish the top from the bottom of the plates after discharging.

EXAMPLE 2 In the same installation as that described in Example 1, 1 50 corrugated plates as defined in Example 1 ,joined together in a load, without spacers, arranged in a suitable metal cage for its introduction into the vat, were impregnated with 80/100 road bitumen at an average temperature of 1820C (under the impregnation conditions).

This time, the impregnation cycle comprised breaking the vacuum and was then as follows: 3 minutes for creating the vacuum (having a value of about 500 mm Hg), 3 minutes for raising the bitumen into the vat up to the overflow, whilst continuing to increase the vacuum in order to raise it to about 600 mm Hg, 12 minutes to recirculating the hot bitumen, under the vacuum then reached, that is to say under a residual pressure of about 1/5 atmosphere, but, within the first 10 minutes, with breaking of the vacuum by a value AP (in mm Hg) and re-establishing, immediately afterwards, of the same vacuum as before, whilst continuing the recirculation (or recycling) under this vacuum for the remaining 2 minutes, and then 6 minutes for emptying the vat and 10 minutes for sweating in vacuo, after which the vat was brought back to atmospheric pressure.

The following results were obtained: Degree of Degree of Surface impregnation impregnation condition at the at the of the top of bottom Average plates No. of AP the of the degree of after experiment (mm Hg) plates plates impregnation sweating 1 0 103 103 103 Excellent 2 200 112 116 114 Good 3 300 116 116 116 Good 4 / 4 600 122 122 122 Poor By following the same procedure, but setting the AP of the partial breaking of the vacuum at 200 mm Hg and this time varying the recycling time (variable t, in minutes), the following results were obtained:: Degree of Degree of Surface impregnation impregnation condition at the at the of the top of bottom Average plates No. of t (in the of the degree of after experiment minutes) plates plates impregnation sweating 1 10 112 116 114 Good 2 8 106 112 109 Good 3 5 100 106 103 Almost perfect 4 2 100 106 103 Almost perfect It is clear that a compromise needs to be sought between the surface condition of the plates after sweating and the degree of impregnation.

EXAMPLE 3 The procedure indicated in Example 1 was followed, but using corrugated plates tinted in bulk beforehand, respectively in accordance with the process of French Patent Application 76/16,263 and the process of the Application for a First Certificate of Addition 78/14,039, attached to the latter, (which applications can advantageously be referred to for greater detail), and, each time, the results obtained were completely similar to those mentioned in Example 1.

EXAMPLE 4 In the same installation as that described in Example 1, grouped plates were impregnated in accordance with the procedure of the said example, and the plates were immediately immersed in hot water and, in accordance with a variant, subsequently subjected to a vacuum again.

By way of example, 8 of the plates of corrugated single-layer cellulosic cardboard (10 corrugations per plate) corresponded to the following specifications: No. of plates 1 2 3 4 5 6 7 8 Weight of the cardboard (g) 3,160 3,190 3,180 3,170 3,170 3,250 3,140 3,120 Weight after impregnation (g) 6,300 6,300 6,290 6,290 6,280 6,300 6,230 6,300 Degree of impregnation 99.4 97.5 97.8 98.4 98.1 93.8 98.4 101.9 Pyrometric measurements showed that the grouped plates left the impregnation bath at approximately the same temperature as that of the said bath, that is to say 1 800 C.

The load of plates at this temperature was immersed in water at 98-1 000C for 1 minute.

The moisture uptake of the central plate was about 57% (in weight/weight).

For the purpose of carrying out other experiments, 18 x 1 8 cm samples of corrugated impregnated cardboard were furthermore produced from some of the plates referenced 1 to 8 above.

One plate could provide 30 samples.

Plates which had just been impregnated and had not yet taken up moisture were used.

The samples to be tested were heated in an oven at 1 800C until they reached a constant temperature, and they were then immersed in water at 98-1 000C as rapidly as possible and for exactly 1 minute.

The experiments (referenced a, b and so on) were carried out on grouped plates, the groups of plates being referenced Gn (n = number of plates).

The weight Wd of the dry plates at 1 800C and the weight Wm of the moist plates (after immersion for 1 minute in water at 98-1 000C and natural draining for 1 minute) were evaluated.

Each group of plates Gn was enclosed for a time t (in minutes) in the vacuum vat, in which a vacuum of 600 mm Hg was created (that is to say a residual pressure of 175 mm Hg (or about 1/5 atmosphere), atmospheric pressure being 775 mm Hg on the day of these experiments).

The weight (Wv, in g) of the samples and the moisture uptake were measured: MUt: after cooling in boiling water and draining, MU2: after subjecting to a vacuum again.

Three series of experiments were carried out: two sets (a and b) of 10 samples G,0, originating from the same plate, were subjected to a vacuum of 600 mm Hg for 1 5 minutes, two sets (a and b) of 10 samples G,,, originating from another plate, were subjected to the same experiments, and three sets (a, b and c) of 9 samples Gg, originating from a third plate, were subjected to this same vacuum for 5 minutes, 1 0 minutes and 1 5 minutes respectively.

The following results were obtained:

W of W of water W of No. of water evaporated residual W of W of Vacuum the (g) MU1 off (g) water (g) cellulose bitumen (in Time t MU2 plate Wd (g) Wm (g) (Wm-Wd) (%) Wv (g) (Wm-Wv) (Wv-Wd) (g) (g) mm Hg) (in minutes) (%) 4 aG10 1,132.2 1,198.4 75.2 6.7 1,171.4 27.0 48.2 566 557 600 15 4.3 bG10 1,117.8 1,192.8 75.0 6.7 1,160.4 32.4 42.6 563 554 600 15 3.8 5 aG10 1,115.7 1,175.2 59.5 5.3 1,147.5 27.0 31.8 563 553 600 15 2.8 bG10 1,122.6 1,173.7 51.1 4.5 1,146.7 27.0 24.1 567 556 600 15 2.1 8 aG9 994.2 1,045.9 51.7 5.2 1,026.5 19.4 32.3 492 502 600 5 3.3 bG9 996.8 1,047.3 50.5 5.1 1,027.0 20.3 30.2 494 503 600 10 3.0 cG9 1,001.8 1,054.7 52.9 5.3 1,031.7 23.0 29.9 496 506 600 15 3.0

Claims (24)

1. A process for impregnating profiled fibrous elements with hot bitumen wherein said elements are impregnated in a vessel which is partially evacuated.

2. A process according to claim 1 wherein the partial vacuum in said vessel is partially or wholly released while said elements are still in hot bitumen.

3. A process according to claim 1 or 2 wherein said bitumen is cycled through said vessel for a predetermined period.

4. A process according to claim 3 wherein the partial vacuum in said vessel is partially or wholly released during an intermediate orfinal stage of said predetermined period, and wherein the vacuum is subsequently restored to approximately its previous value.

5. A process according to claim 4 wherein the partial vacuum in said vessel is restored after the end of the predetermined period, but before or during discharge of the bitumen.

6. A process according to any of claims 1 to 5 wherein the operating pressure is less than one third of an atmosphere.

7. A process according to claim 6 wherein said pressure is substantially one fifth of atmosphere pressure.

8. A process according to any of claims 1 to 7 wherein elements are impregnated while grouped together in a compact load constituting a unit charge.

9. A process according to any of claims 1 to 8 wherein said elements have been previously coloured or tinted.

1 0. A process according to claim 9 wherein the pigment used in the colouring process is applied in the form of a pigment formulation containing a thermosetting or thermoplastic binder in amounts from 0.1 % to 25% expressed as weight of resin solids in the pigment formulation.

11. A process according to claim 10 wherein said thermosetting or thermoplastic binder is present in amounts from 2% to 3% expressed as weight of resin solids in the pigment formulation.

12. A process according to any of claims 1 to 11 wherein the impregnated elements are cooled by immersion in hot water.

13. A process according to claim 12 wherein the impregnated elements are very rapidly cooled to a temperature of approximately 1000C by immersion in hot water.

14. A process according to claim 13 wherein the cooling water is initially at a temperature of 92-1 000C.

1 5. A process according to claim 12, 13, or 14 wherein said elements, after dooling in water, are.

subjected again to a vacuum,

1 6. A process according to claim 1 5 wherein said elements, after cooling in water, are subjected to a pressure of approximately one fifth of atmospheric pressure.

1 7. A process according to any of claims 1 to 1 6 wherein the elements are cellulosic fibrous elements.

1 8. A process substantially as hereinbefore described with reference to the examples.

1 9. A profiled, bitumen-impregnated fibrous element having an internal moisture content of 2 to 7% immediately after manufacture.

20. A fibrous element prepared by a process according to any of claims 1 to 1 8.

21. An element according to claim 19 to 20, having an internal moisture content of 5 to 7% by weight.

22. An element according to claim 1 9 or 20, having an internal moisture content of 2 to 4% by weight.

23. An element according to any of claims 1 9 to 22 when used as a roofing, boarding or sealing material.

24. An assembly of elements prepared according to claim 8 and forming a load without spacing elements.