FR2838736A1 - Ceramic articles production includes dehydration, pressing, drying and heat treatment of a mixture of mineral materials and organic materials mostly consisting of cellulose fibers - Google Patents

Abstract

In the production of a ceramic article, especially a ceramic construction panel of surface area of at least 0.1 square m, obtained from a mixture of mineral and organic materials, the organic materials contain cellulose fibers in amount of at most 15 dry weight %, preferably 5-12 dry weight %, with respect to the weight of the mixture. The proportion of mineral materials in the mixture is at least 80% dry weight. Preferred Features: A suspension obtained from the mixture is dehydrated in a dehydration machine, preferably a Hatschek machine, by a coiling procedure, in order to form the panels. The dehydrated suspension is subjected to pressing or shaping in order to obtain the desired form of the article, followed by drying and thermal treatment for elimination by combustion of cellulosic fibers and other organic compounds, and for sintering of the mineral material.. The mineral particles are selected from clay, silica, feldspar, pyrophyllite, dolomite, limestone, kaolin, enamel, and their mixtures. The mineral particles are preferably in the form of a slurry of silica, feldspar and kaolin, or in the form of a mixture of enamel and a slurry obtained by mixing silica, feldspar and kaolin. Independent claims are given for: (a) a ceramic article obtained by the invented process; and (b) a ceramic panel covering a surface area of at least 0.1 square m obtained by the invented process.

Description

filtration.

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  - The present invention relates to a new process for obtaining ceramic products made from a sheet material containing particles. The classical processes for developing ceramic structures consist of three essential stages: - the preparation of the dough, the shaping,

- the cooking.

  In these conventional processes, the ceramic paste is prepared from

  clay minerals, the most common of which is kaolin.

  The clay material is first ground and reduced to a powder, before being

shaped.

  The shaping itself is generally done by molding and pressing.

  However, these classic processes are characterized by a certain

number of disadvantages.

  On the one hand, the products obtained are very dense and therefore very heavy.

  This characteristic also does not make it possible to supply building materials based on ceramics which are at the same time light, cheap and easily transportable. On the other hand, when these traditional ceramic materials are shaped into a three-dimensional structure, there are often cracks

and cracks during sintering.

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  This is another consequence of the excessively high density at some

  places subject to compression during the shaping step.

  Finally, it must be noted that, owing to the absence of an effective binder, the agglomerated powders or the extruded or pressed wet products are not sufficiently solid to be easily handled after their shaping, in particular in the case of plates whose dimensions make it possible to cover a

surface of at least 0.1 m2.

  As a result, only ceramic plates the dimensions of which cover an area of at most 0.1 m2 are available at present, the cited plates also having the disadvantage of being thick to compensate for their lack of

  cohesion and offer sufficient resistance for their handling.

  In the prior art, it is also described the manufacture of ceramic products by paper fly combining mineral particles intended to be sintered with cellulosic fibers capable of being eliminated by combustion in view

  of the formation of said ceramic products.

  This method offers the double advantage of giving the ceramic structure before firing greater flexibility and internal cohesion than traditional ceramics, and of lightening the ceramic structure after firing by creating

  pores in the ceramic at the places occupied by the cellulosic fibers.

  This structure, which will be described as "ceramic paper", has already been the subject of earlier patents, in particular the patents FR 2 212 777, EP 73 854, US 4

383 890 or FR 2 122 220.

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  In the patents FR 2 212 777, EP 73 854, and US 4 383 890, it is envisaged in particular to mix a fibrous pulp of cellulose with Norwegian fine particles. The purpose of this technique is in fact to avoid the use of binder of the elastomer and latex type, of fixing agents, and of polymer coagulation agents and allows

  to obtain larger ceramic plates.

  However, the Applicant notes that these patents generally envisage a chemical modification of the cellulosic fibers before they are mixed with the mineral material. This constitutes an important obstacle to a simple and

  inexpensive of said industrial methods.

  The Applicant also notes that these old patents and, for the most part, have fallen into the public domain have not been, to her knowledge,

  serious industrial exploitation.

  Wile also noted by itself, following various industrial tests, that the methods described in these patents had two major drawbacks: on the one hand, an insufficient draining problem, in particular at high grammages, on the other hand, wet cohesion of the paper still insufficient at output

of paper machine.

  Obtaining ceramic plates having a thickness of several millimeters has proved, moreover, impossible to obtain by a conventional method of

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  formation of paper, without providing for subsequent laminating of several of said

leaves obtained.

  This solution, however, did not make it possible to obtain ceramic plates at a lower cost and showing no defects after firing, such as cracks or

s separation in thickness.

  On the basis of these observations, the applicant proposes a new process for the formation of ceramic paste, which would not require chemically modifying the cellulosic fibers, and which would implement a device for shaping this ceramic paste other than the conventional devices. paper forming machines, such as Foudrinier flat table machines or round shape machines

type Duoformer or similar.

  To this end, the applicant has had the idea of using and adapting a fiber cement support formation device to the manufacture of these so-called << papers

ceramics >>.

  These machines are known to those skilled in the art under the name

  "HATSCHEK machine", named after their manufacturer.

  One of these machines has in particular been the subject of patent FR 2 305 539,

filed in 1976.

  The Applicant uses the general principle described in this patent for the

  manufacture of these "ceramic papers".

  This principle is based on the use of a series of round shapes rotating at high speed in tanks containing the fibrous composition, the tanks being provided with agitators to keep the mineral load in suspension, the fibrous layers

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  being superimposed on a continuous scrolling fabric having a series of draining devices on its route and brought up to an accumulator roller, which stores the superimposed layers up to the desired thickness before cutting into plates and

subsequent treatments.

  The application of this principle of formation of cement leaves has not, at the present time, been extended to applications of the type of those envisaged by the applicant. However, it turns out that the formation of so-called "ceramic papers" using these HATSCHEK machines makes it possible to obtain characteristics of ceramic products obtained from these ceramic papers superior to those of ceramic products obtained from prior art ceramic papers and this has

  higher speeds and lower cost of implementation.

  In particular, it has been observed that the thickness of these ceramic products can be greatly reduced by using only a small proportion of fibers.

  cellulosic, between 5 and 12% of the total weight of ceramic paste.

  The invention therefore relates to a method of manufacturing ceramic shaped objects, in particular construction panels, obtained from a mixture of mineral materials and organic materials, the organic materials being composed mainly of cellulose fibers, and the proportion of said cellulose fibers in said mixture not exceeding 15% by weight see, and, preferably, being included

between 5 and 12% by dry weight.

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  In this process, the suspension obtained from said mixture undergoes a dehydration stage carried out by means of a dehydration machine by the

  winding process to form panels.

  The dehydration machine can advantageously be a Hatschek machine. The mineral particles are chosen from clay, silica,

  feldspar, pyrophilite, dolomite, limestone, kaolin, enamel and their mixtures.

  The mineral particles may be in the form of a

  slip, mixture of silica, feldspar and kaolin.

  The mineral particles may be specifically a mixture of enamel and a slip obtained by mixing silica, feldspar and kaolin. The proportion of mineral matter in said mixture may be at

less than 80% by dry weight.

  The suspension thus dehydrated will then undergo a pressing step or

  formatting to obtain the desired shape of the object.

  The suspension thus obtained will then undergo, after drying, a heat treatment intended to eliminate by combustion the cellulosic fibers and the like.

organic components.

  Preferably, the heat treatment can also be used to sinter

mineral matter.

  The invention also relates to a ceramic object obtained by the

  manufacturing process described above.

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  Specifically, the invention relates to a ceramic panel covering an area of at least 0.1 m2 obtained by the manufacturing process described above. Other characteristics and advantages of the present invention

  will emerge on reading the detailed description which follows.

  - Figure 1 shows schematically a machine cited HATSCHEK, We have shown in Figure 1 a machine quotes HATSCHEK

  that it was used in the preparatory tests which led to the invention.

  According to this configuration, a sheet (1) is formed by transferring a suspension to an extraction felt (2) by means of a mesh cylinder (3) placed in a suspension tank (4), this operation being repeated as many times as there are tanks or circular mesh cylinders to form an extraction jet, this jet then being wound around the formation roller (5) a precise number of

  times until it reaches a specific thickness, before being cut.

  The ceramic structure obtained then undergoes a shaping process and

  drying in line with that of traditional ceramic materials.

  The shaping is done by pressing the ceramic structure in a

  motile, the shape of which must lead to objects of very divergent forms.

  Due to the presence of cellulosic fibers, the ceramic structure acquires increased flexibility and, as a result, is liable to be cut or deformed without the phenomena of chipping and cracking of the layer.

  composed of inorganic fine particles occur.

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  In this way, the resulting paper can be formed up to a certain amplitude for particular objects and mainly make it possible to obtain ceramic plates and objects of larger areas and of smaller thickness.

  than with traditional techniques.

  The structure thus mi s e in shape still retains an important porous site,

  ranging from 40 to 60% of the total volume, with limited mechanical properties.

  It is then necessary to operate a sintering, that is to say to treat at high temperature the ceramic structure so as to give the finished product a good ...

coheson mecanque.

  During sintering, the particles come closer and weld together: the object gets

  densified with decrease in porosity and linear shrinkage from 10 to 20%.

  In modern processes, this high temperature cooking is done around 1100 to 1500 C, temperature depends directly on the nature of the

mineral components to be sintered.

  The invention differs from this prior art by the need to decompose cooking in two stages, firstly a prior cooking at a temperature between 500 and 800 C, intended to remove the compounds

  cellulosic structure, and, en-quite, the sintering properly cited.

  The final structure therefore comprises a very large number of pores or interstices distributed in a disordered manner in this structure, as a result of the

  burning of cellulose during pre-cooking.

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  Wile retains the shape it was after shaping and its mechanical resistance is comparable to that of a structure of the same shape made

baked clay of full form.

  The present invention will be better understood on reading the examples which follow, given by way of indication and in no way limiting the scope of the invention. Examples 1 to 3: Mix in water and stir well to obtain an aqueous suspension,

  cellulose fibers and slip.

  The cellulosic material used consists essentially of short races

refined to 34 SR.

  The slip used is of the “Gres Ceram” type, quick cooking, mainly containing a mixture of approximately 45% German clay and approximately 55%

Sodium feldspar.

  The powders were ground in a wet condition on ALSING type material to an average particle size of the order of 12 m, with the addition of a flocculating agent, in particular trisodium phosphate in the proportions of 2 parts of phosphate

  trisodium for 1000 parts of powder.

  In Examples 1 to 3, the percentage by dry weight of the cellulose was varied by

compared to that of the slip.

  Therefore, the percentage by dry weight of cellulose in the mixture is

  10%, 6% and 8% respectively in Examples 1 to 3.

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  To this aqueous suspension, a PERCOL flocculant prepared at 0.25 g / l is added at the machine head, in the proportion of 200 g of PERCOL for one tonne of dry mixture. The mixture obtained is introduced into the suspension tanks of a HATSCHEK machine, the machine having a speed of 20 m / mint The suspension is then drained and rolled up on an accumulation roller before being cut to the appropriate format, put in shaped and cooked to obtain the ceramic product. The cooking takes place in two stages, on the one hand, an elimination of the organic compounds between 500 and 800 C, on the other hand, a sintering of the mineral materials towards

1230 C.

  Table 1 shows the results of the measurements made on the ceramic product obtained

  before shaping and observations about these trial trots.

TABLE 1

EXAMPLE 1 EXAMPLE 2 EXAMPLE 3

  Nb of layers 16 18 25 Thickness (in mm) 3.5 4.6 4.6% by dry weight of cellulose fibers 10% 6% 8% in the mixture Dry density (in 1, 05 1.13 1.1 1 g / cm3) Wet density (in 1.62 1.69 1.66 g / cm3)

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  % humidity 35.1 33.1 32.9 grammage (in g / m2) 3050 1 3650 3200 Drainability Very good Acceptable Very good Adhesion to Very good Very good Very good rewinding cylinder Unhooking of None None No cardboard of the reeling cylinder Ash rate 87 89, 4 86.6 (in%) Examples 4 and 5: Mix in water and stir well to obtain an aqueous suspension,

  cellulose fibers and slip.

  The cellulosic material used consists essentially of refined, febrile races.

at 34 SR.

  The slip used is a mixture of 50% mineral powder of the "Gres Ceram" type used in the previous examples and 50 / O of glass powder and feldspar, with a view to achieving a sintering temperature lower than that of mixtures 1 to 3 In Examples 4 and 5, the percentage by dry weight of the

  cellulose compared to that of the slip.

  Therefore, the percentage of cellulose is 8% by dry weight in Examples 4 and

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  To this aqueous suspension, a PERCOL flocculant prepared at 0.25 g / l is added at the machine head, in the proportion of 200 g of PERCOL for one tonne of dry mixture. The mixture obtained is introduced into the suspension tanks of a HATSCHEK machine, the machine having a speed of 20 m / mint The suspension is then drained and rolled up on an accumulation roller before being cut to the appropriate format, put in shaped and cooked to obtain the ceramic product. The cooking stops in two stages, on the one hand, an elimination of the organic compounds enke 500 and 800 C, on the other hand, a sintering of the mineral matters towards

1,120 C.

  During the draining process, only one defect tray was used in Example 5 and two defect trays in Example 6, to reduce the winding moisture of the strands

  and therefore favor the subsequent drying conditions.

  The observations made on the ceramic product obtained show that the positive results, in terms of drainability and load retention in particular,

  obtained in previous tests maintained wind.

  The sintering temperature has also been lowered advantageously compared to

  in the previous tests, going from 1230 C to 1120 C.

  Comparative Example 6: Mix in water and stir well to obtain an aqueous suspension,

  cellulose fibers, a flocculent latex composition and slip.

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  The cellulosic material used consists essentially of short races

refined to 34 SR.

  The role of Europrene E404 latex is also to retain mineral charges.

  The slip used is a mineral powder marketed by Novoceram under the

s reference B30.

  The percentage by dry weight of cellulose in the mixture is tx a = / O.

  The percentage by dry weight of latex in the mixture is. meanwhile, fixes a = / O.

  The mixture obtained is introduced into a machine "cardboard reel>>, which corresponds to a traditional flat table machine terminated by a winding cylinder, 1U having a speed of 40 m / mint The grammage of the sheet reached in output ae mavlllllv - alL'l vlllpll Gllblv "VV vL

500 g / m.

The process "- '--l -v Iv A

  in accordance with the previous examples to arrive at the final ceramic product.

  This test revealed very low charge retention, resulted

ash rate of around 62%.

  Drainability and cohesion hu In addition, after winding, the paper tends to adhere to the cylinder in

  There are difficulties during the unwinding.

  These tests therefore make it possible to confirm the real interest in using a machine with a round shape and accumulator cylinder at the end of the machine, of the HATSCHEK type, for the

  formation of a ceramic plate before it is shaped and fired.

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Claims (8)

  1) Method for manufacturing shaped ceramic objects, in particular construction panels, obtained from a mixture of mineral materials and organic materials, in which the organic materials are composed mainly of cellulose fibers, characterized in that that the proportion of cellulose fibers in said mixture is at most equal to 15% by dry weight and is. preferably between 5 and 12% by dry weight.   2) The manufacturing method according to claim 1, characterized in that the suspension obtained from said mixture undergoes a dehydration step performed by means of a dehydration machine by the winding process to form panels. 3) A manufacturing method according to claim 2, characterized in that the dehydration machine is a Hatschek machine.   4) manufacturing method according to one of claims   precedents, characterized in that the mineral particles are chosen from clay, silica, feldspar, pyrophilite, dolomite,   limestone, kaolin, enamel and their mixtures. 2838736   ) Salt production process, we sell it for this one, characterized in that the mineral particles are in the form   a slip, a mixture of silica, feldspar and kaolin.   6) Manufacturing method according to claim 4, characterized in that the mineral particles wind a mixture of enamel and a slip obtained by mixing silica, feldspar and kaolin. 7) The manufacturing method according to claim 6, characterized in that the prop orti on of mineral matter in the edit   mixture is at least 80% by dry weight.   8) manufacturing method according to one of claims 2   and following, characterized in that the suspension thus dehydrated undergoes a pressing or shaping step to obtain the desired shape of the object.   9) Manufacturing process according to the preceding claim, characterized in that the suspension thus obtained undergoes after drying a heat treatment intended to remove the fibers by combustion.   cellulosics, and other organic components.   ) Manufacturing method according to the preceding claim, characterized in that the heat treatment also serves to sinter the mineral matter.   11) Ceramic object obtained by the manufacturing process   according to one of the preceding claims. 16 2838736   12) Ceramic panel covering an area of at least 0.1   m2 obtained by the manufacturing process according to one of claims 1 at 10.