GB2031475A - Paper product having a high filler content - Google Patents

Abstract

The present invention relates to a process for obtaining a flat product by carrying out a paper-making technique, and to a product thus obtained, wherein, according to the invention, there are added to a fibrous mass, in an aqueous medium, at least one finely divided mineral or organic filler, then three or more successive additions of ionisable polymers, each of opposite polarity from, and preferably also of higher molecular weight than the last.

Description

SPECIFICATION Paper product having a high filler content The present invention relates to a paper product having a high filler content in order to give it specific properties.

Paper product is understood in the present specification to mean a product obtained by carrying out a paper-making technique, but which, in fact, may be related both to papers, cardboard, etc... and to non-woven products, felts, voile, etc..

Attempts have already been made to incorporate fillers in paper during manufacture thereof. However, the results obtained are mediocre, as these fillers pass through the screen of the work table and only a small part thereof remains in the product. Even when using retention agents, and under the best conditions of use, no more than about 15% by weight of filler can be fixed.

Furthermore, products composed of complex sheets are already known, intended for example to insulate or decorate floors or walls, which comprise, as substratum, asbestos millboards, voile or felts composed of glass fibres, ceramic fibres or rock wool. Asbestos is known to present dangers for human health and, consequently, it is being replaced more and more by voile or felts based on glass fibres or rock wool. However, fillers are even more difficult to fix on such voile or felts than in paper and, moreover, whereas asbestos gives compact, resilient products having a pleasant surface appearance whilst requiring only little binding agent, voile or glass fibre or rock wool felts give aerated. brittle products and have a poor surface appearance.

It is an object of the present invention to remedy these drawbacks and to obtain, by a paper-making technique, products with a high filler content.

The purposes of the present invention are as follows: 1. the replacement, in the manufacture of a paper product, of expensive matter such as cellulosic fibres, asbestos, glass fibres, rock wool, synthetic fibres, etc... by inexpensive mineral or organic fillers which may, moreover, give particular properties to the product obtained; 2. the obtaining of dimensionally stable products, even when they are subjected to the action of water or heat; 3. the obtaining of products having high mechanical characteristics, even when they are subjected to the action of water or heat; 4. the obtaining of products of permanent fire-proof character, although asbestos is not used; 5. the obtaining of virtually imputrescible products; 6. the obtaining of products of which the weight per unit area may be between less than 20 g/m2 and more than 500 g/m2.

These purposes are not limiting and others will appear in the course of the following description.

To these ends, the process according to the invention for obtaining a product by carrying out a paper-making technique, is noteworthy in that there are added to a fibrous mass, in an aqueous medium, at least one finely divided mineral or organic filler, then at least one first ionogenic substance so as to form first groups comprising particles of said filler and the polarized molecules of said first substance, then at least one second ionogenic substance, of polarity opposite that of said first substance, so as to form second groups comprising the first groups and polarized molecules of the second substance, the alternate addition of ionogenic substances of opposite polarities being stopped when the groups obtained form structures capable of being treated by paper-making techniques in order to obtain said product.

The fibrous mass is advantageously constituted by wood pulp. However, this fibrous mass may be constituted by all types of mineral or organic fibrous suspensions, such as those based on rock wool, ceramic fibres, glass fibres, polyamide, polyester etc...

Due to the process according to the invention, molecular structures are therefore created which incorporate the particles of filler so that a very solid suspension is obtained, which resists the shearing forces and behaves in the paper-making installations and, particularly on the screen of the work table, in the same way as a paper pulp, which behaviour is conserved up to the presses and drier of said installation.

To obtain such a result, the mineral or organic filler must be in divided form, for example in pulverulent or colloidal form, and it must be sparingly or not at all soluble in water. The dimensions of the particles of filler are preferably at the most equal to 100 ,um, although this size is not limiting.

All types of mineral or organic fillers may be used for carrying out the invention, as a function of the desired properties for the finished product.

Chalk, kaolin, talc, magnesia, dolomite, mica, clays, asbestos, alumina hydrate, etc..

have been successfully used as mineral fillers.

Chalk is very often used due to its low price; on the other hand, an expensive filler such as mica, is used for its electric and electronic properties. Fillers formed by metallic powders such as a powder of aluminium, lead, etc..

have also been used with success. Lead powder is particularly advantageous in view of the properties of sound-proofing, heat or electric conductivity or protection from radioactivity which it gives the finished product.

Powders or emulsions of all types of resins may be used as organic fillers : powders of phenoplast, aminoplast, epoxide, polycarbonate, polyurethane, polyacetate, polyacrylic, polyolefin, polystyrene resins or emulsions of acetate, acrylate, styrene-butadiene, acrylonitril resins, etc... Such an organic filler is generally chosen for the particular properties that it brings, particularly its binding power.

This binding power may appear either dur ing the drying of the voile on the screen, or later in the manufacture of laminates, as is the case of a phenoplast resin subjected at that moment to the action of heat and pressure.

The organic filler may be constituted by ground waste of all types of resins.

The fillers formed by resins therefore intervene in the formation of molecular structures according to the invention in the same way as the mineral fillers, but, in addition, give a binding agent to the mass to which they are added.

The molecular structures or groups thus obtained by mixture of the or each filler with the ionogenic substances may give plastic paper products having a very high breaking load, but a resistance to tear which is generally not sufficiently high. Consequently, it is often advantageous, in order to increase the resistance of the finished product to tear, to add reinforcing fibres such as glass fibres, synthetic fibres, etc... at the same time as the fillers. It is advantageous to add these reinforcing fibres to the wood pulp at the same time as the fillers, before addition of the ionogenic substances, in order to obtain a good dispersion and a good homogeneity, necessary for obtaining a good quality finished product.

In the process according to the invention, the elementary particles of the fillers are associated by the molecules of the ionogenic substances in order to form separate molecular structures which may be maintained in suspension by stirring and capable of resisting shear. This result is obtained by successively treating the particles of filler by ionogenic substances of alternately opposite polarities so as to form longer and longer chains.

It is by the choice of these ionogenic substances (molecular weight and ionogeneity), their order of introduction, their dosage, and the structure of their molecule that the particles of filler are bonded by sufficient forces of connection for the pulpy mass to resist shear.

Such ionogenic substances are generally chosen among the polymers and, as a function of the fillers, experiments have shown that it was sufficient to provide from 3 to 5 different polymers and often 4, to obtain the desired results. These polymers are advantageously introduced by order of increasing molecular weights, although this measure is not compulsory, as will be seen in Example IV hereinbelow.

It is known that the highest macropolymers presently known have molecular weights that may attain 1 5 000 000 and are of anionic type. They have an ionogeneity of the order of 70%. On the other hand, the polymers of cationic type have lower molecular weights, for example of the order of 5 000 000, but their ionogeneity may reach 100%.

Operation may be as follows: At least one finely divided filler, for example, chalk, is dispersed in a fibrous aqueous mass, and the whole is continuously stirred in order to obtain a good homogeneity. A first ionogenic polymer, for example a cationic polymer such as a polyamide-epoxide resin, a polyester-epoxide resin, etc.. is then added.

One or more molecules of this first ionogenic polymer then agglutinate on the various particles of the filler in order to form separate first groups which, in the example chosen, will present a positive electric charge.

If, now, a second ionogenic polymer of opposite polarity (therefore of anionic type in the present example) and of heavier molecule, chosen, moreover, for its binding power (such as a latex, a cellulosic ester or the like), is added, the negative molecules of this second polymer will collect together a plurality of said first groups to form second, more complex groups.

The addition, now, of a third ionogenic polymer of polarity opposite the second (therefore of cationic type in the present example), and of even heavier molecule, for example a polyacrylamide or ester-polyamino-carbonic linear resin will enable the formation of third groups to be obtained by means of the molecules of the third polymer.

By adding a fourth ionogenic polymer of polarity opposite the third, i.e. anionic in the example chosen, (for example a very long straight chain carboxyvinylic polymer), even more complex fourth groups may be obtained by bonding said third groups by means of the molecules of the fourth polymer, and so on, until groups of particles of filler are obtained which are sufficiently long and solid, capable of giving a stable suspension drainable on the screen of a paper-making machine.

The quantities of polymere added at each stage, as well as the reaction times at each stage are considerable for the quality of the final product, as there is interaction between all the polymers. However, it is difficult to determine precise limits for these quantities and these reaction times, as both problem and solution are specific to each case. For each particular case, the nature of the ionogenic substances, their order of introduction, the quantities introduced and the reaction times will be chosen to obtain groups of particles of filler communicating to the mass a solidity in relation to the paper-making machine used, this machine being for example of the type with flat screen or of the hydroformer type with inclined screen.

Of course, the process according to the invention may be carried out discontinuously or continuously. In the first case, the preparation of the pulpy mass is effected discontinuously, by fractions which are stored in vats where the duration of stirring is very long, this obliging the shears to be taken into account during this period and the ionogenic substances to be added in large quantities.

In continuous operation, the suspension is used as soon as it is formed and its resistance to shear may be less, this enabling the quantities of ionogenic substances, and, possibly, the number of these substances, to be reduced.

Examples of quantities and reaction times for precise cases of manufacture of determined products will be found in the following Examples.

EXAMPLE I Manufacture of a dimensionally stable fireproof wallpaper having a weight per unit area of 100 g/m2, according to a discontinuous method conventional in paper-making techniques.

The following are successively introduced into a 1 0m3 hydrapulper: 8000 litres of water 70 kg of slightly refined chemically bleached wood pulp 1 20 kg of ordinary quality pulverulent chalk 1 20 kg of ordinary quality alumina hydrate 30 kg of glass fibres and 2.4 kg of polyamide-epoxide resin previously diluted to 5%.

The mixture is allowed to react for 1 minute, after which the following is added to the suspension: 48 kg of vinylidene-acrylic copolymer resin and the mixture is likewise allowed to react for 1 minute, before adding 1.6 kg of cationic polyacrylamide resin of molecular weight equal to 1 million and the mixture is again allowed to react for 2 minutes, then 0. 1 8 kg of carboxyvinylic polymer is added, and the mixture is allowed to react for 1 minute.

The 5% suspension of matter thus obtained is brought to a proportion of 2.5% by dilution, then is stored in a vat with a view to supplying a paper-making machine with flat screen. After passage in this machine, a final product is obtained having the following characteristics: weight per unit area : 100 g/m2 - thickness : 200 im - breaking load in the dry state: - longitudinal direction 1 50 N/Scm -transverse direction 110 N/Scm - breaking load in the wet state: - longitudinal direction 60 N/5 cm - transverse direction 48 N/5 cm - dimensional stability after 8 days immersion in water : variation less than 0.01 mm/m - elongation or deformation at high temperature (10 mins at 200"C) < 0.2%.

- elongation or deformation in the case of fire : non-inflammable - approximate calorific power : 1 250 cal/g.

EXAMPLE II Manufacture of a board intended for replacing asbestos millboards. As before the following are introduced successively into a 1 Om3 hydrapulper: 8000 litres of water 30 kg of unrefined wood pulp 400 kg of ordinary quality pulverulent chalk 72 kg of glass fibres 0.5 kg of polyamide-epoxide resin (reaction time 1 min.) 45 kg of styrene-butadiene resin (reaction time 1 min.) 1,3 kg of polyaminocarbonic ester (reaction time 2 mins) and 0,07 kg of carboxyvinylic polymer (reaction time 1 min) According to the adjustment of the papermaking machine, a board is obtained whose weight per unit area is between 250 and 500 g/m2 and with a thickness of between 400 and 600 lim, the other characteristics being as follows: - breaking load in the dry state:: - longitudinal direction from 1 20 to 1 80 N/5 cm transverse direction from 110 to 1 60 N/5 cm - breaking load in the wet state: - longitudinal direction from 40 to 55 N/5 cm - transverse direction from 35 to 50 N/5 cm - Elongation or deformation: - at high temperature (10 mins. at 200"C) < 0.2%.

- in the case of fire : non-inflammable -Approximate calorific power : 850 cal/g.

EXAMPLE 111 The process of Example II is repeated, but 200 of the 400kg of pulverulent chalk are replaced by 200kg of talc.

The final product obtained has the same characteristics, but with a smoother surface state.

EXAMPLE IV Continuous manufacture of a board intended for impregnation.

The following are successively introduced into the preceding 10 m3 hydrapulper.

8000 litres of water 40 kg of unrefined wood pulp 440 kg of ordinary quality pulverulent chalk and 20 kg of glass fibres The suspension obtained is continuously stirred and serves to continuously supply a staged reactor constituted by chambers equipped with stirrers, in each of which is injected an ionogenic polymer by a proportioning pump. For a production of 50 kg/minute of dry product, the following are introduced: into a first chamber : 0.25 I/min. of epoxide polyamide into a second chamber: 0.08 kg/min.

of carboxyvinylic resin into a third chamber : 0. 25 kg/min. of polyacrylamide resin.

The reaction times in each chamber are 1 min. for the polyamide-epoxide and carboxyvinylic resin and 2 mins. for the polyacrylamide.

EXAMPLE V Manufacture of a paper product not comprising any cellulosic fibres.

The following are successively introduced into a hydrapulper: 2000 litres of water 5 kg of ceramic fibres 75 kg of ordinary quality pulverulent chalk 5 kg of vinylidene-acrylic copolymer resin 5 kg of acrylic resin 10 kg of glass fibres 0.2 kg of polyamide-epoxide.

The mixture is allowed to react for 1 minute, after which 0.012 kg of carboxyvinylic polymer is added to the suspension and the mixture is allowed to react for 1 minute, then 0.048 kg of polyacrylamide resin is added and the mixture is allowed to react for 1 minute.

The suspension thus obtained supplies a paper making machine and a flat product is obtained, without cellulosic fibres, having a weight per unit area of 250g/m2 and the following properties: - breaking load in the dry state: - longitudinal direction 70 N/5 cm - transverse direction 60 N/5 cm - breaking load in the wet state: - longitudinal direction 25 N/5 cm - transverse direction 20 N/5 cm - dimensional stability after 8 days immersion in water : variation less than 0.01 mm/M - elongation or deformation as high temperature (10 mins. at 200"C) < 0.2%.

Due to the invention, paper products may thus be obtained which, due to their composition, their insensitivity to water, their porosity, their dimensional stability and their fire-resistance, associated with a perfect flatness due to the technique used, may find numerous applications, for example in insulation (surfacing, manufacture of insulating panels, manufacture of complexes, etc...), in coating (coating support, flocking, wall-papers, etc...) in filtration (painting booths, dust-removal, high temperature filtration, etc...) in the production of laminates, etc..

The following advantages of the present invention may be mentioned: 1. The possibility of manufacturing paper products incorporating a very large proportion of fillers.

2. The possibility of using low-cost fillers, on condition that they are in divided form.

3. The possibility of obtaining paper products having specific characteristics, due to the incorporation of fillers.

4. The possibility of obtaining paper products of desired density and/or porosity by adaptation of the dimensions of the structures of the particles of fillers.

5. The possibility of obtaining paper products, without asbestos, having properties similar to products based on asbestos etc...

Claims (11)

1. A process for obtaining a flat product by carrying out a paper-making technique, wherein there are added to a fibrous mass, in an aqueous medium, at least one finely divided mineral or organic filler, then at least one first ionogenic substance so as to form first groups comprising particles of said filler and polarized molecules of said first substance, then at least one second ionogenic substance, of polarity opposite that of said first substance, so as to form second groups comprising first groups and ploarized molecules of the second substance, the alternate addition of ionogenic substances of opposite polarities being stopped when the groups obtained form structures capable of being treated by paper-making techniques in order to obtain said product.

2. A process as claimed in Claim 1, wherein the mineral fillers are chosen from the group including chalk, kaolin, talc, magnesia, dolomite, mica, clays, asbestos, alumina hydrate, aluminium, lead or the like.

3. A process as claimed in Claim 1, wherein the organic fillers are chosen from the group including phenoplast, aminoplast, epoxide, polycarbonate, polyurethane, polyacetate, polyacrylic, polyolefin, polystyrene, acetate, acrylate, styrene-butaniene, acrylonitril resins or the like.

4. A process as claimed in Claim 1, wherein the fibrous mass is wood pulp.

5. A process as claimed in Claim 1, wherein the cationic ionogenic substances are chosen from the polyamide-epoxide, polyesterepoxide, polyacrylamide, ester-polyaminocarbonic resins or the like.

6. A process as claimed in Claim 1, wherein the anionic ionogenic substances are chosen from the vinylidene-acrylics, styrenebutanienes, carboxyvinyls, cellulosic esters or the like.

7. A process as claimed in Claim 1, wherein the ionogenic substances are polymers and said polymers are added to the suspension by order of increasing molecular weight.

8. A process as claimed in Claim 1, wherein reinforcing fibres are added to the suspension, before the introduction of the ionogenic substances.

9. A process as claimed in Claim 1, wherein a reaction time is arranged between two successive additions of ionogenic substances, for the previously added substance.

10. A product obtained by carrying out the process as claimed in any one of Claims 1 to 9.

11. A process substantially as described hereinabove in any one of the foregoing Examples.