Steam jet cooking method for making aqueous resin emulsions and compositions containing such emulsions for coating paper

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The present invention relates to a process for manufacturing aqueous polymer dispersions intended to coat or coat, completely or partially impregnate porous supports, in particular fibrous materials, such as paper. The process is intended to prepare sheet materials sensitive to color by contact with colorless oily marking liquids having basic reaction properties. The term paper used here is understood to mean that it encompasses any fibrous material in sheet or web form.

It has unexpectedly been discovered that a system for a steam jet method of starch cooking can be easily modified to prepare stable aqueous polymer dispersions in the form of spheroidal particles, most of which are spheres of smaller diameter * at 10 microns. This is achieved by subjecting the products to turbulence by steam jet, therefore without mechanical action which is costly and time consuming. With this steam jet process, an aqueous slurry of raw starch is passed through a steam discharge apparatus in order to transform the starch into starch cooked in a restricted area of ​​the apparatus maintained at a predetermined temperature and pressure and with a proportion of starch / slurry d The starch is 1.25 to 5 times the amount of vapor which is condensed as it raises the temperature and pressure of the slurry to predetermined values ​​for proper operation of the system. In general, a sufficient quantity of steam at a given temperature and pressure and in the desired state (in particular the dryness) is mixed, under turbulence, with the starch slurry, with a resulting condensation of steam which is brought into contact with the slurry and with release of outlet steam. In accordance with the present invention, starch is replaced with an acidic polymeric material or is added to such a material used to sensitize the receptor sheets which are used in pressure sensitive recording material systems.

According to the invention, a process is therefore carried out for the preparation of an aqueous dispersion of an acidic polymer material, soluble in oil but insoluble in water and which, moreover, is fusible, a process intended for coating or impregnating paper or other similar product, this process being characterized by the operation consisting on the one hand of introducing an aqueous slurry of particles of this acidic polymeric material into a limited space to obtain a

44897 turbulent vapor jet metering, in a quantity and under temperature and pressure such that the polymer particles melt and subdivide, the average size of said particles being reduced compared with that of the particles of the aqueous slurry, then on the other hand to cooling the dispersion in order to solidify the polymer particles.

Since the same vapor discharge device applied to melt and emulsify the polymer is also applicable for the cooking of starch, this latter operation is preferably carried out simultaneously with the formation of the dispersion of the polymer, so as to create a protective colloid for the polymer particles (which are melted or gelled) forming the dispersion phase. In addition, other products can be passed simultaneously or sequentially through the vapor jet discharge system, including insoluble pigments, such as silica, silica gel, clays, calcium carbonate, etc; binders such as latex or gums; and wetting agents, dispersants or lubricants which are not degraded by the temperatures involved. If calcium carbonate is used, it is preferable to mix it with an extremely divided silica, using a dispersing agent for this carbonate, for example a vitreous complex phosphate produced by a thermal process. A certain dispersant based on polyphosphate which is particularly suitable is for example the product widespread under the name of Calgon Composition T * manufactured by the company Hagan Chemicals & control Inc, in Pittsburg, United States, product which, in combination with calcium carbonate , forms lamellae of low viscosity and having good stability with regard to conservation and alkalinity.

The resulting acidic polymer dispersion, especially if it is combined with a protective colloid such as the starch which forms the binder, is particularly suitable for being applied alone or in combination with chromogenic materials for the production of pressure-sensitive papers, such as than those described in French patent N ° 1,470,333. Any suitable method, continuous or in series, can be applied to manufacture the polymer with protective colloid. ''

The present invention therefore provides a polymer in the form of fine spheroidal particles. With this process, a degree of fineness equivalent to that of known grinding processes can be obtained.

44897 mechanical, with bulky devices, but this mechanical grinding * is ineffective by the preparation times and for the energy required and most often there is a fouling of the apparatuses for manufacturing slurry and even of the tanks and the pipes.

Mechanical grinding naturally does not make it possible to obtain practically spherical polymer particles, comparable to those which are produced with the present process.

Since the slurry, subjected to the steam jet in the corresponding phase, must be cooled before normal use for coating the paper, the above-mentioned easily dispersible pigments are added after the application of the steam jet and before vapor condensation. This is one of the reasons for the economy of the process, since the pigments are used in much larger amounts compared to the starch and the polymer, so that their subsequent addition saves unnecessary operations of heating and cooling of the entire final coating composition.

The term vapor discharge apparatus which has been used above is understood in the sense of a mixing apparatus in which the vapor is introduced under pressure in the form of a jet and a slurry also introduced under pressure, brought to the steam jet path for mixing of the two.

Suitable polymeric products which are soluble in oil but insoluble in water can be used, such as for example the phenol-formaldehyde or phenol-acetylene polymers.

Among the phenol-formaldehyde polymers which can be used, mention may be made of the genera known under the name of novolaks, characterized by their solubility in ordinary organic solvents and which, in the absence of crosslinking agents,^VzTosibles permanently.

Another useful group of phenol polymeric materials is that of alkyl acetone acetylene resins which are soluble in ordinary organic solvents and which have permanent fusibility if not treated with crosslinking agents. In general, the phenolic polymer which can be applied for the invention, is characterized by the presence of free hydroxyl groups, such as methylol, which tends to promote the infusibility or the transverse bond or crosslinking of the polymer. These groups are also characterized by their solubility in liquid organic solvents and their relative insolubility in aqueous media. For example, the resoles, if they are still

44897 soluble, can be used although their properties tend to change over time.

Various oil-soluble but water-insoluble phenolic polymers, such as those having OH groups, can be used for conversion to a stable dispersion, but the following may be preferred:

formaldehyde / butyl phenol p-tert resin. formaldehyde / chlorophenol resin or other aliphatic and aromatic substituted phenol-formaldehyde resins in which the electron-releasing group is in the ortho or para position of the phenol. Among these resins, mention may be made of Bakelite CKM-5254 * which is a phenol-formaldehyde resin with 100 paraphenyls, the softening point of which is between 90 and 107 ° C. The general formula of this type of resin is:

<img file="FR2073470A1_D0001.tif" />

in which n is an integer between 3 and 5 and R is phenyl or another substitute for the groups mentioned above.

Polymerization of a monomeric phenol to give a compound of the above formula gives a polymer having methylene bridges and no free para-methylol group. The presence of para-methylol groups at the para positions of the phenol chain of the finished polymer could later give rise to a transverse bond. But this is not desirable, because it tends to cause the polymer to take "thermally or even is already set".

In general, it is preferable to use, as starting material, an aqueous slurry of a coarsely ground thermoplastic polymer (10 to 20 microns) based on para phenyl, for example one which has several repeated units, at the minus three times_r as in the trimer. Such a slurry can be produced by mechanical grinding, for example in a friction mixer. The polymer obtained is therefore considered to be coarsely ground, but only by comparison with a very small

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44897 2073470 particle size (from about 0.25 micron to about 10 microns in diameter), for spherical particles produced by the steam jet.

The conversion of the mechanically ground solid polymer into fine particles of the order of 0.25 to 10 microns, preferably from 0.25 to 3 microns, according to the process of the invention, is carried out by a melting action and emulsion of the vapor on the polymer particles, by the turbulent passage of the aqueous polymer slurry in the steam jet apparatus mentioned above. Depending on the melting point of the polymer, the emulsion obtained contains, after cooling below the melting point, stable suspended particles of spheroidal shape, the size of which varies between approximately 0.25 microns for the lower limit and 10 microns maximum for the upper limit.

By the action of starch acting as a protective colloid, the stability over time of the dispersion is found to be very greatly increased. Likewise, the acid properties of the paper containing the microfine acid polymer particles are improved as a result of the greater number of colored areas per unit area, this being due to the exceptionally fine particles of the polymer.

Aging tests show that the latter is slower with the paper sensitized using the dispersion according to the invention, which is due to the protective action of the colloid provided by starch, gum, or other adhesive. hydrophilic that * we put in the coating.

The steam jet cooking process can be preceded by preheating the slurry containing the polymer to a temperature equal to or higher than the melting point or softening point of the polymer, for example at least 50 to 55 ° C, the steam being at

281 g / cm? and at a temperature of 127 ° 0, when the melting point of the polymer is between 50 and 55 ° 0. Polymers with high melting points, of the order of 105 ° C, for example, can also be preheated to about 93 at 99 ° C, then subjected to the steam jet at 190 ° C, under pressure of 492 g / cm2. Alternatively, a tamdem jet of steam can be applied, the first jet providing preheating to melt the polymer, followed by the final jet at high speed to ensure the desired turbulence and the resulting formation of the desired stable dispersion.

One of the advantages of the steam jet device mentioned for carrying out the method according to the invention is that the emulsion

44897 of the polymer is ensured without mechanical action and without the product sticking to the walls of an apparatus or of the container where the stirring takes place. The emulsifying power, by application of the only vapor in said apparatus, depends on the speed and the turbulence of the jet of vapor and on the quantity of vapor necessary to melt the polymer and to disperse it into fine particles in the liquid suspension medium. . The polymer particles, although in the liquid state, remain insoluble in water.

The accompanying drawing shows schematically an apparatus ser10 vant to implement the present method. A mixing tank 10 is provided with stirrers 11 used for mixing an aqueous slurry 12 of a polymer product, which is either formed in the tank 10, or introduced in the form of a slurry, mixing which is carried out with other products of the final dispersion.

Four arrivals of products 13, 14, 15 and 16 are shown to introduce various compounds to be mixed into the tank 10. These arrivals have taps 17 controlling the flow and can also be used for the introduction of aqueous slurries of polymers, starch, silica and / or other compounds to be mixed in the tank.

Whatever the way of introduction of the ingredients, the mixture 12 is formed in the tank 10 in the form of an aqueous slurry, the compounds being in the desired proportions, the solids content being duly controlled.

Porridge 12 can have the following composition:

Compound Weight in Kilog.

Polymer

Starch

Silica

6,8

4,0

1,4

Kg, t

12.2 dry weight (la)

22.2 kg of porridge at 55> solids.

From the tank 10, the slurry is sucked up by a pump 18 comprising a line 19 and under pressure in a discharge line

20, by a tap 20a, then in a mixing or discharge device generally designated by 21. This system 21 comprises a steam jet device 21a constituted by a cylinder 22 provided with a venturi 23, the orifice 24 allows steam to pass under a higher pressure than that of the slurry in the pipe

20; the flux is discharged at high speed into an annular chamber

Ί

44897 which surrounds the lower part of the cylinder 22. The chamber 26 also surrounds a coaxial tube 27 comprising a treatment zone 28. The steam inlet 25 comprises taps 29 and 30 controlling the flow of steam in the cylinder 22. A valve needle

31 in the cylinder 22 makes it possible to adjust the opening of the orifice 24 and consequently the volume of vapor discharge passing through this orifice.

The steam thus discharged causes the slurry to pass into the chamber 26, through the conduit 20 and into the end 27a of the tube 27 in which the mixture of bmn'11 ie and steam takes place at high speed. During this mixing, the adjustment of the needle 31 and the space between the venturi and the end 27a, creates conditions making it possible to convert the slurry of the polymer particles into a stable dispersion.

The operation continues and there is an excess of uncondensed vapor in contact with the slurry and with the emulsion in which the latter is transformed, passing through the treatment zone 28.

The excess of uncondensed steam can vary over wide limits, but an excess of about 25%? steam compared to the theoretical value is preferable; in other words, the quantity of steam introduced into the treatment zone should be at least 1.25 times (preferably 1.5 to 3 times) the quantity of steam which must be condensed by increasing the temperature of the bouil25 binds, compared to that which is maintained in the treatment area.

From the device 21a, the emulsion formed is discharged through a conduit 31a provided with a return valve 32, into a rapid chamber 33. The vapor is released in an upper outlet conduit 34, while the liquid dispersion which is then cooled, is brought into a lower discharge conduit 35, then into a mixing and storage tank 36..

After passing the slurry 12 through the steam jet apparatus, the quantity of the steam condensate must bring the solid parts to 35 to 55% by weight of the dispersion obtained by steam jet.

If a higher proportion of solids is desired, this can be achieved by adding more dry mix (la) to the slurry. If, on the contrary, less solids are desired, it suffices to dilute the dispersion in water.

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Additive products such as slurries, latex, solutions and the like can be introduced into the mixing tank 36 by suitable inlets such as 37 ₃ 38, 39 and 40, which makes it possible to obtain a coating (indicated by 41) which, in general, has a solids content of 15 to 70> by weight of the composition of the coating.

While polymers of the phenylephenol type can be emulsified by passing the aqueous slurry of the mechanically ground polymer through the vapor jet system just described, it is preferable when the polymer dispersion is to be used to form a coating or coating, to include in the resin a hydrophilic material (also called a binder) which is already in colloidal form or which is capable of being brought into this colloidal state by pulsating through a jet of vapor with the polymer, which * gives a protective colloid for the polymeric material which constitutes the dispersed phase. A colloidal material which can be preferred is raw starch from all sources, such as corn or wheat starch, or root starch, but in general, various starches and gums can be used in granular form. and not cooked. Oxidized or ethyl starches or those treated in any other way can also be used.

In the following, a non-limiting formula of a coating composition according to the invention is given:

Products ⁶jo by weight (based on dry solids

Polymer 15 Starch 9 Silica 3 Latex 5 Clay 59 Calcium carbonate _9

100 >

Sufficient water can be added to this dry product formula to obtain a coating slurry whose solids content is between 15 and 70%, or more, preferably between 52 and 58%, if desired. consider tighter limits.

Such a composition containing 50 solids requires an amount of water equal to the weight of dry solids expressed in parts by weight, or 45.35 Kg of water per 45.35 Kg of dry weight of said formula, ie a total weight of 90 , 70 Kg.

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One can use a particularly satisfactory silica in the above formula for the implementation of the present process, that is to say a silica gel such as that which is applied in the manufacture of paper. In the case of special papers for polygraphy, we can use the product called Syloid 72 (manufactured by the company Davison Chemical Co in Baltimore, United States) which acts as a dye adsorbent and plays an important role in that it gives a large internal surface, which improves the sharpness of images while reducing printing blur.

The latex included in the formula may be, for example, a butadiene-styrene latex containing 50% of solids, the pH being for example 6, with a viscosity of 95 cps (at the spinning top of 100 rev / min.), which is compatible with starch, especially in the neutral pH range; it also exhibits great calcium carbonate stability, especially in conjunction with a dispersant such as vitreous phosphate.

As regards the clay used in the formula, mention may be made of the so-called Chinese clays. Clays have the advantage of being cheaper than silicas (like silica gel), but the clay can be left aside to apply silica gels to obtain the desired coating volume. Other additions can be considered in the final dispersion for coating.

For example, one can use the product called Tamol 731 which is a sodium salt of a carboxylated polyelectrolyte manufactured by the company Rohm & Haas, or other surfactants in the proportion of 0.1> by weight of the final dispersion. . Likewise, calcium stearate, which is a lubricant, can be introduced into the final combination, for example in the proportion of one per thousand by weight.

Other possible additive products can be germieides which prevent the growth of bacteria, fungicides which prevent the growth of fungi or even anti-foaming agents.

On the basis of the results obtained by electron photomicroscopy tests (5000x), it is believed to be able to say that the range of dimensions of the polymer particles, before the jet of vapor, can be between wide limits, of approximately 2 to 20 microns maximum and that the major part of the spherical polymer particles is of the order of 0.1 to 10 microns in diameter. It should be noted that the particles appear in photography as