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

SWEDEN (19) SE (12) PUBLISHING LETTERS (51) International Class ^

IBI (21) 7Ö1671O ~ 1

C 08 J 3/06

<img file="SE419552B_D0001.tif" />

PATENT AUTHORITY (44) Application outsourced and outsourced “08—1 0 application document published (41) Application widely available 71-06-16 (22) Patent application received 70-12-10 (24) Maturity date (62) Number of application (86) International filing date (86) Filing date for European patent application (30) Priority information

69-12-15 US 885058 (11) Publication number

419 552

Application filed as: Swedish patent application □ Completed internationally on patent application with number □ converted European patent application with number

KB 3-A4 according to SIS 61 30 13

Ϊ71) Applicant: APPLETON PAPERS, INC., APPLETON, WIS. US

72) Inventor: CW Steele, Wisconsin Rapids, Wis.

74) 0mbud: Brain

54) Name: Process for preparing aqueous polymer dispersions for coating paper and the like

7116710-1

The present invention relates to a process for preparing aqueous polymeric dispersions for coating, impregnating or partially impregnating porous substrates, particularly fibrous materials such as e.g. paper, in the manufacture of sheet material sensitized to be dyed upon contact with colorless, oily mark liquids with basic reactant properties. The term paper here is intended to comprise fibrous material in sheet or web form.

The unexpected discovery has been made that a steam jet process for boiling starch can be readily modified to produce relatively stable aqueous dispersions of polymer in the form of spheroidal particles, the majority of which are spheres having a diameter less than -3.10 mm. This is achieved by steam jet turbulence without costly and time consuming mechanical rubbing. In the aforementioned steam jet process, an aqueous slurry of raw starch is passed through a steam outlet unit to convert the starch to boiled starch in a closed zone of the unit maintained at a predetermined temperature and a predetermined pressure and a suitable steam / starch ratio. to provide from 1.25 to 5 times the amount of steam condensed as said steam raises the slurry to the temperature and pressure selected for the operation of the system. Generally, a sufficient amount of steam of suitable temperature, pressure and suitable quality (dryness) under turbulent conditions is mixed with the starch slurry to effect boiling of the starch with subsequent condensation of the steam brought into contact with the slurry and discharge of spent steam. . According to the invention, the starch is replaced by, or added to, an acidic polymeric material used to sensitize recipient sheets used in pressure sensitive recording material systems.

Thus, according to the present invention, there is provided a process for preparing a water dispersion of a permanently fusible, oil-soluble, water-insoluble novolac for coating or impregnating paper for use in pressure-sensitive recording systems in combination with basic reactive, chromogenic, color-forming materials, and this process is characterized essentially that a water slurry, formed from mechanically ground particles of novolac and a colloid-forming material such as raw starch, in a confined space turbulent is mixed with an amount of escaping steam, corresponding to at least 1.25, preferably 1.5-3, times the amount condensed to raise the temperature and the pressure in the slurry so that the novolac particles melt and decompose to a size within the range of 0.25-10 µm, after which the resulting dispersion is cooled so that the molten particles in it are transferred in solid form.

Since the same vapor outlet system used for melting and emulsifying the polymer is suitable for boiling starch, starch boiling is conveniently carried out simultaneously with the formation of the polymer dispersion to provide a protective colloid for the polymer particles (melted or solidified) forming the disperse phase. In addition, other ingredients may be simultaneously or sequentially passed through the vapor jet type of exhaust system, including insoluble pigments such as silicic acid, silica gel, clays and calcium carbonate, binders such as latex and rubber, and wetting agents, dispersants and lubricants which are not degraded at the temperature in question. When calcium carbonate is used, it is suitably mixed with finely divided silicic acid by means of a dispersant in the calcium carbonate, e.g. a composite glassy phosphate prepared by a thermal process. A particularly suitable polyphosphate dispersant is that known by the trade name Calgon-Composition T sold by Hagen Chemicals &amp; Controls, Inc., Pittsburgh 30, Pennsylvania which, in combination with calcium carbonate, provides low viscosity materials and good aging and alkalinity stability.

7 · 1ί710-1

The resulting acidic polymer dispersion, especially in combination with a protective colloid as a starch as a binder, is particularly suitable for use alone or in combination with chromogenic material in the production of pressure-sensitive paper and the like described in Swedish patent no. The colloid-protected polymer can be manufactured either continuously or batchwise.

The present invention provides the polymer in the form of fine, spheroidal particles. A similar degree of particle fineness can be obtained by the hitherto cumbersome mechanical rubbing machinery, but such mechanical grinding is ineffective in terms of production time and required grinding energy and often results in soiling of the slurry preparation apparatus including containers and tubes. Of course, mechanical grinding does not result in substantially spheroidal polymer particles similar to those obtained by the process of the present invention.

Because the steam jet slurry obtained at the jet stage prior to end use as coating material must be cooled to a temperature consistent with that suitable for paper coating, the aforementioned easily dispersible pigments are added after the steam blowing and steam condensation has taken place. This occurs to a great extent for economic reasons, since the pigments are used in considerably greater amounts compared to the starch and the polymer and the late addition thereof thereby saves unnecessary heating and cooling of the final coating composition.

The term outlet is used herein to denote from the mixing device into which the steam is introduced under pressure in the form of a jet in whose path a slurry, also under pressure, is pumped in to mix with the steam.

Suitable polymeric materials are water-insoluble but oil-soluble acidic polymeric materials such as phenol-aldehyde and phenol-acetylene polymers.

Among the useful phenol-aldehyde polymers are the members of the group commonly called novolacs, which are characterized by being soluble in common organic solvents and permanently fusible in the absence of hardener. Another group of useful phenolic polymer materials are the alkylphenol-acetylene resins, which are soluble in common organic solvents and are permanently digestible unless treated with a hardener.

In general, the phenolic polymer materials useful in the practice of the invention are characterized by the presence of free hydroxyl groups and the absence of groups, e.g. methylol, which promotes digestibility or crosslinking of the polymer, and of its solubility in liquid organic solvents and relative insolubility in aqueous media. Resoles can be used if they are still soluble, but their properties change with aging.

Although various oil-soluble but water-insoluble phenol polymers with free OH groups can be used as the fusible polymer material for conversion to a stable dispersion, the following specific polymers are preferred:

p-tert.-butylphenol-formaldehyde resin p-chlorophenol-formaldehyde resin, and other aliphatic and aromatic substituted phenol-aldehyde resins in which an electron emitting group is in ortho or para position in the phenol. Commercially available oil-soluble, non-heat-reactive phenolic resins are suitable, e.g. Bakelite CKM-5254, which is a 100% p-phenylphenol formaldehyde resin having a softening point between 90 ° and 107 ° C The structural formula for this type of resin is as follows:

<img file="SE419552B_D0002.tif" />

where n is an integer from 3 to 5 and

R is a phenyl or other substituent as above.

Polymerization of a monomeric phenol to obtain a compound of the above structure results in a polymer with methylene bridges and without free methylol groups. Presence of methylol groups in para position in the phenol rings of the final polymer may result in later cross-linking. No substantial crosslinking is desired, as there would then be a tendency to cure the polymer which could cause it to become a curing resin.

7816710-1

In general, it is preferable to use as a starting material an aqueous slurry of a coarsely ground (10-20.10 mm) thermoplastic pphenyl polymer having several repeating units, at least e.g. a trimmer. Such a slurry can be prepared by mechanical machining in an attritor. The resultant ground polymer is called the roughage only in relation to the very low particle size (from about 0.25.10 to about 10.10 mm in diameter) of the spherical particles obtained in the steam jet process.

The conversion of the mechanically ground solid polymer to the very -3-3 low particle size of between 0.25.10 and 10.10 mm and most preferably -3-3 between 0.25.10 and 3.10 mm by carrying out the present invention is achieved by the melting and emulsifying action of the vapor of the polymer particles at the turbulent passage of the aqueous polymer slurry through the aforementioned vapor outlet. Depending on the melting point of the polymer, the resulting emulsion, after cooling to below the melting point of the polymer, contains stably suspended particles of spherical shape and having a size varying from a lower limit of

-3 -3 approx. 0.25.10 mm to an upper limit of 10.10 mm.

Through the function of the starch as a protective colloid, the aging stability of the dispersion is greatly increased. The acidic properties of the paper containing the microfine, acidic polymer particles are also improved due to the greater number of color seats obtained per unit area due to the extremely low particle size of the polymer. Aging data show slower aging of paper sensitized to the improved dispersion by protecting the paper of the present invention from the atmosphere by the action of the colloid obtained from starch, rubber or other hydrophilic adhesive material in the coating composition.

The steam jet boiling may be preceded by preheating the polymer-containing slurry to a temperature at or above the polymer softening or melting point, for example to a temperature of at least 50-55 ° C, using steam at 281 grams / cm 2 and a temperature of 127 ° C. when the polymer has a melting point of about 50-55 ° C. High melting polymers, e.g. similarly, with melting points about 105 ° C, can be preheated to a temperature of about 93-99 ° C and then subjected to steam jet boiling at temperatures up to 190 ° C at 492 grams / cm 2. Alternatively, tandem jet boiling can be used, the first jet boiling being a preheating step to melt the polymer, followed by a final jet

7016710-1 boiling at high speed to ensure turbulence and the resulting formation of the desired stable dispersion.

One of the advantages of the outlet device used in the process of the present invention is that the emulsification of the polymer is accomplished without mechanical rubbing and without the molten or softened polymer sticking to the stirring surfaces or against the wall surfaces of the vessels where the stirring is performed. The efficiency of the emulsification when using steam alone in an outlet device depends on the rate and turbulence of the steam jet and the amount of steam required to melt the polymer and disperse it as very fine particles in the suspension liquid. The polymer particles, although in liquid state, are still water insoluble.

The accompanying drawing shows a schematic front view of a suitable device for carrying out the method according to the invention.

The reference numeral 10 generally shows a mixing tank provided with a stirrer 11 for mixing an aqueous slurry of polymeric material 12, either produced in the tank 10 or introduced into the tank in the form of a slurry, together with other ingredients in the final dispersion. ·

As shown in the drawing, there are four feed lines 13, 14, 15 and 16 for insertion into the tank 10 of the various components to be mixed therein. Each of the conduits 13 through 16 is provided with a valve 17 for controlling the flow of raw material to the mixing tank 10. The respective feed lines 13 through 16 can be used for introducing aqueous slurries of polymer, starch, silicic acid and / or other constituents into the slurry to be prepared or contained in the mixing tank 10. Regardless of the way of incorporating the ingredients into the mixing tank 10, the mixture 12 is prepared in the tank 10 as an aqueous slurry of the various ingredients, with desired ratios of the ingredients to the total solids content controlled within appropriate limits.

Typically, slurry 12 may have the following composition:

7116710-1

Ingredient

Weight in kilograms of polymer starch silicic acid water

6,8

4,0

1,4

12.2 kg dry weight (1a) 10.0

22.2 kg of slurry,

55% solids

From the mixing tank 10, the slurry is removed by the pump 18 with the inlet conduit 19 from the bottom of the tank 10 and pumped under pressure through the outlet conduit 20 and the valve 20a into a jet outlet system, designated in its entirety by the reference numeral 21. The jet outlet system 21, shown schematically, comprises steam jet outlet 21a of known general construction. The jet outlet 21a consists of a hollow cylindrical sleeve 22 which is axially equipped with a throttle assembly 23 provided with a jet forming nozzle 24 through which a high velocity vapor flow (at higher pressure than the slurry in the outlet line 20) flows into the an annular chamber 26 enclosing the lower portion of the sleeve 22. The annular chamber 26 also encloses the upper, open end of the tube 27, which is oriented axially with the jet outlet 21 and together with it forms a treatment zone 28. The steam line 25 is provided with valves 29 and 30 for controlling the vapor flow to the sleeve 22. needle valve 31 in said sleeve 22 adjustably controls the aperture provided by said jet-forming nozzle 24 and consequently the vapor outlet volume through the nozzle.

The steam flowing out then causes the slurry pumped into the chamber 26 through the inlet conduit 20 to flow into the open, upper end 27a of the tube 27, in which high-speed slurry and steam mixing occurs. During such mixing, the adjustment of the needle valve 31 and of the space between the throttle assembly and the upper end 27a of the tube 27 provide the conditions necessary to convert the slurry of polymer particles into a stable dispersion.

During continued operation of the system, an excess of uncondensed vapor should be in contact with the slurry and with the emulsion to which the slurry is converted upon passage through the treatment zone 28.

the excess amount of uncondensed steam can be varied within wide limits, but at least 25% excess relative to the theoretically calculated steam is appropriate, or in other words, the amount of steam introduced into the treatment zone should be at least 1.25 times, and preferably 1.5 to 3 times, the amount of steam condensed as the temperature of the slurry is increased to that prevailing in the treatment zone.

From the jet outlet 21a, the emulsion formed is removed through conduit 31a provided with a check valve 32 to be passed into a steam separator 33. The vapor exits through an upper drain line 34, while the subsequently cooled liquid dispersion of polymer particles is removed through a bore pipe 35 mixing and storage tank 36.

After the slurry 12 has passed through the jet system, the amount of condensate from the steam used will usually give a dry content of between 35 and 55% by weight of the jet-produced dispersion.

If a higher solids content is desired, a composition with such a higher solids content can be obtained by adding enough of the dry mixture (1a) to the slurry and passing it through the jet system. If a lower dry content is desired, the jet-produced dispersion need only be diluted with water.

Additives in the form of liquid slurries, latex, solutions and the like can be introduced into the mixing tank 36 through suitable conduits, e.g. lines 37, 38, 39 and 40, to provide a coating composition, denoted by reference numeral 41, which generally has a dry content in the range of about 15 to 70% by weight based on the coating composition.

While the phenylphenol polymers described can be emulsified by passing an aqueous slurry of the mechanically ground polymer through the radiation system shown and described herein, when the aqueous polymer dispersion is to be used for coating purposes, suitable to include in the resin a hydrophilic material (hereinafter sometimes called a binder) which is already in colloidal form or may be transferred to colloidal form by passing along with the polymer through the jet outlet system thereby providing a protective colloid for the polymeric material constituting the dispersed phase. The suitable colloid-forming material is raw starch, e.g. corn starch or root starch, but in general various starches and rubbers in grainy and uncooked form can be used. Oxidized, ethylated and otherwise treated starches can also be used.

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The following is a typical coating composition which can be processed according to the process of this invention, wherein the constituents are stated in weight percent.

Ingredient polymer starch silicic acid latex clay calcium carbonate

Weight percent (calculated on dry content) 15 in total 100.

Sufficient water is added to obtain a slurry for coating purposes with a dry content within the wide range of from 15 to 70% by weight, or more preferably within the narrower range between 52 and 58% by weight of the slurry.

A coating composition containing 50% solids would require an amount of water equal to the weight of dry matter expressed in parts by weight, 45.35 kg of water per each 45.35 kg of dry weight in the previous recipe, or a total wet weight of 90.70 kg.

A particularly suitable type of silicic acid for use in the above recipes for processing in accordance with the present process is a silica gel used in the manufacture of duplicate paper. Used as a component in coating composites for special duplication paper, a silica gel known as Syloid 72 (sold by Davison Chemical Co., Baltimore, Maryland) serves as a color adsorbent and plays an important role in providing a large interior surface thereby promoting sharp image density with reduced feathering. footprint.

The latex included in the recipe may conveniently be a styrene-butadiene latex containing 50% solids, has a pH of about 6.0, a Brookfield viscosity of 95 cps (100 rpm, // 4 spindle), is miscible with starch, especially in the neutral pH range, and has a high calcium carbonate viability, especially with a dispersant such as a glassy phosphate.

As clay in the above recipe, coating clays including those known as kaolin are suitable. Clay has the advantage of being cheaper than silicic, e.g. silica gel, but clay can be omitted and silica gel used to give the average density of the coating desired. Other

7816710-1 additives may be included in the final dispersion used for coating purposes. Tamol 731, which is believed to be the sodium salt of a carboxylated polyelectrolyte and sold by Rohm &amp; Haas, or other suitable surfactants, can be used in an amount of about 0.1% by weight of the final dispersion. Similarly, calcium stearate may be included in the final composition as a lubricant for coating in amounts up to one part per 1000 parts by weight.

Other permitted additives include antibacterial agents to prevent bacterial growth, antifungal agents to prevent fungal growth, and anti-foaming agents.

Based on the results of scanning electron microscopic studies at a magnification of 5000 times, the applicant believes that the size range of the polymer particles prior to the radiation outlet treatment is generally -3 to about 2 x 10 to 20 x 10 mm maximum dimension, and that the majority of the spheroidal polymer particles, obtained after the jet outlet-3 stage has a diameter of about 0.1 x 10 to 10 x 10 mm. It is to be noted that the particles, despite the polymer's tendency to fuse in suspended, molten state, appear in photographs as free-standing, almost perfect spheres of varying sizes.

The essential components of the coating composition where starch is the colloid-forming binder are as follows:

a polymer as defined herein, in the form of generally free-standing spheroidal particles, the majority of which have a maximum diameter of less than about 10 x 10 mm, a gelatinized starch, associated with said polymer, in an amount sufficient for to ensure the formation of a stable aqueous dispersion of colloid-protected resin spheres, and sufficient water to provide a dry content of between about 15 and 75% by weight of the dispersion.

The colloidal binder, whether gelatinized starch, latex or other water-dispersible hydrophilic binder, should be present in a minimum amount of about 5% by weight of the solid polymeric material. Generally, a surfactant which is miscible with the binder (and any other constituent which may be present in the final coating composition of which the aqueous polymer dispersion is a part) is included in the slurry which is

7816710 to the jet outlet, but the surfactant may be added later in the preparation of the coating slurry. Anionic surfactants which act as dispersants for pigments such as clay are suitable.

In coating paper, the process used has significance for the amount of solids present in the coating composition used. Commonly used methods include, among other things, roller, air knife, and tow blade coating. If the coating composition is applied with an air knife, the composition should have a dry content between a minimum of 15 and a maximum of 40% by weight, while in the case of roll coating and tow coating the corresponding figures are from 30 to 70%. In each case, the range of the practical coating weights (dry content) of polymer per rice of 500, 64 x 96 cm, or a total of 307 m, should be from a minimum of 0.113 to 0.136 kg to a maximum of 0.453 to 0.543 kg of polymer per rice, with an average range of from 0.226 to 0.272 kg of polymer per rice.

7016710-1