US1668760A - Thermoplastic pulp - Google Patents

Description

Patented May 8, 1928.

UNITED STATES 1,668,760 PATENT OFFICE.

ALBERT L, CLAIPP, OF DANVERS, MASSACHUSETTS,'ASSIGNOR TO BENNETT, INCOR- PORATED, OF BOSTON, MASSACHUSETTS, A CORPORATION ,OF MASSACHUSETTS.

THERMOPLASTIC PULP.

N Drawing. Application filed December 8, 1922, Serial No. 605,722; Renewed October 19, 1925.-

The object of thisinvention is to produce what I may term an aqueous pulp of thermoplastic materials whieh are nonadhesive in make-up roll of a paper machine, and also.

maybe mixed with fibrous material to give strength thereto and then sheeted on a paper machine. A further object of the invention is thus to place these materials in the condition in which it is possible to form a fibrous sheet containing a maximum quantity thereof, or, in other words, a sheet having a high concentration ofsuch materials. Where such materials are formed into an 2 emulsion by the use of soap or other equivalent colloidal or emulsifying agent, the dispersion is such that it is diflicult to fix the dispersed materials upon and retain them in the felted fibers, with the result that much of theemulsified material is necessarily wasted.

I have discovered that it is possible to produce an aqueous mass which greatly resembles a fibrous pulp or paper stock by treating the thermo-plastic compounds so as to subdivide them in water; and, to distinguish the resultant product from true emulsions, I have termed this product an aqueous thermo-plastic pulp. I have found that, by melting such thermo-plastic compounds as natural or blown asphalt, parafiin, carnaubaor -Montan wax, resins such as rosin, or mixtures thereof or mixtures of other equivalent materials which are not adhesive at ordinary temperatures in the presence of water, and by rapidly stirring them into hot water and then chilling the mass, I can produce a pulp-like product in which the thermo-plastic material is in relatively finely divided discrete particles. For those thermo-plastic compounds which when in molten condition have a relatively high surface tension, I find it necessary to use in the water some compound or material for reducing such surface tension and which will operate in the nature of a dispersing agent. For this purpose, I have found sodium silicate in relatively small quantities to be eminently satisfactory. Again I have found that with certain thermo-plastic com pounds, better results are secured by adding to the water in which the thermo-plastic compound is mixed a quantity of a finely dlvided substance such as wood flour or finely divided sawdust. Nearly all thermoplastic compounds have a relatively high surface tension when in a molten condition, and for forming a pulp of such compounds, the water, into which they are stirred, must contain a dispersing agent which reduces the surface tension, and I have found no better material for this purpose than sodium silicate. Wood flour likewise has apparently the property of reducing the surface tension of such thermo-plastic compound, in combination with sodium silicate, and assists in the formation of a granular pulp. Also the wood flour has the property of reducing the adhesive or sticky characteristic of any gum or asphalt that might be used. Thus, provided a soft gum or asphalt were used, it would be necessary to use a relatively larger proportion of wood flour. With such materials, however, as Montan wax, which when molten is characterized by high penetrabili'ty and low surface tension, it is not necessary to utilize a dispersing agent or surfacetension-reducing agent such as sodium silicate, but greater care must be exercised in the formation of a pulp even with Mont-an wax to secure a pulpy'mass.

In producing an aque'ouspulp of Montan wax, one may proceed as follows: '50 parts by weight of water is placed in a mixing ap paratus containing stirrers or agitators which may be rapidly revolved, and is heated therein to a temperature approximating its boiling point. 7 5 parts of Montan wax is heated in a separate vessel to a temperature of about 280 F., and, while the water is being rapidly agitated, the Montan wax is poured therein and is thoroughly stirred into the water to form a more or less syrupy much the same as water may he s ueezed from a handful of paper pulp. The iscrete particles do not remain permanently in suspension as they tend to settle very rapidly, but, so long as the temperature of the pulp is maintained below the solidifying point of the thermo-plastic compound, the particles do not coalesce or form a solid mass. In practicing the process as just described, great care must be exercised to chill the mass by the addition of cool water at the proper time, when the mass has a syrupy appearance within a relatively few seconds after the Montan wa'x has been poured into the water, as otl1erwise.the continued beating or stirring of th qmass would result in a solidification and agglomeration of the particles and their separation from the water in large lumps or balls. I

Sometimes it is highly desirable to form a pulp of a mixture of thermo-plastic compounds such as asphalt, rosin and Montan wax; or, a mixture of acid resins (e. g. rosin and copal) Montan wax, lime resinate and a drying oil, such as China wood oil; wherein the mixture has a higher surface tension, when molten, than Montan wax. In either case, it is desirable to use a sodium silicate solution in the formation of the pulp to act as a dispersing agent and surface-tensionreducing agent. The following example will illustrate how a procedure may be carried out in such case. parts by weight of airblown asphalt having a melting point of 260 F., 30 parts of rosin and 10 parts of Montan wax are melted together to form a physically homogeneous fluid mixture. Into an agitator adapted to be heated, I place 250 parts of water in which are dissolved 20 parts of sodium silicate. The sodium silicate solution is heated to a temperature of approximately the boiling point of water, e.v g. 180 to 210 F., and, while this hot solution is being rapidly stirred and agitated, I now pour and stir into it 250 parts of the thermo-plastic compound. As soon as a syrupy mass appears (this taking only a relatively few seconds, say 10 to 15 seconds), cold water is added to the mass with the result. that an aqueous pulp is produced in which the thermo-plastic mixture is dispersed in discrete solidified particles. This aqueous pulp, as well as that producedby the example first herein given, may (as will be subsequently explained) he placed in a beating engine together with fibrous material and utilized in the formation of a fibrous felted sheet.

Air-blown asphalt, having a melting point of 220 to 260 F has a relatively highsurface tension when molten, and, in forming an aqueous pul of this compound alone, I preferably emp 0y both sodium silicate and wood in fine subdivision, such as wood flour or finely divided sawdust. When sawstirred into the mixture in the a itator.

soon as a' homogeneous syrupy mlxture 1s se-- dust is used, it should be capable of passing through a 10-mesh sieve, but, when Wood flour is employed, it is very finely divided much like wheat flour and is capable of passing through a 100-mesh sieve. To 350 parts by weight of water are added 300 parts of 60 B. sodium silicate and 45 parts of wood flour. These are thoroughly stirred together and the mixture is heated to approximately the boiling point of Water or a little below. Assuming that the blown asphalt has a melting point of 260 F., it is heated in a separate vessel to about 400 F. so that it is fluid, and 1100 parts of this blown asphalt are poured into and rapidllky cured, cold water is added for the purpose of chilling or freezing the discrete particles of the asphalt with the result that a granular pulp is obtained. The discrete particles comprise Wood flour and asphalt. The pulp, like the others previously described, may be washed to free it of sodium silicate, but this is not necessary when the pulp is to be used in the material of a fibrous sheet.

The three examples, which I have given, merely serve to illustrate the procedure which is followed in practicing my process and those skilled in the art will readily appreciate that substantially all thermo-plastic compounds (which when solid and in the presence of water are nonadhesive) may be formed into a pulp. Of course the relative proportions of thermo-plastic compound to sodium silicate or to wood flour may be changed or varied as occasion may require. An advantage in utilizing wood flour or finely divided sawdust is that I am able thereby to reduce the proportion of sodium silicate. Thus, in the lastexample hereinbefore given, in the event that the proportion of wood flour is decreased, the proportion of sodium silicate must be increased. If no wood flour is employed, it would be necessary to use approximately 500 to 600 parts of sodium silicate. v

One of the great advantages of an aqueous thermo-plastio pulp produced as herein described, is that I am able to incorporate in a fibrous sheeta very-large proportion of thermo-plastic compound and to secure a maximum retention of such compound in the fibers. As a result of this, the beater may be supplied with certain relative proportions o pound, and a sheet produced having very nearly these roportions.

is that it may be formed on a forming roll or cylinder mold of a wet machine' and transferred to the make-up roll, but the layer formed on the make-up roll cannot be removed because of its inherent lack of strength. In this respect, the pulp is esfiber and-thermo-plastic com- One of the peculiar characterlstics of the thermo-plastic pulp wet machine.

sentially different from emulsions of thermo-plastic compounds which are incapable of being formed on the forming roll of a Still another advantage of the thermo-plastic pulp produced as herein described, is that, for its retention upon cellulose or other fibers, it is not necessary to use any size or precipitating or coagulating agent, since it mixes thoroughly with fibrous materials. Again, because of these characteristics, it is possible to use a minimum quantity of fiber and a maximum quantity of a thermo-plastic pulp, using just enough fiber to secure a felting action in the sheet.

By selecting such thermo-plastic compounds having the desired characteristics, it is possible to produce paper or board for a great many different purposes or uses and having quite varying properties or characteristics, this depending in part also upon the character of the fibers which are utilized in forming the paper or board. The herein described aqueous thermo-plastic pulp may be utilized with fibers of many different kinds, such as ground wood pulp, chemical wood pulp, mixed papers, rags, hair, rope stock, etc., depending upon the result which it is desired to secure. Thus, in the manufacture of a water-proof board, I may utilize the pulp described in the second ex-- ample, in which case one may proceed as follows: Into a beating engine is placed a quantity of sulphate pulp, which is beaten to secure the desired degree of hydration; after which the beating roll is lifted from the bed plate and an equivalent amount of thermo-plastic pulp, formed of asphalt, rosin'and Montan wax (figuring the weight of the thermo-plastic compound to the Weight of the dry fiber), is added, whereupon the operation of the roll is continued I until a thorough mixture of the furnish is secured. The material is now transferred to the vat of a cylinder or wet machine and the laminations are built up on the make-up roll until a board of the desired caliper or thickness is secured. This is now out, removed and dried, and is then passed through heated calender rolls, the temperature of which is sufficient to effect the coalescence of the thermo-plastic compound throughout the sheet.

Of course, as previously indicated, it will be understood that the foregoing is given merely as an example and that the proportions of thermo-plastic compound to fiber may be varied as required. I have found it possible to form a sheet in which the proportion of fiber to thermo-plastic compound is as one to four. Of course, in lieu of sulphate pulp, one may, as I have previously stated, use any other fiber which may be desired. While, as I have said, it is not necessary in the beater to use any precipithe aqueous mixture.

tating or coagulating agent, nevertheless, inasmuch as the thermo-plastic pulp has mixed with it sodium. silicate, it is desirable to conserve the latter; and, to this end, after the mixing of the thermo-plastic pulp with the fibrous material has been accomplished, one may add alum or other precipitating agent for precipitating the aluminum silicate on the fibers. I do not mean that one need not usea size, if it be regarded as desirable, because of course it is possible to add to the pulp, and to precipitate on the fibers thereof, any sizing compounds which may be regarded as desirable according to the common methods heretofore followed.

'thermo-plastic compound in finely divided discrete particles or granules.

2. A process of producing an aqueous pulp of a normally solid thermo-plastic com pound, which comprises melting such compound, heating a water solution of sodium silicate,-stirring the molten compound into the sodium silicate solution to disperse the compound in the solution, and then chilling the mass to solidify the compound in discrete particles.

3. In the process of producing a pulp or suspension of a normally solid thermo-plastic compound inwater, those steps which comprise forming and heating an aqueous sodium silicate solution, and then mixing such solution and the thermo-plastic compound while the latter isin a molten condition.

4. In the process of producing a pulp or suspension of a normally solid thermo-plastic compound in water, those steps which comprise forming and heating an aqueous sodium silicate solution, having a body of finely divided wood mixed therewith, and then introducing and stirring the thermoplastic compound, in molten condition, into 5. In the process of producing a pulp or suspension of a normally solid thermo-plastic compound in water, those steps which comprise forming and heating an aqueous sodium silicate solution, then mixing therein the thermo-plastic compound while in a molten condition, and finally chilling the mass, whereby the thermo-plastic compound is solidified in discrete particles in the water.

6. In the process of producing a pulp or suspension'of a normally solid thermo-plastic compound in water, those steps which comprise forming and heating an aqueous sodium silicate solution, having a body of finely divided Wood mixed therewith, then introducing and stirring the thermo-plastic compound, in molten condition, into the aqueous mixture, and finally adding to the mass a body of water at a temperature below the solidifying point of the thermoplastic compound.

7. A process of producing an aqueous pulp of a normally solid thermoplastic compound, which comprises melting said compound to fluid condition, forming an aqueous solution of sodium silicate, heating said solution to a point approximating the boiling point of water, rapidly stirring the n'iolten compound into the aqueous solution to form a syrupy mass, and then adding cool water, whereupon the thermo-plastic compound is solidified in the form ot'discrete particles dispersed in the water.

8. A process of producing an aqueous pulp of a normally solid thermo-plastic compound, which comprises melting said compound to fluid condition, forming an aqueous solution of sodium silicate, andmixing a quantity of wood flour therewith, heating said solution to a temperature approximating the boiling point of water, stirring the molten compound into the aqueous mixture, and then adding cool water to the mass.

9. An aqueous thermO-plastic pulp comprising a sodium silicate solution containing discrete solidified particles or granules of a normally solid thermo-plastic compound,

said pulp being of such nature and consistency that the water may be squeezed from a handful thereof.

10. An aqueous thermo-plastic pulp comprising a sodium silicate solution containing discrete solidified particles or granules of a normally solid thermo-plastlc compound and wood flour, said pulp being of such nature that it may be formed on the cylinder mold of a paper machine.

11. An aqueous thermo-plastic pulp comprising a sodium silicate solution containing discrete solidified particles or granules of a normaly solid thermo-plastic compound, and finely divided wood.

12. A process of producing an aqueous pulp of Montan wax, which comprises melting the wax, stirring it into a heated body of water until a syrupy mass is obtained, and then chilling the mass to solidify the wax as discrete particles.

13. A thermo-plastic pulp consisting of discrete particles of Montan wax suspended in water containing a dispersing agent.

14. An aqueous thermo-plastic pulp consisting of a sodium silicate solution having in suspension therein discrete, solidified particles of a normally'solid thermo-plastic compound.

In testimony whereof I have aflixed my signature. i

ALBERT L. CLAPP.