US1981573A - Pulp forming process - Google Patents

Description

Patented Nov. 20, 1934 UNITED STATES- 1,981,573 PULP FORMING rnoosss Earl Stafford, Fairlawn, N. J., assignor to The Richardson Company, Lockland, Ohio, a corporation of Ohio No Drawing. Application July 18, 1930, Serial No. 468,996

.8 Claims. (or. 92-21) My invention is addressed to the field of pulps of fibrous material in water suspension, with which there is incorporated a bituminous or other heat plastic, waterproofing substance, the

whole being feltable on a screen. Particularly my invention is related to a way of producing a pulp of the general character described above, in which the bitumen exists in minute, uncoated particles in an intimate yet non-adherent association with the fibers. A method for making what I have termed a premix or bituminous pulp containing distributed heat-plastic materials, is set forth in Patent #l,'771,150, to Earl P. Stevenson and Harry A. Buron, dated July 22, 1930. A characteristic of this process is the production of a pre-association of binder and fibers before a pulping stage, by a mixing operation. Before this mixing operation, the fibrous material, while it may be wetted, will not be pulped, i. e., it will not be a fiber-liberated stock in which water is present in amounts suflicientto act as a circulating medium. The resultant bituminous pulp contains the binder substance in minute uncoated particles in intimate admixture, but in stable and substantially adherent association with the fibres.

I am also familiar with attempts made in the.

paper stock with mineral filler or pigment. Such an operation has not proven of commercial value for several reasons: (1) It is restricted to the use of very hard heat plastics such as bitumens having a ball and ring softening point of 200 F. or higher; (2) it is difficult to grind even the harder of these heat plastics, as many of them, notably the bitumens, are not true solids and exhibit the property of plastic flow under pressure of grinding and local heating; (3) it is not readily possible to secure the distribution and/or association required for high retention in the felted sheet.

It is.an object of my invention to secure the results comparable to those obtainable by adding finely ground dry heat plastic binder to pulp in a paper mill beater, while avoiding the above mentioned dimculties heretofore encounteredwhen attempting to so combine a pulp and a .55 heat plastic binder, particularly that of retention in the felted sheet.

Another object is to provide for the handling of heat plastic materials, which can not be sufficiently softened at ordinary steam pressures to so be readily amenable to the process of Stevenson avoid a prolonged rod mill operation. It is furand Buron above referred to, in which characteristically the binder must be in a non-solid condition. Other heat plastics which may be desired in paper are subject to some degeneration or decomposition on prolonged heating at relatively high temperatures in the. presence of water.

A characteristic which investigation up to the present has shown to be commercially advisable in the production of pulps containing a binder substance, is the comminution and distribution of the binder substance in the presence'of the fibrous material. It is an object of the present invention toprovide a new way of efiecting the comminution and distribution of binder material in the presence of fibrous material in water suspension.

These and other objects which may be pointed out hereinafter, or which will-be apparent to one skilled in the art upon reading these specifications, I accomplish by that certain process and in that certain series of steps of which I shall now describe a preferred embodiment.

Briefly, I accomplish the objects of my invention by carrying on a combined pulping and incorporating process in an instrumentality suitable for the purpose, and among a number of such instrumentalities which are satisfactory, I have found the rod mill exemplary, and in some instances, preferably. Rod mills may be made continuous in their action, and this is of practical importance.

Carrying out my process, I introduce into a rod mill, preferably fitted for continuous operation, a pre-formed pulp of fibrous material, or fibrous material and water not pulped at all, or in a semi-pulped condition. Commercial practicability under any given circumstance will determine which I use; and an advantageous characteristic of a rod mill operation is its flexibility. It is under many circumstances a satisfactory pulping device.

Where pre-pulped materials are fed into the rod mill, its function will be largely that of a mechanism for comminuting and distributing the bituminous material therethrough. Ordinarily in commercial operation I prefer to use a pulped but unrefined stock such as that which is the product of a breaker beater operating upon waste papers. Sulfite, kraft and other fibers are also satisfactory, and my process is not limited to any fibrous material. Rags may be used; but these are preferably first pulped or semi-pulped, because the mechanical action in the rod mill will not be suflicient to liberate the fibers therefrom unless it is quite prolonged. For economy I prefer to 115 ther generally preferable to introduce the stock into the mill in such a condition that the mechanthe asphalt will be sumcient to finish the fit- An exemplary asphalt of considerable utility in my process is one called Stanolind B. It. has a high susceptibility factor, in that it is quite hard and non-tacky at room temperature, but may be liquefied substantially below the boiling point of water. Other examples are blends of the above asphalt with Gilsonite. As an example of a nonbituminous plastic, shellac may be cited as one .which has been handled with satisfactory results.

The mixed stock may be fed into the rod mill continuously and also continuously discharged therefrom. It will be found to be in condition for felting upon a screen; but it may be further refined, as by beating or jordaning, if desired, and it may be diluted or thickened as will be found desirable. It is to be pointed out that when the bitumen or other heat plastic exists during the rod mill operation in a hard form, the action of the rod mill is to crush it up into a very fine degree of sub-division, and to mix it into the fibers at the same time, which, per se, I believe to be a novel operation. It is also to be pointed out that my invention is not restricted to the use of the rod mill, other types of pulping apparatus being satisfactory for the purpose. As exemplary of these may be mentioned the swing-hammerbeater. The ordinary hollander is not satisfactory for the reason that itsaction is dependent upon circulation, and it is intense only over one relatively small. area, namely, the area of contact of the roll with the bed plate.- I have not found it possible to incorporate bitumen in any commercially satisfactory manner by grinding it with fibrous material in a paper mill beater.

While I am not able wholly to explain the improved results obtained by mechanical comminution in the presence of fibrous materials, I attribute this in part to the more uniform sized particles thereby obtained. In the straight grinding, for instance, of a hard and brittle bitumen the particle sizes may vary over a wide range and include some that are so fine as to pass readily through the fiber filter formed by felting on a machine. The more uniform grinding herein obtained is, I believe, due to the protective action ,of the fiber in interposin'g a cushion between con- Patent, is

1. That process of producing a pulp of fibrous material in water suspension, and containing a heat plastic material in intimate association therewith, which consists in simultaneously reducing a fibrous material to apulp, and a heat plastic to a comminuted form, in the presence of sufllcient water to act as a circulating medium, through the mechanical action of a revolving rod mill.

2. That process of producing a pulp of fibrous circulating medium, the said grinding being accomplished during the process of fiber liberation, in a revolving rod mill.

3. That process of producing a pulp of between 5 and 10% consistency and containing waterproofing substance, which comprises starting with a pulp of fibrous material in water suspension and mechanically disintegrating in a revolving rod mill a bituminous substance in the presence of said pulp and distributing it therethrough in minute, uncoated particles of subouslydistributed therethrough a bituminous substance in minute uncoated particles in suspension, which comprises grinding a bituminous substance in the'presence of a suspension of fibrous material in water sufficient to act as a circulating medium, the grinding being-accomplished I during the process of fiber liberation, in aball mill.

6. That process of producing a fibrous material in water suspension, having homogeneously distributed therethrough a. heat plastic substance in minute, uncoated particles in suspension, which I comprises simultaneously reducing ,a fibrous material to a pulp and a heat plastic material to a comminuted form, in the presence of suflicient water to act as acirculating medium, said reduction being accomplished by causing the fibrous material andthe heat plastic to pass continuously between impacting surfaces.

'7. In the manufacture of a fibrous thermoplastic composition, the method which comprises subjecting fibrous material and free thermoplastic binder in the presence of each other in an aqueous medium to a rod milling treatment, the thermoplastic binder being brittle and pulverizable at the temperature of the treatment.

8. In the manufacture of a fibrous thermoplastic composition, the method which comprises simultaneously introducing fibrous matcrial and free solid thermoplastic binder in lump form together with water to provide a consistency of about 3% to 20% by weight of total solids into a rod mill, and passing the mixed materials through the mill while subjecting them to a pounding disintegrating treatment as fresh .materials are fed thereto, the thermoplastic binder being brittle and pulverizable at the temperature of the disintegrating treatment.

EARL STAFFORD.

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