US1993265A - Manufacture of paper embodying alkaline earth metal carbonate fillers - Google Patents

Description

Patented Mar. 5, 1935 UNITED STATES PATENT QFFICE MANUFACTURE OF PAPER EMBODYING ALKALINE EARTH METAL CONATE rmnns No Drawing. Application February 28, 1933, Serial No. 658,942

Claims.

This invention relates to the manufacture of paper and it has particular application to the sizing and filling of paper wherein alkaline earth metal carbonate fillers are employed.

Alkaline earth metal carbonates, notably calc i um carbonate, have been proposed as fillers for paper heretofore and have been utilized to some extent for this purpose. However, their use has not met with favor in connection with a rosin- 10 alum or similar size, due to the unsatisfactory quality of the resulting paper'product. It has generally been considered that the alkalinity of the carbonates functions to destroy or seriously impair the rosin-alum size. As a result, it has been almost universal practice to utilize other fillers, particularly clay, whichis relatively inert under the acidic conditions developed in the sizing of paper with alum. I

Clays which have a sufiicient degree of whiteness are relatively rare and correspondingly expensive. On the other hand, carbonates, and particularly calcium carbonate, of a satisfactory quality so far as color and degree of fineness are concerned, are available in almost unlimited quantities and at a cost which is substantially less than the cost of clay. For this purpose naturally occurring carbonates which have been reduced to the desired degree of fineness by trituration or otherwise, as well as artificial carbonates such as precipitated chalk or the byproduct of causticizing processes such as are commercially employed in the manufacture of caustic soda for use in the manufacture of soda pulp, may be used. Moreover, it is fairly generally held that the deterioration of paper is accelerated by acidic conditions such, for example, as may be brought about by the use of a large proportion of alum, and that a reduction of acidity brings about a corresponding increase in life of the paper.

In view of the foregoing, as well as other factors, many proposals have been made with the -view of minimizing or obviating undesirable modifications of these ideas have been proposed, but none to date has been satisfactory.

The object of the present invention is to provide a method of sizing and filling paper using alkaline earth metal carbonates, and particularly 5 calcium carbonate, as a filler, whereby the shortcomings and disadvantages of the prior processes are overcome; whereby a carbonate such as is readily available on the market may be employed without preliminary treatment; equipment such as is already installed in the standard paper plants may be utilized without extensive or expensive alterations; whereby a paper of a quality, particularly as regards life and resistance to ink penetration are concerned, 15 is at least as good as corresponding grades of present day paper; and finally, whereby the cost of sizing and filling paper is reduced below the cost of paper which has been filled with present day fillers, notably clay.

According to the present invention, the wood or textile fibers or mixture of the two are formed into a pulp of the usual working consistency and freeness, thereafter arosin size, for example, is introduced and thoroughly distributed therein. Subsequently, suflicient alum is added to precipi tate the size. Under these conditions, if calcium carbonate were introduced or present, it would destroy the size and a paper of unsatisfactory quality would be obtained. In practicing the present invention,.c2irbon dioxide, or a gas or reagent containing carbon dioxide, is introduced into the mix and an equilibrium condition therewith is attained or approximated by thorough agitation or intermingling. Thereafter the carbonate filler may be introduced with no apparent deteriorative or destructive action on the size. The filler is then thoroughly distributed throughout the pulp mixture and a soluble base such as soda ash is added, after which the batch is again thoroughly mixed and finally formed into sheets in the usual manner. Under some conditions the resulting paper product may be found to contain filler spots. This shortcoming may, however, be easily and completely overcome by substituting for the soda ash prescribed hereinabove a doc of aluminum hydroxide, which preferably should be distinctly basic. To this end one may add alum and soda ash to the beater whereby the floc is formed in the beater, or, the fioc may be formed in separate vessel and subsequently added to the beater. Very satisfactory results, both from the standpoint of convenience and quality of product, have been obtamed by the use of sodium aluminate in lieu whereby the m .of the soda ash-alum floc.

This material not only provides the desired alkalinity, but also supplies the necessary alumina for the production of the aluminum hydroxide floc.

The presence of the carbon dioxide-which, incidentally, should preferably be kept in contact with the mixture as long as the mixture undergoes vigorous beating or agitation under conditions whereby the dissolved carbon dioxide might be expelled and the proportion thereof thereby reduced materially, appears to act as an impediment or inhibitor to the destructive action which would otherwise take place upon the introduction of the carbonate filler into the pulp containing the rosin and alum size. It has been observed in a number of experiments that the pH value of the contents of the beater varies from 6.2 to 7.2 when carbon dioxide is utilized in conjunction with the calcium carbonate filler. On the other hand, when the carbon dioxide is omitted, the pH value of the contents of the beater is approximately 7.8 to 9.0. Under these latter conditions, no appreciable sizing. has been observed. The presence of the carbon dioxide reagent, therefore, functions to maintain a pH value at which the alkalinity or acidity of the batch is such as to realize good sizing without inducing the destruction of the size, which appears to be brought about at the higher pH values that are observed when no carbon dioxide is employed.

The source of the carbon dioxide reagent is optional, and one may introduce pure gaseous carbon dioxide, solid carbon dioxide, or flue gas which is high in CO2 content, for the purpose of maintaining the desired pH value or otherwise rendering the calcium carbonate passive to the size.

The addition of the alkaline floc or floc producing agent, following the addition of the filler, and for this purpose sodium aluminate is preferred, as compared to other basic mixtures, insures a uniformly well sized sheet having inordinately good ink penetration qualities. The product thus obtained has been found to have an ink penetration of from 5 to 7 minutes when tested under the usual conditions for this test.

A specific example of one embodiment of my invention is hereinafter set forth:

One hundred twenty-five parts (by weight) of sulfi te pulp are distributed in 7000 parts (by weight) of water by means of a beater of standard design to the usual or ordinary degree of freeness, after which 2.5 parts of rosin size (2% on the basis of the air-dried pulp) are introduced in the usual dispersed condition and evenly distributed by continuing the beating operation for 15-20 minutes. Two and one-half parts of commercial paper makers grade alum (2% on the basis of the air-dried pulp) are added and the beating operation is continued for an additional period of 15-20 minutes.

Carbon dioxide is then introduced until the solution appears to be saturated. This may be introduced from a cylinder or as solid carbon dioxide. After this. 43.75 parts of calcium carbonate filler (35% on the basis of the air-dried pulp) are added and uniformly distributed throughout the batch in the usual manner. To the resulting mixture there is then added one part of soda ash (.8% on the basis of the airdried pulp). After 15 minutes of mixing, the pulp is removed from the beater and formed into sheets. In lieu of soda ash, one may add one part of commercial sodium aluminate (80-85% NazAnoo, (3% on the basis of the Y air-dried pulp). Sheets produced in the usual manner from this mixture have unusually satisfactory properties both as regards uniformity and ink penetration.

Obviously, the foregoing procedure may be varied as to the size of batch; as to the relative amount of water, which, it is to be noted, may be reduced substantially from that specified to approximate more closely the ratio commonly employed in paper mills; as to the method of forming the sheet; the ratio of ingredients employed; and the precise conditions of operation as above set forth. The several steps of adding reagents to the pulp may be effected in a single beater or progressively in subsequent stages of the progress of the pulp to the sheet-forming machine; thus, for example, the alkaline floo may be added to the mixture in the stuff chest.

Moreover, the addition of other ingredients such as dyes,lpigments, and other agents, commonly employed in the manufacture of paper, including clay, may be incorporated without departing from the spirit of the present invention, it being understood that the specific conditions are exemplary only. Similarly, other sizing agents, such as the stearates, may be substituted for the rosin size.

What I claim is:

1. A method of sizing paper wherein an alkaline earth metal carbonate is employed as a filler and in combination with a size consisting of rosin and alum, that comprises introducing the rosin size and alum and adding a carbon'dioxide reagent before adding the carbonate filler.

2. A method of sizing paper wherein an alkaline earth metal carbonate is employed as a filler in combination with a rosin size and alum, that comprises introducing the rosin size and alum to precipitate the size, adding a carbon dioxide reagent before adding the carbonate filler, and finally, adding a soluble basic material before forming the film.

3. A method of sizing paper wherein an alkaline eartlr metal carbonate is employed as a filler in combination with a rosin size and alum,that comprises, first, introducing the rosin size and alum to precipitate the size, subsequently addsize and alum to a pulp, subsequently introducing carbon dioxide into the aqueous suspension, thereafter adding a calcium carbonate filler, and finally adding sodium aluminate before forming the paper sheet.

5. In the manufacture of paper wherein a rosin size and a calcium carbonate filler are employed, the step which consists in maintaining a pH value of approximately 6.2-7.2 by means of carbon dioxide during and subsequent to the addition of calcium carbonate to the pulp containing the rosin-alum size.

6. The method according to claim 5 and further characterized in that a basic floc is added to the resulting mixture before forming the paper sheet.

7. The method as defined in claim 5 and further characterized in that sodium aluminate is added to the resulting mixture before forming cium carbonate filler to the resulting mixture while maintaining a pH value of the pulp me dium of approximately 6.2-7.2 by means of carbon dioxide, subsequently adding a relatively small quantityof sodium aluminate as compared to the amount of size and alum employed, and finally forming the paper sheet.

9. The method of sizing paper wherein an alkaline earth metal carbonate is employed as a filler in combination with a sizing material, the step which comprises maintaining the said aqueous medium charged with carbon dioxide havin a pH value 0! approximately 6.2-7.2 during the addition of the carbonate filler to the pulp mixture.

10. In the manufacture of paper wherein a rosin size and a calcium carbonate filler are employed, the step which comprises maintaining the pH value not substantially greater than 7.2 during and subsequent to the addition of the carbonate filler to the pulp mixture by the ad dition thereto of carbon dioxide.

COLVER P. pm.