US1904251A

US1904251A - Paper manufacture

Info

Publication number: US1904251A
Application number: US533872A
Authority: US
Inventors: Rafton Harold Robert
Original assignee: Raffold Process Corp
Current assignee: Raffold Process Corp
Priority date: 1931-04-29
Filing date: 1931-04-29
Publication date: 1933-04-18
Anticipated expiration: 1950-04-18

Description

' Patented Apr, 18, I933 tab sar -1s team PATENT OFFI ROLD ROBERT -RAFTON, OF ANDOV'ER, MASSACHUSETTS, ASSIGNOR TO FFOLD PROCESS GORPORATION, A CORPORATION OF MASSACHUSETTS PAPm MANUFACTURE no Drawing. Application filed April as,

This invention relates to the manufacture of paper filled with alkaline filler.

The principal object of this invention is to improve the running qualities on the paper 5 machine of paper filled with alkaline filler.

An important object is the minimizing of sticking on the paper machine in the manufacture of such paper.

. A further object is the minimizing of the,

sticking of the web to the press rolls of the paper machine in the running of sized paper filled with alkaline filler.

A further object is the production of higher alumina content rosin size precipitates in the manufacture of paper filled with alkaline filler, particularly by the employment of sodium aluminate therein. 9

Other objects and advantages of this invention will become apparent during the 2 course of the following description.

In my copending application Serial No.

304,171, filed September 5,1928, now matured into Patent No. 1,803,646, issued May 5, 1931, I describe a method of substantially eliminating foam in the running of unsized papers filled with an alkaline filler, in one modification of which an amount of sodium resinate insuflicient to impart a substantial degree of sizing to the paper is added in the beater,

.. precipitated therein with alum, and then the precipitate which has been deteriorated by contact with alkaline filler is restored at the wetend of. the paper machine with a further quantity of alum. In my copending application Serial No. 304,174, filed September 5,

1928, now matured into Patent No. 1,803,649,

issued May 5, 1931, I describe a similar process wherein sodium resinate is added in the beater, and alum is added for purposes of precipitation at the wet end of the paper machine.

In my copending applications Serial Nos. 304,168 and 304,172, both filed September 5, 1928, now matured respectively into Patents Nos, 1,803.643 and 1,803,647, loot-h issued May 5, 1931, I describe two' processes similar to the above except that in these two cases there is present, a suflicient amount of size to produce a substantially sized aper.

In the running 0 substantially unsized 1931. Serial No. seas-22.

paper according to the methods referred to in the first two cited applications, no difliculty has been experienced in regard to any tendency of the stock to stickon the paper machine. On the other hand in running sized paper according to the methods described in the tent than the types previously used. Fur-- thermore it is well known in the paper industry that changes in the freeness of the stock on the paper machine will change the sticking characteristics of the stock. However in certain cases after all the known expedients had been tried, there seemed to be a greater sticking tendency in the stocks run according to the methods disclosed in the two cited applications last referred to above than in clayfilled paper stocks run under similar conditions on the same paper machines.

In the course of an investigation conducted to determine the cause of this sticking, it was observed that the pH values of the stocks on the wires of the paper machines in the cases where my said methods were practiced were usually higher than in the cases where stocks containing no filler or containing inert filler such as clay were being run. As a result of this observation, the composition of rosin size precipitates prepared at difierent pH values was determined, i. e. to a series of samples of diluted rosin size were added respectively the amounts of alum necessary to produce successively lower pH values. It was found that the precipitates produced at the higher pH values were'very sticky and diflicult to filter, this being particularly the case at pH values higher than 7, Whereas the precipitates produced at pH values of 7 or lower were substantially non-sticky, and filtered relatively easily.

An analysis of the precipitates produced as above showed that the alumina content of the. precipitates varied according to the pH at which the'precipitate had been produced,

the amount of alumina increasing with decrease in pH.- The increase was very marked in an experiment, in the first part of which a sample of rosin size was precipitated with an amount of alum previously found to give a definite pH, in this instance 8.5, at which pH the precipitation of the rosin size was not complete. The precipitate was then filtered off, further alum addedto the filtrate, and a further filtration made. By repeating this process, a series of precipitates was obtained, made from solutions of rosin size of successively lesser pH values and precipitated with amounts of alum which gave still lower definite pH values. As stated, the alumina content of this series of preciptates rose rapidly with decrease in the final pH. It therefore appeared that in view of the 'difliculty ofmaintaining a very low pH on the paper machine in the presence of alkaline filler, if it were possible to increasethe alumina content of the size precipitate, that the sticking qualities of the such size precipitate might be markedly altered.

After considerable experimentation it was found that by a special procedure alumina could be introduced into a size precipitate at any given pH in quantities much greater than would normally be introduced at that pH were the size merely precipitated at that pI-I with alum. This was accomplished by mixing the size, prior to its precipitation with alum, with a compound of aluminum which did not cause its precipitation, preferably a non-acid compound of aluminum, preferably in soluble form. A suitable compound ofaluminum for carrying out this procedure wasfound to be sodium aluminate. Sodium aluminate was mixed with size prior to the precipitation thereof, and then precipitation with an acidic material such as alum was effected at a high pH value such as 8. When precipitation of other similar samples was effected at successively lower pH values and it was found that the alumina content of the thus produced precipitates was greatly increased overthose produced at similar pH values where no sodium aluminate had been admixed with the size. In effect it was found that precipitates produced from rosin size at relatively high pH values could be made with as great or even a much greater alumina content than those produced with alum alone at a relatively low pH. The precipitates so produced with a high content of alumina even at a relatively high pH were found to be substantially less sticky, than the similar low alumina prec pitates made at the same pH. Likewise the h gh alumina content precipitates produced at lower pH values were also found to be substantially non-sticky. It is thus seen that by utilizing this data it is possible to produce rosin size precipitates in practical operation which are substantially nonsticky even though the pH at which they are precipitated may be high and/or the pH of the stock on the wire may be neutral or even higher, due to the presence of alkaline filler.

Instead of employing sodium aluminate or other alkaline aluminate with the size I may actually prepare the size by original solution of the rosin with sodium aluminate, or with sodium aluminate in conjunction with other alkalies. This is a convenient method as by so doing one less constituent has to be handled, and also part of the alkalinity of the sodium aluminate is used up in the solution of the rosin during the preparation of the size and hence the subsequent quantity of acidic material required materially reduced.

Instead of using sodium aluminate orother alkaline aluminate I have found that it is possible to prepare a solution of an aluminum compound at a pH value at which aluminum hydroxide or hydrate would ordinarily be precipitated, by. having present a precipitation inhibitor such for example as a citrate, either citric acid, or a soluble citrate such as sodium, potassium or ammonium citrate, be-

ing suitable. In such case a solution of sodium citrate for example may be added to alum and snflicient alkali, such as sodium carbonate for example, may be added to raise the pH of the alum to neutrality or even higher without the precipitation of alumina taking lace. When such a neutralized or alkalinized substantially non-precipitating aluminum solution is prepared and added to rosin size, and then the rosin size precipitated in the presencethereof by the addition of an acidic material such as alum, the precipitate thus obtained is substantially non-sticking. There has not as yet, however, been sufficient analytical data adduced to prove conclusively t at the rosin size precipitates so obtained havea higher alumina content than a normal rosin size precipitate, but from the trend of data so far obtained such a conclusion seems to be probable. Instead of citric acid or citrates as precipitation inhibitors, other ma terials may be used such for example as tarfor precipitation is trates, but the citrates seem to be most effective materials yet tried. Aluminum citrate itself may also be used directly, instead of mixing a compound of aluminum and a. citrate.

I am aware of the fact that it has previously been known to use sodium aluminate in connection with rosin size in the beater, and also to dissolve rosin size with sodium aluminate, and precipitate such sizes in the beater. However any such size precipitates, or pr ec1p1- tates made by the citrate method as indicated plained the constituents of the mix, that the facts ad-,

the alum may duced herein become capable of utilization.

In the preferred practice of my invention. size such as rosin size is added to fibrous niaterial iii a beater. An aluminate such as sodium aluminate should be present, and it is suitably added mixed with the size; or instead of the aluminate being present independently, the rosin size used maybe made with sodium aluminate. The size is precipitated in the beater with an; acidic material such as alum, in which case it, due to the presence of alkaline filler in the stock in the beater, the size precipitate is deteriorated, it is restored, preferably with a. alum, by the addition thereof under conditions favoring the minimizing oi the time and/ or intimacy of contact of the constituents of the mix, for example at the wet end of the paper machine. Or the size may be originally precipitated by the alum added at the wet end of the paper machine, or both the size and be added at the wet end oil the paper machine, or the size may he added at that point to a stock to which alum has previously been added. lln the latter case of course the aluininate must accompany the size when added. The alkaline filler may be added in the heater or at the wet end of the paper machine,.as described in various of my copcnding applications in which it is disclosed that alkaline filler and/or alum may. be added to the fibrous mix at the wet end of the paper machine. in addition to my copending applications already noted; reference is made to my applications Serial Nos.

304,167 and 304,175, both filed September 5, 1928, and No. 321,754 filed November 2 1-, i928, now matured respectivel into Patents Nos. 1803;642 and 1,803,650, both, issued May 5,

various possibilities of the precipitation of size in papers filled with alkaline tillers have been thoroughly discussed in my said prior applications, but according to the improvethat a very satisfactory amount to'employ is further quantity of 1931, and 1,808.071, issued June 2,1931, The

an amount of aluminate which represents on the amount of dry rosin in the rosin size used. A quantity of alum for precipitation of the size is then used which would beat least suflicient, but preferably in some excess over that quantity required, to give a neutral or slightly acid reaction with said amount of size and said amount of aluminate. It is not possible to give in general the quantity of alum required owing to the great variability in the amount of alkali present in sodium f 10-15% of alumina calculated as A1 0 based aluminates, but the minimum quantity required can be easily determined in the laboratory by a simple stoichiometrical titration. From the above it will be apparent thatother things being equal it is desirable to use the sodium aluminate as weakly alkalineas possible. L

With respect to the amount of precipitation inhibitor suitably to be resent when this modification of my invention is to be employed,.while I do not limit myself'thereto,

l have found that an amount oi sodium citrate equal to approximately 50% calculated as weight of dry commercial citrate on the weight. of dry alum which is neutralized or alkalinized is a suitable quantity to employ. The neutralized or allralinized alum to he used may suitably be approximately 75% dry alum based on weight of? dry size employed.

, Cross reference is here made to my copending applications Serial Nos. 319,719, 319,720 and 319,721, all filed November 15, 1928, now matured respectively into Patents Nos.

1,808,0t7,1,808,068 and 1,808,069, an issued June 2, 1931, wherein there is described methods of incorporating into a paper an inorganic alkali metal salt with a pH value greater than '10, which is precipitable by material which depresses its hydronyl ion con-- centration, it will be noted that sodium aluminate is such a compound but no claims specifically to sodium aluminate, aremade therein,

lln my various copending applications refcerrcd to herein as well as in others, i have discussedin full the principle on which the expression minzingthe time and/or intimacy' of contact oi mix is based, Briefly it is that alkaline filler, which" always is present in the stock from which paper made in great stoich iometrical excess over the acidic constituent, acts uponthe' acidic constituent to the ultimate destruction thereof and/or the destruction of the edect maintained by such constituent. (The acidic'con stituent so-called may be one which is actually acid, and/or one which such as asize precip'tate is capable of being afiected or deteri: orated by an alkaline material). The action just referred to has been found to depend upon the time of contact of the acidic and "w constituents d also upon the inthe constituents of thev tilled with alkaline filler is i timacy of contact of these constituents. Agitation such as normally occurs in papermaking procedure in stuff chests or the like accel crates the rate of reaction, but agitation at low concentrations while having some effect is not nearly so deleterious. Based on this principle a practical application has been developed whereby, by minimizing the time and/or intimacy of contact of the acidic and alkaline constituents, the acidic constituent and/or the efiect produced thereby, is sub stantially preserved in an alkaline filler mix. With the present types of paper machines and the present arrangement, of apparatus usually employed in paper machine operation, the contact of the acidic material and the'alkaline constituent at any time prior to I preferred practice the passage of the stock from the-last stufi chest, which is commonly called the machine chest, results in great deterioration of complete destruction of the acidic material. Additionof one or both of these constituents, as well as other materials such as size, sodium silicate, starch and the like as set forth in my various copending applications, at a point subsequent to the passage of the stock from the machine chest, after which point according to present day operating practice the stock remains in concentrated condition only for a very brief interval of time or addition preferably at or subsequent to the point of dilution, i. e. at the wet end of the paper machine, serves to substantially conserve the acidic material and/or effect thereof in the fibrous mix. It is the application of this principle which I utilize .in connection with the precipitation of rosin size in the presence of substantially non-acid aluminum compound as set forth in the description of the of my invention given above.

I have also found that the introduction of sodium aluminate is. at times desirable in the manufacture of substantially unsized paper filled with alkaline filler, and that it may be incorporated into such paper in general according to the methods herein discussed even in the absence of rosin size or in compound whose solubility the presence of an amount of rosinsize insuflicfent to impart a substantial degree of sizing to the resulting paper. The use of sodium aluminate or of a non-acid aluminum is maintained by the presence of a precipitation inhibitor presents a means for. introducing into a paper mix an acidic aluminum compound without the direct addition thereto of such compound, when an audio condition is also material is added thereto, which can react with the non-acid aluminum compound to produce an acidic aluminum compound.

In the practice of my invention instead .of sodium aluminate or of a substantially nonacid aluminum compound whose precipitzv' tion is inhibited by the action of a precipitation inhibitor, I may employ as equivalents with a measure of success similar compounds of other metals suchas tin, zinc,- and the like,

but from the experiments so far conducted I find that the aluminum compounds are the I silch as a mineral or other acids, particularly metallic salts such as compounds of aluminum, zinc, tin, or the like.

The term paper mix as used herein is intended to mean a mix of various constituents including fibre from which paper may be made, either alone or after the addition of other ingredients.

By the term alkaline filler I mean substantially water insoluble filler which when ag tated in contact with freshly boiled distilled wate say for an hour, will impart a pH value to suchwater greater than 7.0, that is. which will be on the alkaline side of the neutral point. Among fillers included in this group may be mentioned calcium carbonate, of which lime mud from the causticiz salts, or physically associated mixtures of these with one or more other acid soluble materials of a substantially Water'insoluble nature. V Where I speak of sizing, paper, or the like, as containing alumina, do not mean to restrict myself to the presence of any definite compound of aluminum therein, but rather I use the term in its ordinarily accepted meaning to indicate that acompound of aluminum is present, the aluminum content of which may be determined by analytical procedure as alumina (A1 0 When I use the word paper herein, I use it iln the broad sense to include products of manufacture of all types and of all weights and thicknesses, which contain as an essential constituent a considerable amount of pre pared fibre and which are capable of being produced on a Fourdrinier, forming, felting, chine.

Bythe term wet end of the paper macylinder, or other chine, ll intend to include those instrumentalities employed in paper manufacture by which and/or in which a relatively concens trated paper mix is diluted, and treated, conveyed or fed up to the point of web-forma-V tion, such as the mixing box, and proportioning devices, rifiers, troughs, screens, head boxes, inlets and the like, including also instrumentalities used in the white water cycle.

It is to be understood that my invention is not dependent upon or limited by any theory expressed herein; and as no one theory of the mechanism of sizing has as yet found gen- 7 ing that the alumina is integral the proportions of ingredients, and the arrangement of steps may he widely varied mix,

. acid aluminum compound.

witlmut departing from. the s irit of my in vent-ion or the scope or the su joined claims,

it claim: 1 1; lln a method of manufacturing paper filled with alkaline filler wherein material is added to a'paper mix under conditions tavoring the minimizing of the timeand/or intimacy or contact of the constituents of the the step of adding to said mix a non- 2. ln a. method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the min mizing of the'time and/or intimacy of contact of the constituents-oi; the

mix, the step of adding to said mix a nonacid aluminum compound in soluble condition, I

3. in a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions iavoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the step of adding to said mix a soluble non-acid aluminum compound precipitahle hy acidic material.

l. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions tutoring the minimizing oi the time and/or intimacy of contact of the constituents of the mix, the steps of adding to said mix a solulole non-acid aluminum compound precipitable by acidic material, and acidic material.

5. in a methodor manufacturing "papcr filled with alkaline filler whei'ein material is added to a paper mix underconditions favorregulating I filled with alkaline filler wherein material 'ing the ing the minimizing of the time and/or iiitimacy of contact of the constituents of the mix, the ste of adding to said mix a soluble non-aci aluminum compound precipitable by metallic salt, and a metallic salt,

6. In a method vof manufacturing paper filled with alkaline filler wherein material is added to a paper. mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the steps of adding to said mix a soluhle non-acid aluminum compound precipitable by alum, and alum.

7. lln a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituentsof the mix, the step of adding to said mix a, nonecid aluminum compound soluhle due to the presence of a prec'ip'itation inhibitor.

8. In a method of manufacturing paper filled with alkaline filler wherein material is 1 added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the step of adding to said mix a non acid aluminum compound soluble due to the pres ence of n precipitation inhibitor, said inhihitor comprising a citrate'radicle,

9. in a method of manufacturing is added to a paper mix under conditions favorminimizing of the time and/or intit macy of mix, the steps oil adding to said mix a nontacid aluminum compound soluhle due to the presence ofa precipitation inhibitor, acidic material, I

10; Ina method of manufacturing paper tilled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy oi contactoi the constituents of the mix, the step of adding to said mix sodium aluminate.

llflilln a method ofmanufacturing filled with alkaline filler wherein material is. added to a paper mix under conditions iavoring the minimizing otthe time and/or intimacy of contact of the constituents oi'the contact of the constituents of the ltd mix, the steps oi adding to said mix sodium aluminate and'acidic material.

12, in a method of manufacturing tilled with alkaline filler wherein material is added to a paper mix under conditions ra on ing the minimizing of the time and/or in timacy oipontact oi. the constituents of the mix, the steps of adding to said mix sodium aluminate and alum.

13. in a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy paper 5 of 'contact of the constituents of the p mix, the step of precipitating size in the presence ofa non-acid compound of aluminum. I

14. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under .conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix,.the step of precipitating size in the presence of a non-acidcompound of aluminum in soluble condition.

15. In a method of manufacturing paper filled with alkaline filler wherein material is 1 added to a-paper mix under conditions favortimacy of contact of the constituents of the mix, the step of precipitating size inthe presence of a non-acid compound of aluminum soluble due to th presence of a precipitation inhibitor.

v16. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the step of precipitating size in the presence of a non-acid compound of aluminum soluble due to the cipitation inhibitor, said ing a citrate radicle. i

17. In a method of manufacturing paper filled with alkaline filler wherein material is added .to a paper mix under conditions favoring the minimizing of the time and/or inhibitor comprisintimacy of contact of the constituents of the mix, the step of precipitating size witha'cidic material in the presence of a non-acid compound of aluminum in soluble condition. 18. In a method of manufacturing paper 40 filled with alkaline filler wherein material is added to a paper mix under conditions avoring the minimizing of the time and/or Intimacy ofcontact of the constituents of the mix, the step of precipitating size with metallic salt in the presence of a non-acid compound of aluminum in soluble condition.

19. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or Intimacy of contact of the constituents of the mix, the in the presence of a non-acid compound of aluminum in soluble condition. a

20. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of'the mix, the step of precipitating size in the 1 presence of sodium aluminate.

21. Ina method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favormg the minimizing of the time and/or ining-the minimizing of the time and/or in-,

presence of a prestep of precipitating size with alum timacy of contact of the constituents of the mix, the step of precipitating size with acidic material in the presence of. sodium aluminate.

22. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper under conditions favoring the minimizing ofthe time and/or intimacy of contact of the constituents of the mix, the step of precipitating size with alum in the presence of sodium aluminate.

23. In a method of manufacturing paper filled with alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the step of precipitating rosin size in the presence'of a non-acid compound of alum.

24. In a method of manufacturing paper filled with alkaline filler wherein material is addedto a papenmix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents of the mix, the step of precipitating rosin size in the presence of a non-acid compound of aluminum in soluble condition.

25. In'a method of manufacturing paper filledwith alkaline filler wherein material is added to a paper mix under conditions favoring the minimizing of the time and/or intimacy of contact of the constituents ofthe mix, the step of precipitating rosin, size in the presence of mdium aluminate.

26. In the manufacture of paper filled with alkaline filler the step comprising the addition to the paper mix of an inorganic alkali metal salt with a pI-Ivalue greater than 7 .0, which is precipitable by material which depresses its hydroxyl ion concentration,under conditions favoring the minimizing of the time of contact of the constituents of the mix.

27. In the manufacture of paper filled with alkaline filler the step comprising the addition to the paper mix of an inorganic alkali metal salt with a pH value greater than 7.0, Which is precipitable by material which depresses its hydroxyl ion concentration, under conditions favoring the minimizing of the time and intimacy of contactof the constituents of the mix. I

28. In the manufacture of paper filled with alkaline filler the step comprising the addition to the paper mix at the wet end of the paper machine of an inorganic alkali metal salt with a pH- value greater than 7.0, which is precipitable by material which depresses its hydroxyl ion concentration.

29. In the manufacture of paperfilled with alkaline filler the step comprising the addi- 30. In the manufacture of paper filled with alkaline filler the step comprising the addition to the paper mix of an inorganic alkali metal its hydroxyl ion concentration, and a precip-' itant therefor.

32. In the manufacture of paper filled 41. Filled paper comprising fibrous material, alkaline filler comprising calcium carbonate, and alumina derived from sodium aluminate. 1

42. Filled paper comprising fibrous material, alkaline filler comprising calcium carbonate, and sizing containing alumina derived at least in part from substantially soluble non-acid compound of aluminum.

43. Filled paper comprising fibrous material, alkaline filler comprising calcium carbonate, and sizing containing alumina derived at least in part from sodium aluminate. In testimony whereof I aflix my signature.

' HAROLD ROBERT RAFTON.

with alkaline filler, the step which comprises providing in the fibrous mix a size precipitate containing alumina derived at least in part I from a substantially soluble non-acid compound of aluminum. Y

33. In the manufacture of paper filled with alkaline filler comprising calcium carbonate, the step which comprises providing in the fibrous mix a size precipitate containing alumina derived at least in part from sodium aluminate. I

34. In the'manufacture of paper filled with alkaline filler, the step comprising the addi tion to the fibrous mix of substantially soluble non-acid. aluminum compound.

35. In the manufacture of paper filled with alkaline filler comprising calcium carbonate,

the improvement comprising the addition to v the fibrous mix of size and substantially soluble nonacid aluminum compound.

36. Inithe manufacture of paper filled with alkaline filler comprising calcium carbonate, the step comprising the addition to the fibrous mix of sodium aluminate.

,37. In the manufacture of paper filled with. alkaline filler the step comprising the addition to the fibrous mix of an inorganic alkali metal salt with a pH value greater than 7.0

which is precipitableby' depression of its hydroxyl ion concentration.

38. In the manufacture of paper filled with alkaline filler comprising calcium carbonate,

the improvement comprising the addition to the fibrous mix of size and an inorganic alkali I metal salt with a pH value greater'than 7.0 which is precipitable by depression of its hydroxyl ion concentration.

39. Filled paper comprlsing fibrous material, alkaline filler, and alumina derived from substantially soluble non-acid compound of aluminum.

40. Filled paper comprising fibrous material, alkaline filler comprising calcium car- .bonate, and alumina derived from substantially soluble non acid compound of aluminum.