US1793194A - Fiber product and process of producing same - Google Patents

Description

Patented Feb. 17, 1931 UNITED STATES PATENT OFFICE GEORGE A. RICHTER, F BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE FIBER PRODUCT AND PROCESS OF PRODUCING SAME v No Drawing.

In the papermaking industry, wood pulp Application filed October 25, 1926. Serial No. 144,180.

a drier sheetconsisting of such a blend, for

prepared at the pulp mill is frequently I have'discovered that such a sheet is apformed into heavy sheets which are baled and sold to paper mills in a form known to the trade as drier sheet. Drier sheet contains a considerably lower percentage of water than wet pressed pulp which is marketed by some pulp mills. Shipmentin the form of drier sheet is'more economical in certain instances, as it minimizes freight charges,

At the paper mill the pulp is hydrated by beating prior to its formation into paper. There are certain pulps, however, which are more diflicult to hydrate than others. For

example, kraftpulp and high alpha cellulose 'pulp are much more difiicult to hydrate than sulphite pulp. The form in which the pulp is purchased also determines in -some measure its hydrating qualities. Thus, a drier sheet is generally more difiicult to hydrate than T wet pressed fiber.

Because of the varying hydratabilities of various pulps certain paper mills which may have suflicient beating capacity for satisfactorily handling an easily hydratable pulp,

such as sulphite, may have insuflicient capacity for satisfactorily handling another pulp, such as kraft or alpha pulp without greatly cutting down the production capacity of the mill. Consequently, certain of such paper mills when employing kraft pulp or alpha pulp, for example, do not hydrate such pulps sufliciently to obtain a paper of maximum strength, whereas other such mills do not purchase and handle such pulps.

The primary object of this invention is to make available for satisfactory use diflicultly hydratable pulps, such as kraft or alpha pulp, to papermakers unequipped with sufiicient b-eating capacity to handle such pulps.

Another object is to make such pulp satisfactorily available in the form of drier sheet. A further object is to increase the beating capacity of paper mills which are equipped with sufficient beating capacity to handle such ul s.

P B i'iefly stated, these objects may be realized by producing at the pulp mill ready for marketing to papermakers, a blend of unbeaten and beaten fiber and more particularly proximately as readily hydratable by beating as an easily hydratable pulp, such as sulphite pulp.

'It is highly desirable to manufacture and market such a blend of beaten and unbeaten fiber when a high alpha cellulose fiber suitable for use as a cotton rag substitute for the manufacture of high grade Writing papers is being produced at a pulp mill. Such alpha fiber may be produced by digesting unbleached pulp, and more particularly sulphite pulp, under the proper time, temperatureand pressure conditions in an alkaline solution of prescribed concentration, and then bleaching the resulting fiber. The alkaline solution is efl'ectiv'e in selectively dissolving and removing non-alpha cellulose constituent from the pulp, yielding a fiber especially high in alpha cellulose content and which, for convenience of designation, will hereinafter be termed alpha fiber. Such alpha fiber approximates to a remarkable degree the characteristics of rag fiber, and may be used 'as a rag fiber substitute in the manufacture of high grade writing papers. It possesses the great advantage that it may be produced at a' unit cost considerably below that of cotton or rag fiber.

The rag-like characteristics of alpha fiber assert themselves when it is desired to hydrate such fiber by beating. Thus, whereas sulphite fiber is readily hydrated by beating, it is much more difiicult to hydrate alphafiber which is comparable in this respect to high grade new rags. To produce a paper of optimum strength, it is of course necessary to beat alpha fiber until adequate hydration to cement the fibers together for formation into paper has taken place. Insufiicient hydration results in the production of a bulky, low strength, wild paper. Certain paper mills, however, purchase cheap or used rags, such as the so-called thirds and blues, for papermaking. Such cheap rags are materially more receptive to hydration than alpha fiber, so that such mills frequently experience considerable difficulty when alpha fiber is purchased and employed as a substitute for rags, as their beating capacity or available power may be insuflicient to permit beating beyond that employed for hydrating their usual cheap rag stock.

In actual practice, it has been found that the higher the potential strength, tear resistance and folding endurance of alpha fiber,

the lower is its initial slowness, and the less readily does it hydrate. While it is possible to produce alpha fiber which is more receptive to hydration, such procedure results in a pronounced and unfavorable change in characteristics. For example, by underdigesting the raw pulp in an alkaline solution of reduced alkalinity, or by overbleaching the alkaline-digested pulp, an initially slower alpha fiber, which is more receptive to hydration, may be produced. The slower alpha fiber, however, possesses a materially lower tear resistance, as an underdigested alpha fiber is harsher and lower in alpha cellulose content than the usual alpha fiber, and an overbleached alphafiber is also of lower alpha cellulose content, has ahigher copper numher and oxycellulose content, and poorer ageing qualities. Again it is, of course, possible to beat the alpha fiber partially at the pulp mill, and market the partially beaten fiber,'but I have found that such procedure is inexpedient and disadvantageous particularly when the fiber is marketed in the form of drier sheets, for such sheets of partially beaten fiber are diflicultly rehydratable by beating. Moreover, when such fiber is rehydrated to the proper extent by beating at the paper mill and formed into paper, such paper does not possess optimum strength and tear resistance, for by such processing the fiber is reduced'in length not only by the initial partial beating at the pulp mill, but also by the extensive beating necessary at the paper mill. The difliculty of rehydrating the fiber is perhaps due to the fact that the hardened hydrated cellulose cements the fibers together and stifi'ens the drier sheets to a dense board-like condition so that the beater must perform the function of disintegrating the dense sheet into its constituent fibers in addition to causing a hydration of such individual fibers to the proper extent.

In accordance with this invention, an alpha fiber of optimum quality is produced which may be satisfactorily and economically employed by paper mills as a substitute for cheap rags without necessitating a beating of the pulp beyond that required for such rags. This is accomplished by homogeneously blending into the usual unbeaten alpha fiber a small proportion of such beaten fiber. For example if 10% to 20% of thoroughly beaten fiber stock be homogeneously blended or mixed with 90% to of unbeaten fiber stock, the productmay be formed into a soft, absorptive drier sheet, which may thereafter be easily distintegrated and hydrated for paper formation. The blend is materially more receptive to hydration by beating than unbeaten fiber, being comparable in this respect to an easily hydratable pulp, such as sulphite, and results in a paper of optimum strength and tear resistance. Thus experiments in dicate that, whereas the unbeaten fiber acquires a slowness of about eight minutes in a given period of time, a drier sheet blend consisting of about 10% thoroughly beaten fiber homogeneously mixed with about 90% unbeaten fiber, will acquire a slowness of about fourteen minutes when beaten under the same conditions for the same time period. Furthermore, since the preponderance of fiber in this drier sheet is in unbeaten condition and possesses its original fiber length, on heating the blend for the necessary period of time, which approximates that of an easily hydratable pulp, paperof maximum strength and tear resistance may be produced therefrom.

It is a simple and practical procedure to beat thoroughly 2. portion of the fiber production at the pulp mill, and to blend the beaten fiber in desired proportion with the unbeaten fiber. The extent to which a relatively small portion of the fiber is beaten may be varied as desired, a well-beaten fiber homogeneously blended in proportion of about 10% to 20% with the unbeaten fiber being found very satisfactory for general requirements, although in certain instances it may be preferable to over-beat the fiber to a slimy consistency and to blend such fiber in smaller proportion, say 5% to 10%, with unbeaten fiber. An alpha fiber blend of beaten and unbeaten fiber produced in accordance with this invention permits paper mills employing low grade rags to substitute advantageously such fiber for such rags, without requiring an increased beating capacity. This means that paper mills which are now unable to hydrate satisfactorily a suflicient quantity of alpha fiber to maintain paper making machine operation at an economical rate, may be supplied with a fiber blend, such as herein described, and thus operate economically and satisfactorily. Furthermore, paper mills equipped with sufficient beating capacity may have their beating capacity increased from about 25% to 35%.

This invention, while especially applicable to the production of an alpha fiber blend in sheet form suitable for use as a rag substitute, may be extended to the production of fiber blends of beaten and unbeaten kraft fiber, or fiber of various other origins. Thus a blend of unbeaten and beaten kraft fiber may be satisfactorily employed in a paper mill which is unequipped to handle the usual kraft pulp.

I claim:

1. As an article of manufacture, cellulose fiber consisting of unbeaten chemical wood pulp homogeneously blended with like beaten or hydrated pulp.

2. As an article of manufacture for use in the manufacture of paper, a sheet of cellulose fiber consisting of unbeaten chemical wood pulp homogeneously blended with similar beaten or hydrated pulp.

3. As an article of manufacture, a cellulose fiber blend consisting of a preponderance of unbeaten chemical wood pulp and a smaller proportion of similar beaten pulp. I

4. As an article of manufacture, a sheet of cellulose wood pulp consisting of a preponderance of unbeaten chemical pulp, homogeneously blended with a smaller proportion of similar beaten pulp.

5. As an article of manufacture, a sheet of cellulose fiber suitable for use as a cotton rag substitute and consisting of a preponderance of unbeaten high alpha cellulose wood fiber homogeneously blended with asmaller proportion of like beaten fiber. v

6. As a new article of manufacture for use in the manufacture of paper, a drier sheet consisting of a predetermined proportion of an unbeaten diflicultly-hydratable cellulose pulp free from encrusting materials, and a predetermined proportion of such pulp but in a hydrated condition, all in a homogeneous mixture, the unbeaten pulp predominating in amount. I

7. As a new article of manufacture for use in the production of paper, a drier sheet of cellulose pulp, such sheet comprising in predetermined proportions an unbeaten difficultly-hydratable pulp free from encrusting materials, and a hydrated or beaten pulp all in a physically homogeneous blend or'mixture.

8. That step which, comprises homogene- 10. A process which comprises homogeneously blending a subordinate proportion of beaten chemical wood pulp together with a preponderant proportion of similar unbeaten pulp, and sheeting the blend.

'11. A process which comprises homogeneously blending a subordinate proportion of difficultly-hydratable fiber free from, encrusting materials, which has been beaten, together with a preponderant proportion of similar unbeaten fiber, and sheeting the blend.

12. A process which comprises homogeneously blendinga subordinate proportion of a diificultly-hydratable fiber free from encrusting materials with a preponderant proportion of similar unbeaten fiber, and forming the blend into drier sheet.

13. As a new article of manufacture for use in the production of paper, a drier sheet of cellulose pulp free from encrusting materials, such sheet comprising unbeaten, difficultly hydratable cellulose fiber and a relatively small proportion of similar fiber beaten or hydrated to a slimy consistency.

14. A process which comprises blending a subordinate proportion of difiicultly hydratable fiber which has been beaten, together with a preponderant proportion of similar unbeaten fiber, forming the fiber blend into a sheet, disintegrating the sheet, beating the fiber, and running it off on a paper machine.

15. As an article of manufacture, a blend or mixture of a preponderant proportion of previously-liberated wood pulp in unbeaten condition and a subordinate proportion of previouslydiberated wood pulp beaten or hydrated to a slimy consistency.

16. As an article of manufacture, a blend or mixture of a preponderant proportion of chemical wood pulp in unbeaten condition and a subordinate proportion of chemical wood pulp beaten or hydrated to a slimy consistency.

17 As an article of manufacture, a blend or mixture of a preponderant proportion of wood pulp of high alpha cellulose content in unbeaten condition and a subordinate proportion of wood pulp of high alpha cellulose content beaten or hydrated to a slimy consistency.

18. As an article of manufacture, a drier sheet formed of a blend of wood pulp of high alpha cellulose content in unbeaten condition and a relatively small proportion of pulp of high alpha cellulose content beaten or hydrated to a slimy consistency.

In testimony whereof I have aflixed my signature.

GEORGE A. RICHTER.