US2161763A - Process of making paper pulp - Google Patents

Description

Patented June 6, 1939 UNITED. STATES PATENT OFFICE Champagne Paper Corporation, New N. Y., a corporation of New York York,

No Drawing. Application October 6, 1937, Serial No. 167,582

1 Claim.

The present invention relates to the production of high grade paper stock from straw of the nature of flax and hemp.

A feature of the present invention is an im- 5 proved method of treating straw of the nature of flax straw in such a manner as to facilitate the removal of ligneous and incrusting constituents thereof, and thereby facilitate the subsequent bleaching of the resulting paper stock.

The invention is applicable in processing straw of the nature of flax straw and particularly flax which is raised primarily for the seed rather than for the fiber. Such flax straw is diificult to process in that the seed flax straw is allowed to mature in the fields and this fact renders the same more difilcult to process than tow produced from fiber flax straw which does not fully mature before harvesting. Paper stock produced from seed flax straw is particularly difiicult to bleach.

According to the present invention the flax straw or other straw of the nature of flax straw is de-seeded and preferably broken advantageously by the employment of a conventional type of flax brake which is employed for de-seeding and breaking the straw in one operation with a resultant minimum loss of fiber.

The crude fiber or tow resulting from the breaking operation is then subjected to a predigestion operation in the presence of water at a steam pressure ranging from 60 to 80 pounds per square inch-and preferably approximately 75 pounds per square inch for a period of time of approximately 25 to 40 minutes. This treatment has been found to be efficacious in removing certain substances agent, primarily for the treatment of the ligneous and incrusting constituents present therein. This 45 step is carried out eifectively by an aqueous solution of, or yielding sodium hydroxide and sulphur,

at suitable temperatures and preferably in a pressure cooker or digester.

Excellent results have been obtained by an 50 aqueous solution of sodium hydroxide and sulphur, and in my present invention I effect a marked saving in the amount of chemicals used over that heretofore employed. l

The predigested tow resulting from the diges tion of the tow in the presence of water at a steam pressure of from 60 pounds to 80 pounds per which cement or bind theflber to the woody porsquare inch, for from 25 to 40 minutes may be subjected to a digestion operation with a mixture of sodium hydroxide and sulphur in the presence of water with a substantial saving of chemicals. While not definitely established, this saving of 5 chemicals is probably the result of two factors:

(a) The predigestion operation is undoubtedly instrumental in causing the removal of more substances than is caused by mere immersion of tow in water at or near room temperature.

(b) The predigested tow does not absorb or retain so much water as does tow which is simply immersed in water at or near room temperature. As a result it has been found practical to cook the predigested material with less water than is usu- 15 ally used in the case of water immersed tow. This means that less chemical is required because the concentration of the chemicals as determined by the amount of water and chemicals present is one of the determining factors in the cooking 20 operation.

, While the predigestion operation has associated with it certain disadvantages, as for example, additional steam is used in the predigestion operation and in commercial practice some time is 25 required to heat the digester and contents to the pressure required, and to allow the digester and contents to cool, yet it is estimated that the saving in chemicals effected by the predigestion operation more than offsets the disadvantages set out above, and in addition the resulting product is measurably superior to any which has heretofore been produced by known methods.

While relatively specific proportions, with regard to pressures and time employed have been set out in this specification, yet it is to be understood such proportions may be varied within-relatively wide limits without departing from the spirit of the invention.

I claim: v

That improved method of producingbleached pulp from flax or hemp tow, which consists in jecting the tow to a predigestion operation in t e presence of water at a steam pressure of from 60. to 80 pounds per square inch for from 2 5 to 40 minutes, then washing the tow, then subjecting the tow to a cooking operation in a digester with a solution of water of approximately 2 to 4 times the dry weight of the fiber, and 10 percent to 20 percentsodium hydroxide, and one-half'to four percent sulphur, the quantities of the chemicals employed in the solution belngbased on the dry weight of the tow, then washing the cooked fiber to remove water solubieimpurities, and'bleaching