CS235754B1 - A method for treating a base paper for melt impregnation - Google Patents

Abstract

The invention relates to a method for processing carbonized papers, especially for packaging technology, but also for other uses. The purpose of the invention is to reduce the consumption of fusible impregnating agent while maintaining the properties of the product. The stated effect is achieved by processing the paper on a paper machine in an undried state by pressure between two rollers.

Description

The invention relates to a method of processing base paper for impregnation with melts.

So far, paraffin paper has been mainly produced, and paraffin is comparable in price to pulp. Given that paraffin is a petroleum product and pulp is a product that is constantly being renewed, it seems advantageous to reduce the paraffin content in paraffin papers. In addition, paraffin in the interfiber space represents only a ballast substance that does not affect either the barrier or mechanical properties. Refined melts are increasingly used, which are more expensive than paper and whose excessive consumption increases the raw material requirements of the product.

The above-mentioned shortcomings are eliminated by the method of processing the base paper according to the invention. The essence of the invention lies in the method of processing undried paper at a dry matter of 75 to 85% by passing it between metal rollers at a line pressure of 10 ⁴ to 5.10^ N/m. The paper is then dried on drying rollers to a dry matter of over 90%. Processing undried paper by pressure between rollers is more efficient than the usual processing of dried paper on a machine calender. When calendering paper dried to 90% on a machine calender, a bulk density of usually below 1 g/cm^ is achieved, which corresponds to a porosity of 0.35. When impregnating such paper, the consumption of the impregnating agent, which is placed between the fibers, is 35 volume percent. When calendering the same paper at a dry matter of 75 to 85%, a bulk density of around 1.25 g/cm^ is achieved, which corresponds to a porosity of 0.20. When impregnating this paper, a only 20 volume percent of impregnator. Calendering of under-dried paper therefore reduces the consumption of impregnator, which is between the fibers and therefore has low efficiency, by an average of one third.

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23S 754

To treat the paper by pressure between the rolls in an undried state, it is necessary to equip the paper machine with a two-roll stand in the drying section at a point where the paper reaches 75 to 85% dry matter or with a pressure device for the drying roll, which would replace this press stand. The second method is more advantageous in terms of space consumption. The paper is sufficiently smoothed by this treatment and it is not necessary to process it on a machine calender.

By processing the base paper according to the invention application, the paper retains its vapor tightness (impermeability to water vapor) while significantly reducing the amount of paraffin. Processing according to the invention application also improves the tear strength of the paper, which increases the processability of the paper in packaging machines and the resistance of the paper package during handling. Reducing the amount of impregnating agent will not adversely affect any technically useful property of the paper. The processing method according to the invention can be applied in paper mills that produce paper for melt finishing, namely for paraffin impregnation, hot-melt coatings, extrusion with plastic substances, laminating foils with melt and for similar products, Example.

The pulp milled at 35°SR was processed into paper intended for paraffin impregnation. The paper was prepared without calendering, further processed on a mechanical calender and finally processed by pressure at a dry matter of 75 to 85%. The paper was impregnated with paraffin and its water vapor permeability was determined (Table 1).

The pulp milled at 45°SR was processed into paper for waxing. It was pressure-treated in the undried state, another sample was calendered on the machine in the usual manner, and finally an uncalendered sample was prepared. The paper was waxed and the water vapor permeability was determined. The properties are given in Table 2,

Melt-impregnated papers are used for the production of demanding packaging, especially where barrier properties are required, but they are also used in the production of some technical papers.

235,754

Table 1. compares impregnated papers that were waxed without treatment, after conventional machine calendering, and papers treated by compression at a dry matter content of 75 to 85%

Table 1 · . , Papi flat ground to 35 ^U SR sample Volume Weight Content of prop ust» paraffin for H _? 0x/ 0 relative pair strength , breakage unedited 0.730 24% 0.1375 100 alandrated 0.865 23% 0.1328 120 processed in an undried state 1,074 15.5% 0.1168 138. x/ in grams per in 24 hour,· Table 2 compares and ?also papers that have been waxed without treatment, after processing and pressing according to the invention,» three calenders and papers edited at Table 2 Papi plane milled at 45°SR

sample Volume Weight Paraffin content passage for HpO steam xX 0 relative tear strength unedited 0.932 19.6% 0, 1099 100 calendered 1,030 16.75% 0.1090 107 ;work in an undried state 1,230 13.2% 0.1037 . l?l. » x/ in grams per m in 24 hours

SUBJECT OF THE INVENTION

Claims (1)

SUBJECT OF THE INVENTION 235 754 Processing method for impregnating the backing paper melts, wherein nedosušený paper dry matter 75-85% passes between metal rollers while a pressure of 10 ⁴ to 5.1Ο ⁴ N / m.