FI66944B - FOERFARANDE FOER FRAMSTAELLNING AV SMOERPAPPER RESPEKTIVE SMOERPAPPERSMASSA - Google Patents

Description

66944

The present invention relates to a process for the preparation of greaseproof pulp and pulp pulp, respectively, and to a process for the production of greaseproof pulp by grinding bleached sulphate pulp.

Butter paper, a specialty paper used to wrap greasy products, is traditionally made from sulfite-cellulose pulp. In order to achieve the desired quality of the paper, the cellulosic pulp must be ground until it reaches the properties required of the butter pulp. The cellulose pulp must therefore be easy to grind, clean and free of odorous flavors.

As small and medium-sized sulfite pulp mills are being shut down due to contamination problems, attempts have been made to use bleached sulphate cellulose pulp for the manufacture of butter paper. Because ordinary sulfate pulp is difficult to grind, it requires significantly more grinding energy and, in addition, expensive auxiliary chemicals to obtain approximately the same grease retention properties as sulfite pulp.

It is an object of the present invention to provide a process for producing a satisfactory spread paper from sulphate pulp, while at the same time obtaining advantages over both sulphite pulps and sulphate pulps used previously.

The process according to the invention uses a high-yield sulphate pulp from which lignin has been removed with oxygen and alkali, and according to the invention the pulp is bleached with chlorine, alkali and hypochlorite and the bleached pulp is ground. In other words, the invention uses a high-yield lignin-depleted pulp for the production of butter paper after chlorine / alkali / hypochlorite bleaching and milling of the pulp.

The sulphate pulp used as a starting point for the preparation of the pulp pulp according to the invention is the known high-yield desulphurised pulp described in U.S. Patent 4,093,511 and TAPPI 59 (11): 77 (1976). This sulphate pulp is prepared with a hemicellulose-preserving cooking solution, preferably a polysulphide liquor with a polysulphide content of 2-12 g / l and prepared by the Moxy process to a relatively high lignin content corresponding to a kappa number of about 60, cf. TAPPI 58 (8): 172 (1975). After partial washing, the pulp is further stripped of lignin to about 30 ° C with oxygen and alkali at about 110 ° C in a suitable reactor. The pulp is then further bleached in three stages with chlorine, alkali and sodium hypochlorite, respectively, to a brightness of 80-85% SCAN. the mass is 3 66944 particularly easy to grind, so that it acquires ras-retaining properties. The pH at the end of the hypochlorite bleach should preferably be 7.0-8.0 and most preferably 7.0-7.5. These are unusually low values. On the other hand, it is advantageous to grind the pulp in an alkaline environment, i.e. at a pH of at least 7.0 and possibly even 10.0.

An experiment performed on this pulp in the laboratory showed that it is much better suited for the production of tissue paper than ordinary sulphate pulp marketed for this purpose. Compared to tissue paper made from sulfite pulp, high yield sulfate pulp gave a cleaner product with satisfactory grease-retaining properties. In addition, the paper had better wet strength properties than the sulfite pulp, thus causing fewer breaks in the paper machine and thus giving higher paper production. The need for grinding energy was approximately the same as for the sulphite pulp, i.e. substantially lower than for the sulphate pulp currently marketed for kraft paper purposes.

The strength properties of the finished product were also considerably better than is usually the case when using sulphite pulp as a starting material. Good strength was manifested in the better recyclability of the paper produced during the test period. Recyclability is a feature that becomes more important with the time demands of advanced printing and high-speed packaging machines.

The odorants and flavors contained in the sulphate pulp and the resin content are so low compared to the sulphite pulp that no problems arise. On the other hand, sulphite pulp made of pine wood can cause taste and odor problems in the product as well as acute resin problems, but sulphite pulp made of spruce wood can also cause problems in this respect.

Other features of the invention will become apparent from the following description and claims. The invention is further illustrated by means of examples.

Example 1

The high-yield sulfate pulp was continuously prepared in a steam-phase Kamyr digester from a mixture of spruce and pine chips. Production was about 350 tons / day. 19.5% active alkali, calculated as NaOH / tn dry chips, was added. Val-alkali contained about 6-8 kg of polysulfide sulfur / liter and was obtained by the Moxy method. The sulfide content of the white liquor was about 40% before oxidation in the Moxy reactor. The Moxy process is described in more detail in U.S. Patent 4,093,511. The temperature of the cooking zone was about 160 ° C with a cooking time of about.

2.5 hours.

A partial flow of about 70 tn / day was taken out of the blower line of the boiler and fed to the reactor via an "in-line" refiner. Alkali, oxygen and steam were mixed into the mass in the grinder. The addition of oxygen and alkali was 35 kg O2 and 50 kg NaOH / tn, respectively. The steam demand corresponded to an increase in temperature from about 85 ° C to 110 ° C with a pulp consistency of 10%. The residence time of the pulp in the reactor was about 30 min at 5 atmospheric pressure before the pulp was diluted and blown into the tank.

Lignin removal with oxygen and alkali reduced the mass number of the pulp from about 0 to about 30. A sample of this pulp was further bleached in the laboratory in three steps with chlorine, alkali and sodium hypochlorite (6.5% chlorine, 2.5% NaOH and 2.7% hypochlorite + 0.2% NaOH at pH 5,66944 at approximately 7.0 at the end of the hypochlorite step) to a brightness of 85 % SCAN. The pulp thus obtained was compared with the conventional sulphate pulp used in the manufacture of parchment paper. The result of the comparison is shown in Table 1.

It can be seen from Table 1 that high yield sulphate pulp from which lignin had been removed with oxygen and alkali was much easier to grind to a high degree of grinding and good grease-retaining properties than conventional sulphate pulp sold to various manufacturers of tissue paper. Conventional sulfate pulp is so difficult to grind that the paper requires the addition of expensive chemicals, such as carboxymethylcellulose, to have satisfactory grease-retaining properties.

table 1

Eg pulp according to 1 Conventional sulphate-^ pulp -__ pulp (bleached) _ time rev. 7000 9000 10500 10500 13500 15000 PFI refiner SR number 77 82 86 60 74 77

Favored 74 118 244 1? 4? sus 120.5 124.5 121.5 123.5 122.5 125.5 14.6 4.6 0.94 206 45.4 37.9

Cellular ..... ... .... , no no no .. . traces traces powerful. . . . . . . . .

distus J not at all at all

Example 2

A partial flow of pulp of about 50 tn / day was taken from the blow line in a conventional Kamyr boiler, in which an oral yield sulphate pulp was prepared as described in Example 1. A total of about 400 tn of such pulp was bleached in an oxygen reactor under the same conditions as described in Example 1 6 66944 and then pressed in a screw press n.

To 27% of dry matter. The kappa number of the pulp entering the reactor averaged 51.1, while the kappa number at the reactor outlet was 30.7. The pulp was then transported to a sulfite plant. Here, the production of cellulose was stopped, and both the bleach mill and the paper mill used oxygen-bleached pulp for about 5 days.

In the bleaching plant, about 6.5% chlorine was added to the pulp in the first stage, about 2.5% NaOH in the second stage and approx.

3% active chlorine as sodium hypochlorite in the third step at 40-42 ° C. The pH was about 7.0 at the end of the third stage.

For grinding, the pulp was buffered with a mixture of sodium dicarbonate and NaOH so that the pH of the pulp after grinding was still at least 7.0.

The mill's standard kraft paper products were manufactured with very good quantitative and qualitative results. As an example of the achievements, Table 2 shows the results of a pulp according to the invention together with the requirements for a high-quality pulp having a gram weight of 55.

Table 2

Analytical data on the pulp (granular weight requirements_55) set for pulp (gram-made butter paper 55) according to the invention

Opacity, phV ^ 60 61

Pin number, s ^ 1800 1800

Air permeability 0 0

Puncture resistance ^ 26 31

Longitudinal tear strength ^ 19 22

Transverse tear strength> 22 25

Benzene ^ 300 500 Wet strength,% ^ 30 34

Number of commas <^ 20 4 2

Area of commas, mm ^ 1 0.18 66944

The paper described in Example 2 was examined for odor and taste at the Sentralinstitutt for industriell forskning, Oslo, and the laboratory Verpackungslabor fiir Lebensmittel und Getränke, Vienna. In SI, the paper was analyzed by gas chromatography and compared with the corresponding analysis of ordinary butter paper made from sulfite pulp. The analyzes show a significantly smaller surface area under the chromatography curve for the product of the invention, which means that no odor and taste problems are to be expected. In said laboratory in Vienna, plant parchment and greaseproof paper according to the invention were prepared, which were compared by the macurate. The end result was that when the butter surface was covered with two grades of paper, no differences in taste were observed in the butter, so that both papers could be considered equivalent in terms of imparting flavor to fat products. Vegetable parchment is a substance that is currently used as packaging paper for butter in most countries.

The paper of the invention described in this example was also sent to three different customers for processing on mill machines. Everyone considered the paper very recyclable.

It is thus found that according to the invention it is possible to produce very good quality butter paper from sulphate pulp with grinding requiring considerably less energy compared to previously used sulphate pulps and without the addition of expensive chemicals.

Claims (5)

66944 A process for producing pulp and pulp, respectively, using high-yield lignin from which oxygen and alkali have been removed, characterized in that the pulp is bleached with chlorine, alkali and hypochlorite and the bleached pulp is ground. Process according to Claim 1, characterized in that the sulphate pulp is prepared by boiling it in a cooking solution which preserves hemicellulose, preferably with a polysulphide solution with a polysulphide content of 2 to 12 g / l. Process according to Claim 2, characterized in that a polysulphide liquor prepared by the Moxy process is used. Process according to one of Claims 1 to 3, in which the lignin is removed with oxygen and alkali, characterized in that the sulphate mass is boiled to a kappa number of 40 to 100 and, after removal of the lignin, the number of pieces is 15 to 40. Process according to one of Claims 1 to 4, characterized in that the bleaching of the sulphate pulp in the hypochlorite stage is carried out in such a way that the pH of the pulp at the end of this stage is 7.0 to 8.5, preferably 7.0 to 8.0 and preferably 7 , 0 to 7.5. Process according to one of Claims 1 to 5, in which the bleached sulphate pulp is ground, characterized in that the pH is from 7.0 to 10.0, preferably from 7.5 to 10.0.