SE439509B - SET TO MAKE GREASE PREPARATION RESPECTIVE GREASE PAPER - Google Patents

Description

8095737-4 2 high yield sulfate pulp which is delignified and which is described in U.S. Patent No. H 093 511 and in TAPPI 59 (11): 77 (1976). This sulphate pulp is prepared with a hemicellulose-preserving cooking liquid, preferably a polysulphide liquor with a polysulphide content of 2 - 12 g per liter and which is prepared according to the Moxy process to obtain a relatively high lignin content corresponding to a kappa number of about 60, as shown of TAPPI 58 (8): 172 (1975). After partial washing, the pulp is further delignified to a kappa number of about 30 with oxygen and alkali at a temperature of about 110 ° C in a suitable reactor. The pulp is further bleached in three steps with chlorine, alkali or sodium hypochlorite and a brightness of 80-85% SCAN. If the bleaching of the sulphate pulp in the hypochlorite step is carried out so that the pH value of the pulp at the end of this treatment step is 7.0-8.5, it has been found that the resulting pulp is particularly easy to grind so that it acquires greaseproof properties. The pH at the end of the hypochlorite bleaching should preferably be in the range 7.0-8.0 and most preferably 7.0-7.5. These are unusually low values. On the other hand, it is preferable to grind the pulp in an alkaline environment, ie at a pH value of at least 7.0 and possibly as high as 10.0.

Testing of this pulp in the laboratory showed that it was significantly better suited for the production of greaseproof paper than ordinary sulphate pulp marketed for this purpose.

In comparison with greaseproof paper from sulphite pulp, the high-yield sulphate pulp gave a cleaner product with satisfactory greaseproof properties. The paper also had better wet strength properties than the sulphite pulp and thus resulted in fewer breaks in the paper machine and thus higher paper production. The need for grinding energy was approximately the same as for sulphite pulp, ie significantly lower than for the sulphate pulp hitherto marketed for greaseproof purposes. The strength properties of the finished product were also significantly better than usual, as sulphite pulp forms the starting material. The better strength was shown in the form of better convertibility of the paper produced during the test period. Convertibility is the feature that is becoming less and less 8006737-4 less important with the current demands of advanced printing and fast packing machines.

The content of odors and flavors as well as resin in the sulphate pulp used is at such a low level in relation to the sulphite pulp that no problems arise at all. The sulphite pulp, which is made from pine wood, on the other hand, can give taste and odor of an undesirable kind as well as acute resin problems, but also sulphite pulp from spruce can cause problems in this respect.

Further features of the invention appear from the following description and from the claims. The invention is illustrated by the following examples.

Example 1 A high yield sulphate pulp was prepared in a continuous vapor phase Kamyr boiler starting from a mixture of spruce and pine chips. The production was about 350 tons per day. 19.5% of active alkali calculated as NaOH per tonne of dry wood chips were added.

The white liquor had a content of about 6-8 grams of polysulfite sulfur per liter and was produced by the Moxy process. The white liquor sulphidity was about 40% before the oxidation in the Moxy reactor.

For a more detailed description of the Moxy process, reference is made to U.S. Patent No. H 093 511. The temperature in the cooking zone was about 160 ° C at a cooking time of about 2.5 hours.

A partial mass stream of about 70 tonnes per day was taken from the boiler's blow line, which was fed to a reactor via an "in-line" refiner. In the refiner, lye, oxygen and steam were mixed into the pulp. Oxygen and alkali addition corresponding to 35 kg O 2 and 50 kg NaOH per tonne of pulp. The steam demand corresponded to a temperature increase from about 85 ° C to 110 ° C at 10% pulp consistency. The residence time of the pulp in the reactor was about 30 minutes at 5 atmospheres pressure before the pulp was diluted and blown into a tank.

The oxygen / alkali delignification resulted in a reduction in the kappa number of the pulp from cza 60 to cza 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 with a pH of about 7.0 at the end 8006737-4 of the hypochlorite step) to a brightness of 83% SCAN. The pulp obtained in this way was compared with a conventional sulphate pulp for the production of greaseproof. The results of the comparison are shown in Table 1.

It can be seen from Table 1 that the oxygen / alkali delignified high yield sulphate pulp was much easier to grind to a high degree of grinding and greaseproof properties than the conventional sulphate pulp sold to various producers of greaseproof paper. The conventional sulphate pulp is so heavily ground that the paper requires the addition of expensive chemicals, such as carboxymetallic cellulose, in order to obtain satisfactory greaseproof properties.

Table l Pulp according to example l Conventional sulphate pulp (bleached) Grinding time 7000 9000 10500 10500 l3500 15000 rpm PPI grinder SR number 77 82 85 50 7U 77 Dewatering fi 71+ 118 2141! l7 37 47 Wear index 120.5 l2U .5 121.5 I 123.5 122.5 125.5 Nm / g Air permea- lU .6 4.6 0.94 206 U5, U 37.9 bility, nm / Pa Blistering Hint. Hint. Strong None None None Example 2 From the blast line of a continuous Kamyr boiler, in which high-yield sulphate pulp was produced in the manner described in Fig. 1, a partial stream of about 50 tons per day was extracted from the pulp. A total of about H00 tons of such pulp was bleached in the oxygen reactor under the same conditions as described in Example 1 8006757-4 and then pressed in a screw press to a dry content of about 27%. The mass into the reactor had an average kappa number of 51.1, while the kappa number at the outlet of the reactor was 30.7. The pulp was then transported to a sulfite factory. Here, the cellulose production was stopped and both the bleaching plant and the paper mill were run on the described oxygen-bleached pulp for about 5 days.

In the bleaching plant, the mass was added about 6.5% chlorine in the first step, about 2.5% NaOH in the second step and about 3% active chlorine in the form of sodium hypochlorite in the third step at a temperature of 40-4200. The pH was about 7.0 at the end of the third step. Before grinding, the pulp was buffered with a mixture of sodium dicarbonate and NaOH so that after grinding the pulp still had a pH of at least 7.0.

The factory's normal greaseproof products were produced with good quantitative and qualitative results. As an example of the result obtained, Table 2 shows values for the grease-proof pulp according to the invention and the requirements placed on the grease-proof pulp with a gram weight of 55 and high quality.

Table 2 Requirements for greaseproof pulp Analysis data for grease- with a gram weight of 55 and proof ~ pulp with a gram-high quality weight of 55, prepared according to the invention Opacity, phV 2 60 61 Tappi-tal, s} l800 1800 Air permeability 0 0 Bursting strength 2 26 31 Longitudinal tear strength 2 19 2? Transverse tear strength) 22 25 Bentzen) 300 500 Wet strength,% 2 30 3U Number of stains ¿20 H Area of the stains, mm2 g 1 0.18 8006737-4 The paper described in Example 2 has been examined for odor and taste vid Sentralinstitutt for industriell forskning, Oslo, 'och Verpackungslabor für Lebensmittel und Getränke, Wien. At the Central Institute (SI), the paper was analyzed in a gas chromatograph and compared with a corresponding analysis of ordinary greaseproof paper, made from sulphite pulp.

The analysis shows a significantly smaller area under the chromatographic curve for the product according to the invention, which means that there would be no risk of odor and taste problems. At the laboratory in Vienna, a vegetable parchment and a greaseproof paper were compared, which was produced according to the invention of a taste panel. The result was that after covering a butter surface with both paper qualities, no taste differences could be detected in the butter, whereby both types of paper can be counted as equivalent with regard to the transfer of taste to fat products. Vegetable parchment is the material used today for wrapping paper for butter in most countries.

The paper according to the invention described in this example was also sent to three different customers for conversion on the factory machines. All found the paper very well convertible.

It thus appears that according to the invention it is possible to produce a greaseproof paper of very high quality from sulphate pulp with significantly reduced energy requirements during grinding in comparison with previously used sulphate pulps and without the need to add expensive chemicals.

Claims (6)

8006737-4 fr 'P A T E N * T K R A V 1. Methods of preparing greaseproof pulp and greaseproof paper, respectively, characterized in that an oxygen / alkali delignified high-yield sulphate pulp with chlorine, alkali and hypochlorite is bleached and the bleached pulp is ground. 2. A method according to claim 1, characterized in that the sulphate mass is prepared by digestion with a hemicellulose-preserving cooking liquid, preferably a polysulphide liquor with a polysulphide content of 2-12 grams per liter. 3. A method according to claim 2, characterized in that a polysulphide liquor prepared according to the Moxy process is used. 4. A method according to any one of claims 1-3, characterized in that the sulphate mass is digested to a kappa number of 40-100 and oxygen / alkali lignified to a kappa number of 15-40. 5. A method according to any one of claims 1H, characterized in that the bleaching of the sulphate mass in the hypochlorite step is carried out so that the pH value of the pulp at the end of the step is 7.0 ~ 8.5 and preferably 7.0 -8.0 and most preferably at 7.0-7.5. 6. A method according to any one of claims 1-5, characterized in that the bleached sulphate pulp is ground at a pH value of 7.0-10.0 and preferably 7.5-10.0.