FI56871C - PAPPER MED LAOG VIKT OCH GOD STYVHET - Google Patents

Description

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Patent-och registerstyrelsen Aniökan utlagd och utl.skrlft «n publlcerad 31.12.79 (32) (33) (31) Pyydetty etuoikeus— Begird prlorltet 18.03.71

Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 2113216.1-1 »5 (71) Feldmuhle Aktiengesellschaft, Fritz-Vomfelde-Platz 1+, Diisseldorf-Ober-Kassel, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Volker Franzen, Diisseldorf-Golzheim,

This invention relates to paper having good rigidity and low weight. The present invention relates to paper with good rigidity and low weight. weight paper used in office and duplicating machines.

Office technology has developed enormously over the last ten years, which has led to ever-increasing work speeds, especially with regard to copying methods and documentation and electronic data processing. Thus, there is a xerographic method known to everyone in everyday life that has completely supplanted previous conventional copying methods based on photographic methods.

The increasing working speeds of equipment used for these purposes, such as freezing machines and reading devices, place significant demands on the properties of the papers used in these devices. As a result, a particular disadvantage so far has been that the papers used must have a relatively high weight. Unobstructed passage of the paper through the device is achieved only when the paper is sufficiently rigid. On the other hand, these papers must be well foldable and have a certain resilience and sufficient opacity. As a result, it has not previously been possible to reduce the basis weight of such paper, and the basis weight of the paper recommended by the manufacturers of the devices 2 2 56871 is also in the order of 90 g / m 2.

This has the considerable drawback that the thickness and weight of such copies are often greater than those of the original. The ever-increasing volume of paper and the associated problems of office space, required storage space and postage costs have created a significant need to develop paper that has good rigidity and low weight, but nevertheless meets all requirements and passes freely through commercially available equipment. For this purpose, the usual post-processing options available to the paper manufacturer, such as impregnation or coating of the paper, are not suitable at all. Impregnating the raw paper makes the paper rigid throughout so that the paper no longer has the necessary foldability and flexibility. Different coating methods, which could eliminate this drawback because they can improve the surface in different ways, do not achieve the desired effect due to the fact that the weight of the coating cancels out what is saved in the weight of the raw paper.

According to the invention, this considerable problem is solved by a paper with good rigidity and low weight used in office and duplicating devices, which is provided on both sides with a tough-elastic outer layer. and a spacious inner layer according to the claims.

The viscoelastic outer layers give such paper the necessary rigidity and the paper is easily foldable, yet sufficiently flexible and opaque due to its spacious (fluffy) inner layer. By using such a structural principle, it is possible to reduce the weight of such papers used in office and duplicating equipment by 35-70 g. The most suitable basis weight depends on the particular application and device, but is in any case considerably lower than the basis weight of the papers commonly used for this purpose to date. The tough-elastic property of the outer layers is therefore necessary because the paper, despite their necessary rigidity, must have a standard refractive index and the outer layers must not break even if the papers are folded repeatedly.

The technical problem underlying the invention can be particularly advantageously solved with a low-weight paper whose tough-elastic outer layers are formed from the reaction products of hydroxyl- and / or amino-containing high polymers and their crosslinkable compounds having a molecular weight of more than 2,000, in particular 30,000 to 90,000. The preferred molecular weight range is slightly dependent on the basis weight of the base paper. The lower the basis weight, the higher the molecular weight of the high polymer should be too deep to prevent penetration or even saturation. Therefore, according to a preferred embodiment of the invention, the tough elastic outer layer further contains a thickener such as , which does not take part in the crosslinking reaction but allows the viscosity to be adjusted as well as possible and which prevents the polymer from penetrating the base paper <The impregnation of the paper can advantageously be made more difficult by using glued base paper and thus maintaining the paper ply principle #

Suitable hydroxyl and / or amino group-containing high polymers are, in particular, polyvinyl alcohols, in particular highly hydrolysed "types, starches and starch derivatives, such as ethoxylated starches and the olefins of acrylics and methacrylic acid. , propylene, vinyl acetate and vinyl chloride.

The high polymers suitably contain, as an additive, a further 10 to 60% by weight of protein compounds, such as casein and soy protein, based on the weight of the large polymer. These properties further increase the rigidity. However, the proportion of protein compounds should not exceed 60% by weight, as the outer layers will otherwise become too brittle and will no longer be sufficiently elastic-elastic and thus repeatedly foldable,

Aldehydes, aldehyde-cleaving compounds or precondensates formed with aldehydes, such as form- and acetaldehyde-formaldehyde, glyoxal and hexamethylene-tetramine, which are known for their crosslinking action on hydroxyl- and / or amino-containing high polymers, can be used as crosslinking compounds.

Particularly suitable are low weight papers in which the crosslinking of high polymers is achieved by allowing these aldehyde compounds to act together with cyanamide. The use of cyanamide has the significant advantage that cyanamide has the additional effect of forming bridges between the base paper and the outer layer. This additional attachment of the outer layer and its simultaneous anchoring to the base paper is of considerable importance, especially in the case of duplicating papers, which will be discussed later,

The crosslinking reaction is suitably accelerated by the addition of catalysts such as NaCl, NH 4 Cl, HCl or Levis acids.

4,56871

As already mentioned above, in the production of the low-weight papers according to the invention, it is important that the components forming the tough-elastic outer layers do not completely saturate the base paper. Measures to prevent this have already been mentioned above, such as the use of high molecular weight high polymers, the use of thickeners and the use of glued base paper. On the other hand, it is of course necessary that the paper can be coated with outer layers using conventional techniques in the paper industry and, where possible, conventional equipment, i.e. coating equipment, where it is particularly important that the coating be as thin and smooth as possible. Therefore, the preparation is expediently carried out by contacting the components of the viscoelastic outer layers, in particular the high hydroxyl group-containing polymers and the crosslinking agents, only immediately before they are applied to a paper which can prevent the crosslinking reaction from starting too early and the fact that the components are applied successively to the paper, i.e. first the high polymers and then the crosslinking agents. This has the advantage that both components only come into contact with each other on paper and therefore there is no risk of them interacting for a longer time before application and solidifying due to cross-linking and clogging of containers and applicators that are difficult to clean. .

Some preferred embodiments of the invention have been described above using, as an example, outer layers formed of high hydroxyl group-containing high polymers and crosslinking agents. This preferred embodiment is therefore so important because, in addition to the low weight, good stiffness and nevertheless good foldability, the papers used especially for duplicative methods, especially xerographic methods, must have a large number of other properties obtained by using the preferred embodiment.

Thus, such papers are required to retain their writability and printability and to be sufficiently opaque to have the highest possible surface conductivity so that no electrostatic charges are formed when fed through devices such as copiers and readers, which causes the sheets of paper to stick together; -elastic outer layers are not film-forming, 5 56871 but retain their air-permeable properties so that they can be retained in the equipment by suction air, are heat-resistant and do not turn yellow under the effect of heat, and the outer layers are not removable, so there is no dusting or soiling, the stiffness and puncture resistance are not lost in heat, otherwise the thermoplastic outer layers would be unusable for all heat applications and the outer layers could be formed in aqueous form if possible; from this phase.

Outer layers made of hydroxyl- and / or amino-containing high polymers and crosslinking agents meet all these requirements particularly well. However, the invention is not limited to this particularly preferred embodiment, but relates to the broader inventive idea that combining a relatively bulky (fluffy) inner layer with tough-elastic outer layers provides the required rigidity and puncture strength with low basis weight while the paper is easily foldable and has has sufficient opacity.

Foldability and other mechanical properties of particular importance in the case of low weight papers can thus be further improved by using a raw paper made in an alkaline medium, suitably at a pH of 7.2 to 9.7, for the production of the paper according to the invention. The bonds between the fibers of such raw paper are better, which is of particular importance for the uses of these low weight papers.

The following explains by way of example the preparation of a paper with good rigidity and low weight: Example 1: 60% sulphate softwood cellulose and 40% sulphate hardwood cellulose are ground in a conventional manner to a degree of grinding of 38 ° S.R. and 6% calcium carbonate is added as a filler. At pH 7.8-8, a paper sheet is then formed on a paper machine, which is glued in a conventional manner in papermaking by adding a ketene dimer (Aquapel, manufactured by Hercules Powder Comp) and fixing with a cationic polyamide resin (Cymene 557, manufactured by Hercules o

Powder Compl). The surface weight of the paper thus prepared is 47 g / m when air-dried. The scraper device is used to coat the paper on both sides with a layer weighing 1.5-1.7 g / m (solids content) on each side. The preparation solution required for this coating is formed as follows:

To an aqueous solution of 120 g / l of highly hydrolysed medium and high viscosity vinyl alcohol having a degree of polymerization of 1700 to 1800 corresponding to a molecular weight of 75000 to 80000 and a degree of saponification of 99.9% is added 6 56871 of the same amount of aqueous solution of 120 g / l. 1 melamine formaldehyde precondensate. Both said solutions may be mixed with each other only immediately before use and therefore both solutions are continuously and evenly dispensed through a small mixing vessel by means of a feed pump into the coating tank and into the overflow of this mixing vessel.

The crosslinking reaction is then performed at a temperature above 100 °, preferably 125 ° C or even higher in the drying section of the paper machine.

Example 2: 20% of finely bleached wood chips, suitably with a degree of grinding of 75-82 ° SR, is ground together with 40% of long-fiber sulphate cellulose, 25% of hardwood cellulose and 15% of decoagulated waste paper to a homogeneous material, with a degree of grinding of 35-40 ° SR The paper is glued in the usual way with hat glue and alum and prepared as a web at a pH of 4.5-4.8. The scraper is coated with a mixture of 50 parts of bone glue, 50 parts of high polymerized highly hydrolyzed polyvinyl alcohol, 25 parts of urea-formaldehyde preconde may and 0.5 parts of sodium bentonite. The aldehyde precondensate is added as above only immediately before coating.

The solids content of the lubricating mass depends on the required viscosity 2 in the scraper device and the desired coating. Here, too, a coating of 1.5-3 g / m on each side is sufficient.

Example 3: 40% long-fiber sulphate cellulose 50% sulphate birch cellulose and 10% wood-free waste paper are prepared in a conventional manner on a sheet of paper by adding 10% kaolin. pH 7.8. Bonding is performed with a ketene dimer (Aquapel) and a nitrogen-containing retention aid (Luresin K 20,

Badische Anilin- & Soda Fabriken), An adhesive press is used to apply a surface treatment composition having the following composition: 6% high hydrolysed polyvinyl alcohol (e.g. Mowiol 75/77, Farb-Verken Hoechst AG) 6% melamine-formaldehyde precondensate (e.g. Madurit ) and 2% monomeric cyanamide.

In this case, the components are only mixed together immediately before they are applied to the paper web. After the size press, the paper web is heated in the next drying to as high a temperature as possible and is preferably rolled hot, avoiding cooling,

Example 4 corresponds to Example 3. In this example, half of the vinyl alcohol is replaced by bone gelatin.

Claims (8)

A paper of low weight and good rigidity for office and duplicating machines, characterized in that the paper has a mass sizing, has a porous inner layer and is coated on both sides with a viscous-elastic outer layer consisting of hydroxyl- and / or amino-containing from the reaction product of high polymers and their crosslinking aldehydes, aldehyde donors or precondensates formed with aldehyde and that the basis weight of the paper is 35 to 70 g / m 2. Paper according to Claim 1, characterized in that the hydroxyl- and / or amino-containing high polymers contain from 10 to 60% by weight of bleach compounds, based on the weight of the high polymers. Paper according to Claim 1 or 2, characterized in that the high polymers containing hydroxyl and / or amino groups have a molecular weight of more than 2,000, preferably 30,000 to 90,000. Paper according to one of Claims 1 to 3, characterized in that the viscoelastic outer layer formed from a mixture of hydroxyl- and / or amino-containing high polymers and crosslinking agents contains a non-reactive thickener for controlling viscosity and preventing penetration. Paper according to Claim 3, characterized in that the crosslinking agent further contains from 10 to 50% by weight of cyanamide. Method for producing paper according to one of Claims 1 to 5, characterized in that the components of the tough-elastic outer layers are mixed together only immediately before they are applied to the paper or are applied successively to the paper. Process according to Claim 6, characterized in that the crosslinking reaction is accelerated by the addition of catalysts. 7 56871 Process for the production of paper according to Claim 6 or 7, characterized in that paper produced in an alkaline medium at a pH of 7.2 to 9.7 is used as raw paper.