DE2113216B2 - LIGHTWEIGHT PAPER OF HIGH STIFFNESS AND PROCESS FOR ITS MANUFACTURING - Google Patents

Description

subordinate weights of the usual papers. The property of tough elasticity in the outer layers is necessary because, despite the required stiffness of the paper, that which is usual for office papers The number of folds is guaranteed by the nut and the outer layers must not break open even with repeated folding.

The technical problem on which the invention is based is solved particularly advantageously by a lightweight paper, the tough elastic outer layers of which are formed by the reaction product of high polymers containing hydroxyl and / or amino groups and compounds that have a crosslinking effect on them, the high polymers of which have a molecular weight of over 2000, preferably vtn 5,000 to 30,000. The most favorable molecular weight range is somewhat dependent on the basis weight of the base paper. The lower the surface weight , the higher the molecular weight of the high polymer should be in order to prevent it from penetrating too deeply or even from impregnating through. Therefore, in a preferred embodiment of the invention, the viscoplastic outer layer additionally contains thickeners, such as bentonites, which are not included in the crosslinking reaction, but make it possible to optimally control the viscosity and prevent penetration of the base paper. A thorough impregnation is advantageously made more difficult in that the base paper is gelir.'t.

High polymers containing hydroxyl and / or amino groups are particularly suitable Polyvinyl alcohols, especially the highly hydrolyzed types, starches and starch derivatives such as ethyxylated Starch and oxyalkyl esters of acrylic and methacrylic acid and amides of these acids, the synthetic high polymers also having copolymers other olefinically unsaturated compounds such as ethylene, propylene, vinyl acetate and vinyl chloride, can represent. +0

The high polymers expediently also contain an additive of 10 to 60 percent by weight Protein compounds such as casein and soy protein - based on the weight of the high polymers. These Components bring a further gain in rigidity. About 60 percent by weight should be the proportion of Protein compounds do not work, however, because otherwise the outer layers become too brittle and sufficient toughness and thus no longer a sufficient number of folds is guaranteed.

As crosslinking substances, find in their crosslinking effect on hydroxyl and / or high polymers containing amino groups with known aldehydes, aldehyde-releasing substances or with Precondensates built up from aldehydes, such as formaldehyde and acetaldehyde, glyoxal and hexamethylenetetramine, melamine-formaldehyde, urea-formaldehyde, application.

Lightweight papers in which the crosslinking reaction to the high polymers consists in an interaction of these aldehyde compounds with cyanamide are very particularly suitable. The use of cyanamide has the considerable advantage that cyanamide takes on an additional function and creates a bridge bond between the base paper and the outer layer. This additional strengthening of the outer layer and simultaneous anchoring with the base paper is of very considerable importance, especially for duplicating papers, which will be discussed further below.

The crosslinking reaction is expediently accelerated by adding catalysts such as NaCl. NH ₄ Cl. HCl or Lewis acids.

As already stated, it is important in the production of the lightweight paper according to the invention that the components for di. tough elastic outer layers do not impregnate the base paper. In order to prevent this, measures have already been mentioned to use high polymer with a sufficiently large molecular weight, the additional use of thickeners and the use of a sized base paper. On the other hand, it is of course necessary that the outer layers can be applied according to the usual techniques of the paper industry and, if possible, with conventional devices, ie coating units, it being particularly important that the application is as thin and uniform as possible. For this reason, the components for the viscoplastic outer layers, i.e. in particular the high polymers containing hydroxyl groups and the crosslinking substances, are expediently brought together during production immediately before application to the paper, thus preventing the crosslinking reaction from starting and the theological properties change the mixture unfavorably. Another beneficial variant of the process consists in applying the components to the paper one after the other, ie first the high polymers and then the substances with a crosslinking effect. This has the advantage that the two components only come together on the paper and so there is no risk of the two components acting on each other for a long time before application due to machine downtime, carelessness and the like, the corresponding vessels and Add application units, which then have to be laboriously cleaned again.

In the previous embodiments, the invention is based on the advantageous example of outer layers of high polymers preferably containing hydroxyl groups and substances that have a crosslinking effect on them has been described. This preferred embodiment is therefore so important because especially with papers for duplication processes, especially xerographic processes in addition to the requirement of light weight, Rigidity and nevertheless good foldability, such a paper has a whole range of other properties should have, as guaranteed by the preferred embodiment.

So it is required of these papers

a) that they can be written on and printed on and that they are sufficiently opaque,

b) that they have the highest possible surface conductivity, so that no electrostatic Charging occurs while going through the devices such as photocopiers and receipt readers that use the disturbing sticking of the leaves caused,

c) that the tough elastic outer layers are not film-forming, but their air permeability is retained, so that they in with suction air the devices can be held,

d) that they are heat-resistant and do not yellow when exposed to heat.

e) that the outer layers are not abrasive and therefore do not pose a risk of dust and dirt given is.

f) that the stiffness and compressive strength are not lost in the heat, so that for all purposes. which are exposed to heat, thermoplastic outer layers are useless,

g) that the outer layers can be formed as far as possible from the aqueous phase.

Outer layers made of hydroxyl and. or high polymers containing amino groups and substances having a crosslinking effect on them are particularly good. because the relatively voluminous inner layer in connection with viscoplastic outer layers achieves the required rigidity and compressive strength with a low weight per unit area and thus the paper is easy to fold and has sufficient opacity.

The foldability and other mechanical properties of lightweight papers Increased importance is therefore further improved in that a base paper is used for the production of the paper according to the invention finds that in an alkaline medium it is expedient to produce in a pH range from 7.2 to 9.7. A Such base paper has a better fiber to fiber bond, which is suitable for the purpose of this lightweight papers are of particular importance.

The following is the production of a lightweight, high rigidity paper using a Example described.

example 1

60 », 3/4 sulphate needle pulp and 40% sulphate leaf pulp are brought to a freeness of 38 ° SR in the usual way and 6% calcium carbonate is added as a filler. At a pH of 7.8 bit-8, a paper sheet is then formed on the paper machine, which is sized in the manner customary in papermaking by adding a ketene dimer and fixing it with a cationic polyamide resin. Using a knife coater, the paper is prepared on both sides with a spread of 1.5 to 1.7 g / m ² (anhydrous) on each side. The preparation solution used for this spread is prepared in the following way:

The same amount of an aqueous solution of 120 g / l melamine-formaldehyde precondensate is added to an aqueous solution of 120 g / l of highly polymerized medium and high viscosity vinyl alcohol with a saponification level of 99.9% . The two solutions mentioned must first be mixed take place shortly before use, and for this reason the two solutions are constantly and evenly dosed into this mixing vessel via a small mixing vessel with a feed pump to the coating pan and overflow.

The crosslinking reaction is then carried out in the dryer section of the paper machine at a temperature of over 100 ² C, expediently 125 ^{3 C or above.}

Example 2

20 ⁰ O of a fine wood pulp with a freeness of preferably 75 to 82 "SR. Bleached, are ^{ground with 40 n} o long-fiber sulphate pulp, 2:> ^υ _u hardwood pulp and 15" ο de-stiped waste paper to a whole substance with a freeness between 35 and 40 ^c SR mixed. The paper is fully sized in the usual way with resin size and alum and extended at a pH of 4.5 to 4.8 . A mixture of 50 parts of milk gelatine, 50 parts of high-polymer, highly hydrolyzed polyvinyl alcohol, 25 parts of urea-formaldehyde precondensate and 0.5 part of sodium bentonite is coated on a Γ ..kelstrsichanlage. The Al-

As above, z ₀ dehyde precondensate is only added immediately before application.

The solids content of the coating slip depends on the viscosity required under the doctor blade and according to the desired order. Also here ge an application of 1.5 to 3 g / m ² per side is sufficient.

Example 3

Made from 40% long fiber sulphate pulp, 50 ° / o sulphate birch pulp and 10% wood-free waste paper is more common

, O China clay formed by the addition of 10 ⁰ / a paper sheet. The pH is 7.8. Sizing is done with ketene dimer and a nitrogenous retention agent. On a

A surface preparation compound of the following composition is applied to the size press:

6 ° / o highly hydrolyzed polyvinyl alcohol, 6% melamine formaldehyde precondensate

and 2% monomeric cyanamide.

Here, the components are only mixed immediately before being applied to the paper web. the The paper web is heated as high as possible in the drying process following the size press expediently wound hot while avoiding cooling.

Example 4

Same as example 3. In this case half of the vinyl alcohol is replaced by bone gelatin.

Claims (11)

1 2 Claims - Office technology has undergone a revolutionary development in the last ten years. 1. Lightweight paper with high rigidity maclit, which is particularly useful in terms of copier speed Use in office and duplication drives and in documentation and electronic machines, characterized by a 5 data processing to ever higher levels of workload Inner layer and both viscoelastic velocities. So everyone is out see outer layers, which from ο ^ m Uinset- familiar the xerographic process, the tion product of hydroxyl and / or amino containing the conventional copier process groups that were customary up to that point High polymers and on them based on photographic processes, crosslinking compounds formed io has completely replaced. are. The ever higher working speeds of the 2. Lightweight paper according to claim 1. devices used for this purpose, such as copiers characterized in that the hydroxyl and / and document readers are based on the properties of the in or high polymers containing amino groups IO these devices used papers considerably up to now 60 percent by weight of protein compounds. It has been included to this day, based on the weight of the Hochpo- partig, that the papers used for it are more cautious. have moderately high weight.: n. A one 3. Lightweight paper after one of the flawless passage through the devices is only characterized by the preceding claims, if these papers show a sufficient degree that the hydroxyl and / or amino groups have. On the other hand, these papers containing pen-containing high polymers must have a molecular weight that is easy to fold and also have a certain elasticity and of more than 2000, preferably 5000, sufficient opacity. For these greens up to 30,000. 4. Lightweight paper according to one of the tes of such papers is not possible, and the area of the preceding claims, characterized in that the device manufacturers ν Tschreiben also indicate that the tough-elastic outer layers are of the order of 90 g / m ² . not participating in the Verigungsreaktion This is associated with the considerable disadvantage that Have thickeners. such copies in their strength and weight 5. Leicl.'gev ^ chtiges paper according to one of which is often considerably higher than that of the original. at Claims 1 to 3, characterized in that 30 of the flood of paper, which rises inexorably, and the crosslinking substances aldehydes, with associated problems of the office space, the aldehyde-releasing substances or aldehyde-required storage areas and postage costs are built-up precondensates. there is an urgent need for an easy 6. Lightweight paper according to claim 3, important high stiffness paper, all of which characterized in that the crosslinking we meet 35 requirements and a faultless one kenden substances additionally contain 30 to 150Ge passage through the Vorrichwicht% cyanamide available on the market. guaranteed. The usual, 7. A method for producing an easily available sustainable paper according to any one of claims 1 treatment options, such as impregnation to 6, characterized in that the composite 40 or coating of the paper, completely. An impregnation of the raw paper for the viscoplastic outer layers first results in a rigidity which is immediately available prior to application to the paper, so that the required foldability be brought together. imd elasticity of the paper is no longer given. 8. A method for producing a light coating process that can eliminate this disadvantage, important paper according to one of claims 1 45, because they represent surface refinements, brinbis 7, characterized in that the components also do not have the desired effect, because a gene for The tough elastic outer layers save weight in the base paper due to the weight can be applied to the paper one after the other. of the line is canceled again. 9. A method for producing a lightweight, according to the invention, this is urgently pending important paper according to any one of claims 1 50. The problem is solved by a lightweight paper to 8, characterized in that the cross-linking high rigidity for use in office and branching reactions by adding catalysts to a variety of devices, which is accelerated by a voluminous in-layer and tough-elastic outer layer on both sides 10. A method for producing a light-weight layer, which consists of the reaction product of hywichtigen paper according to one of claims 1 55 and / or amino group-containing high polybis 9, characterized in that meren as base paper and this cross-linking compound in an alkaline environment at a pH range fertilize is formed. Paper produced from 7.2 to 9.7 is used. Such paper is obtained from the tough elastic will. Outer layers the absolutely necessary stiffness 11. Process for producing a lightweight and is because of its voluminous inner layer important paper according to one of claims 1 nevertheless easily foldable, still sufficiently elastic and to 10, characterized in that as raw pa- of sufficient opacity. Through this construction principle pier a sized paper is used. it is possible that the weight of such a paper for office and reproduction equipment in one 65 can be pressed down from 35 to 70 g. The invention relates to a lightweight paper. The most suitable basis weight depends on the high rigidity for use in office and residential applications and depending on the device diversification machines. gigantic, but is in any case considerably below the previous