FI58368C - FOERFARANDE FOER FRAMSTAELLNING AV FLERSKIKTSPAPPER OCH -KARTONGER - Google Patents

Description

I .¾: V

-ιΤη, fftl # · «ANNOUNCEMENT r Q 7 /: O

Ma ™ ^ UTLÄGCN I NGSSKRIFT $ ° ® ® C (45) Patent.-Ay'inr.; · Tty 12 01 1031 (£ pVj & Patent weidelat VV ^ (51) Kv.! K? /Ln*.CI.3 D 21 H 1/40 FINLAND — FINLAND (21) ikκ «« * ιΐΜΐΜΛΐυ · -? «· Μ * ΐΜβΐο» ΐη * 752556 (M) HikamispUvt — Af »& knlnpdi | 12.09 * 75 ^ ^ (23) Alkupllvf — GlMghutadtf 12.09 * 75 (41) Tullut lulkMul - BIMt offuntDg 03.0U.76 ^ tantti · And the National Board of Registration (44) NlhtivtaJp ™] «kuLLkai ^ n pvm.-

Patent and registration certificates '' AmMcm utjugd och utUkrWun pubHcund 30.09.80

(32) (33) (31) Pjrrduttjr utuolltwi —Begird prior It * t 02.IO.7U

Federal Republic of Germany-Förbundsrepubliken lyskland (DE) P 2UU6971-U

(71) Rohm GmbH, Kirschenallee, 6100 Darmstadt, Federal Republic of Germany-Forbundsrepubliken Tyskland (DE) (72) Helmut Neumann, Goddelau, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (7U) Leitzinger Oy (5U) Method for multi-layer The present invention relates to a process for the production of high basis weight papers and paperboards and possibly with layers of different materials. The paper machine cannot produce high-quality papers and paperboards with a basis weight of more than 200 g / m in one operation on the wire. Therefore, heavy papers and cartons usually need to be made by gluing together several webs of paper. In this method, the working speed cannot exceed 30 to 40 m / min. Aqueous solutions of starch, animal glue and casein are used as binders, the aqueous portion of which must be evaporated off after gluing. In order to increase the working speed and save the heat demand to evaporate the water, heavy papers and cartons are also produced by felting several layers of paper together in a paper machine, i.e. a paper web carried by one wire is allowed to pass over another wire on top of another. the paper web sheeting process is still ongoing. Both layers 1 are joined together by continuous removal of water. In a corresponding manner, a larger number of layers can also be felted together. However, the mere mechanical connection of the different layers for many applications is not strong enough because the papers and boards tend to crack. The addition of binders to the different paper layers and the spraying of the dispersions between the layers to be joined does not lead to a stronger bond.

It is an object of the present invention to provide multilayer papers and cartons on a paper machine at its normal speed and to firmly bond the layers together. This task is solved by applying an aqueous suspension of a thermoplastic plastic having a ^ Amaks value of at most 70 ° C and a particle size of 10 to 300 μm to the paper web on top of the wire, sucking the water portion far out, placing the paper web received by the second paper wire wet in the plastic-coated paper web. on top, optionally introducing one or more other layers of paper as indicated by feeding a plastic suspension and a wet paper web and sealing the joined paper layers together at a temperature above the plastic under pressure. Due to their large size, the plastic particles applied from the aqueous suspension do not penetrate when the water portion of the suspension is removed or penetrate only slightly into the paper web and form a layer of private bonding particles on its surface. After the second paper web is placed on top, the layer of binder particles contacts the other layers and provides a strong adhesion between them when the interconnected layers in the dry part of the paper machine or in the subsequent hot calender are brought to a temperature where the plastic is in the thermoplastic state. In this case, no film formation regularly occurs, but the plastic particles remain for the most part separated from each other, but penetrate the paper layers in contact with each other in the thermoplastic state. When cooled to room temperature, the plastic stiffens and forms a durable and strong joint between the layers.

The process according to the invention can be carried out in paper machines at a standard speed, for example 100 to 150 m / min. Since most of the water in the plastic suspension is sucked out, no increased energy requirements are generated in the dry part of the machine. The method according to the invention makes it possible to combine two or more paper webs with a dry weight of 2 always up to 200 g / m and thus to produce cartons with a dry weight of always about 2000 g / m 2. The layers to be joined together can be of similar thickness and quality. Very preferably, the method according to the invention is suitable for the production of papers and cartons in which one or more layers are of inferior material and one or preferably both outer layers are of inferior material. For example, wood abrasive, unbleached cellulose or a material derived from waste paper can be used as the inner layer, while relatively thin layers of fully bleached cellulose are used for the outer layers. For many purposes, it is sufficient for the second outer layer to be formed of fully bleached cellulose and the second outer layer to be semi-bleached cellulose. For the outer layers, thicknesses of 50 to 100 g / m, preferably 60 to 80 g / m dry weight are usually sufficient, while the weight of the middle layer or the sum of the weights of several middle layers is often more than 100 g / m.

Each layer of paper divided into a multi-ply paper or board structure is provided by a special wire. The wires are arranged relative to each other in such a position that a web received from one wire and assembled from one or more layers can be guided on top of the next wire. One such device is best implemented with multiple planar wires, but in principle it is also possible to allow the planar wires to co-operate with the circular wires.

The plastic suspension is fed into the ears before the two paper webs are brought together inside the suction area. This is done through the front end pool. The particles contained in the plastic suspension must be coarser than the pore size of the paper web to be laminated. In very fine-fiber pulp, a plastic particle size of 10 μm is sufficient, while in coarse-fiber material a particle size of up to 300 μm is used. Even larger particles make an increased binder charge necessary and can cause unevenness in the finished paper or board. Usually particle sizes of 50 to 100 pm are best.

The proportion of plastic in the suspension is not critical, as even a large excess of water can be absorbed quickly. A plastic content of 1 to 5% by weight of the suspension has proved to be appropriate. The amount of suspension is dimensioned so that the plastic parts provide a tight coating on the surface of the layer without contacting each other or, after post-treatment in the thermoplastic state, flow together into a closed film. The amount of binder from 10 to 100 g, preferably from 20 to 50 g / m, generally gives high strength to the joint. The proportion of binder in the finished paper or board may be in the range of 15 to 50% by weight based on the weight of the fibers.

The plastic used as a binder must be thermoplastic so that the plastic particles penetrate or adhere to the spaces between the fibers at temperatures of 100 - i2> 0 ° C at 4 58368 or in a subsequent hot calender or press at temperatures of 180 ° C. Thermoplastic plastics with a t a1fS value of up to 70 ° C are suitable for the process according to the invention. Preferably t,

AmaKs · value below 30 ° C, for example in the range 10 - 20 ° C tA, __ ___is Λ max · “value characterizes the characteristic used for thermoplastic plastics and indicates the maximum damping in the rotational vibration test (DIN 53 445). ,

A large number of suitable thermoplastic plastics are known. They are preferably all or most of the alkyl esters of acrylic acid having 1 to 8 carbon atoms in the alkyl residue or alkyl esters of mectaryl acid having 4 to 8 carbon atoms in the alkyl residue. Esters of methacrylic acid having 1 to 4 carbon atoms and containing aliphatic alcohols such as styrene, acrylonitrile and other monomers with “values above 70 ° C in polymerized polymers alone may be subdivided into the structure of plastics used in limited quantities, limiting their proportion the t ^ - ^ g value of the finished copolymer. Further suitable plastics can be obtained from vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride or mixtures thereof as well as mixtures of butadiene with esters of styrene, acrylonitrile or mectaryl acid.

Aqueous suspensions containing said plastics in the form of particles of the indicated size can be prepared according to the suspension polymerization process. In this case, the particles are more or less spherical in shape. However, it is also possible to start from the corresponding aqueous dispersions of suitable plastics and to convert them into suspensions of the desired particle size by careful coagulation. The primary particle size of aqueous plastic dispersions is generally less than 1 μm.

With the slow addition of coagulants known per se, such as acids, concentrated saline solutions, polycationic compounds, such as aluminum sulphate or polyethyleneimine, with vigorous stirring, the dispersions begin to coagulate to a large extent to form particles of uniform particle size. As soon as the agglomerate particles 1

for the method of the invention are in a suitable size range, not I

add more coagulant. If the suspension prepared in this way contains private particles of undesirably large particle size, they can be easily removed by filtration through a sieve of suitable mesh size. The preparation of plastic suspensions is not an object of the invention.

5 58368

To prevent the plastic particles from settling in the suspension, a water-soluble thickener, for example carboxymethylcellulose, polyvinyl alcohol, alginate or polysodium acrylate or methacrylate, is dissolved therein. To stabilize 1 to 5% plastic dispersions, an addition of 0.1 to 1% of thickeners is sufficient.

The joining of the paper webs to be joined can take place simultaneously with or in connection with the suction of the paper portion of the plastic dispersions. Once the desired number of layers of paper have been joined together, the web passes into the dry part of the paper machine in a manner known per se. A pressing device is connected to this, in which the paper web passes between a pair of rollers and a large part of the still adhering water is released. In this case, no strong connection is yet achieved between the different layers of paper. Regular adhesion of the paper layers to each other on a regular basis is only achieved in the drying zone at a temperature of 80 to 120 ° C. If the tmax value of the plastic is very high and sufficient adhesion is not achieved under the drying conditions, the dry paper web can be allowed to pass through a hot calender or the resulting paper or board can be further processed in a hot press.

The bond between the different paper layers obtained by the method according to the invention can be stronger than the paper layer itself. The tear strength of the paper and board can then be further increased by attaching a binder to the paper layers themselves. Suitable for this are plastic dispersions which are added to the paper pulp and which pass from there onto the paper fibers and precipitation with a coagulant. Likewise, plastic suspensions used in the present method for joining layers can be added to the pulp. However, the dispersion of the plastic suspension used for impregnating the paper layers can also be added. While the coarse plastic particles remain on the surface of the paper, the dispersion particles penetrate the paper itself. If the pulp has been pretreated with a coagulant, the dispersion particles penetrating the paper will precipitate on the surface of the fibers. Cationically controlled plastic dispersions are also able to adhere to paper fibers without such pretreatment. With a binder content of 10 to 20% by weight of the fibers, a splitting strength <inside the paper layers is provided in the different paper layers, which splitting strength corresponds approximately to the splitting strength between the different paper layers. If desired, the total amount of plastic inside and between the layers can be increased to, for example, 80 to 100% by weight of the fibers.

6 58368 The papers and paperboards made in accordance with this invention are suitable for all known uses of papers and paperboards having a low basis weight per unit area weight (e.g. · '

Example 1 *

In Holland, a pulp-water mixture / with a degree of grinding of 38 ° SR is prepared from bleached softwood pulp and bleached hardwood pulp at a pulp density of 1.2% and diluted to a pulp density of 0.1%. From this, a paper web with a basis weight of 65 g / m (dry) is produced on a wire in a manner known per se. The second wire is used to make a second paper web from the same stock-water mixture. On top of this paper web, an aqueous suspension containing 5% by weight of bead plastic consisting of butyl acrylate and methyl methacrylate with an average bead size of 0.06 mm is allowed to run from inside the suction zone, water is sucked off and the paper web received by the first wire is deposited. The combined paper web passes through press rolls in a dry section where it is dried at 120 ° C. The finished two-ply paper 2 has a basis weight of 160 g / m 2 and contains about 20% by weight of plastic.

Example 2

The procedure of Example 1 is repeated, but a cationically stabilized acrylic resin dispersion is added to the stock-water mixture in an amount of 20% calculated as dry matter on the dry weight of the fibrous material. The dispersion adheres completely to the surface of the fibers. In addition, a small amount of polyacrylamide is used as well as an antifoam.

The paper webs are treated and co-assembled as in Example 1. The resulting paper has a total plastic content of 40% and is non-cracking, water and solvent resistant and has low air permeability. It is suitable for the production of abrasive papers.

Example 3

The procedure of Example 1 is repeated, but instead of the plastic spray suspension 7 S8368, a pre-coagulated plastic dispersion is added. To pre-coagulate, a 60% anionic acrylic resin dispersion with a film softening temperature of 17 ° C (according to DIN 53 445) is gradually mixed with an amount of cationic water-soluble melamine resin (trade name Madurit MV 160, Casella) to form a coagulate gel. with a size of 0.04 mm. The resulting suspension is diluted to a solids content of 2% and applied to the surface of the paper web in a settling tank.

The resulting paper has a total plastic content of 20% (solid) and is not cracked.