FI113287B - A method for making multilayer paper / board - Google Patents

Description

113287 5

The present invention relates to a method of producing a multilayer paper / board using a media layer preventing / reducing the intermixing of layers in the headbox and in the web formation area.

10 The interest in the production of multi-ply paper / board has steadily increased, as various pulp layers with different properties can be combined to give the product to be manufactured, i.e. paper / board, many different properties depending on the combinations. The desired features are often incompatible and therefore compromise on the desired features of the product has to be made. For example, a pulp layer made from recycled 15 / recycled paper can be used between two fresh pulp layers to provide high quality paper at a lower cost than environmentally friendly recycled pulp. However, the problems with making multilayer paper are that using a multilayer headbox does not achieve a good enough layer cleanness, whereby the middle layer easily mixes with the top layer and is visible! »· • ',: 20 in products with unwanted properties. There have been several attempts to prevent the layers from blending, such as e.g. by introducing long spacer lamellae far into the forming region, providing a gas wedge or air wedge by blowing air between the layers to be fed, using '' layers of varying consistency, or using foam multiplate box technology. Examples of some prior art solutions are described in more detail in the following publications.

US 4,445,974 discloses a multilayer headbox for forming a multilayer web. In this apparatus, air jets are introduced between the mass layers in such a way that *; · 'That the wedges keep the layers of mass separated from each other for as long as possible:: 30 until the dewatering begins. In this context, it has been found that the layers:. · · The mixing depends on the time the layers are in contact before the dewatering begins, as well as on the turbulence of the surfaces facing each other.

U.S. Patent No. 2, 113287 to U.S. Patent 4,376,014 discloses a headbox for making cardboard for forming a multilayer web. In this case, the web is generally made up of three different layers so that the consistency of the middle mass layer is significantly higher than that of the edge layers. This combination produces a Mote with 5 smooth surfaces and good bending stiffness.

A process for making absorbent paper products such as paper towels, toilet paper, face wipes and the like is described in U.S. Patent No. 5,102,501. In this process, the layered fibrous web is formed from hydrophilic fibers dispersed in an aqueous carrier with bends, wrinkles, and other irregularities, this pulp is applied to the forming web and dewatered in a short time to maintain its characteristic properties and softness to the product. In a preferred embodiment of this process, the fibers are dispersed in a foamable medium comprising water, air and a surfactant. 15 There may be several layers of fiber pulp.

It is an object of the invention to provide a method for producing multilayer paper which does not have the problems of prior art.

> · »| The process for producing multilayer paper according to the invention is characterized by what is claimed.

• · • ·

In the method according to the invention, an insulating medium layer is introduced between the layers of the pulp by a multilayer headbox, which prevents the pulp layers from admixing with each other after the process no longer has a solid partition between the layers.

• ·, There may be several layers of mass, but at least two, and the masses may be the same * »... or different. The medium layer is fed to the mass flow from the turbulence generator, through the surfaces of the intermediate lamellae separating the mass layers, or from the outlet end of the intermediate lamellae.

A suitable insulating medium is a substance which has a viscosity which is significantly higher than the viscosity of the insulating material. However, the viscosity of the medium must not be too high, since the medium must mix sufficiently with the pulp layers in the drainage region to provide the product with a sufficiently uniform and desirable structure in the paper / board thickness direction. Preferably, the viscosity of the medium decreases as the shear force of the flow end increases. This promotes mixing of the medium with the pulp layers by the pulses of the wire section. The medium can be introduced as a thick liquid or also as 5 small bubble foams between the mass layers. The viscous medium comprises a water-miscible or water-soluble compound or agent which may be, for example, a long chain polymer used as a thickener. Preferred media include cellulose derivatives such as cellulose ethers, hydroxyethylcellulose, hydroxypropylcellulose, methylhydroxyethylcellulose, methylcellulose, carboxymethylcellulose, polyurethanes, diurethanes, polyacrylates, polyacrylamides, polyacrylamides, polyacrylates,

In the following, the invention will be further illustrated by some preferred embodiments shown in the figures, but which are not intended to be limited thereto.

Fig. 1 shows a turbulence generator 10 of a multilayer headbox, through which an opening ... · 11 between the media layers lamellas 41, 42 is fed a medium solution between the mass layers 20 and 30. 21, 22, 31, 32 show lamellae of pulp layers.

20; ·; * Fig. 2 shows an intermediate lamina 12 located in a turbulence generator 10, at the end of which 13 is fed through openings 14 a solution of medium between the pulp layers. The medium may also be fed from the openings on the surface of the intermediate lamellae. 1

Fig. 3 shows a multilayer headbox 100 according to the invention, in which the medium M2 is introduced between the mass layers Mj and M3.

The medium, preferably comprising an aqueous medium or a small bubble foam, is pumped / fed from the orifice of the turbulence generator and / or the ends of the intermediate lamellae and / or • 1: 30 from the surface of the intermediate lamellae between the mass layers. The thickness of the intermediate layer is 0.5 to 10 mm, preferably 1 to 5 mm. The medium may comprise either one compound or a mixture of several compounds 113287. In the early stages of the process in the headbox lip duct, lip jet and in the initial portion of the track formation area, the medium holds the layers apart, but the medium is partially mixed with the adjacent layers by the shear forces of the wire drainage elements below.

5

By using the process according to the invention, a very good layer purity is achieved. As a result, more environmentally friendly recycling pulp and thinner layers of fresh pulp in surface layers can be used on the inner layers of paper or board. By applying the invention, it is also possible to use in the middle layer raw materials which provide a high bulk to the paper but which are not suited to the surface of the paper type produced due to its color or other properties.

With a medium such as e.g. carboxymethylcellulose may have fiber-reinforcing (reinforcing) properties, whereby the strength of the paper can be increased or, without loss of strength, weaker and cheaper raw materials may be used. 1 I * · *

Claims (4)

5, 113287 A method for producing multilayer paper / board, characterized in that an insulating medium layer 5 is fed between the layers by means of a multilayer headbox through the outlet end (13) of the interlayer separators (12) or through the surfaces of the interleaves. Process according to claim 1, characterized in that the medium comprises a long chain polymer. 10 Process according to one of claims 1 or 2, characterized in that the medium comprises cellulose derivatives, cellulose ethers, hydroxyethylcellulose, hydroxypropylcellulose, methylhydroxyethylcellulose, methylcellulose, carboxymethylcellulose, polyurethanes, diurethanes, polyacrylates, polyacrylates, polyacrylates, polyacrylates, polyacrylates, polyacrylates. Method according to one of Claims 1 to 3, characterized in that the medium is supplied as an aqueous solution or as a bubble foam. ; \ 20 * »» I «t I» I • 1 ♦ * 6 113287