Method for depositing particles and a binder system on a base fabric.

METHOD FOR MANUFACTURING WET PRESS FELT AND WET PRESS FELT

The invention relates to a method as defined in the preamble of claim 1. The invention further relates to a wet press felt as defined in the preamble of claim 2.

This invention relates to the manufacture of a water-absorbent fabric or felt for use in paper machines. In particular, it is directed to a method by which a uniform layer of polymeric resin bodies can be placed on a textile-based fabric and fixed to form a porous, elastic surface.

One of the most important components in modern paper machines is a water-absorbing machine felt or wire. These so-called wires are relatively large continuous belts in shape and are made on a customer-specific basis according to the requirements of the paper maker, which include the size of the belt to be placed on a particular machine and the quality of the paper made on the machine.

These are the wires used in the press section of the paper machine. Here, the wires have at least two important functions because they both support the wet fibrous web as it is transferred to the final paper product and absorb water from this web to a large extent.

This is easier to understand if the press section is viewed in relation to other parts of the paper machine. The first part immediately before the pressing part is the forming part, where the wet fibrous web is formed by spraying a liquid wood fiber pulp suspension onto a fine film or mesh. Much of the water leaves the web at this stage, but water still forms the majority of the weight of the web as it reaches the end of the forming part. As a result, the web has little structural cohesiveness at this point and requires support so as not to disintegrate and cause problems in machine operation.

From the forming part, the web continues to the pressing part. Here, the press felts provide the necessary support to the web as it passes through the press, where a large amount of additional water is pressed away. Many paper machine press sections have two or more blankets and quite often the wet web is supported or surrounded by two felts as the web passes through the press section. In any case, in the compression zone, in the narrow area between the compression rollers, the compression takes place so that the felt absorbs the water compressed from the wet web.

From an economic point of view, it is important that the felt be able to remove as much water as possible as the web passes through the press section. This is because when the web leaves this part, it enters the drying section, where all the remaining water is evaporated *

using temperature rollers. The cost of this heating is reduced if the optimum amounts of water are absorbed into the felt in the pressing section, because then less water has to be removed in the drying section.

To this day, wool has been the main raw material in the manufacture of press felts. As the term blanket implies, one of the final steps in making these machine belts was felting, where the woven wool fabric was soaked and massaged to create a soft surface. Today, however, with the development of synthetic materials, the use of wool has greatly decreased.

Current synthetic materials have the advantage over wool of greater strength, durability, and better resistance to chemicals and bacteria. The term felt, strictly speaking, is no longer appropriate for these fabrics because, strictly speaking, they cannot be felted. Instead, alternative fabrication steps are used in their fabrication to provide them with surface properties and finishes similar to true blankets. For example, the so-called batt-on8 9 0 8 8 base felts, now widely used and forming the industry standard, have a woven undergarment with a needle-attached felt surface and surface characteristics similar to wool felts. In addition, a large number of other structures are available, including nonwoven compression felts. However, despite the absence of wool and the traditional felting process in manufacturing, they are still commonly, if not universally, referred to as felts in the paper industry.

Compression felt is described by factors such as fiber amount, tissue type, permeability, and surface properties. The choice of felt for use on a particular machine depends on the design and operating parameters of the machine, the quality of the paper produced, and the desired surface finish.

As discussed above, there are alternatives for use in place of common batt-on-base press felts. For example, U.S. Patent No. 4,571,359, entitled Papermaker's Wet-Press Felt and Method of Manufacture, discloses a novel paper machine felt consisting of a textile backing having a surface layer of polymeric resin bodies fused together to form a porous elastic surface. In practice, however, it has proved difficult to position the resin bodies so that they are evenly distributed on the surface of the substrate. The object of the present invention is to solve the above problem.

The object of the present invention is to enable the resin bodies to be spread and bonded evenly on the underlay of the press felt. In other words, the present invention relates to a method of making a paper machine wet press felt as described in U.S. Patent No. 4,571,359.

The method according to the invention is characterized by what is stated in the claim

1. The wet press felt according to the invention is characterized by what is stated in the claim

2.

In the method, a homogeneous foam consisting of polymeric resin bodies, a binder and a suitable solvent is applied to the surface of the fabric. The foam, homogeneous in the distribution of the resin bodies, is thick enough in composition to be smoothed with suitable rods or blades so that a uniformly thick layer appears on the fabric. Thus, the purpose of the foam is only to apply the resin pieces to the surface of the substrate. Thereafter, the solvent component of the foam is evaporated off by heat, leaving an evenly distributed structure of resin bodies fused together on the surface of the fabric.

One critical parameter in a homogeneous foam is its viscosity, which must be sufficient to prevent it from flowing through the fabric. In this case, the polymer body material as a whole remains on the surface of the fabric.

Figure 1 shows one embodiment with which the method according to the invention can be implemented.

Figure 1 shows a textile backing fabric 1 when coated according to the invention. It is assumed that the base fabric 1 is held taut and smooth and is moved in the direction indicated by the arrow in any suitable manner not shown.

In order to ensure that the coating is uniformly thick on the substrate 1, the method uses a horizontal surface 2 which supports the substrate from below, i.e. from the non-coated side, throughout the process. In this way, the independent of the base fabric is prevented and the foam is placed in an evenly thick layer.

The foam of the polymeric resin bodies, the bonding material and the solvent, stored in a device (not shown), is placed on the base fabric 1 through a suitable nozzle 4. The polymeric resin bodies may be as shown in my patent

9 08 8 in U.S. Pat. No. 4,571,359, i.e. they have an average diameter of approximately 0.15 to 5 mm. The preferred size is about 0.5 mm. By selecting the size of the pieces and their distribution when placed on the substrate, the final opening size and distribution of the wet press felt according to the invention can be adjusted. Polymeric resins are represented by polyolefins such as polyethylene, polyurethanes, including polyether and polyester polyurethanes, and the like. The binder may be high temperature resistant resins such as polyamide and polyimide resins which are used as liquids and which cure into a solid film on heat. Water is quite suitable as a solvent, although others may be used as well.

The leveling blade 5, which is directed to push the extra foam 3 from the base fabric 1, softly and evenly distributes the foam 3 on the surface of the base fabric into a uniformly thick layer.

The uniformly coated base fabric 6 then passes under the heat source 7, which evaporates the solvent from the foam 3 and melts the polymer resin bodies together and into the base fabric 1. The heat source treatment temperature must be high enough to soften the polymer resin bodies but below the decomposing temperature. This also hardens the binder and, as mentioned above, evaporates the solvent. The finished product 8, a belt with a porous elastic surface, comes from under the heat source 7 on the right side of the picture.