FI91549C - Method for treating a dry formed web of material - Google Patents

Description

91549

A method for treating a dry formed material web

The present invention relates to a method for compacting a dry-formed web of material containing fibrous material by bonding 5 webs of material by means of a binder component and a heat treatment.

In the current so-called. in thermobonding processes, the base fiber material, e.g., wood or glass fiber, is compounded with separate binder particles or fibers. The binder 10 is usually a thermoplastic fiber, e.g. polyethylene. So-called bicomponent fibers are also known, the core part of which can be, for example, stronger polypropylene and the sheath part softer polyethylene, which has the desired bonding properties in the temperature range used for the base fiber material. In this way, the binder fibers can also be made to withstand stress, whereby the bridges between the fibers of the base materials formed by them are strengthened.

The raw materials of the thermobonding process, one or more base fiber grades and binder fibers, are mixed and formed into a web by a dry forming method, which is a well-known papermaking method. Reference is made, for example, to Finnish patents 62386, 58804 and 66948. Efforts have been made to solve problems related to the formation of material paths • 25 mm. With forming parts according to EP patent 188454 and US patent 4375488.

Indeed, current forming techniques make the material paths sufficiently uniform to be suitable for the production of end products. A problem has become the bonding step of the webs 30, in which the fibers are bonded together with binder fibers under the influence of heat and compression. Compression is required to seal the web so that contact is made between the various fibers and adhesion is formed between the binder fibers and the base fibers as the thermoplastic component 35 melts or softens. In practice, this is done in connection with a transfer unit with heated rollers, usually arranged separately above and below the web. The material web is transported after the tarpaula through a lap flow furnace where the final fiber bonding takes place. However, it has been shown that condensation does not take place in the desired way in the final product, in which case its mechanical properties are also poor. This in turn is due to the fact that the dry material web formed of loose fibers polishes strongly in the transfer unit, causing the loss of material-10 and incomplete condensation in the material web.

The object of the present invention is to provide a method by which the above-mentioned problems are substantially overcome and by means of which the mechanical properties of the material web are substantially improved. In order to achieve the effect of TS, the method according to the invention is characterized in that, in order to prevent polychaining of the web of material, at least one side thereof is moistened by spraying water on its surface before the step of binding the web of material.

Quite surprisingly, it has been found that a very small addition of water to the material pathway provides significant improvements in both the behavior of the material pathway during the binding step and its mechanical properties. Moisture has always been undesirable in dry forming processes, and even now it can only be added to a very limited extent. Surprisingly, it is small: the amount of land needed to significantly reduce the polyation of at least the mixture of wood and plastic fibers.

Other preferred embodiments of the invention are characterized by what is set out in the following claims.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 shows an overview of a dry forming line and a web thermobonding line, Figure 2 shows an embodiment of a method Elma according to the invention in a material web transfer station.

II

91549 3

Figure 1 shows a dry forming line 1 in which drum formers 2 are used to form a web of material on a wire. The material web is transferred from the forming line 1 through a transfer unit 3, where the compression of the material web is carried out, through a flow-5 to a furnace 4, a calender station 5, a cooling station 6 and finally to a winding station 7, where the finished material web is wound on a roll 8.

Figure 2 shows the implementation of the method according to the invention in the material web transfer station 3 of Figure 1. The dry formed material web is introduced from the dry forming section line 9 to the transfer station 3. A fibrous material, e.g. 75% cellulose based and 25% thermoplastic fiber, e.g. bi-component fiber and pressed by the wire 9 first from above between the compactor roll 10 and 15 between its counter roll 11, then from below between the embosser 12 and its counter roll 13, the web of material being transferred to the wire 14 above the transfer unit 3. The length of the fibers used may be cellulose-based fibers. on average 1-3 mm and for bicompo-20 nent fibers 2-20 mm.

Thereafter, the material path 16 moves to the wire 15 leading to the flow-through furnace.

According to the invention, water is sprayed onto the surface of the material web in small drops from the nozzle 11a 17 from above just before the material web is conveyed through the nip formed by the compactor roll 10 and its counter roll 11. Correspondingly, the material web is sprayed with water below the nozzle 18 before the material web 16 is introduced between the nip formed by the pattern roll (embosser) 12 and its counter roll 13. Preferably, the counter rollers 11, 30 and 13 are rubber coated. The amount of water brought by the water jet to the surface of the material web is very small, e.g. 1-10 g / m2 on each side of the material web. The size of the water droplets is generally not very critical, because in the compression nip there is a further distribution of moisture evenly over the entire width of the track.

91549 4

The compactor and pattern rollers are heated to heat the material web to a bonding temperature, e.g., 120 ° C. The temperature can be made suitable, e.g. in the range of 100-160 ° C, according to the speed of the material web (capacity) and its thickness, as well as the properties of the binder component used.

The experiments have been performed on pulp-based fibers, the surface weight of which has varied between 50 and 220 g / m2, but the method is suitable for handling material webs weighing at least 600 grams per square meter. Experimentally, it has been found that the spraying of water reduces the polyamide of the web by 40% with the addition of about 2 g / m 2 of water, after which there is no further substantial improvement with the addition of water. Correspondingly, the tensile strength of the web, measured as a 50 mm strip load capacity, is improved from about 1,900 grams for a completely dry web to about 2,500 grams by adding 2 g / m 2 of water to more than 2,900 grams with 8 g / m 2 of water. and more. In addition, the wetting according to the invention eliminates a large part of the disadvantages caused to the Polyn machinery and the breathing air.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to the es inter ks set forth above, but may vary within the scope of the following claims.

li

Claims (8)

91549 A method of compacting a web of material (16) containing a dry-formed fibrous material by bonding the material web by means of a binder component and a heat treatment, characterized in that at least one side is moistened by spraying water before spraying the material. A method according to claim 1, characterized in that water is sprayed onto the surface of the web (16) at the root before the web of the nip is conveyed by a nip formed by a pair of rollers (10,11; 12,13) in which at least one of the rolls (10; 12) is heated to the binding path of the material web (16). A method according to claim 2, wherein the material web (16) is heated on its distal side by means of a compact roller (10), characterized by spraying water on the surface of the material web before it is fed to the nip formed by the compactor roll (10) and its counter roll (11). A method according to claim 2, wherein the material web (16) is heated on both sides by successive pairs of rollers (10, 11; 12, 13), characterized by the fact that water is sprayed on the surface of the material web just before it. 25 guides to a nip formed by a roller * (10; 12) heating each side of the material web (16) and its counter roll (11; 13). Method according to one of Claims 1 to 4, characterized in that the water is sprayed in small droplets on each side of the material web from 1 to 10 g / m 2. Method according to one of Claims 1 to 5, characterized in that the material web (16) formed on the handrail consists mainly of wood or cellulose fibers and thermoplastic binder fibers. A method according to claim 6, characterized in that the basis weight of the material web to be treated is 50 to 600 g / m 2. 91549 Method according to one of Claims 1 to 7, characterized in that the temperature of the roller (10; 12) which heats the second material web (16) is 100 to 160 ° C, depending on the binder component used and the production rate. II 91549