METHOD OF PRODUCING DRY FORMED FIBRE MATERIAL

Abstract: The invention relates to a method of producing dry formed fibre material. This production takes place in at least two steps, a first step comprising formation of a cohesive, handleable material web under compression and supply of a reduced amount of binder compared with what is the case in a one-step process, and in that subsequent steps comprise finally treating the material web by adding the remaining amount of binder and completing up to full final grade by adding colour pigment and additive for obtaining other properties such as wet strength, flame resistance, surface friction etc.

Description: Method of producing dry formed fibre material The present invention relates to a method of producing a we of dry formed fibre material. In a preferred embodiment in accordance with the present invention there is described the manufacture of a web of cellulose fibres, so-called dry formed paper or dry formed tissue, but the method according to the invention is of course also suitable in the manufacture of webs of other kinds of fibre. When webs of different structures and properties are to be manuf ctured, there are certain problems in changing over between different qualities when the material is ready- processed in a normal 1-step process. A certain tuning-up period is required to achieve continuity of specified grade, and during this period an amount of material is produced which is outside acceptable delivery grade and must therefore be rejected. This means that there will be an extra cost and an efficiency loss in the expensive, high-production plant, which requires long runs per grade to give good profitability and low production costs per quantity unit of delivery- approved material. A very clear example of this is in running of coloured material for paper napkins, of which perhaps ten different colours could be available for delivery. The grade change Lime wilh cleaning results in both costs and trouble as well as "lost production" in the highly productive paper machine. Careful planning of production is required, with the necessity of accumulating run-off orders so that machine utilization will be high. Such production gives small flex¬ ibility and small possibility of adjusting to variations in market demands with respect to special grades. One object of the present invention is to achieve a method of the type mentioned in the introduction, in which the dis¬ advantages have been eliminated that have been present in already known production methods described above in connec- tion with webs of dry-formed material. The essentially dis¬ tinguishing features of the method in accordance with the invention are disclosed in the following claims. As a result of the present invention there is achieved an economic and rational solution to the above-described problem, this solution being to divide up manufacture into at least two mutually separated steps. The first of these steps involves processing a base material without colour or chem¬ ical additives apart from the standard components required for making a cohesive, handleable material web. A subsequent step, generally the second step, comprises processing this base material to a final grade specifically for a given order, very good flexibility and low production costs thus being achieved. Several advantages are achieved in this way, since it is only necessary to run white material, which means that a greater through-put speed on the machine can be ob¬ tained since lesser amounts of binder solution need to be dried out, longer runs can be made in the machine, storage becomes more simple, since master reels only need to consist of white base material, and there is also lower total wastage. In the subsequent manufacturing operations, i.e. generally step 2, there are also obtained further advantages such as larger flexibility in colour selection, greater ease in supplying additives, greater variation opportunities when embossed patterns are used, better economy by being able to make shorter runs of specific, called-for qualities. The equipment used for subsequent processing does not need to be situated in direct connection to the high-production paper machine, but can be in an adjacent factory or at an external converter. In other words, step 2 and possible further operations can be arranged in simpler, cheaper machines, whereby the expensive high-production paper machine can b better utilized. The invention will now be described in more detail below, with the aid of a preferred embodiment. In step 1, fibres are formed into a web which is compressed, supplied with binder and dried to a process degree corre¬ sponding to 20-90 % of the final grade, preferably 60-80 %, and is reeled into so-called master reels. These reels of semi-fabricated material can be produced with high machine utilization, since there are only a few basic types of material composition and treatment for the different webs, which can then be given uniform properties and high quality.The reels can be readily buffer-stored to await further processing in a following step. The type and quality of binder can be selected differently in step 1 for the two sides of the web, so that subsequent processing can give specific properties to each side. A re- generable type of binder is preferably used, to enable re¬ cycling of waste material from that first step. The web is processed to a final delivery grade in step 2, with specified properties in respect of such as colour, ab¬ sorption, surface friction, flame resistance, embossing etc, apart from the basic "strength property" (wet strength, freedom from fluff etc). More binder is applied in step 2, the remaining ingredients for giving desired properties being mixed into this binder. Particularly with colouring, the two-step process gives a result which is difficult to achieve with other methods used up to now. The colour pigment in the binder which is used is uniformly distributed over the whole surface and covers the fibres to a depth such that a satisfying visual colour im- pression is obtained, which can be the same on both sides when so required. The binder in step 2 can be applied in different forms such as liquid (solution, dispersion, sus¬ pension) , paste and foam, and with different methods such as gravure printing, flexographic printing, screen printing, roller application or spraying.

Claims: Claims 1. Method of producinig dry formed material, characterize in that production takes place in at least two steps, a firs step comprising the formation of a cohesive, handleabl material web under compression and the supply of a reduce amount of binder to a process grade constituting 20-90 % o that achieved in a one-step process, and in that subsequen steps comprise finally processing the material web by addin the remaining amount of binder and completing up to full final grade by adding colouring pigment and additives to obtain other properties such as wet strength, flame resist¬ ance, surface friction etc. 2. Method as claimed in claim 1, characterized in that during the first step fibres are formed into a web, which is compressed and supplied with a reduced amount of binder, a process degree corresponding to 60-80 % of the final grade being obtained. 3. Method as claimed in claim 1 or 2, characterized in that the production takes place in two steps. 4. Method as claimed in any one of the preceding claims, characterized in that the binder supplied in the first step is of regenerable type for enabling recycling of waste material, and that in the second step the binder supplied is of a type such that it inhibits the regenerability of the binder used in the first step simultaneously as it additively gives full binder strength to the material web. 5. Method as claimed in any one of the preceding claims, characterized in that the ingredients giving the remaining properties are included in the binder which is added in the second step, for giving desired final grade of the material web.

Inventors: SVENSSON SVEN, SVENSSON, SVEN
Applicants: DUNI BILA AB, DUNI BILAA AB
Application year: 1989
Main classification: D21H5
IPC codes: D04H1, D06M13, D21F9