FI112803B - A method for making a non-woven fabric and a non-woven fabric - Google Patents

Description

112803

A method for making a non-woven fabric and a non-woven fabric

The invention relates to a method for producing a nonwoven fabric as disclosed in the preamble of claim 1. The invention also relates to a non-woven fabric as disclosed in the preamble of claim 9.

For the production of nonwovens by the dry method, a product is formed from the raw materials into a moving substrate by means of an air stream. Traditionally, binder fibers have been added to such a raw material to keep the formed nonwoven fabric together. The heat applied to the fibrous web moving over the substrate provides the binding fibers with a space where they bind the fibers together. An alternative is a liquid binder which is sprayed onto the web and activated by heat.

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An alternative to using a special binder fiber or other binder is mechanical bonding. One advanced technique is the use of fine fluid jet spun-lacing. The jets are directed to a fiber layer on the substrate, which runs at a given no-20 speed. The jets pick up the fibers and wrap them together, and since the substrate is open, for example a wire, the jet liquid can run to the other side of the substrate through the substrate. The advantage is that special ·. these heat-binding binder fibers are not needed if the raw materials used are • long enough. Affordable connective fibers and materials are traditionally non-biodegradable, which is: a clear disadvantage when thinking about non-woven products; waste.

European Patent Publication No. 491383 discloses a wet process wherein the polyester fibers (PET) are formed into a mat. in the wetformer, and with the aid of the fibrous binder fiber, thermal bonding is performed prior to the wrapping bonding. Here is formed. most commonly, a pre-web in which the fibers are bonded by heat bonding, whereupon a plurality of pre-webs are superimposed and this assembly 35 is subjected to winding binding.

2 112805

A prior art nonwoven material which can be used as a basic raw material in the manufacture of nonwovens is a so-called non-woven material. fiber obtained by the solvent spinning method. It is a cellulose fiber which is prepared by dissolving cellulose in a specific solvent without making a derivative, followed by spinning into an aqueous precipitation bath. The solvent used is an amine oxide solution which is spun into water or aqueous solution to form fibers. This technique is described in particular in British Application Publication No. 2001320 and International Publication No. WO95 / 35399, the latter of which mentions the fibrillation tendency of the fibers obtained. This tendency makes the fibers particularly good for use in particular in connection with wrapping. Fibers also have good absorption properties, which makes it an attractive material for absorbent products. The fibers are also referred to as "Lyocell fiber".

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The use of cellulose-based raw materials to the maximum extent has the advantage that the product can be made completely biodegradable without the use of conventional binder fibers or materials. However, problems may arise in spite of the wrapping bond, however, in the depth of assembly, i.e. strength, of the product.

It is an object of the invention to eliminate the above drawbacks and to provide a process by which a good strength product can be prepared without separate binders. It is also an object of the invention to provide a product having the above good properties. To accomplish these purposes, the method according to the invention is essentially characterized in what is disclosed in the characterizing part of claim 1 below. Correspondingly, the product according to the invention is characterized by what is stated in the characterizing part of the attached claim 9.

· 30: In the method, the fibrous web is formed by a dry method of cellulose fibers prepared by solvent-spinning through an amine oxide solution, in addition to being pre-bonded to the fibrous web before wrapping by raising the temperature of the fibrous web and contacting it with the mechanical forming surface.

: This prevents the fibers from being excessively washed out during wrapping because they are lightly pre-bonded to each other. Em.

112803 3 In addition to fiber quality, other cellulose fibers can also be used as blended fibers. The pre-tying can be performed with a hot calender located prior to the tying point in the web running direction.

A product characterized by having been subjected to the aforementioned pre-binding prior to binding, has a higher strength value and yield than a product obtained by conventional methods. The product can be used to make various types of absorbent articles, whereupon it can be used as various disposable wipes, such as moisture wipes, or for the thicker layers of absorbent disposable articles, such as children's diapers, menstrual pads, incontinence diapers, and the like. Because the parts of the product are both pre-bonded and bound, they are not easily detached, which would be a disadvantage, especially for hygiene and hospital products.

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The invention will now be described in more detail with reference to the accompanying drawing, which shows a side view of a manufacturing line applying the manufacturing process.

In the drawing, of the fibers used as raw materials, a web w is formed on a continuous substrate 1 which allows air to pass through. Fiber - importing airflow ·. on the opposite side of the backing from the base 1 is a suction box into which air is led. From the point of formation, the web w is carried forward to the point j where it is wetted by a water jet device 2. The amount of water sprayed by the device 25 is adjusted so that the web is wetted evenly but its water content is not appreciably increased. Thereafter, the wetted surface, i.e. the upper surface of the web, is calendered by a hot roll 3 against which the unheated roll 4 on the other side of the substrate 1 presses the web. As the web w passes through the calender of rolls 3 and 4; 30, it is transferred to another support 5 which supports it from above. Thereafter, the lower surface of the non-moistened surface is moistened with a water jet device 6 of the same type as in the first moistening unit! 2. Afterwards, the substrate 5 and the web w are removed

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Through the calender 7 and 8, whereby the roll 7 below which is in contact with the lower surface of the web 35 w is a hot roll.

The web w is then moved again to a new support 9, which supports it from below. The web w is transferred to a binding station 10 where, in a known manner, the web w is subjected to a weaving binding by directing the water jets from above so that the fibers pre-bonded under the influence of heat and moisture are finally mixed together. Fine jets of water are fed through a suitable nozzle device from above through web w, and water passing through substrate 5 9 is collected on one side. Subsequently, the substrate 9 together with the web w is passed through a dryer 11, after which the finished web, i.e. the nonwovens can be removed from the substrate 9, for example by pulling it on the roll 12. Thus, the fibrous web is manufactured in the same line. so that at the end a continuous product is obtained which can be rolled up or otherwise collected.

The substrates 1.5 and 9 may be known water and air permeable forming substrates, such as wires of suitable mesh size.

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It is essential for the pre-bonding of the fibers that it is carried out without binders by utilizing elevated temperature (higher than the production line) and mechanical shaping which is thus accomplished by compression of the webs 3, 4 and 7, 8. Alternatively, other types of surfaces may be used in which the web w is brought into contact for pre-bonding to provide sufficient strength. The effect of heat can be enhanced by wetting the surface of the web w before its conductor. from contact with the heating and forming surface. In order to achieve an effective interaction between heat and working (pressure), the temperature must be at least 80 ° C and the pressure expressed as the line pressure on the web is at least 9 kg / cm. When utilizing moisture, the moisture content of the web should be at least 5% by weight. The optimum values are a temperature of about 100 ° C, a line pressure of about 21 kg / cm and a humidity of about 10% by weight. Em. values are given for a web speed of 5 m / min. For example, as the speed of the run 30 increases, the calender temperature can be increased.

The temperature of the wetting water can also be utilized such that if hot water or steam is used, the surface following the wetting point need not necessarily be hot, whereby the required heat is supplied through the wetting water and the work is performed on the unheated surface. In this case, for example, the calendars rolls 3,4 and 7,8 of the drawing may both be unheated.

112803 5

As noted above, solvent-spinning fibers are an important component of the fibrous web. Such fibers are prepared by dissolving cellulosic fibers, most commonly some wood fibers, in an amine oxide solvent, most commonly in a water-soluble tertiary amine N-oxide. A commonly used substance for this purpose is an aqueous solution of N-oxide of N-methylmorpholine. Other equivalent substances are N-oxide of N, N-dimethylcyclohexylamine, N-oxide of N, N-dimethylethanolamine and N-oxide of Ν, Ν-dimethylbenzylamine. A method for making fibers 10 and their tendency to fibrillate is described in International Publication No. WO 95/35399.

The tendency for fibrillation can be determined by measuring a Canadian standard freeness, C.S.F., from a fiber suspension. Fibrillation tends to be good if the fibers (6g 5mm long fibers in 2L water) reach a certain C.S.F. value after a certain number of revolutions in a TAPPI standard T-205 om-88 lab diffuser. The fibrillation tendency is good if the C.S.F. value measured according to TAPPI standard T-227 om-94 is 400 ml or less after 270,000 revolutions of the diffuser.

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Em. the fibers may be the majority of the total weight of the finished nonwoven fabric, pre- ·. as a sign, it can be made entirely of these fibers. However, it is also possible to use blended fibers, whereby all the fibers are brought together in a well-mixed air stream to the point of formation.

Most preferably blended fibers are natural fibers and / or cellulose-modified fibers, such as viscose fibers, that is to say fibers of natural polymeric structure which are biodegradable. Natural fibers include, for example, wood fibers, for example a relatively long fibrous mechanical or fibrous pulp commonly used in papermaking. Viscose fiber is made from regenerated cellulose: staple fiber obtained. When using the above-mentioned natural fibers, use solvent-spinning fibers! the proportion may be as low as, for example, between 2 and 50 wt. · 35, that is, in a way they act as binding fibers.

112803 6

It is to be understood that the invention is not limited only to the method disclosed in the preceding description, but can be modified within the scope of the inventive idea set forth in the claims. Other types of web w exports than those shown in the drawing may also be used in the line. It is possible that the web w is only treated on one side by the pre-binding method described, but to achieve a uniform effect, it is preferable to treat the web on both sides before the binding. Naturally, the basis weight, i.e. the net weight, of the nonwoven web w and the finished nonwoven can vary within known limits and depending on the intended use of the nonwoven web, most commonly between 30 and 300 g / m 2.

Claims (10)

112803 A process for producing a nonwoven fabric, wherein the fibrous web (w) 5 is formed by a dry process on a substrate (1) and the fibrous web is wound-bonded, characterized in that the fibrous web (w) is formed at least partly from cellulose fibers produced by solvent-spinning and prior to wrapping, the fibrous web (w) is pre-bonded by raising the temperature of the fibrous web and bringing it into contact with a mechanical shaping surface, such as a roll (3), in its displacement path. 15 Method according to Claim 1, characterized in that the fibrous web (w) is wetted before contact with said surface. Method according to Claim 1 or 2, characterized in that both the upper and the lower half of the fibrous web are brought into contact with the surface causing mechanical deformation. A method according to any one of claims 1 to 3, characterized; by wetting the fibrous web prior to bonding. ·! 25 Method according to one of Claims 1 to 4, characterized in that the fibrous web is subjected to a hot calendering process. 6. A method according to claim 4, characterized in that the fibrous web is moistened with hot water or water vapor, while at the same time providing a temperature rise at least to a large extent. Process according to any one of the preceding claims, characterized in that in addition to the solvent-spinning cellulose fibers 35, natural fibers and / or cellulose conversion fibers are used as the fiber web. 112803 The process according to claim 7, characterized in that the fibers produced by the solvent-spinning process have a content of 2 to 50% by weight. Non-woven fabric made by the dry process and reinforced by a binding process, characterized in that it is made of at least partly solvent-spinning cellulose fibers prepared by means of an amine oxide solution which has been pre-bound according to any of the claims 1-6. 10 t * 1 I <I 112803