Method for adding chemicals to a nonwoven material

Abstract

A method of adding a chemical additive to a fiber web of nonwoven material including cellulose pulp fibers and synthetic fibers and / or filaments. A hydrojet liquid including the chemical additive is used in at least one hydrojet treatment step, which includes at least one vacuum collecting box. The hydrojet liquid is applied to the fiber web for penetrating the fiber web at a pressure of at least 5 bar but not more than 100 bar, in such a manner so that the chemical additive is penetrated into the fiber to fiber intersections of the nonwoven material.

Description

CROSS REFERENCE TO THE RELATED APPLICATION [0001] This application claims the 35 USC 119(e) benefit of prior U.S. Provisional application Ser. No. 60 / 530,906 filed on Dec. 22, 2003.TECHNICAL FIELD [0002] The invention relates to a method for adding a chemical additive to a fiber web of nonwoven material comprising cellulose pulp fibers and synthetic fibers and / or filaments. BACKGROUND OF THE INVENTION [0003] Typical properties of nonwoven include the ready ability to absorb tensile stress energy, their drapability, and good textile-like flexibility, properties that are frequently referred to as bulk softness, a high surface softness, and a high specific volume with a perceptible thickness. Further desirable properties are as high a liquid absorbency as possible and, depending on the application, a suitable wet and dry strength as well as an attractive visual appearance of the outer product surface. These properties, among others, allow nonwoven to be used for example as cleaning wip...

AI Technical Summary

Benefits of technology

[0013] The chemical additive is added to give a certain desired effect in the nonwoven material. All the desired features according to the invention where one wish to enhance certain properties and get the added chemicals into the bulk will prosper from the claimed method. The invention permits the chemical additive to penetrate into the fiber-to-fiber intersections in the nonwoven material. The added chemical additive is forced into the fiber-fiber intersections by the high-pressure fluid jets, such as water jets. The high pressure water jets created by the hydrojet assembly in the hydrojet treatment will move the fibers in the material and will thus allow the chemical additive to go into the fiber to fiber intersections. The chemical additive will penetrate into and throughout the whole material and not only treat the surface.

[0014] The hydrojet liquid used in the hydrojet treatment step for penetrating the fiber web is preferably applied in an amount such that the hydrojet liquid replaces exchangeable water within the fiber web, whereby the fiber web is saturated with the hydrojet liquid comprising the chemical additive. Since the machine speeds are high it is most probable that it is the capillary water in pores and capillaries, which is exchanged. The method according to the invention results in a good retention of the chemical additive. The high retention of the chemicals added in the material has a high influence of the nonwoven material properties, such as linting as well as the softening effect of course.

[0018] In the embodiment where the chemical additive comprises a softening agent, penetration is especially desirable since the bulk properties are enhanced as the hydrogen bonds at the fiber-fiber intersections are broken in the material or at least softened or loosened up by the softening chemicals. Decreasing or reducing the inter-fiber bonding within the web when the nonwoven web comprises cellulose fibers to a certain degree can thus increase the softness and bulk. But also the stiffness of the material will be lower as the softeners will influence the fibers throughout the material. Also for other chemical additives such as wet strength agents, the effect of the additives will be greater since all of the fiber to fiber intersections are treated and not only the surface of the nonwoven material web.

[0019] Wet strength agents are primarily added to reduce the linting. The expression “low linting” means a low release of fibers from a web, i.e. that a wipe, for example, does not release fibers onto the object that is wiped. Wet strength agents can also enhance the wet strength, especially when a high content of cellulose pulp is used in the nonwoven material. The term ‘wet strength’ also refers to the ability of the material to maintain its integrity and function in a wet condition.

[0020] It is also worth to emphases that the nonwoven material with its improved properties preferably could be produced in an inline process. This provides many advantages; among others that there is no need to dry the material several times, since all is done in the same process. Pressing is sometimes optional to get a smoother web, but when chemicals are added according to the claimed method, there is no need for such a pressing action. The nonwoven material web treated with softeners or debonders will already have a softer feel and therefore no pressing is needed. When there is no pressing step, the natural bulk in the material is kept, which in turn have several positive effects to absorbency, softness through bulk, drapability stiffness, the elasticity in the web, etc.

Problems solved by technology

If fibers are released from the nonwoven material surface or from the bulk they will during use eventually end up on the object that is wiped, something highly undesirable in many applications.

One of the disadvantages of adding chemicals in the wet end of the manufacturing process is that the retention of different chemicals added in the wet end onto the fibers is generally relatively poor.

However, the low strength of the bond between the added chemical and the fiber does not withstand the hydroentanglement process step.

The enriched chemicals in the hydroentanglement water cleaning system will cause a number of problems.

For example, filters could be clogged, e.g. in cases of wet strength agents are added, and further it may cause stops in the production process.

When for example surfactants are added, there might also be problems with foam formation, and also there is a risk that the flocks in the flocculation are broken, etc.

In addition to all this, the chemical cost may be very expensive.

Further, the yield and efficiency of the chemical additive is very low.

When chemicals on the other hand are added after the hydroentanglement, e.g. by spraying, the smoothness of the surface will be improved, but only limited improvement of the softness as to e.g. drapability stiffness and bulk softness will be obtained.

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