EP0054628B1 - Process for simultaneously and continuously strengthening and coating a fleece fabric - Google Patents

Description

The invention relates to a process for the simultaneous, continuous solidification and coating of a nonwoven fabric with a binder and with an adhesive, in which the binder is counter-pressed from one side synchronously against the adhesive compound printed on the other side in the form of partial areas that cover it, the Partial areas have a distance from each other.

Such a method is known from Japanese published patent application 1667/1975. The binder and the adhesive compositions are applied during the passage of the nonwoven through a pair of engraving or sieve rollers.

Binders primarily serve to bond the fibers of a nonwoven fabric to one another and thereby give it strength. The more fibers are glued together, the greater the strength. It is therefore desirable that the binder penetrate into the interior of the treated nonwoven and, after it has solidified, is distributed as evenly as possible over the entire cross-section. In particular, crosslinkable polymeric substances are used as binders for practical use.

In contrast, the adhesive compositions applied to the surface of fixing inserts serve to enable bonding with another substance. Common adhesive compositions are thermoplastic substances, and the activation is effected by applying pressure and heat, for example with the aid of an iron. In contrast to the binder, it is therefore desirable that the adhesive should not penetrate into the interior of the nonwoven used, even when ironing, but should be available as completely and concentrated as possible for the mutual bonding of the superimposed surfaces.

The method mentioned at the beginning makes it possible to apply the binder and the adhesive composition congruently to the top and to the bottom of the nonwoven used. Due to the identical printing process used in the treatment of the top and bottom surfaces, however, the same press-in forces result, and it is therefore extremely difficult to practically implement the desired different press-in of binder and adhesive. Mutual modification of the size of the applied partial areas is not possible, and higher printing speeds can lead to an unclean print image and thus to undefined properties of the fixing insert obtained, especially when treating non-pre-consolidated nonwovens.

From European patent application 12776 a method is known which enables the consolidation of a nonwoven fabric by printing on a UV-curable binder and subsequent irradiation with a high-pressure mercury lamp at working speeds of more than 50 m / min. The application of an adhesive is not addressed.

The invention has for its object to develop the above-mentioned method in such a way that a simultaneous, continuous printing of a binder and an adhesive on an unconsolidated nonwoven fabric in the form of partial areas with a congruent center line ensures a precise printed image on both sides, and which makes it possible to vary the specific order quantity on both sides as well as the mutual injection.

According to the invention, this object is achieved with the characterizing features of the patent claim. Advantageous configurations are referred to in the subclaims.

In the method according to the invention, a binder which can be crosslinked by UV rays is printed from the underside against a thermoplastic adhesive composition applied to the top of the nonwoven fabric by the powder dot or screen printing method. The binder is then crosslinked by UV rays, the dose being selected so that there is at the same time a geometrical inherent stabilization of the shape of the adhesive mass areas, which is sufficient in terms of preventing divergence and thus of impurities in the printed image during the transfer and subsequent finishing treatment in a sintering channel or a dryer.

In order to achieve complete crosslinking of the binder distributed over the cross section of the nonwoven after printing, the UV radiation is operated with excess energy. This excess energy, which expediently makes up more than half of the electrical energy used, is used according to the invention to glue the partial surfaces of the nonwoven fabric, which are raised in relief above the binder, from the surface of the nonwoven fabric, essentially consisting of adhesive particles, as far as possible to one another or to the surface of the nonwoven fabric that a change in the geometric shape and in particular a divergence during the transfer into the subsequent dryer or into the subsequent annealing chamber is prevented. The electrical or radiation energy used ensures complete crosslinking of the binder pressed into the nonwoven fabric within the partial areas while at the same time stabilizing the partial adhesive areas. A particularly favorable ratio between UV and heat radiation is given with medium and high pressure mercury lamps if they are directed against the surface of the printed nonwoven fabric from both sides without the use of special filters and / or special cooling. The use of an overdose of the claimed energy distribution is generally not disadvantageous, but rather favors a high degree of contour sharpness on both sides at the highest working speeds NEN print image. It is an advantage to be emphasized that it is retained even if vibrations or shaking movements are transmitted to the fleece by external influences. Their suppression is often extremely difficult in the process stage mentioned, although it must also be taken into account that the nonwovens under discussion here with a basis weight range of 10 to 50 g / m ² and a working width of more than 1 m are in many cases extremely sensitive to air vibrations react.

The printing processes used for the application of the adhesive and the binder basically belong to different types, which means that the two substances, which are intended to perform different tasks, can be applied in a favorable mutual coordination. It is also essential that at least one of the two opposing printing cylinders has soft-elastic properties that compensate for differences in thickness or elasticity of the printed nonwoven during the printing process to such an extent that a disturbance in the printed image generated is avoided.

The binder is applied using a high pressure, flat or gravure cylinder with a soft, elastic jacket made of rubber. In all three cases, the binder is pressed well into the interior of the nonwoven. The high-pressure process also combines the further advantage of a particularly high elasticity of the surface with a good protection against soiling compared to fiber components detaching from the surface of the printed nonwoven fabric.

In the case of high-pressure and planographic printing, the specific amount of binder applied can be continuously changed by adjusting the printing device used. If a corresponding change is required when using an intaglio printing process, the use of a correspondingly modified printing roller is necessary.

Modified printing rollers are still required if the size of the sub-areas is to be modified using the high, flat or gravure printing process. Such a modification can consist, for example, of an increase in the diameter if the aim is to prevent the adhesive from penetrating into the interior of the fixing insert when the fixing insert is ironed with an outer material having poor absorbency.

The adhesive can be printed on the nonwoven in dry form as a powder using the powder point method or in the form of a paste-like suspended powder using a screen printing method. With the powder dot process, it is not necessary to subsequently remove the carrier liquid required for the use of the screen printing process, as a result of which the specific energy consumption is lower. However, the amount of adhesive applied per unit area cannot be changed continuously by simply changing the angle of attack of the squeegee, as in the screen printing process, but a changed application roller is required. For the production of pronounced mass products with a constant, specific adhesive mass application, therefore, the use of the powder dot process lends itself, while the screen printing process is preferred for the production of lower production rates of fixing inserts with specific adhesive force.

In both cases, all relevant adhesive compositions can be processed, for example those based on polyolefin, polyurethanes, copolyamides or copolyesters. The melting point is generally in the range between 100 and 130 ° C. The particle size of the powder used must be relatively fine in order to enable adequate mutual pre-bonding using the excess energy from the UV crosslinking of the binder.

Good results are generally achieved if the maximum particle diameter is less than 0.2 mm in at least 95% of all cases in the powder dot process and less than 0.1 mm in at least 95% of the cases in the dispersion printing process.

The partial areas of binder and adhesive are printed with an overlapping center line in an identical surface pattern on the top and bottom of the nonwoven. They are relatively fine, and can have a mutual center-to-center distance of 1 mm, for example, with a diameter of 0.4 to 0.7 mm. In contrast, the fibers used for the production of such fixation inserts have a length of at least 25 mm, and their mutual association follows an irregular pattern. It is assumed that all parameters are involved if distortions of the fleece during the treatment in the printing unit could not be observed.

example 1

With the help of several carding devices standing in the longitudinal direction, a 25 g / m ² heavy nonwoven fabric made of 100% polyester fibers 1.7 dtex / 40 mm is produced at a speed of 60 m / min. The fleece is passed through a pair of rollers which are set against one another and heated to a surface temperature of 150 ° C., and is compacted in the process with a line pressure of 15 kp / cm. The fleece is then passed immediately through a printing device according to FIG. 1. The upper printing roller is a screen printing stencil 1 with a 25 mesh screen. The hole diameter is 0.45 mm, the template thickness is 0.19 mm. A squeegee 3 which is adjustable in the inclination to the vertical is arranged in the screen printing cylinder.

With this screen printing cylinder 1, an aqueous paste paste 2 is printed, which 40% by weight of a ternary copolyamide powder Contains laurolactam, caprolactam and AH salt (based on adipic acid-hexamethylene diamine) with a maximum particle diameter of 10 to 80 g and a melting point of 115 ° C and which is adjusted to a viscosity of 15,000 m Pas sec by adding an acrylate thickener with ammonia . The coating on the fleece 4 is 30 g / m ² when wet and 12 g / m ² after drying ^,

The lower pressure roller 5, i.e. the second roller from above is designed as a rubber high-pressure roller. The rubber is resistant to organic liquids and has a Shore A hardness of 65. The division of the high-pressure pattern is absolutely identical to that of the screen printing cylinder, while the diameter of the printing surfaces is 0.8 mm. The engraving depth is 0.4 mm.

The binder mixture described below is transferred from the tub preheated to 60 ° with prepolymers 6 via the rubber immersion roller 7 and the chrome-plated transfer roller 8, which is also heated to 60 ° C. and provided with a 60 mesh engraving, to the rubber high-pressure roller. The speed of the dipping roller 8 is set such that a pressure application of 2.5 g / m ² results from the high-pressure roller on the nonwoven.

The two pressure rollers are set in such a way that the center points of the partial surfaces printed on both sides lie congruently one above the other.

The binder mixture has the following composition.

After leaving the printing unit, the fleece is transported with the help of a metal carrying belt through a light lock into an exposure box, where it is passed through 2 rows of high-pressure mercury lamps with an output of 200 watts / cm - one row each from above and below . The binder cures instantly. The fleece leaves the exposure box through a second light lock and is then passed through a stenter frame of 15 m length, in which the adhesive is dried and sintered at a circulating air temperature of 115 ° C.

After the stenter frame, the material web is trimmed on both sides with the help of cutting units and divided in the middle, so that 2 webs of 90 cm wide, non-woven interlining can be rolled up.

The interlining nonwoven fabric obtained is very soft and drapable, excellent washable and dry-cleanable, and can be processed perfectly on all conventional fixing devices.

Example 2

• Hochgekräuselte Polyamidfaser 1,7 dtex/40 mm Schnittlänge 40 Tle.
• Hochgekräuselte Polyamidfaser 3,3 dtex/51 mm Schnittlänge 30 Tle.
• Polyesterfaser 1,6 dtex/40 mm Schnittlänge 30 Tle.

With the help of a number of carding machines, which are at right angles to the machine direction, and of transverse layers, a cross-laid fleece is placed on a slatted table. The basis weight of the nonwoven web running at this speed is 27 g / m ² , the web width 1-95 cm. The fiber mix consists of

• Crimped polyamide fiber 1.7 dtex / 40 mm cutting length 40 parts
• Crimped polyamide fiber 3.3 dtex / 51 mm cutting length 30 parts
• Polyester fiber 1.6 dtex / 40 mm cutting length 30 parts

The nonwoven fabric is passed through a pair of heated rollers as in Example 1. The surface temperature of the rollers is 190 ° C, the line pressure is 30 kp / cm, the peripheral speed is 25 m / min.

Immediately after passing the heated rollers, the fleece is passed through a printing device according to Figure 2.

The lower 3 rolls, including the prepolymer tub, are identical to those of Example 1, as are the composition of the prepolymer mixture and its temperature, and the roll heating of the transfer roll.

The top roller is designed as a powder point applicator roller 9. The print pattern is designed as a 25 mesh row dot. Its division is absolutely identical to the 25-mesh grid of the high-pressure rubber roller 5 underneath, the printing surfaces also having a diameter of 0.8 mm with a likewise circular design. The depth of engraving of the cells is 0.25 mm and their diameter is 0.40 mm.

The powder roller is heated to a surface temperature of 68 ° C. 15 g / m ^{2 of} a ternary copolyamide powder 10 with a maximum particle diameter of 1 to 20 μm and a melting range of 120 to 130 ° C. are thus applied.

3 g / m ^{2 of} the UV-curable prepolymer binder mixture described in Example 1 are applied from below using the high-pressure roller 5 made of rubber at the same time and to the same locations on the web. After leaving the printing unit, the web runs through the exposure box described in Example 1, the binder being cured and the adhesive compound surfaces being geometrically stabilized. The already slightly pre-glued adhesive mass points are finally sintered in a subsequent infrared field (radiator temperature 400 ° C). After passing through a cooling roller, as in Example 1, the web is cut into 2 webs, each 90 cm finished width, and rolled up.

The result is a particularly soft, multi-directional interlining fleece of high volume, good drapability, and excellent resistance to laundry and dry cleaning.

In both examples, the circular partial surfaces made of binder have a larger diameter than the partial surfaces made of adhesive. The adhesive which melts when the fixing inserts are thermofixed is thereby better prevented from penetrating into the fixing insert than if the partial surfaces lying one above the other have the same diameter. In addition to the regular area grids described, the partial areas can be applied in any other desired area grid, for example also in the frequently preferred scatter grid with statistical orientation. In addition to round training, any other desired shape is possible.

Claims (5)

1. A process for continuously consolidating a nonwoven and simultaneously coating it with a binder and with an adhesive composition, in which process the binder is synchronously counter-printed from one side against the adhesive composition, printed on from the other side, in the form of matching part-surfaces, the part-surfaces being spaced apart from one another, characterised in that a binder crosslinkable by ultraviolet radiation is printed onto the nonwoven from the underside by means of a relief-printing, planographic printing or gravure-printing cylinder having a soft, resilient rubber covering, that a thermoplastic adhesive composition ist printed onto the nonwoven from the upper face by the powder dot or screen printing process and that subsequently the nonwoven is irradiated with light which contains 10 to 30% of its total energy in the form of ultraviolet radiation, the total power being so chosen that the binder becomes crosslinked and the geometrical distribution of the adhesive composition becomes intrinsically stabilised, after which the nonwoven receives a final treatment by drying and/or sintering of the adhesive composition.

2. A process according to claim 1, characterised in that a mercury medium pressure or high pressure lamp with a power of 80 watt/cm is used to crosslink the binder and to stabilise the adhesive composition.

3. A process according to claim 1 or 2, characterised in that the screen printing or powder dot process employs an adhesive composition powder of which at least 95% has a maximum particle diameter of less than 0.1 mm or less than 0.2 mm, respectively.

4. A process according to any of claims 1 to 3, characterised in that the binder and the adhesive composition are printed onto the nonwoven in a regular or irregular surface grid.

5. A process according to any of claims 1 to 4, characterised in that the binder is printed onto the material in surface regions which overlap the surface regions covered by the adhesive composition.

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