Printed nonwoven web with microdot bonded pattern

Abstract

The present invention relates to a printed nonwoven web that includes a pattern of fused embossed bonds and that is printed on the web. The present invention further relates to a method of making such a nonwoven web and uses of such a nonwoven web.

Description

[Technical Field]

[0001] The present invention relates to a nonwoven web comprising a pattern of fused embossed bonds on at least one surface thereof and having printing applied to the same surface. The present invention further relates to a method of making such a nonwoven web and uses of such a nonwoven web. [Background technology]

[0002] In the hygiene industry, nonwoven webs are used extensively as materials for making products such as baby diapers or adult incontinence products. Webs comprising or consisting of spunbond nonwoven materials and bonded by calendar embossing have become the industry standard for many applications. Not only do these webs have desirable product properties, but they can also be produced economically on high-speed lines. Some applications require materials to be printed with text, graphic patterns, or images. Most typically, printing these materials is facilitated by flexographic ink printing, in which the nonwoven web is fed at high speed into a flexographic printing unit, where ink is transferred directly to the web surface from a printing roll. However, image quality is limited when ink printing calendered bonded nonwoven webs that contain a pattern of fused-embossed bonds on the printing surface because the bonds have a darker color and contrast than the rest of the fabric, causing the print to appear pixelated and uneven. Summary of the Invention

[0003] SUMMARY OF THE INVENTION An object of the present invention is to improve the image quality of printing on calender-bonded nonwoven webs without compromising production efficiency and economy. Against this background, the present invention provides a printed nonwoven web containing a pattern of fused embossed bonds, wherein the nonwoven web is ink printed on a surface exhibiting a pattern of bonds, the pattern of bonds satisfying the following conditions: (a) the number of bonds on the surface is 70 / cm 2 More than 75 / cm2 (b) The average area size of each individual junction is 1.5 mm 2 Smaller, preferably 1.35mm 2 and (c) the average center-to-center distance between bond points is less than 1.5 mm, preferably less than 1.3 mm. The bond pattern is preferably uniform across the entire surface of the fabric. This condition is representative of the use of more and smaller bonded points than was used in the prior art. Smaller bonded points result in a surface with a more uniform appearance. This is particularly advantageous for subsequent printing, as it makes the print appear more uniform. The reason is that if a portion of a printed design contains bonded points, that portion will appear a slightly different color than the unbonded printed surface due to differences in smoothness and opacity. Smaller bonded points and a denser bond pattern make this phenomenon less noticeable, resulting in a cleaner-looking printed design.

[0004] In one embodiment, the bond area, defined as the percentage of the total surface area occupied by the bond points, is less than 18%, preferably less than 15%, more preferably less than 12%, and even more preferably less than 11%. The smaller the overall bond area, the smaller the overall area with slightly different coloring. Therefore, a smaller overall bond area also contributes to improved print quality. Each printed nonwoven web can be produced by a process in which a nonwoven web is bonded by calendar embossing to form a nonwoven web containing on at least one surface thereof a pattern of fused embossed bond points that meet the above criteria, and the nonwoven web is ink printed on the surface that exhibits the pattern of bond points. Preferably, the ink printing is flexographic printing. In a flexographic printing unit, the nonwoven web typically passes over the surface of a print roll. The print roll includes a replaceable cylindrical sleeve folded around a core cylinder. The sleeve contains a mirrored master of the desired image as a 3D positive relief. Ink is transferred from an ink reservoir to the print roll from an anilox roll, which has surface cells for distributing the ink. A doctor blade scrapes off excess ink from outside the cells. The print roll contains a mirrored master of the desired image as a 3D positive relief.

[0005] Alternatively, the ink printing can be inkjet printing. This printing method may not offer the line speeds of flexography, but it is more flexible in terms of personalization and modification. Digital printing can be achieved with inkjet printing. The ink can be water-based or solvent-based, and the surface can be dried after application. Alternatively, the ink can be UV-curable, containing reactive monomers and / or oligomers, pigments, and photoinitiators, and the surface can be irradiated with UV light after application. UV-curable inks are advantageous in terms of improving adhesion and reducing VOC emissions. The bond pattern formed by the present invention can be manipulated over a wide range of printing resolutions. Specifically, the contact areas on the printing roller are typically dot-like, and the dots are arranged in lines. The line screen, expressed in lines per centimeter, is representative of the printing resolution. In one embodiment, the line screen may be between 15 L / cm and 50 L / cm. To obtain good printing quality, a printing resolution of greater than about 30 L / cm may be used.

[0006] In one embodiment, the nonwoven web is a spunbond or spunmelt nonwoven material. Preferably, the material is formed from polyolefin fibers. Suitable polyolefins include, for example, polypropylene (PP), polyethylene (PP), or copolymers including propylene or ethylene-based copolymers (co-PP; co-PE). Spunbond nonwoven materials can be further combined with the same or different spunbond (S) layers and / or meltblown (M) layers to obtain SS, SMS, or similar types of multilayer webs. During bonding, the material travels over the surface of a calender roll having embossing projections on its surface that meet the above criteria. In a preferred embodiment, bonding involves ultrasonic bonding, where ultrasonic vibrations are introduced into the embossing projections, fusing the fibers together by ultrasonic welding. In another embodiment, thermal bonding is used, where the embossing projections are heated, fusing the fibers together by thermal welding. For optimal production efficiency, the steps of the method, on the one hand, laying and bonding the fibers to form the nonwoven material, and on the other hand, printing on the nonwoven, are preferably carried out inline. Alternatively, for greater flexibility, an offline setup can be used in which a pre-manufactured nonwoven material is printed separately.

[0007] Generally, the line speed for forming and printing the nonwoven material, whether together in an in-line setting or separately in an off-line setting, is preferably at least 100 meters per minute, more preferably greater than 150 meters per minute, and even more preferably greater than 200 meters per minute. The printed nonwoven webs of the present invention can be used in hygiene products such as baby diapers, sanitary napkins, or adult incontinence products. Alternatively, the nonwoven webs can be used in medical applications such as gowns, face masks, care pads, or bed sheets. Additionally, the nonwovens can be used in household products such as wipes and cleaning towels. By reducing the distance between bonded points, the bond pattern becomes less noticeable, resulting in a print quality that is very close to that achievable with other nonwoven types that are bonded without bonded points, such as air-through carded ones. Because the bonded dots are so small, they do not interfere with print quality. At the same time, production efficiency and product quality remain high. Specifically, calendar-bonded nonwovens have superior physical properties to nonwovens bonded by other methods, such as air-through bonding. Further details and advantages of the invention will become apparent from the figures and examples described below. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic configuration of a production line for making printed nonwoven webs according to the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing the principle of flexographic ink printing. [Figure 3] FIG. 1 is a schematic diagram of a typical flexographic ink printing layout used for printing nonwoven fabrics. [Figure 4] FIG. 1 illustrates a bonding pattern used in the prior art. [Figure 5] 1A and 1B illustrate bonding patterns according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] An exemplary machine configuration for producing a printed nonwoven web 10 according to the present invention is shown in FIG. The configuration includes a conveyor belt and two spunbond machines 20, 22 arranged side by side on the conveyor belt. In each spunbond machine, molten thermoplastic polymer is extruded through holes in a die. The extruded fiber strands are then cooled and drawn / stretched to form endless fibers, which are then laid onto the conveyor belt or, in the case of a second lamination, onto a first web previously deposited on the conveyor belt. Each of the spunbond machines 20, 22 is equipped with a pair of precompression rollers 21, 23 for precompressing the respective web. The pre-compressed web is then bonded in bonding unit 25 by calender embossing, which involves running the fabric over the surface of a calender roll having a pattern of embossing protrusions on its surface. A heat or ultrasonic energy source introduces heat or ultrasonic energy into the protrusions, fusing the web at each location to provide a pattern of bond points corresponding to the pattern of protrusions on the calender roll surface. Following splicing, a printing process takes place in a printing unit 30, which will be described in more detail below. The product web is finally wound onto a product roll 40. 2 shows a flexographic printing unit 31 including a manifold for transferring ink onto the surface of anilox roll 34. The manifold contains an ink reservoir 32 and a doctor blade that acts as a retaining blade and a scraper blade. The surface of anilox roll 34 contains cells that allow the ink to be distributed appropriately to be transferred to print roll 36. The surface of print roll 36 contains a mirrored master of the desired image as a 3D positive relief. Print roll 36 transfers ink to nonwoven web 10 while counter-rotating impression cylinder 37 presses nonwoven web 10 against print roll 36.

[0010] As shown in Figure 3, multiple units 31 including a manifold 33, anvil roll 34 and print roll 36 are arranged around a common impression cylinder 37 for multicolor printing in printing unit 30. A drying or curing unit 38 follows in-line. Figure 4 shows a pattern of embossing projections on the surface of a calendar roll conventionally used to produce a common type of web. It includes oval embossing projections 26 of varying length d1 and width d2. The bond area is approximately 0.25 mm. 2 The distances a and b between the projections 26 are greater than 1.5 and greater than 2.5, respectively, and are set so that the number of projections per area is about 50 and the bonding area (meaning the proportion of the total surface area occupied by flat projection surfaces) is about 18%. Figure 5 shows a pattern according to the invention, which is symmetrical and includes circular embossing protrusions with a diameter d of 0.4 mm. The bond area is therefore approximately 0.125 mm 2 The pitch a (= b) between the junctions is 1.12 mm. As a result, the number of junctions per area is 80 / cm 2 , the total bonding area is 10%. [Example]

[0011] The examples compare the print quality of the microdot material of the present invention and a standard bonded nonwoven material. All tests were performed on the same 17 g / m 2 The test was carried out on a standard nonwoven material of polypropylene 3-layer spunbond (SSS). The comparative test samples were bonded using the bond pattern shown in Figure 4. The inventive test samples were bonded using the bond pattern shown in Figure 5. All samples were printed with the exact same print image using flexographic ink under the exact same conditions (screen, sleeve, ink used, printing machine, etc.). The measurement procedure was as follows: In the first step, identical sections of the print samples to be compared were glued onto white paper and scanned (resolution: at least 300 dpi) to create a PDF. Each PDF was then opened in Adobe Photoshop 2023, precisely adjusted to the area to be measured, and converted to grayscale. A gradation step was then applied to separate dark, uneven areas from uniform areas. After the gradation curve was applied, pixels were displayed as black. For this purpose, a certain sensitivity was set so that different luminance values ​​could be measured. The sensitivity setting was determined using an X-Rite Exact measuring device, using the L value of the darkest tone of the area to be measured. The default sensitivity value (input value) for an L value of 75 was 48. If the L value deviated from +1, the sensitivity value decreased by 2. If the L value deviated from -1, the sensitivity value increased by 2.

[0012] Finally, with the help of the histogram, we can read how many deviant black pixels there are in the printed area and compare the values ​​between the two types of materials. In all pressure ranges where the L value is below 85, the inventive material has less deviation than the comparative material. This was found for four different photographs P1 to P4, which are printing designs used in the absorbent hygiene industry. The results are shown in Table 1 below. [Table 1]

[0013] This was observed for a variety of different solid monochrome prints (rectangles), and the corresponding results are shown in Table 2 below. [Table 2]

[0014] [Table 3]

Claims

1. 1. Use of a printed nonwoven web for the manufacture of a hygiene product, the printed nonwoven web comprising a uniform pattern of fused embossed bond points across the entire surface of the fabric, the surface of the fabric having the pattern of bond points being ink-printed; The junction pattern must be: (a) The number of junctions on the surface is 70 / cm 2 It is super, (b) The average area size of each individual junction is 1.5 mm 2 Less than, and (c) the average center-to-center distance between the bond points is less than 1.5 mm; The above-mentioned use satisfies the above.

2. The number of junctions on the surface is 75 / cm 2 The use according to claim 1, wherein the

3. The average area size of each individual junction is 1.35 mm 2 The use according to claim 1, wherein the

4. 2. The use according to claim 1, wherein the bond area, defined as the percentage of the total surface area occupied by the bond points, is less than 12%.

5. The use according to any one of claims 1 to 4, wherein the hygiene product is a diaper.

6. 6. The use according to claim 5, wherein the web is a spunbond or spunmelt nonwoven web.

7. The use according to any one of claims 1 to 4, wherein the web is a spunbond nonwoven web or a spunmelt nonwoven web.

8. 1. A method for producing a printed nonwoven web, comprising: laying fibers and bonding them by calendar embossing to form a nonwoven web containing a pattern of fused-embossed bond points; and forming a nonwoven web having an ink-printed surface by flexographic printing that exhibits the pattern of bond points, wherein the steps of laying fibers and bonding to form a nonwoven material on the one hand and printing on the nonwoven material on the other hand are carried out in-line, wherein the line speed is at least 100 meters per minute; the pattern of bonds is uniform across the surface of the fabric; The junction pattern must be: (a) The number of junctions on the surface is 70 / cm 2 It is super, (b) The average area size of each individual junction is 1.5 mm 2 Less than, and (c) the average center-to-center distance between the bond points is less than 1.5 mm; The method as described above, wherein

9. The number of junctions on the surface is 75 / cm 2 The method of claim 8 , wherein the temperature is greater than 1000° C.

10. The average area size of each individual junction is 1.35 mm 2 The method of claim 8 , wherein the

11. 9. The method of claim 8, wherein the bond area, defined as the percentage of the total surface area occupied by the bond points, is less than 12%.

12. 9. The method of claim 8, wherein the line speed is at least 200 meters per minute.

13. The method of claim 8, wherein the line screen has a flow rate of 15 L / cm to 50 L / cm.

14. The method of any one of claims 8 to 13, wherein the web is a spunbond nonwoven web.

15. The method of any one of claims 8 to 13, wherein the calendar embossing comprises ultrasonic embossing.

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