Needling through carrier sheets to form loops

Needle punching the carrier sheet to form a loop

Technical field

The present invention relates to a method for manufacturing a loop product having a hook-and-loop fastener, and the product manufactured by the method.

Background technique

The contact fixture as a fixing system is particularly suitable for lightweight disposable clothing, such as diapers. In research to provide an economical loop material, there have been some recommendations other than weaving, such as needle punching of light-weight, fibrous nonwoven felt. Some of these needle felts are then drawn to achieve a lighter basis weight and cost-effectiveness, in which the ring structure is fixed by different bonding methods. For example, US6329016 introduces such a method.

Reducing fiber content can reduce costs, but it will also affect the overall performance or load-bearing capacity of ring materials, as well as the dimensional stability and processing efficiency of ring products. The choice of fiber material is often affected because the ring material needs to be weld-compatible with the base layer to which it is permanently connected (such as the outer layer of a diaper).

Summary of the invention

In various aspects, the present invention relates to a method of manufacturing a ring fastener article. The method includes placing a fiber layer on the first side of the carrier sheet, and then needle punching the fibers of the fiber layer through the carrier sheet by piercing the sheet with a needle. During the needle punching process, the needle penetrates the holes formed in the sheet to pull The pulling fiber part further includes forming a fiber loop protruding from the hole on the second side of the carrier sheet. The fiber on the first side of the pierced sheet has adhesive, and then the adhesive is melted onto the carrier sheet to fix the bottom of the ring.

According to one aspect of the present invention, a method of manufacturing a ring fastener article includes placing a fibrous layer on a first side of a film carrier sheet, the total density of the fibrous layer is less than about 5 ounces/square yard and the total back of the film is less than Approximately 0.005 inches. In the needle punching process, the film is pierced through the film by pulling the fiber part through the hole formed in the sheet, and then the fibers of the fibrous layer pass through the film and are formed from the hole on the second side of the carrier sheet. The stretched fibrous ring. The needling density is at least 100 punctures per square centimeter. There is adhesive on the fibers on the first side of the pierced film, and then the adhesive is melted onto the film to fix the bottom of the ring.

Preferably, the needling density is about at least 200 puncture holes per square centimeter, and particularly preferably at least 250 puncture holes per square centimeter. The needle is preferably bifurcated and is a 25-gauge needle or smaller diameter needle, particularly preferably a 35-gauge needle or smaller diameter needle. In various implementation examples, the needle pierces the carrier sheet to a distance between about 2 mm and 8 mm, preferably between about 3 mm and 4 mm, this distance being measured from the entry side of the sheet. It is generally preferred that the needle pierce the carrier sheet from its first side. In some implementation examples, the needling density and perforation distance can be selected so that the ring is formed with a textured pattern.

The fiber density is preferably less than about 3 ounces per square yard (100 grams per square meter), and particularly preferably less than about 1.5 ounces per square yard (66 grams per square meter). The fibers preferably have an average pull length of less than about 6 inches (15 cm), particularly preferably less than about 4 inches (10 cm), and the fibers preferably have a nominal strength of at least 3.0 g/denier. Preferred are fibers between about 2-10 denier, such as fibers between about 3-6 denier. In some cases, the fibers are crimped.

The film preferably has a total thickness of less than about 0.003 inches (0.08 mm), particularly preferably less than about 0.002 inches (0.05 mm), and sometimes about 0.001 inches (0.03 mm). In some examples, the film is pre-printed with graphics, which can be seen from the second side of the carrier sheet after melting.

In some cases, protrusions are formed on the film, and the protrusions extend from the general plane of the perforation of the film, and the protrusions carry the load against the fibers passing through the holes.

In some embodiments, the fibers are arranged on the support sheet of the front carded fiber layer. The fibers can also be overlapped to form a fiber layer.

In some embodiments, the fibers comprise polyester resin. In some other embodiments, the fibers may be selected from a group of materials including polyethylene, polypropylene, nylon, and their copolymers. Films can also be selected from the same set of copolymers. For some applications, the film is preferably a blown polyethylene film. In some embodiments, the fiber is a resin whose melting temperature is higher than the melting temperature of the resin of the film.

In some applications, the carrier sheet, fiber, and adhesive basically contain a single recyclable matrix resin or biodegradable material. For example, the carrier sheet, fiber, and adhesive basically contain polylactic acid to produce a biodegradable product or contain polypropylene to produce a recycled product.

In some applications, the method includes embossing the second side of the carrier sheet after melting to create the desired pattern on the ring. Such a pattern may include, for example, a raised layer of rings surrounded by areas of corrugated fibers.

In some applications, the adhesive is in powder form.

In some other cases, the adhesive includes a second thin film sheet. In some applications, the adhesive may be pre-printed with a graphic that can still be seen from the second side of the carrier sheet after melting. Preferably, the second film sheet contains a resin that is more likely to be compatible and welded with the carrier sheet resin than the fiber resin. Preferably, the total thickness of the second film sheet is less than about 0.003 inches (0.08 mm), particularly preferably less than about 0.002 inches (0.05 mm), and in some applications, less than 0.0005 inches (0.01 mm). In some embodiments, the second film sheet is preheated before being placed on the fibers.

In some applications, only selected areas of the carrier sheet are needle-punched, and other areas are not needle-punched, so that loops are formed only in selected areas. In some such applications, it is also possible to place more fibers in selected areas of the carrier sheet, and place fewer fibers in other areas of the carrier sheet. This method involves, in some applications, removing fibers from other areas after needle punching is complete. In some cases, the adhesive is only used in selected areas of the carrier sheet.

The total weight of the ring fastener including the carrier sheet, fibers and melted adhesive is preferably less than about 15 ounces per square yard (500 grams per square meter). In some applications, the total weight is less than about 10 ounces per square yard (330 grams per square meter), or even less than about 5 ounces per square yard (160 grams per square meter), or in some cases even less than about 2.5 ounces per square meter. Square yard (85 grams/square meter).

The total thickness of the fastener article including the carrier sheet, ring, and molten adhesive is preferably less than about 0.1 inches (2.5 mm). In some applications, the total thickness is less than about 0.05 inches (1.3 mm), or even less than about 0.025 inches (0.64 mm). Advantageously, the molten adhesive and the carrier sheet can together form a base sheet from which the ring extends. The total thickness of the base sheet is less than about 0.005 inches (0.13 mm), or preferably less than about 0.001 inches (0.03 mm). ).

In some applications, the carrier sheet includes a stretchable resin film. For example, the carrier sheet can be needled in a stretched state and then loosened to increase the ring density. In this case, the adhesive is the second sheet of stretchable resin film.

In some cases, the carrier sheet is excessively needle punched, which can sufficiently perforate the film, and the carrier sheet becomes swollen as a result. Thus, by using a stretchable material, such as a stretchable resin sheet, as an adhesive, a stretchable ring fastener product can be formed. In some applications, prior to melting, the material of the carrier sheet will generally form discrete areas separated by cracks extending between the through holes formed by the needled carrier sheet.

According to another aspect of the present invention, a method of manufacturing a ring fastener product, the method comprising placing a fiber layer on a first side of a carrier sheet. Then the fibers of the fibrous layer are needled through the carrier sheet by piercing the sheet with a needle. During the needle punching process, the needle pulls the fiber part through the holes formed in the sheet to form holes on the second side of the carrier sheet. Fibrous ring stretched from the middle. The fibers on the first side of the needle punched sheet are coated with an adhesive in the form of particles, and the particles of the adhesive enter the voids formed between adjacent fibers around the holes in the carrier sheet. The adhesive is then melted onto the carrier sheet to secure the bottom of the ring.

In some applications, the adhesive is a dry powder, preferably with a nominal particle size of less than about 20 microns. The adhesive should contain a resin that is sufficiently compatible with the carrier sheet to form a bond when melted.

In different embodiments, the adhesives all contain polyethylene powder, or are generally selected from a group of raw materials containing polyethylene, polyester, EVA, polypropylene and their copolymers and are in powder form.

When applied to light-weight clothing, the adhesive is applied to the puncture sheet with a coating density of less than about 2 ounces/square yard (66 grams/square meter), preferably less than about 1 ounce/square yard (33 grams/square meter) ), or even sometimes less than about 0.5 ounces per square yard (17 grams per square meter).

The adhesive basically contains loose particles, which may be irregular in shape or, for example, generally spherical. In some embodiments, the adhesive is in the form of a ground powder.

In some embodiments, melting the adhesive includes heating and pressurizing the first side of the pierced sheet. For example, it can be pressurized by a rotating roll or a flatbed laminator.

In some cases, the carrier sheet is a resin film, or a paper sheet or a non-woven, woven or knitted material.

According to another aspect of the present invention, a method of manufacturing a ring fastener includes placing a fiber layer on a first side of a carrier sheet. The second side of the carrier sheet rests on the support plate, and the fibers of the fiber layer are needled through the carrier sheet by piercing the sheet with a needle. During the needle punching process, the needle pulls the fiber part through the holes formed in the sheet. A fiber loop extending from the hole to the support plate is formed on the second side of the carrier sheet. The adhesive is coated on the fibers on the first side of the piercing sheet, and the ring extends into the support plate, and pressure is applied on the first side of the piercing sheet to melt the adhesive in the area where the carrier sheet is supported by the support plate.

In some embodiments, the support plate includes a bed of nails with the tops of the nails contacting the second side of the carrier sheet and the loop extending between adjacent nails. The density of nails is preferably at least about 150 nails/square inch (23 nails/square centimeter), particularly preferably at least about 250 nails/square inch (39 nails/square centimeter) or even 300 nails/square inch (47 nails/square centimeter) or More. Preferably, the nominal diameter of the nail is between about 0.005 and 0.015 inches (0.13 and 0.38 mm), and the length is at least about 0.1 inches (2.5 mm), which is longer than the piercing distance of the needled carrier sheet.

In some embodiments, the support plate is a screen that is in contact with the second side of the carrier sheet, and the ring passes through an aperture in the screen. The screen is preferably of wire. The metal wire preferably has a nominal diameter between about 0.02 and 0.03 inches (0.5 and 0.8 mm), and particularly preferably between about 0.023 and 0.028 inches (0.6 and 0.7 mm). The metal wire is preferably metallic and particularly preferably copper wire. The mesh openings preferably have a nominal width between about 0.05 and 0.2 inches (1.3 and 5.1 mm), and particularly preferably, the nominal width is between about 0.06 and 0.1 inches (1.5 and 2.5 mm).

In some embodiments, pressure is applied by placing a heated surface on the adhesive on the first side of the carrier sheet. The heating surface may be, for example, the peripheral surface of a rotating roller. The hot surface is preferably maintained at a sufficiently high temperature and pressed on the adhesive for a sufficient time so that the adhesive melts in the area supported by the support plate without significantly melting the fiber resin.

According to another aspect of the present invention, a method of manufacturing a ring fastener product includes placing a fiber layer on a first side of a carrier sheet. The fibers of the fibrous layer are needled through the carrier sheet by piercing the sheet with a needle. During the needle punching process, the needle pulls the fiber part through the holes formed in the sheet to form holes in the second side of the carrier sheet. Fibrous ring stretched out. The carrier sheet is needled to fully perforate the carrier sheet, and the carrier sheet becomes swollen. A stretchable material is placed on the fibers on the first side of the piercing sheet, and then this stretchable material is melted onto the carrier sheet to fix the bottom of the ring.

In some embodiments, the stretchable material includes a stretchable resin film.

In some examples, the carrier sheet includes a resin film, preferably the film thickness is less than about 0.003 inches (0.08 mm).

In some applications, prior to melting, the material of the carrier sheet will generally form discrete areas separated by cracks extending between the through holes formed by the needled carrier sheet.

Preferably, the needle punch density of the carrier sheet is at least 250 holes/cm². The diameter of the needle is preferably at least about 0.03 inches (0.75 mm), and the fiber density is preferably less than about 2 ounces per square yard (66 grams per square meter).

According to another aspect of the present invention, a method of manufacturing a ring fastener product includes placing a fiber layer on a first side of a carrier sheet. The fiber is between about 2 and 10 denier. The fibers of the fibrous layer are needled through the carrier sheet by piercing the sheet with a needle. During the needle punching process, the needle pulls the fiber part through the holes formed in the sheet to form holes in the second side of the carrier sheet. Fibrous ring stretched out. The maximum distance of the needle punch is less than about 7.0 mm from the first side of the carrier sheet, and the diameter of the needle is less than about 0.036 inches (0.9 mm). The adhesive is coated on the fibers on the first side of the piercing sheet, and then melted onto the carrier sheet to fix the bottom of the ring.

Preferably, the needle punch density of the carrier sheet is at least 200 holes/cm². The fiber density is preferably less than about 3 ounces per square yard (100 grams per square meter), and particularly preferably less than about 1.5 ounces per square yard (66 grams per square meter). The carrier sheet preferably has a nominal thickness of less than about 0.003 inches (0.08 mm), or even less than about 0.002 inches (0.05 mm). The nominal strength of the fiber is preferably at least 3.0 g/denier, and the fineness is between about 3 and 6 denier.

In some embodiments, the carrier sheet comprises a polymer film. Ideally, protrusions are formed on the film, the protrusions protruding from the general plane of the hole in the film, and the protrusions carry the load against the fibers passing through the holes. The film can be, for example, a blown polyethylene film.

Preferably, the fiber is a resin having a melting temperature higher than that of the film resin. The fiber may comprise polyester resin, or may be selected from a group of materials including polyethylene, polypropylene, nylon, and copolymers thereof.

Preferably, the maximum distance of needling is between about 3 and 4 mm from the first side of the carrier sheet.

In some preferred applications, the adhesive consists of a thin film sheet. Advantageously, the adhesive can be pre-printed with graphics, which can still be seen from the second side of the carrier sheet after melting. Preferably, the film sheet contains a resin that is more compatible with the carrier sheet resin than fiber resin and has a total thickness of less than about 0.003 inches (0.08 mm), or even less than about 0.002 inches (0.05 mm). In some cases, the method includes preheating the film sheet before applying the adhesive to the fibers.

The total weight of the ring fastener product including the carrier sheet, fibers and melted adhesive is preferably less than about 15 ounces per square yard (500 grams per square meter). The total thickness of the fastener article including the carrier sheet, ring and molten adhesive is preferably less than about 0.1 inches (2.5 mm). In some examples, the melted adhesive and the carrier sheet together form a base sheet from which the ring extends. The total thickness of the base sheet is less than about 0.005 inches (0.13 mm).

According to another aspect of the present invention, a method for generating hookable loops in selected areas on a carrier sheet, the method comprising placing a fiber layer on the first side of the carrier sheet. The fibers of the fiber layer are needled through the selected area of the carrier sheet by piercing the sheet with a needle. In the needle punching process, the needle pulls the fiber part through the holes formed in the selected area of the sheet on the second side of the carrier sheet. A fibrous ring protruding from the hole is formed. Coating the adhesive on the fibers of the selected area on the first side of the piercing sheet, and then melting the adhesive on the carrier sheet to fix the bottom of the ring.

Preferably, the total thickness of the adhesive is less than about 0.003 inches (0.08 mm). The needle punch density of the carrier sheet is preferably at least 200 holes/cm². The fiber density is preferably less than about 3 ounces per square yard (100 grams per square meter). The nominal thickness of the carrier sheet is preferably less than about 0.003 inches (0.08 mm), or even less than about 0.002 inches (0.05 mm). The fibers preferably have a nominal strength of at least 3.0 g/denier and a fineness between about 3 and 6 denier.

In some embodiments, the adhesive is a water-impermeable sheet that covers the fibers and holes to form a barrier to prevent liquid from flowing through the holes formed in the carrier sheet due to needle punching. In some cases, the water-repellent sheet is a discrete sheet part that is placed in selected areas, while other areas are not covered with this adhesive.

In some cases, the adhesive is pre-printed with graphics, and the graphics can still be seen from the second side of the carrier sheet after melting.

In some applications, the adhesive is a dry powder or in a liquid state.

In some examples, the second side of the carrier sheet is placed on the support plate and is needled, and the adhesive is coated on the carrier sheet while the ring protrudes from the hole and enters the support plate.

Some embodiments include, after melting, the carrier sheet is cut to form dispersed sheet products, each sheet product having at least one area with loops and another area without loops. In some embodiments, the dispersed sheet portions form the outer layer of disposable clothing such as diapers, and the looped area is used to releasably hook the convex contact fastener element to secure the clothing to the wearer.

In some embodiments, the carrier sheet includes a polymer film. The film is preferably formed with protrusions that protrude from the general plane of the hole in the film and carry the load against the fibers passing through the hole.

The total weight of the ring fastener product including the carrier sheet, fibers and melted adhesive is preferably less than about 15 ounces per square yard (500 grams per square meter). The total thickness of the fastener article including the carrier sheet, ring and molten adhesive is preferably less than about 0.1 inches (2.5 mm). In some embodiments, the melted adhesive and the carrier sheet together form a base sheet from which the ring extends. The total thickness of the base sheet is less than about 0.005 inches (0.13 mm).

According to another aspect of the present invention, the ring fastener product has a fiber layer, a film carrier sheet and an adhesive. The fiber layer is located on the first side of the film carrier sheet and has a total density of less than about 5 ounces per square yard. The total thickness of the film is less than about 0.005 inches (0.1 mm) and contains at least 100 holes per square centimeter. The fiber ring protrudes from the through hole on the second side of the carrier sheet. The adhesive is located on the fiber on the first side of the piercing film, wherein the adhesive is melted onto the film to fix the bottom of the ring.

The fiber density is preferably less than about 3 ounces per square yard (100 grams per square meter), and particularly preferably less than about 1.5 ounces per square yard (66 grams per square meter). The fibers preferably have an average pull length of less than about 6 inches (15 cm), particularly preferably less than about 4 inches (10 cm), and the fibers preferably have a nominal strength of at least 3.0 g/denier. Preferred are fibers between about 2-10 denier, such as fibers between about 3-6 denier. In some cases, the fibers are crimped. In some cases, the fibers are combed and overlapped to form a fiber layer.

The film preferably has a nominal thickness of less than about 0.003 inches (0.08 mm), particularly preferably less than about 0.002 inches (0.05 mm), or even particularly preferably less than about 0.001 inches (0.03 mm). Preferably, there are at least 200 perforations per square centimeter in the film, particularly preferably at least 250 perforations per square centimeter. In some examples, the film is pre-printed with graphics, which can still be seen from the second side of the carrier sheet after melting.

In some cases, protrusions are formed on the film, and the protrusions extend from the general plane of the holes in the film, and the protrusions carry the load against the fibers passing through the holes.

Measured from the first side of the sheet, the ring preferably extends between 2-8 mm. Especially preferably, the ring extends between 3-4 mm. The loop extension distance and perforation density can be selected to form a textured pattern of loops on the loop.

In some embodiments, the fibers comprise polyester resin. In some other cases, the fiber is selected from a group of materials including polyethylene, polypropylene, nylon, and their copolymers. Films can also be selected from the same set of copolymers. For some applications, the film is preferably a blown polyethylene film. In some examples, the fiber is a resin whose melting temperature is higher than the melting temperature of the resin of the film.

In some embodiments, the carrier sheet, fiber, and adhesive substantially all contain a single recyclable matrix resin or biodegradable material. For example, the carrier sheet, fiber, and adhesive basically contain polylactic acid that can form biodegradable products or polypropylene that can form recycled products.

In some examples, embossing is performed on the second side of the carrier sheet to create the desired pattern on the ring. Such patterns include, for example, raised layers of rings surrounded by areas of creped fibers.

In some embodiments, the adhesive is in powder form.

In other cases, the adhesive includes a second thin film sheet. The adhesive can be pre-printed with graphics, and the graphics can still be seen from the second side of the carrier sheet after melting. Preferably, the second film sheet contains a resin that is more likely to be compatible and welded with the carrier sheet resin than the fiber resin. Preferably, the total thickness of the second film sheet is less than about 0.003 inches (0.08 mm). In some examples, the second film sheet is preheated before being placed on the fibers.

In some applications, the carrier sheet only has perforations in selected areas, and there are no perforations in other areas, so that loops are formed only in selected areas. In some such applications, it is also possible to place more fibers in selected areas of the film carrier sheet, and place fewer fibers in other areas of the film carrier sheet. In some cases, the adhesive is only used in selected areas of the carrier sheet.

The total weight of the ring fastener product including the carrier sheet, fibers and melted adhesive is preferably less than about 15 ounces per square yard (500 grams per square meter). In some applications, the total weight is less than about 10 ounces per square yard (330 grams per square meter), or even less than about 5 ounces per square yard (160 grams per square meter).

The total thickness of the fastener article including the carrier sheet, ring, and molten adhesive is preferably less than about 0.1 inches (2.5 mm). In some applications, the total thickness is less than about 0.05 inches (1.3 mm), or even less than about 0.025 inches (0.64 mm). Advantageously, the molten adhesive and the carrier sheet can together form a base sheet from which the ring extends. The total thickness of the base sheet is less than about 0.005 inches (0.13 mm), or preferably less than about 0.001 inches (0.03 mm). ).

In some applications, the carrier sheet includes a stretchable resin film. For example, the carrier sheet can be needled in a stretched state and then loosened to increase the ring density. In some such cases, the adhesive is a second sheet of stretchable resin film.

In some cases, the carrier sheet is excessively needle punched, which can sufficiently perforate the film, and the carrier sheet becomes swollen as a result. Thus, by using a stretchable material, such as a stretchable resin film, as an adhesive, a stretchable ring fastener product can be formed. In some applications, the material of the carrier sheet will generally form discrete areas separated by slits extending between the through holes formed by the needled carrier sheet. Some other aspects of the present invention are reflected in products, including ring products, rollers with ring materials, and single-piece clothing with rings, all of which are produced by the method described above. Other aspects are reflected by the equipment that implements the method described above, and reflected in a continuous method or a series of methods.

The present invention provides a ring material that can withstand special cutting and peel loads due to its weight and cost, especially when it is used in conjunction with an appropriately sized male fastener element. Because the tensile strength of the fastener product matrix is at least partially derived from the carrier sheet (or, when the adhesive is a sheet product, from the adhesive sheet), only enough fibers to produce a fixed loop structure are required , Reducing the demand for high-strength fibers. The adhesive can be selected from materials that do not need to be compatible and welded with the fiber material, because the ring structure can be fixed by directly melting the adhesive on the carrier sheet, and the adhesive can be directly melted on the carrier sheet to seal the fiber and the mechanical fixing ring. The bottom of the structure. Because of their fastening properties, fiber materials are preferred, and adhesives can be selected to be compatible with the base layer in specific applications.

The loop material provided by the present invention has very low unit weight, total weight and thickness of fibers, and is particularly suitable for low-cycle disposable clothing and applications.

The use of powdered or other loose granular adhesives can reduce the total weight of the adhesive used to fix the ring structure, because the adhesive can penetrate between the fibers and enter the ring structure near the hole of the carrier sheet before melting The matrix area. The vibration of the powder fiber before melting contributes to this penetration.

The present invention provides an economical method capable of producing hookable loops on a carrier sheet without loops by selective needle punching. In certain applications, such a carrier sheet can then be processed into the base layer, such as into the outer membrane of a disposable diaper. This omits the step of bonding the ring material and the base layer when producing such a product, and part of the ring material becomes the base layer.

From all aspects, the present invention can provide an economical stretchable ring product.

The detailed description of one or more embodiments of the present invention will be made in the following specification in conjunction with the accompanying drawings. Through the description, drawings and claims, other features, purposes and beneficial effects of the present invention will become apparent.

Description of the drawings

Figure 1 shows the process of forming a loop on the carrier web by needle punching and bonding.

Figures 2A-2D sequentially show the needle piercing the fiber through the carrier film supported by the nail.

Figures 3A-3D sequentially show the needle passing through the piercing fibers of the carrier film supported by the screen.

Figure 4 shows a needle punched film spot pressed with a backing material.

Figure 5 shows a modified puncture process using a powder adhesive instead of the backing sheet.

Figure 6 is an enlarged view showing the powder binder between the fibers of the carrier web.

Fig. 7 is an enlarged view of the ring structure.

Figure 8 shows the structure of the finished ring article.

Figure 9 is a perspective view of an embossed ring surface.

Figure 10 is a top view of the apparatus and process of forming a loop through a stretchable carrier web.

Fig. 11 is an enlarged perspective view of a ring product formed by needle punching a carrier film to separate the film.

Figure 12 shows the process of forming a loop only in the dispersed area of the carrier web.

Figure 13 is a top view of a sheet product formed by the process shown in Figure 12, from which a single diaper face can be die-cut.

Fig. 14 is a perspective view of a disposable diaper having a diaper surface cut from the article shown in Fig. 13.

Fig. 15 is a perspective view of the process of applying the dispersed substrate sheet to the needle punched area of the carrier web.

Figure 16 shows the needling and bonding process using a flatbed laminator.

Similar reference signs in different drawings refer to similar elements.

detailed description

First, according to Fig. 1, when the film sheet 14 is continuously unwound from the spool 16, the carded layer 10 of fibers 12 is placed on top of it. The fiber 12 and film 14 are then fed to the needling station 18, where the film is pierced from the fiber side. The needle is guided through the template 19 above the fiber and pulls the fiber through the film to form a loop on the back of the film. During the acupuncture process, the film is supported on the nail bed 20, which extends from the driving support belt 22. The driving support belt 22 can move with the film through the acupuncture station. The film is supported on the screen or by the standard lower pallet (Not shown) support. The stationary reaction plate 24 located under the belt 22 provides the reaction pressure during the acupuncture process. After the needling is completed, the film is still on the nail bed 20, the substrate film 26 is placed on the fiber side of the film 14 and the two film sheets are bonded together under the pressure of the heating roller 28 toward the nails 20. After bonding, the finished ring product 30 is wound on the bobbin 32.

We have found that relatively fine fibers 12 can be used to form useful loop products as above. In this embodiment, the unit weight of the fiber layer 10 is only about 1.0 ounce/square yard (33 grams/square meter). Fiber 12 is a stretched and crimped polyester fiber, 3-6 denier, about 3 feet (7.5 cm) of tugged length. It has been found that fibers with a strength of at least 2.8 g/denier have good closure properties. In many applications, fibers with a strength of at least 5 g/denier or higher (preferably even 8 g/denier or higher) are particularly preferred. high). For the usual case of loop-limited closures, the higher the ring strength, the stronger the closure performance. The fibers of the fiber layer 10 are in a stretched, molecularly oriented state, and have been drawn at a stretch rate of at least 2:1 (that is, at least twice their original length) in a cooling state where molecular orientation can occur, So that the fiber strength reaches about 4.8 g/denier. The fiber in this example has a circular cross-section and is crimped, and the crimp rate is 7.5 crimps/inch (3 crimps/cm). It is available under the trade name T-3367PET-794W from EI Du Pont de Nemours & Co., Wilmington, Delaware, USA 6×4 fibers. When choosing the denier of the looped fiber, the size of the hook should be considered. Generally, a fiber with a lower denier and a smaller hook should be selected. For applications where larger hooks (thus larger diameter loop-forming fibers are preferred) and low circulation, low strength fibers or larger diameter fibers can be used. As an alternative to the circular cross-section fiber, the fiber has a slope, for example, a pentagonal or pentagonal cross-section fiber with other cross-sectional shapes can facilitate knot formation during the needling process.

Various synthetic or natural fibers can be used. In some embodiments, wool and cotton fibers can also have sufficient fiber length. At present, it is preferred to use thermoplastic staple fibers with sufficient strength to make thin, low-cost loop products that have good closing properties when paired with small molded hooks. For example, polyolefin (for example, polypropylene or polyethylene), polyester (for example, polyethylene terephthalate), polyamide (for example, nylon), acrylic acid and mixtures thereof, alloys, copolymers Co-extrudates with them are suitable. Polyesters are currently preferred. A small proportion of metal fibers can be added to products with a certain degree of conductivity. For example, a ring product with about 5-10% of fine metal fiber can be used effectively, such as grounding or other electronic applications.

The fiber layer 10 may be cross-overlaid before being stacked with the film 14. In this case, a carding machine (not shown) combs the short fibers to produce a web of fibers 12, which is then taken up by a pulling conveyor belt of a cross-winder (not shown). The cross winder has a winding conveyor capable of reciprocating a horizontal conveyor belt. The cross winder spreads the carded fiber web flat on a horizontal conveyor belt, for example, about 60 inches (1.5 meters) wide and about 1 inch (2.5 cm) thick, and crosses multiple layers of the fiber web (criss-crossed). The web) is laminated to form a fiber layer, for example, about 90-120 inches (2.3-3.0 meters) wide and about 4 inches (10 cm) thick. In the carding process, these fiber webs are stretched and carded into a cloth-like fiber layer containing mainly parallel fibers. When almost all the fibers are stretched in the carding direction, the fiber layer has a certain strength when stretched in the carding direction, but there is almost no strength when stretched in the direction crossing the carding direction, because the strength in the cross direction only comes from the fiber. A little tangles between. In the cross-overlapping process, the combed fiber layer is placed in a zigzag-shaped flower shape that is folded to form a fiber layer 10 with multiple layers of interlaced diagonal fibers. The oblique layer, which stretches in the direction of the cross overlap, crosses the conveyor belt more often than it is stretched along it. For example, fibers have been used to overlap and overlap to form fiber layers, such fiber layers extend about 6-18 degrees from the transverse direction of the finished product at any location. Material properties and production processes are affected by the angle of intersection. In preparation for needling, the fibrous layer 10 is gradually compressed in a tapered clamp between a horizontal conveyor belt (not shown) and a moving top conveyor belt (not shown), and the thickness is reduced to about 1 inch. As a result, relatively thin, low-density fiber layers can be produced.

In this embodiment, the fiber layer 10 is placed on a blown polyethylene film 14 to make bags and other packaging products. The thickness of the film 14 is approximately 0.002 inches (0.05 mm). Even thinner films can be used with good results. For some special applications, other carrier mesh materials can be used instead of the film 14. For example, the fibers can be pierced into a paper feed sheet or a sheet of lightweight cotton fiber.

In this embodiment, the needle punching station 18 needle punches the fiber-covered film 14 with a total needle punch density of approximately 250 holes/cm 2. Under this needle density and this film thickness, in order not to damage the film, it was found that small 38-gauge fork tufting needles are sufficient, and the remaining film is sufficiently interconnected, and the film can still exhibit a certain size in its plane. stability. Under the same parameters, the larger 30-gauge needle can split the film into small, discrete pieces entangled between the fibers.

Figures 2A-2D sequentially show the process of forming a ring structure by needle punching. The forked needle pierces the fiber layer 10 (FIG. 2A), and some individual fibers 12 will be trapped into the hole 36 in the forked end of the needle. When the needle 34 pierces the film 14 (FIG. 2B), the capture fibers 12 are pulled by the needle through the hole 38 formed in the film and into the other side of the film. As shown in the figure, the film 14 is supported on the nail 20 during this process, and the pierced needle 34 enters the space between adjacent nails. Alternatively, the film 14 may be supported on a screen or a lower support plate (not shown) formed with holes matching the needles. As the needle 34 continues to penetrate (FIG. 2C), pressure is applied to the capture fiber to pull the fiber layer 10 downward against the film 14. In this embodiment, the total penetration depth Dp is approximately 3.5 mm. This distance is measured from the entrance surface of the film 14 and can form a good loop structure without excessively stretching the fibers on the fiber layer. Excessive piercing depth can draw loop fibers from the early formed tufts, resulting in the formation of sparse loop areas. A penetration depth of 2-5 mm can also be used in this embodiment, although a penetration depth of 3.5 mm is currently preferred. When the needle 34 retreats (FIG. 2D), a part of the capture fiber 12 reaching the back side of the carrier web remains in the form of a plurality of individual loops 40 from a common total fiber bundle (trunk) trapped in the film hole 38 42 stretched out. As shown in the figure, the residual stress around the holes of the membrane 14 strives to restore the membrane to a flat state, exerting a small pressure on the fibers in the holes, thereby helping to secure the bottom of the ring structure. The film can also help resist the tension exerted on the fibers on the fiber side of the film, which tension attempts to pull the loop back into the hole. In order to match the size of the protruding fasteners commonly used on disposable clothes and similar clothes, the final ring structure preferably has a total height HL of about 0.040-0.060 inches (1.0-1.5 mm).

Referring again to FIG. 1, in some embodiments, a wire mesh is used instead of the nail bed 20 and the drive support belt 22 for a similar loop forming process. Figures 3A-3D sequentially show the process of needle-punching fibers through a carrier film supported on a screen instead of a nail bed. In these cross sections, two of the wire 35 containing the screen represent the screen. The screen is formed with holes between the wires 35, and when the fibers 12 are drawn through the membrane 14, the needles 34 pass through these holes. Suitable screens can be made from materials including bronze, copper, brass, and stainless steel. It has been found that a brass wire screen with a nominal diameter WD between about 0.02 and 0.03 inches (0.5 mm and 0.8 mm) or preferably between about 0.023 and 0.028 inches (0.6 mm and 0.7 mm) will not be bent too much. bouncy. The nominal width SW of the holes on the screen is between about 0.05 and 0.2 inches (1.3 and 5.1 mm), or preferably between about 0.06 and 0.1 inches (1.5 and 2.5 mm), to achieve this. Such screens are available from McMaster-Carr Supply Company of Elmburst, Illinois, under the trade name 9223T41.

4, in this embodiment, the backing film 26 is a continuous polypropylene sheet, only about 0.001 inches (0.025 mm) thick. The backing sheet 26 is preferably welded compatible with the carrier web (that is, the film 14), but does not have to be compatible with the material of the fiber 12. For example, a high-strength fiber material can be selected as a resin whose melting temperature is higher than either of the two films. After the hot rolling, the front and back films and the top dispersion point 42 of the nail 20 are permanently connected together. When the screen is used as a support plate, the front and rear films are permanently connected together in the form of a cross-hatched grid instead of scattered points. This grid reflects the structure of the screen. Whether the weld seams are scattered points or interconnected lattices can also be used to fix the fibers 12 sandwiched between the films to help strengthen the ring structure. When the ring structure is safely placed between the nails 20, the bonding of the two films is started so that no pressure is used to disperse the ring during the bonding process.

1 again, in this embodiment, the temperature of the surface of the roller 28 is maintained between about 350 and 400 degrees Fahrenheit (177-266 degrees Celsius), and about 50 pounds per square inch is applied between the roller and the substrate film. (3.5 kg/cm²) pressure for about 5 seconds, a suitable bonding effect will be obtained. The roller 28 has an adaptable outer surface, or a belt-like form. As an alternative to heating rollers, a flat fabric laminator can be used to apply a controlled layer pressure for a considerable period of time. Such a flatbed laminator is available from Glenro Company of Paterson, New Jersey, USA. Any layer of film can be preheated if necessary. For example, the infrared heater 44 may be used to heat the substrate film before pressing. In some embodiments, the finished ring product 30 passes through a cooler (not shown) before being wound.

The nails 20 on the nail bed 22 are arranged in rows and columns. The density of the nails is about 280 nails/square inch (45 nails/square centimeter), preferably between about 200-300 nails/square inch (31-47 nails/square inch). cm). Each nail 20 is approximately 0.010 inches (0.25 mm) in diameter and approximately 0.25 inches long (6.4 mm), preferably straight so as to be able to withstand the pressure required to laminate the backing material to the carrier web. In most embodiments, it is preferred that the nails do not penetrate the film 14 during the bonding process, but each nail can provide sufficient support to form a reinforced bond point between the layers. A series of rigid pin cards can be used instead of the continuous soft band shown. In discontinuous product production methods, for example, in order to prepare a dispersion sheet of ring material, a piece of film 14 and a piece of fiber layer 12 can be laminated on a single card clothing such as a carding machine fiber web, so as to perform on the card clothing. Remove the previous needling and subsequent bonding.

Referring to FIG. 5, in another embodiment, the powder adhesive 46 is deposited on the fiber side of the needled film, and then melted onto the film by a roller 28 or a flatbed laminator. For example, polyethylene powder with a nominal particle size of about 20 microns can be sprinkled on the fiber layer of the polyethylene film, with a sprinkling density of only about 0.5 ounces/square yard (17 g/square meter). Such particles are either round, irregularly shaped or approximately spherical as disclosed in Equistar Chemicals LP of Houston, Texas. Preferably, the powder shape and particle size are selected so that the powder penetrates into the voids between the fibers and contacts the underlying film, as shown in the enlarged graph in FIG. 6. In many applications, it is also preferred that the powder is a material whose melting temperature is lower than that of the ring fiber, so that the fiber remains substantially intact during the melting process and the powder binder is melted onto the fiber or carrier web. In either case, the powder mechanically bonds the fibers to the membrane near the support pins and secures the ring structure. If the amount is sufficient, the powder 46 can also form at least part of the reinforcement of the finished ring product in order to permanently bond the ring material to a compatible base layer. Because different powders can be mixed, other powder materials, such as polypropylene or EVA resin, can be used for this purpose by using a suitable carrier mesh material.

FIG. 7 is an enlarged view of the ring structure 48, which includes a multi-layer ring 40 extending from a common trunk 43 passing through the holes of the film 14, which is formed by the method described above. As shown in the figure, the loop 40 protrudes from the film below to mate with the hooked products. This fit is at least partly due to the longitudinal stiffness of the fiber bundles 43 in each product, which passes through the holes in the film material. It is achieved by shrinking and fixing the fibers between the film and the liner. This vertical rigidity is used to resist the continuous crushing or flattening of the ring structure. This crushing or flattening occurs when the ring material is wound or when the finished product of the ring material is later added to the extrusion packaging. . The elasticity of the fiber bundle 43, especially the elasticity at its junction with the substrate, causes the structure 48 that is overwhelmed by the heavy backlog load to straighten itself when the load is removed. As can be seen from this figure, the different loops 40 of the structure 48 protrude upward from the film to different heights, which is believed to improve the performance of the fixture. Because each structure 48 is formed at the puncture site of the film 14 during the needling process, the density and position of the individual structures can be easily controlled. Preferably, there is a sufficient distance between adjacent structures so that the mating protruding fixing member (not shown) can be easily inserted into the ring structure area.

Referring to FIG. 8, the front carrier web 14, which forms part of the fiber 12 of the loop, and the substrate 26 together form a stable bottom plate 50 from which the loop structure 48 extends. Because of the lower fiber content in the bottom plate and the thinness of the front and back layers, the thickness tm of the bottom plate 50 is only about 0.008 inches (1.2 mm) or less, preferably less than about 0.005 inches, and even as low as about 0.001 inches in some cases (0.025 mm). The thickness tf of the front carrier film 14 is less than about 0.003 inches (0.08 mm), preferably less than about 0.002 inches (0.05 mm) and even particularly preferably less than about 0.001 inches (0.025 mm). The thickness tb of the backing film 14 is less than about 0.003 inches (0.08 mm), preferably less than about 0.002 inches (0.05 mm) and even particularly preferably less than about 0.0005 inches (0.01 mm). The total thickness T of the finished ring article 30 is less than about 0.1 inches (2.5 mm), preferably less than about 0.05 inches (1.25 mm), and in some cases less than about 0.025 inches (0.6 mm). The total weight of the ring fastener article including the carrier sheet, fibers and melted adhesive is preferably less than about 15 ounces per square yard (500 grams per square meter). In some applications, the total weight is less than about 10 ounces per square yard (330 grams per square meter), or even less than about 5 ounces per square yard (167 grams per square meter), or in some cases, even less than about 2.5 Ounces per square yard (85 grams per square meter).

If the backing material 26 is chosen to be liquid impermeable, the entire ring article 30 can be formed as a liquid barrier. If the fiber 12 is selected as an absorbent fiber, such as cotton fiber or cellulose acetate, the final ring product can wick liquid into the bottom plate through the exposed ring 40.

The use of a transparent film 14 as the front carrier web allows the image 52 to be pre-printed onto the back substrate layer so as to be visible from the ring side of the finished ring article. The small bonding points 42 between the film layers and the low density of fibers in the bottom plate have not been found to significantly reduce the visibility of the image. This is very useful, for example, it can be used in the ring material of children's products (such as disposable diapers). In this case, a child's favorite image can be printed on the ring material, and it can be permanently bonded to the front side of the diaper chassis to form the joining area of the diaper tabs. The image can also be pre-printed on any surface of the carrier film 14.

1, in some cases, the ring side of the bonded ring product is embossed with a desired embossing pattern before winding. In this embodiment, the ring product passes through a nip between the drive embossing roller 54 and the backup roller 56. The embossing roller has a pattern of raised areas, which can continuously squeeze the ring structure in the direction of the film and can even melt a part of the fiber in these areas. The raised print can only be used to improve the organizational structure or aesthetic requirements of the final product.

Figure 9 shows the finished ring product 30, viewed from the ring side, which has been embossed and printed with a honeycomb pattern 58. In this implementation, the image 52 printed on the adjacent side of the back substrate layer can be clearly seen through the laminated material. Various other embossing patterns include, for example, a square or diamond grid formed by intersecting lines, or a pattern in which a ring structure is extruded rather than in a dispersed area of a desired shape, such as a circular padding of a ring. The embossing pattern can also squeeze the ring to form a desired pattern or text on the ring material.

In some embodiments, the fibers are pierced into the stretchable carrier web. Referring to FIG. 10, the transversely stretched film web 14 is wound on a cloth spreader 60, and the cloth spreader 60 transversely stretches the film web to at least about 110% of its original width. The fiber 12 is then placed on a stretched web, and the web covered by the fiber is then needled before it returns to its original width. In this embodiment, the liquid adhesive is sprayed by the sprayer 62 onto the relaxed net. The adhesive is then curled by the ultraviolet light source 64 before winding. Elastic adhesives can be used to provide stretchable finished ring materials. Alternatively, the adhesive can be applied and curled while the web is in a stretched state, so that the finished material can be folded after the web is relaxed. By needle punching the net 14 when it is in a stretched state, the net will in some cases provide greater shrinkage of the loop structure of the fiber bundle. Moreover, the density of the ring structure of the final product is greater than the needle punch density.

1, in some cases, the needling parameters (such as needle size, needling density) can be selected so that the carrier web 14 is actually decomposed during the needling process. However, we have found that this is not necessary for some applications, and such a structure is beneficial for other applications. For example, in one case, a 0.002 inch (0.05 mm) polyethylene film covered with fibers is needled with a 30 gauge fork needle, with a perforation density of 250 holes/cm2, which will form the structure shown in Figure 11. In the structure, the fibers 12 themselves truly form the only communication in the needled sheet. The film 66 maintains the form of a dispersed portion 66 separated by a slit 67 extending between adjacent loop fiber bundles 43. This structure is dimensionally stable enough to be laminated into a stretchable backing film, such as polypropylene or polyethylene film from Tredegar Film Products Company of Richmond, Virginia. During the lamination process, the dispersing sheet 66 of the carrier film is bonded into a stretchable substrate to ensure that the final ring product can be elastically stretched in its plane while further fixing the bottom of the ring structure.

In another process, as shown in Fig. 12, the fiber-covered carrier net is only needled in the necessary areas, and other areas are not needled. The fibers in the non-needled area remain generally loose and can be easily removed from the carrier web, such as by the vacuum device 68. The removed fibers are easily combed again and thus recycled. The carrier web 14 is then laminated into a backing web 26 by fusing the fiber covered area and the needle punched area and the non-fiber covered area of the carrier web. The laminate is then rolled up for later use. In this way, it is possible to produce materials with loops only in the required areas. Such a product can be, for example, a continuous sheet product, from which the outer diaper cover of the diaper can be punched, as shown in FIG. 13. Each diaper body panel 70 is cut along a dashed line 72 to contain discrete loop patches 74 where the fiber-covered film has been needled. The pre-printed pattern (not shown) on the substrate film is displayed on the ring patch 74 and the die cut, and can be seen through the ringed and non-ringed areas of the carrier web.

The die-cut diaper cover 70 forms a disposable diaper as shown in FIG. 14, with a covering surface and an inner portion and a porous film 76 sandwiched with an absorbent core (not shown), and a ring patch 74 is placed to receive the matching diaper drape Sheet 78, the diaper flap 78 carries the patch 80 of the convex fixing member to releasably fix the diaper to the baby. Because the ring structure is formed of the material that forms the outer surface of the diaper, there is no risk of the ring material delamination or undesirable separation from the diaper body.

In another bonding process shown in FIG. 15, the dispersed patch of the substrate 26 is used to cover the needled and fiber-covered areas of the carrier web 14, and the other areas of the carrier web are not covered and not laminated. . Each backing patch 26 is pressed and bonded by a roller 82 to be positioned so as to cover the fibers remaining on the back of the carrier web. The fluid-impermeable patch 26 can be used to seal the needle puncture holes, thereby producing a fluid-impermeable finished product with a particularly low weight and nominal thickness. In some applications, the substrate patch 26 is pre-coated with an adhesive that bonds the substrate to the film and fibers. During the labeling process, the patch 26 can be transferred to the carrier 14 on the endless conveyor belt 84, as shown in the figure.

Referring to FIG. 16, in another embodiment, the acupuncture station 18 includes a stationary lower support plate 86. The lower support plate 86 has a flat upper surface with a set of holes formed on the surface. The needle 34 penetrates the carrier 14 and then penetrates These holes. The upper support plate 19 prevents the needled product from retreating following the needle. After the needle punching is completed, the product is in a static state to be wound for subsequent bonding, or it is moved directly from the needle punching station into the bonding station, such as into the flat plate laminator 88. The laminator 88 has up and down conveyor belts 90a and 90b, which move together with the needled carrier and the backing material 26 between a series of opposing, air-controlled pressure plates, which control the heating of these materials and apply pressure to make These materials are bonded. If desired, a row of protrusions, ridges or nails can be provided on a laminator conveyor belt to separate the bonding points and/or embossing.

The above process can economically produce high-content ring materials with excellent fixing properties. It can also be used to produce ring materials whose ring materials and substrate materials are selected to achieve the best quality. For example, the ring fiber material can be selected for high fixing strength, and the backing material can be selected for easy bonding with other materials without damaging the ring fiber.

The material of the ring product can also be selected because of other required properties. In one case, the loop fiber, carrier web, and backing are all formed of polypropylene, making the finished loop product easy to recycle. In another case, the ring fibers, carrier net and substrate are all formed of biodegradable materials, making the finished ring products more environmentally friendly. There are already high-strength fibers of biodegradable polylactic acid, for example, the fiber of Cargill Dow LLC under the trade name NATUREWORKS. In another embodiment, carbon fibers are needled into the KEVLAR film and bonded with silicone or other high-temperature adhesives to produce a ring material with excellent fire resistance.

For many applications, the fiber can be polyester, polyethylene, polypropylene, nylon, or a copolymer of two or more resins. High-strength, high-melting-temperature resin short fibers can be mixed with lower-melting-temperature resin fibers, and the lower-melting-temperature resin melts during the bonding process to further fix the ring formed by the high-strength fibers. In some cases, fibers having a high-strength core coated with a low melting temperature resin can be used.

The carrier web may be a solid sheet, such as a thin film sheet that is not porous before needling. In some other cases, non-woven, woven or knitted materials can be used as the carrier web. Suitable films include polyester, polyethylene, polypropylene, nylon and their copolymers. It is also possible to use a paper sheet, with an adhesive pre-adhered on the fiber side to help bond the fibers and/or the backing layer to the paper sheet.

The polymer backing layer or adhesive can be selected from suitable polyethylene, polyester, EVA, polypropylene, and their copolymers. You can also use paper, fabric, or even metal. The adhesive can be liquid or powder, and can even be pre-coated on the fiber side of the carrier web before laying the fibers. In some cases, separate adhesives or backing layers cannot be used because they are rarely recyclable.

In one test, 3 denier crimped polyester fibers were carded and laid on a 0.002 inch (0.05 mm) thick blown polyethylene film sheet. The fibers were in the form of fiber mats with a unit weight of approximately 1.0 ounce/square yard ( 33 g/m²). Then, a 38-gauge tufting needle is used to needle punch the fiber-covered film from the fiber side with a needle punching density of 250 holes/cm 2 and a needle punching depth of 3.3 mm. The back of the needled material is bonded to a 0.001 inch (0.025 mm) thick polyethylene sheet, which rests on the nails of density and diameter described above. For a ring that is matched with a molded hook product with a density of approximately 264 CFM-29 type hooks per square centimeter, the average peel of the ring is about 500 g/inch when tested in accordance with ASTM D5170-91 (200 g/cm²), the hook product is available from Velcro USA, Manchester, New Hampshire. When matched with the same hook products, according to ASTM In the D5169-91 test, the average shear of the ring material is about 7000 g/in² (1100 g/cm²). This roughly corresponds to the point-unbonded nonwoven loop material that is widely used in disposable diapers. When hooked, the average peel is about 215 grams/inch (86 grams). /Square centimeter) and the average shear is about 3100 grams/square inch (500 grams/square centimeter) level. Hooked with Velcro USA's CFM-85 palm tree hook, the loop material has about 600 g/inch (240 g/cm) peel and 6000 g/square inch (930 g/cm2) The shear, corresponding to about 300 g/inch (118 g/cm) of shedding and 3000 g/square inch (465 g/cm) of the non-bonded nonwoven ring material.

In another embodiment, the ring article is prepared as in the test just described, except that the fiber is 6 denier, the needle punch density is 225 holes/cm 2 and the needle punch depth is 4.4 cm. This loop material has about 550 g/inch (215 g/cm) shedding and 5000 g/square inch (775 g/cm2) shear when matched with CFM-29 hook products, and CFM-85 hook When the products are matched, they have a shedding of about 270 g/inch (105 g/cm) and a shear of 5500 g/inch (850 g/cm).

A number of embodiments of the invention have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the present invention. Therefore, other embodiments also fall into the protection scope of the subsequent claims.