JPH0320507B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a meltblown microfiber web (hereinafter referred to as meltblown web or simply web) that is characterized by high abrasion resistance and is particularly suitable as a medical nonwoven fabric.
The present invention relates to an improved meltblown microfiber nonwoven fabric (hereinafter referred to as meltblown fabric or simply fabric) comprising: The present invention is directed to nonwoven fabrics, particularly medical fabrics. As used herein, the term "medical fabric" refers to fabrics used for surgical drapes, surgical gowns, instrument packaging, and the like. Such medical fabrics are required to have certain properties that are sufficient for their intended use. These properties include strength, the ability to resist the penetration of water and other liquids, often referred to as strike-through resistance, breathability, flexibility, drapability, sterilization, and bacterial barrier properties. will be included. The use of microfiber webs in applications requiring barrier properties is known in the prior art. Microfibers are fibers having a diameter of less than 1 micron to about 10 microns. Microfiber webs are often referred to as meltblown webs because they are typically produced by a meltblown process. It is generally known that a high degree of waterproofness and superior performance can be achieved without significantly impairing breathability by using relatively small diameter fibers in a fabric structure. Conventionally, microfiber web fabrics manufactured for use in medical fabrics are made by laminating or bonding spunbond thermoplastic fiber webs, films, or other reinforcing webs to provide the necessary strength. It was a composite of microfiber webs. Another important property for both nonwovens and medical fabrics is abrasion resistance. Resistance to surface abrasion is important not only for the performance of the nonwoven, but also for the appearance of the nonwoven. For example, fuzz of cut fibers at the surface is particularly undesirable in medical fabrics. In addition, surface abrasion also affects the strike-through resistance and bacteria-buying properties of medical fabrics. Lining and pilling or clumping of surface fibers are also unsuitable for many wipe applications. Spunbond fiber webs, films, or other reinforcing webs are used on the exterior surfaces of meltblown fiber products to provide surface abrasion resistance. U.S. Patent No. 4,041,203 describes drapeability, breathability,
A nonwoven fabric made by bonding a microfiber web and a spunbond web has been disclosed for the purpose of manufacturing a medical fabric with good waterproofness and surface abrasion resistance. U.S. Pat. No. 4,196,245 discloses a combination of meltblown or microfiber and perforated film, or meltblown and perforated film and spunbond fabric. British Patent Application No. 2132939 discloses that a medical device comprising melt blown microfibers dot-fused to a reinforced non-woven web made of discontinuous fibres, such as a dry or wet web made of stable fibers, is disclosed. Suitable meltblown nonwoven laminates are disclosed. Although the above-mentioned fabric may have a better balance between waterproofness and breathability compared to other conventional technologies that do not use microfibers, it has a surface reinforcement layer made of relatively thick diameter fibers. Adding a value imposes constraints on its benefits. Hotchkiss et al., U.S. Patent No. 4,436,780, uses a meltblown fiber layer in the center layer and spunbond layers on both sides to provide low fuzziness, less streaking (wiping marks), and an absorbent fiber layer. A meltblown wipe with improved properties is disclosed. It is generally known to highly compress the web, add adhesive, or increase the amount of adhesive to improve the surface abrasion resistance of meltblown webs and reduce fuzz. The present applicant has also proposed in Japanese Patent Application No. 61-184343 a method for obtaining a medical nonwoven fabric from a non-reinforced web or an ultrafine fiber web. The nonwoven fabric is unreinforced, as it does not require lamination or bonding with other types of webs or films to provide adequate strength for use in medical applications. This nonwoven fabric has a good balance of waterproofness, strength, breathability, and other appearance properties, and is superior to conventional nonwoven fabrics. However, as explained in this application, small amounts of adhesive are applied to the surface of the fabric to make the nonwoven fabric particularly useful for use in highly abrasion resistant applications. British Patent Application No. 2104562 discloses a method of heating the surface of meltblown fabric to make it fuzz resistant. Some degree of heat and compression to improve the abrasion resistance of the microfiber web,
For example, methods such as embossing are generally known. The above fabrics with reinforcing webs must be assembled using two or more web forming techniques, resulting in a complex process and high cost. Additionally, bonding a conventional fiber web with microfibers, compressing it, or applying an adhesive to the microfiber web stiffens the fabric, especially when high strength is desired. The present invention provides an embossed web constructed of meltblown microfibers with improved wet and dry surface abrasion resistance that pilling occurs after more than 15 cycles. This abrasion resistance is improved without the use of additional adhesives and without sacrificing the drape or hand of the material. According to the invention, surface abrasion resistance is achieved by adding a surface layer in which the average fiber diameter is greater than 8 microns and 75% of the fibers are composed of meltblown fibers having a fiber diameter of at least 7 microns. improvement is achieved. The surface layer is as described in the above-mentioned patent application 1986-
It is bonded to a melt blown core web (hereinafter referred to as core web) as described in No. 184343 by hot embossing or other methods. Bonding of the surface layer to the core web and hot embossing of the core web are performed in one processing step. Furthermore, when manufacturing a core web and a surface layer web in a single nonwoven fabric manufacturing process using a large number of ferrules, the surface layer is formed on top of the core web, and the initial natural bonding force between them is high. There is no need to bond it to the core web. Because there is no need to apply additional adhesive,
The present invention also provides a method of manufacturing meltblown microfiber webs without additional processing steps such as adhesive application, adhesive drying, and/or curing. It also appears to occur during curing or drying of the adhesive. It is also possible to eliminate damage caused by active heating, which adversely affects the drapability and feel of the nonwoven fabric. Hardening of the nonwoven fabric by using adhesive solutions is also eliminated, thereby allowing processing conditions of the core web to be selected to best optimize other properties. In addition, by using a surface layer composed of meltblown fibers, it is possible to obtain a nonwoven fabric that has both drapability and surface abrasion resistance.
This cannot be achieved by applying adhesive.
The use of melt blown fibers to form the surface layer is economically advantageous and also reduces the technical burden required to produce the nonwoven fabric. That is, the present invention provides an improved meltblown or microfiber fabric with improved surface abrasion resistance without the use of adhesives. Used as medical cloth or wiping cloth, or for other purposes. In a preferred embodiment, the fabric of the invention comprises e.g.
Consisting of an unreinforced melt-blown microfiber fabric with improved surface abrasion resistance such that pilling occurs only at a greater number of cycles, the fabric is suitable for use as a medical fabric and has a The minimum value of grab tensile strength is greater than 0.8N/g/ ^m2 , and the minimum value of Elmendorff tear strength to weight ratio is
It is greater than 0.04N/g/ ^m2 . In a most preferred embodiment of the invention, the embossed non-reinforced fabric has at least a number of pilling cycles.
It has a wet abrasion resistance of 30 cycles and a dry abrasion resistance of at least 40 cycles in which pilling occurs. These properties are combined with waterproof properties, which are desirable properties when this fabric is used for medical purposes.
It can be provided in a form that combines breathability, especially drapability. In its broadest aspects, the invention comprises providing a meltblown microfiber web with a surface layer comprised of meltblown fibers, the surface layer having an average fiber diameter greater than 8 microns, and at least 75% of the fibers being It has a fiber diameter of at least 7 microns. In many textile applications, the surface layer is laminated to other webs, such as by emboss bonding, or by other known methods. That is, the surface layer may be formed separately from other nonwoven fabrics and thermally bonded thereto, but preferably the surface layer is thermally bonded so as to form separate and discontinuous bonding areas. Alternatively, the surface layer may be formed with a high initial natural adhesion, making it unnecessary to bond the surface layer to the rest of the web, but the hot embossed fabric may Sometimes it's desirable. The fabrics of the present invention exhibit improved wet and dry abrasion resistance and are particularly useful as wipes or medical fabrics. In its broadest aspects, the method of the present invention involves the modification of a conventional melt-blowing apparatus, such as that shown in the above-mentioned Japanese Patent Application No. 61-184343 and shown in FIG. 1, to provide high velocity secondary air. It can be carried out using a In this equipment, the thermoplastic resin is fed into the hopper in the form of pellets or granules.
0. Extruder 1 for pellets
1, and the temperature is controlled by several heating zones in the extruder to raise the temperature above the melting point of the resin. The extruder is driven by motor 12 and the resin moves through the heating zone of the extruder and into die 13. The base 13 has several heating zones. As shown in FIG. 2, the resin enters the heating chamber 29 located between the upper die plate 30 and the lower die plate 31 from the extruder. The upper and lower die plates are heated by a heater 20 to raise the temperature of the die and the resin in the heating chamber 29 to a desired temperature. The resin is then extruded through a plurality of small holes in the surface of the die. Usually, there are about 12 small holes per 1 cm of die width. An inert heated gas, usually air, is pumped via line 14 into chamber 19 and into the die. This heated gas, better known as primary air, then flows into gas slots 32, 33 located on either side of resin aperture 17. At the point where the resin exits the small hole 17, the resin is finely divided into fibers by this heated gas. The width of slots 32 and 33 is called an air goat. The fibers are conveyed by heated gas onto a web-forming perforated conveyor or receiver 22;
A mat or web 26 is formed. Vacuum box 2 connected to a suitable vacuum line 24
3 is commonly used to more effectively deposit the fibers. Conveyor 22 is driven around rollers 25 to continuously form the web. The exit of the small hole 17 and the exits of the gas slots 32 and 33 may be on the same plane or may be on different sides. FIG. 3 shows the case where the end of the small hole is located inside the plane of the die and slots 32 and 33. Such an arrangement is called a negative setback. Setback dimensions are indicated by the spaces between the arrows in FIG. Figure 4 shows the physical setback. The ends of the small holes 17 project outside the plane of the die and slots 32 and 33.
Setback dimensions are indicated by the spaces between the arrows in FIG. Adopting a negative setback allows you to freely adjust the air goat without adversely affecting the quality of the produced web.
Preferably, the method employs a negative setback. The fabric of the present invention comprises at least one surface layer and a core web. Preferably, the fabric consists of a core web and surface layers disposed on both sides of the core web. As used herein, the term surface layer refers to a web composed of fibers having a weight of less than 50% of the total weight of the fabric.
Preferably the weight of the surface layer web is about 25% of the total weight of the fabric, more preferably about 25% of the total weight of the fabric.
It is between 15% and 25%. The surface layer web may be formed separately from the core web and then overlapped in face-to-face relationship. When this method is adopted, the weight ratio of the surface layer web must be approximately 6 g/m ² in order to smoothly overlap the surface layer web and the core web.
Another method is to form the surface layer web and the core web on different web surfaces. For example, the core web fibers are deposited on the surface layer web deposited on the conveyor 22, and the surface layer web is formed on the core web fibers. There is a way to use it as a receiver. In this preferred method of the invention, approximately 3 g/m ² of the surface layer web is deposited on a conveyor to form a receiver for the core web, or approximately 3 g/m ² of the surface layer is deposited on the core web acting as a receiver. They may be deposited on top of each other, or a combination of the two may be used. Alternatively, the fibers of the surface layer web may be deposited on both sides of the core web in a separate web forming step. after,
For example, the core web and the surface layer web may be laminated by a method such as hot embossing. When depositing the surface layer web on the core web, high initial interfiber adhesion or natural adhesion can be applied to the web, such as by increasing the die temperature, not using secondary air, or shortening the web formation distance (details will be discussed later). If the surface layer is formed under conditions that provide adhesive strength, there is no need to laminate the surface layer web to the core web, for example, by hot embossing, and there is no need to emboss the surface layer. The core web may or may not be embossed before the fibers of the surface layer web are deposited onto the core web. The embossed fabric laminates of the present invention exhibit wet surface abrasion resistance that requires at least 30 cycles to produce pilling and dry surface abrasion resistance that requires at least 40 cycles to produce pilling. As discussed below, the fabric of the present invention can be fabricated using only one melt blown die by increasing the polymer delivery rate and reducing the primary air that forms the surface layer web by the method described above. It is possible to form the The most preferred method of making the fabric of the present invention uses multiple dies. In a most preferred aspect, the present invention comprises an improved unreinforced meltblown microfiber fabric for use as a medical fabric, the fabric having a minimum grab tensile strength to weight ratio of at least 0.8 N/g. / ^m2 , and the minimum value of Elmendorff tear strength to weight ratio is at least
It is 0.04N/g/ ^m2 . The invention will now be described in more detail with respect to this preferred embodiment. The requirements for medical grade fabrics are very strict. It must have sufficient strength to withstand tearing or tension under normal conditions of use, such as in an operating room. This is true for fabrics used in operating room fabrics such as surgical gowns, cleaning garments, or surgical drapes. One of the measures of fabric strength is the graph tensile strength. Grab tensile strength is usually
It is expressed as the load required to pull apart, or cut, a 10cm wide sample of fabric. How to test the grab tensile strength of nonwoven fabrics
Described in ASTMD1117. Medical nonwovens must also be highly resistant to tearing. Tear strength or tear resistance is
Usually measured by the Elmendorf tear test method as described in ASTM D1117. The grab tensile strength of the weakest commercially available medical fabrics, measured in the weakest direction, or perpendicular to the machine direction, is in the range of 45 Newtons (N), and the weakest direction tear strength is approximately 2N; At such strength levels, the fabric can tear, and higher levels are generally desired. Grab tensile strength level is approx.
65N or higher, and tear strength levels of around 6N or higher allow the medical fabric to be used in a wider range of applications. Preferred fabrics of the invention have a high strength to weight ratio, i.e. both grab tensile strength and tear strength exceed the above-mentioned values at the desired weight ratio, and generally their weight ranges from 14 to 85 g/m ² . Medical fabrics also need to be repellent to liquids such as blood, which is a necessity everywhere in hospital operating rooms. Such liquids are the preferred medium by which microorganisms are transported from one location to another, and liquid repellency (or herein water repellency) is an important feature of medical fabrics. Water repellency is mainly influenced by the pore structure of the fabric, and its scale is
It is given by the "hydrostatic head" test described in AATCC 127-1977. In a hydrostatic head test, the pressure is measured in units of the height of the water column required for water to penetrate and penetrate the sample fabric. Hydrostatic head testing is an effective method of evaluating the inherent water repellent performance of medical fabrics because their resistance to liquid penetration is ultimately governed by the fabric's pore structure. The hydrostatic head value of medical fabrics, excluding impermeable films or microfiber webs, is generally 20 to 30 cm of water column. These values are not optimal for gowns and drapes, especially when used in situations where the risk of infection is high. A value of 40cm or more is desirable. Unfortunately, prior art disposable fabrics with high hydrostatic head values have had drawbacks such as poor breathability and relatively low strength.
The fabric of the present invention was able to achieve a high level of liquid repellency. Breathability is also a desirable property for medical fabrics.
This is especially the case when the fabric is used as outerwear. The breathability of a fabric is related to its moisture vapor transmission rate (MVTR) and breathability. Most of the fiber webs used in medical fabrics are expensive.
Since it has an MVTR value, the measurement of breathability is suitable as a quantitative test method to judge the difference in breathability. Generally speaking, the larger the opening in the fabric structure, the greater its breathability. A highly compressed, dense web therefore has a very small pore structure, resulting in a fabric with poor air permeability and poor breathability. Even as the weight of the fabric increases, its breathability decreases. Air permeability scale is ASTMD737
The Frazier air porosity test is described in . Frazier air porosity is 8m ³ /
Wearing medical outer clothing made of fabric with a lower than min/m ² for a long time can cause discomfort. The fabrics of the present invention can provide good breathability without sacrificing water repellency or strength. Medical fabrics must have good drape properties, and this property is measured in a variety of ways, including the Cusick drape test. In the oak drape test, a circular fabric sample is sandwiched concentrically between smaller horizontal disks.
The fabric hangs downward around the lower disc. The shadow of the sagging sample is cast onto a tree ring of paper that is the same size as the unsupported portion of the fabric sample. Draw the outline of the shadow on paper shaped like a tree ring.
Measure the mass of annual paper. Cut the paper along the trace of the shadow and measure the mass of the ring-shaped inner part corresponding to the shadow. The drape factor is the mass of the inner ring divided by the mass of the annual ring, multiplied by 100. The lower the drape coefficient, the better the drapability of the nonwoven fabric. The fabric of the present invention exhibits high drapability when measured using the method. Drapability correlates well with softness and flexibility. In addition to the above-mentioned properties, medical fabrics require antistatic and flame retardant properties. It must also have good abrasion resistance and must not shed small fluff balls, usually called lint. In addition to the above-mentioned properties, preferred fabrics of the present invention differ from prior art meltblown webs in that the average length of the individual fibers of the web is greater than the average length of the fibers of prior art webs. There is. The average length of fibers in the core web is 10
cm, preferably longer than 20 cm, and most preferably in the range 25-50 cm. Also,
The average diameter of the fibers in the core web is less than 7 microns. The fiber diameter distribution is such that at least 80% of the fibers have a diameter of 70 microns or less, and preferably 90% of the fibers have a diameter of 7 microns or less. In the description of this invention, the term "web" refers to an unbonded web formed by a melt blown process. The term "fabric" refers to a web after it has been joined by hot embossing or other means. Preferred fabrics of the invention have a core web comprised of fibers having an average fiber length greater than 10 cm and at least 80% of the fibers having a fiber diameter of 7 microns or less; It consists of a non-reinforced melt blown embossed fabric having 75% of the fibers having a fiber diameter of at least 7 microns and a surface layer disposed on one or both sides of a core web. In the preferred fabric manufacturing process of the present invention, the fibers of the core web are contacted with high velocity secondary air immediately after the fibers exit the die. The fibers of the surface layer may or may not be in contact with the high velocity secondary air.
This secondary air is circulating air at room temperature or outside temperature. The secondary air can also be cooled if desired. Secondary air is pumped from a suitable source through supply lines 15 to distributors 16 located on either side of the die. Generally, the length of the distributor is the same as the length of the exposed surface of the die. The distributor is provided with an inclined surface 35 having an opening 27 adjacent to the die surface. The velocity of the secondary air can be adjusted by increasing the pressure in the supply line 15 or by using a buffle 28. Opening 27 by Batsuful
, thereby increasing the velocity of air exiting the distribution box under constant flow conditions. The fabrics of the present invention differ from prior art microfiber-containing fabrics in the way they utilize a melt-blown process to produce a surface layer comprised of fibers with properties different from those of the microfibers in the core web, and in that the fibers in the core web and When formed into a surface layer web and hot embossed as described herein, a nonwoven fabric with a high strength-to-weight ratio, good surface abrasion resistance, and good drapability is obtained. Prior art melt blown techniques practiced in producing application-related fabrics typically produce microfibers with average fiber diameters in the range of about 1 to 10 microns. Within a given web, a range of fiber diameters exists, and in order to take full advantage of the microfiber structure as a suitable overmaterial, it is necessary to reduce the diameter of these fibers. It is therefore common practice to produce webs or batts having an average fiber diameter of less than 5 microns, and sometimes less than 2 microns. In such prior art processes, the average length of such fibers is typically 5 to 10 cm. As discussed with prior art fabrics, webs formed from such fibers have low strength and abrasion resistance. The tensile strength and abrasion resistance of such webs depends primarily on the bonding between the fibers that occurs when the fibers are deposited on the web forming conveyor. In conventional practices of melt blown technology, some fiber-to-fiber surface adhesion occurs because the fibers can be deposited on a web forming conveyor before they are fully solidified. Their semi-molten surfaces fuse together at the intersection. The creation of such bonds is sometimes referred to as natural adhesion. The higher the degree of natural adhesion, the higher the integrity of the web. However, if excessive natural adhesion of the thermoplastic fibers occurs, the web becomes hard, rough, and extremely brittle.
The strength of such unembossed webs is practically inadequate for applications such as medical fabrics. Heat bonding these webs generally improves strength and abrasion resistance. However, as mentioned above, it is not possible to produce meltblown microfine fabrics with good surface abrasion resistance without the use of surface reinforcing elements or adhesives, which can be used in particular for surgical gowns, cleaning gowns, drapes, etc. It was impossible until now. In forming the core web of preferred fabrics of the present invention, fibers are produced that have longer fiber lengths than prior art fibers. Fiber length is measured using a rectangular wire form. Forms like this start from 5cm
It has span lengths in 5cm increments up to 50cm. Double-sided adhesive tape is cut into strips and attached to the wire to provide an adhesive site for collecting fibers from the fiber stream. Each wire form is first passed through the fiber stream in a direction perpendicular to the stream, closer to the web forming conveyor than to the melt blown die. Average fiber length is approximately determined based on the number of individual fibers traversing a wireform of increasing span length. A substantial portion of the fibers is longer than 10cm and the average fiber length is at least 10cm
If the web is larger than 20 cm, preferably larger than 20 cm, then when the web formed in this way is embossed, it is possible to obtain an embossed fabric that has high strength and other desirable features as a medical fabric. . Fabrics with highly desirable properties can be made when the average fiber length is in the range of 25 to 50 cm. In order to maintain the liquid penetration resistance of ultrafine fibers, it is necessary to keep the diameter of the fibers low. In order to exhibit high waterproofness, it is necessary that the average fiber diameter of the core web of the present invention be 7 microns or less. At least 80% of the fibers must have a diameter of 7 microns or less. Preferably at least 90% of the fibers have a fiber diameter of 7 microns or less. The smaller the width of the fiber diameter distribution, the more likely it is that the excellent balance of properties of the present invention can be achieved. On the other hand, although it is possible to produce nonwoven fabrics with an average fiber diameter larger than 7 microns and obtain high strength, the final waterproofness of such nonwoven fabrics will be low, and it is difficult to produce low-weight fabrics with high waterproofness. That is impossible. Even if a meltblown fiber core web is formed in such a way that little natural adhesion occurs, and the web retains little or no integrity, fabrics that are heat embossed with this web are webs with very high initial strength. It has higher strength than Tsutsuta cloth and has a better appearance. That is, the strongest embossed fabric is formed from the weakest unembossed web having the above-mentioned fiber diameter. The higher the degree of initial interfiber adhesion, the harder and more brittle the cloth becomes, and the more the grip strength and tear strength deteriorate. As the natural adhesion is reduced, the resulting fabric after hot embossing will not only be stronger but also more flexible and drapeable. Because the level of web integrity is relatively low, it is useful to measure the strength of unembossed webs by strip tensile strength measurements. This measurement method uses a 2.54 cm wide sample and a gripping surface with a minimum width of 2.54 cm (ASTMD1117). For prior art meltblown fabrics, the machine direction (MD) strip tensile strength of the naturally bonded web is generally greater than 30%, and sometimes 70% or more, of the strip tensile strength of the bonded fabric. That is, the contribution of natural adhesion to the strength of the embossed fabric is very large. In the fabric of the invention, the contribution of the natural adhesion of the core web is less than 30%, preferably 10%, of the strip tensile strength of the bonded fabric.
It is smaller than %. For example, for a nylon 6 meltblown web made under prior art conditions and weighing approximately 50 g/ ^m2 , the strip tensile strength in the machine direction is 10 to
It is 20N. In preferred fabrics of the present invention, the strip tensile strength of the unembossed core web is such that the strip tensile strength of the unembossed core web is
It is necessary to suppress it to 10N or less, preferably 5N or less. In other words, if long fibers are formed and deposited in such a way that initial fiber-to-fiber adhesion is low,
Individual fibers are strong, and the inherent strength of the fibers themselves can be utilized to the fullest. Although it is necessary to create the fibers of the core web so that the initial interfiber adhesion is low and 80% of the fibers have a fiber diameter of 7 microns or less, such webs have high surface abrasion resistance even when embossed. In order to improve surface abrasion resistance without becoming
Adhesives are often applied to the surface of such fabrics. The application of adhesive has a negative effect on the drapability of the fabric, so the amount of adhesive applied must be kept to a small amount; in reality, the amount of adhesive that can be applied while maintaining adequate drape is limited. , a wear resistance that is somewhat satisfactory but not very high can be obtained. In the fabric of the present invention, the use of adhesives and their negative effects on drapability can be avoided by providing a surface layer of microfibers on one or both sides of the core web.
The fibers of the surface layer have an average fiber diameter greater than 8 microns, with 75% of the fibers having a fiber diameter of at least 7 microns. In a further preferred embodiment, the surface layer is formed to have high initial interfiber adhesion. In summary, this preferred fabric of the present invention, unlike the conventional melt blown webs of the prior art,
A core web composed of fibers with a long average fiber length, low interfiber bond strength, high individual fiber strength, and a small fiber diameter and relatively narrow distribution range to increase liquid penetration resistance. , and at least one surface layer with large fiber diameter and preferably high interfiber bond strength. The method of producing the desired core web and surface layer properties of this preferred fabric of the present invention is based on the adjustment of key process variables and their interactions to achieve the desired fiber, web and fabric properties. Such process variables include extrusion temperature, primary air flow and its temperature, secondary air flow, and deposition distance (distance from die to deposition surface).
Examples include. The influence of these variables on important desired web and surface layer properties is discussed below. If the die melt temperature for both the core web and the surface layer can be maintained, for example, typically 10-35°C lower than that recommended in the prior art, the strength of the individual fibers is significantly improved. Generally, in the method of the present invention, the die melt temperature is less than about 75° C. above the melting point of the polymer. In forming the core web, the velocity and temperature of the primary and secondary air must be adjusted to maximize fiber strength at the zero span length of the polymer. The high velocity secondary air used in the method of the present invention serves to increase the time and distance over which the fibers of the core web are fragmented while providing fiber strength. The use of secondary air in the process of forming the surface layer fibers is not critical and is preferably excluded when forming a preferred surface layer with high initial fiber-to-fiber adhesion. The fiber length achieved in the core web and in the surface layer is influenced by the velocity of the primary and secondary air, the degree of polymer degradation and, as a particularly important factor, the uniformity of the air flow. It is important to maintain a high degree of uniformity in air and fiber flow, avoiding the occurrence of large amplitude turbulence, eddies, streaks, and other flow irregularities. Introducing high velocity secondary air cools and preserves the molecular orientation of the fibers to form stronger fibers that are more resistant to cuts caused by uneven air flow. helps control the flow of air and fibers. Web forming air flow and deposition distance are clearly important in depositing the core web fibers as a low strip tensile strength web on the web forming conveyor. In the process of the invention, the deposition distance is typically 0 to 50 cm. First of all, in order for the core web to have minimal interfiber adhesion, it must arrive on the web forming conveyor in a relatively solid state and free of surface tackiness. It is possible to locate the web forming conveyor or receiver at a distance from the die to give the fibers time to set. However, if the distance is too long, e.g.
cm longer, it becomes difficult to maintain good uniformity of air and fiber flow, resulting in "roping"
occurs. Roping is a phenomenon in which individual fibers become entangled with each other in the airflow to form thick fiber bundles. Excessive roping reduces the ability of the resulting nonwoven to resist liquid penetration and also results in an inferior appearance. A highly uniform primary airflow allows for better fiber attenuation and relatively long deposition distances without roping. The amount of primary air is also an important factor. For a given polymer delivery rate and deposition distance, a sufficient amount of air must be used to maintain good separation of the fibers in the air and fiber flow and to minimize the degree of roping. There must be. The use of a secondary air system is also important to achieve low fiber-to-fiber adhesion of the core web without roping. As already mentioned, high velocity secondary air is effective in uniforming the flow of air and fibers. This thus offers the possibility of increasing the deposition distance without causing undesirable roping. Furthermore, since the secondary air is kept at ambient temperature or, if desired, lower, it also helps to cool and solidify the fibers within a short period of time, thus eliminating the need for intentionally large deposition distances. It disappears. Secondary air system ensures uniformity of flow,
In order to influence the cooling and deceleration rate of the fibers, the velocity needs to be high enough so that the flow is not completely overwhelmed by the primary air flow. In order to provide this desirable airflow characteristic in the process of the present invention, the secondary air velocity is 30 m/min.
sec to 200 m/sec or more is effective. As is clear from the above, methods that can be used to achieve low interfiber adhesion in unembossed core webs include:
There are various methods and combinations of primary and secondary airflow, temperature, and deposition distance. The particular process parameters depend on the polymer used, die and air system design, production rate, and desired product characteristics. The unembossed core web or layers of unembossed core web must be joined to form this preferred fabric of the invention. It has proven advantageous to employ thermal bonding methods for this purpose. In the most preferred method of the invention, the core web or layers of the core web are thermally bonded and the surface layer is thermally bonded and laminated to the core web in a single step of hot embossing. Both ultrasonic embossing rolls using heat and mechanical embossing rolls using pressure can be used. In connection with the present invention, it is preferred to use a mechanical embossing system for dot bonding using an engraved roll on one side of the fabric and a hard smooth roll on the other side. 0.01~0.02 between the bottom roll and top roll to avoid "pinholes" in the fabric
It has been found desirable to provide a gap as narrow as mm. For the intended use of the fabric produced according to the invention, the total embossed area will range from 5 to 30% of the total fabric area, preferably from 10 to 30%.
Must be in the 20% range. In the example described to illustrate the invention, the emboss area is 18%. Emboss pattern is 0.76mm×
The diamond pattern is 0.76 mm square, with 31 diamonds arranged per 1 cm ² of the roll surface. The embossing pattern employed is not critical, and any pattern may be used as long as it has an adhesion area of 5 to 30% of the cloth surface. The principles of the invention are applicable to any commercially available resin, such as polypropylene, polyethylene, polyamide, polyester, or any melt-proneable polymer or polymer blend. It is particularly advantageous to use polyamides, especially nylon 6 (polycaprolactam), because of their excellent appearance, resistance to degradation by cobalt irradiation, good balance of properties, and overall ease of processing. has been found. As already mentioned, preferred fabrics of the invention have a weight of 14 to 85 g/ ^m2 . The weight of the surface layer is approximately 6 g/m ² when formed separately from the core web.
Moreover, when formed at the same time, it is about 3 g/m ² . To achieve the desired overall weight of the fabric, the weight of the surface layer is usually 10 to 15 g/kg, since if a heavy surface layer is used, the weight of the core web must be low. ^m2 or less. The minimum value of the ratio of Grab tensile strength to weight of this fabric is greater than 0.8 N/g/m ² and the minimum value of the ratio of Elmendorf tear strength to weight is greater than 0.04 N/g/m ² ; The dry and wet surface abrasion resistance evaluated by the number of cycles at which pilling occurs is greater than 15 cycles. Preferred fabrics as disposable medical fabrics that require high strength and high abrasion resistance have a weight greater than 60g/ ^m2 , a minimum grab tensile strength of 65N or greater, a minimum Elmendorf tear strength of 6N or greater, Dry surface abrasion resistance is at least 40 pilling cycles and wet surface abrasion resistance is at least 30 pilling cycles. The fibers, webs, or fabrics produced according to the present invention may be combined in various combinations with other fibers, webs, or fabrics having different properties to produce products with special properties. It will be understood that it can be formed. The examples described below are intended to further explain the present invention, and should not be construed as limiting the content or scope of the present invention. Example 1 In the following examples, webs 1, 2, and 3 were manufactured under the conditions listed in Table 1 below.

[Table] −Inlet ℃
Extruder temperature 275 275 300

−Outlet ℃

[Table] Web 1 was produced under conditions similar to those described in the above-mentioned Japanese Patent Application No. 184343/1986 in order to optimize both barrier properties and strength in the final nonwoven state. It is something. web 2
This is an example in which the fabrication conditions of Web 1 were modified, i.e., the die temperature and primary air velocity were lowered to slightly sacrifice barrier properties, but a fabric with high fabric strength was produced. It is. Web 3 has an average fiber diameter of 9.8 microns with increased polymer delivery and reduced primary air velocity;
It is produced by forming a fiber layer in which 80% of the fibers have a fiber diameter greater than 7 microns. Furthermore, the die temperature was increased to increase the initial interfiber adhesion of the web 3. Table 2 shows the physical properties of the embossed fabrics made from Webs 1, 2, and 3. Table 3 shows the processing conditions for manufacturing the embossed cloth whose physical properties are shown in Table 2.

【table】

[Table] As shown in Table 2, Fabric 5 has a higher grab tensile strength than Fabric 4, but its barrier properties are lower as is clear from hydrostatic pressure. Abrasion resistance remains the same. Fabrics 6 and 7 have improved abrasion resistance by using web 3 as a surface layer.
Because fabrics 6 and 7 incorporate web 3 as a surface layer, the standardized grab tensile strength is reduced. This is because although incorporating web 3 increases the weight of the fabric, it does not increase the grab tensile strength per unit weight as much as web 2 does. Cloths 6 and 7 are formed by the surface layer of web 3.
The hydrostatic pressure of is slightly increased and the abrasion resistance is significantly increased. Dry abrasion resistance was measured by the method described below. Place the fabric sample to be tested onto the foam pad on the lower test plate. Attach a 7.6 cm x 12.7 cm sample of standard Lytron finish abrasion cloth to the top plate.
Place it in contact with the fabric test sample. At this time, place the fabric test sample so that the machine direction of the fabric test sample matches the machine direction (length) of the Lytron finished fabric. A weight of 1.1 kg is placed on the upper plate, the lower plate is rotated at a constant speed of 1.25 revolutions/minute, and one rotation of the plate is recorded as one cycle. The fabric test sample is inspected using a magnifying glass after the first 5 cycles and every 5 cycles thereafter. Record the number of cycles in which pilling occurs and also record the number of cycles in which holes appear in the fabric test sample. Pilling is defined as the breaking off of fibers that have begun to form clumps or pilling.
Four fabrics are tested and the average number of cycles at which pilling occurs and the average number of cycles at which the fabric tears occur are recorded. Wet surface abrasion resistance was measured using a similar test method.
However, the difference is that the cloth cycle attached to the lower plate is wetted with 5 drops of pure water, and a 0.2 kg weight is placed on the upper plate. Example 2 In the following example, webs 8, 9, 10
and No. 11 were produced under the conditions shown in Table 4 below.

[Table] Mouth ℃

[Table] The process conditions for webs 8, 9, 10 and 11 are ultimately within the conditions described in the above-mentioned Japanese Patent Application No. 184343/1983. Web 8 was manufactured under conditions that optimize both strength and barrier properties when the fabric is finally finished. Web 9 is
Compared to Web 8, it was produced under slightly different conditions, lowering the die temperature and primary air velocity, producing a fabric with higher fabric strength at the cost of a slight sacrifice in barrier properties. Web 10 has an average fiber diameter of about 9 microns with increased polymer delivery and reduced primary air velocity, with 80% of the fibers being
It is manufactured by forming a fiber layer having a fiber diameter larger than microns. Die temperature is web 9
and 10. Web 11 was manufactured under almost the same manufacturing conditions as web 3, but was manufactured under different manufacturing conditions in that secondary air was not used to increase the initial interfiber adhesion. The die temperature for producing web 11 was higher than the temperature used for producing web 10 to increase initial interfiber adhesion. Table 5 below shows the physical properties of embossed fabrics produced using Webs 8, 9, 10, and 11 under the conditions shown in Table 3. Fabric 13 is coated with Primacor 4990, an 80/20 copolymer of ethylene and acrylic acid manufactured by Dow Chemical Company, on both sides of fabric 12.
It was applied at 3g/ ^m2 .

【table】

【table】

[Table] As is clear from Table 5, the surface abrasion resistance of the fabric 13 has increased, and the oak drape has significantly increased. Adding more adhesive improves abrasion resistance, but worsens drapability. The surface abrasion resistance of fabric 14 is much greater than that of fabric 13, and there is no associated decrease in drapability.
The surface abrasion resistance of fabric 15 is even more improved than that of fabric 14. This increase is considered to be due to an increase in the initial interfiber adhesive strength of the web 11. In view of the foregoing, it is apparent that the present invention provides a novel unreinforced meltblown microfiber fabric with high surface abrasion resistance that satisfies the objects, objectives, and advantages set forth above. Although the invention has been described in terms of specific embodiments, many different modifications will occur to those skilled in the art in light of the foregoing description.
Clearly, improvements are possible. Therefore, all modifications and improvements that come within the spirit and broad scope of the appended claims are to be considered to be included in the present invention.

[Brief explanation of the drawing]

FIG. 1 is an overall diagram of the melt blown process. FIG. 2 is a cross-sectional view showing the arrangement of the die and the arrangement of the secondary air source. FIG. 3 is a detailed partial sectional view of an extrusion die illustrating a negative tape setback. FIG. 4 is a detailed partial sectional view of an extrusion die illustrating a positive setback. 10...Hopper, 11...Extruder,
13...Die, 16...Distributor, 17...
...Small hole, 20...Heater, 22...Receiver, 26...Web, 32, 33...Slot.

Claims (1)

Claims: 1. An improved melt-blown microfiber nonwoven fabric having improved abrasion resistance, said nonwoven fabric having a minimum grab tensile strength to weight ratio of 0.8 N/g/m ² and a at least one unreinforced meltblown microfiber core web having a minimum Elmendorf tear strength ratio of 0.04 N/g/ ^m2 , said core web having a reference weight in the range of 14 g/ ^m2 to 85 g/ ^m2. and the nonwoven fabric further comprises at least one unreinforced surface web on the core web, the surface web being a melt blown thermoplastic having an average fiber diameter of 8 microns or more, 75% of which has a diameter of at least 7 microns. comprising fibers and having a wet and dry surface abrasion resistance against pilling of greater than 15 cycles and a basis weight in the range of 3 g/m ² to 10 g/m ² , said surface web comprising:
A meltblown microfiber nonwoven fabric in continuous contact with at least one core web. 2. The melt-blown microfiber nonwoven fabric according to claim 1, wherein the melt-blown microfiber nonwoven fabric is heat embossed in discontinuous and separate bonded areas, the area of which occupies 5 to 30% of the fabric surface. 3. The melt-blown microfiber according to claim 1, which has a wet abrasion resistance of at least 30 pilling cycles and a dry abrasion resistance of at least 40 pilling cycles. Non-woven fabric. 4. Claim 1, which has a weight of 60 g/m ² or less, a minimum grab tensile strength of 65 N or more, and a minimum Elmendorf tear strength of 6 N or more
The melt-blown microfiber nonwoven fabric described in Section 1. 5. The melt-blown microfiber nonwoven fabric according to claim 1, wherein the surface layer has an average fiber diameter of about 9 microns. 6. At least 80% of the fibers of said core web.
has a diameter of 7 microns or less, and the strip tensile strength due to continuous adhesion of these fibers accounts for 30% of the strip tensile strength of the entire nonwoven fabric.
%, and the nonwoven fabric has a surface area of less than 5%.
further said nonwoven fabric has a dry surface abrasion resistance greater than 30 cycles against pilling;
The improved meltblown microfiber nonwoven fabric of claim 1 having a wet surface abrasion resistance against pilling of greater than 40 cycles. 7. The improved meltblown microfiber nonwoven fabric of claim 6, wherein the surface layer has an average fiber diameter of about 9 microns. 8. A method for producing a melt-blown microfiber nonwoven fabric having improved abrasion resistance, comprising: (1) a minimum grab tensile strength to weight ratio;
0.8 N/g/m ² and a minimum Elmendorf tear strength to weight of 0.04 N/g/m ² , forming at least one core web having a reference weight ranging from 14 g/m ² to 85 g/m ² (2) consisting of meltblown thermoplastic fibers having an average fiber diameter of 8 microns or more, 75% of which has a diameter of at least 7 microns;
(3) forming at least one unreinforced surface layer having a reference weight in the range from 10 g/m ² to 10 g/m ² and a wet and dry surface abrasion resistance against pilling of greater than 15 cycles; A method for producing a meltblown microfiber nonwoven fabric, comprising: the surface layer being in continuous contact with the core web. 9. A method for producing a meltblown microfiber nonwoven fabric comprising meltblown microfibers according to claim 8, wherein the surface web has an average fiber diameter of about 9 microns. 10. The method of manufacturing a meltblown microfiber nonwoven fabric according to claim 8, further comprising the step of hot embossing the laminate in separate and discontinuous adhesive areas. 11 A fiber-forming thermoplastic polymer resin in a molten state is extruded through a row of small holes in a heated nozzle into a stream of inert gas to attenuate the resin to form fibers, and the fibers are deposited on a deposition surface. In the method of forming a web and thermally bonding the web to form a cloth, (a) the polymer melt temperature is maintained at a level that minimizes molecular decomposition in the first heated nozzle, and the primary air velocity, volume, and temperature are controlled; , controlling the polymer delivery rate and exit temperature to ensure that the average fiber diameter is greater than 8 microns and 75% of the fibers are at least 7 microns in diameter.
forming a first layer of fibers having a fiber diameter of microns and depositing the fibers on a deposition surface at a deposition distance to form a first surface layer web with good fiber-to-fiber adhesion; ) Maintaining the polymer melt temperature in a second heated nozzle at a temperature that minimizes molecular decomposition and controlling the velocity, volume, and temperature of the primary air so that at least 80% of the fibers have a fiber diameter of 7 microns or less. to form fibers with an average fiber length greater than 10 cm, introduce a highly uniform high velocity secondary air flow sufficient to cool the fibers and keep them separated, and over the deposition distance. forming a web with low interfiber adhesion prior to depositing fibers and embossing the web to form a nonwoven fabric; and overlaying the fibers of the core web onto the first surface layer web. A method for producing a melt-blown microfiber nonwoven fabric having surface abrasion resistance. 12c A patent further comprising the step of forming a second surface layer web made of the same fibers as the first layer web in a third heating nozzle, and overlapping the second surface layer web on the uncoated surface of the core web. A method for producing a meltblown microfiber nonwoven fabric according to claim 11. 13. The method for producing a meltblown microfiber nonwoven fabric according to claim 11 or 12, wherein the surface web has an average fiber diameter of about 9 microns. 14. The method for producing a melt-blown microfiber nonwoven fabric according to claim 11 or 12, further comprising the step of heat-embossing the web.