阅读说明：本技术 一种阻燃型莱赛尔长丝及其制备方法 (Flame-retardant lyocell filament and preparation method thereof ) 是由 宫怀瑞 徐良平 何留根 张红艳 张磊 于 2021-10-25 设计创作，主要内容包括：本发明涉及家用纺织品技术领域,特别是涉及一种阻燃型莱赛尔长丝及其制备方法。所述制备方法包括以下步骤：S1.将莱赛尔长丝的纤维原料溶于N-甲基-吗啉-N-氧化物的水溶液中,得到纤维原料溶液,随后向纤维原料溶液中加入阻燃剂,超声分散,得到纺丝原液,所述阻燃剂包括纳米水滑石粉；S2.将纺丝原液经螺杆挤压机挤出、过滤、纺丝、凝固浴成型得到丝束,接着洗涤、上油、烘干,得到所述阻燃型莱赛尔长丝。本发明通过向纤维原料溶液中添加阻燃剂,赋予了莱赛尔长丝阻燃性能；利用水滑石层状结构的可插层性,改善了纳米水滑石粉体阻燃剂在纤维原料溶液中的分散性,进而改善了莱赛尔长丝的阻燃性能；通过超声作用有效抑制了纳米水滑石粉体颗粒的团聚,进一步改善了莱赛尔纤维的阻燃性能。本发明的莱赛尔长丝手感柔软,舒适性好。(The invention relates to the technical field of household textiles, in particular to a flame-retardant lyocell filament and a preparation method thereof. The preparation method comprises the following steps: s1, dissolving a fiber raw material of lyocell filaments in an aqueous solution of N-methyl-morpholine-N-oxide to obtain a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and performing ultrasonic dispersion to obtain a spinning solution, wherein the flame retardant comprises nano-hydrotalcite powder; s2, extruding the spinning solution by a screw extruder, filtering, spinning, forming by a coagulating bath to obtain tows, and then washing, oiling and drying to obtain the flame-retardant lyocell filament. According to the invention, the flame retardant is added into the fiber raw material solution, so that the flame retardant property of the lyocell filament is endowed; the dispersibility of the nano hydrotalcite powder flame retardant in the fiber raw material solution is improved by utilizing the insertion layer property of the hydrotalcite layered structure, so that the flame retardant property of the lyocell filament is improved; the agglomeration of nano hydrotalcite powder particles is effectively inhibited through the ultrasonic action, and the flame retardant property of the lyocell fiber is further improved. The lyocell filament yarn provided by the invention is soft in hand feeling and good in comfort.)

1. The preparation method of the flame-retardant lyocell filament is characterized by comprising the following steps of:

s1, dissolving a fiber raw material of lyocell filaments in an aqueous solution of N-methyl-morpholine-N-oxide to obtain a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and performing ultrasonic dispersion to obtain a spinning solution, wherein the flame retardant comprises nano-hydrotalcite powder;

and S2, extruding the spinning solution obtained in the step (1) through a screw extruder, filtering, spinning, forming through a coagulating bath to obtain tows, and then washing, oiling and drying to obtain the flame-retardant lyocell filament.

2. The method for preparing the nano hydrotalcite powder according to claim 1, wherein the nano hydrotalcite powder has a particle size of 80-200 nm.

3. The preparation method according to claim 1, wherein in step S1, the nano hydrotalcite powder is modified with a modifier and then mixed with an aqueous solution; the modification treatment steps of the nano hydrotalcite powder are as follows: sequentially adding the modifier and the nano hydrotalcite powder into water, stirring for 2-3h at 70-80 ℃ and 550-700r/min, filtering, washing and drying to obtain the modified nano hydrotalcite powder.

4. The process according to claim 3, wherein the modifier comprises an alkyl phosphate diester salt and/or an alkyl phosphate monoester salt.

5. The process according to claim 4, wherein the modifier comprises an alkyl phosphate diester salt and an alkyl phosphate monoester salt.

6. The preparation method according to claim 5, wherein the mass ratio of the alkyl phosphate diester salt to the nano hydrotalcite is 3-6: 100, respectively; and/or the mass ratio of the alkyl phosphate monoester salt to the nano hydrotalcite is 1-2: 100.

7. the preparation method according to claim 1, wherein the mass ratio of the flame retardant to the fiber raw material is 15-30: 100, respectively;

and/or, the concentration of the fiber raw material in the spinning solution is 10 wt% -20 wt%.

8. The production method according to claim 1, wherein the flame retardant further comprises an inorganic boron-based flame retardant;

and/or an organic phosphorus-based flame retardant;

and/or, an ammonium salt flame retardant.

9. The method as claimed in claim 1, wherein the power of the ultrasound is 340-380W, and the time is 1-3 h;

and/or, in the spinning process, the spinning speed is 40-60m/min, the pore diameter of the spinneret plate is 60-100 μm, the length of the pore capillary is 400-600 μm, and the length of the air gap is 6-9 cm;

and/or the concentration of the coagulating bath is 5-15 wt%, the pH is 9-10, and the temperature is 0-15 ℃;

and/or in the washing process, the temperature of the adopted washing liquid is 70-90 ℃, the time is 1-3h, and the mass ratio of the washing liquid to the tows is 15-25: 1; and/or in the oiling process, the temperature of the adopted oil bath is 80-90 ℃, the time is 1.5-3h, and the mass ratio of the oil bath to the tows is 1: 10-20 parts of; and/or the drying temperature is 120-150 ℃ and the drying time is 20-30 min.

10. The flame-retardant lyocell filament produced by the production process according to any one of claims 1 to 9.

Technical Field

The invention relates to the technical field of household textiles, in particular to a flame-retardant lyocell filament and a preparation method thereof.

Background

The regenerated cellulose fiber is a fiber produced by using natural cellulose such as cotton, hemp, bamboo, tree, etc. as a raw material, and only changing the physical mechanism of the cellulose without changing the chemical structure of the natural cellulose. Regenerated cellulose fibers mainly include the following two main classes: conventional ordinary cellulose fibers and differentiated cellulose fibers. Wherein, the differential cellulose fiber mainly comprises lyocell fiber, modal fiber, bamboo fiber, chitin fiber, copper ammonia fiber and the like.

Lyocell fiber, commonly known as velvet, is produced in the middle of the 90 s of the 20 th century, and is a regenerated cellulose fiber spun from wood pulp mainly made of coniferous trees as a raw material and an aqueous solution of N-methyl-morpholine-N-oxide (NMMO for short). "lyocell" fibers have many of the excellent properties of both natural and synthetic fibers: the fabric has the advantages of soft hand feeling, good drapability, high stiffness, high dry and wet strength, high swelling property (dry and wet volume is 1:1.4), easy dyeing, good spinnability, crease resistance, stable size, safety and environmental protection, and the dry and wet strength is 85 percent. The raw material cellulose of the lyocell fiber has wide source and low price. The lyocell fiber can be blended with cotton, wool, hemp, acrylic fiber, terylene and the like, and is widely applied to high-grade fabrics such as underwear, garment ready-made clothes and the like.

In order to meet diversified application requirements, higher requirements are also put forward on the performance aspect of textiles. In addition to comfort, textiles are also required to be flame retardant, antimicrobial, skin care, and the like. At present, attempts have been made to add flame retardants (generally inorganic flame retardants) to the spinning dope during the preparation of lyocell fibers to improve the flame retardant properties of the fibers.

However, the flame retardant performance of the flame retardant lyocell fiber prepared by the existing method is to be further improved.

Disclosure of Invention

In view of the above disadvantages of the prior art, the present invention aims to provide a flame retardant lyocell filament and a preparation method thereof, which are used for solving the technical problem that the flame retardant property of the flame retardant lyocell fiber prepared by the existing method is to be further improved.

In order to solve the problems, the invention is realized by the following technical scheme:

one of the purposes of the invention is to provide a preparation method of flame-retardant lyocell filament, which comprises the following steps:

s1, dissolving a fiber raw material of lyocell filaments in an aqueous solution of N-methyl-morpholine-N-oxide (NMMO for short), obtaining a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and performing ultrasonic dispersion to obtain a spinning solution, wherein the flame retardant comprises nano-hydrotalcite; (ii) a

And S2, extruding the spinning solution obtained in the step (1) through a screw extruder, filtering, spinning, forming through a coagulating bath to obtain tows, and then washing, oiling and drying to obtain the flame-retardant lyocell filament.

In the present invention, the term "filament" is a chemical fiber form, specifically a filament having a long continuous length.

In the present invention, the term "flame retardant" refers to a substance having the ability to significantly delay the spread of a flame.

Optionally, the nano-hydrotalcite powder has a particle size of 80-200nm, preferably 80-120 nm.

Optionally, in step S1, the nano hydrotalcite powder is modified by the modifier and then mixed with the aqueous solution; the modification treatment steps of the nano hydrotalcite powder are as follows: sequentially adding the modifier and the nano hydrotalcite powder into water, stirring for 2-3h at 70-80 ℃ and 550-700r/min, filtering, washing and drying to obtain the modified nano hydrotalcite powder.

Optionally, the modifier comprises an alkyl phosphate diester salt and/or an alkyl phosphate monoester salt.

Alternatively, the modifier comprises an alkyl phosphate diester salt and an alkyl phosphate monoester salt.

Optionally, the mass ratio of the alkyl phosphate diester salt to the nano hydrotalcite is 3-6: 100.

optionally, the mass ratio of the alkyl phosphate monoester salt to the nano hydrotalcite is 1-2: 100.

optionally, the mass ratio of the flame retardant to the fiber raw material is 15: 30-100, preferably 20-30: 100.

optionally, the concentration of the fiber raw material in the spinning dope is 10 wt% to 20 wt%, preferably 12 wt% to 18 wt%.

Optionally, the flame retardant further comprises an inorganic boron-based flame retardant.

Optionally, the inorganic boron-based flame retardant comprises boric acid.

Optionally, the mass ratio of the inorganic boron flame retardant to the nano hydrotalcite is 1-3: 1, preferably 1-2: 1.

optionally, the flame retardant further comprises an organic phosphorus-based flame retardant.

Optionally, the organophosphorus flame retardant comprises an alkyl phosphonic acid.

Optionally, the alkyl phosphonate includes dimethyl methylphosphonate or diethyl ethylphosphonate.

Optionally, the mass ratio of the organic phosphorus flame retardant to the nano hydrotalcite is 1-10: 1, preferably 3 to 6: 1.

optionally, the flame retardant further comprises an ammonium salt flame retardant.

Optionally, the ammonium salt flame retardant comprises ammonium molybdate, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, or ammonium hydrogen phosphate.

Optionally, the mass ratio of the ammonium salt flame retardant to the nano hydrotalcite is 4-10:1, preferably 5-10: 1.

optionally, the power of the ultrasound is 340-; the time is 1-3h, preferably 2-3 h.

Optionally, in the spinning process, the spinning speed is 40-60m/min, preferably 45-50 m/min; the pore diameter of the spinneret plate is 60-100 μm, preferably 75-90 μm; the length of the pore capillary is 400-600 mu m, preferably 500-600 mu m; the length of the air gap is 6-9cm, preferably 7-8 cm.

Optionally, the concentration of the coagulation bath is 5 wt% to 15 wt%, preferably 5 wt% to 10 wt%; the pH is 9-10, preferably 9.2-9.8; the temperature is 0 to 15 ℃ and preferably 0 to 10 ℃.

Optionally, the temperature of the adopted washing liquid is 70-90 ℃, preferably 70-80 ℃ in the washing process; the time is 1 to 3 hours, preferably 2 to 3 hours; the mass ratio of the washing liquid to the tows is 15: 1-25: 1, preferably 20: 1-25: 1.

optionally, the temperature of the oil bath adopted in the oiling process is 80-90 ℃, and preferably 80-85 ℃; the time is 1.5 to 3 hours, preferably 2 to 3 hours; the mass ratio of the oil bath to the tows is 10-20: 1, preferably 15 to 20: 1.

optionally, the drying temperature is 120-150 ℃, preferably 120-145 ℃; the time is 20-30min, preferably 25-30 min.

The invention also aims to protect the flame-retardant lyocell filaments prepared by the method.

As described above, the flame-retardant lyocell filament and the preparation method thereof provided by the invention have the following beneficial effects:

according to the invention, the flame retardant is added into the fiber raw material solution, so that the flame retardant property of the lyocell filament is endowed.

The invention utilizes the insertion layer property of the layered structure of the nano hydrotalcite powder to insert the fiber raw material into the layers, improves the dispersibility of the nano hydrotalcite powder flame retardant in the fiber raw material solution, and further improves the flame retardant property of the lyocell filament.

The invention effectively inhibits the agglomeration of nano hydrotalcite powder particles through the ultrasonic action, so that the nano hydrotalcite powder is better adsorbed on the surface of the fiber raw material, and the flame retardant property of the lyocell filament is further improved.

According to the invention, the nano hydrotalcite powder is modified by the modifier, so that the dispersibility of the nano hydrotalcite powder in the fiber raw material solution is improved, the nano hydrotalcite powder is adsorbed on the surface of the fiber raw material more, and the flame retardant property of the lyocell filament is further improved.

According to the invention, the nano hydrotalcite powder flame retardant is compounded with the inorganic boron flame retardant and/or the organic phosphorus flame retardant and/or the ammonium salt flame retardant for use, so that the flame retardant property of the lyocell filament can be further improved.

Because the natural plant fiber is used as the raw material and has the advantages of soft hand feeling, good comfort and the like, the lyocell filament yarn provided by the invention has soft hand feeling and good comfort.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

The invention provides a preparation method of flame-retardant lyocell filaments, which comprises the following steps:

s1, dissolving a fiber raw material of lyocell filaments in an aqueous solution of NMMO to obtain a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and performing ultrasonic dispersion to obtain a spinning solution; the flame retardant comprises nano hydrotalcite powder;

wherein, the particle size of the nano hydrotalcite powder is 80-200nm, preferably 80-120 nm;

the mass ratio of the flame retardant to the fiber raw material is 15-30: 100, preferably 20 to 25: 100, respectively;

in the spinning solution, the concentration of the fiber raw material is 10 wt% -20 wt%, preferably 12 wt% -18 wt%;

the ultrasonic intensity is 340-; the time is 1 to 3 hours, preferably 2 to 3 hours;

s2, adding the spinning solution obtained in the step (1) into a screw extruder, further dissolving at 90-120 ℃, filtering, spinning, forming by a coagulating bath to obtain tows, washing in hot water at 70-80 ℃ for 1-3h, oiling in an oil bath, and drying to obtain the flame-retardant lyocell filaments;

wherein, the temperature of the coagulating bath is preferably 0-15 ℃, and more preferably 0-10 ℃; the concentration is 5 to 15 weight percent, preferably 5 to 10 percent; the pH is 9-10, preferably 9.2-9.8;

the mass ratio of the hot water to the tows is 15-25: 1, preferably 20 to 25: 1;

the temperature of the adopted washing liquid is 70-90 ℃, and preferably 70-80 ℃; the washing time is 1-3h, preferably 2-3 h; the mass ratio of the hot water to the tows is 15: 1-25: 1, preferably 20: 1-25: 1;

in the spinning process, the spinning speed is 40-60m/min, preferably 45-50 m/min; the pore diameter of the spinneret plate is 60-100 μm, preferably 75-90 μm, and the length of the capillary tube is 400-600 μm, preferably 500-600 μm; the length of the air gap is 6-9cm, preferably 7-8 cm;

in the oiling process, the temperature of the adopted oil bath is 80-90 ℃, and preferably 80-85 ℃; the time is 1.5 to 3 hours, preferably 2 to 3 hours; the mass ratio of the oil bath to the tows is 10-20: 1, preferably 15 to 20: 1.

in another embodiment of the present invention, the flame retardant further comprises boric acid; the mass ratio of boric acid to nano-water talcum powder is preferably 1-3: 1, more preferably 1-2: 1.

in another embodiment of the present invention, the flame retardant further comprises an organic phosphorus-based flame retardant comprising dimethyl methylphosphonate or diethyl ethylphosphonate; the mass ratio of the organic phosphorus flame retardant to the nano hydrotalcite is 1-10: 1, preferably 3 to 6: 1.

in another embodiment of the present invention, the flame retardant further comprises an ammonium salt flame retardant, the ammonium salt flame retardant being ammonium molybdate, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, or ammonium hydrogen phosphate; the mass ratio of the ammonium salt flame retardant to the nano hydrotalcite is 4: 1-10: 1, preferably 5: 1-10: 1.

in another embodiment of the present invention, in step S1, the nano hydrotalcite powder is modified by the modifier and then mixed with the aqueous solution; the modification treatment steps of the nano hydrotalcite powder are as follows: sequentially adding a modifier and nano hydrotalcite powder into water, stirring for 2-3h at 70-80 ℃ and 550-700r/min, filtering, washing and drying to obtain the modified nano hydrotalcite powder, wherein the modifier comprises alkyl phosphate diester salt and/or alkyl phosphate monoester salt, and the mass ratio of the alkyl phosphate diester salt to the nano hydrotalcite powder is 3-6: 100, respectively; the mass ratio of the alkyl phosphate monoester salt to the nano hydrotalcite is 1-100: 2-100.

Example 1

A preparation method of flame-retardant Lyocell filaments comprises the following steps:

s1, dissolving a fiber raw material wood pulp of lyocell filaments in an aqueous solution of NMMO (N-methyl-MO) to obtain a fiber raw material solution, then adding a nano hydrotalcite powder flame retardant with the particle size of 100nm into the fiber raw material solution, and dispersing for 2 hours under the ultrasonic power of 360W to obtain a spinning solution;

wherein, the concentration of the wood pulp in the spinning solution is 12 wt%; the mass ratio of the nano-hydrotalcite to the wood pulp is 20.5: 100, respectively;

s2, adding the spinning stock solution obtained in the step (1) into a screw extruder, further dissolving at 95 ℃, filtering, spinning at the spinning speed of 50m/min, the pore diameter of a spinneret plate of 75 microns, the length of a pore capillary of 500 microns and the length of an air gap of 7cm, vertically stretching the sprayed filaments in air, solidifying and forming in an NMMO (N-methyl-amino-methyl) aqueous solution with the temperature of 0 ℃, the concentration of 10 wt% and the pH of 9.2, washing in hot water at 80 ℃ (the mass ratio of the hot water to the filament bundle of 20: 1) for 2h, treating in an oil bath at 85 ℃ (the mass ratio of the oil bath to the filament bundle of 25: 1) for 2h, and drying at 145 ℃ for 30min to obtain the flame-retardant lyocell filament.

Example 2

A preparation method of flame-retardant Lyocell filaments comprises the following steps:

s1, mixing nano hydrotalcite powder (the particle size is 100nm), boric acid and ammonium phosphate according to a mass ratio of 3: 1: 10, mixing to obtain a flame retardant;

dissolving the fiber raw material wood pulp of the lyocell filaments in an aqueous solution of NMMO to obtain a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and performing acoustic dispersion for 3 hours under the ultrasonic power of 360W to obtain a spinning solution;

wherein the concentration of the wood pulp in the spinning solution is 15 wt%; the mass ratio of the flame retardant to the wood pulp is 20.5: 100, respectively;

s3, adding the spinning solution obtained in the step (2) into a screw extruder, further dissolving at 115 ℃, filtering, spinning at the spinning speed of 40m/min, the aperture of a spinneret plate of 100 mu m, the length of a pore capillary of 400 mu m and the length of an air gap of 6cm, vertically stretching the sprayed filaments in air, solidifying and forming in an NMMO aqueous solution with the temperature of 15 ℃, the concentration of 15 wt% and the pH of 9.8, washing for 1h in hot water at 90 ℃ (the mass ratio of the hot water to the filament bundle is 25: 1), treating for 3h in an oil bath at 90 ℃ (the mass ratio of the oil bath to the filament bundle is 25: 1), and drying for 30min at 120 ℃ to obtain the flame-retardant lyocell filaments.

Example 3

A preparation method of flame-retardant Lyocell filaments comprises the following steps:

s1, adding ammonium molybdate into diethyl ethylphosphonate, uniformly stirring, then adding nano hydrotalcite powder with the particle size of 80nm, and stirring to obtain a flame retardant;

wherein the mass ratio of the nano-water talcum powder to the diethyl ethylphosphonate to the ammonium molybdate is 1: 4: 5;

dissolving the fiber raw material wood pulp of the lyocell filaments in an aqueous solution of NMMO to obtain a fiber raw material solution, then adding a flame retardant into the fiber raw material solution, and dispersing for 1h under 350W ultrasonic power to obtain a spinning solution;

wherein the concentration of the wood pulp in the spinning solution is 20 wt%; the mass ratio of the flame retardant to the wood pulp is 30: 100, respectively;

s2, adding the spinning solution obtained in the step (1) into a screw extruder, further dissolving at 90 ℃, filtering, spinning at the spinning speed of 60m/min, the pore diameter of a spinneret plate of 60 mu m, the length of a pore capillary of 600 mu m and the length of an air gap of 9cm, vertically stretching the sprayed filaments in air, solidifying and forming in an NMMO aqueous solution with the temperature of 5 ℃, the concentration of 8 wt% and the pH of 10, washing in hot water at 85 ℃ (the mass ratio of hot water to filament bundle is 20: 1) for 2h, treating in an oil bath at 84 ℃ (the mass ratio of oil bath to filament bundle is 24: 1) for 2.5h, and drying at 135 ℃ for 21min to obtain the flame-retardant lyocell filaments.

Example 4

The present embodiment is different from embodiment 1 in that: in step S1, the nano hydrotalcite powder is modified with a modifier and then mixed with an aqueous solution; the modification treatment steps of the nano hydrotalcite powder are as follows: sequentially adding modifier and nano hydrotalcite powder into water, stirring at 75 deg.C and 600r/min for 2.5 hr, filtering, washing, drying at 110 deg.C for 1.5 hr to obtain modified nano hydrotalcite powder,

wherein the modifier consists of sodium n-dodecyl phosphate diester and sodium n-dodecyl phosphate monoester, and the mass ratio of the sodium n-dodecyl phosphate diester to the nano hydrotalcite is 5:100, respectively; the mass ratio of the sodium n-dodecyl phosphate monoester to the nano hydrotalcite is 1.5: 100.

example 5

This embodiment is different from embodiment 4 in that: the modifier is only n-dodecyl sodium phosphate, and the mass ratio of the n-dodecyl sodium phosphate to the nano hydrotalcite is 6.5: 100.

Example 6

This embodiment is different from embodiment 4 in that: the modifier is only n-dodecyl sodium phosphate monoester, and the mass ratio of the n-dodecyl sodium phosphate monoester to the nano hydrotalcite is 6.5: 100.

Comparative example 1

This comparative example differs from example 1 in that: not under ultrasonic conditions.

Performance detection

The finished fibers of examples 1-6 and comparative example 1 were processed into fabrics, and the combustion performance of the fabrics was tested according to GB/T5454-1997 textile combustion test oxygen index method, with the results shown in Table 1.

Table 1 results of performance testing

Source	Limiting oxygen index/%)
		Example 1	27.5
Example 2	30.4
		Example 3	31.2
Example 4	32.5
		Example 5	29.3
Example 6	29.7
		Comparative example 1	22.4

As can be seen from Table 1, the lyocell filaments of examples 1 to 6 were significantly improved in limiting oxygen index as compared with comparative example 1.

The lyocell filament of example 1 has an increased limiting oxygen index of about 23% as compared with comparative example 1.

The lyocell filament of example 2 has an increased limiting oxygen index of about 11% as compared with example 1.

The lyocell filament of example 4 has an increased limiting oxygen index of about 18% as compared with example 1.

The lyocell filaments of example 4 had an increased limiting oxygen index of about 11% and about 9%, respectively, as compared with those of examples 5 and 6.

In conclusion, the flame retardant property of the lyocell filament is obviously improved.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.