JPWO2019205947A5 - - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to the field of nonwoven materials, and more particularly to an ultra- lightweight thermal insulating melt-blown nonwoven fabric and its manufacturing method.

Non-woven fabrics are fabrics that are formed without the need for spinning and weaving, just by orienting or randomly arranging textile short fibers or filaments to form a web structure, and then using mechanical, heat bonding or chemical methods. Be reinforced.

At present, there are various processes for preparing nonwoven fabrics. A method for preparing blown nonwovens has been proposed. In CN 104446333 A, PP (polypropylene) fibers are silanized with APTES (3-amino propyl triethoxy silane) and then immersed in a TEOS (tetraethoxy silane) solution, hydrolysis and co-crosslinking gel reaction, A non-woven fabric with a thin _SiO2 airgel layer is produced, then dipping, co-hydrolysis, co-cross-linking gel reaction are alternately performed multiple times and then dried to obtain PP fiber-reinforced _SiO2 gel material. CN 106838547 A discloses a powder-free nanovoided insulation thermal insulation felt (board) and a method of making the same, according to which the fibers are sheeted or rolled using conventional needlepunching or carding techniques. A fibrous base material of shaped felt is produced, then a binder is immersed or sprayed on the fiber surface of the base material, and finally a nanovoid insulation material polished on the fiber is sprayed to obtain a heat insulating felt ( board).

However, all of the above methods have certain technical problems. However, since the bulk density difference between PP and airgel is large, it is difficult to obtain a nonwoven fabric with uniformly dispersed airgel and adjustable particle size in a melt blown apparatus with a limited melting zone. In CN104446333 A, after silanizing the surface of the PP fiber, immersion in the TEOS solution, co-hydrolysis, and co-crosslinking gel reaction must be performed multiple times, so the process is complicated and time-consuming. chemical modification has to be carried out immediately, which reduces the mechanical performance of the PP fiber and reduces the mechanical performance of the final product. In addition, the _SiO2 xerogel, which is not in direct contact with the surface of the PP fiber, is very easy to fall off during use, shortening the service life of the material, causing deterioration of the use environment and harming the health of the user. In CN 106838547 A, a heat insulating felt (plate) that does not fall off powder is prepared by a method that combines three layers: a fiber layer, an adhesive layer, and a nanovoid heat insulating layer. content and penetration depth into the fiber substrate are greatly affected by the size of voids between fibers in the fiber substrate. corresponds to a filtering material, it is difficult to achieve the effect of blocking the nanovoid heat insulating material only on the outer surface of the substrate and dispersing the nanovoid heat insulating material uniformly. Foreign matter easily adheres to the material, which affects performance such as appearance and air permeability.

The present invention solves the problems of low uniformity of airgel dispersion, uncontrollable particle size , and easy falling off of airgel during use in the preparation of airgel modified nonwoven fabric by melt blown method in the existing technology. To provide a melt - blown nonwoven fabric for heat and heat insulation and a method for producing the same.

To achieve the above objects, according to one aspect of the present invention, a method for preparing airgel-modified polypropylene is provided. The preparation method prepares the airgel-modified polypropylene by the propylene polymerization process, which adds the airgel and mixes with the reactants with low viscosity before or during the polymerization reaction to achieve uniform dispersion of the airgel. with the proviso that the reactants comprise propylene monomers, catalysts and adjuvants, the particle size of the airgel is between 20 nm and 100 μm, and the porosity is between 40% and 99.9% , the bulk density is 3-500 g/L, and the volume fraction accounts for 20%-60% of the volume of the ultra-light heat insulating heat-retaining melt-blown nonwoven fabric prepared by airgel-modified polypropylene.

Furthermore, the propylene polymerization process is a gas phase propylene polymerization process, a slurry propylene polymerization process or a liquid phase propylene polymerization process.

Further, in the gas phase propylene polymerization process, the addition of airgel and mixing with reactants with low viscosity, mixing airgel with propylene monomer, or mixing with catalyst, or alone in the polymerization reactor. Including adding and mixing with the reactants or combining any of the above mixing schemes.

Furthermore, in the slurry method propylene polymerization step, adding the airgel and mixing with a reactant with low viscosity, mixing the airgel with a slurry liquid consisting of a catalyst and a hydrocarbon solvent, or mixing with a propylene monomer or added alone to the polymerization reactor and mixed with the reactants, or any combination of the above mixing schemes.

Furthermore, the slurry method propylene polymerization step further includes deashing and precipitating the obtained polypropylene raw material to separate the solvent and the random body , followed by kneading.

Further, in the liquid phase propylene polymerization process, the addition of airgel and mixing with reactants with low viscosity, mixing the airgel with propylene monomer, or mixing with catalyst, or alone in the polymerization reactor. Including adding and mixing with the reactants or combining any of the above mixing schemes.

Furthermore, it includes flash distillation separation to remove the random copolymer in the liquid phase propylene polymerization step.

According to another aspect of the present invention, there is provided a method for preparing an ultra-lightweight thermal insulating melt-blown nonwoven fabric. The preparation method includes preparing an airgel-modified polypropylene by any of the above methods, and feeding the airgel-modified polypropylene into a melt-blown apparatus to prepare an ultra-lightweight, heat-insulating, heat-retaining melt-blown nonwoven fabric.

According to still another aspect of the present invention, there is provided an airgel-modified polypropylene prepared by any of the airgel-modified polypropylene preparation methods described above, wherein the airgel size in the airgel-modified polypropylene is 15 nm to 100 μm. .

According to still another aspect of the present invention, an ultralight heat insulating melt-blown nonwoven fabric prepared by the method for preparing an ultralight heat insulating meltblown nonwoven fabric described above, wherein the airgel size is 15 nm to 10 μm. A heat insulating melt-blown nonwoven fabric is provided.

According to the technical solution of the present invention, without adding any dispersing aid, airgel with different particle size and porosity can be selected and used, and the amount of airgel added can be changed to improve the mixing method. , To prepare airgel-modified polypropylene particles with good melt-blown performance with airgel uniformly dispersed and melt-blown polypropylene nonwoven fabric with ultra-light heat insulation and heat retention function, the airgel in the nonwoven fabric does not fall off easily during use, Long service life.

It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other unless contradictory. Hereinafter, the present invention will be described in detail by combining examples.

In order to solve the problems of low uniformity of airgel dispersion, uncontrollable particle size , and easy falling off of airgel when preparing airgel-modified nonwoven fabrics by melt blown method in the existing technology, the present invention provides: Based on an in-situ polymerization method, propylene monomer is used as a raw material to determine specific airgel characteristic parameters ( particle size , porosity, bulk density (3-500 g/L) (bulk density: The mass of the unit volume is the mass of the unit volume including the pores inside and outside the particles and the voids between the particles), etc.), and by limiting the amount of airgel added and the mixing method, the statistical size of the airgel can be adjusted and dispersed uniformly. and a modified polypropylene with good melt-blown performance, which can be obtained through melt-blowing to obtain an airgel-modified melt-blown PP (polypropylene) nonwoven fabric with good heat insulation and heat retention function provide a way. According to the present invention, the airgel existing in the technology of preparing airgel felt (board) by the existing fiber filling method easily falls off, the service life is short, the use environment deteriorates, and the user's health is damaged. Problems can be effectively avoided.

According to an exemplary embodiment of the present invention, a method for preparing airgel modified polypropylene is provided. The preparation method prepares the airgel-modified polypropylene by the propylene polymerization process, which adds the airgel and mixes with the reactants with low viscosity before or during the polymerization reaction to achieve uniform dispersion of the airgel. with the proviso that the reactants comprise propylene monomers, catalysts and adjuvants, the particle size of the airgel is between 20 nm and 100 μm, and the porosity is between 40% and 99.9% , the bulk density is 3-500 g/L, and the volume fraction accounts for 20%-60% of the volume of the ultra-light heat insulating heat-retaining melt-blown nonwoven fabric prepared by airgel-modified polypropylene.

In the present invention, the catalyst can be Ziegler-Natta catalyst system, metallocene catalyst system, and the amount used is 30-0.8 kg. pp/g. cat (0.1-5 ppm), the auxiliary agent can be hydrogen, and the amount used is 50-1000 ppm.

According to the technology of the present invention, under the condition that no dispersing agent is added, airgel with different particle size and porosity can be selected and used, and the amount of airgel added can be changed to improve the mixing method. It is possible to prepare airgel-modified polypropylene particles that are uniformly dispersed and have good melt-blown performance, and melt-blown polypropylene nonwoven fabrics that have ultra-light heat insulation and heat retention functions. In addition, since the airgel modified polypropylene is obtained by in-situ polymerization, such a preparation method provides a polymer with uniform powder dispersion and tunable particle size , and during processing, the melt of the polypropylene melts on the surface. Due to the action of tension and channel shear force, the airgel is covered in the polypropylene substrate, and the airgel in the nonwoven fabric does not fall off during use, and has a long service life.

According to a typical embodiment of the present invention, the propylene polymerization process is a gas phase propylene polymerization process, a slurry propylene polymerization process or a liquid phase propylene polymerization process.

According to an exemplary embodiment of the present invention, in the gas phase propylene polymerization process, adding airgel and mixing with reactants with low viscosity, mixing airgel with propylene monomer, or mixing with catalyst or added alone to the polymerization reactor and mixed with the reactants, or any combination of the above mixing schemes.

According to a typical embodiment of the present invention, in the slurry propylene polymerization step, the addition of the airgel and mixing with the low-viscosity reactant is performed by mixing the airgel with the slurry-like liquid comprising the catalyst and the hydrocarbon-based solvent. or mixed with propylene monomer, or added alone to the polymerization reactor and mixed with the reactants, or any combination of the above mixing schemes.

Preferably, the slurry propylene polymerization step further includes deashing and precipitating the obtained polypropylene raw material to separate the solvent and the random body , followed by kneading.

According to an exemplary embodiment of the present invention, in the liquid phase propylene polymerization process, the addition of airgel and mixing with the low viscosity reactants, mixing the airgel with propylene monomer, or mixing with the catalyst. or added alone to the polymerization reactor and mixed with the reactants, or any combination of the above mixing schemes.

Preferably, the liquid phase propylene polymerization step includes flash distillation separation to remove the random copolymer .

According to an exemplary embodiment of the present invention, a method for preparing an ultra-lightweight thermal insulating melt-blown nonwoven fabric is provided. The preparation method includes preparing an airgel-modified polypropylene by any of the above methods, and feeding the airgel-modified polypropylene into a melt-blown apparatus to prepare an ultra-lightweight, heat-insulating, heat-retaining melt-blown nonwoven fabric.

According to an exemplary embodiment of the present invention, airgel modified polypropylene is provided. The airgel-modified polypropylene is prepared by any of the preparation methods described above, and the airgel size in the airgel-modified polypropylene is 15 nm to 100 μm.

According to an exemplary embodiment of the present invention, an ultra-lightweight thermal insulating melt-blown nonwoven fabric is provided. The ultralight heat insulating melt-blown nonwoven fabric is prepared by the above preparation method, and the size of airgel in the ultralight heat insulating meltblown nonwoven fabric is 15 nm-10 μm. The nonwoven fabric has merits such as being lightweight and having a high heat-retaining effect.

Hereinafter, the beneficial effects of the present invention will be further described by combining the examples, and the steps or raw materials not described in detail in the following examples can be realized by technical means or ordinary raw materials commonly used in the field. can.

Example 1
Gas phase method:
Dehydration drying was performed on the airgel by the method of heat drying or dehydrating agent. An inert gas or a deoxidizing agent was used to deoxidize the dehydrated airgel to obtain a dry, deoxidized aerogel.

Ultra high activity catalyst TiCl ₃ /diisobutyl dimethoxy silane/MgCl ₂ /Et ₃ Al (mass ratio 25:55:21:53, TiCl ₃ is 8 ppm), purified propylene monomer, hydrogen ( 150 ppm), dehydrated and deoxidized airgel (2 wt % of propylene) are sequentially charged into the first horizontal stirred bed reactor, stirring is started, the temperature is raised to 71° C., and the pressure is 2.25 MPa. The obtained polypropylene powder is charged into the second horizontal stirred bed reactor by means of a powder conveying fan, and at the same time, the purified propylene monomer and hydrogen are added to the second horizontal stirred bed reactor and stirred. is started, the temperature is increased to 71° C. and the pressure is 2.25 MPa. After the polymerization reaction, the polypropylene powder is separated from gas in a bag filter, dried and deactivated in a degassing chamber, and enters an extrusion granulation system for kneading and granulation.

Polypropylene (PP) melt-blown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 715 g/10 min.

The above polypropylene particles are melt blown with ordinary polypropylene melt blown equipment and process parameters, the thermal conductivity coefficient is 0.029 W / (m K), and the airgel is the final ultralight insulation An aerogel-containing melt-blown polypropylene nonwoven was obtained, which occupied 56% of the volume fraction of the heat-retaining melt-blown nonwoven. The specific melt blown parameters are a die temperature of 245° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 145° C. and a hot air velocity of 500 m/s.

Example 2
Liquid phase method:
The airgel was subjected to dry deacidification pretreatment in the same manner as in Example 1.

3000 kg of purified propylene monomer is put into a 12 m ³ polymerization vessel, dehydrated and deoxidized airgel is added to the polymerization vessel through the raw material addition port, stirring is started, and then the catalyst TiCl ₃ /AlEt ₂ Cl / Lewis base. (TiCl ₃ is 50 ppm, the aluminum/titanium molar ratio is 11, and the Lewis base/titanium molar ratio is 3.), hydrogen (150 ppm) is added, the temperature is increased to 75° C. and the pressure is 3. At .5 MPa, start the polymerization. The reaction is terminated by polymerizing until conversion reaches 70%-80%, unreacted propylene monomer is discharged, polypropylene is taken into the flash still, flash distillation is followed by air passage and discharge. Polypropylene powder was obtained by extrusion granulation to obtain polypropylene particles.

Polypropylene (PP) melt-blown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 898 g/10 min.

The above polypropylene particles are melt-blown with ordinary polypropylene melt-blown equipment and process parameters, the thermal conductivity coefficient is 0.031 W/(mK), and the airgel is the final ultra-lightweight heat insulation and heat insulation An aerogel-containing melt-blown polypropylene nonwoven was obtained, accounting for 49% of the volume fraction of the melt-blown nonwoven. The specific melt blown parameters are a die temperature of 240° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 140° C. and a hot air velocity of 400 m/s.

Example 3
Slurry method:
The airgel was subjected to dry deacidification pretreatment in the same manner as in Example 1.

Catalyst TiCl ₃ /AlEt ₂ Cl/Lewis base (TiCl ₃ is 50 ppm, aluminum/titanium molar ratio is 11, Lewis base/titanium molar ratio is 3), hydrogen (150 ppm) is prepolymerized. It is charged into a reactor, mixed with hexane as an inert solvent until it becomes a slurry liquid, and a certain amount of gaseous purified propylene is added under nitrogen blanket conditions to polymerize at a temperature of 10-25°C for 1-2 hours. to obtain a prepolymerized catalyst.

The prepolymerized catalyst and the dehydrated and deoxidized airgel are put into liquid refined propylene, stirring is started, the temperature is raised to 70° C., and the pressure is 1.0 MPa to initiate polymerization. The reaction is terminated by polymerizing until conversion reaches 70%-80%, unreacted propylene monomer is discharged and the polypropylene is taken into a flash still and flash distilled followed by passing air and washing. , centrifugal separation, drying, taking out to obtain polypropylene powder, extrusion granulation to obtain polypropylene particles.

Polypropylene (PP) meltblown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 912 g/10 min.

The above polypropylene particles are melt-blown with ordinary polypropylene melt-blown equipment and process parameters, the thermal conductivity coefficient is 0.035 W / (m K), and the airgel is the final ultra-lightweight heat insulation and heat insulation An aerogel-containing melt-blown polypropylene nonwoven was obtained, accounting for 40% of the volume fraction of the melt-blown nonwoven. The specific melt blown parameters are a die temperature of 240° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 140° C. and a hot air velocity of 400 m/s.

Example 4
Slurry method:
The airgel was subjected to dry deacidification pretreatment in the same manner as in Example 1.

Dehydrated deoxidized airgel, catalyst TiCl ₃ /AlEt ₂ Cl/Lewis base (TiCl ₃ is 50 ppm, aluminum/titanium molar ratio is 11, Lewis base/titanium molar ratio is 3), hydrogen (150ppm) was charged into the prepolymerization reactor, mixed with hexane, an inert solvent, until slurry became liquid, and under nitrogen blanket conditions, a certain amount of gaseous purified propylene was added, and the temperature was adjusted to 10-25°C. A prepolymerized catalyst was obtained by polymerizing at temperature for 1-2 h.

The above catalyst is added to the liquid purified propylene, stirring is started, the temperature is raised to 70° C. and the pressure is 1.0 MPa to initiate polymerization. The reaction is terminated by polymerizing until conversion reaches 70%-80%, unreacted propylene monomer is discharged and the polypropylene is taken into a flash still and flash distilled followed by passing air and washing. , centrifugal separation, drying, taking out to obtain polypropylene powder, extrusion granulation to obtain polypropylene particles.

Polypropylene (PP) melt-blown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 804 g/10 min.

The above polypropylene particles are melt-blown with ordinary polypropylene melt-blown equipment and process parameters, the thermal conductivity coefficient is 0.030 W / (m K), and the airgel is the final ultra-lightweight heat insulation and heat insulation An aerogel-containing melt-blown polypropylene nonwoven was obtained, accounting for 52% of the volume fraction of the melt-blown nonwoven. The specific melt blown parameters are a die temperature of 245° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 145° C. and a hot air velocity of 500 m/s.

Example 5:
Gas phase method:
Dehydration drying was performed on the airgel by the method of heat drying or dehydrating agent. An inert gas or a deoxidizing agent was used to deoxidize the dehydrated airgel to obtain a dry, deoxidized aerogel.

Ultra-high activity catalyst _TiCl3 /diisobutyldimethoxysilane/ _MgCl2 / _Et3Al (mass ratio is 25:55:21:53, _TiCl3 is 8ppm), purified propylene monomer and hydrogen (150 ppm) are sequentially charged into the first horizontal stirred bed reactor, stirring is started, the temperature is raised to 71° C., and the pressure is 2.25 MPa. The obtained polypropylene powder was introduced into the second horizontal stirred bed reactor by means of a powder-conveying fan, and at the same time the dehydrated and deoxidized airgel (first horizontal stirred bed reactor 0.8 wt% of the propylene in the vessel), purified propylene monomer and hydrogen are added, stirring is started, the temperature is raised to 71°C, and the pressure is 2.25 MPa. After the polymerization reaction, the polypropylene powder is separated from the gas by a bag filter, dried and deactivated in a degassing chamber, and enters an extrusion granulation system for kneading and granulation.

Polypropylene (PP) melt-blown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 1206 g/10 min.

The above polypropylene particles are melt-blown with ordinary polypropylene melt-blown equipment and process parameters, and the thermal conductivity coefficient is 0.058 W / (m K), and the airgel is the final ultra-light insulation and heat insulation. An aerogel-containing melt-blown polypropylene nonwoven was obtained, accounting for 23% of the volume fraction of the melt-blown nonwoven. The specific melt blown parameters are a die temperature of 245° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 145° C. and a hot air velocity of 500 m/s.

Comparative Example 1:
Slurry method:
The airgel was subjected to dry deacidification pretreatment in the same manner as in Example 1.

Catalyst TiCl ₃ /AlEt ₂ Cl/Lewis base (TiCl ₃ is 50 ppm, aluminum/titanium molar ratio is 11, Lewis base/titanium molar ratio is 3), hydrogen (150 ppm) is prepolymerized. It is put into a reactor, mixed with hexane as an inert solvent until it becomes a slurry liquid, and a fixed amount of gaseous purified propylene is added under a nitrogen blanket condition, and polymerized at a temperature of 10 to 25° C. for 1 to 2 hours. to obtain a prepolymerized catalyst.

The prepolymerized catalyst and the deoxidized airgel are added to the liquid purified propylene, stirring is started, the temperature is raised to 70° C., and the pressure is 1.0 MPa to initiate polymerization. The reaction is terminated by polymerizing until conversion reaches 70%-80%, unreacted propylene monomer is discharged and the polypropylene is taken into a flash still and flash distilled followed by passing air and washing. , centrifugal separation, drying, taking out to obtain polypropylene powder, extrusion granulation to obtain polypropylene particles.

Polypropylene (PP) melt-blown specific material in GB/T 30923-2014 plastics was used to test the above polypropylene, resulting in a melt index of 1327 g/10 min.

The above polypropylene particles are melt-blown with ordinary polypropylene melt-blown equipment and process parameters, the thermal conductivity coefficient is 0.084 W/(m K), and the airgel is the final ultralight heat insulation and heat insulation An aerogel-containing melt-blown polypropylene nonwoven was obtained, accounting for 10% of the volume fraction of the melt-blown nonwoven. The specific melt blown parameters are a die temperature of 240° C., a distance from the die to the catcher of 0.152 m, a hot air temperature of 140° C. and a hot air velocity of 400 m/s.

As described above, the above embodiments of the present invention can achieve the following technical effects.

1) Provided a simple and efficient airgel mixing method, and obtained airgel-modified PP, ultra-light heat insulation and heat retention PP melt-blown non-woven fabric with good melt-blown performance.

2) It became possible to adjust the particle size and dispersibility of airgel in polypropylene and its melt-blown nonwoven fabric.

The above is only a preferred embodiment of the present invention, and does not limit the present invention, and various modifications and variations can be made to the present invention by those skilled in the art. All modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims (9)

Preparing an airgel modified polypropylene, wherein the airgel is added and mixed with the reactants prior to or during the in-situ polymerization reaction to achieve uniform dispersion of the airgel. An airgel modified polypropylene is prepared by a polymerization process, wherein the reactants include propylene monomer, a catalyst, and an auxiliary agent that does not contain a dispersing aid, and the particle size of the airgel is 20 nm to 100 μm; The porosity is 40%-99.9%, the bulk density is 3-500g/L, the airgel accounts for 20%-60% of the volume of the heat insulating melt-blown nonwoven fabric, and the auxiliary agent is hydrogen. to be and
A method for preparing a heat-insulating heat-retaining melt-blown nonwoven fabric, comprising: putting the airgel-modified polypropylene into a melt-blowing device to prepare a heat-insulating heat-retaining melt-blown non-woven fabric . 2. The preparation method according to claim 1, wherein the propylene polymerization step is a gas phase propylene polymerization step, a slurry propylene polymerization step or a liquid phase propylene polymerization step. In the gas phase propylene polymerization step, adding airgel and mixing with the reactants, mixing the airgel with propylene monomer, mixing with a catalyst, or adding alone to the polymerization reactor , mixing with the reactants, or any combination of said mixing schemes. In the slurry method propylene polymerization step, adding an airgel and mixing it with the reactants; mixing the airgel with a slurry liquid comprising a catalyst and a hydrocarbon solvent; or mixing the airgel with a propylene monomer; or added alone to the polymerization reactor and mixed with the reactants, or any combination of said mixing schemes. 5. The preparation method according to claim 4, wherein the slurry method propylene polymerization step further comprises deashing and precipitating the obtained polypropylene raw material to separate the solvent from the random body, followed by kneading. In the liquid phase propylene polymerization step, adding airgel and mixing with the reactants, mixing the airgel with propylene monomer, mixing with a catalyst, or adding alone to the polymerization reactor , mixing with the reactants, or any combination of said mixing schemes. 7. The preparation method according to claim 6, characterized in that in the liquid phase propylene polymerization step, the random copolymer is removed by flash distillation separation. The preparation method according to claim 1, wherein the airgel size in the airgel-modified polypropylene is 15 nm to 100 µm. A heat-insulating heat-retaining melt-blown nonwoven fabric prepared by the preparation method according to any one of claims 1 to 8, characterized in that the size of the airgel is 15 nm-10 μm.