CN116724153A

CN116724153A - Meltblown webs made from polypropylene

Info

Publication number: CN116724153A
Application number: CN202180089698.7A
Authority: CN
Inventors: A·梅达德; F·奥-牧泰利; H·N·A·M·斯汀贝克斯-曼廷; H·科尔麦林克; T·V·M·恩多罗; G·博文; R·J·P·施普尔; M·多赫曼
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2020-12-08
Filing date: 2021-12-07
Publication date: 2023-09-08
Also published as: EP4259864A1; US20240035203A1; WO2022122722A1

Abstract

The present invention relates to a meltblown web comprising meltblown fibers obtained by: a) Melt mixing a propylene-based polymer, a first peroxide and a second peroxide at a temperature of 180 ℃ to 240 ℃, preferably 200 ℃ to 220 ℃, wherein the first peroxide is at a first temperature T _1/2 1 having a half-life of 1 hour, said second peroxide at a second temperature T _1/2 2 has a half-life of 1 hour, wherein T _1/2 2 is higher than T _1/2 1, and b) processing the composition obtained by step a) by a melt blowing process at a temperature of 240 ℃ to 300 ℃, preferably 245 ℃ to 280 ℃, to provide the melt blown fibers.

Description

Meltblown webs made from polypropylene

The present invention relates to meltblown webs made from meltblown fibers made from polypropylene compositions and their use.

Meltblown webs are widely used in the hygiene and filtration industries. Important properties of meltblown webs include static head and air permeability. Meltblown webs may be made from polypropylene. In known methods of making melt blown webs, polypropylene having a high melt flow index is subjected to a melt blowing process. It is known to obtain polypropylene with a high melt flow index by viscosity reduction of propylene with a lower melt flow index, which is typically done using peroxides or hydroxylamine esters. Viscosity reduction is also commonly described as "visbreaking," melt converting, "" modified rheology, "or" controlled rheology.

WO2007126961 discloses a process for producing propylene polymer pellets comprising mixing a pure propylene polymer with a hydroxylamine ester compound to form a blend, wherein the pure propylene polymer exhibits an MFR of 50dg/min to 400dg/min, and pelletizing the blend. These pellets are used to make nonwoven fabrics. The mixing and granulating steps occur at a temperature below the temperature at which the hydroxylamine ester compound is substantially thermally degraded, preferably no higher than 250 ℃. The blend exhibits an MFR of 1 to 4 times that of the pure propylene polymer. The blend pellets are heated to form a high MFR polymer and thereby produce fibers. The high MFR polymer exhibits an MFR of about 400 to 3500 dg/min.

EP3034522 describes a meltblown web comprising meltblown fibers made from a polypropylene composition comprising a polymeric nucleating agent, wherein the polypropylene composition has been visbroken without the use of a peroxide. Visbreaking is performed by hydroxylamine esters. Can be used forExamples of commercially available hydroxylamine esters areCR76, which is commercially available from BASF.

US20160311944 describes a process for preparing rheology-controlled polypropylene characterized by comprising a stage of mixing a propylene polymer with at least one low-reactivity organic peroxide, wherein after the stage of mixing the polypropylene it comprises at least one peroxide having at least 70% active oxygen. As an example of the low-reactivity organic peroxide, trigonox311 is mentioned. As examples of organic peroxides which are not low-reactivity organic peroxides, trigonox101, trigonox 301 and Luperox 130 are mentioned. It should be mentioned that the polypropylene obtained can be used for the production of nonwoven fabrics, such as spunbond fabrics and meltblown fabrics.

EP3081677A2 discloses a process for preparing controlled rheology polypropylene characterized by comprising a stage of mixing a propylene polymer with at least one low reactive organic peroxide.

EP384431A2 discloses a process for making a normally solid, gel-free propylene polymer material having a branching index of less than 1 and having a strain hardened extensional viscosity from a normally solid, amorphous to predominantly crystalline propylene polymer material having no strain hardened extensional viscosity, the process comprising:

(1) Mixing a peroxide having a low decomposition temperature with a linear propylene polymer material in a mixing vessel in the substantial absence of atmospheric oxygen or its equivalent, the material being at room temperature to 120 ℃,

(2) Heating or maintaining the resulting mixture at room temperature to 120 ℃ in the substantial absence of atmospheric oxygen or its equivalent for a time sufficient to decompose the peroxide and cause substantial fragmentation of the linear propylene polymer material to form substantial long chain branches but insufficient to cause gelation of the propylene polymer material;

(3) The propylene polymer material is treated to substantially deactivate all free radicals present in the propylene polymer material in the substantial absence of atmospheric oxygen or its equivalent.

It is an object of the present invention to provide a meltblown web having desirable properties such as high static head and low air permeability.

Accordingly, the present invention provides a meltblown web comprising meltblown fibers obtained by:

a) Melt mixing a propylene-based polymer, a first peroxide and a second peroxide at a temperature of 180 ℃ to 240 ℃, preferably 200 ℃ to 220 ℃, wherein the first peroxide is at a first temperature T _1/2 1, the second peroxide having a half-life of 1 hour at a second temperature T _1/2 2 has a half-life of 1 hour, wherein T _1/2 2 is higher than T _1/2 1, and

b) Processing the composition obtained by step a) by a melt blowing process at a temperature of 240 ℃ to 300 ℃, preferably 245 ℃ to 280 ℃, to provide a melt blown fiber.

According to a further aspect, the present invention provides a process for making a meltblown web comprising meltblown fibers, comprising the steps of:

According to the present invention, a meltblown web is produced from a polypropylene composition comprising two or more types of peroxides having different decomposition temperatures. In step a) of the process of the present invention, heating at a lower temperature activates mainly the peroxide having a lower decomposition temperature and thereby a partially visbroken polypropylene is obtained. Such partially visbroken polypropylene compositions, which may optionally be formed into pellets, are converted to meltblown fibers at elevated temperatures. The initial visbreaking and optional pelletization and the final visbreaking by melt blowing can be performed from different materials at different locations.

Surprisingly, the meltblown webs according to the present invention have desirable properties such as high static head and low air permeability. Surprisingly, it was found that these properties of the meltblown articles according to the invention are better than those of meltblown articles made by melt blowing polypropylene which already has a high melt flow index.

It is noted that US4897452 discloses a process for producing polypropylene pellets by adding two free radical generators G1 and G2 to a polymer, the half-life of G2 being at least 20 times the half-life of G1 at the pelletisation temperature. Non-tacky pellets with good reproducibility were obtained. US4897452 does not mention melt blown webs. Examples of the radical generator G1 are given, each of which has a half-life of 1 hour at a temperature of 105 to 119 ℃ except that di-t-butyl peroxide has a half-life of 1 hour at a temperature of 146 ℃. Examples of the radical generator G2 include diisopropylbenzene hydroperoxide, which has a half-life of 1 hour at a temperature of 154 ℃ and a half-life of 0.1 hour at a temperature of 207 ℃. In example 1, pellets were converted to continuous filaments having a melt index of 190g/10min measured according to ASTM method D1238 condition E at 190 ℃/2.16 kg. This is below the melt index of filaments typically used to make meltblown webs.

Step a)

Step a) comprises melt mixing under conditions where mainly the first peroxide has a visbreaking effect. The composition obtained by this step may sometimes be referred to herein as a partial visbreaking composition.

The melt mixing is carried out at a temperature of 180 ℃ to 240 ℃, preferably 210 ℃ to 230 ℃.

The duration of the melt mixing can be suitably selected by the person skilled in the art depending on the targeted viscosity properties, for example 0.01 to 0.03 hours.

Prior to this melt mixing step, there may or may not be a step of obtaining the mixture (which may or may not be in pellet form) under conditions where essentially no visbreaking occurs. The mixture so obtained may sometimes be referred to herein as a pre-visbreaking composition.

The pre-visbreaking composition may be prepared by reacting a propylene-based polymer, a first peroxide and a second peroxide at a temperature not exceeding T1 (wherein T _1/2 1 at least 50 ℃ higher than T1) and forming the mixture into pellets. The duration of mixing can be appropriately selected by the person skilled in the art. Preferably, T1 is 0 to 60 ℃, e.g. 10 to 30 ℃.

Preferably, the propylene-based polymer has a melt flow index MFI of, for example, 0.1 to 60dg/min, such as 0.1 to 1.0dg/min, 1.0 to 5.0dg/min, 5.0 to 15dg/min, or 15 to 60dg/min, measured according to ISO1133-1:2011 at 230 ℃ and 2.16kg _A 。

The composition obtained by step a) has a second melt flow index MFI determined by ASTM D1238-13 (2 mm die) at 190℃and 2.16kg _B . Preferably, the MFI _B With MFI _A The ratio of (2) is 5 to 100, for example 8 to 80.

Preferably, the MFI _B From 10 to 300dg/min, for example from 100 to 200dg/min.

The composition obtained by step a) may be formed into pellets before being subjected to step b).

Step b)

Step b) includes processing the composition obtained from step a) by a melt blowing process to provide melt blown fibers, which composition may be in the form of pellets. Step b) is carried out at a temperature at which both the first peroxide and the second peroxide have a visbreaking effect. The composition obtained by this step may sometimes be referred to herein as a highly visbroken composition.

The melt blowing process for providing the melt blown fibers is conducted at a temperature of 240 ℃ to 300 ℃, more preferably 245 ℃ to 280 ℃.

The meltblown fibers have a third melt flow index MFI as measured by ASTM D1238-13 procedure C (1 mm die) at 230℃and 2.16kg _C 。

Preferably, the MFI _C With MFI _A The ratio of (2) is 5 to 100, for example 8 to 80.

MFI _C Greater than MFI _B . Preferably, the MFI _C With MFI _B The difference between them, i.e. MFI _C -MFI _B At least 30dg/min, more preferably at least 40dg/min, more preferably at least 50dg/min, more preferably at least 60dg/min, more preferably at least 70dg/min. Preferably, the MFI _C With MFI _B The difference between them, i.e. MFI _C -MFI _B At most 100dg/min, for example at most 90dg/min.

Preferably, the MFI _C 100 to 300dg/min, e.g., 150 to 250dg/min.

Meltblown webs are nonwoven structures composed of meltblown fibers that are manufactured by a meltblowing process. The meltblowing process is typically a one-step process in which high velocity air blows molten thermoplastic resin from an extruder die onto a conveyor or a receiving screen to form a fibrillated self-adhesive web.

Preferably, the meltblown fibers have an average filament fineness of at most 5 μm.

In some embodiments, step b) comprises processing the mixture of the composition obtained from step a) and other polymer by a melt blowing process to provide a melt blown fiber. Preferably, the other polymer is a propylene-based polymer. Preferably, the weight ratio between the pellets and the other polymer is 80:20 to 100:0, e.g. 90:10 to 100:0 or 95:5 to 100:0. More typically, however, step b) comprises processing the composition obtained from step a) by a melt blowing process in the absence of other polymers to provide melt blown fibers.

The invention also provides articles comprising the meltblown webs according to the invention. Preferably, the article is selected from: filter media, (e.g., air filters such as clean room filters, ventilation filters, HVAC (heating, ventilation, and air conditioning) filters, mask filters, respirator filters, vacuum cleaners and room air cleaners filters, liquid filters such as water filters, food and beverage filters, and chemical and solvent filters), medical/surgical gowns, medical/surgical drapes, medical/surgical masks, diapers, feminine hygiene products, sanitary napkins, adult incontinence products, absorbent pads, wipes (including household wipes and industrial cleaning wipes and sanitary wipes), oil barriers, food fat absorbent wipes, protective clothing, face masks (including industrial masks), wet wipe articles for electronic products (e.g., battery separators and cable bags), adhesives (e.g., hot melt adhesives), insulators (e.g., garment thermal insulators and sound insulation articles), composite nonwovens. The present invention also provides a method of making an article comprising a method of making a meltblown web according to the present invention.

The invention also provides the use of a meltblown web according to the invention for the manufacture of an article selected from the group consisting of: filter media (e.g., air filters such as clean room filters, ventilation filters, HVAC (heating, ventilation, and air conditioning) filters, mask filters, respirator filters, gas mask filters, vacuum cleaner filters, and room air cleaner filters, liquid filters such as water filters, food and beverage filters, and chemical and solvent filters), medical/surgical gowns, medical/surgical drapes, medical/surgical masks, diapers, feminine hygiene products, sanitary napkins, adult incontinence products, absorbent pads, wipes (including household wipes and industrial cleaning wipes and sanitary wipes), oil and gas barriers, food fat absorbing wipes, protective apparel, masks (including industrial masks), wet wipe articles for electronic products (e.g., battery separators and cable bags), adhesives (e.g., hot melt adhesives), insulators (e.g., garment thermal insulators and sound insulation articles), composite nonwovens.

The weight per unit area of the meltblown web is set according to the application and the properties sought, such as permeability, static head, and mechanical properties. In general, it is preferred that the meltblown webs have at least 1g/m ² Preferably 1 to 250g/m ² Is a weight per unit area.

If the meltblown web according to the invention is produced as a single layer web (e.g. for air filtration purposes), it preferably has at least 1g/m ² More preferably at least 4g/m ² More preferably 7 to 250g/m ² More preferably 8 to 200g/m ² Is a weight per unit area. It can also be used as a multilayer, such as SMS-web (spunbond, meltblown, spunbond)Viscosity) or SSMMS (spunbond, meltblown, spunbond) production, for example for hygiene and/or medical applications. In such a case, the weight per unit area of the meltblown web may typically be at least 0.8g/m ² More preferably at least 1g/m ² More preferably 1 to 30g/m ² Still more preferably 1.3 to 20g/m ² 。

The meltblown webs according to the present invention are single layer webs or multi-layer structures as described above, and the meltblown webs contained in the multi-layer structures may be combined with other layers, i.e., polycarbonate layers or the like, depending on the desired end use of the article being produced.

Preferably, the meltblown webs according to the invention have a static head (3 rd drop, cm H) of at least 65mbar ₂ O resp.mbar) measured according to nwsp.080.6 (R0) method of 2015 described in the experimental section.

Preferably, the meltblown webs according to the invention have a concentration of at most 440L/m measured according to NSWP.070.1.R0 (pressure drop set to 200 Pa) ² Air permeability per sec.

Propylene-based polymers

The propylene-based polymers used according to the present invention may be produced by any known polymerization technique and any known polymerization catalyst system. As technology, slurry polymerization, solution polymerization or gas phase polymerization may be mentioned; as catalyst systems, ziegler-Natta catalysts, metallocene catalysts or single-site catalytic systems may be mentioned. All of which are known per se in the art.

The propylene-based polymer may be, for example, a propylene homopolymer or a random propylene copolymer or a heterophasic propylene copolymer.

The propylene homopolymer may be obtained by polymerizing propylene under suitable polymerization conditions. Propylene copolymers can be obtained by copolymerizing propylene and one or more other alpha-olefins, preferably ethylene, under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is described, for example, in Moore, E.P. (1996) Polypropylene Handbook, polymerization, characation, properties, processing, applications, hanser Publishers:New York.

The random propylene copolymer may contain up to 10 wt% comonomer units. The comonomer units may be ethylene monomer units and/or alpha-olefin monomer units having from 4 to 10 carbon atoms, preferably ethylene, 1-butene, 1-hexene or any mixture thereof.

The heterophasic propylene copolymer consists of:

(a) Propylene-based substrates

Wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least 70 wt% propylene monomer units and at most 30 wt% comonomer units selected from ethylene monomer units and alpha-olefin monomer units having 4 to 10 carbon atoms, based on the total weight of the propylene-based matrix,

wherein the propylene-based matrix is present in an amount of 60 to 95 wt.%, based on the total heterophasic propylene copolymer, and

(b) Dispersed ethylene-alpha-olefin copolymers

Wherein the dispersed ethylene-alpha-olefin copolymer is present in an amount of 40 to 5 wt.%, based on the total heterophasic propylene copolymer, and

wherein the sum of the total amount of the matrix based on propylene and the total amount of the dispersed ethylene-alpha-olefin copolymer in the heterophasic propylene copolymer is 100 wt%.

Heterophasic propylene copolymers are typically prepared in one or more reactors by polymerizing propylene in the presence of a catalyst followed by polymerization of an ethylene-alpha-olefin mixture. The resulting polymeric material is heterogeneous, but the specific morphology generally depends on the preparation process and the ratio of monomers used.

The heterophasic propylene copolymer employed in the process according to the invention may be produced using any conventional technique known to the skilled person, for example multistage process polymerization, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combination thereof. Any conventional catalyst system may be used, such as ziegler-natta or metallocene. Such techniques and catalysts are described, for example, in WO06/010414; polypropylene and other Polyolefins, studies in Polymer Science, elsevier 1990 by Ser van der Ven; WO06/010414, U.S. Pat. No. 4,439,054 and U.S. Pat. No. 5, 4472524.

Preferably, the heterophasic propylene copolymer is produced using a ziegler-natta catalyst.

Heterophasic propylene copolymers can be prepared by a process comprising:

-polymerizing propylene and optionally ethylene and/or alpha-olefins in the presence of a catalyst system to obtain a propylene-based matrix, and

-subsequently polymerizing ethylene and alpha-olefin in the presence of a catalyst system in a propylene-based matrix to obtain a dispersed ethylene-alpha-olefin copolymer. Preferably, these steps are carried out in different reactors. The catalyst systems of the first and second steps may be different or the same.

Heterophasic propylene copolymers consist of a propylene-based matrix and a dispersed ethylene-alpha-olefin copolymer. Propylene-based substrates typically form a continuous phase in heterophasic propylene copolymers. The amount of propylene-based matrix and dispersed ethylene-alpha-olefin copolymer can be determined by ¹³ C-NMR measurements, which are known in the art.

The propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least 70 wt% propylene monomer units and at most 30 wt% comonomer units selected from ethylene monomer units and alpha-olefin monomer units having 4 to 10 carbon atoms, for example at least 80 wt% propylene monomer units and at most 20 wt% comonomer units, at least 90 wt% propylene monomer units and at most 10 wt% comonomer units, or at least 95 wt% propylene monomer units and at most 5 wt% comonomer units, based on the total weight of the propylene-based matrix.

Preferably, the comonomer in the propylene copolymer of the propylene-based matrix is selected from ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene, preferably ethylene.

Preferably, the propylene-based matrix consists of propylene homopolymers.

Melt flow index MFI (in heterophasic propylene copolymer blends) of propylene-based matrix measured according to ISO1133-1:2011 (2.16 kg/230 ℃)Prior to incorporation into the compositions of the present invention), i.e., MFI _PP May be, for example, at least 0.1dg/min, at least 0.2dg/min, at least 0.3dg/min, at least 0.5dg/min, at least 1dg/min, at least 1.5dg/min and/or, for example, at most 50dg/min, at most 40dg/min, at most 30dg/min, at most 25dg/min, at most 20dg/min. MFI measured according to ISO1133-1:2011 (2.16 kg/230 ℃) _PP May be, for example, 0.1 to 50dg/min, such as 0.2 to 40dg/min, such as 0.3 to 30dg/min, such as 0.5 to 25dg/min, such as 1 to 20dg/min, such as 1.5 to 10dg/min.

The propylene-based matrix is present in an amount of 60 to 95 wt%. Preferably, the propylene-based matrix is present in an amount of 60 to 80 wt%, such as at least 65 wt% or at least 70 wt% and/or at most 78 wt%, based on the total heterophasic propylene copolymer.

The propylene-based matrix is preferably semi-crystalline, i.e. it is not 100% amorphous nor 100% crystalline. For example, the propylene-based matrix is at least 40% crystalline, such as at least 50%, such as at least 60% crystalline and/or such as up to 80% crystalline, such as up to 70% crystalline. For example, the propylene-based matrix has a crystallinity of 60% to 70%. For the purposes of the present invention, crystallinity of the propylene-based matrix was measured according to ISO11357-1 and ISO11357-3 in 1997 using Differential Scanning Calorimetry (DSC), using a scan rate of 10 ℃/min, with a sample of 5mg, and a second heating profile using 207.1J/g as a theoretical standard for 100% crystalline material.

In addition to the propylene-based matrix, the heterophasic propylene copolymer also comprises a dispersed ethylene-alpha-olefin copolymer. The dispersed ethylene-alpha-olefin copolymer is also referred to herein as the "dispersed phase". The disperse phase is embedded in the heterophasic propylene copolymer in discontinuous form. The particle size of the dispersed phase is typically 0.05 to 2.0 microns, as determined by Transmission Electron Microscopy (TEM). The amount of dispersed ethylene-alpha-olefin copolymer in the heterophasic propylene copolymer may sometimes be referred to herein as RC.

The amount of ethylene monomer units in the ethylene-alpha-olefin copolymer may be, for example, 20 to 65% by weight relative to the ethylene-alpha-olefin copolymer. The amount of ethylene monomer units in the dispersed ethylene-alpha-olefin copolymer in the heterophasic propylene copolymer may sometimes be referred to herein as RCC2.

Preferably, the alpha-olefin in the ethylene-alpha-olefin copolymer is selected from alpha-olefins having 3 to 8 carbon atoms. Examples of suitable alpha-olefins having 3 to 8 carbon atoms include, but are not limited to: propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene. More preferably, the α -olefin in the ethylene- α -olefin copolymer is selected from the group consisting of α -olefins having from 3 to 4 carbon atoms and any mixtures thereof, more preferably, the α -olefin is propylene, in which case the ethylene- α -olefin copolymer is an ethylene-propylene copolymer.

The MFI of the dispersed ethylene-alpha-olefin copolymer (prior to incorporation of the heterophasic propylene copolymer into the composition of the present invention), i.e.the MFI rubber, may for example be at least 0.001dg/min, at least 0.01dg/min, at least 0.1dg/min, at least 0.3dg/min, at least 0.7dg/min, at least 1dg/min and/or for example at most 30dg/min, at most 20dg/min, at most 15dg/min, at most 10dg/min, at most 5dg/min or at most 3dg/min. The MFI rubber may be, for example, 0.001 to 30dg/min, such as 0.01 to 20dg/min, such as 0.1 to 15dg/min, such as 0.3 to 10dg/min, such as 0.7 to 5dg/min, such as 1 to 3dg/min. The MFI rubber was calculated according to the formula:

wherein the method comprises the steps of

MFI heterophasic is the MFI (dg/min) of a heterophasic propylene copolymer measured according to ISO1133 (2.16 kg/230 ℃),

the MFI matrix is the MFI (dg/min) of a propylene-based matrix measured according to ISO1133 (2.16 kg/230 ℃),

the matrix content is the fraction of propylene-based matrix in the heterophasic propylene copolymer,

the rubber content is the fraction of ethylene-alpha-olefin copolymer dispersed in the heterophasic propylene copolymer. The sum of the matrix content and the rubber content was 1. For the avoidance of any doubt, log in the formula means Log ₁₀ 。

The dispersed ethylene-alpha-olefin copolymer is present in an amount of 40 to 5 wt%, based on the total heterophasic propylene copolymer. Preferably, the dispersed ethylene-alpha-olefin copolymer is present in an amount of 40 to 20 wt%, such as at least 22 wt% and/or such as up to 35 wt% or up to 30 wt%, based on the total heterophasic propylene copolymer.

In the heterophasic propylene copolymer in the composition of the present invention, the sum of the total weight of the matrix of propylene and the total weight of the dispersed ethylene-alpha-olefin copolymer is 100 wt% of the heterophasic propylene copolymer.

First peroxide and second peroxide

First peroxide at a first temperature T _1/2 1, the second peroxide having a half-life of 1 hour at a second temperature T _1/2 2 has a half-life of 1 hour. T (T) _1/2 2 is higher than T _1/2 1. I.e. the first peroxide is more reactive than the second peroxide at a lower temperature. For example T _1/2 2-T _1/2 1 is 5 to 20 ℃ or 10 to 15 ℃.

Preferably T _1/2 1 is 120 to 145 ℃, preferably 125 to 140 ℃, more preferably 128 to 137 ℃. Examples of the first peroxide include 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane (e.g., trigonox manufactured by Akzo Nobel ^TM 101 With T at 134 DEG C _1/2 1。

Preferably, the first peroxide has a half-life of 0.1 hour at a temperature of 140 to 180 ℃, more preferably 150 to 170 ℃.

Preferably T _1/2 2 above 145 ℃ and up to 180 ℃, preferably up to 170 ℃, e.g. above 145 ℃ and up to 150 ℃ or at least 155 ℃ and up to 170 ℃. Further, preferably, the second peroxide has a half-life of 0.1 hour at a temperature of 165 to 188 ℃. Examples of the second peroxide include 3,6, 9-triethyl-3, 6, 9-trimethyl-1, 4, 6-triperoxonane (e.g., trigonox manufactured by Akzo Nobel ^TM 301 With T at 146 DEG C _1/2 2 and a half-life of 0.1 hours at a temperature of 170 ℃; and 3,5, 7-pentamethyl-1, 2, 4-trioxepane (e.g., trigonox manufactured by Akzo Nobel) ^TM 311 With 16)T at 6 DEG C _1/2 2 and a half-life of 0.1 hour at a temperature of 185 ℃.

Preferably, the amount of the first peroxide relative to the propylene-based polymer is from 100 to 2000ppm.

Preferably, the amount of the second peroxide relative to the propylene-based polymer is from 100 to 8000ppm, preferably from 1000 to 8000ppm.

Other additives

The melt mixing in step a) may comprise mixing other additives, such as nucleating agents; stabilizers, such as heat stabilizers, antioxidants, UV stabilizers; colorants such as pigments and dyes; a clarifying agent; a surface tension regulator; a lubricant; a flame retardant; a release agent; a flow improver; a plasticizer; an antistatic agent; an external elastic impact modifier; a foaming agent; inorganic fillers such as talc and reinforcing agents; and/or components that enhance the interfacial bond between the polymer and the filler, such as maleated polypropylene. The skilled artisan can readily select any suitable combination of additives and amounts of additives without undue experimentation.

It is to be noted that the invention relates to the subject matter defined in the independent claims, alone or in combination with any possible combination of the features described herein, preferably in particular those combinations of the features presented in the claims. It is therefore to be understood that all combinations of features relating to the composition according to the invention, to the method according to the invention, and to the composition according to the invention and to the method according to the invention are described herein.

It is further noted that the terms 'comprising' do not exclude the presence of other elements. However, it is also to be understood that the description of the products/compositions comprising certain components also discloses products/compositions consisting of these components. A product/composition composed of these components may be advantageous because it provides a simpler and economical process for preparing the product/composition. Similarly, it is to be understood that the description of the method as including certain steps also discloses a method consisting of those steps. The method consisting of these steps may be advantageous because it provides a simpler and more economical method.

When values are mentioned for lower and upper limits of a parameter, it is also understood that ranges disclosing combinations of values for the lower and upper limits are also disclosed.

The invention will now be elucidated with the aid of the following examples, to which, however, the invention is not limited.

The following materials were used.

PP22: propylene homopolymer having an MFI of 22dg/min according to ISO1133-1:2011 (230 ℃ C./2.16 kg)

PP11: propylene homopolymer having an MFI of 11dg/min according to ISO1133-1:2011 (230 ℃ C./2.16 kg)

PP3: propylene homopolymer with MFI of 6dg/min according to ISO1133-1:2011 (230 ℃ C./2.16 kg)

Stabilizer package: irganox 3114, irgafos 168, calcium stearate in a weight ratio of 40:85:35

Trigonox101 (2, 5-dimethyl-2, 5-di (T-butylperoxy) hexane, having a T of 134 DEG C _1/2 1

Trigonox 301 (3, 6, 9-triethyl-3, 6, 9-trimethyl-1, 4, 7-triperoxonane) with T at 146 DEG C _1/2 2

Comparison PP: propylene homopolymer HL712FB, available from Borealis, has an MFI of 1200dg/min in accordance with the product data sheet, ISO 1133. Analysis of HL712FB showed that HL712FB contained a stabilizer package comparable to the stabilizer packages for Ex1, ex2 and Ex3, and that it contained 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane (referred to as "Irgatec" in table 2).

The components shown in table 1 were melt mixed at the temperature shown in table 1 for 0.025 to 0.030 hours and made into pellets.

The MFI of the pellet composition was measured by ASTM D1238-13 (2 mm die) at 190℃and 2.16 kg.

Pellets were subjected to a melt blowing process in a Hills melt blowing pilot line using a die with 0.25mm diameter holes and 35 holes/inch. The melting temperature was set at 250℃and the air temperature at 275 ℃. The processing parameters are summarized in table 1.

The MFI of the fibers of the meltblown web was measured by ASTM D1238-13 procedure C (1 mm die) at 230℃and 2.16 kg.

The static head of the meltblown web was measured. The static head was determined by static pressure testing according to the nwsp.080.6 (R0) method revised in 2015. Testing was done using a Textest FX3000 hydrostatic head tester, 100cm prepared as described herein ² Is clamped in place over a water-filled test head. Purified water was used as a test liquid at 23℃and 100cm ² The water pressure under the sample was increased at 60mbar/min on the fabric sample. The test is ended when the triple drip penetrates the sample.

Breathability is the measure of the barrier properties of a fabric in terms of air volume per unit area of fabric per unit time. 20cm was extracted from the fabric prepared as described herein using a Texas Instruments (Lab Air 3300) machine with a pressure drop set at 200Pa ² The air permeability was measured for fabric samples of (c). The sample is clamped in place and the air flow rate through the sample is increased until the pressure drop reaches 200Pa. The flow rate of air and the volume of air per unit area per unit time were measured. This procedure was based on nswp.070.1.r0 (pressure drop set at 200 Pa).

Thus, polypropylene with various MFI is mixed with Trigonox101 and Trigonox 301 and heated at temperatures of 214 to 226 ℃ at which visbreaking mainly occurs due to Trigonox 101. The MFI of the pellets was measured at 190 ℃ instead of 230 ℃ so as to limit the occurrence of visbreaking during MFI measurement.

As shown in the above table, these pellets were formed into meltblown webs at temperatures of 250℃or 290 ℃. The MFI of the melt blown web was measured using the half die method (ASTM D1238-13 procedure C (1 mm die)) at 230 ℃, which allowed the MFI of the high flow polypropylene to be measured.

The meltblown webs obtained according to the present invention were found to have high static head and low air permeability. The static head is higher and the air permeability is lower than with a melt blown web of comparative polypropylene CEx4 (only one peroxide). The static head was higher compared to using a melt blown web of comparative polypropylene CEx5 (hydroxylamine only, no peroxide).

The compositions of the examples of the present invention have better processability in the melt blowing process than the compositions of CEx5, CEx6 and CEx 7. CEx5 and CEx7 require higher temperatures (290 ℃) to convert the composition to a meltblown web using a melt blowing process, and the composition of CEx6 cannot be converted to a meltblown web because its MFI is too low.

Claims

1. A meltblown web comprising meltblown fibers, the meltblown fibers being obtained by:

a) Melt mixing a propylene-based polymer, a first peroxide and a second peroxide at a temperature of 180 ℃ to 240 ℃, preferably 200 ℃ to 220 ℃, wherein the first peroxide is at a first temperature T _1/2 1 having a half-life of 1 hour, said second peroxide at a second temperature T _1/2 2 has a half-life of 1 hour, wherein T _1/2 2 is higher than T _1/2 1, and

b) Processing the composition obtained by step a) by a melt blowing process at a temperature of 240 ℃ to 300 ℃, preferably 245 ℃ to 280 ℃, to provide the melt blown fiber.

2. The meltblown web according to claim 1, wherein T _1/2 1 is 120 to 145 ℃, preferably 125 to 140 ℃, more preferably 128 to 137 ℃.

3. The meltblown web according to any preceding claim, wherein T _1/2 2 above 145 ℃ and up to 180 ℃, preferably up to 170 ℃, e.g. above 145 ℃ and up to 150 ℃ or at least 155 ℃ and up to 170 ℃.

4. The meltblown web according to any preceding claim, wherein the second peroxide has a half life of 0.1 hours at a temperature of 165 to 188 ℃.

5. The meltblown web according to any preceding claim, wherein said first peroxide is 2, 5-dimethyl-2, 5-di (t-butylperoxy) hexane and/or said second peroxide is 3,6, 9-triethyl-3, 6, 9-trimethyl-1, 4, 6-triperoxonane and/or 3,5, 7-pentamethyl-1, 2, 4-trioxepane.

6. The melt blown web according to any one of the preceding claims, wherein the amount of the first peroxide relative to the propylene-based polymer is from 100 to 2000ppm and the amount of the second peroxide relative to the propylene-based polymer is from 100 to 8000ppm, preferably from 1000 to 8000ppm.

7. The meltblown web according to any preceding claim, wherein the propylene-based polymer is a propylene homopolymer, a random propylene copolymer, or a heterophasic propylene copolymer.

8. The melt blown web according to any one of the preceding claims, wherein the propylene-based has a first melt flow index MFI of 0.1 to 60dg/min, such as 0.1 to 1.0dg/min, 1.0 to 5.0dg/min, 5.0 to 15dg/min, or 15 to 60dg/min, measured according to ISO1133-1:2011 at 230 ℃ and 2.16kg _A 。

9. The melt blown web according to any one of the preceding claims, wherein the composition obtained by step a) has a second melt flow index MFI of 10 to 300dg/min, e.g. 100 to 200dg/min, determined according to ASTM D1238-13 (2 mm die) at 190 ℃ and 2.16kg _B 。

10. The melt blown web according to any one of the preceding claims, wherein the melt blown fibers have a third melt flow index MFI of 100 to 300dg/min, such as 150 to 250dg/min, measured according to ASTM D1238-13 procedure C (1 mm die) at 230 ℃ and 2.16kg _C 。

11. The meltblown web according to any preceding claim, wherein MFI _C -MFI _B At least 30dg/min, more preferably at least 40dg/min, more preferably at least 50dg/min, more preferably at least 60dg/min, more preferably at least 70dg/min, and/or wherein the MFI is _C -MFI _B At most 100dg/min, for example at most 90dg/min, where MFI _C Represents the melt flow index of the meltblown fibers, as measured by ASTM D1238-13 procedure C (1 mm die) at 230℃and 2.16kg, wherein MFI _B Represents the melt flow index of the composition obtained by step a), determined according to ASTM D1238-13 (2 mm die) at 190℃and 2.16 kg.

12. The melt blown web according to any one of the preceding claims, wherein the composition obtained by step a) is formed into pellets and the pellets are subjected to step b).

13. Use of pellets for the manufacture of a melt blown web, wherein the pellets are manufactured by: a) Melt mixing a propylene-based polymer, a first peroxide and a second peroxide at a temperature of 180 ℃ to 240 ℃, preferably 200 ℃ to 220 ℃, wherein the first peroxide is at a first temperature T _1/2 1 having a half-life of 1 hour, said second peroxide at a second temperature T _1/2 2 has a half-life of 1 hour, wherein T _1/2 2 is higher than T _1/2 1) and forming said composition obtained by step a) into pellets.

14. An article comprising the meltblown web according to any one of claims 1-12, preferably wherein the article is selected from the group consisting of: filter media (e.g., air filters such as clean room filters, ventilation filters, heating, ventilation and air conditioning filters, mask filters, respirator filters, vacuum cleaners filters and room air cleaners filters, liquid filters such as water filters, food and beverage filters and chemical and solvent filters), medical/surgical gowns, medical/surgical drapes, medical/surgical masks, diapers, feminine hygiene products, sanitary napkins, adult incontinence products, absorbent pads, wipes, including household wipes, industrial cleaning wipes and sanitary wipes, oil and gas barriers, food fat absorbent wipes, protective clothing, masks, wet wipe articles including industrial masks for electronic products such as battery separators and cable bags, adhesives, such as hot melt adhesives, insulators, such as garment thermal insulators and acoustic insulation articles, composite nonwovens.

15. Use of the meltblown web according to any of claims 1-12 for making an article selected from the group consisting of: filter media (e.g., air filters such as clean room filters, ventilation filters, heating, ventilation and air conditioning filters, mask filters, respirator filters, vacuum cleaners filters and room air cleaners filters, liquid filters such as water filters, food and beverage filters and chemical and solvent filters), medical/surgical gowns, medical/surgical drapes, medical/surgical masks, diapers, feminine hygiene products, sanitary napkins, adult incontinence products, absorbent pads, wipes, including household wipes, industrial cleaning wipes and sanitary wipes, oil and gas barriers, food fat absorbing wipes, protective garments, masks, wet wipe articles including industrial masks for electronic products, e.g., battery separators and cable bags, adhesives, e.g., hot melt adhesives, insulators, e.g., garment thermal insulators and sound insulation articles, composite nonwovens.