MXPA00005172A - Method for the continous preparation of thermoplastically processible polyurethanes - Google Patents

Abstract

A process for the continuous production of thermoplastically, processable homogeneous polyurethane elastomers, having improv softening properties, comprises mixing in a stirred tubular reactor to essentially full conversion whereby the ratio of the init stirred speed (m/s) and the throughput (g/s) does not exceed 0.03 (m/g). A process for the continuous production of thermoplastically, processable homogeneous polyurethane elastomers (I) having improved softening properties, comprises:(A) mixing a diisocyanate;and (B) a mixture of (B1) 1-85 equivalent%(w.r.t. isocyanate groups in (A)) of a compound having an average of 1.8-2.2 active hydrogen atoms per molecule and an average number average mol. wt. of 450-5000 g/mol;and (B2) 15-99 equivalent%(w.r.t. isocya groups in (A) of a chain extender having an average of 1.8-2.2 active hydrogen atoms per molecule and mol. wt. of 60-400 g/mol a (C) 0-20 wt.%of processing aids and additives whereby the NCO:OH ratio of (A):(B) is 0.9:1-1.1:1. (A) and (B) are homogeneously mixed in a stirred tubular reactor to essentially full conversion whereby the ratio of the initial stirred speed (m/s) and the throughput (g/s) does not exceed 0.03 (m/g).

Description

Procedure for the continuous production of processable polyurethanes as thermoplastics with improved softening behavior. Description of the invention: The invention relates to a process for the continuous production of processable polyurethanes such as thermoplastics (with improved softening behavior) in a tubular mixer.

Thermoplastic polyurethane elastomers have been known for a long time. They are of technical use due to the combination of their valuable mechanical properties with the known advantages of thermoplastic processability at low cost. Through the use of different chemical structural components a wide variety of mechanical properties is achieved. An overview of TPUs, their properties and uses is provided in, for example, Kuntstoffe 68 (1978), pages 819 to 825 or in Kautschuk, Gummi, Kuntstoffe 35 (1982), pages 568 to 584.

TPUs are composed of linear polyols, mainly polyester polyols or polyol ether, organic diisocyanates and short chain diols (chain extenders). To accelerate the formation reaction, catalysts can also be added. For the adjustment of properties the structural components can be varied in relatively ref .; 119854 wide molar relationships. It has resulted in effective polyol ratios to chain extenders from 1: 1 to 1:12. In this way, products are obtained in the range of 70 Shore A to 75 Shore D.

The synthesis of the processable polyurethane elastomers as thermoplastics can be carried out in stages (prepolymer dosing process) or by means of a simultaneous reaction of all the components in one step (one shot stage dosing process).

TPUs can be obtained continuously or discontinuously. The most known technical production methods are the tape process (GB-A 1,057,018) and the extrusion process (DE-A 1964834, DE-A 2302564 and DE-A 2059570). In the extrusion process, the starting substances are metered into a propeller reactor, there the polyaddition occurs and it is transformed into a uniform granular form. The extrusion process is comparatively simple, but has the disadvantage that the homogeneity of the product thus obtained, because of the simultaneous passage of the mixture and reaction, is not sufficient for many uses. In addition, the softening behavior of the TPUs and the molding bodies thus obtained is limited. TPUs that melt easily, such as those used for example for melting sheets or sintering products, can not be obtained by these procedures or only in a limited way.

In the state of the art, additional production methods are also known in which the starting substances are first mixed in a mixing zone at temperatures which do not give rise to polyaddition, and are then reacted in a reaction zone which reaches the desired reaction temperature. The mixing and reaction zones are preferably formed as static mixers.

According to DE-A 2823762 homogenous products are obtained by the one-stage process. According to EP-A 747409, it is dosed according to the prepolymerization process and homogeneous TPUs with improved mechanical properties are obtained.

Therefore the aim was to provide a simple procedure with which it was possible to obtain homogeneous TPUs with improved softening behavior, of low cost and technically simple.

This object has surprisingly been achieved by obtaining the TPU under special process conditions continuously in a stirred tubular reactor (tubular mixer), by the one-stage dosing process, in which the total TPU reaction is carried out substantially. With this procedure, homogeneous TPU products are obtained and they melt clearly better.

The object of the invention is a one-stage dosing process for the continuous production of homogeneous, processable polyurethanes such as thermoplastics with improved softening properties in which, one or more diisocyanates (A) and a mixture (B) exhibiting hydrogen atoms with Zerewinitov activity of Bl) from 1 to 85% equivalents, referred to the isocyanate groups of (A), of one or more compounds with at least 1.8 and at most 2.2 hydrogen atoms with Zerewinitov activity per molecule of average and one weight molecular weight M "from 450 g / mol to 5,000 g / mol, B2) from 15 to 99% equivalents, referred to the isocyanate groups in (A) of one or more chain extension agents with at least 1.8 and at the most 2, 2 hydrogen atoms with Zerewinitov activity per molecule of average and a molecular weight of 60 g / mol to 400 g / mol, as well as from 0 to 20% by weight, based on the total amount of TPU, of other adjuvants and additives (C), adding components (A) and (B) in an NCO: OH ratio of 0.9: 1 to 1.1: 1, they are reacted, essentially to complete the reaction, in a stirred tubular reactor of non-forced transport, characterized in that the peripheral speed ratio of the agitator (m / s) in the tubular reactor to flow rate (g / s) exceeds the value of 0. , 03 (m / g).

Examples of organic diisocyanates (A) are aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, such as those described, for example in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136.

In particular, mention may be made, for example, of aliphatic diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexanediisocyanate, 1-methyl-2,4- and 2,6-cyclohexanediisocyanate, and the corresponding mixtures thereof. "isomers, 4, 4 '-, 2, 4' - and 2, 2 '-dicyclohexylmethane diisocyanate, as well as the corresponding mixtures of aromatic isomers and diisocyanates such as 2,4-toluylene diisocyanate, mixtures of 2,4- and 2,6- toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 2, 2'-diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate and / or 2, 4 Liquid diphenylmethane diisocyanate modified with urethane, 4,4'-diisocyanatodiphenylethane (1, 2) and 1,5-naphthylene diisocyanate 1,6-hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, isomer mixtures are preferably used s of diphenylmethane diisocyanate with a content of 4,4'-diphenylmethane diisocyanate greater than 96% by weight and especially 4, '-diphenylmethane diisocyanate and 1,5-naphthylene diisocyanate. The diisocyanates mentioned can be used separately or in the form of mixtures with each other. They can also be used together with up to 15% by weight (calculated with respect to the total diisocyanate) of a maximum of one polyisocyanate which gives rise to a processable product such as thermoplastic. Examples: triphenylmethane-4,4 ', 4"-triisocyanate and polyphenylpolymethylenepolyisocyanate.

As component Bl), linear polyols with terminal hydroxyl having an average of hydrogen atoms with Zerewinitov activity of 1.8 to 3.0, preferably to 2.2 per molecule and with an average molecular weight of 450 to 5,000 are preferably used. For production reasons these often contain small amounts of non-linear compounds. Frequently, therefore, we speak of "essentially linear polyols". Polydiolyesters, polydiol ethers or polydiolcarbonates or mixtures thereof are preferred.

Suitable polydiol ethers can be obtained by reacting one or more alkylene oxides with from 2 to 4 carbon atoms in the alkylene moiety with a starter molecule containing two active hydrogen atoms attached. As alkylene oxides, mention may be made, for example, of ethylene oxide, 1,2-propylene oxide, epichlorohydrin and 1,2-butylene oxide and 2-oxide., 3-butylene. Those of preferred use are ethylene oxide, propylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide. The alkylene oxides can be used separately, alternating one after the other or as mixtures. Suitable initiator molecules are, for example: water, aminoalcohols such as N-alkyldiethanolamines, for example N-methyldiethanolamine and diols, such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol and 1,6-hexanediol. If appropriate, mixtures of initiator molecules can also be used. Suitable polyethers are also polymerization products of tetrahydrofuran containing hydroxyl groups. Trifunctional polyethers can also be used in proportions of from 0 to 30% by weight, based on the bifunctional polyether, but at most in an amount which gives rise to a processable product as a thermoplastic. The essentially linear polydiol ethers preferably have a molecular weight of 450 to 5,000. They can be used either separately or in the form of mixtures with each other.

Polydiolyesters can be obtained, for example, from dicarboxylic acids having 2 to 12 carbon atoms, preferably from 4 to 6 carbon atoms, and polyvalent alcohols. Suitable dicarboxylic acids are, for example, aliphatic carboxylic acids, such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used separately or as mixtures, for example in the form of a mixture of succinic, glutaric and adipic acids. For the preparation of the polydiolyesters it may be advantageous to use, instead of dicarboxylic acids, the corresponding carboxylic acid derivatives, such as diesters of carboxylic acid having 1 to 4 carbon atoms in the alcohol moiety, carboxylic acid anhydrides or chlorides of carboxylic acids. Examples of polyhydric alcohols are glycols of 2 to 10, preferably 2 to 6 carbon atoms, such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, , 2-dimethyl-1,3-propanediol, 1, 3-propanediol and dipropylene glycol. Depending on the desired properties, the polyvalent alcohols can be used alone or, as the case may be, as a mixture between them. Also suitable are carboxylic acid esters with the aforementioned diols, especially those with 4 to 6 carbon atoms, such as 1,4-butanediol or 1,6-hexanediol, condensation products of omega-hydroxycarboxylic acids, for example omega-hydroxycaproic acid and preferably lactone polymerization products, for example omega-caprolactones, substituted where appropriate. The polydiolyesters used are preferably ethanediol polyadipate, 1,4-butanediol polyadipate, ethanediol-1,4-butanediol polyadipate, 1,6-hexanediol-neopentyl glycol polyadipate, 1,6-hexanediol-1,4-butanediol polyadipate. and polycaprolactone. The polydiolyesters have average molecular weights of 450 to 5,000 and can be used alone or in the form of mixtures.

As component B2), diols or diamines with from 1.8 to 3.0, preferably 2.2 hydrogen atoms with Zerewinitov activity per molecule on average and an average molecular weight of 60 to 400, preferably 2 to 3 aliphatic diols are preferably used. to 14 carbon atoms, such as for example ethanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and especially 1,4-butanediol. However, diesters of terephthalic acid with glycols of 2 to 4 carbon atoms are also suitable, such as, for example, terephthalic acid-bis-ethylene glycol or terephthalic acid-bis-1,4-butanediol, hydroxyalkylene ethers of hydroquinone, for example 1,4-di (β-hydroxyethyl) hydroquinone, ethoxylated bisphenols, such as, for example, 1,4-di- (3-hydroxyethyl) bisphenol A, (cyclo) aliphatic diamines, such as isophorone diamine, ethylene diamine, 1, 2 -propylenediamine, 1,3-propylenediamine, N-methyl-propylene-1, 3-diamine, N, N'-dimethylethylenediamine and aromatic diamines, such as, for example, 2,4-toluylenediamine and 2,6-toluylenediamine, 3, 5 -diethyl-2,4-toluylenediamine and 3,5-diethyl-2,6-toluylenediamine and primary mono, di, tri or tetra substituted 4,4'-diaminodiphenylmethane with alkyl. It is also possible to use mixtures of the chain extenders mentioned above. In addition, small amounts of triols can be added.

In addition, conventional monofunctional compounds can also be used in small amounts, for example chain switches or mold release aids. Examples which may be mentioned are alcohols such as octanol and stearyl alcohol or amines such as butylamine and stearylamine.

In order to obtain TPU, the structural components can be added to the reaction, where appropriate in the presence of catalysts, adjuvants and / or additives, preferably in quantities such as the ratio of equivalents of NCO groups A) to the sum of groups reactive with respect to NCO, especially OH groups of the low molecular weight diols / triols B2) and polyols Bl) is from 0.9: 1.0 to 1.1: 1.0, preferably from 0.95: 1.0 to 1, 10: 1.0.

Suitable catalysts according to the invention are the conventional tertiary amines known in the state of the art, such as, for example, triethylamine, dimethyl-cyclohexylamine, N-methylmorpholine, N, N'-dimethylpiperazine, 2- (dimethylaminoethoxy) ethanol, diazabicyclo- [2, 2, 2] -octane and the like, as well as especially organic metal compounds such as titanic acid esters, iron compounds, tin compounds, for example tin diacetate, tin dioctoate, tin dilaurate or dialkyl tin salts of acids aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like. The preferred catalysts are organic metal compounds, especially esters of titanic acid, iron and / or tin compounds.

In addition to the components of TPUs and catalysts, adjuvants and additives C) can also be added up to 20% by weight, based on the total amount of TPU. They can be pre-dissolved in one of the components of the TPU, preferably in the component Bl), or also, if appropriate, dosed once the reaction is carried out to a mixing equipment connected subsequently to the stirred tubular reactor, as for example in an extruder. Examples are lubricants such as fatty acid esters, their metal soaps, fatty acid amides, fatty acid esteramides, silicone compounds, inter-layer anti-adhesion agents, inhibitors, stabilizers against hydrolysis, light, heat and coloration, flame retardants. , colorants, pigments, inorganic and / or organic and reinforcing fillers. The reinforcing agents are in particular fibrous reinforcing substances, such as, for example, inorganic fibers, obtained according to the state of the art and which can also be applied with a glue. More detailed data can be obtained on the adjuvants and additives mentioned in the specialized literature, for example in the monograph by J.H. Saunders and K.C. Frisch: "High Polymers", Vol. XVI, Polyurethane, Parts 1 and 2, Verlag Interscience Publishers 1962 or 1964, Taschenbuch der Kunstoff-Additive, by R. Gáchter and H. Müller (Hanser Verlag München 1990) or in the document DE-A-2901774.

Other additives that can be incorporated into the TPU are thermoplastics, for example polycarbonates and terpolymers of acrylonitrile / butadiene / styrene, especially ABS. Where appropriate, other elastomers may be used such as rubbers, ethylene / vinyl acetate copolymers, styrene / butadiene copolymers, as well as other TPUs. Furthermore, conventional plasticizers such as phosphates, phthalates, adipates, sebacates and esters of alkylsulfonic acids are suitable for incorporation.

The production process according to the invention is preferably carried out as follows: The components A) and B) are heated separately from one another, preferably in a heat exchanger, at a temperature between 50 ° and 220 ° C and are dosed in liquid form simultaneously and continuously to a stirred transport tube. forced (tubular mixer) with a length-to-diameter ratio of 1: 1 to 50: 1, preferably 2: 1 to 20: 1.

The agitator mixes the components with a number of revolutions preferably of 200 to 5,000 rpm. The number of revolutions of the agitator is adjusted according to the invention so that the peripheral speed ratio of the agitator diameter in m / s flow rate (sum of the dosages of components A) + B), and optionally C), in g / s exceeds the value of 0.03 m / g. A value greater than 0.06 m / g is preferred.

The agitator is a mechanical uninterrupted rotary transport agitator, preferably monoaxial. Arms, rods, rotors, grids, blades or propellers can be used as mixing elements.

In the tubular reactor (tubular mixer) the TPU formation reaction according to the invention takes place, essentially up to complete reaction, ie > 90%, referred to the use component A). The residence time required for this, depending on the flow rate, reaches the tube material used, the reaction temperature and the catalyst, from 2 seconds to 5 minutes. For economic reasons, the mentioned conditions are preferably adjusted to a residence time in the tubular mixer from 5 to 60 seconds.

The reaction temperatures reach without here, according to the starting temperature of the starting components, values of 140 ° to 300 ° C, preferably above 220 ° C.

The reaction mixture is fed to the tubular mixer continuously. It can be deposited directly on a support. After tempering at temperatures of 60 to 180 ° C and subsequent cooling, the TPU mass can be granulated. In a continuous production process, the support is a continuous conveyor belt.

In a special variant according to the invention, the reaction mixture in the tubular mixer is dosed directly in a continuous-operation kneader and / or extruder (for example a double-shaft kneader ZSK), in which they can mix additional adjuvants at temperatures of 120 to 250 ° C in the TPU. At the end of the extruder, it is also granulated.

The TPU obtained with the production process according to the invention can be processed into injection molded articles, extrusion articles, especially melt sheets, coating compositions or sintering types and coextrusion types that melt easily, such as laminates, calenders and types of muddy dust. With a good homogeneity is characterized, as well as the molding bodies obtained with them, above all by a low softening temperature.

The invention is explained in more detail by means of the following examples.

Examples Examples 1 to 5 TPU formula for examples 1 to 5: 1,4-Butanediol polyadipate 54 parts by weight (molecular weight of about 820) 1,4-Butanediol 7.4 parts by weight 4,4'-Diphenylmethane diisocyanate 37 parts by weight Ethylene-bis-stearylamide 0.2 parts by weight Weight Tin Dioctoate 200 ppm Example 1 (ZSK procedure different from that of the invention (comparative example)): The polyester, in which 200 ppm (based on the polyester) of tin dioctoate was dissolved as a catalyst, was heated with butanediol at 145 ° C and dosed continuously to the first shell of a ZSK 83 (Werner / Pfleiderer company) . In the same housing, 4,4'-diphenylmethane diisocyanate (130 ° C) and ethylene-bis-stearylamide were dosed. The first nine cases of the ZSK (quasi-adiabatic) were not heated. By means of the heat of reaction released, temperatures of up to 240 ° C were reached. The last 4 cases cooled down. The number of revolutions of the propeller amounted to 270 rpm, the flow rate at 10,000 g / min.

From the end of the propeller the molten mass was extracted in the form of a cord, cooled in a water bath and granulated.

The results of the corresponding tests of the products are given in the table.

Example 2 (Tubular mixer procedure ZSK): The above polybutanediol ester mixture was metered continuously with the tin dioctoate at the lower end of a tubular mixer. At the same time, 4,4'-diphenylmethane diisocyanate (130 ° C) was pumped continuously into the feed site adjacent to the lower end of the tubular mixer. The flow rate was 9,000 g / min. The tubular mixer heated to 240 ° C had a diameter of 7 cm and a length / diameter ratio of 7: 1. The agitator equipped with bars of the tubular mixer rotated at 1800 rpm. The produced TPU was discharged through the upper end of the tubular mixer and dosed directly into the first feed site (shell 1) of a ZSK 83. Ethylene-bis-stearylamide was dosed into the same housing. The adjustment of the parameters of the ZSK was analogous to Example 1. The quasi -adiabatic temperature adjustment of the housing showed that no heat of reaction was produced.

From the end of the propeller, the hot melt was extracted as a cord, cooled in a water bath and granulated.

Examples 3-5 (Tubular mixer process without extrusion): This procedure was carried out analogously to Example 2. An unheated tubular mixer with a diameter of 4.2 cm and a length / diameter ratio of 2.7 was used. The flow rate was 520 g / min, the number of revolutions at 500, 1,000 or 3,000 rpm.

The polybutanediolyester mixture was heated to 170 ° C and 4,4'-diphenylmethane diisocyanate at 80 ° C.

The reaction at the end of the tubular mixer amounted to 99% equivalents based on 4,4'-diphenylmethane diisocyanate.

The TPU was dosed continuously on a metal support laminated for 30 minutes, tempered at 110 ° C and granulated.

Obtaining blown TPU sheets from examples 1-5 The corresponding TPU granules were melted in a single-shaft extruder 30 / 25D Plasticorder PL 2000-6 from the company Brabender (dosage 3 kg / h, 185-205 ° C) and extruded through a film blower head damdo a tubular sheet.

Obtaining injection molded TPU bodies from examples 1-5 The corresponding TPU granules were melted in an injection molding device D60 (32 helices) from the company Mannesmann (mass temperature around 225 ° C) and molded into plates (125 mm x 50 mm x 2 mm).

Dynamic-mechanical analysis (DMA) with temperature With the products, a corresponding dynamic-mechanical measurement of a die-cut test body of the injected cast iron plates (50 mm x 12 mm x 2 mm) was carried out in a torsional vibration test with the temperature, analogously to the norm DIN 53445.

The measurements were carried out with the RDA 700 of the company Rheometrics at 1 Hz in the temperature range from -125 ° C to 200 CC with a heating rate of 1 ° C / min.

For the characterization of the softening behavior according to the invention, the temperature at which the charging module G 'reaches the value of 1 MPa (softening temperature) is given in the following table.

Mechanical test at room temperature The modulus at 100% elongation was measured in the cast iron bodies according to DIN 53405.

Results: * E n g lish compa ng e e n e ng n e n All homogenous blowing films are obtained from all products.

The products obtained by the tubular mixer process according to the claim show, compared to the products obtained by the normal ZSK process, with the same mechanical properties at room temperature and with an equally good sheet homogeneity, a clearly reduced softening temperature.

This melting behavior is especially advantageous for melting sheets of TPU and in the area of sintering.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (1)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: . A process for the continuous production of processable polyurethanes such as thermoplastics with improved softening behavior in which one or more diisocyanates (A) and a mixture (B) exhibiting hydrogen atoms with Zerewinitov activity of Bl) from 1 to 85% equivalents, referred to the isocyanate groups in (A), of one or more compounds with at least 1.8 and at most 2.2 hydrogen atoms with Zerewinitov activity per molecule of average and one weight molecular weight M "from 450 g / mol to 5,000 g / mol, B2) from 15 to 99% equivalents, based on the isocyanate groups of (A) of one or more chain extenders with at least 1.8 and at the most 2, 2 hydrogen atoms with Zerewinitov activity per molecule of average and a molecular weight of 60 g / mol to 400 g / mol, as well as from 0 to 20% by weight, based on the total amount of TPU, of other adjuvants and additives (C), adding the components (A) and (B) in an NCO: 0H ratio of 0.9: 1 to 1, 1: 1, they are reacted essentially to complete the reaction, in a stirred tubular reactor of non-forced transport, characterized in that the peripheral speed ratio of the agiador (m / s) in the tubular reactor at flow rate (g / s) exceeds the value of 0, 03 (m / g). A process according to claim 1, characterized in that the compound Bl) containing hydrogen atoms with Zerewinitov activity is a polydiolyester, polydiol ether, polydiol carbonate or a mixture thereof. A process according to claim 1, characterized in that the compound B2) containing hydrogen atoms with Zerewinitov activity is ethylene glycol, butanediol, hexanediol, 1,4-di- (3-hydroxyethyl) hydroquinone, 1,4-di- (β-) hydroxyethyl) bisphenol A or a mixture thereof. A process according to claim 1, characterized in that the diisocyanate A) is 1,6-hexamethylenediacyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate or mixtures of diphenylmethane diisocyanate isomers with a content of 4,4'-diphenylmethane diisocyanate greater than 96% by weight. A process according to one or more of claims 1 to 4, characterized in that the reaction mixture obtained in the tubular mixer is dosed to an extruder and, where appropriate, adjuvants and / or other components are added thereto. A process according to one or more of claims 1 to 5, characterized in that the formation components of the TPU A), Bl), B2) are reacted in a stirred tubular reactor for 60 seconds up to a conversion > 90%, referred to the use component A). Use of the polyurethanes obtained according to the process of claims 1 to 6 for obtaining articles of injected cast iron and extrusion articles. r Process for the continuous production of processable polyurethanes such as thermoplastics with improved softening behavior. SUMMARY OF THE INVENTION A process for the continuous production of processable polyurethane elastomers such as thermoplastics with improved softening behavior in a tubular reactor with a peripheral speed ratio of the agitator (in m / s) of the tubular reactor at flow rate (in g / s) greater than 0.03 m / g.