EP0360708B1 - Polyamide imide yarns and their production - Google Patents

Abstract

The present invention relates to heat-resistant filaments, yarns and fibres based on polyamide-imide. They have a polydispersity index I </= 2.2, a tenacity at break >/= 45 cN/tex, a Young's modulus >/= 3.8 GPa, an elongation </= 25%, a colour defined by the luminance gamma > 25%, the whiteness W < 30 and the yellowing index YI > 170. In addition, they have very good stability to light, quantified by the retention of the mechanical characteristics. They find wide application in work and protective clothing.

Description

The present invention relates to thermostable synthetic yarns based on polyamide-imide with improved properties.

It also relates to a process for obtaining such threads.

It is already known, according to FR 2 079 785 to prepare shiny yarns based on polyamide-imide obtained by polycondensation of a diisocyanate with an aromatic acid anhydride in the presence of a metal dicarboxybenzene sulfonate and optionally a aromatic diacid, and containing at least 3% of sequences derived from dicarboxy-3,5 benzene sulfonate alkali or alkaline earth, by wet spinning of a solution of polymer in N-methylpyrrolidone, in an aqueous coagulating bath also containing N -methylpyrrolidone then drawing, washing, drying and drawing.

However, such wires have mechanical characteristics which are too weak for certain applications and too yellow-brown coloring and exhibit thermal degradation and poor resistance to photodegradation.

• des unités amide-imide (A) de formule :
  
• des unités amide (B) de formule :
  
  
          -NH-R-NH-CO-R₂-CO-
  
  
  
• et éventuellement des unités amide (C) de formule :
  
  dans lesquelles R représente un radical aromatique divalent, R₁ représente un radical aromatique trivalent, R₂ représente un radical aromatique divalent et M un métal alcalin ou alcalino terreux, les unités A représentant 80 à 100 % de l'ensemble des unités, les unités B représentant 1 à 5 % de l'ensemble des unités et les unités C représentant 0 à 20 % de l'ensemble des unités, la sommes des unités A + B + C étant égale à 100 %.

The polyamide-imide threads according to the present invention have characteristics clearly superior to those of the polyamide-imide threads of the prior art. They have the following chemical structure:

• amide-imide units (A) of formula:
  
• amide units (B) of formula:
  
  
  -NH-R-NH-CO-R₂-CO-
  
  
  
• and optionally amide units (C) of formula:
  
  in which R represents a divalent aromatic radical, R₁ represents a trivalent aromatic radical, R₂ represents a divalent aromatic radical and M an alkali or alkaline earth metal, the units A representing 80 to 100% of all the units, the units B representing 1 to 5% of all units and C units representing 0 to 20% of all units, the sum of units A + B + C being equal to 100%.

The yarns according to the invention are also characterized by a polydispersity index I ≦ 2, 2 a toughness ≧ 45 CN / tex, a Young's modulus ≧ 3.8 GPa, an elongation ≦ 25% and a color defined by the luminance Y> 25%, the degree of white DB <30, the yellow index IJ> 170.

Preferably, the toughness is of the order of 50 to 55 cN / tex, the module ≧ 4 GPa, the luminance Y> 30%, the degree of white <28, the index of yellow> 190.

The light stability of PAIs according to the invention can also be greatly improved compared to that of PAI yarns known hitherto. It is evaluated by the retention of mechanical properties: tenacity at break ≧ 50%, working at break ≧ 18%, elongation ≧ 35%. The light stability is measured according to the method described below.

• d'au moins un diisocyanate de formule : OCN-R-NCO dans laquelle R est un groupe aromatique divalent tel que le diphénylméthane-4,4 diisocyanate et de préférence le diphényléther 4,4'diisocyanate ou leurs mélanges, avec :
• un anhydrique acide aromatique tel que l'anhydride trimellique,
• un diacide aromatique tel que l'acide téréphtalique,
• et éventuellement un dicarboxybenzène sulfonate de métal alcalin ou alcalino terreux de préférence le dicarboxybenzène sulfonate de sodium ou de potassium.

According to the present invention, the term polyamide-imide (PAI) is understood to mean polymers obtained by polycondensation in any suitable solvent:

• at least one diisocyanate of formula: OCN-R-NCO in which R is a divalent aromatic group such as 4,4-diphenylmethane diisocyanate and preferably 4,4'-diisocyanate diphenyl ether or their mixtures, with:
• an anhydrous aromatic acid such as trimellic anhydride,
• an aromatic diacid such as terephthalic acid,
• and optionally an alkali or alkaline earth metal dicarboxybenzene sulfonate, preferably sodium or potassium dicarboxybenzene sulfonate.

et de préférence

et R₁ de préférence un radical

   R₂ de préférence un radical

et M est de préférence Na ou K.The yarns according to the invention have a chemical structure as defined above in which R is a radical such that:

and preferably

and R₁ preferably a radical

R₂ preferably a radical

and M is preferably Na or K.

According to the present application, the PAI wires are also characterized by a value of the polydispersity index I ≦ 2.2. This index corresponds to the ratio Mw / Mn , the values of Mn and Mw being determined by gel exclusion chromatography (GPC) in the NMP at 80 ° C. and 0.1 mole / liter of lithium bromide, the masses being expressed relative to a polystyrene calibration.

The polydipersity index of the PAI yarns according to the invention remains low: it corresponds to a narrowing of the distribution of the molecular masses. Surprisingly, it remains low at the level of the finished threads despite the various treatments undergone by the filaments during their preparation.

et de l'allongement à la rupture %. Les valeurs correspondent à une moyenne de 20 mesures.Surprisingly, the threads according to the invention also have excellent mechanical and thermal characteristics, much superior to those of the polyamide-imide threads according to FR 2 079 785. In particular, the toughness is greater than or equal to 45 cN / tex, of preferably 50 or 55 cN / tex. The measurement is carried out on a manual or automatic dynamometer with constant gradient of elongation on a wire test piece subjected to longitudinal traction until it breaks. The dynamometer is connected to a calculator which provides the numerical values of the strength (dtex) of the breaking strength (cN) of the breaking toughness =

and elongation at break%. The values correspond to an average of 20 measurements.

The elongation at break is measured as indicated above. It is less than or equal to 25%.

obtenu au départ de la courbe force/allongement. La force spécifique (ténacité) correspond au rapport:

Δl étant l'accroissement de la longueur de l'éprouvette à l'instant t auquel correspond le titre réel et lo la longueur initiale de l'éprouvette.The longitudinal Young E modulus of the PAI wires according to the invention is ≧ 3.8 GPa, preferably ≧ 4 GPa. This is the report

obtained at the start of the force / elongation curve. The specific force (tenacity) corresponds to the ratio:

Δl being the increase in the length of the test piece at time t to which the actual titer corresponds and lo the initial length of the test piece.

• la luminance γ % > 25 %, de préférence > 30 %
• le degré de blanc DB < 30, de préférence < 28,
• l'indice de jaune IJ > 170, de préférence > 190, mesurées de la manière suivante :
• l'échantillon est broyé dans un moulin à café de façon à obtenir une bourre de quelques millimètres d'épaisseur et 4 cm². La bourre est placée entre 2 plaques de verre, le tout placé dans un appareil de marque "Elrepho" (Zeiss). Les résultats suivants sont obtenus :
• Y % : la luminance qui donne un classement de l'échantillon dans l'échelle des gris et qui traduit l'impression de clair et de foncé ;
• Y % = 100 correspond à un blanc parfait
• Y % = 0 correspond à un noir parfait.

According to the invention, the PAI yarn is also characterized by a low surface coloration which is evaluated by three essential values:

• luminance γ%> 25%, preferably> 30%
• the degree of white DB <30, preferably <28,
• the yellow index IJ> 170, preferably> 190, measured as follows:
• the sample is ground in a coffee grinder so as to obtain a flock a few millimeters thick and 4 cm². The wad is placed between 2 glass plates, the whole placed in an apparatus of mark "Elrepho" (Zeiss). The following results are obtained:
• Y%: the luminance which gives a classification of the sample in the gray scale and which translates the impression of light and dark;
• Y% = 100 corresponds to a perfect white
• Y% = 0 corresponds to a perfect black.

The degree of white defines a point of color in the chromaticity plane.

The yellow index is an expression of color purity in yellow.

• une rétention de ténacité à la rupture ≧ 50 %, de préférence ≧ 52 %,
• une rétention de travail à la rupture ≧ 18 %, de préférence ≧ 20 %,
• une rétention de l'allongement ≧ 35 %, de préférence ≧ 38 %.

PAI yarns according to the invention can also have good light stability measured after exposure under severe aging conditions and quantified by:

• a retention of fracture toughness ≧ 50%, preferably ≧ 52%,
• work retention at break ≧ 18%, preferably ≧ 20%,
• retention of elongation ≧ 35%, preferably ≧ 38%.

The light stability measurements are carried out in an enclosure which makes it possible to experimentally study the photoaging of polymers in a dry atmosphere. The samples to be tested are placed on a cylindrical turret animated by a circular rotational movement located in the center of a parallelepipedic enclosure, the four corners of which are occupied by a "medium pressure" mercury vapor lamp type MAZDA MA 400 Watts. The envelope only lets through radiation above 300 nm (solar spectrum). The temperature in the enclosure is 60 ° C.
Procedure : The 1.4 cm paper window to which the sample is fixed when determining the mechanical properties on INSTRON is itself placed on one of the 24 supports of the chamber turret. After the exposure, we recover the paper window and determine the mechanical characteristics monofilament according to the method for determining the mechanical properties indicated above.

The results are presented in the form of curves giving the percentage of mechanical characteristics remaining in an exposed fiber compared to an unexposed fiber as a function of the duration of exposure. The values obtained depend on the starting monomers, the best results being obtained with the 4'-diphenyl ether diisocyanate.

Comparisons have also been made with the sons of PAI according to FR 2 079 785.

The yarns according to the invention have a clear superiority compared to known PAI yarns.

The yarns according to the invention also have a much better thermal resistance than that of known PAI yarns: it is evaluated by the rate of degradation corresponding to a percentage of weight loss as a function of time at a temperature of 375 °, in air.

The isothermal degradation of PAI yarns according to the invention is generally ≦ 3% per hour, and preferably ≦ 2% per hour.

The level of this degradation also depends on the starting monomers, the best results being obtained with the 4'-diphenyl ether diisocyanate.

The filaments, threads, fibers according to the present invention can be used alone or mixed with natural or synthetic threads or fibers in order to modify or improve certain properties. They are particularly interesting for the production of work and protective clothing, thanks to their mechanical properties and their thermal and light resistance. In addition, the yarns obtained are easy to dye in all colors with basic dyes.

The PAI yarns according to the present invention are obtained by wet spinning from solutions of polymer in a solvent or solvent mixture. The concentration of the spinning solutions is between 4 and 35%, preferably between 5 and 35%. The polymers are dissolved in a solvent or solvent mixture containing from 5 to 100% by weight of dimethylethylene urea of pH <7 and 0 to 55% of an anhydrous aprotic polar solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, tetramethylurea or γ butyrolactone.

The solutions which can be used in the process according to the invention must have a viscosity of between 100 and 200 poises, preferably between 150 and 160 poises. They can also contain various adjuvants such as pigments, matifiers to improve certain properties.

The PAI solutions are spun in a binary or ternary aqueous coagulating bath containing a solvent or solvent mixture in proportion of 30 to 80% of solvent and 20 to 70% of water, preferably 40 to 70% of solvent (s).

x 100, V2 étant la vitesse des rouleaux d'étirage,
V1 celles des rouleaux délivreurs. Le taux d'étirage des fils à l'état de gel est d'au moins 100 %, de préférence au moins 110 % ou même plus.The solvent used can be dimethylformamide, dimethylethylene urea or a mixture thereof. The spinning bath is maintained between 15 and 40 ° C, preferably 20 to 30 ° C. The length of the coagulating bath is adaptable generally depending on the solvent concentration and the temperature. Baths with a higher solvent content generally make it possible to obtain yarns with better stretchability, therefore better final properties. However, when the solvent concentration is higher, a longer bath length is necessary.
The filaments leaving the coagulating bath in the gel state are then drawn, for example in air at a rate defined by the ratio $\frac{\text{V2}}{\text{V1}}$

x 100, V2 being the speed of the stretching rollers,
V1 those of the delivery rollers. The rate of drawing of the strands in the gel state is at least 100%, preferably at least 110% or even more.

After drawing the filaments are washed by known means to rid them of the solvent (s). This washing can be carried out for example in successive tanks in which water circulates against the current or on washing rollers or by any other means, preferably at room temperature.

The washed filaments are then dried by known means, for example in a dryer or on rollers. The temperature of this drying can vary within wide limits as well as the speed which is higher the higher the temperature. It is generally advantageous to carry out drying with gradual rise in temperature, this temperature possibly reaching and even exceeding 200 ° C. for example.

The filaments are then subjected to hot over-stretching to improve their mechanical qualities and in particular their toughness, which may be advantageous for certain jobs.

This hot over-drawing can be carried out by any known means: oven, plate, roll, roll and plate, preferably in a closed enclosure. It must be carried out at a temperature of at least 150 ° C, which can reach and even exceed 200 to 300 ° C. Its rate is generally at least 150% but it can vary within wide limits depending on the qualities desired for the finished yarn. The total draw rate is at least 250%, preferably at least 260%.

The drawing and overdrawing assembly can be carried out in one or more stages, continuously or discontinuously with the preceding operations. In addition, secondary stretching can be combined with drying. For this, it is sufficient to provide, at the end of the drying, a higher temperature zone allowing overstretching.

EXAMPLES 1 to 3 -

A PAI solution is prepared from: - trimellic anhydride (ANTM) 40 mole% - isophthalic acid (AI) 8 mole% - sodium salt of 5 isophthalic acid (AiSNa) 2 mole% - 4,4 ′ diphenyl ether diisocyanate (DIDE) 50 mole%
in dimethylethylene urea of pH ≦ 7 so as to obtain a concentration of 21%, the polydispersity index of the polymer is 1.78.

The solution, of viscosity 598 poises, is extruded in an aqueous coagulating bath containing dimethylethylene urea. The filaments come out of the coagulating bath in the gel state and are drawn into air at ordinary temperature. They are washed with water in a bath to remove the solvent and dried on rollers.

The washed and dried filaments are over drawn in an oven maintained at a high temperature and then rewound. The precise conditions of the process are gathered in table 1 below:

The mechanical properties of the wires obtained from the tensile tests are brought together in the following table 2, compared to wires obtained from a solution of PAI in N-methypyrrolidone and spun under the conditions of French patent FR 2079 785 filed 02/12/1970 (Example 3C). TABLE 2 Ex. Elongation% Tenacity cN / tex GPa module Temperature: TG ° C Polydipersity index. I 1 21.2 45 6.2 254 2.05 2 17 46 6.4 265 2.05 3 C 29 33 3.6 278 3

- Surface coloring :

Ex. 1 Ex. 2 Ex. 3C Luminance γ% 31.1 33 21.8 Degree of white DB 26.4 27 37.7 IJ Yellow Index 194 197 164

- Light stability (after 40 hours of exposure in the enclosure)

Ex. 1 Ex. 2 Ex. 3C - Retention fracture toughness 52% 55% 31% .work breaking 20% 22% 5% .elongation 38% 39% 17%
- After exposure in the enclosure for only 20 hours, according to the method described above, we also notice in a spectacular way the significant drop in mass of PAI polymer according to Example 3C: M w goes from 147,120 to 62,950, ie a loss of 84,170. On the other hand, a polymer according to the invention loses significantly less:

M w goes from 116,400 to 99,720, ie a loss of 16,680. Similarly, the polydispersity index of the polymer according to the invention after exposure goes from 2.05 to 2.13 whereas, according to example 3C, the polydispersity index goes from 3 to 4.12.

It is therefore found that the drop in mechanical properties reflects a more significant degradation of the polymer chains for the wires of Example 3C than for the wires according to the invention.

- Thermal resistance :

Kinetics of degradation, i.e. weight loss as a function of time represented by V in% .hour ⁻¹ 375 ° C in air Ex. 1 Ex. 2 Ex. 3C Degradation rate% h⁻¹ 2 1.9 6.8

- EXAMPLE 4 -

A polymer identical to that described in Examples 1,2,3 but with a polydipersity index I = 1.85 is prepared.

Les propriétés mécaniques des fils sont les suivantes : Ex. Allongement % Ténacité cN/tex Module GPa Température TG °C Indice de Polydipersité. I 4 23 51 6,3 265 2,2 The solution of this polymer in the DMEU has a concentration of 21% and a viscosity of 781 poises. It is spun under the following conditions:

The mechanical properties of the wires are as follows: Ex. Elongation% Tenacity cN / tex GPa module Temperature TG ° C Polydipersity index. I 4 23 51 6.3 265 2.2

- Surface coloring :

- luminance γ% 31 - Degree of white DB 25 - IJ yellow index 196

- Light stability (after 40 hours of exposure in the enclosure)

- Polydispersity index : after 20 hours of exposure 2.2 - Thermal resistance :

Degradation kinetics (% .h⁻¹): 2

- EXAMPLES 5 to 7 :

A solution of PAI with the same chemical structure as that described in Example 1 is prepared in a mixture of DMEU / DMF in proportion 72/28. The polymer obtained has a polydispersity index I = 1.73 and the concentration solution 21% has a viscosity of 405 poises.

It is extruded in an aqueous coagulating bath, then the filaments are drawn and treated under the conditions set out in Table 3 below:

The mechanical properties of the wires obtained are collated in the following table 4: TABLE 4 Ex. Elongation% Tenacity cN / tex GPa module Polydipersity index. I 5 10.2 55.3 9.87 2.2 6 14.03 46 6.45 2.15 7 13 56.4 9.9 2.2

- Surface coloring :

Ex. 5 Ex. 6 Ex. 7 Luminance γ% 30 31 31 Degree of white DB 25 26 25.4 IJ Yellow Index 195 194 197

- Light stability : (after 40 hours of exposure)

Ex. 5 Ex. 6 Ex. 7 Nomex - Retention fracture toughness 50% 52% 55% 47% .work breaking 19% 21% 21% - .elongation 35% 35% 37% 16% . module 100% 100% 100% 80%

By way of comparison, a polymetaphenyleneisophthalamide fiber known commercially under the trade name Nomex T 450 was subjected to the same photodegradation test as the fibers of the invention. The retention of certain properties is indicated in the table above.

- Thermal resistance :

Ex. 5 Ex. 6 Ex. 7 Degradation rate% h⁻¹ 2.1 1.9 1.8

Claims (15)

1. Synthetic filaments, yarns and fibres based on heat-resistant polyamide-imides which comprise :

   - amide-imide units (A) of formula :

   

   - amide units (B) of formula :
   
   
           -NH-R-NH-CO-R₂-CO-
   
   
   

   - optionally amide units (C) of formula :

   

   in which each of R and R₂ denotes a divalent aromatic radical, R₁ a trivalent aromatic radical and M an alkali or alkaline-earth metal, the units (A) representing 80 to 100 % of all the units, units (B) 1 to 5 % of all the units, units (C) 0 to 20 % of all the units, the sum of the units A + B + C being equal to 100 %, and which have :

   - a polydispersity index I ≦ 2,2

   - a rupture tenacity ≧ 45 cN/tex

   - a Young's modulus ≧ 3,8 GPa

   - an elongation ≦ 25 %

   - a colour defined by the luminance Y > 25 %, the whiteness W < 30, the yellowness value YV > 170,

   characterized in that they are producing by wet spinning a solution of polyamide-imide, of concentration of between 4 and 35 % in a solvent or solvent mixture containing 5 - 100 % by weight of dimethylethyleneurea and 0 - 55 % of an anhydrous polar solvent such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, tetramethylurea or γ-butyrolactone, in a binary or ternary aqueous coagulating bath containing a solvent mixture in a proportion of 30 - 80 % by weight of solvent and 20 - 70 % of water, maintained at a temperature of between 15 and 40°C, in drawing the filaments in the state of a gel by at least 100 %, in washing with water and in then drying by known means, and overdrawing the filaments by at least 150 % at a temperature of at least 150°C, the total draw ratio being at least 250 %.
2. Process for obtaining heat-resistant synthetic filaments, yarns and fibres based on polyamide-imides according to claim 1, characterized in that the coagulating bath contains, as solvent, dimethylformamide, dimethylethyleneurea or their mixture.