DE2209076A1 - Flexible flat structure - Google Patents

Description

EGG. DU PONT DE KEMOURS AND COMPANY 10th and Market Streets, Wilmington, Delaware 19 898, V.St.A.

Flexible flat structure

The invention relates to synthetic, non-woven fabrics, in particular paper made from synthetic organic polymers.

Nonwoven fabrics such as paper are known, e.g. U.S. Patent 2,999,788. This patent describes the production of fibrids from various polymers as well as the use thereof for the manufacture of synthetic paper. It is also known to be made up of fibrids infusible aromatic polyamides can be used to produce paper with good heat behavior, which resists decomposition at elevated temperatures and has good thermal insulation properties. Such paper is suitable for electrical insulation at high temperatures. It has also been shown to be technically valuable to have short fibrids Combining fibers (commonly referred to as "flakes") made from infusible aromatic polyamides.

- 1 - 209837/0859

ΗΤ-230

The paper described above is usually improved in its mechanical properties by calendering at high temperatures and pressures; however, calendering does not give the paper a good tensile strength ημτ , but also increases its brittleness. If the calendering is carried out under less severe conditions in order to prevent the increase in brittleness, it is found that the paper obtained in this way has suffered a technically unacceptable decrease in its elongation at break.

However, many of the papers according to the invention have a high Elongation at break and at the same time only a low level of brittleness (hereinafter referred to as flexural strength). Further the paper according to the invention has surprisingly good behavior in the heat and good folding resistance.

The invention relates to a flexible sheet-like structure, consisting consisting essentially of a nonwoven, unfused, intimate mixture of (1) about 15 to 90 percent by weight Fibrids made from an infusible aromatic polyamide and (2) about 10 to 85 percent by weight short polyester fibers. The flat structures show good behavior in heat, i.e. they resist decomposition at high temperatures, and also have good flexural strength.

According to a preferred embodiment, according to the invention polyester fibers used have an initial modulus of less than 85 and preferably less than 80. the end Paper made from such fibers has a high elongation at break.

Preferably the weight ratio of fibrids to fibers is at least 1: 1 and for electrical insulation purposes at least 1.2: 1. Usually the fibrids form at least 50 percent by weight and sometimes at least 60 percent by weight of the Paper.

- 2 209837/0859

HI-230 3

It has been found that flexible sheet structures made from selected fiber materials, namely from fibrids made from infusible aromatic Polyamides and polyester fibers, good behavior in heat, high flexural strength and depending on the "The polyester concerned also have a good elongation at break.

The flat structures are paper-like and can be used according to Yerfahren and produce with gate directions, as they are common in the paper industry. In this way, the fibrous materials, i.e. the fibrids and the short fibers, together into a mixture slurry, then in the Fourdrinier machine or by making scoop paper in a hand scoop with a Form sieve is processed into paper.

Fibrids are small, non-granular .; fibrous or sheet-like particles that are not rigid. Two of its three dimensions are micron-sized. As a result of their smallness and Flexibility can be put down in a mechanically interwoven form, as is usually the case with those made from wood pulp Paper is the case. Fibrids can be produced by converting a polymer from its solution in a fibrid production device, as in the USA patent 3 018 091 is described, fails under the action of high shear forces.

For use according to the invention, the fibrids are made from manufactured infusible aromatic polyamides. Aromatic polyamides in this sense are polymers in which each of the

0 R

HI

repeating amide units -G-N-, in which R is a hydrogen atom or denotes an alkyl radical having 1 to 6 carbon atoms, via each of the nitrogen and carbon atoms Ring carbon atom of two different aromatic ring radicals is bonded. As an "aromatic ring" there is a resonance here having carbocyclic ring. "Infusible" are polymers that are already decompose before they begin to melt.

209837/0859

HT-230 tf

The infusible aromatic polyamides can by reaction an aromatic dicarboxylic acid chloride with an aromatic diainine. The carbonyl groups of the Dicarboxylic acid chloride and the amino groups of the diamine can be in the o-, p- or m-position to one another; the m position is preferred. The reaction takes place at low temperatures, e.g. below 100 ° C. Aromatic aminoacyl compounds can also be used use. Other polymer-forming components which do not have an aromatic nucleus can also be used in amounts of less than about 10 mole percent without affecting the physical and chemical properties of the Polyamides used to make the pibrids are impaired. Substi- * tuenten, such as lower alkyl, lower alkoxy groups, halogen atoms, Nitro groups, lower carbalkoxy groups or other groups be bound, which do not form a polyamide during the polymerization. However, it is preferable to use completely aromatic, i.e., unsubstituted diamines and dicarboxylic acid chlorides.

Typical examples of aromatic rings are

and the same. Suitable polyamides are detailed in U.S. Patent 3,094,511 and in British Patent 1 106 190 described :. A preferred aromatic polyamide is poly (m-phenylene isophthalic acid amide). According to the invention The polyamides used preferably have inherent viscosities of about 1.2 to 2.0, determined at 25 ° C on a solution in Ν, Ν-dimethylacetamide, which is 4 percent by weight, based on the solution containing lithium chloride, with a polyamide concentration of 0.5 g per 100 cm of solution.

Once the pibrids have been prepared, they are dispersed in an aqueous medium to form a slurry, which is then used for

- 4 -209837/0859

ΗΤ-230 5 "

Production of the paper is used according to the invention. Preferably the slurry contains less than about 1 percent by weight fibrids.

The polyester fibers used in the present invention are short fibers commonly referred to as "curls". Preferably, the polyester flakes consist of fibers less than 2.54 cm in length with an optimal length of about 0.6 cm. Suitable yarns or cables from the polyester are made in a conventional manner, e.g. with a screw saw cutting device, cut to the desired flake length and then slurry the flakes in an aqueous medium dispersed. Preferably the slurry contains less than 1 weight percent flake.

Linear polycondensation products are used here as "polyesters" referred to, which in their polycondensate chain carbonyloxy binding

»».
residues -CO included. Polyesters which contain oxy-carbonyloxy radicals, as well as copolyesters, perpolyesters and the like, are also within the scope of the invention. The polyesters can optionally contain additives such as matting agents, additives which affect viscosity, pigments and the like. The threads produced from these polyesters can have a wide variety of cross-sectional shapes, such as round, multi-wing or hollow.

Examples of linear polyesters are polyethylene terephthalate, polyethylene terephthalate isophthalate (85:15), polyethylene terephthalate hexahydroterephthalate (90:10), polyethylene terephthalate 5- (sodium sulfo) isophthalate (97: 3), poly (p-hexahydroxylylene terephthalate), poly (diphenylolpropane isophthalate), the polyethylene naphthalenedicarboxylates (especially those derived from the 2,5 and 2,7 isomers) and poly (hexamethylene bibenzoate). Polyethylene terephthalate and terephthalic acid copolyester, in which about 80 mole percent of the dicarboxylic acid units Terephthalate units are preferred as the polyester.

- 5th 209837/0859

ΗΤ-£ 230

Preferably, the polyesters have an intrinsic viscosity \ of 0.3 "to 1.15, determined on a dilute solution in a group consisting of 3 parts by weight of methylene chloride and 1 part by weight of trifluoroacetic acid solvents" The intrinsic viscosity is the limiting value of the natural logarithm of the ratio of The viscosity of the solution to the viscosity of the solvent, divided by the concentration of the solution of polymer, when the concentration approaches zero.

The polyester is spun from the melt into threads that are drawn in a known manner. Have suitable threads Titers of about 0.5 to 10 denier or more; Fibers with the higher titers, however, cannot be tied into paper as easily such as fibers of lesser titers, and therefore titers less than about 5 denier are preferred. Particularly preferred fibers with titers between about 1 and 3 den.

The polyester filaments then become fibers as described above cut by flake length, which are slurried in an aqueous medium.

For producing the flexible sheet-like structure according to the invention the slurries of the fibrids and the fibers are in certain proportions to form a paper stock with one another mixed in the headbox of the paper machine is entered, where it is spread evenly on the wire screen forming the paper. If the stock is over the If the sieve runs off, water runs off and this run-off is carried out in a conventional manner, for example by applying a vacuum supports the formation of the fiber mat on the wire screen. The wet "sheet, which is the weight ratio of paper solids to water can be 1: 4 to 1: 8, is removed from the wire screen and placed in the dry section of the machine introduced. The drying section has the task of the water drive off without damaging or destroying the paper web. Drying is done by running the wet web over the

- 6 209837/0859

HT-230 ¹ year

The surface of steam-heated drying pots is transferred into contact with the surface. The drying pots, of which 40 or More can be arranged in two rows are in two sections divided, each section being driven independently of the other so that the sheet slightly as it dries can be stretched out. The degree of this stretching depends on the special conditions; the total degree of stretching but is usually on the order of about $ 5 »· For better contact with the surface of the drying pots, the web is pressed against the underside by means of porous drying "felts" of the lower drying pots. The vapor pressure in the drying pots can be in the range from 2 to 10 atmospheres and increases in the machine running direction. Before the paper is discharged from the machine, it reaches a maximum temperature, which does not exceed 185 C. Under normal processing conditions the paper contains about 2 to 10 ^ Water based on the weight of the damp paper.

If necessary, the wet paper web produced in this way can be calendered, since the physical properties of the paper are in the generally improved when exposed to high temperatures and pressures. You can't go under such calender conditions work that the polyester flakes melt. The calender pressures can range from about 36 to 101 kg / cm. You can work at room temperature; however, it is preferred to operate at one calender temperature of at least about 175 ° C. The highest calender temperature depends on the melting point of the polyester flakes. Usually the upper limit of the calender temperature is around 240 ° C.

Many papers containing polyester flakes can be calendered between 200 and 240 ° G.

The paper according to the invention can optionally by Layer bonding of several non-calendered webs to one another

~ 7 - 209837/0859

HT-230 fc

are produced during calendering, so that a laminate is obtained. The adhesion between the layers of a multi-layer paper is "significantly enhanced by treating all bonding surfaces with a corona discharge, i. with the soft, blue discharge that the incomplete indicates electrical breakdown in a gas at or near atmospheric pressure. This treatment is particularly suitable for wet or dry calendering at temperatures below 285 ° C. The corona discharge treatment is carried out by placing the paper web between a grounded electrode, usually a steel roller coated with a dielectric, and a high voltage electrode to pass through. Treatments and plants of this type are in the art of Production of foils and cellulose paper is known. To treat the paper layers according to the invention one works with an electrical discharge of about 0.1 to 1.0 W per 30.5 cm / min treatment speed per 2.54 cm electrode width. The distance between the electrode and the roller is usually equal to about three times the thickness of the paper web.

If necessary, an inhibitor can be added to the paper to give it resistance to oxidative degradation at higher levels To lend temperatures. Oxides, hydroxides and nitrates of bismuth are preferably used as inhibitors. Particularly effective inhibitors are bismuth hydroxide and nitrate.

Also binders, e.g. acrylic polymers and the like, can be added to the pulp slurry prior to papermaking or added to the finished paper web on the coating press.

Preferably, the paper is compressed to a thickness of about 0.002 to 0.076 cm by calendering. The paper has one good heat resistance and flexural strength, and the preferred one Paper also has good elongation at break and good mechanical adaptability.

20983 7/0859

ΗΤ-230 3

The thermal behavior of the paper can be determined by measuring the high temperature aging properties of the paper. In this determination, the mechanical properties of the paper are measured before and after exposure to a certain temperature for a certain period of time. The mechanical properties of the paper according to the invention do not deteriorate in this determination as much as those of the paper-like products made of polyesters or the papers which contain aliphatic polyamide flakes instead of polyester flakes. For example, from a diagram of the service life of a paper sheet at 2 percent elongation in hours depending on the aging temperature, the temperature at which the paper can no longer withstand an elongation of only 2 fo after 1000 hours of exposure to heat is a commercially available laminate made of a non-woven polyester layer is at 179 ° C, for a paper according to the invention at 235 ° C and for a paper made of a commercially available aromatic polyamide at 290 ° C.

The preferred papers according to the invention are those in which the initial modulus of the polyester flakes is less than and preferably less than 80 g / den. In the broadest sense of the invention, the initial modulus is insignificant and can even be 120 or more. The initial modulus is the ratio of the change in tension to the change in strain in the initial, rectilinear portion (ie, before the yield point is reached) of a stress-strain curve after any crimp has been removed by smoothing. This ratio is calculated from the tension expressed as the force (gramic) per unit of the linear density (den) of the original sample to the elongation _s expressed as the percentage elongation, ie

Beginning module.

ten: The lower the initial modulus, the lower the resistance to stretching. Which is made using this poly whether terflocken low initial modulus of paper,

- 9 _ 20983 7/0859

HT-230 JO

has a surprisingly high elongation at break. A paper according to the invention, in which the elongation at break of the polyester flakes is about 45 #, has, for example, twice as high an elongation at break as a paper in which the polyester flakes are replaced by flakes made from an aromatic polyamide, although the elongation at break of the aromatic polyamide flakes is about is the same as that of the polyester flakes, namely about 45 fits and although the tensile strength of the two papers is about the same. The aromatic polyamide flakes have a higher initial modulus than the polyester flakes. Paper with good elongation at break is particularly suitable for applications where mechanical adaptability is important. "Adaptability" means that the paper conforms smoothly to the shape of the object around which it is wrapped. Good adaptability is not only associated with high elongation at break, but also with high folding strength and a low initial modulus. Paper in which the initial modulus of the flakes is in the range from about 20 to 80 is particularly preferred. The outstanding adaptability of the paper according to the invention is particularly noticeable in the case of light paper (ie paper with a thickness of less than 0.15 mm).

In the following examples, in which all percentages are based on total weight unless otherwise specified the paper properties are determined according to the following test standards:

Thicken ASTM D-374

Apparent Density, ASTM D-374 and TAPPI T-410 Basis weight: thickness

Dielectric through- ASTM D-149 and MIL-I-24024 Impact resistance

Tensile Strength and ASTM D-882-61T
Elongation at break

Heat aging ASTM-1830

Tensile Strength- ASTM-D-1708 (Micro Method)

Shaft of the heat paper

■ 10 209837/0859

ΗΤ-230 Μ

Folding strength. ASTM-D-2176-63T (according to Kondi tion at 24 ° C and 55 relative humidity using a Tinius-Olsen fold strength tester).

example 1

This example explains the production of fibrids, flakes and paper and shows the superiority of the paper according to the invention over similarly produced paper aromatic polyamide fibrids and aromatic polyamide flakes.

Manufacture of the fibrids

A solution of poly (m-phenylenisophthalsäureamid), the 14-1 f> polyamide contains, has a Tiscosität between 50 and 75 Poise and an inherent Yiscosität of about 1.6, is the FibridenerZeugungsvorrichtung described in the USA Patent 3,018,091 fed. The polyamide solution contains 77.5% dimethylacetamide, 2 % water and 6.5 % calcium chloride. The polyamide solution is fed to the fibrid generator at a rate of 54.6 kg of pesticides per hour. The precipitation takes place with a precipitant, the composition of which is controlled so that it contains 30 to 40 % dimethylacetamide, 58 to 68 % water and 2 % calcium chloride. The flow rate of the precipitant to the fibrid generating device is 62.5 kg per kg of polyamide solution. A rotor speed of 7000 rpm produces the shear forces necessary to form fibrids of good quality suitable for papermaking. The content of the fibrids of dimethylacetamide and chloride to 1.0 or 0.3 fo ^, based on the polyamide is by washing with water, decreased. The fibrids are then refined at a consistency of 0.8 fo in a "36-2 Sprout-Waldron" disk mill to a degree of grinding according to Schopper-Riegler of 300 to 400 ml. The size of the fibrids is characterized as follows according to Clark's fiber classification:

- 11 -

2098 3 7/0859

2J0 ■

Mesh size of the back

Sieve, mm held, tf *

1.41 1.0

0.59 8.0

0.297 38.0

0.149 34.0

A total of 81.0

Manufacture of polyester flakes

Polyester flakes are made from drawn polyethylene terephthalate threads with an initial modulus of 43 g / den, an elongation at break of 33 ^, a tensile strength of 4.3 g / den and a melting point of 265 ° C. The threads are cut to lengths of about 6.35 mm. The fibers have got a thread count of 1.5 den.

Manufacture of the paper

The fibrids are at a concentration of 0.6 £ in an aqueous medium together with the Polyesterflockenaufschlämmung, having a concentration of 0.23 ° F in water, at a weight ratio of fibrids to floc of about 1.5: 1.0 (£ 60 fibrids and $ 40 flakes) fed to a mixing tee. The mixture is fed into the headbox of a paper machine and then onto a wire mesh to make a paper web. The wet web is removed from the wire mesh and fed to a dryer in order to reduce its moisture content with the aid of drying pots heated by steam to a maximum temperature of 137 ° G. The partially dried paper is then wound into a roll that serves as a supply for making the calendered paper. The properties of this partially dried, non-calendered paper are shown in Table I.

The non-calendered paper is then heated by infrared dried and a calender with a single roll mouth

- 12 2098 3 7/0859

2203076

HT-230

fed. The roll mouth temperature "is 240 ° C and the Pressure between the rollers 107 kg / cm. The paper comes with calendered at a speed of 9 m / min. The properties of the calendered paper also emerge Table I.

Manufacture of paper with aromatic polyamide flakes

Aromatic polyamide flake fibers are made from poly (m-phenylenis oph thai acid amide) having an inherent Tiscosität of 1.5 by dry spinning from a solution containing 67 $ dimethylacetamide, 9 ° f contains calcium chloride and 4 <f water. The spun threads are flooded with an aqueous liquid and contain 100 % dimethylacetamide, 45 % calcium chloride and 30 to 100% water, based on the dry polyamide. The filaments are washed and reduced to about 0.10 or 0.5 tf ° to an extraction stretching process in which the chloride content and the Dim e thy Iac etamidgehalt, stretched. The drawn threads are brought to crystallize on rollers at about 340 ° C. A moderate further stretching during crystallization increases the total stretching ratio to 5.0, and threads with a titer of 2 denier are obtained. Typical properties of these threads are an initial modulus of 94 g / denier, an elongation at break of 28 fo and a tensile strength of 4.5 g / denier. The threads do not melt, but rather decompose quickly above 371 C. The threads are cut into flake fibers with a length of 0.68 cm. These fibers are slurried in water at a concentration of $ 0.23.

The flakes of poly (m-phenylene isophthalic acid amide) fibers are then combined with the fibrids prepared as described above of poly (m-phenylene isophthalic acid amide), and paper is made as described above.

The properties of the non-calendered and the calendered Papers are summarized in Table I.

- 13 209837/0859

O I. (O OO I. co -J CD OO
cn (O

Thickness, 10 cm basis weight, g / m Apparent density, g / cm

Tensile strength (MR *), g (force) / cm per g / m

Elongation at break (MR), $> modulus, 10 ³ kg (force) / cm ²

* MR = machine direction.

Table I.

Polyamide fibrid paper
and polyester flakes

before the
Calendering , 36 12th 47 ,1 O , 4 37 13th 5

after this before the Calendering Calendering 5 12th 47 49 1.01 0.39 44 39 9.9 3.2 15.7 7.7

Paper made from polyamide fibrids and polyamide flakes

after calendering

49
0.94

5.5
19.6

CD CD O

HT-230 £ -

As can be seen from the table above, the has aromatic
Paper containing polyamide flakes only part of the elongation at break of the paper containing the polyester flakes.
The calendered polyester flake paper according to the invention also adapts more smoothly to the shape when wrapping wires
■ the wires, without kinking, than the calendered paper, which contains the aromatic polyamide flakes.

Example 2

This example explains the use of other calender conditions and the influence of the titer of the polyester fibers
on the properties of the paper.

In the UJ.OÖCII] example, the fibrids and fibers described in Example 1 are used, but polyester flakes with a denier of -3 denier and a length are also used
1.0 cm is used. The paper is produced according to Example 1, with the difference that the calendering without preheating (the moisture content of the paper is $ 6, based on the dry weight of the paper) at 175 ° C and
a roller pressure of 116 kg / cm at a conveying speed of 31 m / min. The properties of the
calendered papers are shown in Table II.

- 15 -

2 0 9 B 3 7/0 8 5 9

ητ-ου λ II Polyester, Tabel 3.0 den Aromatic Polyester, 7th Polyamide, 1.5 den 71 2.0 den 7th Thickness, 10 "'cm 8th 72 1.04 ρ
Basis weight, g / m 64 Apparent density, 1.08 36 g / cm x ⁵ 0.83 7.0 Tensile strength (MR *), 38 g (force) / cm per g / m 48 8.8 Elongation at break (MR), fo 4.4

* MR = machine direction.

Example 3

This example illustrates the manufacture of paper with low and with a high flake content according to the invention.

A fibrid slurry similar to that of Example 1 with a moisture content of 20 f * is dispersed in water with the aid of a grinder ("British Standard Disintegrator") to form a slurry which contains 1.20 percent by weight of fibrids, based on the weight of the slurry. This slurry is diluted to a consistency of $ 0.30 and refined for 30 seconds at high speed in a Waring blender. Part of this slurry is then mixed with a slurry of aromatic polyamide flakes and another part with a slurry of polyester flakes and made into paper as described in Example 1. The slurries are mixed in a hand vat (Noble and Wood) and the water is allowed to drain through a 0.149 mm sieve. The deposited paper is removed from the screen, thoroughly dried and pressed in a printing press under a pressure of 89 kg / cm between stainless steel plates at 240 ° C. The properties are shown in Table III.

- 16 -

20983 7 / 08.5 9

Tabel

III

I. Sew ratio Fibrids: flakes —J Titer den Thickness, 10 "" ⁵ cm Weight per unit area, ro g / a CD Seem to be you CO
CO te, g / cm ^5: co Tensile strength (MR *) g (force) / cm CD per g / m ² OO
cn Elongation at break CO (MR), Io

polyester

Aromatic polyami d

Fold strength (MR) '10 * pallet cycles

9: 1 1 , 5 3 , 0 1.5 1: 3 1 , 5 3 , 0 9 2.0 :1 , 0 1 2.0 : 3 , 0 1.5 3.0 8th 8th 25th 3.0 7th 10 23 2 8th 30th 2 9 23 23 62 63 202 26th 59 60 203 62 98 58 212 210 0 , 78 0 , 81 0.81. 203 0 , 82 0 , 60 0.86 , 78 0.66. , 64 0.92 0.90 28 27 20th 0.76 18th 16 25th 0 25th 9 0 16 27 30th 9 , 4 8th , 3 3.8 18th 3 , 9 2 , 6 7.1 , 4 1.3 , 5 9.8 11.6 44.3 3.5 7.1 6th 1.1 1 12.2 12.4 81.1

ro
ν »
ο

* MR = machine direction.

ΗΤ-230

Example 4

This example explains the high folding resistance of the inventive Paper.

Paper is made from aromatic polyamide fibrids using aromatic polyamide flakes and polyester flakes produced according to example 1. Three non-calendered paper webs are treated with corona discharges and the treated layers by calendering under high pressure at 230 ° C bound together on a 0.25 mm thick paper. The properties of the paper webs are shown in Table IV, from the the higher folding strength of the paper containing the polyester flakes can be clearly seen.

tab Thickness, 10 ~ ⁵ cm hurry IV Paper with Basis weight, g / m Paper with polyester Apparent density, g / cm aromatic flakes Tensile strength (MR *), Polyamide flakes 26th g (force) / cm per g / m 24 264 Elongation at break (TCR), fo 241 0.99 Folding strength (MR), 1.01 10 ⁵ fall cycles 47 67 10.5 7.1 36.0 6.9

* MR = machine direction.

Example 5

This example explains the good heat aging behavior of the paper according to the invention, the paper with regard to its properties are compared with other papers made using other fibers in combination with aromatic polyamide fibrids.

- 18 -

20983 7/0859

HT-230

A paper is made using aromatic polyamide fibrids with polyester flakes (1.5 denier) and another paper from the same fibrids and flakes from an aliphatic polyamide (polyhexamethylene adipamide) of 3 »0 den manufactured. In "both cases the ratio of fibrids is to flakes 1.5: 1. Both types of flakes are produced according to Example 1. The paper is conventionally used in a 82 cm long sieve machine. Both papers are “compacted at 240 ° C; that containing the polyester flakes Paper is calendered while the paper containing the aliphatic polyamide flakes is pressed in the platen press. The properties of both papers after different aging times at 220 ° 0 are shown in Table V.

The paper containing the polyester flakes retains a greater proportion of it after aging in air at 220 ° G original dielectric strength than the aliphatic polyamide flake treated under the same conditions containing paper.

- 19 -

2 0 9 8 3 7/0859

T SO μ i ° R ** μ fo R ** tensile strenght Elongation at break (MEt) Elongation at break (MR *) a b e 1 1 e V 100 100 (MD *) fo R ⁰ Jo R 101 62 g (force) / cm 11.8 100 17.5 100 96 57 per g / m 4.2 36 2.9 17th Paper containing polyester flakes 87 52 50 3.2 27 2.6 15th Time, Dielectric 94 39 32 3.4 29 4.2 24 Hours. Breakthrough 92 49 35 3.6 31 2.7 15th O strength 92 41 24 3.7 31 3.6 21st 48 V / 25.4 Aliphatic ^ 44 3.4 29 1.9 11 96 941 Dielectric 47 Paper containing polyamide flakes 192 954 Breakthrough
strength 40 tensile strenght 284 901 V / 25.4 (MD *)
g (force) / cm 768 819 963 per g / m 1536 887 593 48 867 546 28 861 499 26th Time, 377 25th Hours. 469 19th O 397 20th 48 15th 96 192 284 768 1536

* ■ MR = machine direction
** #R = <fo the original dielectric strength has been retained.

- 20 -

209837/0859

HT-230 Aj

The paper according to the invention is particularly suitable for Electrotechnical application purposes as insulation "at high temperatures, e.g. above 135 ° 0. The paper is therefore to be wrapped around of electrical wire, as a motor slot lining or suitable as insulation in oil-filled transformers.

• - 21 -

20983 7/0859

Claims (2)

EGG. du Pont de Nemours and Company HT-23O Claims Π Λ Flexible surface pattern, consisting essentially of a non-woven, unfused intimate mixture of fibrids and short fibers, characterized in that the Mixture of 15 to 90 percent by weight of fibrids from an infusible aromatic polyamide and 1.0 to 85 percent by weight consists of short polyester fibers, with the proportions of the two components adding up to $ 100. 2. Flat structure according to claim 1, characterized in that the polyester has an initial modulus of less than 85 g / den. ■ - 22 209837/0859