Thermotropic copolyester, composite and its use, shaped article, core/sheath-yarn, woven fabric and moulded fabric

Description:

The present invention pertains to a thermotropic copolyester, a composite comprising said copolyester as a matrix resin, the use of the composite, a shaped article comprising said copolyester, a core/sheath-yarn comprising the thermotropic copolyester as a wrapping yarn, a woven fabric comprising said yarn and a moulded fabric obtained by moulding the woven fabric.

Thermotropic copolyesters are known. Chua et al. describe in Polymeric Materials: Science & Engineering (2002), vol. 87, pages 125-126 a random copolyester synthesized from 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, sebacic acid and hydroquinone. However, there is a need for a further thermotropic copolyester.

Therefore, the object of the present invention is to provide a further thermotropic copolyester.

Said object is achieved by a thermotropic copolyester consisting of a random sequence of structural units, wherein the structural units comprise a unit derived from 4-hydroxy benzoic acid, a unit derived from 6-hydroxy-2-naphthoic acid, a unit derived from suberic acid, a unit derived from sebacic acid and a unit derived from hydroquinone.

Surprisingly, the thermotropic copolyester according to the invention exhibits significantly improved values of strength at break and elongation at break if compared with a thermotropic copolyester of the same inherent viscosity, i.e. of the same molecular weight but synthesized from 4-hydroxybenzoic acid, 6-hydroxy-2- naphthoic acid, sebacic acid and hydroquinone. So, surprisingly the mere introduction of a unit derived from suberic acid into a random thermotropic copolymer consisting of a unit derived from hydroxybenzoic acid, a unit derived from 6-hydroxy-2- naphthoic acid, a unit derived from sebacic acid and a unit derived from hydroquinone significantly increases the values of strength at break and elongation at break of the thermotropic copolyester resulting by said introduction.

The thermotropic copolyester according to the invention consists of a random sequence of its structural units. Within the scope of the present invention the term "random sequence" means that sequence, in which the structural units follow one another in the copolymer chain as the result of the statistical probability of its units to copolymerize with each other.

Within the scope of the present invention the term "structural unit" means the chemical structure of said unit in the chain of the copolymer according to the present invention.

Within the scope of the present invention the term "unit derived from" means the chemical structure of the corresponding monomer, from which said unit is derived.

The thermotropic copolyester according to the invention can be synthesized easily by one of the know copolymehzation techniques, e.g. by a conventional 2-step melt polymerization process, i.e. in the first step acetylation of the aromatic hy- droxyl groups and in the second step copolymehzation under nitrogen via trans- estehfication. At the end of the second step a vacuum is applied to ensure the formation of a high molecular weight.

In a preferred embodiment of the thermotropic copolyester according to invention the structural units consist of a unit derived from 4-hydroxy benzoic acid, a unit derived from 6-hydroxy-2-naphthoic acid, a unit derived from suberic acid, a unit derived from sebacic acid and a unit derived from hydroquinone.

The molar contents of the structural units of the invention's thermotropic copolyester may be varied in broad ranges. However, below a content of 10 mol % of the unit derived from 4-hydroxybenzoic acid the liquid crystalline phase of the copolyester might get lost. Above a content of 40 mol % of the unit derived from 4-hydroxybenzoic acid the melting point of the copolyester increases and consequently the nematic window decreases significantly.

Therefore, in a further preferred embodiment the thermotropic copolyester of the invention consists of 10 mol % to 40 mol % of the unit derived from 4-hydroxybenzoic acid, 10 mol % to 40 mol % of the unit derived from 6-hydroxy-2-naphthoic acid, 5 mol % to 20 mol % of the unit derived from suberic acid, 5 mol % to 20 mol % of the unit derived from sebacic acid and 10 mol % to 40 mol % of the unit derived from hydroquinone.

In an especially preferred embodiment the thermotropic copolyester of the invention consists of 25 mol % to 35 mol % of the unit derived from 4-hydroxybenzoic acid, 25 mol % to 35 mol % of the unit derived from 6-hydroxy-2-naphthoic acid, 7.5 mol % to 12.5 mol % of the unit derived from suberic acid, 7.5 mol % to 12.5 mol % of the unit derived from sebacic acid and 10 mol % to 40 mol % of the unit derived from hydroquinone.

To ensure an optimised random structure of the resulting copolyester, i.e. a structure, wherein the formation of blocks of one of the structural units is minimized, it is preferred, that the content of the unit derived from 4-hydroxy benzoic acid equals that of 6-hydroxy-naphthoic acid and the content of the unit derived from suberic acid equals that of sebacic acid.

In another preferred embodiment the thermotropic copolyester according to the present invention exhibits an inherent viscosity η _ιn h of at least 0.5 dL/g, which corresponds to a molecular weight of approximately 15 000 g/mol, and up to 1.0 dL/g, which corresponds to a molecular weight of approximately 29 000 g/mol.

In an especially preferred embodiment the thermotropic copolyester exhibits an inherent viscosity η _ιn h of al least 0.75 dL/g, which correspond to a molecular weight of approximately 22 000 g/mol, and up to 1.0 dL/g, which corresponds to a molecular weight of approximately 29 000 g/mol.

The molecular weights of the thermotropic copolyesters according to the invention can be further increased e.g. by a chain extension reaction in the solid state under vacuum at a temperature of approximately 30 ⁰ C below the melting temperature of said thermotropic copolyester.

Composites, which comprise as a matrix resin a mixture of 50 wt.-% crosslinked phenol/formaldehyde - polymer and 50 wt.-% polyvinylbutyral and as reinforcing fibers aromatic polyamide fibers, especially poly-p-phenylene terephthalamide fibers are known e.g. in ballistic applications to exhibit a high ballistic protection. However, such composites because of the crosslinked state of the phenol/formaldehyde - polymer are restricted to that geometrical composite-form in which the cross-linking took place. Any attempt to convert said composite-form into another one leads to a destruction of the composite.

The thermotropic copolyester according to the present invention surprisingly allows to skip the crosslinked phenol/formaldehyde - polymer from the matrix resin mixture and to manufacture composites with reinforcing fibers, which composites exhibit a ballistic protection, which may be as high or even higher than in the known composites with a crosslinked phenol/formaldehyde - polymer. However, because of the thermoplastic nature of the thermotropic copolyester of the present invention a composite comprising reinforcing fibers and a matrix resin comprising

the thermotropic copolyester of the present invention allows the manufacturer of such composites to produce said composites in an always identical geometrical form, e.g. in the form of a plate and to deliver e.g. said plates to his customers, which can bring the plates into a manifold of desired geometrical forms by a simple heat/pressure-transforming procedure of the delivered composite.

Therefore, a composite comprising a matrix resin and reinforcing fibers and which is characterized in that the matrix resin comprises a thermotropic copolyester according to the present invention is also part of the present invention.

Within the scope of the present invention the term "reinforcing fibers" includes all natural or synthetic fibers, which because of their breaking strength are suited to reinforce composites. Preferably, reinforcing fibers having a tenacity at break of at least 80 cN/tex, more preferably of at least 120 cN/tex and most preferably of at least 150 cN/tex are suited.

In a preferred embodiment of the composite according to the present invention the reinforcing fibers are aromatic polyamide fibers, i.e. fibers, that were manufactured from aromatic polyamides, wherein at least 85 % of the amide (-CO-NH-) linkages are directly bound to two aromatic rings. Especially preferred within the scope of the present invention as reinforcing fibers are fibers spun from poly-p-phenylene terephthalamide, which can be obtained under the trade name Twaron ^® from Teijin Aram id.

The reinforcing fibers of the composite according to the present invention can be present in any form known for reinforcing fibers.

For example the reinforcing fibers of the composite according to the present invention can be present as staple fibers of equal or different lengths, which are distributed isotropically and more or less homogenously in the matrix material.

Furthermore, especially for ballistic applications, the reinforcing fibers of the composite according to the present invention can be present as at least one unidirectional layer. Such layers can be arranged upon one another in parallel alignment or cross-plied at an angle.

In another preferred embodiment, especially for ballistic applications, the composite according to the present invention is characterized in that the reinforcing fibers are present as at least one woven fabric, wherein the number of woven fabrics depends on the desired application of the composite. For ballistic applications said number depends on the energy of the impact, which the composite has to withstand. For a lot of ballistic applications suitable values for said number may range from 5 to 30, more preferred from 10 to 20.

In a further preferred embodiment of the composite according to the present invention the matrix resin comprises the thermotropic copolyester of the present invention and a thermoplastic copolymer, which preferably is a polyvinylacetal and especially preferred a polyvinylbutyral (PVB).

In a preferred embodiment of the composite according to the present invention the thermoplastic polymer contains a plastisizer, which may be dioctyl phthalate. The plastisizer is added to improve the processability of the PVB and to lower its glass transition temperature T ₉ . For example, neat PVB with a weight average molecular weight M _w of about 100 000 exhibits a T ₉ of about 70 ⁰ C, whereas PVB containing 25 % and 50 % of said plastisizer, exhibits a T ₉ of about 30 ⁰ C and 5 ⁰ C, respectively. It was found, that due to the lower T ₉ the modulus of elasticity at room temperature decreases, which improves the ballistic properties of the composite comprising said PVB/plastisizer-mixture.

The matrix resin of the composite according to the present invention may consist completely of the inventive thermotropic copolyester. It was found, that such a composite with aromatic polyamide reinforcing fibers and with that inventive ther-

inotropic copolyester, which up to now was synthesized with the highest molecular weight, exhibits a some what lower ballistic protection than a composite comprising as the matrix resin a mixture of 50 wt.-% crosslinked phenol/formaldehyde - polymer and 50 wt.-% polyvinylbutyral (prior art composite) and the same aromatic polyamide reinforcing fibers. However, it can be expected, that a further increase of the copolyester ^* s molecular weight will increase the ballistic properties of the composite according to the present invention.

The inventors of the present invention found, that, if the matrix resin consists of less than 100 wt.-% of the inventive thermotropic copolyester and the difference to 100 wt. -% is the thermoplastic polymer and optionally the plastisizer mentioned before, the resulting composite according to the invention exhibits a better ballistic protection, which may even exceed that of the prior art composite identified above.

Therefore, in a preferred embodiment the composite of the present invention is characterized in that the matrix resin contains the thermotropic copolyester (TC) according the invention, the thermoplastic polymer (TP) and the plastisizer (P) in a weight ratio TC : TP : P in the range from 20 : 60 : 20 to 80 : 15 : 5 and even more preferred in a weight ratio TC : TP : P in the range from 40 : 45 : 15 to 60: 30 : 10.

In another preferred embodiment the composite of the present invention is characterized in that the matrix resin consists of the thermotropic copolyester according to the present invention and a thermoplastic elastomer, which preferably is a styrene-ethylene-butadiene-styrene block-copolymer. Such a block-copolymer can be obtained under the trade name Kraton ^® from Shell International Petroleum Company.

A preferred embodiment of the composite according to the present invention is characterized in that the matrix resin contains the thermotropic copolyester (TC) according the invention and the thermoplastic elastomer (TPE) in a weight ratio

TC : TPE in the range from 20 : 80 to 80 : 20 and even more preferred in a weight ratio TC : TPE in the range from 60 : 40 to 40 : 60.

In still another preferred embodiment of the composite according to the present invention the matrix resin (MR) and the reinforcing fibers (RF) are present in a weight ratio MR : RF, wherein MR : RF is in the range from 10 : 90 to 40 : 60, and wherein even more preferred MR : RF is in the range from 15 : 85 to 25 : 75.

In general the composite of the present invention can be used to manufacture articles for a lot of application fields.

The thermotropic copolyester of the present invention exhibits high values of strength at break, e.g. up to 42 MPa and elongation at break e.g. up to 8 % and said values are combined with a high modulus up to e.g. 1.9 GPa. So, a composite comprising the thermotropic copolyester according to the present invention and reinforcing fibers is well suited to be used in all kind of applications, where the composite has to withstand a high impact of kinetic energy as for example in ballistic applications.

Therefore, the use of the composite according to the present invention to manufacture articles for ballistic applications such as vests, helmets and armour panels is also a part of the present invention.

The onset of thermal degradation of the thermotropic copolyester of the present invention lies at high temperatures, which may be up to about 360 ⁰ C, whereas its melting range lies much lower, for example in the range of 120-150 ⁰ C. So, the thermotropic copolyester according to the present invention exhibits a very broad processing window. Furthermore, the viscosity of said copolyesters in said processing window is very low. Consequently, the thermotropic copolyester according to the present invention can be used advantageously as a processing aid to reduce the viscosity of known (high viscosity) thermoplastics.

Therefore, the use of the thermotropic copolyester according to the present invention as a viscosity reducing processing aid is part of the present invention as well.

Because of the thermoplastic nature of the copolyester according to the present invention said copolyester as such can be processed easily into a shaped article. Therefore, a shaped article essentially consisting of a thermotropic copolyester according to the present invention is also part of the present invention. Within the scope of the present invention the term "essentially consisting of means either, that the shaped article according to the present invention is present in pure form or may contain processing aids, e.g. in the case, wherein the shaped article is a film or a fiber, sizing agents, fillers, flame retardant materials, UV-inhibitors, antimicrobial additives or combinations of any two or more of said processing aids.

A preferred embodiment of the shaped article according to the present invention is a film, which can be manufactured by conventional film-forming techniques, e.g. by extruding a melt of the thermotropic copolyester according to the present invention through a slit-nozzle or by hot-press moulding said copolyester. The film displays excellent mechanical properties (storage modulus E' about 4 GPa) and high toughness (about 15 % elongation at break).

Another preferred embodiment of the shaped article according to the present invention is a fiber, which can be spun with conventional spinning equipment. Such a fiber according to the present invention may be present as a monofilament or as a multifilament or as a yarn manufactured from said monofilament or as a yarn manufactured from said multifilament.

Furthermore, a core/sheath-yarn is part of the present invention, which comprises i) a core yarn, which comprises reinforcing fibers having a tenacity at break of at least 80 cN/tex and ii) a sheath wrapped around the core yarn and comprising a fiber according to the present invention.

The reinforcing fibers comprised in the core of the core/sheath-yarn of the present invention may be any of the known reinforcing fibers, e.g. aramide fibers, polyben- zoxazole fibers, polybenzthiazole fibers, polybenzimidazole fibers of mixtures of said fibers, wherein said fibers and fiber-mixtures, respectively may be present as staple fibers, which form a staple fiber yarn or as filaments, which form a multifilament yarn.

The fiber according to the present invention is wrapped around the core yarn resulting in a wrapped sheath, which may cover the core of the invention's core/sheath-yarn partly or completely.

The core/sheath-yarn according to the present invention can be processed on a loom, e.g. in plain weave, to yield a woven fabric comprising a core/sheath-yarn according to the present invention, which is part of the present invention, too.

Furthermore, the woven fabric comprising a core/sheath-yarn according to the present invention can be moulded by applying a temperature above the melting point of the fiber wrapping the core of the core/sheath-yarn according to the present invention. If necessary, the application of pressure may accompany said temperature application. After cooling the moulded woven fabric below the melting point of the fiber wrapping the core of the core/sheath-yarn according to the present invention a moulded fabric obtained by moulding the woven fabric according to the present invention results. Such a moulded fabric is also part of the present invention.

So, the thermoplastic nature of the copolyester forming the wrapping fiber of the core/sheath-yarn of the woven fabric allows to manufacture a manifold of three- dimensional structured reinforcing fabrics simply by hot moulding, optionally under pressure.

The invention will be described in detail in the following.

Reagents and materials

4-hydroxybenzoic acid (4-HBA) and sebacic acid (SEA) are purchased from Al- drich. Hydroquinone (HQ), suberic acid (SUA) and acetic anhydride are obtained from Fluka. 6-hydroxy-2-naphthoic acid (HNA) is purchased from Ueno Fine Chemicals Industry, Ltd. All monomers are used as received with the exception of SUA, which is recrystallized prior to use from ethyl acetate and acetone respectively.

Measuring methods

The inherent viscosity η _ιn h of the copolyesters is measured at a concentration of 1.0 g dL ^"1 in a mixture of phenol:1 ,1 ,2,2-tetrachloroethane (weight ratio 60:40) at 30 ⁰ C using an Ubbelohde capillary viscosimeter (100/B 825).

The molecular weight of the copolyesters is determined by GPC using a 4 g/mL solution of the copolyester in (1 ,1 ,1 ,3,3,3-hexafluorene isopropanol/potassium trifluoroacetate) and a 2x PSS PFG linear XL 7μ, 300 x 8 mm separation column filled with modified silica and calibrated with polymethyl methacrylate standards of 50 000 Daltons. Absolute molecular weights are determined by light scattering, which is performed online in combination with the GPC using a Viscotek TDA 302 Tetra Detector Array.

The glass transition temperature T ₉ upon heating (10 ⁰ C min ^"1 ), the melting temperature T _m , the crystallization temperature T ₀ and the melting range of the copolyesters are measured by DSC (Differential Scanning Calorimetry) using a PerkinElmer Sapphire DSC.

The nematic range, i.e. the temperature range in which the copolyesters exist in a nematic liquid crystal phase, is observed by optical microscopy using a Nikon Eclipse E600 Pol polarizing microscope equipped with a Mettler-Toledo FP82HT hot stage. The powdered copolyester samples are sandwiched between two glass

sides and heated rapidly to 300 ⁰ C to form a thin uniform molten film. The samples are then cooled at a rate of 5 ⁰ C min ^"1 and then reheated to 400 ⁰ C at a heating rate of 5 ⁰ C min ^"1 .

The tensile properties strength at break, elongation at break and modulus of the copolyesters are measured on a Zwick 1445 tensile tester equipped with a 100 kN force cell at a test speed of 0.5 mm at room temperature using films of the copolyesters. The films are prepared from the copolyesters by hot-press moulding said copolyesters at a pressure of 0.7 MPa at a temperature of 160 ⁰ C for 2 minutes.

The ballistic protection of the composites is determined as V ₅₀ - value using 9 mm x 19 VRM/-DM 41 ammunition according to DIN 52290.

Example 1 : Synthesis of a thermotropic copolyester according to the invention with η _in h = 0.79 dL/g corresponding to a molecular weight of approximately 22 000

A 1 liter three-neck round-bottom flask equipped with a glass paddle stirrer, a Lie- big condenser and a nitrogen inlet, is charged with 120.75 g (0.875 mol) 4- hydroxybenzoic acid (4-HBA), 164.5 g (0.875 mol) 6-hydroxy-2-naphthoic acid (HNA), 75.75 g (0.375 mol) sebacic acid (SEA), 62,25 g (0.375 mol) suberic acid (SUA), and 82.5 g (0.75 mol) hydroquinone (HQ) under nitrogen flow. So, the feed composition given in mol-% is 26.92 mol % 4-HBA, 26.92 mol-% HNA, 11.54 mol- % SEA, 11.54 mol-% SUA, and 23.08 mol.-% HQ.

A catalytic amount of potassium acetate (20 mg) is added to the mixture followed by 365 g (3.58 mol) acetic anhydride (10 mol-% excess). After adding of the acetic anhydride the mixture is heated to 140 ⁰ C and held at this temperature for 1 hour during which the acetylation takes place.

Next, the mixture is heated gradually for 3 hours to 270 ⁰ C, during which the byproduct acetic acid is distilled off. At the final state of the copolymerization the nitrogen flow was closed and a vacuum (about 10 mbar) is applied for about 0.5 hours in order to remove last traces of acetic acid and to ensure the formation of a high molecular weight copolyester.

A viscous yellow-coloured copolyester melt is obtained, which is poured out of the flask under nitrogen and left to solidify. The collected copolyester A is processed into a powder and is used for further processing and analysis.

Example 2: Synthesis of a thermotropic copolyester according to the invention with η _in h = 0.45 dL/g corresponding to a molecular weight of approximately 13 000

A copolyester is synthesized in the same manner as in example 1 but with the difference that at the final state of the copolymerization the vacuum is 30 mbar resulting in copolyester B with a lower molecular weight than that of copolyester A.

Comparative example 1 : Synthesis of a comparative copolyester with η _in h = 0.46 dL/g corresponding to a molecular weight of approximately 13 000

A comparative copolyester is synthesized in the same manner as in example 2 but with the difference, that no suberic acid (SUA) is used. With a feed composition of 26.92 mol % 4-HBA, 26.92 mol-% HNA, 23.08 mol-% SEA, 0.00 mol-% SUA, and 23.08 mol.-% HQ a comparative copolyester C results.

The thermal properties of the copolyesters A-C are summarized in table 1 and their mechanical properties in table 2.

Table 1 : Thermal properties

Table 2: Mechanical properties

As can be seen from table 1 the thermotropic copolyester B according to the present invention and the comparative copolyester C exhibit at practically the same inherent viscosity, i.e. at practically the same molecular weight no significant differences regarding their thermal properties.

However, as can be seen from table 2 the thermotropic copolyester B according to the present invention exhibits a 25 % increase in strength at break and a 38 % increase in elongation at break, if compared with the comparative copolyester C having practically the same inherent viscosity and molecular weight, respectively. So, surprisingly the mere introduction of a unit derived from suberic acid into a random thermotropic copolymer consisting of a unit derived from hydroxybenzoic acid, a unit derived from 6-hydroxy-2-naphthoic acid, a unit derived from sebacic acid and a unit derived from hydroquinone significantly increases the values of strength at break and elongation at break of the thermotropic copolyester resulting by said introduction.

As can be seen in table 2 by comparing the copolyesters B and C said introduction surprisingly results in a slightly increased modulus. Consequently, the area under the strength/elongation-curve of the thermotropic copolyester according to the invention is higher than the said area of the comparative copolyester without a unit derived from suberic acid. This means, that the surprising effect of an increase of strength at break and elongation at break generated by the inventive insertion of a unit of suberic acid into the prior art copolyester C is additionally accompanied by a second surprising effect given by the slightly increased modulus. So, the thermotropic copolyester according to the invention exhibits an higher energy uptake on impact than the comparative copolyester.

The comparison of the inventive thermotropic copolyesters A and B in table 2 shows, that increasing the inherent viscosity and correspondingly the molecular weight results in the same slightly increased modulus and in a further increase of strength at break and elongation at break, i.e in a further increase of energy uptake on impact.

Comparative example 2: Manufacture of a comparative composite CC

A composite consisting of

- 10 layers of 40 cm x 40 cm basket 2x2 woven fabric of type CT 736 SC consisting of poly-p-phenylene terephthalamide yarn from Teijin Aramid (yarn type Twaron ^® 2000, linear density 1680 dtex, 1000 filaments, tenacity at break 2350 mN/tex) as the reinforcing fibers and

- 9 layers of prepreg film (Durapreg type 4228 manufactured by Roll Deutschland GmbH) each film consisting of 50 wt.-% crosslinked phenol/formaldehyde and 50 wt.-% polyvinylbutyral as the matrix resin is manufactured as described in the following:

9 of said prepreg films are cut to the shape of said fabrics. Then a package is formed by stacking 1 fabric layer and 1 prepreg film layer in an alternating sequence and beginning said stacking with the fabric layer resulting in a package, which consists of 9 prepreg film layers and 10 fabric layers, wherein fabric layers form the top and the bottom of the package. Then said package is placed in a hydraulic press, wherein a pressure of 10 bar and a temperature of up to 150 ⁰ C is applied for 10 minutes. That means, a temperature program is run from room temperature to 150 ⁰ C and back to room temperature. The heating and cooling rate is 10 °C min ^"1 .

The resulting comparative composite CC consists of 12 wt.% matrix resin and 88 wt.-% woven fabric.

Example 3: Manufacture of an inventive composite IC-1

An inventive composite consisting of 10 layers of the same woven fabric as in comparative example 2 and of a matrix resin consisting of 100 wt.-% of the ther- motropic copolyester A according to the present invention is manufactured as described in the following: The matrix resin is added as a powder, which powder is homogenously distributed between the layers of the fabric. For this purpose a first fabric layer is provided and strewn with a first powder layer. Onto said first powder layer a second fabric layer is laid and strewn with a second powder layer et cetera until on the ninth fabric layer a ninth powder layer is strewn. Finally a tenth fabric layer is laid onto the ninth powder layer. This results in a package consisting of ten fabric layers and 9 powder layers, wherein fabric layers form the top and the bottom of the package. Then said package is placed in a hydraulic press, wherein a pressure of 10 bar and a temperature of 160 ⁰ C is applied for 10 minutes. That means, a temperature program is run from room temperature to 160 ⁰ C and back to room temperature. The heating and cooling rate is 10 ⁰ C min ^"1 .

The resulting inventive composite IC-1 consists of 20 wt.% matrix resin and 80 wt. % woven fabric.

Example 4: Manufacture of an inventive composite IC-2

An inventive composite is manufactured as in example 3 but with the difference, that the matrix resin consists of a homogenous mixture of 50 wt.-% of the thermo- tropic copolyester A according to the present invention, 37.5 wt.-% polyvinylbutyral and 12.5 wt.-% of the plastisizer dioctyl phthalate obtained from Acros. The mixing procedure of the said components of the matrix resin is described in the following: First, plastisized polyvinylbutyral is prepared by mixing the polyvinylbutyral with the dioctyl phthalate in a brabender type batch mixer for 10 minutes at 170 ⁰ C and 120 rpm. Next, the copolyester A is mixed with the plastisized polyvinylbutyral in a batch mixer for 10 minutes at 170 ⁰ C and 120 rpm resulting in the mixture described above. Said mixture is pulverized and then a composite is manufactured as in example 3.

The resulting inventive composite IC-2 consists of 20 wt.% matrix resin and 80 wt.-% woven fabric.

Example 5: Manufacture of an inventive composite IC-3

50 wt.-% copolyester A is mixed with 50 wt.-% Kraton GX 1675 (manufactured by Shell) in a batch mixer for 10 minutes at 170 ⁰ C and 120 rpm. The resulting mixture is pulverized. Then with said pulverized mixture an inventive composite IC-3 is manufactured as in example 3, except, that the maximum temperature of the temperature program is 195 ⁰ C.

The resulting inventive composite IC-3 consists of 20 wt.% matrix resin and 80 wt.-% woven fabric.

Table 3 summarizes the ballistic protection given as V ₅₀ - values of the comparative composite CC and of the composites IC-1 , IC-2 and IC-3 according to the present invention.

Table 3: V ₅₀ - values

As can be seen in table 3 by comparing the prior art composite CC with the inventive composites IC-2 and IC-3 the substitution of the crosslinked phenol / formaldehyde-resin by the inventive copolyester A results in composites with the same or even with a slightly higher V ₅₀ - value.

The comparison of the prior art composite CC with the inventive composite IC-1 shows, that the latter exhibits a lower V ₅₀ - value. However, it can be expected, that increasing the molecular weight of the inventive copolyester above the molecular weight of the inventive copolyester A, i.e. above 22 000, results in a higher V ₅₀ - value in an inventive composite, the matrix resin of which consists completely of said inventive copolyester with correspondingly higher molecular weight.