(19)
(11)EP 2 812 364 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
25.03.2020 Bulletin 2020/13

(21)Application number: 13705343.5

(22)Date of filing:  07.02.2013
(51)International Patent Classification (IPC): 
C08F 8/34(2006.01)
C08L 31/04(2006.01)
C08K 3/06(2006.01)
C08F 18/08(2006.01)
(86)International application number:
PCT/US2013/025086
(87)International publication number:
WO 2013/119769 (15.08.2013 Gazette  2013/33)

(54)

SULFUR MODIFIED POLYVINYL ACETATE (PVAc)

SCHWEFELMODIFZIERTES POLYVINYLACETAT (PVAC)

POLY(ACÉTATE DE VINYLE) (PVAC) MODIFIÉ PAR DU SOUFRE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 07.02.2012 US 201261596050 P

(43)Date of publication of application:
17.12.2014 Bulletin 2014/51

(73)Proprietors:
  • Saudi Arabian Oil Company
    Dhahran 31311 (SA)
  • King Fahd University of Petroleum and Minerals (KFUPM)
    Dhahran 31261 (SA)

(72)Inventors:
  • AL-MEHTHEL, Mohammed
    Dhahran 31311 (SA)
  • AL-IDI, Saleh, H.
    Dhahran 31311 (SA)
  • HUSSEIN, Ibnelwaleed, A.
    Dhahran 31261 (SA)
  • WAHHAB, Hamad, I. Al-Abdul
    Dhahran 31261 (SA)
  • SULEIMAN, Mohammed, A.
    Dhahran 31261 (SA)

(74)Representative: Stafford, Jonathan Alan Lewis et al
Marks & Clerk LLP 1 New York Street
Manchester M1 4HD
Manchester M1 4HD (GB)


(56)References cited: : 
WO-A1-2004/076554
US-A- 2 075 045
WO-A1-2010/120482
  
  • Scientific Polymer: "SCIENTIFIC POLYMER PRODUCTS. INC. Material Safety Data Sheet", , 1 June 1996 (1996-06-01), XP055343089, Retrieved from the Internet: URL:http://scientificpolymer.com/wp-conten t/uploads/2013/12/347.pdf [retrieved on 2017-02-07]
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

Field of the Invention



[0001] This invention relates to modified polyvinyl acetate polymer. More particularly, this invention relates to sulfur modified polyvinyl acetate polymers, free from asphalt, bitumen or like compounds, having improved properties relative to unmodified polyvinyl acetate polymers.

Background of the Invention



[0002] Sulfur is a co-product of oil and gas production that is produced in ever increasing quantities. For example, sulfur is currently produced at a rate of approximately 10,000 tons/day in Saudi Arabia. The rate of production is expected to increase to 12,000 tons/day in a few years. Although sulfur is a vital resource that is useful for the manufacture a myriad of products, the abundance of sulfur has resulted in worldwide reduction of its price. As worldwide sulfur supplies increase, the storage of the sulfur will present an environmental hazard. New uses of sulfur present one solution to the problem of storing the vast quantities of sulfur.

[0003] Previous studies relating to the degradation of PVAc in vacuum using TGA revealed a two stage decomposition. The first mass loss commenced at about 250°C and continued to about 375°C, after which an inflexion preceded the second and final mass loss that ultimately led to complete decomposition of the polymer. The first mass loss stage was assigned mainly to the release of acetic acid and simultaneous formation of double bonds in the polymer backbone. The formation of both acetic acid and trans-vinylene species have been explained by comparison with pyrolytic cis or syn elimination of low molar mass ester model compounds. It was found that the addition of free radical inhibitors did not prevent elimination of acetic acid. However, previously studies also showed the formation of several volatile products using free radical mechanisms. It has also found that the acetic acid generated has a catalytic effect on degradation. This behavior has been compared to the catalytic effect of HC1 on PVC.

[0004] Prior investigations have been conducted into inert and oxidative thermal degradation mechanism of PVAc and EVA copolymers using semi-crystalline and amorphous EVA having a VA content in the polymer backbone ranging from about 9 to 73% by weight. More specifically, EVA emulsions of Airflex EN 1035 and Airflex EAF 60 (55 and 60% solids in water, respectively) from Air Products containing 73 and 60% by weight vinyl acetate were utilized. The thermal study was performed over a temperature range of about 200°C (to remove water and monomers) to about 600°C and 650°C for inert and oxidative conditions respectively. The inert degradation of PVAc as measured using a TGA coupled with mass spectrometry (TGA-MS) showed two degradation steps: the first and most intense step is deacytelation, which occurs between about 300 and 400°C. The end of the first thermal degradation step of PVAc in air has been reported to be around 310°C, corresponding to a loss of 95% of the acetic acid formed in the degradation process. Studies have shown that the major volatile degradation product is acetic acid, with smaller amounts of ketene, water, methane, carbon dioxide and carbon monoxide also being formed. Analysis of the degraded sample at 400°C shows a highly regular unsaturated material. The second step of degradation involves a dehydrogenation reaction.

[0005] Thus, there exists a need to provide a modified polymer having improved properties, such as increased melting point, while at the same time providing a use for excess sulfur.

[0006] US2075045A describes a thermoplastic made by combining polymerized vinyl acetate and sulfur and uses of this combination.

[0007] WO 2010/120482A1 describes sulfur-extended polymers for use in asphalt binders and road maintenance.

Summary



[0008] Generally, sulfur modified polymer compositions, free from asphalt, bitumen or like compounds, and methods of making same are provided. Specifically, a method for preparing sulfur modified polyvinyl acetate polymers having increased melting points relative to the unmodified polymer is provided. Also provided is a sulfur modified polyvinyl acetate polymer composition prepared according to the method of Claim 1 of the appended claims.

[0009] In one aspect of the present invention there is provided a sulfur modified polyvinyl acetate polymer composition prepared according to the method of appended Claim 1, wherein the polymer composition includes a polyvinyl acetate polymer; sulfur, wherein the sulfur is present in an amount between 50% and 70% by weight. In some embodiments the composition is free from asphalt, bitumen or like compounds.

[0010] The sulfur is effective to modify the melting point of the polyvinyl acetate polymer. In certain embodiments, at least a portion of the sulfur is present in elemental form. The sulfur modified polyvinyl acetate polymer composition has a melting point that is between 10°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer. In certain embodiments, the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 10°C and 30°C greater than the melting point of the unmodified polyvinyl acetate polymer. In certain embodiments, the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 20°C and 40°C greater than the melting point of the unmodified polyvinyl acetate polymer. In certain embodiments, the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 30°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer.

[0011] In certain embodiments, the polyvinyl acetate polymer has a molecular weight of between about 10,000 and 125,000.

[0012] In another aspect, a method for preparing a sulfur modified polyvinyl acetate composition is provided according to Claim 1 of the appended claims. Optionally the composition is free from asphalt, bitumen or like compounds. The method includes the steps of providing a polyvinyl acetate polymer, wherein the polyvinyl acetate polymer has a melting temperature of less than about 140°C; and heating the polyvinyl acetate polymer in the presence of elemental sulfur to a temperature of between about 150°C and 200°C and mixing the polyvinyl acetate polymer and sulfur such that elemental sulfur is incorporated into the polyvinyl acetate polymer to produce a sulfur modified polyvinyl acetate polymer where between 50 and 70% by weight sulfur based on the weight of the sulfur modified polymer is incorporated into the polyvinyl acetate polymer; and the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 10°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer.

[0013] Between about 50 and 70% by weight sulfur is incorporated into the polyvinyl acetate polymer. In certain embodiments, the polyvinyl acetate polymer and sulfur are mixed for at least about 15 minutes.

Brief Description of the Drawings



[0014] 

Figure 1 is a stress-strain curve comparing pure polyvinyl acetate and sulfur modified polyvinyl acetate.

Figure 2 is a thermal analysis curve of sulfur.

Figure 3 is a thermal analysis curve of a polyvinyl acetate sample.

Figure 4 is a thermal analysis curve of a second polyvinyl acetate sample.

Figure 5 is a thermal analysis curve of a sulfur modified polyvinyl acetate sample.

Figure 6 is a thermal analysis curve of another sulfur modified polyvinyl acetate sample.

Figure 7 is a thermal analysis curve of another sulfur modified polyvinyl acetate sample.

Figure 8 is a thermal analysis curve of another sulfur modified polyvinyl acetate sample.


Detailed Description of the Invention



[0015] Polyvinyl Acetate (PVAc) samples, free from asphalt, bitumen or like compounds, of different molecular weights were modified using elemental sulfur. The sulfur modified polyvinyl acetate polymers showed increased resistance to melting (i.e., increased melting point for the modified polymer) and produced a softer polymer than the original, unmodified polyvinyl acetate polymer. Polyvinyl acetate polymers were selected that had a melting temperatures of less than about 140°C. The addition and mixing of sulfur was performed at a temperature greater than the melting point of the polyvinyl acetate polymer, in the range 150° - 200°C. Alternatively, the addition and mixing of sulfur can be performed in the range of about 150 - 160°C, alternatively between about 160 and 170°C, alternatively between about 170 and 180°C, alternatively between about 180 and 190°C, alternatively between about 190 and 200°C. In general, the temperature at which the sulfur addition and mixing take place is maintained at a temperature that is below the decomposition temperature of the polymer. Sulfur was added to the polyvinyl acetate polymer in amounts up to about 50% by weight of the polymer to produce modified polymers having significantly different and unexpected mechanical properties, as compared with the pure polymers. In addition to the increase in melting point of the modified polymer, the addition of sulfur to the polyvinyl acetate polymers also produced a polymer material that was softer and more ductile in comparison with pure polyvinyl acetate polymers and showed no strain hardening like the homopolymer. In certain embodiments, the addition and mixing of sulfur described herein can be used for other polymers having similar melting point ranges.

[0016] One advantage of the sulfur modified polymers is that the polymer can then be produced at a highly competitive cost because sulfur is very abundant and much cheaper than the polymer. This allows for the vast quantities of sulfur that are produced as a byproduct of oil and gas production to be utilized, thereby eliminating environmental concerns associated with the storage thereof.

[0017] The sulfur modification of the polyvinyl acetate polymer can result in an increase in the melting points of the polymers by between about 10°C and about 50°C.

[0018] Further, the sulfur modified polyvinyl acetate polymer differs from that of the unmodified polyvinyl acetate polymer because the sulfur composition becomes part of the polymer structure and at high content. The sulfur modified polymers can be used in adhesives and as an oil resistant polymer. In alternate embodiments, the sulfur modified polymer finds use for use in crack repair of concrete structures.

Examples



[0019] Polyvinyl acetate polymers obtained from Scientific Polymer Products, Ontario, NY, USA were used as received. The technical specifications of the polymers are provided in Table 1. Elemental sulfur (99.9% purity) from Saudi Aramco was used.
Table 1. Characterization of Polymers.
ResinProduct #Class of PolymerManufacturerTm, °CVA, %MwDensity g/cm3
PVAc1 1019 Polyvinyl acetate Scientific Polymer 70* 100 15000 1.1700
PVAc2 347 Polyvinyl acetate Scientific Polymer 105* 100 100000 1.1700
*softening temperature as reported by the product data sheet


[0020] The sulfur modified polymers (SMP) were prepared in a Haake PolyDrive melt blender. In an effort to include as much sulfur as possible into the polymer blend, the composition of sulfur used was 50% and 70% by weight were employed. The Haake PolyDrive melt blender is designed for use as a computer-controlled torque rheometer. The pure polymer and sulfur-polymer blends were mixed in the melt blender at 100 rpm for various different blend times. The blender thus acts as a batch stirred reactor with a constant volume. Samples were collected following the mixing process and analyzed by different techniques. Blends of PVAcl/sulfur, containing 50% by weight sulfur were prepared in the melt blender. The blending time, Tm, was 10 minutes and reaction temperature was 200°C. This sample preparation procedure was repeated for blend times, Tm =15 min and 20 min. The above procedure was also repeated using PVAc2 and PVAcl. The samples were prepared at different processing times to investigate the effect of processing time on total sulfur content and the amount of bonded sulfur in the SMP. Estimating the amount of total sulfur in the SMP was possible, however estimating the amount of bonded sulfur in the SMP was unsuccessful. Three blend samples (PVAcl/S (50:50); PVAcl/S (30:70) and PVAc2/S (50:50)) were prepared at processing time of 15 min.

[0021] A Vario EL elemental analyzer was used to determine the amount of free sulfur present in SMP. The thermal behavior of the pure resins and blends was determined by means of a TA Q1000 DSC. Samples of 7-10 mg were weighed and sealed in aluminum hermetic pans. Melting temperature measurements were performed by heating samples from room temperature to 250°C at a heating rate of 10°C/min, with a nitrogen purge gas at a flow rate of about 50 mL/min.
Table 2: Mechanical Properties of pure and sulfur modified PVAc
PropertyPure PVAcPVAc + 50% Sulfur
Young's Modulus (MPa) 4.31 1.93
Yield Strength (MPa) 21.51 9.05
% Elongation 68.32 30.84


[0022] As shown in Table 2, the addition of sulfur to the polyvinyl acetate resulted in a softer material which demonstated a drop in mechanical properties as the material started to elongate freely after the yield point (no strain hardening behavior). Table 3 provides the results of analysis technique used to estimate total sulfur present in the SMP. The results closely match the actual amount of sulfur used in the blending process. The SMP is not soluble in hot alcohol or hot acetone.
Table 3. % of Sulfur (S) in SMP.
No.Sample IDMwS, wt. %Time (min)Temp (°C)Total Measured Sulfur (wt. %)
1 PVAc1 15000 50 10 200 55.9
2 PVAc1 15000 50 15 200 53.4
3 PVAc1 15000 50 20 200 51.1
4 PVAc2 100000 50 10 200 47.3
5 PVAc2 100000 50 15 200 49.8
6 PVAc2 100000 50 20 200 50.4
7 PVAc1 15000 70 10 200 71.0
8 PVAc1 15000 70 15 200 69.5
9 PVAc1 15000 70 20 200 71.6
10 PVAc2 100000 70 10 200 73.0
11 PVAc2 100000 70 15 200 70.9
12 PVAc2 100000 70 20 200 65.8


[0023] Figures 2 - 8 show the DSC melting thermograms of the pure sulfur, PVAc and several of the sulfur modified polyvinyl acetate blends. Pure sulfur exhibited two distinct peaks at approximately 106°C and 122°C, as shown in Figure 2, indicating the melting transition of two crystal constituents. Pure PVAcl (Mw = 15000) shown in Figure 3 shows a gradual softening transition as the temperature increases up to 150°C. Pure PVAc2 (Mw = 100000) shown in Figure 4 display a strong peak at around 40°C and a weak peak around 160°C. It is not believed that the weak peak corresponds to the thermal degradation of PVAc, which is believed to occur at above 227°C. Figure 5 shows the DSC thermograms of several different blends of PVAcl/sulfur (having 50:50 compositions) prepared at different blending times. A single melting peak around 120°C for each of the blends corresponds to the thermogram observed in the pure sulfur indicating the presence of sulfur in each of the blends. As shown in Figure 6, increasing the sulfur content in the blend results in a similar trend wherein the thermograms of the various polymer blends show similar melting peaks associated with the presence of free sulfur. As shown in Figures 7 and 8, the observed peaks correspond to those of sulfur and the pure polyvinyl acetate polymer sample, which may correspond to a new material resulting from the reaction of sulfur and the polymer.

[0024] Although the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations can be made. The scope of the present invention is determined by the following claims.


Claims

1. A method for preparing a sulfur modified polyvinyl acetate composition, the method comprising the steps of:

providing a polyvinyl acetate polymer, wherein the polyvinyl acetate polymer has a melting temperature of less than 140°C; and

heating the polyvinyl acetate polymer in the presence of elemental sulfur to a temperature of between 150°C and 200°C and mixing the polyvinyl acetate polymer and sulfur such that elemental sulfur is incorporated into the polyvinyl acetate polymer to produce a sulfur modified polyvinyl acetate polymer, where between 50 and 70% by weight sulfur based on the weight of the sulfur modified polymer is incorporated into the polyvinyl acetate polymer; and the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 10°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer.


 
2. A sulfur modified polyvinyl acetate polymer composition prepared from a polyvinyl acetate polymer having a melting point of less than 140°C according to the method of Claim 1, the polymer composition comprising sulfur, wherein the sulfur is present in an amount between 50% and 70% by weight based on the weight of the sulfur modified polymer, such that the sulfur modified polymer has an increased melting point as compared to the melting point of the polyvinyl acetate polymer, where the sulfur modified polyvinyl acetate polymer composition has a melting point between 10°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer.
 
3. The polymer composition of claim 2, wherein the composition does not contain asphalt, bitumen, and combinations thereof.
 
4. The polymer composition of any of the preceding claims, wherein at least a portion of the sulfur is present in elemental form.
 
5. The polymer composition of any of claims 2 to 4, wherein the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 20°C and 40°C greater than the melting point of the unmodified polyvinyl acetate polymer.
 
6. The polymer composition of any of claims 2 to 4 wherein the sulfur modified polyvinyl acetate polymer composition has a melting point that is between 30°C and 50°C greater than the melting point of the unmodified polyvinyl acetate polymer.
 
7. The polymer composition of any preceding claim, wherein polyvinyl acetate polymer has a molecular weight of between 10,000 and 125,000.
 


Ansprüche

1. Verfahren zum Herstellen einer schwefelmodifizierten Polyvinylacetatzusammensetzung, wobei das Verfahren die Schritte umfasst des:

Bereitstellens eines Polyvinylacetatpolymers, wobei das Polyvinylacetatpolymer eine Schmelztemperatur von weniger als 140 °C aufweist; und

Erhitzens des Polyvinylacetatpolymers in Gegenwart von elementarem Schwefel auf eine Temperatur zwischen 150 °C und 200 °C und Mischens des Polyvinylacetatpolymers und Schwefels derart, dass der elementare Schwefel in das Polyvinylacetatpolymer integriert wird, um ein schwefelmodifiziertes Polyvinylacetatpolymer herzustellen, wobei zwischen 50 und 70 Gew.-% Schwefel, auf das Gewicht des schwefelmodifizierten Polymers bezogen, in das Polyvinylacetatpolymer integriert werden; und die schwefelmodifizierte Polyvinylacetatpolymerzusammensetzung einen Schmelzpunkt aufweist, der zwischen 10 °C und 50 °C höher als der Schmelzpunkt des unmodifizierten Polyvinylacetatpolymers ist.


 
2. Schwefelmodifizierte Polyvinylacetatpolymerzusammensetzung, die aus einem Polyvinylacetatpolymer, das einen Schmelzpunkt von weniger als 140 °C aufweist, dem Verfahren nach Anspruch 1 entsprechend hergestellt wird, wobei die Polymerzusammensetzung Schwefel umfasst, wobei der Schwefel in einer Menge zwischen 50 und 70 Gew.-%, auf das Gewicht des schwefelmodifizierten Polymers bezogen, vorliegt, derart, dass das schwefelmodifizierte Polymer einen erhöhten Schmelzpunkt im Vergleich mit dem Schmelzpunkt des Polyvinylacetatpolymers aufweist, wobei die schwefelmodifizierte Polyvinylacetatpolymerzusammensetzung einen Schmelzpunkt zwischen 10 °C und 50 °C höher als der Schmelzpunkt des unmodifizierten Polyvinylacetatpolymers aufweist.
 
3. Polymerzusammensetzung nach Anspruch 2, wobei die Zusammensetzung keinen Asphalt, Teer und Kombinationen davon enthält.
 
4. Polymerzusammensetzung nach einem der vorhergehenden Ansprüche, wobei mindestens ein Teil des Schwefels in elementarer Form vorliegt.
 
5. Polymerzusammensetzung nach einem der Ansprüche 2 bis 4, wobei die schwefelmodifizierte Polyvinylacetatpolymerzusammensetzung einen Schmelzpunkt aufweist, der zwischen 20 °C und 40 °C höher als der Schmelzpunkt des unmodifizierten Polyvinylacetatpolymers ist.
 
6. Polymerzusammensetzung nach einem der Ansprüche 2 bis 4, wobei die schwefelmodifizierte Polyvinylacetatpolymerzusammensetzung einen Schmelzpunkt aufweist, der zwischen 30 °C und 50 °C höher als der Schmelzpunkt des unmodifizierten Polyvinylacetatpolymers ist.
 
7. Polymerzusammensetzung nach einem vorhergehenden Anspruch, wobei das Polyvinylacetatpolymer ein Molekulargewicht zwischen 10 000 und 125 000 aufweist.
 


Revendications

1. Procédé de préparation d'une composition de poly(acétate de vinyle) modifié avec du soufre, le procédé comprenant les étapes de:

fourniture d'un polymère de poly(acétate de vinyle), le polymère de poly(acétate de vinyle) présentant une température de fusion inférieure à 140°C; et

chauffage du polymère de poly(acétate de vinyle) en présence de soufre élémentaire à une température comprise entre 150°C et 200°C et mélange du polymère de poly(acétate de vinyle) et du soufre de sorte que le soufre élémentaire est incorporé dans le polymère de poly(acétate de vinyle) pour produire un polymère de poly(acétate de vinyle) modifié avec du soufre, où entre 50 et 70 % en poids du soufre sur la base du poids du polymère modifié avec du soufre est incorporé dans le polymère de poly(acétate de vinyle); et la composition polymère de poly(acétate de vinyle) modifié avec du soufre présente un point de fusion qui est entre 10°C et 50°C supérieur au point de fusion du polymère de poly(acétate de vinyle) non modifié.


 
2. Composition polymère de poly(acétate de vinyle) modifié avec du soufre préparée à partir d'un polymère de poly(acétate de vinyle) présentant un point de fusion inférieur à 140°C selon le procédé selon la revendication 1, la composition polymère comprenant du soufre, le soufre étant présent en une quantité comprise entre 50 % et 70 % en poids sur la base du poids du polymère modifié avec du soufre, de sorte que le polymère modifié avec du soufre présente un point de fusion accru en comparaison avec le point de fusion du polymère de poly(acétate de vinyle), où la composition polymère de poly(acétate de vinyle) modifié avec du soufre présente un point de fusion entre 10°C et 50°C supérieur au point de fusion du polymère de poly(acétate de vinyle) non modifié.
 
3. Composition polymère selon la revendication 2, dans laquelle la composition ne contient pas d'asphalte, de bitume, et de combinaisons de ceux-ci.
 
4. Composition polymère selon l'une quelconque des revendications précédentes, dans laquelle au moins une partie du soufre est présente sous forme élémentaire.
 
5. Composition polymère selon l'une quelconque des revendications 2 à 4, dans laquelle la composition polymère de poly(acétate de vinyle) modifié avec du soufre présente un point de fusion qui est entre 20°C et 40°C supérieur au point de fusion du polymère de poly(acétate de vinyle) non modifié.
 
6. Composition polymère selon l'une quelconque des revendications 2 à 4 dans laquelle la composition polymère de poly(acétate de vinyle) modifié avec du soufre présente un point de fusion qui est entre 30°C et 50°C supérieur au point de fusion du polymère de poly(acétate de vinyle) non modifié.
 
7. Composition polymère selon l'une quelconque des revendications précédentes, dans laquelle le polymère de poly(acétate de vinyle) présente un poids moléculaire compris entre 10 000 et 125 000.
 




Drawing

















Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description