RUBBER COMPOUNDS FOR USE IN PRODUCING VEHICLE TIRES

Abstract

The invention provides diene rubber-silica compounds comprising a diene rubber matrix having dispersed therein a silica filler, wherein said silica filler is reversibly coupled to the diene rubber matrix via a dynamic imine bond. In particular, it provides such compounds in which the diene rubber is styrene-butadiene rubber. Such compounds can be vulcanized and are suitable for producing vehicle tire components, such as tire treads.

Claims

1-21. (canceled)

22. A diene rubber-silica compound, comprising: a diene rubber matrix having dispersed therein a silica filler; wherein the silica filler is reversibly coupled to the diene rubber matrix via a dynamic imine bond.

23. The diene rubber-silica compound of claim 22, wherein the diene rubber matrix comprises a blend of styrene butadiene rubber and at least one other diene rubber such as butadiene rubber.

24. The diene rubber-silica compound of claim 22, wherein the silica filler is surface-modified by a coupling agent incorporating the dynamic imine bond and which is bound to the diene rubber matrix, the coupling agent having a structure of formula (I): ##STR00014## wherein: * denotes a point of attachment of the coupling agent to the silica surface; ring B is an aromatic or heteroaromatic group; L.sub.1 is an organic linking group; L.sub.2 is either a direct bond or an organic linking group; R.sup.1 is a functional moiety effective to form a bond with the diene rubber matrix; each R.sub.2 is independently selected from: C.sub.1-6 alkyl; C.sub.1-6 alkoxy; halogen; and a group of formula -L.sub.2-R.sup.1; and n is an integer from 0 to 4.

25. The diene rubber-silica compound of claim 24, wherein: each R.sub.2 is independently selected from: C.sub.1-3 alkyl; C.sub.1-3 alkoxy; halogen; and a group of formula -L.sub.2-R.sup.1; and n is an integer from 0 to 2.

26. The diene rubber-silica compound of claim 24, wherein the coupling agent has a structure of formula (II): ##STR00015## wherein *, L.sub.1, L.sub.2, R.sup.1, R.sup.2 and n are as defined in claim 24.

27. The diene rubber-silica compound of claim 24, wherein the coupling agent has a structure of formula (IV): ##STR00016## wherein *, L.sub.1, L.sub.2, R.sup.1, R.sup.2 and n are as defined in claim 24.

28. The diene rubber-silica compound of claim 24, wherein L.sub.1 is a group of formula (III): ##STR00017## in which: each R is independently selected from OH, C.sub.1-6 alkoxy, and C.sub.1-6 alkyl; and Z is a substituted C.sub.1-12 alkylene group interrupted by one or more groups selected from O, SiR.sub.2 (in which each R is independently OH, C.sub.1-6 alkoxy or C.sub.1-6 alkyl), PR, NR and OP(O)(OR)O (in which R is H or C.sub.1-6 alkyl).

29. The diene rubber-silica compound of claim 28, wherein: each R is independently selected from OH, C.sub.1-3 alkoxy, and C.sub.1-3 alkyl; and Z is a substituted C.sub.1-12 alkylene group interrupted by one or more groups selected from O, SiR.sub.2 (in which each R is independently OH, C.sub.1-6 alkoxy or C.sub.1-6 alkyl), PR, NR and OP(O)(OR)O (in which R is H or C.sub.1-3 alkyl).

30. The diene rubber-silica compound of claim 28, wherein the coupling agent has a structure of formula (V): ##STR00018## wherein: *, L.sub.2 and R.sup.1 are as defined in claim 24; and each R is as defined in claim 28.

31. The diene rubber-silica compound of claim 24, wherein L.sub.2 is a direct bond.

32. The diene rubber-silica compound of claim 24, wherein R.sup.1 is selected from the group consisting of: a mercapto group, a protected mercapto group, a blocked mercapto group, a mono-, di- or poly-sulfidic group, and a group containing a carbon-carbon double bond.

33. The diene rubber-silica compound of claim 24, wherein the group -L.sub.2-R.sup.1 is represented by one of the following structures: ##STR00019## wherein: p is an integer from 1 to 6; and m is an integer from 1 to 6.

34. The diene rubber-silica compound of claim 24, wherein the group -L.sub.2-R.sup.1 is represented by one of the following structures: ##STR00020## wherein: x is an integer from 1 to 6; p is an integer from 1 to 6; and m is an integer from 1 to 6.

35. The diene rubber-silica compound of claim 24, wherein the group -L.sub.2-R.sup.1 is represented by one of the following structures: ##STR00021## wherein: p is an integer from 1 to 6; and m is an integer from 1 to 8.

36. The diene rubber-silica compound of claim 24, wherein -L.sub.2-R.sup.1 is selected from vinyl (CHCH.sub.2), allyloxy (OCH.sub.2CHCH.sub.2), thiol (SH) and methylthiol (SCH.sub.3).

37. A method for producing a diene rubber-silica compound comprising a diene rubber matrix having dispersed therein a silica filler, wherein the method comprises: surface-modifying a silica filler by attachment of a coupling agent which incorporates a dynamic imine bond and which is effective to form a linkage to a diene rubber matrix during compounding and/or vulcanization; compounding the resulting surface-modified silica filler with a diene rubber matrix to produce a vulcanizable rubber composition; and subjecting the vulcanizable rubber composition to vulcanization.

38. The method of claim 37, wherein the silica filler is surface-modified by a coupling agent incorporating the dynamic imine bond and which is bound to the diene rubber matrix, the coupling agent having a structure of formula (I): ##STR00022## wherein: * denotes a point of attachment of the coupling agent to the silica surface; ring B is an aromatic or heteroaromatic group; L.sub.1 is an organic linking group; L.sub.2 is either a direct bond or an organic linking group; R.sup.1 is a functional moiety effective to form a bond with the diene rubber matrix; each R.sub.2 is independently selected from: C.sub.1-6 alkyl; C.sub.1-6 alkoxy; halogen; and a group of formula -L.sub.2-R.sup.1; and n is an integer from 0 to 4.

39. A vehicle tire comprising a vehicle tire component, wherein the vehicle tire component comprises a diene rubber-silica compound, wherein the diene rubber-silica compound comprises a diene rubber matrix having dispersed therein a silica filler, and wherein the silica filler is reversibly coupled to the diene rubber matrix via a dynamic imine bond.

40. The vehicle tire of claim 39, wherein the silica filler is surface-modified by a coupling agent incorporating the dynamic imine bond and which is bound to the diene rubber matrix, the coupling agent having a structure of formula (I): ##STR00023## wherein: * denotes a point of attachment of the coupling agent to the silica surface; ring B is an aromatic or heteroaromatic group; L.sub.1 is an organic linking group; L.sub.2 is either a direct bond or an organic linking group; R.sup.1 is a functional moiety effective to form a bond with the diene rubber matrix; each R.sub.2 is independently selected from: C.sub.1-6 alkyl; C.sub.1-6 alkoxy; halogen; and a group of formula -L.sub.2-R.sup.1; and n is an integer from 0 to 4.

Description

[0212] The invention is illustrated further by way of the following non-limiting Examples and the accompanying figures, in which:

[0213] FIG. 1Schematic showing the procedure employed in the creep testing.

[0214] FIG. 2Uncured Payne effect of the SSBR/silica compounds.

[0215] FIG. 3Cured Payne effect of the SSBR/silica compounds.

[0216] FIG. 4Stress-strain curves of the SSBR/silica compounds at room temperature.

[0217] FIG. 5Reinforcement index of the SSBR/silica compounds.

[0218] FIG. 6Variation of the loss factor (tan ) as a function of temperature of the SSBR/silica compounds.

[0219] FIG. 7Stress-strain curves of the SSBR/silica compounds at 100 C.

[0220] FIG. 8Variation of the strain during creep testing of the SSBR/silica compounds.

EXAMPLES

Testing Procedures:

1. Payne Effect

[0221] Payne effect was measured using a Rubber Process Analyzer, RPA elite (TA instruments) with strain sweeps from 0.1% to 100% for cured samples and for uncured samples, at a frequency of 1.6 Hz and a temperature of 60 C. The cured samples were vulcanized beforehand inside the equipment chamber according to the vulcanization conditions at 160 C.

2. Modulus, Tensile Strength and Elongation at Break

[0222] Modulus, tensile strength (Stress at Maximum Strain) and elongation at break were measured using a universal testing machine Zwick Z05 (Zwick, Germany) operated with a crosshead speed of 500 mm/min according to ASTM D412. Modulus (100% (M100)) and 300% (M300)), tensile strength (Ts) and elongation at break (Eb) were calculated according to the calculations in ASTM D412. The reinforcement index was determined as the ratio of M300 to M100.

3. Rebound

[0223] Rebound, the resilience of a rubber sample based on the ratio of returned to delivered energy, was measured according to ISO 8307 using a testing machine Zwick 5109 (Zwick, Germany). Percentage rebound was calculated according to ISO 8307.

4. Hardness, Shore A

[0224] Shore A hardness was measured according to DIN 53505 using a universal hardness tester (Zwick, Germany).

5. Loss and Storage Modulus, and Loss Factor (tan )

[0225] Dynamic mechanical measurement of the vulcanized samples was carried out using a Gabo-Netzsch Eplexor. Measurements were performed with a frequency of 10 Hz, a dynamic strain of 1% below 0 C. and 3% at room temperature (RT). The change in the strain at RT was investigated due to softening of the rubber at higher temperatures which can generate noise in the measurements.

6. Mechanical Properties at High Temperature

[0226] Mechanical properties of the compounds at 100 C. were measured by a universal testing machine Zwick Z010 (Zwick, Germany) operated with a crosshead speed of 500 mm/min and with a limit strain of 330%. The tests were performed in a temperature chamber at 100 C. Measurements of the dynamic properties of the vulcanized compounds before and after cycling the samples in the tensile machine were carried out on a Gabo-Netzsch Eplexor. Measurements were performed with a frequency of 10 Hz, a dynamic strain of 1% below 0 C. and 3% at room temperature (RT). The change in the strain at RT was investigated due to softening of the rubber at higher temperatures which can generate noise in the measurements. The cycling of the samples was performed in a universal testing machine Zwick Z010 (Zwick, Germany) operated with a crosshead speed of 500 mm/min and with a limit strain of 200%. All samples were cycled 5 times at 100 C.

7. Creep Deformation

[0227] Creep experiments were carried out using a universal testing machine Zwick Z010 (Zwick, Germany). A force of 15 N was applied to the samples, this force was maintained for 1 hour. After this time the stress was released and the changes in the strain of the samples were measured for another hour. The temperature of the experiments was 100 C. FIG. 1 illustrates the procedure for the creep experiments.

Preparation of Rubber Compounds According to the Invention:

[0228] Rubber compounds for tire tread applications were prepared using a non-functionalised solution styrene butadiene rubber (SSBR) as the polymer matrix and silica as the filler. Modification of the silica was performed by reaction of the silica with an amino silane and a benzaldehyde compound in order to obtain a dynamic imine bond. This reaction was either performed during the mixing of the rubber compounds (i.e. in-situ) or prior to mixing with the rubber compounds (i.e. the silica was pre-modified).

Materials:

[0229] Rubber: Non-functionalised SSBR: Sprintan 4601 (Trinseo, Germany) [0230] Silica: ULTRASIL 7000 GR (Evonik Resource Efficiency GmbH, Germany) [0231] 3-Aminopropyltriethoxysilane (Sigma Aldrich, the Netherlands) [0232] 3-Vinylbenzaldehyde (Sigma Aldrich, the Netherlands) [0233] 4-Allyloxybenzaldehyde (Sigma Aldrich, the Netherlands) [0234] 4-(Methylthio)benzaldehyde (Sigma Aldrich, the Netherlands) [0235] TDAE (Hansen & Rosenthal, Germany) [0236] Zinc oxide (Millipore Sigma, Germany) [0237] Stearic Acid (Millipore Sigma, Germany) [0238] Sulfur (Caldic B.V., the Netherlands) [0239] N-Tertiary butyl benzothiazyl sulphonamide (TBBS) (Caldic B.V., the Netherlands) [0240] Bis(3-triethoxysilylpropyl)disulfide (TESPD): Si266 (Evonik Resource Efficiency GmbH, Germany) [0241] Hexadecyltrimethoxysilane (Sigma Aldrich, the Netherlands).

Silica Modification:

[0242] In-situ modification of the silica was performed by reaction with an amino silane (3-aminopropyltriethoxysilane) and each of the following benzaldehydes during mixing of the rubber compounds: 3-vinylbenzaldehyde, 4-allyloxybenzaldehyde, and 4-(methylthio)benzaldehyde).

[0243] Pre-modification of the silica was performed by reaction of silica with the amino silane (3-aminopropyltriethoxysilane) and the selected benzaldehyde in a two-step reaction as follows:

Step 1: Reaction Between the Silica and Amino Silane

[0244] The amount of silica used was 100 g and for the amino silane 8 g. The reaction was performed during 24 hours at 70 C. using toluene as the solvent. The product was filtered after the first step of the reaction.

Step 2: Reaction with the Benzaldehyde

[0245] Reaction between the pre-modified silica and the selected benzaldehyde was carried out for 24 hours at 40 C. using toluene as the solvent. The obtained product was extracted in toluene during 24 hours using Soxhlet units. The quantities employed for the different benzaldehydes were: 4.8 g of 3-vinylbenzaldehyde, 5.9 g of 4-allyloxybenzaldehyde and 5 g of 4-(methylthio)benzaldehyde.

Preparation of Rubber Compounds According to the Invention:

[0246] Rubber compounds (SSBR/modified silica) in accordance with the invention were prepared in an internal mixer (Brabender Plasticorder 350S, Duisburg, Germany) with a fill factor of 0.7, initial temperature of 100 C. and rotor speed of 50 rpm. Samples were prepared according to the formulation in Table 1 and in accordance with the mixing procedure in Table 2.

TABLE-US-00001 TABLE 1 Formulation of rubber compounds in accordance with the invention Quantity (phr = per hundred parts rubber) Examples 1-3 Examples 4-6 Ingredients (E1-E3) (E4-E6) SSBR - Sprintan 4601 100 100 Pre-modified silica - 80 + amount of modifier ULTRASIL 7000 GR + calculated by TGA modifier Un-modified silica - 80 ULTRASIL 7000 GR TDAE 37.5 37.5 ZnO 2.5 2.5 Stearic Acid 2.5 2.5 Sulfur 1.4 1.4 TBBS 2 2 3-aminopropyltriethoxysilane * Benzaldehyde * (3-vinylbenzaldehyde, 4-allyloxybenzaldehyde or 4-(methylthio)benzaldehyde) * The amount of silane and benzaldehyde was adjusted equimolarly for each compound based on the amount of TESPD added in Reference Compound 1 (6.2 phr TESPD) - see Table 5 below

TABLE-US-00002 TABLE 2 Mixing procedure of the rubber compounds Time Action - in-situ modified Action - pre-modified [min:s] silica (E4-E6) silica (E1-E3) Step 1 pre-heating 100 C. - 50 rpm 0.00 Add rubber, mastication 1.20 Add filler, silane Add pre-modified filler, 2.40 Add filler, silane, Add pre-modified filler, TDAE TDAE 4.00 Add filler, Add pre-modified filler, 5.00 Increase torque (increase temperature to 130 C.) 10.00 Stop mixing (reaching 140 C.) Step 2 pre-heating 100 C. - 50 rpm 0.00 Add elastomer pre-mix, mastication 1.00 Addition of benzaldehyde (E4-E6 only), ZnO and Stearic Acid 1.20 Increase temperature 5.00 Stop mixing (reaching 140 C.) Step 3 pre-heating 50 C. - 50 rpm 0.00 Add elastomer pre-mix, mastication 1.30 Add all curatives (sulphur, TBBS) 3.00 Stop mixing

[0247] Details of the final rubber compounds according to the invention are set out in Table 3 below.

TABLE-US-00003 TABLE 3 SSBR/modified silica rubber compounds Example 1 SSBR/silica compound prepared using silica pre-modified (E1) by reaction with 3 aminopropyltriethoxysilane and 3-vinylbenzaldehyde Example 2 SSBR/silica compound prepared using silica pre-modified (E2) by reaction with 3 aminopropyltriethoxysilane and 4-Allyloxybenzaldehyde Example 3 SSBR/silica compound prepared using silica pre-modified (E3) by reaction with 3 aminopropyltriethoxysilane and 4-(methylthio)benzaldehyde Example 4 SSBR/silica compound prepared using silica in-situ modified (E4) by reaction with 3 aminopropyltriethoxysilane and 3-vinylbenzaldehyde Example 5 SSBR/silica compound prepared using silica in-situ modified (E5) by reaction with 3 aminopropyltriethoxysilane and 4-allyloxybenzaldehyde Example 6 SSBR/silica compound prepared using silica in-situ modified (E6) by reaction with 3 aminopropyltriethoxysilane and 4-(methylthio)benzaldehyde

Preparation of Reference Rubber Compounds:

[0248] Two reference rubber compounds were prepared, details of which are shown in Table 4.

TABLE-US-00004 TABLE 4 Reference SSBR/silica compounds Reference 1 SSBR/silica compound in-situ silanized with TESPD Reference 2 SSBR/silica compound in-situ silanized with hexadecyltrimethoxysilane

[0249] In Reference 1 the bifunctional silane coupling agent TESPD was employed to link the silica and SSBR. In Reference 2, a monofunctional silane (hexadecyltrimethoxysilane) was employed for in-situ modification of the silica. The reference compounds were prepared according to the formulation shown in Table 5 and in accordance with the mixing procedure used for the compounds according to the invention shown in Table 2 (in which the silane is TESPD or hexadecyltrimethoxysilane, as appropriate).

TABLE-US-00005 TABLE 5 Formulation of reference compounds Quantity (phr) Ingredients Reference 1 Reference 2 SSBR - Sprintan 4601 100 100 Silica - ULTRASIL 7000 GR 80 80 Si266* 6.2 Hexadecyltrimethoxysilane 9.1** TDAE 37.5 37.5 ZnO 2.5 2.5 Stearic Acid 2.5 2.5 Sulfur 1.4 1.4 TBBS 2 2 *Bis(3-triethoxysilylpropyl)disulfide (TESPD) **The amount of hexadecyltrimethoxysilane was adjusted equimolarly taking as reference the amount of TESPD added in Reference 1

Testing of Rubber Compounds:

[0250] All rubber compounds were subjected to various tests as outlined in the test procedures. Results for the measured Payne effect are shown in Table 6 and accompanying FIGS. 2 and 3.

TABLE-US-00006 TABLE 6 Payne effect of the SSBR/silica compounds Cured - Payne effect Uncured - Payne effect Compound G, kPa G.sub.100%, kPa G, kPa G.sub.100%, kPa Reference 1 (R1) 1151.0 403.6 438.6 153.9 Reference 2 (R2) 1101.7 233.6 453.0 127.3 Example 1 (E1) 2345.2 597.0 551.7 173.3 Example 2 (E2) 5304.7 571.1 758.1 164.0 Example 3 (E3) 4916.4 606.9 723.9 167.0 Example 4 (E4) 3584.1 571.1 834.0 149.1 Example 5 (E5) 5310.0. 533.2 669.0 146.5 Example 6 (E6) 4447.4 559.6 660.4 140.8

[0251] The results for the uncured and cured Payne Effect show that the rubber compounds according to the invention present a higher Payne Effect than the reference compounds indicating a strong filler network. The higher values of G at 100% strain obtained for the cured Payne effect for the rubber compounds of the invention compared to the reference compounds indicates a higher filler-rubber interaction in these compounds. The Payne effect of the compounds of the invention is similar regardless of whether the silica was pre-modified (E1-E3) or modified in-situ (E4-E6).

[0252] Results for the mechanical properties of the vulcanised compounds are shown in Table 7 and accompanying FIGS. 4 and 5.

TABLE-US-00007 TABLE 7 Mechanical properties of the SSBR/silica compounds Ts Eb Reinforcement index Compound (MPa) (%) (M300/M100) Reference 1 (R1) 10.7 465 3.6 Reference 2 (R2) 8.6 1296 1.8 Example 1 (E1) 15.6 458 3.6 Example 2 (E2) 15.7 527 3.3 Example 3 (E3) 16.6 535 3.2 Example 4 (E4) 12.5 500 3.0 Example 5 (E5) 17.0 700 2.9 Example 6 (E6) 14.6 570 3.1

[0253] The results of the mechanical properties show that all compounds of the invention have a reinforcing index comparable to that of Reference Compound 1. All compounds according to the invention show higher elongation at break and also higher tensile strength than Reference Compounds 1 and 2.

[0254] The rebound properties of the compounds and hardness are shown in Table 8. Rebound results show that all compounds of the invention have comparable values to Reference Compound 1. Their dynamic properties are therefore comparable to that of a rubber compound produced using the state-of-the art bifunctional silane coupling agent, TESPD. The rebound level is low for Reference Compound 2 since this contains the covering agent which is not reactive with the rubber and does not couple the silica to the rubber matrix. The higher rebound results for the compounds of the invention are evidence of a high coupling efficiency. With respect to hardness, all compounds according to the invention show higher values than Reference Compounds 1 and 2.

TABLE-US-00008 TABLE 8 Rebound and hardness of the SSBR/silica compounds Compound Rebound at 60 C. (%) Hardness, Shore A Reference 1 (R1) 56.9 52.6 Reference 2 (R2) 44.1 41.2 Example 1 (E1) 56.9 56.6 Example 2 (E2) 53.1 64.8 Example 3 (E3) 53.7 65.3 Example 4 (E4) 52.3 64.9 Example 5 (E5) 51.2 65.8 Example 6 (E6) 51.6 66.3

[0255] Results of the dynamic mechanical measurement of the vulcanized samples are set out in Table 9 and accompanying FIG. 6.

TABLE-US-00009 TABLE 9 Maximum tan and tan at 60 C. and 0 C. of the SSBR/silica compounds Compound tan at 60 C. tan at 0 C. tan maximum Reference 1 (R1) 0.169 0.352 0.693 Reference 2 (R2) 0.203 0.292 0.766 Example 1 (E1) 0.158 0.283 0.616 Example 2 (E2) 0.181 0.248 0.563 Example 3 (E3) 0.185 0.221 0.543 Example 4 (E4) 0.160 0.199 0.538 Example 5 (E5) 0.170 0.209 0.535 Example 6 (E6) 0.161 0.211 0.537

[0256] Analysis of the loss factor (tan ) as a function of the temperature of the compounds of the invention shows E4 and E6 have lower values of tan at 60 C. (indicating better rolling resistance) compared to Reference Compounds 1 and 2, and E5 has a similar value of tan at 60 C. to Reference 1. All compounds according to the invention present lower values of tan at 0 C. and maximum of tan than Reference Compounds 1 and 2.

[0257] The re-connectivity of the new bonds created with the silica modification according to the invention was analysed by studying the mechanical response of the compounds at high temperatures, and analysing the change in dynamic properties after submitting the compounds to a cycling (fatigue test).

[0258] The results of the mechanical properties measured at 100 C. are shown in FIG. 7. These show that all compounds according to the invention how similar resistance to high temperatures. All compounds except for Reference Compound 2 were broken before reaching the limit strain established for the experiment (330% strain). However, all compounds according to the invention reached higher tensile strengths than Reference Compound 1, and E5 also showed a higher elongation at break.

[0259] Results of the dynamic mechanical measurement of the vulcanised compounds before and after cycling in the tensile machine are set out in Table 10.

TABLE-US-00010 TABLE 10 Maximum tan and tan at 60 C. and 0 C. of the SSBR/silica compounds tan tan at 60 C. at 0 C. tan after after maximum tan cycling 5 cycling 5 after cycling at times at tan times at tan 5 times at Compound 60 C. 100 C. at 0 C. 100 C. maximum 100 C. Reference 1 (R1) 0.169 0.203 0.352 0.244 0.693 0.564 Example 4 (E4) 0.160 0.200 0.199 0.251 0.538 0.596 Example 6 (E6) 0.161 0.194 0.211 0.268 0.537 0.600

[0260] Compounds E4 and E6 according to the invention present a better performance in dynamic properties after being submitted to 5 cycles at 100 C. until 200% strain than Reference Compound 1. Both compounds E4 and E6 show after cycling: lower values of tan at 60 C. (indicating better rolling resistance), and higher values of tan at 0 C. and higher maximum of tan (indicating better wet grip) than Reference Compound 1.

[0261] The re-connectivity of the new bonds created with the silica modification according to the invention was further analysed by conducting a creep experiment. The results are shown in FIG. 8. The results show that E4 and E5 reached a higher elongation with the applied force and the recovery of the original shape is almost the same as that of Reference compound 1. With respect to E6, the elongation is significantly lower, but also the residual strain is lower compared to the other compounds.

[0262] The invention has been described with reference to exemplary embodiments. Modifications and alterations are considered to form part of the invention to the extent that they are within the scope of the disclosure and appended claims. The scope of the disclosure should be determined with reference to the claims and is considered to include equivalents.