Carbon black for an elastomer composition

Abstract

Carbon black for use in elastomer compositions of tires and other elastomeric goods. Improvements in carbon black are needed in the areas of material modulus, tear strength, and dynamic heat buildup. These and other needs are met by the compositions and methods of the present disclosure. The present disclosure relates to carbon black having surface area and structural characteristics that enable improved performance of elastomer compositions such as tires.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 353,875, filed on June 21, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure relates to carbon black having surface area and structural characteristics that enable improved performance of elastomeric compositions such as tires.

Background Art

[0003] Carbon black has long been used in dynamic and mechanical elastomeric compositions for reinforcement purposes, but improvements are needed in the areas of material modulus, tear strength, and dynamic heat buildup. These and other needs are met by the compositions and methods of the present disclosure.

Summary of the Invention

[0004] According to an object of the present disclosure, as embodied and broadly described herein, the present disclosure relates, in one aspect, to carbon black, an elastomeric composition comprising carbon black, and methods for its manufacture and use.

[0005] One embodiment of carbon black has a nitrogen surface area (NSA) in the range of about 50 m 2 / g to about 70 m 2 / g, a statistical thickness surface area (STSA) in the range of about 50 m 2 / g to about 70 m 2 / g, an iodine absorption in the range of about 50 mg / g to about 70 mg / g, an oil absorption number (OAN) in the range of about 85 cc / 100 g to about 150 cc / 100 g, and a compression oil absorption number (COAN) in the range of about 70 cc / 100 g to about 100 cc / 100 g.

[0006] The elastomer composition may include at least one elastomer together with the carbon black of the present invention. One embodiment of the composition includes an elastomer in an amount of 100 parts per 100 parts of rubber (phr), and the carbon black of the present invention in an amount ranging from 35 parts per 100 parts of rubber (phr) to 75 parts per 100 parts of rubber (phr).

Mode for Carrying Out the Invention

[0007] This disclosure can be more easily understood by referring to the following detailed description of the present invention and the examples included therein.

[0008] Before disclosing and describing the carbon black, compositions, articles, and methods of the present invention, it should be understood that they are not limited to a particular synthesis method or, unless otherwise specified, to particular reagents, and thus, of course, can vary. It should also be understood that the terms used are for the purpose of merely describing particular embodiments and are not intended to be limiting. In the practice or testing of this disclosure, any methods and materials similar or equivalent to those described can be used, but exemplary methods and materials are described herein.

[0009] All publications are hereby incorporated by reference herein for the purpose of disclosing and describing the methods and / or materials in connection with which the publications are cited.

[0010] A. Definitions Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the practice or testing of the present invention, any methods and materials similar or equivalent to those described herein can be used, but exemplary methods and materials are described herein.

[0011] Unless the context clearly dictates otherwise, the singular forms "a," "an," and "the" include plural references. Thus, for example, references to "carbon black" or "an elastomer" include mixtures of two or more carbon blacks or elastomers, respectively.

[0012] Ranges may be expressed from "about" one particular value and / or to "about" another particular value. When such a range is expressed, another aspect includes from one particular value and / or to another particular value. Similarly, when values are expressed as approximations by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that each of the endpoints of a range is significant both in relation to the other endpoint and independently of the other endpoint. It will also be understood that there are several values disclosed and that each value is disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, "about 10" is also disclosed. It will also be understood that each unit between two particular units is also disclosed. For example, if 10 and 15 are disclosed, 11, 12, 13, and 14 are also disclosed.

[0013] When the term "about" is before a numerical value, the numerical value may vary within ±10% unless otherwise specified.

[0014] "Optional" or "optionally" means that the subsequent described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0015] "Nitrogen surface area (NSA)" and "statistical thickness surface area (STSA)" refer to the nitrogen surface area and statistical thickness surface area measured in accordance with ASTM test method D6556, which is incorporated by reference.

[0016] "Iodine absorption" refers to the iodine absorption value measured in accordance with ASTM D1510.

[0017] "Oil Absorption (OAN)" refers to the oil absorption value measured in accordance with ASTM D2414.

[0018] "Compression Oil Absorption (COAN)" refers to the compression oil absorption value measured in accordance with ASTM D3493.

[0019] "325 Mesh Water Washed Residue" refers to the residue value measured in accordance with ASTM D1514.

[0020] All of the ASTM methods described above are hereby incorporated by reference in their entirety.

[0021] Unless otherwise specifically stated, "phr" is intended to refer to parts per 100 parts of rubber, as commonly understood and used in the rubber industry.

[0022] "Substantially identical reference composition" refers to a composition that is substantially identical in all respects with respect to the components of the composition and the amounts of those components in phr units (within ±10%), but where the carbon black of the present invention is replaced with ASTM N550 grade carbon black (available from Birla Carbon, Marietta, GA, USA). In a further aspect, "substantially identical reference composition" refers to a composition that is substantially identical in all respects with respect to the components of the composition and the amounts of those components in phr units (within ±5%), but where the carbon black of the present invention is replaced with N550 grade carbon black. In a further aspect, "substantially identical reference composition" refers to a composition that is substantially identical in all respects with respect to the components of the composition and the amounts of those components in phr units (within ±2%), but where the carbon black of the present invention is replaced with N550 grade carbon black. In a further aspect, "substantially identical reference composition" refers to a composition that is substantially identical in all respects with respect to the components of the composition and the amounts of those components in phr units (within ±1%), but where the carbon black of the present invention is replaced with N550 grade carbon black. In a further aspect, "substantially identical reference composition" refers to a composition that is identical in all respects (within the range of measurement error) with respect to the components of the composition and the amounts of those components in phr units, but where the carbon black of the present invention is replaced with N550 grade carbon black.

[0023] The carbon black of ASTM N550 grade, i.e., the carbon black used in the reference composition, has the following colloidal properties measured according to the ASTM methods described above. The values listed below may vary within the range of ±10%, ±5%, ±2%, or ±1%. [Table 1]

[0024] The components used to prepare the compositions of the present disclosure, as well as the compositions themselves used within the disclosed methods, are disclosed. These and other materials are disclosed, and where combinations, subsets, interactions, groups, etc. of these materials are disclosed, specific references to the various individual and collective combinations and permutations of each of these compounds may not be explicitly disclosed, but each is specifically contemplated and understood to be described. For example, if a particular carbon black is disclosed and discussed, and some modifications that can be made to several materials containing the carbon black are discussed, specifically, each and all combinations and permutations of the carbon black, as well as possible modifications, are specifically contemplated, unless specifically shown to the contrary. Thus, when classes of carbon blacks A, B, and C are disclosed, along with classes of carbon blacks D, E, and F, and examples of combined carbon blacks, A-D are disclosed, it is intended to mean that each, even if not individually listed, is considered to be disclosed individually and collectively in combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F. Similarly, any subset or combination of these is also disclosed. Thus, for example, the subgroups of A-E, B-F, and C-E are considered to be disclosed. This concept applies to all aspects of the present application, including but not limited to the steps of making and using the compositions. Thus, if there are various additional steps that can be performed, it is understood that each of these additional steps can be performed in any particular embodiment or combination of embodiments of the method.

[0025] Each of the disclosed materials is commercially available and / or methods for its manufacture are known to those of ordinary skill in the art.

[0026] It is understood that the disclosed compositions have a particular function. Certain structural requirements for performing the disclosed function are disclosed, and there are various structures that can perform the same function in relation to the disclosed structure, and it is understood that these structures will typically achieve the same result.

[0027] B. Carbon Black Carbon black is commonly used in the belt and ply areas of tires and other dynamic rubber applications. Rubber components used in such applications are typically subjected to fatigue loading and heat exposure, so the rubber compound should have good material modulus, tear strength, and resistance to heat buildup. ASTM N550 grade carbon black is commonly used in tires and other mechanical rubber formulations. The colloidal properties of the carbon black embodiments described herein surprisingly enable the carbon black to exhibit reduced heat buildup, increased tear strength, and reduced abrasion loss compared to N550 grade carbon black. Without wishing to be bound by theory, it is believed that the improved in-rubber properties may be due to the structure of the carbon black. Embodiments of the carbon black of the present invention (BC2123, 2183, and 2187) have an oil absorption value and an STSA value higher than that of N550 and an STSA value lower than that of ASTM N330 grade carbon black.

[0028] One embodiment of the carbon black has a nitrogen surface area (NSA) in the range of about 50 m 2 / g to about 70 m 2 / g, b) a statistical thickness surface area (STSA) in the range of about 50 m 2 / g to about 70 m 2 / g, an iodine absorption in the range of about 50 mg / g to about 70 mg / g, an oil absorption (OAN) in the range of about 85 cc / 100 g to about 150 cc / 100 g, and a compression oil absorption (COAN) in the range of about 70 cc / 100 g to about 100 cc / 100 g.

[0029] In a further aspect, an exemplary embodiment of the carbon black of the present invention may have a nitrogen surface area (NSA) in the range of about 55 m 2 / g to about 65 m 2 / g. In another aspect, the carbon black of the present invention has a nitrogen surface area of about 55 to about 59 m 2 / g, for example, 55 m 2 / g or 59 m2 It may have a nitrogen surface area (NSA) of / g.

[0030] In one aspect, an exemplary embodiment of the carbon black of the present invention is about 55 m 2 / g to about 65 m 2 It may have a statistical thickness surface area (STSA) in the range of / g. In another aspect, the carbon black of the present invention is about 53 to about 59 m 2 / g, for example, 53 m 2 / g or 59 m 2 / g may have a statistical thickness surface area (STSA).

[0031] In one aspect, an embodiment of the carbon black of the present invention exhibits a difference between NSA and STSA of 11% or less, for example, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less. In a further aspect, an embodiment of the carbon black of the present invention does not exhibit a measurable difference (within the range of error) between NSA and STSA.

[0032] In one aspect, an exemplary embodiment of the carbon black of the present invention may have an iodine absorption in the range of about 50 mg / g to about 70 mg / g. In a further aspect, an exemplary embodiment of the carbon black of the present invention may have an iodine absorption in the range of about 55 mg / g to about 65 mg / g. In another aspect, the carbon black of the present invention may have an iodine absorption of about 53 to about 62 mg / g.

[0033] In one aspect, an embodiment of the carbon black of the present invention exhibits a difference between the iodine absorption and NSA and / or STSA of 11% or less, for example, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less. In a further aspect, an embodiment of the carbon black of the present invention does not exhibit a measurable difference (within the range of error) between the iodine absorption and NSA and / or STSA.

[0034] In one aspect, an exemplary embodiment of the carbon black of the present invention may have an oil absorption number (OAN) in the range of about 900 cc / 100 g to about 145 cc / 100 g. In another aspect, an exemplary embodiment of the carbon black of the present invention may have an oil absorption number (OAN) in the range of about 100 cc / 100 g to about 135 cc / 100 g. In another aspect, the carbon black of the present invention may have an oil absorption amount in the range of about 120 cc / 100 g to about 135 cc / 100 g. In another aspect, the carbon black of the present invention may have an oil absorption amount in the range of about 125 cc / 100 g to about 135 cc / 100 g, for example, 127 cc / 100 g or 130 cc / 100 g.

[0035] In one aspect, an exemplary embodiment of the carbon black of the present invention may have a compressed oil absorption number (COAN) in the range of about 75 cc / 100 g to about 95 cc / 100 g. In a further aspect, an exemplary embodiment of the carbon black of the present invention may have a compressed oil absorption number (COAN) in the range of about 90 cc / 100 g to about 95 cc / 100 g.

[0036] In one aspect, an exemplary embodiment of the carbon black of the present invention may have a 325-mesh water-washed residue of less than about 650 ppm, for example, 300 - 600 ppm, for example, 390 - 400 ppm, 430 - 440 ppm, or 600 - 625 ppm. In other aspects, the 325-mesh water-washed residue may be lower, for example, less than about 20 ppm, for example, 0 - 19 ppm.

[0037] In one aspect, the carbon black of the present invention may have a transmittance of about 80% to about 100%, for example, 80%, 97%, or 98%.

[0038] In one aspect, the carbon black of the present invention can have an average aggregate size of about 100 nm to about 150 nm. In another aspect, the carbon black of the present invention can have an average aggregate particle size of about 110 nm to about 140 nm. In another aspect, the carbon black of the present invention can have an average aggregate particle size of about 115 nm to about 130 nm. In another aspect, the carbon black of the present invention can have an average aggregate particle size of about 115 nm to about 125 nm. In another aspect, the carbon black of the present invention can have an average aggregate particle size of about 115 nm to about 120 nm.

[0039] In one aspect, the carbon black of the present invention can have an aggregate size distribution D50 in the range of about 100 to 150 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D50 in the range of about 110 to 140 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D50 in the range of about 115 to 130 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D50 in the range of about 115 to 125 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D50 in the range of about 115 to 120 nm.

[0040] In one aspect, the carbon black of the present invention can have an aggregate size distribution D10 in the range of about 60 to 90 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D10 in the range of about 70 to 85 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D10 in the range of about 75 to 85 nm. In another aspect, the carbon black of the present invention can have an aggregate size distribution D10 in the range of about 75 to 80 nm.

[0041] In one aspect, the carbon black of the present invention may have an aggregate size distribution D90 in the range of about 150 to 200 nm. In another aspect, the carbon black of the present invention may have an aggregate size distribution D90 in the range of about 160 to 200 nm. In another aspect, the carbon black of the present invention may have an aggregate size distribution D90 in the range of about 160 to 190 nm. In another aspect, the carbon black of the present invention may have an aggregate size distribution D90 in the range of about 165 to 190 nm. The aggregate size and distribution data can be measured as described in ISO Standard 15825-2017 “Rubber Compounding Ingredients-Carbon Black-Determination of Aggregate Size Distribution by Disk Centrifuge Photosedimentometry,” International Organization for Standardization, Geneva (2017).

[0042] In some aspects, the carbon black can be functionalized with many different chemical moieties, ranging from adsorbed molecules, oligomer grafts, and covalently attached specific functional groups. This functionalization is generally thought to occur on the edge sites of the graphene planes at the surface of the carbon black. In various applications, it has become important to improve the surface functionality of carbon black with increased surface group concentration and more uniform surface chemistry, to the extent realistically achievable. Also, it should be understood that it may not be essential to completely cover the surface of the carbon black particles with functional groups, and that significant energy and very intensive processing may be required to make the resulting carbon black overly reactive and add higher levels of functional groups. Without wishing to be bound by theory, the ideal balance is currently thought to be to functionalize each available edge site of each graphene layer that can be functionalized.

[0043] C. Elastomer Composition Another aspect of the present disclosure relates to an elastomer (e.g., rubber) composition containing the carbon black of the present invention. Generally, the rubber composition may include at least one elastomer and any carbon black of the present invention as described above.

[0044] In one aspect, the elastomer composition may include an elastomer in an amount of 100 parts per 100 parts of rubber (phr) and the carbon black of the present invention in an amount in the range of 35 parts per 100 parts of rubber (phr) to 75 parts per 100 parts of rubber (phr).

[0045] Any suitable elastomer may be present in the rubber composition. Non-limiting examples include natural rubber (NR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), natural polyisoprene rubber, butyl rubber, ethylene-propylene rubber, or any blend or combination thereof. Any of the above elastomers may be present in an amount of 100 parts per 100 parts of rubber (phr), alone or in combination, within the combination of rubbers. In a further aspect, the elastomer includes natural rubber (NR), polybutadiene rubber (BR), or any blend or combination thereof. In still a further aspect, the elastomer includes natural rubber (NR) in an amount in the range of 40 to 100 parts per 100 parts of rubber (phr) and polybutadiene rubber (BR) in an amount in the range of 0 to 60 parts per 100 parts of rubber (phr). In another aspect, the elastomer includes natural rubber (NR) in an amount in the range of 40 to 50 parts per 100 parts of rubber (phr) and polybutadiene rubber (BR) in an amount in the range of 50 to 60 parts per 100 parts of rubber (phr). In a further aspect, the elastomer includes natural rubber (NR) in an amount of 50 parts per 100 parts of rubber (phr) and polybutadiene rubber (BR) in an amount of 50 parts per 100 parts of rubber (phr).

[0046] One embodiment of the elastomer composition includes natural rubber (NR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), synthetic polyisoprene rubber, butyl rubber, ethylene-propylene rubber, or any blend or combination thereof. Another embodiment includes natural rubber (NR), polybutadiene rubber (BR), or any blend or combination thereof. Natural rubber (NR) is present in an amount in the range of 40 to 100 parts per 100 parts of rubber (phr), and polybutadiene rubber (BR) may be present in an amount in the range of 0 to 60 parts per 100 parts of rubber (phr).

[0047] In one aspect, the rubber composition exhibits properties equivalent to or better than those of a substantially identical reference composition, but the carbon black has been replaced with ASTM N550 grade carbon black. Embodiments of the rubber composition of the present invention may exhibit, for example, a modulus of elasticity approximately equal to that of the reference composition, a heat accumulation reduced by 5 to 10% compared to the reference composition, an increase in tear strength of 10 to 30% compared to the reference composition, and a reduction in wear loss of about 25% compared to the reference composition.

[0048] Also disclosed are articles comprising any rubber composition of the present invention. Non-limiting examples include, inter alia, any rubber used in dynamic environments such as tires, conveyor belts, extruded profiles, hoses, brake diaphragms, plastic pipes, and the like.

[0049] D. Method A method for preparing the rubber composition of the present invention is also described. In one aspect, the method includes (a) providing an elastomer in an amount of 100 parts per 100 parts of rubber (phr), (b) providing the carbon black of the present invention in an amount in the range of 35 parts per 100 parts of rubber (phr) to 75 parts per 100 parts of rubber (phr), and (c) mixing the elastomer and the carbon black to form a rubber composition.

[0050] It is understood that the elastomers utilized in the disclosed method can include any of the elastomers described above. It is further understood that these elastomers can be present in any of the amounts described herein to provide a rubber composition exhibiting the disclosed properties. Similarly, any oxidized version of the carbon black of the present invention can be used in any of the disclosed amounts to prepare a rubber composition exhibiting the disclosed properties.

[0051] It is further understood that any type of mixing can be utilized to prepare the rubber composition of the present invention. In certain embodiments, the mixing step includes reactive mixing. In still other embodiments, the mixing step includes conventional steps of mixing the components. In yet further embodiments, the mixing step includes blending. In certain embodiments, the mixing step results in a homogeneous composition.

[0052] It is understood that the rubber composition obtained by the method of the present disclosure can exhibit any or all of the properties disclosed above. In yet further embodiments, articles that can be prepared from the rubber composition made by the method of the present invention are described herein.

Examples

[0053] E. Examples The following examples further illustrate the present disclosure. The scope of the present disclosure and the scope of the claims are not limited by the scope of the following examples.

Table 2

[0054] Exemplary embodiments of the rubber composition of the present invention can be prepared according to the loading parameters shown in Table 2.

Table 3

[0055] The aggregate size distribution characteristics of the carbon black of the present invention when measured by disk centrifugal photometry are shown in Table 3.

Table 4

[0056] Table 4 shows an additional comparison between the carbon black of the present invention or rubber compositions containing N330, N339, and N550 carbon black (prepared according to the specifications of Table 2).

Table 5

[0057] Compared with N550, BC2187 provides an equal modulus of elasticity, a reduced heat accumulation of about 8%, an increase in tear strength of about 20%, and a reduction in abrasion loss of about 20%. In contrast, BC2183 provides similar advantages in heat accumulation. BC2187 is in agreement with N550 in terms of M100 modulus of elasticity. In contrast, ASTM N300 series materials have higher tear strength but have problems with an increase in heat accumulation of about 20% - 25%.

[0058] The features and advantages of the present disclosure are apparent from the detailed description, and the claims cover all such features and advantages. Many modifications will occur to those skilled in the art, and any modifications equivalent to those described in the present disclosure fall within the scope of the present disclosure. Those skilled in the art will understand that the concepts on which the present disclosure is based can be used as a basis for designing other methods and systems for carrying out some of the purposes of the present disclosure. As a result, the claims should not be regarded as limited by the description or examples.

Claims

1. A carbon black, comprising a) about 50 m 2 / g to about 70 m 2 / g in the range of nitrogen surface area (NSA), b) about 50 m 2 / g to about 70 m 2 / g of statistical thickness surface area (STSA), c) an iodine absorption in the range of about 50 mg / g to about 70 mg / g, d) an oil absorption (OAN) in the range of about 85 cc / 100 g to about 150 cc / 100 g, and e) a compression oil absorption (COAN) in the range of about 70 cc / 100 g to about 100 cc / 100 g, having the characteristics of the carbon black.

2. The carbon black according to Claim 1, wherein the nitrogen surface area (NSA) and the statistical thickness surface area (STSA) differ by 5% or less.

3. The carbon black according to Claim 2, wherein at least one of the iodine absorption and the nitrogen surface area (NSA) or the statistical thickness surface area (STSA) differs by 5% or less.

4. About 55 m 2 / g to about 65 m 2 The carbon black according to claim 1, having a nitrogen surface area (NSA) in the range of / g.

5. About 55 m² / g to about 65 m² / g 2 The carbon black according to claim 1, having a statistical thickness surface area (STSA) in the range of 2 about 55 m² / g to about 65 m² / g

6. The carbon black according to Claim 1, having an iodine absorption in the range of about 55 mg / g to about 65 mg / g.

7. The carbon black according to Claim 1, having an oil absorption (OAN) in the range of about 90 cc / 100 g to about 145 cc / 100 g.

8. The carbon black according to Claim 1, having a compression oil absorption (COAN) in the range of about 75 cc / 100 g to about 95 cc / 100 g.

9. a) a nitrogen surface area (NSA) in the range of about 55 m 2 / g to about 65 m 2 / g, b) about 55 m 2 / g to about 65 m 2 / g of the statistical thickness surface area (STSA), c) an iodine absorption in the range of about 55 mg / g to about 65 mg / g, d) an oil absorption (OAN) in the range of about 90 cc / 100 g to about 145 cc / 100 g, and e) a compression oil absorption (COAN) in the range of about 75 cc / 100 g to about 95 cc / 100 g, having the characteristics of the carbon black according to Claim 1.

10. The carbon black according to Claim 9, wherein the nitrogen surface area (NSA) and the statistical thickness surface area (STSA) differ by 5% or less.

11. The carbon black according to Claim 10, wherein at least one of the iodine absorption and the nitrogen surface area (NSA) or the statistical thickness surface area (STSA) differs by 5% or less.

12. An elastomer composition comprising at least one elastomer and the carbon black according to Claim 1.

13. An elastomer composition comprising a) an elastomer in an amount of 100 parts per 100 parts of rubber (phr), and b) the carbon black according to Claim 1 in an amount in the range of 35 parts per 100 parts of rubber (phr) to 75 parts per 100 parts of rubber (phr).

14. The elastomer composition according to claim 13, wherein the elastomer comprises natural rubber (NR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), synthetic polyisoprene rubber, butyl rubber, ethylene-propylene rubber, or any blend or combination thereof.

15. The elastomer composition according to claim 13, wherein the elastomer comprises natural rubber (NR), polybutadiene rubber (BR), or any blend or combination thereof.

16. The elastomer composition according to claim 15, wherein the elastomer comprises natural rubber (NR) in an amount in the range of 40 to 100 parts per 100 parts of rubber (phr) and polybutadiene rubber (BR) in an amount in the range of 0 to 60 parts per 100 parts of rubber (phr).

Images