Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-25
2003-03-18
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S433000
Reexamination Certificate
active
06534571
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a desiccant dispersion, and more particularly to a calcium oxide desiccant dispersion for removing moisture from rubber compound formulations during processing.
BACKGROUND OF THE INVENTION
It is well known that the presence of moisture in a rubber compound formulation during the vulcanization process can cause serious deleterious effects in the finished rubber product. At normal vulcanizing temperatures, excessive moisture will “gas-out,” causing surface anomalies such as blistering or voids on the cured rubber product. In addition to being unaesthetic, such surface anomalies invariably reduce the service life of functional rubber products, e.g. tires and extruded rubber products.
Calcium oxide has long been employed in the art as a desiccant to remove excessive moisture from rubber compounds. Though a very effective desiccant for rubber formulations, the extreme hydrophilicity of calcium oxide makes proper handling and storage prior to use extremely difficult. If not properly stored, calcium oxide readily absorbs ambient atmospheric moisture in a reaction yielding calcium hydroxide, thus greatly depleting its effectiveness as a desiccant.
A second problem associated with calcium oxide is that it is typically delivered to the rubber processing industry as a fine powder. Fine, dry powders tend to increase mixing times and formulation viscosities, and are easily airborne. Calcium oxide is extremely caustic to the skin, eyes, and mucous membranes of humans, and therefore creates a hazardous work environment when airborne.
A known calcium oxide dispersion for use in rubber compound processing is Desical-P from Harwick, which is calcium oxide powder dispersed in naphthenic oil. Such paste dispersion has been fairly successful at improving rubber processing properties, such as homogeneity of calcium oxide throughout the rubber formulation, as well as reducing atmospheric moisture absorption during storage. However, a major detriment to such existing paste formulations is that they tend to sweat or exude oil to the surface when stored over time. Such exuded oil makes handling and weighing of the paste quite difficult. In addition, such pastes are provided in bulk form, and must be cut to proper weight before they are added to a rubber compound batch for processing. Such characteristics contribute additional man-hours to rubber processing which translate directly into additional expense. Lastly, though such calcium oxide paste absorbs moisture at a lower rate than calcium oxide powder, such paste still absorbs significant atmospheric moisture when stored.
Consequently, there is a need in the art for a calcium oxide dispersion that is effective as a rubber compound desiccant, yet does not exude oil when stored, has improved desiccant properties over existing dispersions, is easy to handle and cut to weight, and further resists atmospheric moisture absorption during storage.
SUMMARY OF THE INVENTION
A desiccant dispersion for use in rubber compounds comprising 30-94 wt. % calcium oxide and 3-55 wt. % asphalt. A solid desiccant dispersion comprising 30-94 wt. % calcium oxide, 3-55 wt. % light-colored hydrocarbon resin, 0.5-14 wt. % plasticizer, and 0.5-12 wt. % fatty acid agent. A method of making a vulcanized rubber product comprising the steps of a) incorporating a desiccant dispersion into a rubber compound at a rate of 1-20 parts desiccant dispersion per 100 parts of rubber, said desiccant dispersion comprising 30-94 wt. % calcium oxide and 3-55 wt. % asphalt, said rubber compound comprising rubber selected from the group consisting of natural rubbers, synthetic rubbers, and mixtures thereof; and b) vulcanizing the rubber compound to yield the vulcanized rubber product. A rubber compound comprising rubber and the desiccant dispersion is also provided.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
In the description that follows, when a preferred range, such as 5 to 25 (or 5-25), is given, this means preferably at least 5 and, separately and independently, preferably not more than 25. Unless specifically otherwise indicated, all parts are parts by weight and all percents are weight percents, both herein and in the appended claims.
The invented desiccant dispersion has the preferred formulations shown in Table 1. In this formulation or table of components, any preferred or less preferred weight percent or weight percent range of any component can be combined with any preferred or less preferred weight percent or weight percent range of any of the other components; it is not required or necessary that all or any of the weight percents or weight percent ranges come from the same column. The invented calcium oxide desiccant dispersion is in solid form and comprises calcium oxide and asphalt according to a first preferred embodiment of the invention. Preferably, the invented dispersion further comprises fatty acid and plasticizer.
TABLE 1
Preferred composition of invented calcium oxide
desiccant dispersion (Listed in weight percents)
Most
Less
Still Less
Still Less
Component
Preferred
Preferred
Preferred
Preferred
Asphalt
15
10-20
5-30
4-40
8-25
3-55
Fatty Acid
2
1.5-4
1-7
0.5-10
Agent
0-12
Plasticizer
3
2-5
1.5-7
0.5-12
0-14
Calcium
80
75-85
60-90
30-94
Oxide
70-88
45-92
Less preferably, the formulation contains 80 weight percent calcium oxide and 20 weight percent asphalt. The asphalt component in the invented dispersion is preferably a blend of 55, less preferably 50-60, less preferably 45-65, less preferably 40-70, less preferably 35-75, percent asphalt (unoxidized asphalt), and 45, less preferably 40-50, less preferably 35-55, less preferably 30-60, less preferably 25-70, percent oxidized (or blown) asphalt. Less preferably the asphalt component can be 100% oxidized or 100% unoxidized asphalt. The asphalt component preferably has a ring and ball softening point of 65-130, more preferably 69-110, more preferably 72-100, more preferably 75-90, more preferably 77-82, °C. The unoxidized asphalt is preferably a product sold by Sun Refining under the name MONOR. Oxidized asphalt, also known as blown asphalt, is asphalt and is produced by blowing air through asphalt at 400-600° F. followed by cooling. Raising the proportion of oxidized asphalt will raise the softening point of the finished dispersion product.
The fatty acid agent, which is optional, is fatty acids, fatty acid esters, or a mixture thereof. Most preferably, the fatty acid agent is stearic acid because of its compatibility with the majority of rubber compounding formulations, as well as its lubricity. The stearic acid preferably has an acid value in the range of 193-212, and a maximum iodine value of 10. Less preferably, the fatty acid agent is oleic, palmitic, linoleic, or linolenic acid, or a mixture thereof. The fatty acid ester is preferably a triglyceride such as a hydrogenated triglyceride, such as Neustrene 060 from Humko Chemical Company. Other examples of suitable fatty acid esters include Promix 200FE from Flow Polymers, and WB212 from Struktol Corporation. The fatty acid agent is preferably uncrosslinked, and provides lubricity to the dispersion which aids mixing and subsequent extrusion. The fatty acid agent further aids wetting out of the calcium oxide powder, which aids incorporation of calcium oxide powder into a rubber compound by reducing the friction coefficient between the powder and the rubber compound.
The plasticizer component, which is optional, is any known rubber processing oil, wax or softening agent compatible with hydrocarbon dispersions. Preferred plasticizers are paraffinic oil (such as Sunpar 2280 from Sun Refining or Stanlube from Harwick Chemical Company), naphthenic oil (such as Calsol from Calumet Lubricants), aromatic oil (such as Sundex from Sun Refining), pine tar (such as Tartac from CP Hall), paraffin wax (such as 130WAX from Akrochem), or polyethylene wax (such as PE 617A from Allied Signal). Less preferably, the plastic
Cain Edward J.
Flow Polymers, Inc.
Pearne & Gordon LLP
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