Silicone rubber bladder coating system as a process aid for curing tires.Tire curing bladders undergo some of the most abusive operating conditions. These include high temperatures, severe flexing, co-vulcanization and migration of curatives from the unvulcanized tire. Its productive lifetime is a major influence on the operating efficiency of a tire plant. This article will describe room temperature vulcanized vul·ca·nize tr.v. vul·ca·nized, vul·ca·niz·ing, vul·ca·niz·es To improve the strength, resiliency, and freedom from stickiness and odor of (rubber, for example) by combining with sulfur or other additives in the presence of heat silicone rubber Noun 1. silicone rubber - made from silicone elastomers; retains flexibility resilience and tensile strength over a wide temperature range synthetic rubber, rubber - any of various synthetic elastic materials whose properties resemble natural rubber as it is currently used to extend bladder life. Bladder coatings are applied to new bladders before they are installed in the tire press. Starting from the very first tire, the extremely anti-adhesive surface property of the silicone rubber protects the bladder from co-vulcanization and allows easy separation of the vulcanized tire after processing. Without a bladder coating, release comes from an inside tire release agent. Inside tire release agents are sprayed in the interior of an uncured tire before it is pressed and vulcanized. After each cure, a release film is transferred from the sprayed tire to the new bladder. Sufficient coverage on the bladder may require up to 60 cure cycles. Without the bladder coating, the productive lifetime of a new bladder is dependent on the coverage of the release agent sprayed inside each tire. If the release agent is not well atomized and coverage is poor, the unsprayed areas would cross-link and polymerize polymerize /po·lym·er·ize/ (pah-lim´er-iz) to subject to or to undergo polymerization. pol·y·mer·ize v. To undergo or subject to polymerization. to the new bladder. The bladder coating is formulated with dimethyl polysiloxane di·meth·yl pol·y·si·lox·ane n. A polymer composed of alternating silicon and oxygen atoms and having two methyl groups attached; it can, depending on molecular weight, have properties ranging from oils to plastics. lubricants lubricants preparations for the lubrication of passages to reduce frictional injury, e.g. oily preparations, including petroleum jelly, lanolin or water-soluble preparations such as methyl cellulose. , but at quantities not enough to provide continuous lubrication lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid, semisolid, or solid—that permits free action of beyond several cures. Both lubrication and air bleed Printing at the very edge of the paper. Many laser printers, including all LaserJets up to the 11x17" 4V, cannot print to the very edge, leaving a border of approximately 1/4". In commercial printing, bleeding is generally more expensive, because wider paper is often used, which is later are supplied from a variety of available water based silicone silicone, polymer in which atoms of silicon and oxygen alternate in a chain; various organic radicals, such as the methyl group, CH3, are bound to the silicon atoms. emulsions blended with fillers, such as mica, talc and clay. The lubricant Lubricant A gas, liquid, or solid used to prevent contact of parts in relative motion, and thereby reduce friction and wear. In many machines, cooling by the lubricant is equally important. is formulated for specific customer requirements unique to the type of tires and their process. The bladder coating is therefore part of a system whereby the lubricant is applied either inside the unvulcanized tire or directly on the bladder. Between the bladder and the tire, the coating, together with the lubricant, provides excellent release slip, and air bleed. This article will review lab work that characterizes the performance of the bladder coating with various lubricants. Studies were conducted to establish release, lubricity lu·bric·i·ty n. The quality or condition of being lubricious. [Late Latin l  bricit and abrasion abrasion /abra·sion/ (ah-bra´zhun)1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. resistant properties of silicone rubber as a coating to tire curing bladders. These properties were evaluated using repetitive cure cycles with unvulcanized butyl butyl /bu·tyl/ (bu´t'l) a hydrocarbon radical, C4H9. bu·tyl n. A hydrocarbon radical, C4H9. butyl a hydrocarbon radical, C4H9. innerliner and chafer chafer Any of several species of scarab beetle (most in the subfamily Melolonthinae). Adult leaf chafers (genus Macrodactylus) eat foliage; the female deposits her eggs in the soil, and the larvae live underground for years, feeding on plant roots. compounds. The method does not flex nor stretch the butyl material, but utilizes similar temperatures, cure times and pressure conditions to those in the production of passenger tires. This article will describe the performance of the bladder coating with and without inside tire release agents using ten-minute cures at 360oF. Migration of curatives from the chafer compound is shown to be severe to both the butyl bladder and the silicone rubber coating. Experimental Materials The evaluation of the bladder coating was carried out with a curing bladder compound from an undisclosed tire company. Even though the actual formula is not revealed, it is a recipe (ref. 1) typical and representative of the current industry (table 1). Stocks of the halobutyl innerliner and the two chafer compounds were also supplied from the same undisclosed company. The halobutyl innerliner formula is proprietary, whereas the unrevealed chafer formulas are typical recipes (ref. 2) which can be found upon a search of industry technical literature (tables 2 and 3).
Table 1 - curing bladder recipe
Ingredients Parts
Exxon butyl 268 100
Neoprene W 5
HAF black (N-330) 55
Castor oil(*) 5
Zinc oxide 5
SP 1045 resin 10
(*) The use of castor oil is shown in U.S. patent
No. 3,031,423 assigned to the Goodyear Tire & Rubber
Company
Rheometer at 190 [degrees] C (374 [degrees] F)
ts 1 minutes 3.5
t'c (90) minutes 20.0
Press cure, minutes 20
Cure temperature, 190 [degrees] C (374 [degrees] F)
[degrees] C ([degrees] F)
Stress at 300%, MPa (psi) 4.8 (700)
Tensile strength, MPa (psi) 12.8 (1,850)
Elongation, % 720
Hardness, Shore A 68
Table 2 - passenger tire chafer recipe
Raw material class Raw material type Ingredients Parts
Polymers Natural rubber TSR 20 65.0
Polymers SBR SBR 1500 20.0
Polymers Polybutadiene Buna CB 11 15.0
Filler Carbon black N330 60.0
Plasticizer Aromatic process
oil ASTM #101 8.0
Activators Zinc oxide Kadox 920 4.0
Activators Stearic acid Industrene R 1.8
Antidegradants Antioxidant TMQ 1.0
Antidegradants Antioxidant/ 6PPD 1.0
antiozonant
Resin Options Tackifier resin Hydrocarbon
resin 2.0
Total master 177.8
Master Master 177.8
Accelerator Delayed action CBS 0.7
sulfenamide
Sulfur Rubbermakers Harwick #104 2.5
Reinforcing resin Modified phenolic Schenectady SP 3.0
resin 6601
Total finish 184.0
Table 3 - truck tire chafer recipe
Raw material class Raw material type Ingredients Parts
Polymers Natural rubber TSR 20 75.0
Polymers Polybutadiene Buna CB 11 25.0
Filler Carbon black N339 60.0
Plasticizer Aromatic process
oil ASTM #101 5.0
Activators Zinc oxide Kadox 920 5.0
Activators Stearic acid Industrene R 2.0
Antidegradants Antioxidant TMQ 1.0
Antidegradants Antioxidant/ Diaryl 6PPD 0.8
antiozonant
Resin Options Tackifier resin Hydrocarbon
resin 2.0
Total master 75.8
Master Master 175.8
Accelerator Delayed action MBS 1.6
sulfenamide
Sulfur Rubbermakers Harwick #104 2.9
Total finish 180.3
Bladder coating VP- 1069 is a one component, room temperature vulcanizing product imported from Wacker Wacker may refer to:
n. One that fills, as: a. Something added to augment weight or size or fill space. b. A composition, especially a semisolid that hardens on drying, used to fill pores, cracks, or holes in wood, plaster, dispersed dis·perse v. dis·persed, dis·pers·ing, dis·pers·es v.tr. 1. a. To drive off or scatter in different directions: The police dispersed the crowd. b. in naphtha naphtha (năp`thə, năf`–), term usually restricted to a class of colorless, volatile, flammable liquid hydrocarbon mixtures. to 47 percent solids by weight. The water based inside tire release agents are products from Wacker Silicones. Water based inside tire release agent "A" is similar, but is not a Wacker product. Testing The butyl bladder stock was cured at 375oF for 15 minutes into 6 x 6 x 0.075 inch panels. Prior to coating, these were wiped clean with xylene xylene (zī`lēn) or dimethylbenzene (dī'mĕthəlbĕn`zēn), C6H4(CH3)2 and allowed to dry afterwards af·ter·ward also af·ter·wards adv. At a later time; subsequently. afterwards or afterward Adverb later [Old English æfterweard] Adv. 1. for at least 24 hours. Clean panels were coated by dipping them in solutions of the bladder coating (3 parts to 2 in toluene toluene (tōl`y  ēn') or methylbenzene (mĕth'əlbĕn`zēn), C7H8 by weight). The solvent was vaporized va·por·ize tr. & intr.v. va·por·ized, va·por·iz·ing, va·por·iz·es To convert or be converted into vapor. va by placing these newly coated panels in a forced-air oven at 215 [degrees] F for 15 minutes. The coating on the bladder was then allowed to air cure under ambient conditions for at least 48 hours before using the panels. With this method, the average dry coat weight is approximately 50 grams per square meter Noun 1. square meter - a centare is 1/100th of an are centare, square metre area unit, square measure - a system of units used to measure areas . That is about two mills thick (50 microns), comparable to the amounts applied on bladders in the field. The water based inside tire release agent was brushed on precut pre·cut adj. Cut into size or shape before being marketed, assembled, or used: precut fillet of fish; precut construction materials. tr.v. calendered cal·en·der n. A machine in which paper or cloth is made smooth and glossy by being pressed through rollers. tr.v. cal·en·dered, cal·en·der·ing, cal·en·ders sheets of unvulcanized halobutyl innerliner and chafer stocks. These sheets are 5-3/4 inch squares and are 1/10th of an inch thick. The coating was air dried at room temperature for at least 24 hours. The cure-release-lubricity experiments are under conditions similar to those in a tire mold. The lack of stretching and flexing, however, reduces the severity of this test. In a four cavity mold, a fresh unvulcanized innerliner was replaced on each bladder panel after a 10 minute cure at 360oF and 139 pounds per square inch Noun 1. pounds per square inch - a unit of pressure psi pressure unit - a unit measuring force per unit area . The lubricity between the liner and the bladder panel is measured after each cure cycle. The static and dynamic coefficients of friction were measured using Instrumentors slip/peel tester Model SP-101B at 360oF, with a speed of 12 inches per minute under a sled pressure of seven pounds per square inch. The process is repeated until all cure cycles are completed. With six minutes to run lubricities, the total heat exposure time after 100 cure cycles is equivalent to about 27 hours in an oven. Results and discussion Non-coated bladders tested with inside tire release agents Figure 1 shows the lubricity results from each of four experiments run together between non-coated bladder panels and the halobutyl innerliners pre-coated with inside tire release agents "A", E255, XE529503 and E268. The unvulcanized halobutyl innerliner averaged a dry coat weight of 55 grams per square meter of inside tire paint. The average and standard deviation In statistics, the average amount a number varies from the average number in a series of numbers. (statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. for these results are recorded in the legends of the figure. For the non-coated bladders, the orders from the most to the least lubricious lu·bri·cious also lu·bri·cous adj. 1. Having a slippery or smooth quality. 2. Shifty or tricky. 3. a. Lewd; wanton. b. Sexually stimulating; salacious. are as follows: Static: E268 [much greater than] E255 [is greater than] XE529503 [is greater than] "A" Dynamic: E268 [much greater than] "A" [approximately equals] E255 [is greater than] XE529503 [Figure 1 ILLUSTRATION OMITTED] Coated bladders tested with inside tire release agents Figure 2 shows results between coated bladders released against "A", E255, XE529503 and E268. For the coated bladders, the orders from the most to the least lubricious are as follows: Static: E268 [much greater than] E255 [is greater than] XE529503 [approximately equals] "A" Dynamic: E268 [much greater than] "A" [approximately equals] E255 [approximately equals] XE529503 [Figure 2 ILLUSTRATION OMITTED] Tables 4 and 5 show that there are no significant differences in lubricities whether we have a non-coated or a coated bladder panel. These results confirm that the lubricity is primarily controlled by the type of adjuvant adjuvant /ad·ju·vant/ (aj?dbobr-vant) (a-joo´vant) 1. assisting or aiding. 2. a substance that aids another, such as an auxiliary remedy. 3. applied to the innerliner.
Table 4 - static coefficient of friction
Cured butyl bladder Unvulcanized halobutyl innerliner
panels E268 E255
Non-coated 0.13 [+ or -] 0.11 0.26 [+ or -] 0.09
VP1069 coated 0.17 [+ or -] 0.08 0.27 [+ or -] 0.07
Unvulcanized halobutyl innerliner
Cured butyl bladder XE529503 "A"
panels
Non-coated 0.35 [+ or -] 0.11 0.43 [ + or -] 0.19
VP1069 coated 0.42 [+ or -] 0.15 0.48 [ + or -] 0.22
Table 5 - dynamic coefficient of friction
Cured butyl bladder Unvulcanized halobutyl innerliner
panels E268 "A"
Non-coated 0.05 [+ or -] 0.02 0.14 [+ or -] 0.02
VP1069 coated 0.05 [+ or -] 0.02 0.17 [+ or -] 0.02
Unvulcanized halobutyl innerliner
Cured butyl bladder E255 XE529503
panels
Non-coated 0.16 [+ or -] 0.02 0.22 [+ or -] 0.02
VP1069 coated 0.20 [+ or -] 0.02 0.23 [+ or -] 0.02
Coated bladders tested with unvulcanized butyl innerliner and chafer stocks To determine chemical compatibility effects to the bladder from unvulcanized linerstock, the cure-release-lubricity experiment was repeated with no inside tire paints. Figure 3 and table 4 show the results between coated bladders released against non-coated halobutyl innerliner, passenger and truck tire chafer compounds. The orders from the most to the least lubricious are as follows: Static: Passenger chafer approximately equals] butyl innerliner [is greater than] truck chafer Dynamic: Passenger chafer [approximately equals] butyl innerliner [is greater than] truck chafer [Figure 3 ILLUSTRATION OMITTED] After a number of successive cure cycles, the clear bladder coating gradually changed to a translucent translucent slightly penetrable by light rays. white coating. The initially resilient silicone rubber coating gradually changed to a much softer gel-like consistency. The order in which such changes were induced by the unvulcanized stocks are as follows: Truck tire chafer [much greater than] passenger tire chafer [is greater than] halobutyl innerliner Compatibility and abrasion resistance As with unvulcanized stocks, migrating components from inside tire release agents can plasticize plas·ti·cize tr. & intr.v. plas·ti·cized, plas·ti·ciz·ing, plas·ti·ciz·es To make or become plastic. plas the bladder coating. Due to this process, the coating is gelatinous gelatinous /ge·lat·i·nous/ (je-lat´i-nus) like jelly or softened gelatin. ge·lat·i·nous adj. 1. Of, relating to, or containing gelatin. 2. Resembling gelatin; viscous. and can easily be frayed fray 1 n. 1. A scuffle; a brawl. See Synonyms at brawl. 2. A heated dispute or contest. tr.v. frayed, fray·ing, frays Archaic 1. To alarm; frighten. 2. off. Figure 4 shows lubricity results between coated bladders released against four variations of an experimental inside tire release agent, XE529602. These products were formulated with different lubricants and tested for compatibility with the bladder coating. The cure-release-lubricity experiments were continued until the coating abraded off. For lubricants in B and C, the abrasion to the coating was severe enough that the coefficient of friction coefficient of friction n. pl. coefficients of friction The ratio of the force that maintains contact between an object and a surface and the frictional force that resists the motion of the object. started to increase after 120 cures. Lubricants in formulations A and D are much more compatible where the number of cures exceeds 240 cures before any noticeable changes are observed. This method proved an effective screening tool for the evaluation of new products with the bladder coating. [Figure 4 ILLUSTRATION OMITTED] Cure-release-lubricity experiments versus heat aging The cure-release-lubricity experiments were compared against the heat aging process in a forced air oven. The basic principle of the heat aging test is to expose the cured butyl bladder panel to an elevated air temperature for a specified period in a forced air oven. The deterioration of rubber in an air oven is due to the combined effects of oxidation oxidation /ox·i·da·tion/ (ok?si-da´shun) the act of oxidizing or state of being oxidized.ox·idative ox·i·da·tion n. 1. The combination of a substance with oxygen. 2. and thermal aging. 50 hours at 360 [degrees] F in a forced air oven is estimated to be more severe than the total heat exposure after 300 cures on a bladder in a typical tire plant. Unlike our test panels in a forced air oven, the steam side of a bladder is at 360 [degrees] F, whereas the cooler outer surface is exposed to air only when the mold is open. For all cure-release-lubricity experiments the elongations are determined and compared to their original values. Figure 5 shows that elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. decreases over a 50 hour period at 360 [degrees] F for both coated and non-coated bladder panels. After 27 hours in a forced air oven, the elongation shows a small difference between coated, 2.8 [+ or -] 0.1, and non-coated panels, 2.6 [+ or -] 0.1. Experiments with inside tire paints show a similar effect, but with more overlap between coated 3.1 [+ or -] 0.4, and non coated panels, 2.9 [+ or -] 0.4. The differences between the unvulcanized innerliner stocks are significant. On one extreme, the total absences of exposure to any unvulcanized stocks represent a pair of controls. One control is the top "T" and the other is the bottom "B" butyl bladder panel which were together in the same cavity of the mold during the cure-release-lubricity experiment. Controls "T" and "B" average at 3.5 [+ or -] 0.3, whereas, passenger and truck chafer stocks average 2.4 [+ or -] 0. I. The halobutyl innerliner results are slightly less than controls "T" and "B" at 3.1 [+ or -] 0.3. To summarize, the bladder coating exhibits some degree of protection from oxidation to the bladder panels. On the left charts of figure 5, the coated panels show that elongation is retained longer. The diffusion of air through the silicone film delays the oxidation process. It can be seen that as oxidation is allowed to continue, changes in the elongation converge with those of non-coated bladder panels after 50 hours. The bottom right chart of figure 5 shows that another process other than oxidation strongly influences the property of the bladder. Exposures to chafer compounds show a higher loss of elongation than from heat aging. The high curative curative /cur·a·tive/ (kur´ah-tiv) tending to overcome disease and promote recovery. cu·ra·tive adj. 1. Serving or tending to cure. 2. levels in these compounds are most likely responsible for the rapid aging to both the bladder and the bladder coating. Summary From this work it has been determined that experimental data can be employed to develop an effective bladder coating system. Even though the bladder coating, together with a water based silicone emulsion emulsion: see colloid. emulsion Mixture of two or more liquids in which one is dispersed in the other as microscopic or ultramicroscopic droplets (see colloid). Emulsions are stabilized by agents (emulsifiers) that (e.g. , improves bladder life up to 100% longer in the field, the migration of curatives from unvulcanized tires remains the most demanding challenge. For higher performance, developments will focus on systems not only more resistant to migrating components, but also formulated with the intention of eliminating volatile organic carbons. These systems may eventually include a product at 100% solid or an all water based system.
Table 6 - coefficient of friction with no inside
tire paints
Coefficient of VP1069 coated cured butyl bladder panels
friction Passenger Butyl innerliner Truck
chafer
Static 0.57 [+ or -] 0.10 0.59 [+ or -] 0.11
Dynamic 0.45 [+ or -] 0.06 0.46 [+ or -] 0.06
Coefficient of VP1069 coated cured butyl bladder panels
friction Butyl innerliner Truck
chafer
Static 0.72 [+ or -] 0.09
Dynamic 0.55 [+ or -] 0.07
References [1.] W.H. Waddell, R.S. Bhakuni, W.W. Barbin and P.H. Sanetrom, "Pneumatic tire Noun 1. pneumatic tire - a tire made of reinforced rubber and filled with compressed air; used on motor vehicles and bicycles etc pneumatic tyre bicycle wheel - the wheel of a bicycle compounding," Vanderbilt Rubber Handbook, 13th ed. (1990). [2.] Smithers Smithers is a surname, and may refer to: People People with the surname Smithers
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