The development of a one-part heat curable urethane precure retread adhesive.

The retreading of tires consists of their "remanufacture" allowing additional lifetimes to be realized by the tire product by replacing the tread portion of the tire. Early retreading offered an economically attractive alternative to the purchase of a new tire, but in many cases these products suffered from inconsistent service lives. This placed the product as undesirable from the view of the consumer. In the last several decades the quality of retreaded tires has risen to be that rivaling the performance of new tires.

The initial technology used to retread tires involved removing the remaining tread from the used tire casing by cutting or grinding. In this case an uncured rubber strip was typically wound onto the prepared casing. The rubber was shaped and adhered to the casing by "recuring" the tire at temperatures similar to that of the original tire cure in a tire matrix. This resulted in the designation of this process as mold cure. Later, a concept was developed of curing a tread separate from the prepared casing and using an adhesive or tie gum to adhere the tread onto the casing. The "precure" concept made popular in the 1960s allowed additional flexibility to the tire retreader in several aspects of the retreading process.

In the evolution of retreading, many incremental improvements have been made to both processes. The use of a single uncured rubber strip or "camel back" in mold cure retreading provided advantages to this technology. In the area of precured retreading, the development of new adhesives and curing methods provided products having higher quality and increased durability.

Currently, the most practiced art of precure tire retreading typically involves the adhering of a cured rubber tread onto a prepared tire casing using a natural rubber based adhesive or tie gum. The tire casing is prepared by the removal of the remaining tread by the use of a rotary rasp (buffing). A rubber cement is usually applied to the "buffed" tire casing to provide building tack. A precured tread, having a rubber cement applied during its manufacture is cut to the appropriate length to fit the tire casing. The adhesive, prepared as a calendered sheet, is applied to the rubber cement coated side of the tread. The tread/adhesive composite is placed on the tire casing with the tie gum placed against the rubber cement of the tire casing. The tire is placed in a rubber curing bag (envelope), the envelope is sealed against the tire beads and the tire is placed in a heated and pressurized autoclave to effect the curing of the adhesive.

A possible improvement to the precure retreading system would include an adhesive that could be applied in liquid form that might be cured at lower times, temperatures or pressures. This process would have the possibility of dramatically changing the processing of tires in a retreading operation.

It is typically necessary to chemically modify the surface of rubber prior to the application of liquid adhesives. This process, sometimes referred to as priming (as in metal-to-rubber adhesion), is performed to increase the wetting of the rubber surface by liquid adhesives.

The modification of polymer surfaces is a topic worthy of an extensive review in itself (ref. 1). Such modification of polymer surfaces includes the treatment of polymer surfaces by flame, plasma, corona discharge, W energy and chemical compounds. Such chemical compounds include reactive gases like ozone, liquids such as acids, bases, isocyanates and peracids, and solids like peroxides, hydantoins, triazine triones and other oxidizers such as potassium permanganate. Also included are sensitizers that catalytically produce reactive species such as that of singlet oxygen produced by organic dyes such as rose bengal.

Of concern in the selection of a surface modification system in a tire retreading system would be the toxicity, effectiveness and speed of reaction, industrial applicability, environmental friendliness and safety.

It is well known that rubber surfaces typically tend to revert to near the original properties after modification by most treatments. In this process known as reconstruction (ref. 2), the moieties created on the surface of the polymers replate into the bulk polymer, reducing the effectiveness of the treatment. A treatment of choice would reduce the mobility of the rubber surface, thus minimizing its reconstruction.

The work of W. Walles and D. Nagy (ref. 3) is also a cause for concern. They showed that many of the candidate compounds shown to be effective as treatment agents if combined with an improper solvent or carrier liquid can result in an explosive mixture.

The work of Martin-Martinez, et. al. (ref. 4) showed the use of a triazine trione in methyl ethyl ketone provided an acceptable treatment (priming) that apparently did not allow the reconstruction of the surface of styrene butadiene rubber (SBR). Work in our laboratory using this system of treatment showed an apparent embrittlement of the rubber surface at high treatment levels. Treatment of rubber surfaces with this material typically resulted in the formation of flake-like structures at the rubber surface. This was assumed to be excess trione that had recrystallized on the surface of the rubber.

In the area of development of novel adhesives for the purpose of retreading tires, there are two examples of merit.

The initial work in this area was performed by a group at Firestone Tire & Rubber Co., W. Haush and R. Koch (ref. 5), utilizing a polyurea based adhesive modified to allow its curing at room temperature. The adhesive was based on a mixture of prepolymers derived from polyether polyols (Adiprene 367 and/or Adiprene 42) and cured with aromatic diamine/salt complex suspended in dioctylphthalate (Caytur). In order to allow the curing reaction to proceed at room temperature, a polar solvent (acetone) is added to the Caytur to aid in the breaking of the complex which allows the material to react at higher rates at a given temperature.

This system required the pretreatment of the surfaces of the tread and casing with an oxidizing/chlorinating solution of a triazine trione in an inert solvent (butyl acetate).

Particular to this method is the preparation of the adhesive prior to building of the tire. The adhesive is prepared by mixing two components and allowing the adhesive to gel for up to 45 minutes. At this time the adhesive is divided and half is applied to the precured tread and half to the tire casing. The adhesive covered rubber surfaces are then brought into contact with each other and the tread held in place against the tire casing.

The tires prepared by this method were cured for the most part at room temperature with a final step of curing at an elevated temperature under pressure for a period of time. No performance data are provided for tires cured using this technique.

A later advance in this area was by S. Swanson of H.B. Fuller (ref. 6). The adhesives claimed in this work are based on polyether prepolymers and aliphatic polyamines and aromatic diamines. The main advantages realized in this work are those relating to the apparent improvements in the adhesive system. Although specific examples of the adhesive strength between the adhesive and rubber are given, there are no performance data on tires built using this adhesive system. Again, the use of a pretreatment of the rubber surfaces prior to the application of the adhesive is preferred in this invention.

The advantage of these systems was their ability to cure at room temperature. However, both of the adhesive systems consist of two parts that must be accurately dispensed and adequately mixed prior to their application to rubber. These requirements may be considered as a disadvantage in the use of such an adhesive in retreading tires due to the cost and maintenance of such mixing/application equipment. Also the time between mixing and the onset of cure of these materials is short enough to preclude their use with most existing precure retreading equipment systems.

In the work described in this article, one-part urethane adhesives based on a polyester and polyether prepolymers and insoluble polyhydroxyl compound (ref. 7) were implemented to allow the retreading of tires. These materials must be cured at elevated temperatures, but have the advantage of not requiring any mixing and are stable at room temperature, which would allow their use with existing precure retreading systems.

Included is the evaluation of several types of materials to affect the modification of rubber surfaces to allow improved wetting of the rubber surfaces by the adhesives. As tire performance was a major issue in this work, initial steps of developing a commercially feasible tire manufacturing process were also addressed.

Experimental

Materials

All materials were used as received. The one-part polyurethane adhesives were kept frozen until just prior to use. This included UR-1100, TL02 and all the candidates from the experimental design. All solvents used were ACS grade or equivalent. All chemicals were used as received from the manufacturers.

Precured treads

The precured treads were used as received from a Bandag manufacturing plant, except the cement layer was removed by twice buffing using drum brushes. The buffed surfaces of the treads were protected by covering them with a layer of polyethylene until just prior to use.

Tires

The tires used in this evaluation were new Bridgestone tires of the appropriate size as required by the application. The use of new tires was preferred to attempt to maintain a constant tire compound composition among experimentals placed in a particular application. Differences in tread and under tread composition were feared to affect the rubber treatment process.

Equipment

All tires were built on a "Shorty" Brannick EF spreader. The tires were cured in standard Bandag 11 or 22 tire chambers or a special five tire chamber built for this purpose. Prior to curing, the tires were placed in standard Bandag curing bags (envelopes) of the appropriate size. For radial tires the Bandag ARC system was used and for bias tires the Bandag Rim and Tube (RAT) system was used to seal the envelopes against the tire beads.

Procedures

Design of experiments

In the example cited in the text for the study of the tire building process variables, a full factorial design of experiments was employed. The RS1 statistical package obtained from BBN Software Products was used to design the experiment and analyze the data.

In the adhesive optimization example cited in the text, a proprietary design of experiments was used and it was analyzed using the RS1 software package.

Tire building

The tire building procedures varied slightly during the completion of the experimentation, but were comprised of the following basic steps:

* Removal of the tread from the tire using a rotary rasp.

* Cutting a precured tread to a length suitable to fit the casing (see above for tread preparation).

* Applying the pretreatment agent to the surface of the tread and the casing.

* Applying adhesive to the surface of the tread and the casing.

* Applying the tread to the casing by mating the adhesive covered surfaces.

* Placing the ends of the tread in contact with each other and holding the ends in place by stapling.

* Applying several layers of perforated poly film over the tread.

* In most cases, placing a perforated rubber sleeve on top of the poly was employed to aid in holding the tread in place on the casing during the process of the application of the envelope.

* Placing the composite in a tire curing envelope of the appropriate size.

* Sealing the envelope against the tire beads using the appropriate device (see above).

* Curing the tire at the appropriate temperature for the appropriate time. For the one-part urethane adhesives, this was typically 100 [degrees] C for four hours. For the Adiprene based adhesives, ambient temperature was used at the start of the cure and was slowly increased over the 22 hour cure to approximately 35 [degrees] C.

Grooved slick tire building method

In this method a solid piece of rubber (no pattern) was used as the tread. A rib pattern was cut into the tread using a hot knife after curing of the adhesive.

This method was used to build tires for the dedicated trailer test comparing UR-1100 and TL02. A method comprising most of these elements was used to build tires for the comparison of UR-1100, EXP3 and EXP7.

Tire building method (reretreading method)

This was a method that would allow placing patterned tread on the tire without grooving. First the tire was prepared as per the grooved slick method, except no pattern was cut into the tread. A major portion of the new tread was then removed using a rotary rasp. The tire was then "retreaded" using a precured tread and conventional materials.

This method was used to build tires for the nondedicated testing where UR-1100 was compared to TL02.

Tire building method (direct retreading)

In this method the tire is built using the described method using a patterned tread. The tire is placed in the curing chamber and the curing cycle is begun. At a time when the adhesive at the edges of the tread begin to cure, air is injected between the void areas of the tread under the curing envelope.

This method was used to build the tires used for the road wheel evaluation of UR-1100 versus the Adiprene adhesives.

Tire testing - road wheel

The protocol developed for the road wheel testing of the tires was a modified DOT-119 test. The conditions for the test included using the full rated single axle load for the duration of the test, using the specified single axle pressure and testing the tires at 56 kilometers (35 miles) per hour. The tires were allowed to equilibrate at the road wheel room temperature of 38 [degrees] C (100 [degrees] F) for 24 hours prior to testing.

Tire testing - over the road dedicated testing

The dedicated trailer testing was performed at Texas Test Fleet (Devine, TX), with a trailer loaded to the maximum allowable load. The tires used were 11R24.5s prepared using the grooved slick method.

Tire testing - over the road nondedicated testing

The nondedicated testing of tires was performed by placing tires in drive positions at local fleets and monitoring the performance of the tires on at least a monthly basis. All tires were run to wearout or failure unless otherwise indicated.

Adhesion test - 180 [degrees] peel

The adhesion test used in this work was a 5.08 centimeter (2 inch) 180 [degrees] peel test using a 1.27 centimeter (0.5 inch) thick rubber stock. The contact area of the rubber to the adhesive specimen was 1.27 centimeters (0.5 inches) wide. The specimens were failed at 25.4 centimeters (10 inches) per minute at ambient, at 82 [degrees] C (180 [degrees] F) or at 100 [degrees] C (212 [degrees] F).

Adhesion test - lap shear

The adhesion test used in this work was a 5.08 centimeter (2 inch) lap shear test using a 1.27 centimeter (0.5 inch) thick rubber stock. The contact area between the rubber and the adhesive was 1.27 centimeters (0.5 inches) wide and approximately 5.08 centimeters long. The specimens were tested at 25.4 centimeters (10 inches) per minute at ambient temperature.

Adhesion test - butt-splice flex

The durability of the adhesive composites prepared as part of an experimental design were evaluated using a butt-splice flex machine. This machine was built in-house and employed a rocking action (flex) to place a stress on the adhered portion of the specimen. The specimens were constructed by adhering two 1.25 by 10 by 5 centimeters pieces of rubber to provide a specimen 1.25 by 5 by 20 centimeters (figure 1). The specimens were considered failed when at least one half of the surface area of the bondline was exposed.

[Figure 1 ILLUSTRATION OMITTED]

Discussion

In a project of this nature, several technologies had to be developed simultaneously. The selection of the rubber primer system, the development and the evaluation of the adhesives, development of tire building methods and development of testing protocols were all important to the development of the successful product. These will be presented separately in the following text.

Primer system development

The selection criteria of the most desirable primer system for treating the rubber surfaces would include high reactivity (rate and amount) and high longevity of the effect of the treatment. Also in consideration in the selection of this system is the possible undesirable reaction with the brass coating of the tire cord. In a majority of retreaded tires some belt or carcass wire is exposed prior to the application of the tread, so this was of a major concern.

The first step of the primer development was a screening process to evaluate the peel and lap shear adhesions of several rubber/primer/adhesive composites. As the adhesive had not been optimized at this point in time, cohesive failure of the adhesive or tearing into the rubber substrate would suffice as a pass at this level. Table 1 lists the lap shear adhesions of several candidate compounds that were applied from dichloromethane solutions/suspensions. In all cases UR-I 100 was used as the adhesive.

Table 1 - primer system evaluation using lap shear adhesion tests

     Primer                       Adhesion (std. dev.) (MPa)

1,3 dichloro-5,5 dimethyl                       2.69 (0.15)
  hydantoin
n-bromomethyl phthalimide                       2.27 (0.13)
n-iodo succinimide                             2.42 (0.072)
n-chloromethyl phthalimide                     1.88 (0.099)
n-bromo phthalimide                             2.00 (0.17)
l-(cis-3 dichloroallyl)                         1.11 (0.19)
  3,5,7,triaza-1-azonia
  adamantane chloride

As shown in table 1, several candidate primers had acceptable adhesion. The 1,5 dichloro 5,5 dimethyl hydantoin had the highest average strength, but was not statistically different from that of n-bromomethyl phthalimide or n-iodosuccinimide. Additional testing showed that the hydantoin had the most reproducible performance and was thus selected as the primer to be used for this work.

In order to determine the effect of process variables on the adhesion of the rubber/primer/adhesive composite a designed experiment was performed. In this experiment the factors used were the presence of primer (0% or no treatment and 5%), the presence of water (0% and 0.1% by weight of adhesive), aging of the adhesive prior to curing (0 and 180 minutes) and a rubber surface treatment (rough or smooth rubber surface). The strength of the composites was measured at ambient temperature, 82 [degrees] C (180 [degrees] F) or at 100 [degrees] C.

The presence of water was examined in order to determine the possible effect of the application of thin layers of adhesive under humid conditions. To simulate this condition water was mixed into the adhesive just prior to application. The aging of the adhesive composite from the time of assembly to that of curing was performed in order to determine if any change in composite strength would be realized by delaying the cure of an assembled tire. The question of composite strength as a function of substrate surface roughness is always an issue in adhesion. In this case the surface of the rubber was varied from a rough buff as produced using a rotary rasp (RMA 2 or 3) to a very smooth buff surface as produced by buffing with a wire brush.

The primer used in the study was a 5% solution of 1,3 dichloro 5,5 dimethylhydantion in methylene chloride.

The RS1 program was used to analyze data obtained at each of the three temperatures using linear regressions on the three continuous variables, water, primer and aging and the one categorical variable, rubber surface. First order interactions were included in all the models. All continuous variables are scale orthoganalized for modeling purposes.

The linear model obtained at ambient temperature (table 2) shows a high inherent strength of the composite with an intercept of 1.168 MPa. As expected, there was a large positive effect on composite strength by the presence of primer as shown by its large coefficient. It is interesting to note that the presence of water contributed to an increase in strength in the composite by its presence in three terms of the model. The reaction of the adhesive with water would have resulted in a coupling of the prepolymer, doubling its molecular weight and decreasing the number of crosslinker-prepolymer bonds. This should have decreased the modulus of the adhesive which would have been expected to result in a decrease in adhesive strength of the composite. The strength of the composite was also shown to be larger with the use of a smoother buffed rubber. This also might have been expected as the rougher buff surface is achieved by more of a tearing away of the rubber from the surface, resulting in many more crack initiation sites (flaws) per unit area.

Table 2 - coefficient of adhesive process variable effects model produced at ambient temperature

Variable          Coefficient value    Standard        T-value
                              (MPa)       error

Intercept                     1.168      0.0231         50.63
Water                        0.0621      0.0231          2.69
Primer                        0.423      0.0231         18.34
Water x aging                0.0469      0.0231          2.03

Water x surface
treatment
Rough                       -0.0654      0.0231         -2.38
Smooth                       0.0654      0.0231          2.38

Primer x surface
treatment
Rough                        -0.141      0.0231         -6.12
Smooth                        0.141      0.0231          6.12

R-squared                     0.975

R-squared                     0.963
adjusted

The linear models obtained by modeling the data obtained at 82 [degrees] C and at 100 [degrees] C (tables 3 and 4) were interesting in that primer was not a significant contributor to the strength of the composites. The effect of buff texture at the higher temperatures is changed from the lower temperature with the rougher surface having the higher contribution to composite strength. At these temperatures the cohesive strength of the adhesive is low, and some of the composite failure appeared to be due to cohesive failure of the adhesive. The rougher buff rubber in this case might have enhanced the strength of the composite by putting rubber in the route of flaw propagation through the testing specimen (in the adhesive layer).

Table 3 - coefficients of adhesive process variable effects model produced at 82 [degrees] C

Variable          Coefficient value    Standard        T-value
                              (MPa)       error

Intercept                      0.91     0.00833          23.04
Surface
treatment
Rough                        0.0681     0.00833           8.18
Smooth                      -0.0681     0.00833           8.18

R-squared                     0.827

R-squared                     0.815
adjusted

Table 4 - coefficients of adhesive process variable effects model produced at 100 [degrees] C

Variable          Coefficient value    Standard        T-value
                              (MPa)       error

Intercept                    0.0835     0.00480          17.38
Aging                        -0.119     0.00480          -2.47
Surface
treatment
Rough                        0.0262     0.00480           5.45
Smooth                      -0.0262     0.00480          -5.45
Primer x surface
treatment
Rough                      -0.00890     0.00480          -1.85
Smooth                      0.00890     0.00480           1.85
R-squared                     0.766
R-squared                     0.707
adjusted

Tire building method development

In the progression of the experimentation, the tire building method evolved from an initial use of a solid tread (buildup), to that of a patterned tread (high speed).

In the initial work performed in the building of tires, it was noted that the adhesive had tended to gather or "pool" under the void areas of patterned tread. This was especially a problem with treads having a lug tread pattern. The "pools" of adhesive tended to act as the initiation sites for failure during tire testing. To eliminate the pooling of the adhesive, a nonpattern tread was used. This tread consisted of a rubber strip approximately 1.25 centimeters thick, cut to a width that would be appropriate for use with that casing. The use of a solid tread appeared to result in the application of relatively constant pressure across the width of the tread. This modification eliminated the adhesive pooling problem and allowed the construction of tires having uniform bondline thicknesses for subsequent testing. In order to facilitate testing of these tires, a tread pattern had to be carved into the tread. For matters of convenience, a rib pattern was hand carved into the solid tread. To describe the process, the method of tire building was called the "grooved slick" method.

As the tire testing progressed, there was a desire to test larger numbers of tires in more varied applications. In order to meet this need an alternate method of tire building was developed. In this method, the tire was initially retreaded with a slick tread using the liquid adhesive. After the tread was cured in place, the majority of the tread was removed by buffing and a patterned precured tread was "retreaded" in place over the remaining tread using the standard tie gum. In the second "retreading," thinner treads were used to insure a reasonable total tread thickness.

As the final progression in tire building, a method was developed to allow the direct retreading of patterned treads onto tire casings. In this method, the tire is constructed by placing the patterned tread directly onto the adhesive covered casing. The curing cycle of these tires is modified by allowing the adhesive at the edge of the tread to begin to cure and then injecting air between the voids of the treads and the envelope. In most cases this method was found to produce acceptable tires (no or little adhesive pooling).

Road wheel test development

The development of tire testing evolved from a DOT-I 19 road wheel test through selected placement of tires on trucks, to a more severe road wheel test to an aggressive evaluation of tires on trucks in varied applications. In order to increase the severity of the test over that of a DOT-I 19, the full rated load for a single axle application was employed at the start of the test. In most cases the tires were run to extended times, typically 96 or 122 hours.

Adhesive evaluation

The initial evaluation of adhesives consisted of the comparison of candidates from an experimental design using a buttsplice flex test as the main criteria to rank the performance of the adhesives. The evaluation of adhesives in tire applications consisted of three main portions, the evaluation of UR1100 versus EXP7 and EXP3, of UR-1100 versus TL02 using over the road testing and the evaluation of UR-1100 versus Adiprene based adhesives using road wheel testing.

Evaluation of adhesive experimental design candidates

In the development of the one-part urethane adhesives, an experimental design was employed to examine the effect of key compositional parameters of the adhesive on the performance of tires. In order to model the tire performance a buttsplice flex test was employed. A machine (figure 1) to perform the testing was fabricated and tested for reproducibility of specimen failure. Candidates from the experimental design were then used to prepare triplicate specimens and were tested to failure. The data when modeled did not show clear relationships between the fundamental variables of the experimental design and the flex life of the specimens. In order possibly to obtain a relationship for the predominant variable in the study, a limited tire test was initiated to rank two experimental adhesives (EXP3 and EXP7) and a commercially available product, UR-I 100.

Tire testing of UR-1100, EXP3 and EXP7

Again, the results of the experimental design using physical testing (flex test) as a screening tool did not point to any one adhesive formulation as being greatly superior to the others. Therefore, a limited "on the road" tire test was initiated. The tires were built using an early version of the grooved slick method and were placed on the drive positions of three line haul trucks. The trucks had two tires prepared with each of two adhesives and four controls (tires retreaded using gum cushion as the adhesive) as shown below:

   Truck     Adhesives
    #1    UR-1100 and EXP7
    #2    EXP7 and EXP3
    #3    UR- 1100 and EXP3

The examination of the tires showed acceptable performance from all adhesives, but there was significant "chipping" of the tread at the edges. Based on the appearance of the tread edges the adhesives were ranked UR-1100>EXP7 >>>> EXP3.

As a follow up to this experimentation, an evaluation of UR-1100 and EXP7 was conducted. At this point the scaled up production of EXP7 required that the designation of the adhesive be changed to TL02. In this study two trailers in a dedicated test run were equipped with tires prepared with the UR-1100 and TL02 adhesives. Each hub had a tire prepared with each of the adhesives (two tires per hub) with no gum cushion controls.

The results of this study (table 5) clearly showed the superiority of the UR-1100 adhesive in this application. Only two of the eight UR-1100 tires failed to complete the test, and these were removed due to road damage. Only two of the eight TL02 tires completed the test and none of these tires experienced road damage. As the TL02 tires failed, they were replaced with UR-1100 tires. All of the UR-1100 tires that replaced the TL02 tires completed the test with no failures.

Table 5 - evaluation of UR-1100 and TL02 on dedicated trailers at Texas Test Fleet

Adhesive       Accumulated distance      Tire failed?
                            (KM)

UR-1100                  116,000           No
UR-1100                  116,000           No
UR-1100                  116,000           No
UR-1100                  116,000           No
UR-1100                  116,000           No
UR-1100                  116,000           No
UR-1100                   89,000           Road damage
UR-1100                   88,000           Road damage

TL02                     116,000           No
TL02                     116,000           No
TL02                     111,000           Tread debonding
TL02                     101,000           Tread debonding
TL02                      93,000           Tread debonding
TL02                      89,000           Tread debonding
TL02                      76,000           Tread debonding
TL02                      29,000           Tread debonding

UR-1100                   87,000           No
UR-1100                   39,000           No
UR-1100                   28,000           No
UR-1100                   27 000           No
UR-1100                   27 000           No
UR-1100                   23,000           No
UR-1100                   14,000           No
UR-1100                    5,000           No

In addition to the trailer tests, several drive position tests were initiated using TL02 and UR-1100 (table 6). In the evaluation of the TL02 verses the UR-1100 in the line haul application, the testing of the TL02 was terminated because of three failures in less than 10,000 miles on one truck. The UR1100 truck completed the test (to tread wear out) with no failures. In the other applications of the TL02 tires, all tires completed the test (to tread wear out) with no failures. In one waste hauler tire there was a loss of a 10 by 10 centimeter piece of tread, but there was no propagation of failure under any remaining tread.

Table 6 - evaluation of UR-1100 and TL02 in a drive application of commercial trucks

Number        Tire size    Adhesive   Number    Application
of sets                              of tires
of tires

  1            11 R24.5     UR-1100      4      Line haul drive
  2            11 R24.5        TL02      8      Line haul drive

  1            11 R22.5        TL02      4      P&D
  2         285/75R24.5        TL02      8      Line haul drive

  1         285/75R24.5        TL02      4      Line haul drive

  1            10.00-20        TL02      4      P&D
  1             12R22.5        TL02      4      Waste hauler


Number              Comments
of sets
of tires

  1                   No failures
  2                 Test aborted 3
                    early failures
  1                    No failures
  2                 Test aborted 3
                    early failures
  1                 Test aborted 3
                    early failures
  1                    No failures
  1                    No failures

Evaluation of UR-1100 versus Adiprene based adhesives

The evaluation of UR-1100 versus the Adiprene based adhesives was conducted using road wheel testing. The primary intent of this work was to determine the relative differences in the performance of the two adhesive systems with two primer systems. The primer systems used were 1,3 dichloro 5,5 dimethylhydantoin in methylene chloride and triazine trione in butyl acetate.

In this test (table 7), the tires built using the Adiprene adhesive had inferior performance when compared to those prepared with the UR-1100 adhesive. In both cases the Adiprene tires failed at the bondline but there were no failures in the UR- 1100 tires.

Table 7 - evaluation of UR-1100 and Adiprene/Caytur using road wheel performance

Adhesive             Primer      Hours on road      Tire failed?
                                     wheel

UR-1100              Hydantoin        266                 No
UR-1100               Triazine        285                 No
L-42/Caytur          Hydantoin          6                Yes
L-42/Caytur           Triazine         20                Yes

Conclusion

This work has demonstrated the successful application of a one-part heat curable urethane adhesive for use in retreading tires. This work included the development of a surface treatment system for rubber, the development of tire building methods, as well as the selection of the adhesive for this application. The adhesive UR-1100 was shown to be superior over other one-part adhesives, in addition to a room temperature curable Adiprene based adhesive.

References

[1.] W.H. Waddell, L.R. Evans, J. G. Gillick and D. Shuttle-worth, Rubber Chem. and Technol., 1992, 65, 687.

[2.] D.R. Gagnon and T.J. McCarthy, J. Appl. Poly. Sci., 1984, 29, 4335.

[3.] W.E. Walles and D.J. Nagy, U.S. Patent 3,465,674, September 9, 1969.

[4.] J.M. Martin-Martinez, J. C. Fernandez-Garcia, F. Huerta and A. C. Orgiles-Barcelo, Rubber Chem. and Technol., 1991, 64, 510.

[5.] W.R. Haush and R.W. Koch, European Patent 0 316 666 A1, May 24, 1989.

[6.] S.KM. Swanson, U.S. Patent 5,183,877, February 2, 1993.

[7.] S.B. Labelle and J.A Hagquist, U.S. Patent 4,390,678, June 28, 1983.