I don't speed glue yet, but I'm interested.
So I discovered, and now offer to you, a gold mine of cool information about speed glue, cut-and-pasted from the Falicoff patent. Most of the chemistry is deleted -- my eyes glazed over (but I marked the spot with "..."). But lots was informative and surprising to me. (You might not think so.)
Here's a nice browsing menu so you can skip ahead.
Enjoy!
-- Thomas
This invention concerns solvents for adhesive systems and the adhesive systems comprising such solvents, which are useful for a variety of purposes including attaching table tennis rubbers to table tennis blades.
Technical innovations and changes in the regulations relating to the
equipment used in the sport of table tennis have had a major impact on
the sport, affecting the outcome of many high profile tournaments,
including the World Championships. In particular, there have been many
technological improvements made to the table tennis racket and its two
main components--the rubber and the blade--since the formal
organization of the sport by the International Table Tennis Federation
(ITTF) in 1926 (the ITTF is still the world governing body). Modern
table tennis rackets have an "inverted rubber" (also referred to just
as "rubber") which consists of a top sheet made of vulcanized rubber
that is bonded to an inner layer of expanded rubber sponge or
foam. The rubber is adhered to optimized wood or wood-composite
blades. The playing characteristics of modern table tennis rackets
bear little resemblance to the rackets employed in the 1920s or, for
that matter, even those used in the 1950s. A world class player can
produce shots with ball speeds up to 100 miles per hour and ball spins
of up to 9000 revolutions per minute using modern equipment.
In the late 1970s a number of European table tennis players discovered
that certain types of adhesives affect the playing characteristics of
the rubber. These players would remove the rubber from the blade a
short period prior to playing a match and then "reglue" (a commonly
employed term in the sport of table tennis) the rubber onto the blade
using glues based on solvents such as trichloroethylene and
1,1,1-trichloroethane. Prior to this regluing innovation, the only
time a sheet of rubber was glued on was when an old worn out rubber
sheet was to be replaced, or about every three to six months. Most of
the glues employed were the types used to repair inner tubes of
bicycles and automotive tires, the cold one-part vulcanizing
fluids. Players found that with so-called "speed glued rubber," they
could produce shots with increased speed and spin compared to rubber
put on the racket with traditional rubber cements previously employed
in the sport. The main disadvantages of speed glue were that the high
performance effect lasted only a few hours and the rubber had a
shorter playing lifetime than those glued on once with the traditional
rubber cements.
The first players to exploit the benefits of the speed glue effect
were the European players from Yugoslavia and Hungary, including
I. Jonyer, T. Klampar, G. Gergely and D. Surbek. According to Rufford
Harrison, Chairman of the ITTF Equipment Committee, Dragutin Surbek of
Yugoslavia is given the major credit for popularizing this practice
from 1979 to 1983. Surbek was World Doubles Champion in 1979 and
1983. Many coaches and world-class players attribute the dominance of
the European players in the World Championships from 1989 to 1993,
when Sweden won three World Team Titles, to the discovery of the speed
glue effect. The previous twenty-year dominance by the Chinese players
thus came to an end. In fact, the European success, based on the use
of speed glue, was so resounding that many, if not most, of the modern
Chinese players began to emulate the European style.
Numerous speed glue products based on the above solvents, and others
such as toluene, were produced during the 1980s and the early 1990s by
table tennis manufacturers. However, in 1992 and in the years ensuing,
the ITTF decided to phase out the use of certain solvents because of
health considerations. By early 1995, the ITTF prohibited the use of
the following solvents and solvent types in table tennis glue: all
halogenated solvents; all solvents with benzene rings; and
N-hexane. In addition, the ITTF established a policy of randomly
testing players' rackets in major international tournaments to
determine whether the glue met ITTF regulations with regard to the
banned solvents. In the 1995 World Championships, Kim Taek Soo of
Korea was the first player in the history of the sport to be
disqualified for using illegal glue after he had won his quarterfinal
match.
Many players throughout the world continue to use speed glues based on
ITTF-banned solvents in minor and major tournaments because the
performance of the current ITTF-approved speed glues is inferior. In
the U.S., for example, most table tennis dealers continue to sell
speed glues with illegal solvents such as trichloroethylene, which is
a very difficult solvent to obtain in Europe. Further, many players
are able to purchase glues and solvents designed for other
markets. Cold vulcanizing fluids for automotive tire repair and
cigarette lighter fluids are two common products used by players who
re-glue.
Numerous players who have based their game on the now illegal speed
glues find themselves unable to compete against other playing styles
with the currently approved table tennis glues. In the 1995 World
Championships all four finalists were Chinese, an unexpected result
considering the world rankings of the top European players. The style
of play used by certain Chinese players was not affected as much by
the change in performance associated with the new breed of
ITTF-approved speed glues. In 1993 and 1994, the English Table Tennis
Association (ETTA) went even further than the ITTF by banning all
solvent-based speed-glues. The player outcry was so great that the
ETTA reversed itself in 1995 and allowed the ITTF-approved speed glues
to be used in tournaments, ostensibly because English players found
themselves at too great a disadvantage in international tournaments.
Estimates concerning the change in performance of the new approved
glues compared to the old ones vary. One reason for this is that the
performance depends, at least to some degree, on playing styles. A
common figure offered by world class players is that the best
currently approved glues boost performance by about 15% in both speed
and spin compared with non-speed glued rubber. This can be compared
with a 30% boost associated with the old (now prohibited) speed glues.
Christian Lillieroos, a USATT Certified National Coach and National
Coach of the United States Para-Olympic team, recommends that, in
order to get the maximum performance out of the new breed of speed
glues, players must pre-glue the sheets before playing approximately
four or five times. After a few more reglues the glue buildup is so
great as to affect the performance of the rubber. Eventually, the
solvents in the glue cannot penetrate the solid rubber buildup on the
back of the sponge. Without the solvent action on the sponge the speed
glue effect generally is eliminated. In addition, with each successive
application of glue, the weight of the rubber sheet is
increased. Beyond a certain weight, the sheet must be discarded as the
overall racket weight becomes too heavy for the player to
use. Alternatively, the player can attempt to remove the glue buildup
by various means, a very messy and not always successful process.
In order to reduce the amount of rubber build-up on the sponge, many
players employ an ITTF-legal speed glue for three or four speed
gluings and then switch to a blend of illegal solvents which provides
improved performance without adding to the weight of the
sheet. However, there have been a number of problems associated with
the use of these illegal solvents, aside from the fact that they are
not permitted for use by the ITTF. First, the degree of tack remaining
on the rubber after using a solvent blend is not always sufficient to
re-attach the rubber to the wood surface of the blade. Second, the
performance is not consistent from one gluing session to the next. One
possible explanation for this is that the illegal solvents currently
employed for this purpose may degrade the built-up rubber layer
covering the sponge so that the interface has diminished dynamic
properties. Finally, at this time no manufacturer has had a pure
solvent blend approved for use by the ITTF.
Once an adhesive system is applied to a rubber the player must decide
when to attach it to the face of the blade. Some players choose to put
the glue on when it is wet, others when it is dry, and still others
wait until some degree of tack is present. A speed glue or non-speed
glue also generally is used on the blade. The adhesive bond is
considered to be based on a contact cement. As a consequence of the
swelling of the sponge by the solvents in the speed glue, the sheet of
rubber often curls upwards from the blade to such an extent that the
rubber sheet does not adhere over its entire surface to the
blade. Virtually all speed glues will curl the rubber to some
extent. In fact, the degree of curl is used by players as an indicator
of the potential performance of the sheet. Significant curling is a
serious problem for a player as the performance of the sheet will be
impaired. A number of the illegal and legal glues exhibit a tendency
to have insufficient adhesive bond strength to adhere the curled sheet
flat on the blade.
The length of time that a speed glue effect lasts and the consistency
of its performance over a time period are critical parameters for a
player. Many tournaments last for twelve hours or more. With the best
prohibited speed glues, players have to reglue every two to three
hours. Players therefore must reglue up to six times a day. In
addition, there is a waiting period before one can use a speed-glued
racket as it takes a certain amount of time before the full effect is
present. With the new breed of ITTF speed glues the effect is
generally longer, up to about five hours or more. This is certainly
one of the main advantages of the new speed glues for the average
player. However, for the World Class Player the maximum effect from
the allowed glues is only an hour long, barely enough time to complete
a long match (assuming a thirty-minute warmup period prior to the
match). Also, the waiting period before the speed glue effect is
present is somewhat longer (up to one hour) than with the prohibited
glues (approximately 30 minutes). Therefore, it is difficult for the
player to achieve consistent performance from the equipment in
tournament conditions which often have unpredictably scheduled events.
The following summarizes the disadvantages of the present
ITTF-approved speed glues: (1) their speed/spin performance
characteristics are below the original, and now prohibited,
trichloroethylene, 1,1,1-trichloroethane, toluene, hexane, etc. based
glues; (2) they require an initial thick layer of glue to achieve
maximum performance; (3) they typically employ a relatively high
amount of solids which contributes to premature glue buildup problems
and reduced rubber lifetime; and (4) the speed-gluing process can be
an art which requires that players have a considerable base of
personal experience and knowledge.
Although the prohibited speed glues previously set the standard for
the industry, they also have disadvantages. These can be summarized as
follows: (1) they employ potentially harmful solvents, many of which
have been banned altogether for health and environmental reasons in
certain parts of the world; (3) the speed glue effect lasts for only 2
to 3 hours; and (3) although they dramatically increase the speed,
spin, and for some shots the control of the table tennis rubber, for
some players control is difficult to maintain.
The present invention also provides adhesive systems for use in
forming speed glued table tennis rackets. The adhesive system
comprises the solvent systems described above, and from about 2 to
about 10 weight percent solids suitable for speed gluing table tennis
rubbers to table tennis blades.
A method for speed gluing a table tennis racket also is described. The
method generally comprises forming a solvent or adhesive system as
discussed above. The solvent or adhesive system is then applied to a
table tennis rubber, a table tennis blade, or both, wherein the rubber
and/or the blade provide sufficient adhesive to adhere the rubber to
the blade. The rubber is then attached to the blade to form a
speed-glued table tennis racket.
Accordingly, there are several objects and advantages of the present
invention which address the limitations and disadvantages of the known
speed glues.
A first object is to provide a table tennis rubber speed glue which
has speed/spin and control performance characteristics equal to or
better than previously allowed (but now prohibited) speed glues and
currently allowed speed glues on the market.
Another object is to provide a speed glue which maintains its
performance enhancement effect for a period of up to about six hours.
Still another object is to provide a speed glue based on
environmentally safe solvents.
Still another object is to provide a speed glue and pure solvent based
attachment system which provides minimal glue buildup.
Another object is to provide a speed glue and pure-solvent-based
attachment system which has superior tack to reduce the attachment
problems resulting from sheet curling.
I. General Discussion of the Speed Glue Phenomenon
Although Speed Glues are used by hundreds of thousands of table tennis
players throughout the world, there currently appears to be no
coherent theory that adequately explains the phenomenon. Falicoff's
Study and Development of a Non-Toxic Glue and Equivalent Table Tennis
Rubber Sheet, United States Olympic Grant paper, #S93-018-A-TT (1993),
discussed the effect that solvent doping of table tennis sponge has on
its dynamic storage, loss modulus and tan delta values. A number of
DMA tests were carried out at low frequencies (up to 100 Hz) comparing
sponge doped with trichloroethylene and regular sponge. Falicoff found
that solvent-doped sponge has higher dynamic storage modulus (up to
30% higher), lower loss modulus and tan delta values than its
non-doped version over the frequencies studied. However, no theory as
to why this phenomenon occurs was presented. Other papers concerning
the effect that Speed Glue has on table tennis rubber have been
published by the ITTF. However, these scientific papers have not
postulated a theory as to why the solvents perform such a function.
A. Prohibited Original Speed Glues as Standards
The now prohibited, original speed glues were used as standards for
testing the present solvent and adhesive systems. Studies have been
made regarding the performance of trichloroethylene-based table tennis
speed glues versus embodiments of the present solvent and adhesive
systems because the trichloroethylene-based speed glues had the
previous best performance characteristics.
B. Physical Characteristics of Solvents and Adhesive Systems
As stated above, no theory apparently has been established as to which
properties of a solvent are the most relevant for the speed glue
phenomenon. However, the following were deemed significant and were
considered for developing the present solvent and adhesive systems:
(1) vapor pressure between 20 to 25.degree. C.; (2) molecular weight;
(3) melting point; (4) Hansen solubility parameters, including a
solvent's non-polar, polar and hydrogen bonding numbers; (5) density;
(6) dynamic, kinematic viscosity and surface tension; and (7) ability
to swell table tennis rubber sponge.
II. Solvent Systems
...
III. Additional Factors to Consider for Selecting Solvents
...
C. Melting Point
An important physical characteristic of a rubber compound is its
so-called glass transition temperature, Tg. The glass transition
temperature of a table-tennis rubber sponge has a direct bearing on
the frequency-based playing characteristics of the sponge. Above a
certain impact speed (high frequency impact), the rubber can reach the
glass transition temperature and become temporarily embrittled. This
commonly happens in the game of table tennis. The embrittling
phenomenon can be either an advantage or a disadvantage to a
player. However, the phenomenon is virtually unmentioned in the
literature on the sport and is understood on an engineering basis only
for other applications such as automotive tire design. The embrittling
phenomenon may be useful for some shots, as it provides a top-end
limit switch on energy storage at high impact speeds.
...
G. Sponge Swelling
Increasing the thickness of the table-tennis rubber sponge modifies
the performance characteristics of the rubber. The thickness of table
tennis sponge typically varies from about 1.5 mm to about 2.5
mm. Solvent-based speed glues swell the sponge and increase its
thickness by from about 3% to as much as about 10%. This in itself is
one of the main reasons why the speed glue has such a dramatic effect
on performance. With increased thickness the speed imparted to the
ball by the rubber increases. However, if the sponge swells too much
it may not impart as much spin to the ball,
...
ITTF rules mandate maximum overall thickness values of sponge for
various types of rubber. Therefore, it is imperative that the speed
glue not expand the sponge too much or the rubber will be prohibited.
A number of the terpenes, including D-limonene, are ideal solvents for
table tennis sponge as they swell the sponge to a similar extent as
the trichloroethylene-based speed glues. Manufacturers have used this
swelling data to establish thickness specifications for meeting the
above-mentioned ITTF rules.
The degree to which a solvent blend will plasticize the sponge will
affect the performance of the sponge. Plasticizing will affect many
sponge properties including its hardness, modulus and
resilience. While a certain degree of solvent plasticizing would be
beneficial to speed glue effect, beyond a certain point the effect
will hurt the sponge, as the material literally could fall apart.
In conclusion, a solvent's ability to swell the sponge is a primary
property in the speed glue effect and can be more important than its
vapor pressure. This is corroborated by the studies using pure
D-limonene which showed excellent speed glue properties by itself.
H. Cavitation and Water Hammer Effects
Table tennis shots made with speed glued rubber have a characteristic
very loud pop sound, considerably louder and different from those made
with normal rubber. Two possible explanations of this sound are that
the solvent/solvent gas system is either undergoing a phase change
during the impact, i.e. cavitation is occurring, or the sponge/gas
matrix noise occurs as a result of the water hammer effect. If
cavitation occurs this could explain the significant boost in
performance of the speed glued sponge as the explosive forces would
literally propel the sponge tangentially and outward.
Cavitation is a phenomenon well understood in the field of fluid
dynamics and occurs in many types of high velocity fluid based
machines such as pumps. It occurs when a moving fluid encounters a
region of low pressure which is equal to or below the vapor pressure
of the fluid. Under these conditions a number of vapor pockets are
formed. When the fluid stream enters a region of high pressure these
vapor pockets collapse back into a liquid. A partial vacuum occurs in
the region around the droplet of fluid. The force generated (typically
measured in gigapascals) can rip metal off the walls of a piece of
machinery. This phenomenon occurs over a period of a few milliseconds
and is transmitted as a shock wave through the media. The force is
particularly strong at points nearest to the collapse of the vapor.
The water hammer effect occurs when there is an abrupt change in the
velocity of a moving fluid or gas. A good example of this occurs in
the plumbing of a home, when a running water faucet is turned off
suddenly and quickly. A loud noise is heard throughout the home's
plumbing system. At the time of the faucet being turned off the water
molecules directly against the faucet are stopped from moving. The
water molecules some distance away from the faucet continue to move
toward the faucet and compress the fluid. The pressure thus induced
stresses the walls of the pipe throughout the house and a large noise
ensues.
The water hammer effect can occur in many types of media including
fluids and gases. Theoretically it can occur in a very elastic solid
such as a solvent doped sponge, given the right dynamic movement
conditions.
Of the two, the cavitation effect is the most interesting phenomenon,
as it points to an elegant way of increasing the performance of table
tennis rubber. The application of this principle would work as
follows. Table tennis rubber sponge is composed of a network of cells
with small voids approximately 0.05 mm in diameter. Let us assume that
these voids are filled with a suitable vapor and the solid network is
swelled and partially plasticized. During a high frequency impact
these cells would be highly compressed and distorted. For impacts of
small duration, the gas in a majority of the cells would not have time
or the ability to escape. As the volume of the cells shrinks, both the
pressure and temperature would increase. Under certain impact
conditions, the pressure/temperature regime would be such that the
pressure would be equal to or greater than the current vapor pressure
at the new elevated temperature and the gas would phase change to a
liquid. Implosion would occur due to the vacuum created and the cells
would shrink in size even more. As the ball rebounds from the sponge
and the cell expands, there will be a condition in which the pressure
drops below the current vapor pressure of the solvent and the droplet
of solvent will phase shift back to a gas. Assuming that this is in
fact what happens to speed glued rubber, there is a potential for a
noise to occur during the time when the gas changes to a liquid and
also when it reverses back to a gas. Analysis of acoustic recordings
of the phenomenon should reveal whether indeed there are two distinct
sounds; an implosion and explosion sound. Energy will be stored over a
few milliseconds and released in the two phase change cycles into the
sponge over a very short time period. If the system works as
envisioned, the player should theoretically be able to make contact
with the ball at a slow impact speed and achieve a high velocity/spin
shot. This is in fact exactly what happens with speed glued
rubber. The top players can achieve very high velocity and spin shots
without much apparent hand speed or effort.
The cavitation index is used by engineers in a number of fields to
predict whether there is a possibility that cavitation might occur at
a certain point in a fluid stream, in a particular type of equipment,
such as a pump. The cavitation index, C.sub.i, can be defined as
follows:
C.sub.i =.P.sub.o -P.sub.v !/.(D/2)V.sub.o.sup.2 !
where, Po is the pressure at the point in question, Pv is the vapor
pressure of the fluid, D is the density of the fluid, and Vo is the
velocity of the fluid at the point in question.
The Cavitation Index equals zero when the local pressure is equal to
the vapor pressure of the fluid. At this point the fluid will boil. At
values greater than zero, cavitation can still occur. However, the
number is usually established from empirical data. For example, a
particular piece of equipment might have cavitation problems when the
cavitation index is less than 0.1. However, it should be clear from
this equation that cavitation is more likely to occur where there is a
high velocity and density fluid involved.
In the case of the speed-glued sponge most of the solvent will become
a vapor in the walls of the sponge. Therefore, the cavitation
phenomenon would initially occur as a change from a vapor to a liquid
and then back to a gas. If one could establish cavitation indices for
this phenomenon, one could then evaluate the effect that the vapor
density, pressure and velocity of a particular solvent blend has on
the process. Cavitation is also affected by the surface tension of the
fluid, as a low surface tension fluid can more easily move through
small orifices/voids.
It was found that slight modifications to the ratio of the components
of the solvent blends had a major effect on the "sound" of the glued
rubber. 2,2,4-trimethylpentane was found to increase the "sound" of
the preferred solvent systems when used in the range of about 18 to
about 22 parts (by weight) of the total mixture. An explanation of
this is that the vapor pressure of this solvent is lower than the
azeotropic binary, cyclohexane and ethyl acetate. Thus the
2,2,4-trimethylpentane brings the vapor pressure of the solvent blend
closer to the value of trichloroethylene. In addition, the molecular
weight of 2,2,4-trimethylpentane is 114.23, somewhat higher than
either cyclohexane and ethyl acetate. Looking at the formula for the
cavitation index, using 2,2,4-trimethylpentane in the solvent systems
will lower the numerator and likely increase the denominator of the
formula, which will make the solvent blend more likely to cavitate.
In summary, the solvent systems described herein are a novel
substitute for trichloroethylene or toluene in table tennis speed and
spin enhancement solvent and adhesive systems. Although alkanes,
cycloalkanes, esters, unsaturated and many other solvents now
permissible by the ITTF have previously proved unsuitable, mixtures of
these in the right proportions are eminently suitable. By choosing
appropriate solvents, a synergistic mixture can be created which has
properties equal to or better than trichloroethylene and toluene.
IV. Ratio of Solvents in the Solvent Systems
...
V. Adhesive Systems
...
VI. Making Solvent and Adhesive Systems
The solvent and adhesive systems discussed above generally can be made
simply by combining the solvent components to form solvent systems,
combining the solid components, and thereafter combining the solvent
systems with the solid components to form the adhesive systems. The
adhesives can be made in small quantities without having to mill the
solids. The solvent systems generally have been combined with the
solids using an automated mixer, such as a paint shaker (Red Devil or
equivalent), for a period of time to provide adequate mixing for
subsequent application to the rubber and/or blade. Working embodiments
of the invention have continued the mixing by the shaker for a period
of about an hour. It currently is believed that the best results are
obtained when the adhesive systems so formed have viscosities of from
about 200 cps to about 400 cps. Mastication of the materials may
increase the viscosity of the adhesive systems. Further modification
of the viscosity of the adhesive can be accomplished by employing a
filler such as amorphous or precipitated silica.
BACKGROUND OF THE INVENTION
SUMMARY OF THE INVENTION
...
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS