Bond for abrasive tools

In the phenolic bond used for making abrasive tools such as grinding wheels and the like, the addition of certain alkyl or hydroxyalkylcarbamylmethyl triazines improves wet strength properties of the tools.

The invention relates to improvements in rigid abrasive tools, for example 
grinding wheels, bonded with organic polymer bond. More particularly the 
invention relates to new bond compositions for reducing the loss of 
mechanical strength when such abrasive tools are wet. 
We have found that certain curable compositions comprising triazine 
compounds more particularly defined below, when incorporated in the 
composition of rigid grinding tools during manufacture can reduce the 
characteristic deterioration of mechanical strength when the abrasive tool 
is wet. Phenolic resins are the principal ingredient of bonds most widely 
used for making grinding tools of bonded abrasive grain. Other organic 
polymer bonds that are sometimes used include heat-curable resins such as 
shellac and alkyd resins. Novolac phenolic resins are usually used as 
powders which include the novolac resin and a curing agent. Powdered 
hexamethylene tetramine is the curing agent used most widely but other 
powder or liquid curing agents may be used instead, such as aldehydes, 
trimethylol phenol, resole phenolic resins and the like. Many formulations 
for abrasive tool bonds based on thermosetting resins such as phenolics 
have been described. Many variations of such formulations are known for 
making tools having a variety of mechanical properties and grinding 
characteristics. 
One problem that is generally characteristic of abrasive tools bonded with 
organic polymer bond is loss of mechanical strength when wet. An object of 
the invention is to provide new ingredients in thermosetting bond 
compositions which can reduce the loss of mechanical strength of bonded 
abrasive tools when wet. 
U.S. Pat. Nos. 4,708,984 and 4,710,542 described curable compositions 
comprising: 
(a) an active hydrogen-containing material; and 
(b) a triazine composition selected from 
(i) compounds of the formulas 
##STR1## 
wherein at least two R groups are 
EQU --CH.sub.2 NHCOOR.sup.1 
wherein R.sup.1 is selected from alkyl having 1-20 carbon atoms, and 
beta-hydroxyalkyl having 2-18 carbon atoms, and the remainder, if any, of 
R groups are 
EQU CH.sub.2 OR.sup.2 
wherein R.sup.2 is hydrogen or alkyl having 1-12 carbon atoms; and 
(ii) mixtures of the above defined compounds, oligomers of the above 
defined compounds and mixtures of such compounds with such oligomers; and 
(c) a cure catalyst. 
Other triazine compounds of the structural formulas shown above, wherein at 
least two R groups are 
EQU --CH.sub.2 CH.sub.2 CHCOOR.sup.1 
wherein R.sup.1 is alkyl having 1-20 carbon atoms or betahydroxyalkyl 
having 2 to 10 carbon atoms, and the remainder, if any, of R groups are 
selected from Cl, Br, 1 or alkoxy having 1 to about 6 carbon atoms, and 
the synthesis of such other triazine compounds, as well as oligomers 
thereof and mixtures of such compounds or mixtures of such compounds and 
oligomers, were described in U.S. Pat. No. 4,742,118. 
Triazine compositions of the class described above are used in accordance 
with the present invention as additives in improved bond compositions for 
making abrasive articles. The principal component of the curable bond 
composition is a thermosetting curable organic resin, preferably a curable 
phenolic resin. At least part of the bond formulation is one or more of 
the triazine compositions of the class defined above, preferably 
comprising at least one compound in which at least some of the R.sub.1 
components are beta hydroxyalkyl. A most preferred triazine compound for 
use in the invention is 
EQU C.sub.3 N.sub.6 (CH.sub.2 NHCOOC.sub.3 H.sub.8 OH).sub.6. 
A cure catalyst is incorporated with the triazine composition in bond 
compositions of the invention. Salts or complexes of metals such as lead, 
zinc, iron and manganese and preferably tin or titanium can be used. 
Organic salts such as acetates, octoates, laurates and naphthenates are 
preferred salts. Complexes such as tetrabutyldiacetoxy stannoxane, 
dibutyltin dilaurate, dimethyltin dilaurate and acetyl acetonates can also 
be used. Chelates of titanium With acetylacetone, ethylacetoacetate, 
triethanolamine, lactic acid and the like can be used. Also, quaternary 
ammonium compounds, e.g. tetramethylammonium hydroxide can be used. These 
catalysts are used in amounts effective to accelerate cure at the same 
temperatures that are used for curing the phenolics, usually above 
100.degree. C. An amount of cure catalyst in the range from 0.1 to 2% by 
weight based on total weight of the organic binder composition is suitable 
in most cases. 
The abrasive material in the bonded abrasive articles of the invention may 
be any particulate abrasive material that is suitable for the use, such as 
particles ranging in size from fine powders to coarse grits, of either 
natural abrasives such as diamond, corundum, emery, feldspar, quartz, and 
the like or manufactured abrasives such as silicon carbide, various 
aluminas, zirconia, boron nitride, glass, steel wool, angular grit, iron 
shot, etc. 
In a thermosetting bond composition according to the invention, the 
essential resin ingredients of the bond are a thermosetting resin, 
preferably a phenolic resin with a curing agent, and a triazine compound 
of the formula described above with a cure catalyst. Of the resin 
components in the bond composition, the thermosetting resin, e.g. the 
phenolic resin with curing agent, will constitute the major resin 
component of the bond, such as 60 to 95%, preferably from about 80% to 95% 
by weight of the total resin content. In preferred embodiments, the major 
phenolic component is a novolac with its curing agent, together 
constituting from 75% to 100% of the total phenolic content, any remaining 
phenolic being a resole phenolic resin. The other essential resin 
component, in addition to the thermosetting resin, is the triazine 
composition with its cure catalyst. In preferred embodiments of the 
invention the triazine compound and its cure catalyst together constitute 
5 to 40% and preferably from about 5% to about 20% by weight of the total 
resin in the bond composition. In addition to the resins which may include 
curing agents and cure catalyst, the bond composition may also include 
fillers which may constitute up to 30% by weight of the total bond 
composition, and the bond may also include minor amounts of other 
additives. 
Preferred mixtures of abrasive and bond for making cured abrasive tools 
embodying the invention comprise abrasive material constituting about 60% 
to 90% by weight of the mixture. This mixture further comprises a 
thermosetting resin bond composition of the kind described above, 
constituting about 10% to 40% by weight of the total abrasive and bond 
mixture. 
The composition of the abrasive article may include other ingredients in 
addition to the abrasive and bond components, such as wetting agents, 
fillers, modifiers, lubricants and the like. Abrasive articles 
incorporating the invention are bonded abrasive products such as wheels, 
discs, sticks, blocks, cones and the like. 
In our presently most preferred mode of carrying out the invention, 
described in more detail in examples below, we make a bonded abrasive 
article comprising abrasive grains bonded with a bond formulation which 
comprises novolac phenolic resin with a curing agent and a mixture of 
triazine compounds and oligomers obtained by the the reaction described in 
Example 8 of U.S. Pat. No. 4,708,984. This mixture is a liquid mixture of 
hydroxypropylcarbamylmethylated melamines. It contains about 30 to 40 
percent by weight of the triazine compound of the formula 
EQU C.sub.3 N.sub.6 (CH.sub.2 NHCOOC.sub.3 H.sub.8 OH).sub.6 
A cure catalyst is added to the triazine composition.

The invention is described in more detail below by reference to specific 
examples embodying the invention. 
EXAMPLE 1 
To 91.9 parts by weight of abrasive grains of fused alumina is gradually 
added 1.13 parts by wt of a liquid pick up agent described below. The 
liquid and powder are mixed for about 5 minutes until the abrasive powder 
is uniformly wet with the liquid solution. Then 7.0 parts of novolac 
phenolic resin powder which has been premixed with a curing amount of 
hexamethylenetetramine is added and thoroughly mixed with the wet abrasive 
powder for about 15 minutes until the wet abrasive powder has picked up 
the resin powder. This mix is aged for about 18 hours at room temperature 
and then is compressed in an AFS core box assembly using a Dietert No. 315 
Sand Rammer to make 25.4 mm thick AFS test specimens for tensile strength 
testing. 
The specimens are cured at temperature which is gradually increased to 
175.degree. C. over a period of 9 hours. The cured specimens are tested 
for dry tensile strength at break by a standard test method, taking care 
to maintain uniformity in details of preparation, treatment and handling 
of the samples and uniformity of conditions for the test. 
To test for wet strength, specimens identical to those used in the dry 
tensile strength test are immersed in water for ten days then removed and 
immediately tested for tensile strength at break by the same test method. 
Results of the wet and dry tensile strength tests are shown in Table 1. 
Several different mixtures of abrasive and bond are prepared and formed 
into test specimens as described, but using several different liquid 
compositions as the liquid pick up agent. 
For specimens identified as Specimen A, the liquid pick up agent is 
composed of: 
(i) 1.07 parts by weight of the mixture of triazine compounds and oligomers 
obtained by the the reaction described in Example 8 of U.S. Pat. No. 
4,708,984, which comprises about 30 to 40 wt % of the compound 
EQU C.sub.3 N.sub.6 (CH.sub.2 NHCOOC.sub.3 H.sub.8 OH).sub.6, 
and dissolved in an aqueous 70% solution with 
(ii) 0.06 parts by weight of cure catalyst which is 
DABCO-TMR, a quaternary 
ammonium salt in ethylene glycol. 
For control specimens, the mix of abrasive and bond is prepared the same as 
those described above except the liquid pick up agent consists of a liquid 
resole phenolic resin in aqueous solution instead of the liquid 
hydroxyalkylcarbamylmethylated melamines and oligomers. 
Results of the tensile strength tests of the control specimens and the test 
specimens A and B, described above are tabulated in Table 1. 
TABLE 1 
______________________________________ 
Tensile Strength at Break 
Pounds per square inch 
Percent Loss 
Specimen Dry Wet on Wetting 
______________________________________ 
Control 1470 840 43% 
A 1080 840 22% 
______________________________________ 
Results in Table 1 demonstrate the advantage that the loss of tensile 
strength on wetting samples made with the triazine compound additive is 
only about half the loss of strength on wetting of the control made 
without triazine. Although the control has higher dry strength, the 
strengths of the wet samples are about the same.