Note: Descriptions are shown in the official language in which they were submitted.
~O 96~05022 2 1 9 ~ 5 ~ ~ P~ ' 16
I ~ '
ABRASIVE ARTICLE
Field of the Invention
This invention relates to an abrasive article uu" ,,u(i~i, ,9 a cured hot
melt adhesive and to a method of p, ~Udl dliUn.
Backaround of the Invention
Abrasive products are normally prepared by coating one surface of
a substrate with a first binder layer having adhesive properties, often
referred to in the art as the "make". Particles of abrasive material are
5 applied to the coated substrate and partially e",bedded therein. A layer of
a second binder, often referred to as the "size~, is then applied to the
material. The thickness of the second binder layer regulates the amount of
the abrasive material extending above the binder medium. Anti-loading or
anti-static materials having generally been included in a further optional
20 layer, referred to in the art as the asupersize~.
The adhesives used to form the make are generally water- or
solvent-based and include phenolic resins, urea-ru,lllaldehyde~ melamine-
ro""aldel ,yde and co" ~bi~ ,c,liu, ,~ thereof. Other adhesive which have been
used are based on animal hide glue and starch. Similar adhesives have
25 been used for the size.
Many of the known adhesive systems which have been used are of
low solids content requiring a high energy input for drying and the careful
selection of backing materials. In the case of solvent-based adhesives,
apparatus to extract solvent emissions may also be needed. Such
30 extraction apparatus may also extract the fines from the abrasive particles
Ieading to p~u~es~ g problems.
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W096/05022 ~195~541,~;,1 j, P.~ ,3~ 6 --
British Patent No. GB 2,282,144, discloses an abrasive eiement
CUIII,IJI i~ g a substrate bearing layer of a moisture-cured hot melt
polyurethane adhesive having abrasive particles ~",bedded therein.
It has been found that the use of a moisture-cured hot melt
5 poiyurethane adhesive as the make in an abrasive element provides a
number of advantages over traditional water- and solvent-based systems.
The hot melt adhesive is used at 100% solids content and by suitable
selection of the a,), ' " , temperature will maintain the desired
U~i~l lldLioo of the abrasive particles The hot melt adhesive is co"",dtible
10 with many size formulations and allows thè ,, I " , of water-based size
over the make and abrasive particles, the moisture content of the size
pdl Li-,i,Udlil ~g in the curing of the make adhesive ensuring strong bonding
between the make and the size; Other sizes may be employed, e.g., hot
melt or solvent-based formulations, and may be applied before or after
5 curing the make adhesive coating.
Hot meit adhesives are 100% solid polymeric materials which form
bonds on cooling. They are generally composed of a ~" "L,i, IdliOn of
resins, waxes and stabilizers. Coating is normally by die coating or
extrusion, but can also be by spray coating. Moisture-cured polyurethane
20 coatings comprise isocyanate-ltl""i" ' ' In~poly~ which, after
a~ dli~JI 1, are cured by reaction of the residual isocyanate groups with
moisture. The amino groups initially formed react with more isocyanate
groups to fonm urea linkages.
The moisture curing hot melt polyu;ethane (HMPU) may be applied
25 to any substrate which will withstand the l~,, I " I l~" ,pe, ' ~re of the
adhesive. The HMPU may be coated directly on the substrate or a priming
or presize layer may be applied prior to its 1, pl " ,. These priming or
presize layers rnay be solvent-based, water-based or hot melt. The
priming or presize layer is conveniently hot melt since it may readily be
30 applied at the same coating station as the HMPU make. Priming or
presize layers are particularb useful on substrates which have rough
~ .
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~VO96105022 2~9~i4~ r~ 16
surfaces or surfaces with voids e.g., open-cell foams, and woven and non-
woven fabrics, since it assists in s,, loull ,i"g the surface and reduces the
amount of HMPU required for the make, which tends to be a more
expensive ~Il I~Jont:l ll than the presize material. Priming or presize layers
are not normally required on closed-cell foams and other substrates having
a sub~ld, lli.,l'y sealed surFace.
Moisture-curing hol melt adhesives in which the cure involves
il IN,. d~liUI I~ of silyl groups are known in the literature, and some are
available co"""e",; .'j. Such materials can be totally free of isocyanates,
lo as described in GB 2237022, WO 92/05226, GB 2197326, EP 0202491,
US 4,960,844 and Japanese Published Appiication Nos. 4-202585,
~114078. and 3-149277. Moisture-curing hot melts culllclillil~9 both
isocyanate and silyl groups have also been disclosed.
Summarv of the Invention
The present invention utilizes alternative hot melt adhesives not
requiring the use of isocyanates in the ,ult:,udldlioll of abrasive elements.
One aspect of the present invention relates to an abrasive article
cc " ,,u, isi"u a substrate co" ,u, isi"g a first major surface, an adhesive layer
~ 20 on said first major surface of said substrate; said adhesive layer
cu, "~,, isi"g a hot melt adhesive c.u" l~n i:,i"g a polymer cross-linked via
hydrolyzed or cùndt,nsed silyl groups and abrasive particles adhered
therein.
2~ Detailed DescriPtion of the Invention
The adhesive used in the present invention is a 100% solids
resinous formulation which melts to a fluid state at elevated temperatures
r (e.g., in the range 50 to 200~C). At the fluid state, the adhesive may be
coated on a substrate by conventional techniques such as extrusion, die
~, 30 coating, spraying etc. On cooling to ambient lellll,~l Ires, the adhesive
solidifies and further cures to a cross-linked three-di",t:nsiù"al network via
W0 96/05022 ~ r~ 16
the mutual iut~.d~Liul) of silyl groups illculpuldlt:d in the resin, the curing
reaction being activated by moisture.
Abrasive articles of the invention may be manufactured by coating a
surface of a suitable substrate with the hot melt adhesive as described
above, and applying abrasive particles to the molten or semi-molten
adhesive coating so that they become adhered therein. The:,; I ' ~ of
abrasive particles may be, for example, by drop coating or eleuL,u:.ldli~a:'y
coating the particles, both of which are standard techniques in the
abrasives industry. The thickness of the adhesive coating and the
o di~ iul l~ of the particles are preferably such that most if not all of the
particles partially project above the surface of the coating. As the
adhesive cools, it solidifies completely and cures to a three-,li" ,ensic, Idl
network, and hence bonds the particles firmly to the substrate.
The substrate may comprise any of the materials commonly used as
the backing for coated abrasive articles, inc!uding paper, cloth, plastic
films, plastic fibers, fibrous bases, woven and nonwoven webs/fabrics,
foams, foamed polymeric materials, and laminates etc. The substrate, as
described above, optionaliy may be precoated with a suitable resin (=pre-
sized") in order to seal the surface, for example, or otherwise modify its
surface properties. A pre-size may be beneficial in the case of porous
materials and/or irregular surfaces, as in open cell foams, nonwoven webs
etc.
Suitable presizes may be applied as solvent- or water-based
formulations, or as 1 ûû~/ solids hot melt formulations. Hot melt
formulations are preferred and examples include a hot me!t ethylene vinyl
acetate uu" " "~" -"y available from Evode, Stafford, stdrrul d~hil ~l United
Kingdom, under thè trade cle~ J, IdLiun ~Thel " '' ~w 6876~; a hot melt
polyethylene co"""~,uia"y available from r~ "~esotd Mining and t
Manufacturing Company, St. Paul, MN, under the trade deai~, Idliul ~
30 "3748"; a hot melt polyamide cc " " ~ ~1 ui~lly available from Mi. "~esuta
Mining and Manufacturing Company, St. Paul, MN, under the trade
21g~4~
~0 96/05022 = P._llu~ _~J16
desi~, Idliun "3789~. In some circumstances, a pre-formed plastic fllm may
be applied to the substrate, which is a useful option where the substrate is
an open cell foam, or a woven or non-woven fabric.
The abrasive article may ad.liliu, ,a"y comprise a size layer. The
5 size layer may comprise any of the materials conventionally used, but
preferably comprises a II,t"",ost,lli"g resin (e.g., phenol-ru,,,,aldel,yde or
urea-rul " Id~ l ,yde) in the form of an aqueous solution or .li;,~ iu, "
coated and cured according to conventlonal techniques. The water from
such a coating serves to activate the curing reaction in the adhesive layer,
10 while the ll ,t:""us~lli"g resin provides additional strength and controls the
degree to which the abrasive particles project above the surface. Suitable
size materials include a water-based acrylic co"" "e, ~ 'ly available from
Evode, Stafford, Stdrru, d:,hi, t7, United Kingdom, under the trade
d~;ylldliulMDP-90-41û1"; water-based polyurethanes co"""e" 'Iy
5 available from Baxenden, Droitwich, Wulu~ , United Kingdom, under
the trade dea;.~,ldiiun "Wituobond 732', 'Wit~,ubol1d 769" and "W;t~.ubond
788". Other sizes may be employed, e.g., hot melt or solvent-based
formulatlons, which may be applied before or after curing the make
adhesive coating. Additives such as anti-loading 1,~dll,,c~ , static control
20 agents, etc., may be included in the size layer, or coated in a separate
(supersize) layer, in acuc, ddl)(~r3 with known techniques.
The abrasive articles may also comprise a supersize, preferably
dllliluddillg supersize of the type disclosed in U.S. Patent No. 5,164,265
and its equivalent, EP-0433031. Particularly preferred supersize
25 ~",,uc,silions comprise calcium stearate and a fluorinated additive, e.g., a
fluorinated additive cu, "" ,t:, uially available from Mi. "~esold Mining and
Manufacturing Company, St. Paul, MN, under the trade de~ l Idliul~
'FC396n, in a water-based acrylic binder, e.g., a water-based acrylic binder
co"""e" 'ly available from Vinamul, Carshalton, Surrey, United Kingdom,
30 under the trade desiy, Idliul MVinacryl'.
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; f ~
WO 96105022 ~ , 16
The hot melt adhesives useful in the invention comprise a uoss-
linkable polymer having silyl groups, ~,u, t:se, lled by the formula:
-A-Si(R)~m(X)m
in which:
A I ~ul t~ l Ib a divalent organic radical, preferably an optionally
hstitl lt~d alkylene, alkyleneoxy, alkylene-phenylene, or alkylene-oxy-
alkylene chain;
X ,~u, ~:.e, It~ a leaving group ~ .Q,II ~le by hydrolysis, preferably
a halogen atom, e.g., chlorine, or a group R'O or R1COO in which R~ is a
C,.,0, preferably C1~, alkyl or alkoxyalkyl group;
m is 1, 2, or 3, preferably 2 or 3; and
R I tlu~:se~ . a blocking group not ~ ..re..hl~ by hydrolysis, for
example, a C14 alkyl group, a cycloalkyl of up to 8 carbon atoms, or an aryl
group oF up to 10 carbon atoms.
Such silyl groups are readily hydrolyzed by moisture (from the
~6~w:~,ul~ or extemally supplied) to from silanol groups Si - OH, which
condense with one another to form -Si-O-Si- linkages as disclosed, for
example, in WO 92/05226, co"~,uulldil,g to U.S. Patent Nos. 5,227,442;
5,296,561; and 5,397,648.
The silyl groups are covalently bonded to one or more of the
resin(s) constituting the hot melt adhesive. This may be achieved by
grafting reactions carried out on a preformed polymer, or by
cu,uûly",eli~dli,)ll with suitable silane-functional l"opu",e~. Both
d,U~ ~uaulles are fully documented in the literature, for example,
GB 2237022 and WO 92/05226 (~,o"~ .u"di"g to U.S. Patent Nos.
5,227,442; 5,296,561; and 5,397,648). In the resulting polymers, silyl
groups are attached to about 0.1 to 20.0 rnol~/O of the repeating units, more
commonly about 0.3 to 5.0 mol~h. The remaining repeating units may be
derived from any of variety of " ,u, ,u m ~ 1l such as alpha-olefins, acrylates
and other vinyl compounds, as described in the prior art.
.
0 96/05022 ~ ~ 9 ~ r~ ,J-6
The hot melt adhesive may comprise additional resins, especially
tackifying resins, in order to adjust the physical properties such as melt
viscosity. The adhesive may also comprise a catalyst for the curing
reaction, the preferred catalyst being an organotin compound or a titanate,
5 such as dibutyltindilaurate or tetrabutyltitanate. Typical catalyst loadings
- are in the range 0.1 to 2.5% by weight based on the weight of total solids.
In e"lLodi",t" ,1;, of the invention cu,,,,uri~ ,9 an aqueous size coating, a
catalyst may be u""ecessdl y. Hot melt adhesives co, lldil ,i"g a cure
catalyst optionally may be used in two-part form, with the catalyst and
silane-functional resin supplied separately and mixed i"""edidLely priorto
coating or during the coating process e.g., by extrusion through adjacent
dies.
A ,,u"""e,~,ia"y available hot melt adhesive suitable for use in the
invention was supplied by Swift Adhesives Ltd., Twick~l Ihdl ", United
Kingdom, under the trade dt~ , Idliul ~ ~X200/9n. One method for preparing
this adhesive is believed to be as follows: combining a silane grafted
copolymer in an amount of about 15 parts by weight; a hydl u~ndIud
alicylic hy.ll UCdl L,on-solid midblock cu",,udLil,le tackifying resin availablefrom Exxon Chemical Company, Houston, TX, under the trade desiy, IdIion
~Escorez 5380= in an amount of about 40 parts by weight; polybutene -
liquid mid-block uo,,,~,dlil,le plasticizer available from BP Chemicals,
Cleveland, OH, under the trade desiy, IdIion "Hyvis 30= in an amount of
about45partsbyweight;acatalyst",d~ ,bdtil,(1~/Obyweightdibutyltin
dilaurate in ethylene vinyl acetate) in an amount of about 1.7 parts by
weight; and an dl lliU~iddrll available from Ciba Geigy, Ardsley, NY, under
the trade desiy, IdIion ~Irganox 1010" in an amount of about 1 part by
weight.
The silane grafted copolymer (i.e., a silane grafted styrene ABA
block copolymer) can be prepared as follows: 100 parts by weight of a
styrene-ethylene-butylene-styrene block copolymer available from Shell
Chemical Company, Houston, TX, under the trade desiy, IdIion "Kraton
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WO 96/05022 2 19 ~ 5 ~ 6 ~ 16
G1652" can be reacted with two parts by weight of vinyl trimethoxy silane
using 0.17 parts by weight of dicumyl peroxide as a free radical generator
and 0.5 parts by weight of an dl lliU)~iddl 11 available under the trade
dtssi~" IdLion "Flectol H," from Monsanto. The reaction can be carried out in
5 a PR46 Buss Ko-Kneader with the heater units set at 200~CI240~C/160~C
and the die heater at setting number 7. The material produced can be face
cut and air cooled at an output rate of 5.2 kg per hour.
The co,,,,uosiliun can be ho",og~:"i~t:d prior to the addition of the
catalyst. The catalyst can then be mixed in and the UU,l~,UO~iliu" can be
o filled into a container for a hot melt adhesive applicator. A silica gel sachet
may be placed in the filled container before it is sealed. This ~ pd(dlio
is esselllially as described in Example 3 of GB 2237022.
The hot melt adhesive used in a given:,, I ' , will be selected
according to the particular requirements. As a general guide, hot melt
adhesives having viscosities in the range 3,000 to 12,000 mPa.s
(Brookfield) at 120~C are suitable, but those exhibiting higher or lower
values may be dUUlUU~idll~ in certain circumstances. For example, a less
viscous adhesive will normally be required if a lower coating lt:",,ue, ' Ire isto be used, and a more viscous adhesive may be suitable if a higher
20 coating temperature can be tolerated.
The make coating is generally applied by heating the hot melt
adhesive to a temperature at which the viscosity is suitable for coating and
applying the molten material to the substrate by an extrusion die, or
optionally two adjacent dies in the case of two-part cu" "~osiliu". Coating
25 temperatures depend upon the particular adhesive, but are generally in the
range 50 to 200~C, usually in the range 120~ to 160~C. The coating weight
depends upon the surface of the substrate, the presence or absence of a
presize, and the size of the abrasive particles. Coating weights are
generally within the range 1 to 250 g/m2, the lower end of the range being
30 applicable to smooth substrates e.g., paper, and to the use of fine grade
abrasive particles.
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'2195~
~!/O 96105022 ~ P~ J16
;, ~ ~ .
Hot melt size and presize coatings may be applied in a similar
manner to the make coating.
The abrasive particles are generally applied to the coated substrate
i"",.- " ' !y a~tem1p, 1 - " 1 of the adhesive e.g., by passing the substrate
through a curtain of abrasive particles or by t:le-,ll ualdli-, coating.
- Preferably the abrasive particles are heated prior to "Pr' " ~ e.g., from
30 to 15û~C usually about 50~C.
Individual abrasive particles may be selected from those commonly
used in the abrasive art, however, the abrasive particles (size and
culll,uo:,iliul)) can be chosen with the d,uplicdliul ~ of the abrasive article in
mind. In choosing an a,u~Jlu~ridl~ abrasive particle, ~,hdld~ ,a such as
hardness, cc"" "' "'.y with the intended workpiece, particle size,
reactivity with the workpiece, as well as heat conductivity may be
co,~si.l_, ~cl.
The co",,uosiliù" of abrasive particles useful in the invention can be
~ divided into two classes: natural abrasives and manufactured abrasives.
Examples of natural abrasives include: diamond, conundum, emery,
gamet, buhrstone, chert, quartz, sd"d~lu"e, ~.hdl-,e-lully, flint, quartzite,
silica, feldspar, pumice and talc. Examples of manufactured abrasive
include: boron carbide, cubic boron nitride, fused alumina, ceramic
aluminum Dxide, heat treated aluminum oxide, alumina zirconia, glass,
silicon carbide, iron oxides, tantalum carbide, cerium oxide, tin oxide,
titanium carbide, synthetic diamond", la~dl ,ese dioxide, zirconium oxide,
and silicon nitride.
Abrasive particles useful in the invention typically and preferably
have a particle size ranging from about 0.1 ~iu~u~ r to about 1500
~"iu,u",t~ , more preferably ranging from about 0.1 ~iu~u~eler to about
1300 ",iu,u",~ . The abrasive particles preferably have an average
particle size ranging from about 0.1 ~ UIII~,'U. to about 700 ,,,i~,,u,,,t:tt~
more preferably ranging from about 1 to about 150 "~iu~u"~
particularly preferably from about 1 to 80 ",i~,, u, llt:Lt:l ~. It is preferred that
WO 96/0~5022 2 1 ~ S~i 6 r ~ ,316
abrasive particles used in the invention have a Moh's hardness of at
least 8, more preferably about 9; however, for specific,, I ' ,:,, softer
particles may be used.
The temm ~abrasive particle" includes ayu~lu,,,eldlus of individual ,~
abrasive particles. An abrasive ay~lullleldLu is formed when a plurality of
abrasive particles are bonded together with a binder to form a larger
abrasive particle which may have a specific particulate structure. The
plurality of particles which form the abrasive agylu,,,u, ' may comprise
more than on type of abrasive particle, and the binder used may be the
o same as or different from the binders used to bind the agulu,,,e, dLt: to a
backing.
A size may be applied directly after: ?.P " ~ of the abrasive
particles. The size is préferably water-based and may readily be applied
by, e.g., spray-coating or roller-coating. The weight ratio of adhesive to
waterisgenerallywithintherange10:1to1:2,preferablyfrom1:1to2:1.
The coating weight is generally in the range from 1 to 250 g/m2 solids and
is normally deuu, ,du"l on the grade of abrasive particles.
In absence of water-based size, the material may be sprayed with
water or placed in a moist environment to cure the adhesive.
After a,, 1;- ' , of size or water, the material is dried, e.g., by force
drying in a tunnel oven with infrared heaters. Suitable drying ~e",,ut:, ~res
are about 6ûDC and drying times of about 90 seconds are usually
sufficient.
Following drying, the abrasive article is preferably allowed to stand
for a period of at least 24 hours to allow thorough curing.
A particularly prefenred product in dUl,UI dance with the invention is
an abrasive sponge, e.g., a foam strip of thickness in the range 2 to 15 mm
~ having abrasive particles coated on one major surface. The substrate
coated with abrasive particles can be in sheet form or as a web from a roll.
The sponge may be formed in situ in the apparatus upstream of the
,
.
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5 ~
~0 96105022 r~ 16
coating station. Foam blocks, e.g., of a thickness about 25 mm may also
be coated with abrasive particles in dCCu~ danu~ with the present invention.
The present invention is not limited to coating a single surface and
articles havin~ double sided abrasive coatings, which may be of different
abrasive grades, may readily be prepared. Abrasive coating on some or
all sides of a substrate is also possible.
The invention will now be illustrated by the following Examples.
ExamDle 1
o A hot melt adhesive co"""e" idlly available from Swift Adhesives
Ltd., Twickenham, United Kingdom, under the trade deaiy, IdliUI I "X2ûû/9~
was slot coated at about 14û~C onto paper at coating weights of 22, 32,
and 48 grams per square meter, respectively.
Silicon carbide mineral (about 9û grams per square meter),
cullllllel.,idlly available from Arendal, Eydehavn, Norway, having the trade
deaiyl Idliol, ~P22û' was drop coated on to the tacky, uncured coating at
ambient le",~e, ' ~re.
One sample of paper was drop coated after re-heating the adhesive
to 1 6û~C for 60 seconds.
All samples showed sufficient adhesion of mineral to further coat
with size.
A water-based ures/Fu""ald~hyde size mix COllllllt:l uia 'y available
from Dynochem, Duxford, Cdlllblidgeallil~:, United Kingdom, underthe
trade desiy"dliùn "CBUL" was coated onto the samples described above.
Drying/curing was effected for two hours at 80~C.
The abrasive grains in the abrasive layer of the resulting product(s)
felt sharp. A brief cut test was performed as follows: A sample of the
coated abrasive article was converted into a 5.û cm x 15 cm rectangular
sheet and weighed. A dry bnush and a sheet of paper were also weighed.
The paper was larger than a wooden panel which was precoated with a
water based acrylic lacquer CGIlllll~:l 'ly available from Granyte Surface
. -, t~
96/05022 1~ 6
Coatings PLC, Salford, England. The rectangular coated abrasive article
was wrapped around a 5 cm x 2.5 cm rubber block having about a 60
degree l"l_" IdIiul ,al Rubber Hardness. In a manual, hand-held, operation,
the abrasive article on the rubber block was moved in push-pull strokes
5 against the wooden panel sanding the acrylic lacquer. A stroke was the
movement of the operator's hand in a straight line back and forth motion
covering about 25 cm ~ 5 cm in each motion. After 60 strokes, the brush
was used to transfer any dust on the wooden panel to the paper. The
weight of acrylic lacquer removed was tlult" " ,i"ed by, u ..e;~l ,i"g the
o coated abrasive, brush, and paper. In this manual test, 0.2 grams of
acrylic lacquer was removed in 60 strokes which dt:" ,u, lall dIes the
abrasiveness of a coated abrasive article in accol ddl ,ce with the present
invention.
F)t~rnple 2
A polyester film was slot coated with a hot melt adhesive
uc."""~,.,i~.''y available from Swift Adhesives Ltd., Tv.;_ke"l,a"" United
Kingdom, under the trade .lesiy, IdIiull, "X200/9~ at about 140DC using a
coating weight of 40 grams per square meter.
Silicon carbide mineral collllllel.. ially available Arendal, Eydehavn,
Norway, having the trade clesi~, IdIio n UP220" was drop coated onto the
tacky, uncured coating at a mineral weight of 185 grams per square meter.
A water-based phenol-ru, " ,aldel ,yde resin was coated over as a size.
Cure was effected at 11 5~C for five hours, and the product was evaluated
25 as described in Example 1 with similar results.
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