Flexible and extensible coated abrasive material

A coated abrasive material comprising a textile backing--in the form of fabric, webbing, fleece and/or laminated material, base binder, abrasive particles and optionally size coat which is characterized in that the textile backing is extensible and that on the particle side an elastic intermediate layer is applied which lies between the textile backing and the usual base binder. This intermediate layer may contain caoutchouc latex and/or polyurethane and/or polymers, which contain butadiene and/or acrylic acid ester. The flexible and extensible coated abrasive may be used for profile grinding, sanding or polishing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an abrasive material, to a method for its 
manufacture and to the use of this abrasive. 
2. Description of the Prior Art 
The abrasion of profiles is frequently carried out with endless abrasive 
belts which must be guided via an abrasive contact wheel, a drive roll, if 
necessary a reversal roll and a tension roll, etc. 
In order that the abrasive belt can be adapted to the contours of the 
workpiece to be processed, it is pressed from the rear side against the 
workpiece to be abraided by means of a rigid profiled abrasion shoe or 
abrasion block. A further possibility consists in that the workpiece is 
abraided by means of the abrasion contact wheel, the latter also being 
provided with the counterprofile of the workpiece to be processed. 
Other devices for the abrasion of profiles using coated abrasives consist 
of profiled abrasion blocks, abrasion shoes, abrasion contact wheels or 
abrasion wheels which are overlaid by means of a flexible coated abrasive, 
for example using glueing or welding. In order to ensure adaption of the 
abrasive to the profile, it was previously necessary mostly to use 
expensive methods such as for example the cutting or provision of upset 
grooves. 
In each case the requirement exists that the flexible abrasive is adapted 
exactly to the contours of the given profile. 
In German Offenlegungsschrift No. 30 36 991 a device is mentioned for 
abrasion, particularly for surface abrasion of wooden parts, which 
consists in that an abrasive body is used which consists of an elastic raw 
material and which is surrounded at least partially by an endless abrasive 
belt which is elastic. Preferably the belt joint region of the abrasive 
belt is formed elastically. 
In European Patent Application No. 0 052 866 A3, an abrasive belt for 
profile polishing is described which consists of an extensible fabric 
backing coated with abrasive particles, the warp threads of which backing 
running at a sharp angle of 20.degree. to 60.degree. to the belt direction 
and the abrasive belt having longitudinal zones of low extensibility. 
It is true that some earlier known flexible coated abrasives had a certain 
degree of extensibility. This extensibility was however insufficient to 
satisfy the requirements which for example are made upon an abrasive for 
profile grinding. Even the abrasive on the fabric backing in which the 
extensibility was increased according to EP No. 0 052 866 A3, proves to be 
insufficient with difficult profiles. With the use of such an extensible 
abrasive, the breaking off of the abrasive particles is also very 
problematical as soon as it is stretched or extended more than a certain 
extent; such a degree of stretching is often required in profile 
polishing. 
In the already mentioned German Offenlegungsschrift No. 30 36 991 it is 
explained that the manufacture of an elastic abrasive band (with the 
previously known abrasive) would not be possible owing to the disturbance 
of the surface during extension and the resulting breaking off of the 
abrasive particles. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an abrasive device which allows 
good adaption to the workpiece during abrasion, in particular during 
profile abrasion. A further object is to provide an abrasive device which 
can be used for the manufacture of profiled abrasive shoes, profiled 
abrasive blocks and profiled abrasive contact drums or abrasive wheels. 
A flexible and extensible abrasive on a substrate which does not show the 
disruption of the layer and breaking off of the abrasive particles has 
surprisingly been found by manufacturing the abrasive on an extensible 
substrate preferably of textile material which is provided with an elastic 
(stretchable) intermediate layer which lies between the substrate and a 
base binder on which the abrasive particles and optionally covering binder 
are provided.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
FIG. 1 schematically illustrates the coated abrasive material including 
abrasive particles 1, a flexible and extensible textile backing 5, an 
elastic intermediate layer 4, a base binder 3 and a size coat 2. 
The elastic intermediate layer 4 may comprise polyurethane, polyacrylate, 
caoutchouc latex and/or polymers containing butadiene, such as 
acrylnitrile-butadiene-styrene polymers or butadiene-styrene-polymers (cf. 
butadiene-polymers in "Kunststofflexikon" (Synthetics Dictionary 7th 
edition at pages 99 and 100, published by K. Stockhert, Carl Hanser Verlag 
1981). 
If necessary, these polymers can be modified by the addition of curing 
agents or cross-linking agents or as the case may be of curable resins or 
cross-linkable resins, such as phenolic resins, melamine resins, resorcin 
resins, or urea formaldehyde resins, in order to achieve the necessary 
elasticity and adhesion properties within a wide temperature range. Also, 
the elastic intermediate layer 4 may contain inorganic and/or organic 
filler materials. 
It was found that the intermediate layer 4 has, to a greater or lesser 
extent, a pronounced elasticity (in the sense of the description in the 
Kunstofflexikon, ibid. page 151) or in other words a relatively low 
modulus of elasticity (according to DIN 53 475) and also ensures good 
adhesion to the textile backing 5 on the one hand and the base binder 3 on 
the other hand. The modulus of elasticity measured on a test body 
according to DIN 53 457 of the intermediate layer 4 should be no higher 
than 300 N/mm.sup.2, preferably however no higher than 50 N/mm.sup.2. The 
intermediate layer 4 can be applied on the textile substrate 5 by means of 
known methods, for example as a solution in an organic solvent, as an 
aqueous dispersion, or as a melt and if necessary can be chemically 
cross-linked. It is also possible to apply corresponding monomer or 
prepolymer substances to the substrate 5 and to carry out afterwards the 
polymerization and if necessary the cross-linking, for example by means of 
electron bombardment. 
The thickness or amount per unit area of the intermediate layer 4 is not 
critical but depends to a certain extent upon the desired degree of 
extensibility and the nature of the textile substrate 5 i.e. the 
penetration depth into the substrate. In general, the desired results can 
be achieved with amount (dry) between 40 and 120 g/m.sup.2. 
In accordance with one embodiment of the invention , a textile surface 
construction is used as substrate 5 extensible in the longitudinal and/or 
transverse direction having fibers for example of cellulose, cellulose 
acetate, polyamide, polyester, polyurethane and/or caoutchouc polymers in 
the form for example of fabric, webbing, fleece, laminated material, 
layered material or mixed fabrics or mixed webbing which may be attached 
antistatically or with other fastening means. It is also possible to use 
an extensible, non-textile surface construction such as an elastic film 
material. Such substrates have however proved to be less suitable. The 
textile substrate 5 on which (on one or both sides) the elastic 
intermediate layer 4 is carried, can contain greater or lesser proportions 
of elastomers, thanelast fibers (elasthan fibers), elastic fibers, 
elastodiene fiber or threads (cf. Kunststofflexikon, 7th edition, ibid. 
pages 150-153). 
Also highly elastic fibers which are extremely highly deformable and which 
have an elongation at break of more than 200%, usually 500 to 800%, may 
also be included in the textile substrate 5 before the base binder, 
abrasive particles and size coat are applied. 
In the textile surface structure preferably used as backing 5 for the 
abrasive material in the form of a fabric, webbing, fleece, etc. there may 
be used weft fibers and/or warp fibers or yarns of higher elasticity or 
extensibility. Weft or warp fibers or yarns of higher elasticity can be 
manufactured using known methods, for example by entwining cotton fibers 
around a "core" of elastomeric fibers or by using textured or crinkly 
fibers or yarns. 
As the base binder and size coat(s), the usual resin types such as for 
example phenol formaldehyde resins, urea formaldehyde resins or melamine 
formaldehyde resins are used. Preferably, phenol formaldehyde resins are 
used. Also the usual abrasive particles with the usual particle size are 
used for example aluminum oxide (corundum), zirconia alumina, silicon 
carbide, diamond, garnet, flint, emery. 
In order that a flexible coated abrasive can adapt for example true to form 
to a profiled abrasion shoe, a profiled abrasion block, a profiled 
abrasion roll or an abrasion contact wheel, it must first have the 
necessary extensibility adapted to the given profile form, i.e. the coated 
abrasive must be capable of being stretched with comparatively low force 
and without breaking off of abrasive particles around sharply cambered 
parts or around parts which are sharply radiused. An extension of 40% or 
more of the original length of the abrasive sheet corresponds to a typical 
requirement. 
The abrasive device according to the invention is suitable in particular 
for profile polishing or as the case may be for the manufacture of profile 
abraiding elements such as profile abraiding shoes profile abraiding 
blocks or profile abraiding contact rollers or wheels. The said profile 
abraiding elements can be manufactured in an economical manner by using 
the abrasive device according to the invention. The high extensibility 
enables adaption even to difficult profiles, so that the formerly used 
methods, such as cutting apart, the provision of thrust grooves, the use 
of segments having elastic connecting strips and others, are thus rendered 
unnecessary. FIG. 2 shows for example a cross-section of a profiled 
abrasive contact wheel manufactured from the flexible and elastic abrasive 
according to the invention. Reference numeral 8 shows the actual profile 
body which is covered by an abrasive device 6 according to the invention. 
Reference numeral 1 represents the abrasive particles and 7 represents the 
substrate of the abrasive. The periphery of the zone with the largest 
radius of the profile (A) is approximately 40% larger than that in the 
zone with the smallest radius (B). The profile contact wheel is secured on 
a mounting and drive device 9 by means of parts 10 and screw 11. The 
manufacture of the profile contact wheel body 6 and 8 can take place in 
various manners. The profile body 8 can either be manufactured separately, 
for example from wood or plastics according to known methods and 
thereafter the abrasive 6 be provided for example by glueing, or however 
the abrasive body 8 can be manufactured simultaneously with the covering 
abrasive 6 for example by means of injection molding methods from 
polyurethane resin foam. Such a wheel may be used for grinding or 
polishing difficult profiles. 
The extensible textile surface structure 5 can be arranged to be extensible 
in all directions or only in one direction. Preferably it is so 
constructed that extensibility is achieved especially transversely of the 
machine direction or longitudinal direction (with a webbing this 
corresponds in general to the weft direction). The abrasive device 
according to the invention preferably has in the longitudinal and/or 
transverse direction an extensibility of at least 10% under a load of 100 
N/5 cm, most preferably however such an extensibility of at least 25% with 
the same load. The extensibility can be represented by the force-extension 
diagram of FIG. 3 where the extension or elongation of the abrasive is 
represented as a function of the load. On the one axis the load is 
represented in terms of N/5 cm wide strips and on the other axis the 
extension is represented in terms of % of the original length. In the 
diagram are represented four force-extension lines or curves, that is to 
say the curve A, B, C and D. The curves A and B serve for comparison and 
correspond to typical values of a usual abrasive on a substrate. Curve A 
corresponds to the machine or longitudinal direction, and curve B to the 
transverse or weft direction of a typical usual flexible abrasive on a 
webbing substrate (abrasive having the trademard designation "SIATUR JJ" 
of the firm SIA). The lines C and D correspond to the abrasive device 
according to the invention, and represent boundary lines. The curves of 
the abrasive device according to the invention lie in the field left 
(double hatched area) of the boundary line C or preferably in the field 
left (single hatched area) of the boundary line D. The breaking load is 
not represented in the diagram. 
The following examples illustrates the invention: 
EXAMPLE 1 
A fleece of polyamide fibers having a weight of 135 g/m.sup.2 and having a 
breaking extension in the longitudinal direction of 65% and in the 
transverse direction of 90% was coated with a dispersion of a co-polymer 
on the basis of butadiene and styrene (50% solids content). The dispersion 
was applied by means of a doctor blade in an amount of 120 g/m.sup.2 (wet) 
and finally dried for 2 minutes at 120.degree. C. in a surface dryer. This 
polyamide fleece provided with the elastic intermediate layer was then 
used as backing material for a flexible coated abrasive. As base binder 
for the abrasive particles, an aqueous phenol formaldehyde resol filled 
with 20% limestone powder was used; the solid body content amounted to 62% 
by weight. The phenolic resin was applied to the coated side of the 
polyamide fleece in an amount of 70 g/m.sup.2 by means of roll coating. To 
this layer, 160 g/m.sup.2 of commercially available aluminium oxide 
abrasive particles (particle size no. P 120) were applied. The application 
process was carried out according to the electrostatic coating method 
common in the abrasive industry. Next, the coated fleece was hung up and 
the base binder was dried and cured for 15 minutes at 80.degree. C., 15 
minutes at 95.degree. C. and 20 minutes at 120.degree. C. A size coat was 
then applied by a rubber roll in an amount of 260 g/m.sup.2. The size coat 
consisted of the same phenol formaldehyde resol as the base binder but the 
proportion of filler amounted to 50%. The size coat was dried and cured in 
a festoon dryer. The finally cured abrasive was flexed so that the hard 
phenolic resin--abrasive particle--coating was broken into small segments. 
Examination of the finished abrasive material showed that the high 
extensibility measured on the fleece was also present in the abrasive. 
Thus, for example, the extension transversaly amounted to 40% at a load of 
100 N/5 cm. The adhesion of the abrasive layer was very good and 
corresponds to a conventional abrasive with smaller extensibility. The 
abrasive material can be adapted in a true manner to contours on a profile 
abrasion block, this being extended in some zones up to 40% of its 
original length. 
EXAMPLE 2 
As backing, a fabric with elastic weft and a weight of 150 g/m.sup.2 was 
used for the manufacture of a flexible and elastic abrasive material. The 
backing was a cotton fabric in a linen weave whose weft fibers were 
manufactured by spinning cotton around a "Lycra".RTM. fiber core ("Lycra" 
is a registered trademark for the elastic polyurethane fibre of DuPont de 
Nemours, also known as "Spandex"). The ratio of cotton to "Lycra" amounted 
to 90:10 (by weight). This fabric was coated with a doctor blade with 120 
g/m.sup.2 of a dispersion of thermically cross-linkable co-polymers on a 
base of acrylic acid ester (50% by weight). The layer was dried in a flat 
dryer for two minutes at 130.degree. C. The application of the abrasive 
layer was the same as in Example 1; however an abrasive particle size no. 
P 80 was used. Examination showed that the high extensibility of the 
initial web was still present in the final abrasive material. The 
extensibility value amounted to 30% at a load of 100 N/5 cm and to 45% at 
a load of 200 N/5 cm. The adhesion of the abrasive particles proved to be 
very good also after the extension and the manufacture of a profile 
abrasion contact wheel according to FIG. 2. 
EXAMPLE 3 
A fabric having highly elastic textured polyester filament yarn weft and 
cotton warp in twill weave and having a weight of 200 g/m.sup.2 was coated 
with a polyacrylic ester dispersion. This dispersion (40% by weight) was 
applied with a doctor blade to an amount of 80 g/m.sup.2 this case the 
construction of the abrasive coating was the same as in Example 1. The 
extensibility transversely of the finished abrasive was hardly any 
different from that of the raw web. The extension at a load of 80 N/5 cm 
in the weft direction amounted to 24% and the particle adhesion was 
completely satisfactory.