Note: Descriptions are shown in the official language in which they were submitted.
20~a~ 3
15943-001 PATPNT APPLICATION
IMPROVED METHOD AND APPARATUS FOR P~ODUCING
HIGH ABRASION RESISTANCE SURFACE SHEETS,
AND SHEETS PROMJCED TlHEREBY
TECHN~C: AL PIE~LD_OF THE INVENTIQN
The present invention relates in general to impregnated
laminates, and msre particularly to a method and apparatus for applying
abrasion-resistant particles to a surface sheet used in such laminates, and
surface sheets produced thereby.
1~
5 ~ ~
15~43-~ll 2 PAIENT APPLICATION
l~CK~RQUND OF ~IE Tl~VENTIO~I
Laminated materials, such as those formed of paper and
impregnated melamine-formaldehyde resins and the like, find uses as
surfacing materials in countertops, table tops, walls and the like. These
laminates typically consist of a stack of several impregnated paper webs. A
top or surface sheet of the stacked laminate most often cont~ins a pleas;ng
design and/or color. It is desirable to impart abrasion resistance to this top
sheet so that it will not be worn away to expose the undecoratiYe kra~t
paper laminations underneath it.
One way to impart abrasion resistance to the top or surface
sheet is to coat or otherwise apply abrasion-resistant particles to the sheet.
The particles can, for example, be any of several hard minerals such as
alumina or silica. Several methods are known in the art to accornplish this.
U.S. Patent No. 4,940,503 issued to Lindgren et al. illustrates a method of
applying small, dry, hard particles directly on to the sur~ace of a wet
impregnated paper web through a doctor-roll. In another known process,
abrasion-resistant particulate matter such as alumina is applied
electrostatically to a wetS impregnated web and the web then dried. In a
third prior art process, exemplified by U.S. Paten~ No. 4,263,081 issued to
Scher et al., hard particulate ma~ter such as alumina is deposited on the
surface of a dry web using a binder such as microcrystalline cellulose. Ihe
web is then dried and subsequently impregnated with a thermosetting resin.
U.S. Patent No. 4,505,974 issued to Hosler, which patent is fi~lly
incorporated herein by reference, discloses spraying à coated mineral
2~90~
1~943-001 3 PATENT APPLICATION
dispersion onto dry, melamine-formaldehyde resin impregnated decorative
sheets.
These p~ior art methods of applying an abrasion-resistant layer
have various drawbacks. Whell the alumina is simply dropped or
S electrostatically adhered to a wet web, an unsatisfactorily uneven
distribution of alumina re~ults. Further, merely dropping the alumina onto
the wet web does not suf~ciently firmly adhere the alumina thereto.
The use of microcrystalline cellulose as a bincler has
drawbacks when particular visual e~fects, such as pearlescent or opalescent
lû effects, are desired. The highly refraetive nature of microcrystalline
cellulose defeats this visual chalacteristic. Further, according to certain
prior art processes, the application of the grit at an early stage callses
increased wear on the web rollers because of the presence of abrasive
particles. The need therefore exists in the industry ~or an ;mpro~ed method
and apparatus for applying abrasion-resistant particles to a surface sheet
web.
2~9~
15943-001 4 PATENT APP~ICATI(~N
SUMMARY OF THE INVENTIO~
According to one aspect of the invention, a method for
manufacturing abrasion-resistant surface sheets for laminates includes the
steps of impregnating the web with a thermosetting resin; prior to drying
S the web, spraying the impregnated web with a slurry including abrasion-
resistant materials; thereafter drying the impregnated web; and cutting the
web into sheets of predetermined length.
In a preferred embodiment, the step of spraying the slurry of
abrasion-resistant materials is performed by a rotary head which is disposed
above the impregnated web. A preselected number of spray arms are
affixed to ~he rotary head so as to radially and downwardly extend from the
rotary head. A spray pistol is moun~ed on a remote end of each of the
spray arms. A pressuri~ed air pipeline and a slurry pipeline are connected
to each of the spray pistols. As the web passes underneat}l the rotary head,
the rotary head rotates and the spray pistols spray a slurry of abrasion-
resistant particles onto the surface of the web. This provides a more
w~iform coverage than has heretofore been obtained with such methods as
dropping dry particles onto a web or electrostatic adherence.
According to a further aspect of the invention~ a station for
pa~tially drying the web occurs imrnediately after the spray station. Then, a
coating of thermosetting resin is applied to the partially dried web at a
coating station placed after the first drying station. The web is then further
dried in a second drying station. The dried web is then cut into surface
sheets.
5 ~ 3
15943-001 5 PATENT APPLICATION
Top sheets produced by the invention have a paper web
impregnated with a thermosetting resin selecting frorn the group consisting
of melamine-formaldehyde, phenol-formaldehyde, phenol-urea-
formaldehyde, melamine-urea-formaldehyde, urea-formaldehyde and
polyester, and having a resin content between 30 and 80% by weight. The
abrasion-re~istant particles are sprayed onto the upper surface of the web
before drying at a concentration of 1 to 40 grams per square meter. The
particles preferably have a size falling within a Gallssian distribution
centered around 9 microns, and are selected from the group consisting of
alumina, siliea, silicon carbide, boron nitride, diamond and mixtures of the
foregoing. The use of abrasion-resistant particles of this size provides good
abrasion resistance, but does not detract from a pearlescent or opalescent
e~fect contributed by the design of the top sheet.
The present invention provides several technical advantages.
The claimecl me~hod can be put into practice by merely incorporating the
slurry-spraying step into a conventional laminate-producing installation.
This allows existing equipment to be used. Applying the abrasion-resistant
material through spraying allows the process to be highly controllerl and ~o
be controlled independently from the initial impregnation step. Cylinders
which come into contact with the impregnated web prior to the abrasion-
resistant particle application step do not experience any wear from such
particles, which tend to be abrasive themse}ves. The method and apparatus
of the invention also avoid the use of special papers.
2 ~ 9 ~
15943-001 6 PAl'ENT APPLICATION
BRIEF DESCRTPIIO~ OF THE DRAWTNGS
Further aspects of the invention and their advantages will be
discerned with reference to the following detailed description when taken in
conjunction with the drawings, in which like characters identify like
S components and in which:
FIGURE 1 is a schematic diagram of a process for fabricating
abrasion-resistant sur~ce sheets, diagrammatically illustrating several
successive steps in the process,
FIGURE 2 is a detail of FIGURE 1 showing the beginning
stages of the process;
FIGURE 3 is a schematic elevational view of a rotary spray
head according to the invention; and
FIGURE 4 is an elevational sectional detail of a slurry spray
pistol according to the invention.
15943-0(31 7 PA'~NT APPLICA'rION
DETAILED DESCRI~ION OF THE D~WINGS
Referring first to PIGURF, 1, a schematic reprcsentation of
apparatus for the continuous manufacture of abrasion-resistant surface sheets
is shown including a plurality of stations at which different process steps are
pe~formed. At point 100, a continuous paper web is fed into the process.
The paper does not require any special characteristic with respect to the
later application of the abrasion-resistant material. The paper will typically
have a decorative printed design or the like, as is suitable for a top or
surface sheet of a laminate. The web is fed through the various process
stations by use of standard conveying equipment (only schematically
shown~.
At station 101, a first impregnation of the paper web occurs.
The impregnation is performed in a conventiona~ manner. The
impregnation may be carried out with a vessel or bath of melamine-
formaldehyde, phenol-formaldehyde, phenol-urea-formaldehyde, melamine-
urea-formaldehyde, urea-formaldehyde or polyester, with a resin content of
3Q to 80% and preferably between 40 and 60% by weight. Preferably, the
first impregnation step at station 101 is per~ormed using a drip-and-squeeze
process with a resin bath having a viscosity in the range of 20 to 100
centipoises, and with s~queeze rollers 103.
The impregnated web 102 next passes to a station 104, which
includes an enclosed cabin or compartment 106. The web 102 is carried in
a flat condition by a conveyor belt 107 or the like (see Fll~URES 2 and 3).
Inside cabin 106, a slurry of hard particulate matter is sprayed onto the
su~face of the web 102 using pressurized air. The slurry is i~ormed through
2~5~3
15943-001 8 PATENT APPLICAl~ON
a continuous agitation of abrasive particles, water and/or adequate solvents
or binders as well as a dispersion/suspension agent. The
dispersion~suspension agent can be a polyacrylic acid or the like. The
dispersion agcnt prevents the grit from settling down and keeps it dispersed
S in the slurry. The slu~Ty contains an abrasive particle weight in the range
of 5 to 40%. The slurry should have a final viscosity range in between S
and 80 seconds No. 4 Ford cup (1û-200 centipoises), anct more pre~erably,
between 10 and 30 seconds (15-100 centipoises). The surface of the paper
web 102 is sprayed until it is uni~ormly covered with a weight of 1 to 40
1~ grams per square meter and, more preferably, between 2 and 20 grams per
square meter. The abfasive particles can be constituted by any of several
materials, such as alumina, silica, silicon carbide, boron nitride, diamond or
a mixture of any of ~he above.
The particle sixe affects the characteristics o~ the finished
1~ laminate surface in that the greater the particle size, the greater the abrasion
resistance. A particle size between 1 and 100 microns, and preferably
between 2 and 50 microns, is regarded as most adequate. In a particularly
preferred embodiment, a particle size having a Gaussian distribution around
9 microns is used.
One advarltage of the invention is that because the particle
slurry is directly sprayed onto the wet impregnated web 102, no
microcrystalline cellulose or other binder is necessary. Howe~er, where a
binder is desired, any can be used as long as it is compatible with the
impregnation resin applied to the web at station 101. For a melamine-
formaldehyde resin, binders such as modified case;ns, acrylic compounds,
2~91~S3
1~943-0C)1 9 PATENT APPLICATION
polyvinyl alcohols, et cetera can be used in binder:grit weight ratios ranging
from 1:5 to 1:15.
In the instance where the design definition calls for a
pearlescent or opalescent effect in the final surface sheet, the grit size
should be large enough so as not to detract from it. A grit si~e havin,g a
Gaussian distribution around 9 microns ha~ been ~ound not to detract ~rom
the visual characteristics of the finished surface sheet. Microcrystalline
cellulose should be avoided for use with pearlescent top sheets as its highly
refractive nature interfers with the visual effect. The average thickness of
the abrasive particle coating on the web 102 is in the range of 1 to 8
microns.
The beginning steps of the process are illustrated in more
detail in FIGURE 2. From a drum 110, a continuous paper web 112 is fed
via rollers 114 between a photocell 116 ancl a light source 118. Photocell
116 and light source 118 eoact such that when the end of the we~ 112 is
reached1 the photocell 116 will be activated. Photocell 116 is connected by
a relay or the like (not shown) to each of a plurality of valves mounted in
respective spray pistols of the slurry sprayer 108, all of which will be
described below. Web 112 is then guided by rollers 120, 122, 124, 126,
128 and 130 through a vat or both 132 of melamine ~ormaldehyde resin or
other impregnation resin. After impregnation is completed by passage of
Illc wcb 112 tllroll~h tllc s~luee~e rollers 103, the impregnated web 11)2
passes into the spray cabin 106.
A novel rotary sprayer indicated generally at 108 includes a
plurality of spray arms indicated schematically at 134, each arm 134
2~0~3
15943-001 10 PATENT APPLICATION
terminating in a spray pistol 136. The ~ms 134 are connected to a rotary
spray head 138 which is driven to rotate about it3 axis indicated by the
dashed line 140. The rotary spray head 138 may, for example7 be belt-
driven by an apparatus such as a drive belt indicated schematically at 142
S and an eIectric motor indicated schematically at 144. The electric motor
144 has a speed variator which is coupled to the general motor (not shown)
of the apparatus 10. This general motor regulates the speed of the paper
web 112 so as ~o synchronize rotation speed of the head 138 and of the
paper in the apparatus 10.
~he rotary sprayer 108 and associated equipment are illustrated
in more detail in FIGURE 3. In FIGURE 3, ~wo spray arrns 134 are
shown instead of the three arms 134 that are shown in lF;IGURE 2. The
number of spray arms may be varied according to the application. The
spray arms l34 are radially displaced from the axis 140 and are angularly
lS disposed around the circumferen~e of the spr~y head 138 preferably to be
equally separated from each other.
Each spray arm 134 includes an arm segment 146 which is
directly a~fixed to the spray head 138. The arm segment 146 distzllly
terminates in an adjustment sleeve 148. A second arm segment lS0 has a
first proximal end fitted into the adjustment slee~,re 148 and a second distal
end terminating in a sprayer calr.er holder lSl. The adjustmen~ sleeve 14~
includes fasteners for adjustably holding the arm segment 1~0 in place, such
as a screw or screws 154 or the like. A spray carrier 152 is fit~ed into the
carrier holder lSl. The calTier holder 151 lilcewise is an acljustment fitting,
and includes a screw or screws 156 or the like. Carrier holder 151 alls~ws
20~a53
15943-001 11 PAl~NT APPLICATIC)N
Ihe distance from the pistol 136 to the web being treated 158 to be adjusted.
Each sprayer carrier 152 terminates in at least one spray pistol
136. Through adjusting the arm segment 150 with respect to the ~rst arm
segment 146 using the sleeve 148, the radial distance of the pistol 136 from
the axis 140 can be adjusted. The radial arms 134 are adjusted in order to
take into account the differing widths of the impregnated web 158 which
might be treated, which for example may range from 1240 to 1700 mm.
Each spray pistol 136 receives pressurized air in a respective
air pipeline 160 and liquid slurry in a respective slurry pipeline 162. Air
and slurry pipelines 160 and 162 are prefierably sized to be at least 5 mm.
in interior diameter.
The air inside air pipe 160 is compressed, as by a compressor
schematically illustrated at 164, to a pressure in a range o~ 2 to 10 kg/cmZ
in order to impart suitable spraying force to the slurry ernitting from pis~ols
136, with a preferred working range of 2 to 3 kg/cm2. A. slurry pump
schematically il~ustrated at 166 may be used to provide slurry under
pressure to pipes 162. A slurry feed pressure in the range of 1.5 to 4
Icg/cm2 has been ~ound suitable ~or operating the spray pistols 1369 with a
preferred slurry pressure of 1.5 to 2 kg/cm2.
The spray pistols 136 each produce a conical spray or haze
168 which is sprayed onto the surface of the impregnated web 158. It is
prefelTed that a single pipe or a line 17V be used to convey the pressurized
air into the spray head 138, at which point air pipe 170 branches into a
plurality of pipes or lines 160. Similarly, a sin,gle pipe 172 car:nes the
pressurized slurry from the slurry pump 166 into the rotary head 138,
2~9~.~53
15943-001 12 P~TENT APPL,I~A~ON
where it branches into a plurality of slurry pipelines 162 equal in number to
the number of spray pistols 136.
FIGURE 4 is a detailed elevational sectional view of a single
spray pistol 136. A body 174 of the pistol 136 has formed therein a central
S bore 176 which is formed around a pistol axis 178. The bore 176 has a
tapered low~r orifice 180. Received into the bore l76 i~ a needle 182
having a frusto-conical end surface 184 adaptable to seat on the tapered
sur~ace of orifice 180. The elongate needle 182 extends into a top portion
186 of ~hc pistol 136 having relatively thin sidewalls 188. Sidewalls 188
define a lower chamber 190 and an upper chamber 192. A spring 194 is
operable to exert force between a needle flange 196, affixed to needle 182,
and a pistol cap 198. The cap 198 includes a central bore 200 adaytable to
slidably receive a top end 202 of the needle 182 when the needle 182 is in
an upward or open position.
The flange 196 slides in close registry with Ihe sidewalls 188
of top portion 186. A sealing gas~et or ring 204 allows a coaxial up-and-
down sliding motion of the needle 182, but nevertheless substan~ially
hermetically separates the lower chamber 190 from the bore 176.
The air pipe 160 branches into a first length 206 regulated by
a remotely controlled valve 208, and a second branch 212. Extending ~rom
the remotely controlled valve 208 to ~he lower chamber 190 is a pipe
segment 210. When the valve 208 is open, pressurized air from pipe 160
flows into the lower chamber 190, urging the needle flange, 188 in an
upward direction against the bias exerted by the spring 194. The upward
urging of the needle 182 will cause frustoconical surface 184 to unseat itself
2~90~3
15943-001 13 PATENT APPLICATION
from the tapered surface of orifice 180, causing sloped orifice 180 to open.
Separately, branch 212 communicates the air pipe 160 with an annular
outlet 214. Air flowing out of the outlet 214 imparts downward spray force
to the slurry.
S The slurry is fed by slurry pipe 162, and enters into bore 176
and out through the orifice 180. When air ceases to flow through pipe 160,
or when the remotely controlled valve 208 is turned off, the spring 194
forces the needle 182 into registry with the sloped walls of the orifice 18û,
thus cutting off the spraying of slurry from pipe 162.
Remotely controlled valve 208 preferably is controlled by the
photocell 116 (FIGURE 2). When the photocell 116 senses that the end of
th~ web 112 has passed it, it will cut o~f the spraying of slurry from each
of the pistols 136 by closing the respective remotçly controlled valves 208.
The cap 198 may be removed for servicing of the spray pistol interior.
Returning to FIGURE 1, once the web lS8 has been sprayed
to deposit a layer of hard particulate matter, the web 158 is passed to a first
drying oven station 216. Once the web 158 has partially dried in the oven
216, it is preferably passed to a coating station 218 at which a second
coating of melamine or other thermosetting resin is applied to the surface of
the web. It is preferred that this be performed ~y a roller-coating operation
as indicated by roller 220. The meiamine or other thermosetting resin used
at station 218 can have a viscosity in the range of 30 to 300 centipoises.
The additional coa~ing provides the surface of the web with
v~ious special characteristics as desired. Along with a second resin, other
2~90~5~
15943-001 14 PATENT APPLICArl~ION
additives may be added to the web at this point~ such as finer abrasive
particles, pearlescent pigments, and other materials
After the roller coating step, a web 222 is produced which is
passed to a second drying stage or oven 224, The dried web 226 is
S subsequently passed to a cutting stage 228 at which the web 226 is cut into
surface sheets 230 having a desired length These may be subsequently
used in n laminating process to crcate lamirlates for use in countertops,
walls, partitions and the like The surface sheets 230 may be subjected to
laminating temperatures and pressures that are normally used in higher
pressure laminates, such as a temperature in the range of 120 to 160 C.,
depending upon the type of resin used, and pressure of 70 to 120 k;lograms
per square centimeter
The present invention provides several technical advantages. It
may be put into practice by merely incorporating the innovative spray step
I5 shown at 104 into an installation having otherwise conventional process
steps The abrasive coating is applied in a direct and very controllable
fashion in a step which is independent from the initial dip-and-squeeze
impregnation which takes place at step 101. The squeeze cylinders 103 do
not suffier from abrasion due to abrasive particles, as the abrasive slurry is
sprayed onto the surface of the web only after excess resin is squeezed out
of the web in the first impregnation step This, in turn, reduces ~he number
of fail(lres ~nd increases the lifetime of the process equipment. The present
invention also avoids the use of speciaI papers where abrasion resis~ance is
desired. Because of the spray method used, there is no need for a binder
such as microcrystalline cellulose. The lack of such a binder, which has a
2 ~ 3
15943-001 15 PATENT APPLICATION
tendency to be highly refractive, allows the surface sheet to take on any
other variety of different YiSUal characteristics, including pearlescence or
opalescence.
The surface sheets 230 finally produced are there-fore based on
~ web that is first impregnated with a first resin at a dip-and-squee~e 101~
Subsequently, a layer of abrasion-resistant particles is applied to the web at
station 104. In a preferred embodiment, the web is completed with the
application of a second thermosetting resin, which may be the same or
different from the resin initially applied at step 101. This allows additional
materi~ls to be placed on the sur~ace of the surface sheet, such as finely
divided abrasive particles and the lilce.
In summary, a novel method and apparatus for spraying a
particulate slurry of abrasion-resistant particles onto an impregn2ted web,
and a novel surface sheet produced thereby, have been disclosed in the
above detailed description. However, the present invention is not limited to
the specific embodiments of the invention but only by the scope and spirit
of the claims which follow.
