Note: Descriptions are shown in the official language in which they were submitted.
2 ~8 ~
INLAID GRANITE PLA8TIC FLOOR TILE
BACKGROUND AND SUMMARY OF THE INVENTION
This is a continuation-in-part of application Serial No.
819,135 filed January 10, 1992 which is a continuation-in-part
of application Serial No. 589,595 filed September 28, 1990
which is a continuation-in-part of application Serial No.
413,208 filed September 27, 1989, now U.S. Patent No.
4,965,299.
In one embodiment, the present invention relates to an
inlaid tile in which filled colored polymeric chips are
uniformly dispersed throughout a filled thermoplastic mass
which may be of a different color. The chips remain discrete
during high temperature processing in an intensive mixer such
as a Banbury mixer or mixing mill. By the invention, an
inlaid tile is produced with decorative plastic chips which
are dispersed throughout a thermoplastic base so that the
chips remain discrete and non-smearing and do not elongate
during processing.
Previous compositions having chips contained within a
base material are described, for example, in the following
U.S. patents: 3,787,280 to Conger et al.; 3,966,857 to
Charlton et al; 4,054,699 to Brinkley; and 4,501,783 to
~iragami et al.
By the present invention, there is provided an improved
inlaid floor tile in which colored chips are formulated with
polymers, stabilizers, fillers, cross linking agents and
pigments which differ from the thermoplastic base. The tile
base is produced with polymers, stabilizers, fillers,
processing aids, pigments and internal lubricants or fillers
coated with lubricants. The lubricants are used in the
thermoplastic base to reduce processing temperatures and shear
in the intensive mixer so that the decorative chips remain
discrete particles and do not flow during processing.
T~ A= A~; m_n~ the ch ins which are added to the
~086311 ll
being made of pigmented polyester or epoxy or by a ceramic
technique. Alternatively, a mixture of coated mineral chips
and partially cross linked resinous chips may be employed. By
the addition of such chips, there is produced a tile product
having a granite appearance or effect.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a vertical cross-sectional view of a portion of
the tile composition of the present invention, containing the
tile base with particulate materials dispersed therein.
Fig. 2 is a vertical cross-sectional view of another
embodiment of the tile product of the present invention,
containing the tile base with angular coated mineral chips
dispersed therein.
Fig. 3 is a vertical cross-sectional view similar to Fig.
2, containing the tile base with round coated mineral chips
dispersed therein.
Fig. 4 is a vertical cross-sectional view similar to Fig.
2, containing the tile base with a mixture of round coated
mineral chips and partially cross linked chips dispersed
therein.
Fig. 5 is a top view showing the surface of the present
tile product employing a relatively sparse amount of chip
materials.
Fig. 6 is a top view similar to Fig. 5 but showing the
` use of a relatively heavy amount of chip materials.
.,1
DES~RIPTION OF THE PREFERRED EMBODIMENTS
In the embodiment of the invention as shown in Fig. 1,
, there is provided a tile product 10 having a tile base 12 with
particles or chips 14 uniformly dispersed throughout the base
12 as shown.
; In accordance with the present invention, techniques
which may be employed to produce the polymeric phase of the
chip formulation include:
~a~31~
1. Cross linking
2. Com~ination of partially cross linking and high
melting thermoplastics in which each chip is formulated with
partial cross-linking and the remainder of the chip polymeric
phase is high melting thermoplastic.
As an example of chip production, the chips may be
produced by mixing the ingredients in an intensive mixer, such
as a steam-jacketed Banbury mixer operating at 40 to 46 rpm
with steam at 310 F. Mixing continues until the combination
of the heat provided by the steam and the shear action of the
mixer produces a temperature in the material bein~ mixed of
about 350 F., and under such conditions the ingredients
become a molten mass. The mass is then calendered to produce
a sheet approximately 100 mils thick. The sheet is heated to
400 F. by use of radiant heat or other means to partially
cross link the polymeric ingredients, after which the sheet is
cooled and ground into small chips with the dust -200 mesh
being screened out. In an alternative embodiment the
calendered sheet may first be ground into chips and then fed
into a fluidized bed to effect cross linking of the polymeric
components.
The size of the chips employed in the invention include
particles in which the major portion, about 94 to 100 wt.
percent, has a U.S. mesh size of between 10 and 200 mesh, and
including an additional portion of 0 to 1 wt. percent of a
size which is retained on a 10 U.S. mesh screen and a portion
of 0 to 5 wt. percent which passes through a 200 U.S. mesh
screen. In a prPferred embodiment the chips have a Shore D
hardness range of 75 to 88. In the embodiment as shown in
Fig. 1, the chips produced by the present invention preferably
are not round but angular and non-uniform in shape, having
sharp ed~es and with the chip size of the major portion being
uniformly distributed throughout a U.S. mesh size of 10 to 200
mesh, preferably 14 to 40 mesh.
In one embodiment of a chip composition, the mesh size
3 1 ~
specification was as follows.
U.S. Mesh Size % bv wt
+14 0
-14 to +16 2% max
-14 to +18 22 to 32~ !
-14 to +25 70 to 90%
-40 2% max
An example of a chip formula is as follows: ¦
Chip Formula % bv wt
1. Polyvinyl Chloride Homopolymer 35.0
2. Phenolic Resin 7.0
3. Pentaerythritol 1.0
4. Magnesium oxide 1.0
5. -40 Mesh Limestone (420Microns) 55.9
6. Red Pigment (oxide) o.l
Total 100.0
With regard to the chip formula, ingredient No. 1 is the
main thermoplastic synthetic polymer component of the chips
and is present in an amount of about 25 to 80 weight percent
of the chip composition, depending on the filler level of the
chips. In addition to the above stated example, the
thermoplastic polymer component may alternatively be one or
more of the following: (a) a copolymer of polyvinyl chloride
with polyvinyl acetate; (b) polyester resin; or (c)
chlorinated polyethylene, and need not necessarily have a
softening temperature higher than the polymers used in the
tile base since it will be partially cross-linked during chip
manufacture.
Ingredient No. 2 functions as a plasticizer which will
liquify initially for the initial phase in the Banbury mixer
but is then irreversibly cross linked with ingredients 3 and
4 at 400 F and will not liquify again. The plasticizer may
also be polyester or epoxy resin or a combination of said
resins. The plasticizer may be present in an amount of about
0 to 10 weight percent of the chip composition. In a
;preferred embodiment, the amount of plasticizer is about 5 to
9 weight percent of the chip composition.
During chip production, the polyvinyl chloride or other
thermoplastic polymer component cross links or partially cross
1 ;nkc w;~h ~n~Cillm oxide and ~entaervthritol. The Phenolic
~8~
resin also cross links with magnesium oxide and
pentaerythritol.
Any of various colored pigments may be employed in the
chip composition. A high melting thermoplastic in the form of
an acrylic resin such as polymethyl methacrylate polymer may
be employed in combination with the phenolic resin to enhance
the flowability. Such a high melting thermoplastic will soften
or flow during chip production but will not soften or flow
during the second phase of tile production in which the chips
are mixed with the tile base material. In another embodiment,
an epoxy resin is employed instead of the phenolic resin and
melamine is added to cross link the epoxy.
In the production of the ~hips by a combination of
partially cross linking and high melting thermoplastics,
approximately 9 to 40 weight percent of the total chip
formulation is cross linked. Thus approximately at least 18
weight percent of the chip polymeric phase is cross linked.
The amount of cross linking is controlled by the temperature
and time employed during chip production as well as by the
amount of cross linking agent employed.
The high melting thermoplastics include those materials
which do not soften or flow at the temperatures employed
during mixing of the chips with the tile base material in the
intensive mixer. The high melting thermoplastic materials may
include, for example, a combination of acrylic resin and PVC.
The high melting thermoplastic component can be present in an
amount of about 5 to 50 weight percent of the total chip
composition.
In the event that cross linked chips are employed without
high melting thermoplastics, it is not necessary to employ
lubricant in the base material, provided the chip material is
irreversibly cross linked.
By the use of partial cross linking in chip production
along with high-melting thermoplastics, processing time
2 ~
more down to a time of about 15 seconds. Such a feature is
highly advantageous in reducing the amount of line time so
that the process can be carried out in an efficient and
economical manner.
The -40 mesh limestone functions as a filler in the chip
formula. Other suitable filler materials such as alumina
trihydrate may be employed. The chip composition contains
about 10 to 75 weiqht percent filler.
The amount of chips employed in the tile base is
generally about 2 to 20 weight percent of the total
formulation of chips and base.
As an example of production of the tile composition of
the present invention, the tile base may first be produced by
adding the ingredients to an intensive mixer such as a steam-
jacketed Banbury mixer having steam at 310 F. and operating
at 40 to 46 rpm, with mixing for a period of about 2 minutes
until the ingredients become a molten thermoplastic mass, at
which time the cross linked chips previously produced can be
added. After an additional mixing period of about 20 seconds
to 1 minute, the molten mass at a temperature of about 300
F. is dropped to a two roll heated mill where a sheet is
formed. The sheet is calendered to thickness, then cooled and
cut into tiles of the desired size such as 12" x 12". The
sheet can also be embossed. The thickness of the final tile
product is generally about .0625 to .231 inch.
An example of a tile base formula is as follows:
Tile Base Formula % b~ wt
1. Resin mixture 40% PVC homopolymer
and 60~ PVC, PVA Copolymer 13.0
2. Ground Limestone -40 Mesh and finer 59.8
3. Plasticizer DINP 4.0
4. Zinc Stearate (Lub) .02
5. Stabilizer Synpron 1751 Calcium Zinc Type .88
; 6. Hi-Plex 100 Pfizer Surface treated CaC03
; with Calcium Stearate 10.0
7. Processing aid alpha methyl styrene 1.5
8. Talc 7 Micron lO.o
9. Pigment (Tio2~ 0.8
Total lOO.Oo
With regard to the tile base formula, ingredient No. 1 is
the main thermoplastic synthetic polymer component of the tile
base and is present in an amount of about 10 to 25 weight
percent of the tile base. The thermoplastic base component
may be produced from any suitable filled polymer, such as that
formed of a vinyl polymer, including a homopolymer, a
copolymer or a combination of the two. Thus the thermoplastic
polymer component may, for example, be a combination of from
about 40 to 100 weight percent, preferably about 40 to 80
weight percent, of PVC homopolymer and from about 0 to 60
weight percent, preferably from about 20 to 60 weight percent,
of a copolymer of PVA and PVC. The thermoplastic polymer
component may also be formed of polypropylene or polybutylene
materials.
Ingredient No. 2 functions as a filler in the tile base.
Other suitable filler materials may be employed. The amount
of filler in the tile base can be about 50 to 85 weight
percent.
Ingredient No. 3 functions as a plasticizer and may be
present in an amount of about 3 to 6 weight percent of the
tile base.
With regard to the lubricant component, it is possible to
obtain the desired lubricating property by the use of any one
of ingredients Nos. 4, 5 or 6. In this regard, ingredient No.
6 may be employed in amounts of up to 20 percent and this
surface treated limestone includes a small amount of lubricant
which acts to control the drop temperature and shear forces.
By the use of a lubricant component in the tile base, the drop
temperature may be maintained at 300~ F. or less so that the
chips when added will not soften or melt and also the abrasion
of the pigmented mineral coated chips will be reduced. In
this regard, the amount of lubricant employed is generally in
an amount of about 0.10 to 1.0 percent by weight of the tile
base. Satisfactory lubricants include calcium stearate, ~inc
stearate, and stearic acid, as well as various oleates and
8 ~ 3 ~1 ~
palmitates '~nown in the art.
With regard to that portion of the process in which the
molten mass is dropped to the two roll mill, a short time
interval such as about 20 seconds after addition of the chips
is desirable before the material is dropped, in order to
maintain definition of the chips. At least about 20 seconds
in the high intensity mixer is needed to obtain proper chip
dispersal in the base material. Thus a time interval of about
20 seconds to 3 minutes (the entire Banbury mixing time),
preferably from about 20 seconds to 1 minute, is usually
employed. The chips may be subject to bleeding or breaking if
mixed for longer periods of time. Also shear forces develop
upon addition of the chips which could cause the temperature
to rise above 300 F., thus softening the chips.
The use of reaction temperatures in the range of about
300 to 400 F. is particularly desirable when PVC is employed,
in order to maintain the stability of the PVC component. At
temperatures above 400 F., the PVC degrades and there is not
sufficient time for proper utilization of the PVC. At
temperatures below about 280 F., on the other hand, PVC will
not process or fuse properly.
In one embodiment of the invention, the chips and the
tile base had a formulation hardness as follows, based upon a
77 F. indentation test in accordance with Federal Test Method
Standard No. 501:
Chips - 4 to 6 mils at Gauge 90 to lO0 mils
Base - 9 to 11 mils at Gauge 125 mils
In another embodiment of the present invention, the tile
composition is produced by a method in which from about 2 to
20 weight percent of the total initial composition of the
partially cross linked _hips as described previously are added
to the previously described tile base formulation on a two
roll blending mill and a mottled mill pad is formed. The mill
pad is then calendered to a thickness of 60 to 120 mils and
~r~l~n~ ; nt~ ~h i n~ hetween 14 to 40 mesh. The round chiPs are
5 3 1 ~
reformed into a sheet by one of the following methods:
1. By consolidating the reheated chips, at a
temperature of about 190 to 240 F., between the rolls of a
sheeter mill.
2. By pressing the chips into a thermoplastic base
sheet between the rolls of a calender. The chips are normally
at a temperature between 210 to 300 F. The thermoplastic
base sheet may be at a temperature such as about 300 F. The
thermoplastic base sheet, which may have a composition such as
that employed for the tile base formulation previously
described, may also contain about 5 to 10 weight percent of
the total composition of partially cross linked chips.
The tile smooth surface finish and final thickness are
achieved by running the sheet through a series of calenders.
Then the sheet is cooled and cut into tile in a punch
press.
In a further embodiment of the present invention,
approximately 5 to 10 percent by weight of the total initial
composition of partially cross linked chips as described
previously are added to the previously described thermoplastic
tile base formulation in an intensive mixer such as a Banbury
mixer. The batch is mi~ed and dropped at 300 to 350 F. on a
two roll mill where a mill pad is formed. The pad is
calendered to gauge through a series of calenders, where an
additional 1 to 10 weight percent of the total composition of
partially cross linked chips as described previously are
spread on the sheet surface between calenders. Here the chips
of a size between 14 and 40 mesh are pressed into the surface.
Since the chips are partially cross linked, a smooth surface
without chip pattern elongation is achieved.
Important concepts which are employed in the present
invention include:
1. Use of cross linked materials which are irreversibly
cross linked so as to produce the desired chips which remain
~;crr~t~ nnn-cm~arin~ and do not elonqate during processing.
`~ 3 1 ~
The cross linked product is insoluble in tetrahydrofuran (THF)
indicating irreversible cross linking and the formulation can
be also partially cross linked as indicated by partial or
extremely slow solubility in THF, so as not to flow at
intensive mixer temperature at which the chips are added to
the thermoplastic base.
2. Use of either one or a combination of (a) partial
cross linking and (b) high melting temperature thermoplastics
to produce chips which do not flow at the temperatures
required in the intensive mixer. The partially cross linked
materials are those which will not flow at temperatures of up
to 350 F. when PVC is employed.
3. The crosslinking of the plasticizer phase of the chip
formulation after it has been used to aid in the initial
processing of the PVC thermoplastic polymers.
4. The use of chips which are partially cross linked to
the degree necessary to minimize chip elongation at the point
where the chips are added to the process. When chips are
added to the intensive mixer where shear forces are high and
the temperature is about 300 degrees F, a high degree of cross
linking is required to prevent smearing and elongation.
Whereas, when the chips are added between the calender rolls,
shear forces and temperatures are lower and as a result the
degree of cross linking can be reduced. By reducing the cross
linking, a small amount of flow without elongation can be
achieved which improves tile surface smoothness.
5. Use of lubricants in the thermoplastic base to
reduce the processing temperatures and shear in the intensive
mixer such as a Banbury so that the partially cross linked and
high melting temperature polymers decorative chips remain
discrete particles and do not flow during processing. In this
way, the mixing temperature is controlled so it is below the
softening point of the chips. The drop temperature, when the
molten batch is dropped onto the mill, is generally around
30~ F. when PVC is employed.
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6. Use of chips and thermoplastic base materials which
are highly filled to provide a tile product which is
dimensionally stable and can be easily cut on the punch
presses employed to cut the tile. The chips will generally
contain about 10 to 75 weight percent filler and the base
material will contain about 50 to 85 weight percent filler.
In another embodiment of the present invention, the same
tile base formulation as previously described is employed but,
rather than adding partially cross linked resinous chips, the
chips are colored, coated mineral chips of a mineral such as
quartz with the coating being made by a ceramic technique, or
coated with a pigmented polyester or epoxy resin. In an
alternative embodiment, a mixture of coated chips and the
previously described partially cross linked resinous chips
having the same particle size range as the coated chips is
employed. By the addition of such chips to the tile base
formulation as described herein, there is thus produced a tile
product having a granite appearance or effect as shown in
Figs. 5 and 6.
When polyester or epoxy coated chips are employed, the
coating resin used is a commercially available polyester or
epoxy resin which encapsulates the mineral chips such as
quartz, feldspar or glass which can be in the form of solid
beads with a pigmented coating. The liquid polyester coating
is fused to a solid state by the addition of peroxide
hardeners. Clear or transparent mineral chips are chosen so
the color shows through the chips from all surfaces and thus
wear cannot be detected.
The polyester coating is a thermosetting synthetic resin
produced by the esterification of polybasic acid or anhydride
with polyhydric alcohols.
For example the unsaturation is achieved by the use of
dibasic anhydride or fumaric acid. The unsaturated acid or
anhydride is reacted with alcohols such as ethylene and
~ ~ 8 ~
In addition to the unsaturated dibasic acid, a saturated
acid can also be used such as phthalic anhydride or adipic
acid in the mixture. A higher proportion of unsaturated acid
gives a more reactive resin system and improves high
temperature stiffness of the coating which is useful in the
high temperature mixing of base tile and coated mineral chips
in the Banbury mixer.
More saturated acid lowers the reactivity of the reaction
and reduces the heat of the exothermic cures and gives the
polyester coating less stiffness at high temperatures.
A styrene monomer is used to thin the resin making it
pourable and making it possible to coat the mineral chips.
The ingredients of the polyester resin are mixed in a
resin kettle and are polymerized by a step reaction. The
reaction results in a viscous liquid with a molecular weight
range of 1000 to 2000. After cooling, the mixture is thinned
with styrene to a pourable viscosity. An inhibitor such as
hydroquinone is used to prevent premature polymerization.
Tv~ical Formulation *
Inqredient PHR Mole
Phthalic Anhydride 28.86 0.2
Maleic Anhydride 19.11 0.2
Propylene Glycol 14.83 Q.2
Ethylene Glycol 12.10 0.2
Styrene 30.00 0.3
Hydroquinone 02 Trace
104.92**
* Source Chem. Eng. News 37, #51, 56 Dec. 21, 1959
** About 5 pounds of water is eliminated during
esterification.
Pigment paste between one and ten percent by weight are
added to give the resin coating the desired color. Cure is
'2~3~1
benzoyl peroxide. An accelerator such as a cobalt naphthenate
can also be added to speed up the cure.
The mineral chips are coated with ~ to ~ mils of colored
liquid polyester polymer in a mixer. After the coating
hardens the colored mineral chips are ready for use in the
base tile to produce the granite appearance. An example of a
commercially available polyester coated quartz material
employed in the invention is manufactured by Clifford W. Estes
Co. of Lyndhurst, NJ.
Epoxy resin-containing pigments can also be used to coat
clear or transparent mineral chips. A typical epoxy resin is
made by condensing epichlorohydrin with bisphenol A. To leave
epoxy groups on each end of the polymer an excess of
epichlorohydrin is used. The reaction results in a viscous
liquid polymer. The reaction is carried out in a NaOH
solution. The epoxy resin is then cured with a polyamine.
The pigments and a curing compound are added to the epoxy
coating resin before encapsulation of the mineral chips.
The important factors to be considered when producing
inlaid aggregate plastic floor tile with epoxy or polyester
coated mineral chips are as follows:
1. The adhesion of pigmented polymeric coating to the
mineral chips at the high shear and high temperatures
encountered during mixing of the chips and the tile base
formulation in the Banbury mixer.
2. The use of internal lubricants in the tile base
formulation ~o minimize coating abrasion during the intensive
Banbury mixing.
3. The use of clear or transparent mineral chips so the
coating will show through the back of the chips and thus
coating wear during service will not affect chip color.
When ceramic coated chips are employed, the ceramic
coating is generally in the form of clay, pigments and water
plus other materials which are fused into a ceramic glaze
~ c h~ kn~^,wn methods.
3 ~ ~
Different types of glazes may be employed to change the
abrasive characteristics and color. The thickness of the
ceramic coating is about 0.5 to l.5 mils. The shape of the
ceramic coated particles can be round or angular. The round
chips give less equipment wear problems. Other minerals which
may be employed for the chips, in addition to quartz and
apatite, include feldspar, anorthite, also known as lime
feldspar, and glass.
In carrying out the invention, the coated mineral chips,
having a Mohs hardness of 5 to 8 and a particle size of 44 to
2,000 microns, are added to the tile formulation in an amount
of from about 2 to 20% by weight of the total formulation.
The mixture is combined in a mixer or a blending mill.
The mixed batch, from a mixer such as a Banbury mixer at
a cemperature of 300 to 350 degrees F., is dropped to a mill
where it is formed into a pad about one inch thick.
Alternatively, the coated chips may be added in the blending
mill, rather than in the Banbury mixer, so as to minimize wear
on the Banbury type mixers.
The mill pad is calendered to a gauge of 150 to 250 mils.
After the calendering step, additional chips in the amount of
about l to 10% by weight of the total formulation may be
spread on the top surface of the sheet via a vibrating
spreader and pressed in with a roller. These additional chips
may be either colored coated mineral chips such as those first
added or may be the previously described partially cross
linked resinous chips of the same particle size range as
described for the coated chips, or a combination of both
types. The sheet is then calendered to a final 1/a inch
thickness during calendering. The sheet is then cut into 12"
x 12" x 1/a" tiles or other sizes.
The abrasive characteristics and clearness of the mineral
chips are significant features of the invention. The abrasive
characteristics can be influenced by selectinq the coating so
as to control the abrasiveness and the wearing ability of the
2086311
final product and also to reduce wear problems caused by the
action of hard particles on the processing equipment during
manufacture of the product. Also translucent or clear mineral
is preferably selected for the chips so the colored coating
will be visible and show through the back as well as the
surface of the chips and as a result as the chips wear the
color will not change. Thus, for example, the particles can
be made of a clear quartz material having a Mohs hardness of
8 and by using the pigmented polyester or ceramic coating over
rounded quartz, the abrasive characteristics can be reduced.
In the embodiment of the invention as shown in Fig. 2,
there is provided a tile product 20 which includes a tile base
12 with angular coated mineral chips 22 uniformly dispersed
throughout the base 12.
The embodiment of Fig. 3 shows a tile product 30 which
includes a tile base 12 with round coated mineral chips 24
uniformly dispersed throughout the base 12 and with additional
round coated mineral chips 24 having been spread on the top
surface of the tile base 12 and pressed in.
The embodiment of Fig. 4 shows a tile product 40 which
includes a tile base 12 with a mixture of round coated mineral
chips 24 and partially cross linked chips 26 uniformly
dispersed throughout the base 12 and with additional chips 24,
26 having been spread on the surface of the tile base 12 and
pressed in.
In another embodiment of the present invention, the
coated mineral chips are added at a two roll mixing mill after
the hot base from the intensive mixer has been formed into a
pad covering the mill front roll. The pad from the mill
containing the coated chips is removed from the roll by a
knife. The pad is formed into a continuous sheet of the
desired thickness by a series of calenders, then cut into
tiles by a punch press.
Rework materials generated by reject tiles and press
webbing are ground into chips about ~ inch in size. The
(2 ~
rework chips are heated to about 240 degrees F and fed either
back to the mill or spread on top of the sheet between the
calenders where the sheet temperature is about 300 degrees F.
By using this method, none of the abrasive ceramic chips
enter the intensive mixer, thus avoiding rapid mixer wear.
After the first calender, between 2 and 10 weight
percent, based on the total formulation, of coated mineral or
partially cross linked chips or a combination of both can be
added to the surface of the sheet to compensate for the
skinning effect, primarily caused by the mill. These chips
are pressed into the sheet by either a pressure roll or a
calender.
Figs. 5 and 6 show the granite appearance or effect
obtained with the present invention and the different result
obtained depending on whether the amount of chip materials
employed is relatively sparse (Fig. 5) or relatively heavy
(Fig. 6).
In the selection of the additional chips which are spread
on the top surface of the tile base, the features to be
considered include those of the coated mineral chips, having
the advantages of not breaking down during mixing and being
relatively inexpensive, and the partially cross linked
resinous chips, having the advantages of providing some degree
of flow and with improved surface effect such as smoothness.
The main reason for spreading additional chips on the top
surface is to overcome the "skinning effect" caused primarily
by the mill and also by the calender. As the mill pad is
processed, the surface chips tend to skin over with base
formulation and as a result such surface chips become less
visible. To compensate for this effect, additional chips are
spread on the top surface and pressed in by roller or calender
roll. The tiles can also be sanded to remove the skin.
In one embodiment in which heavy surface coverage with
chips was desired, such as shown in Fig. 6, the chips employed
for surface coverage had a mesh size range of -35 to +100.
8 ~ 3 1 ~
Preferably 96 to 100 weight percent of the surface chips were
in this range, with O to 2% allowed as larger size chips and
o to 2% allowed as smaller size chips.
The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments are therefore to be
considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims rather than by the foregoing description, and
all changes which come within the meaning and range of
equivalency of the claims are therefore intended to be
embraced therein.
What is claimed and desired to be secured by Letters
Patent iso
