U.S. patent application number 14/121421 was filed with the patent office on 2016-03-10 for moldable engineered stone.
This patent application is currently assigned to Safas corporation. The applicant listed for this patent is Safas corporation. Invention is credited to Yifang Zhao.
Application Number | 20160068439 14/121421 |
Document ID | / |
Family ID | 55275320 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160068439 |
Kind Code |
A1 |
Zhao; Yifang |
March 10, 2016 |
MOLDABLE ENGINEERED STONE
Abstract
This invention provides a moldable engineered stone composition
comprising an ethylenically unsaturated acrylic polymer capable of
being covalently crosslinked, a mineral particulate, and an ionic
crosslinking agent which forms ionic bonds within the syrup of
unsaturated acrylic polymer via unreacted acid groups, causing
thickening prior to curing and prior to the formation of covalent
bonds via the double bonds of the polymer chain. The composition is
then capable of being extruded and molded in a press. Articles
formed by curing the composition and methods for producing the
composition are also disclosed.
Inventors: |
Zhao; Yifang; (Randolph,
NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Safas corporation |
Clifton |
NJ |
US |
|
|
Assignee: |
Safas corporation
Clifton
NJ
|
Family ID: |
55275320 |
Appl. No.: |
14/121421 |
Filed: |
September 4, 2014 |
Current U.S.
Class: |
524/558 ;
264/331.18 |
Current CPC
Class: |
B29C 48/022 20190201;
C04B 26/06 20130101; B29K 2035/00 20130101; B29C 67/243 20130101;
B29K 2033/12 20130101; B29K 2105/24 20130101; B29K 2069/00
20130101; C08F 265/06 20130101; C04B 26/06 20130101; B29K 2509/14
20130101; C04B 2111/542 20130101; C08F 220/14 20130101; B29C 48/07
20190201; B29L 2007/002 20130101; B29C 39/026 20130101; B29K
2105/16 20130101; C08F 220/14 20130101; C08F 265/06 20130101; B29C
2035/047 20130101; C04B 14/06 20130101; C08F 220/1804 20200201;
C08F 222/102 20200201; C08F 220/06 20130101; C04B 14/22 20130101;
C04B 14/048 20130101; C08F 230/08 20130101; C08F 222/102 20200201;
C08F 220/1804 20200201; C08F 220/06 20130101 |
International
Class: |
C04B 26/06 20060101
C04B026/06; B29C 39/02 20060101 B29C039/02; B29C 47/00 20060101
B29C047/00 |
Claims
1. A moldable engineered stone composition, comprising: (a) 15 to
20% by weight of the composition of a matrix resin comprising a
syrup of an unsaturated acrylic polymer containing from 1 to 10% by
weight of the polymer of an acrylic carboxylic acid copolymerized
with monounsaturated esters and having unreacted acid groups, and
from 1 to 5% by weight of the polymer of a crosslinking acrylic
monomer, (b) from 80 to 85% by weight of the composition of a
mineral particulate, (c) from 0.20 to 5% by weight of the
composition of an ionic crosslinking agent, said ionic crosslinking
agent forming ionic bonds with said unreacted acid groups, said
ionic bonds causing a thickening prior to covalent crosslinking,
and (d) a free radical polymerization initiator.
2. The moldable composition of claim 1 wherein the ionic
crosslinking agent is a divalent metal oxide or hydroxide.
3. The composition of claim 2 wherein the metal oxide is magnesium
or calcium oxide.
4. The composition of claim 2 wherein the metal hydroxide is
magnesium or calcium hydroxide.
5. The composition of claim 1 wherein the acrylic polymer is a
methyl methacrylate polymer and the monomer comprises methyl
methacrylate.
6. The composition of claim 1 wherein the mineral particulate is
comminuted quartz, granite, glass, sand, or combinations
thereof.
7. The composition of claim 5 wherein the methacrylate polymer
comprises 25 to 30% of the syrup and is dissolved in the methyl
methacrylate monomer.
8. A cured article formed by curing the composition of claim 1.
9. The article of claim 8 formed from an extruded sheet.
10. A method of preparing a molded engineered stone composition
which comprises: (i) forming a composition of: (a) from 15 to 20%
by weight of the composition of an unsaturated acrylic polymer in
the form of a syrup, containing from 1 to 10% by weight of the
acrylic polymer of an acrylic carboxylic acid copolymerized with
monounsaturated esters and having unreacted acid groups, and from 1
to 5% by weight of the acrylic polymer of a crosslinking acrylic
monomer, (b) from 80 to 85% by weight of the composition of a
mineral particulate, (c) from 0.25 to 0.5% by weight of the
composition of an ionic crosslinking agent and (d) a free radical
polymerization initiator, (ii) forming such composition into a
sheet, (iii) allowing the viscosity of the sheet to increase until
the sheet has been solidified, said viscosity increasing via a
formation of ionic bonds between said ionic crosslinking agent and
said unreacted acid groups, and (iv) molding the sheet into a
formed article at elevated temperatures to cause curing of the
molded article.
11. The method of claim 10 wherein the composition is extruded on
to a flat surface to form the sheet.
12. The method of claim 10 wherein the acrylic polymer is a methyl
methacrylate polymer and the monomer is methyl methacrylate.
13. The method of claim 10 wherein the formed sheet is cured at
elevated temperatures in a closed mold.
Description
FIELD OF THE INVENTION
[0001] This invention relates to moldable engineered stone and
methods for making such engineered stone.
BACKGROUND OF THE INVENTION
[0002] Synthetic stone products are well known and are in great
demand due to their ability to be manufactured in a wide variety of
shapes, patterns and colors that cannot be consistently found in
nature. Such compositions are for example described in U.S. Pat.
Nos. 4,664,954, 4,085,246, 4,678,819, 4,734,452, 5,043,377 and
5,055,327. Synthetic stone compositions generally contain from 50
to 80% by weight of mineral particulate in a crosslinked resin
matrix. The disadvantage of the described stone compositions is
that when molded they result in surfaces which reflect the
properties of the resin more than the properties of the mineral
particulate contained in the compositions.
[0003] Engineered stone compositions on the other hand resemble
natural stone to a greater degree but have much better
fabricability compared to natural stone and are useful in slab or
sheet form in both interior and exterior walls of buildings, indoor
and outdoor floors, fireplaces, table and counter tops, tiles and
an assortment of other uses for natural stone. Engineered stone
compositions contain a higher percentage of a mineral particulates,
generally in the range of 80 to 95% by weight, in a resin matrix as
compared to moldable synthetic stone compositions and provide a
stone-like surface. Such compositions are described in U.S. Patent
Nos. 6,387,985 and 7,727,435. The disadvantage of known engineered
stone compositions is the limited means of producing the composite
and the shape of the products obtained. Engineered stone is formed
by casting methods and requires both vibration and a vacuum in
order to obtain a properly compacted, bonded structure of the
mineral particulate and to eliminate any entrapped air. Casting can
be a serious problem in commercial manufacture of the slabs since
it is a batch process subject to property variations from batch to
batch. Casting methods furthermore require extensive set up and
cleanup operation in order to resume production after completion of
a run.
SUMMARY OF THE INVENTION
[0004] This invention provides engineered stone compositions that
can be extruded and molded avoiding the problems associated with
casting and is based on the discovery that carboxylic acid groups
of the polymer in a matrix resin interact with certain metal oxides
and hydroxides to form ionic links that greatly increase the
viscosity of the matrix resin to the point of solidifying the
composite of the matrix resin and a mineral particulate prior to
curing the composite.
[0005] More specifically this invention provides methods for
engineered stone products that can be molded in varying shapes.
[0006] The engineered stone products of the present intervention
are obtained from a composition comprising a mineral particulate in
a matrix of an unsaturated acrylic polymer capable of being
crosslinked with additional monomer through a free radical
initiator forming covalent bonds containing unreacted carboxylic
acid groups, a free radical initiator, and an ionic crosslinking
agent. The engineered stone products are obtained from this
composition by free radical initiated crosslinking of the acrylic
polymer.
[0007] The present invention provides a method of forming
engineered stone articles, which comprises continuously extruding a
crosslinkable acrylic resin containing at least 80% by weight of
the total composition of a mineral particulate in the form of a
sheet and thereafter forming and curing the sheet in a mold by
means of covalent crosslinking and recovering a finished article
from the mold with a smooth stone-like surface.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The present invention is directed to an engineered stone
composition that can be cured in a mold and to a method of
manufacturing of engineered stone products comprising extruding the
moldable composite comprising a mixture of a matrix resin and a
particulate in the form of a sheet with sufficient coherence and
solidity to be molded in to shapes in a conventional molding
press.
[0009] The goals of the present invention are achieved by employing
as the matrix resin an acrylic polymer having incorporated in the
polymer chain unreacted acrylic acid groups in addition to
unsaturated bonds capable of being covalently crosslinked through
the reaction of additional monomer and a free radical initiator
with (2) an ionic crosslinking agent capable of ionic crosslinking
through the carboxylic acid groups of the acrylic polymer and (3)
having admixed therewith a mineral particulate in at least 80%
concentration. The ionic crosslinking agent is essential to allow
the formation of a solid but flexible sheet that can be cured in a
mold. In the absence of such the resulting cured sheet contains
defects including incomplete bonding of the particulate to the
matrix resin and visible voids in the matrix. Ionic crosslinking
agents suitable for use in the present invention are generally
divalent metal oxides or hydroxides which are capable of reacting
with organic acids. Preferred ionic crosslinking agents are calcium
and magnesium hydroxides. The present invention is based on the
discovery that the carboxylic acid groups of the matrix resin react
with the metal oxide or hydroxide to form ionic linkages that
rapidly increase the viscosity and solidify the composite of the
matrix resin and mineral particulate sufficiently to form a solid
coherent sheet that can be handled for placement in a mold before
covalent crosslinking is initiated to form the rigid, crosslinked
engineered stone structure in the mold. The concentration of the
free carboxylic acid groups and the metal oxide or hydroxide can be
varied to adjust the rigidity of the extruded sheet and the
rapidity in which the extruded sheet is solidified. Thus increasing
the concentration of either or both the carboxylic acid group in
the acrylic polymer and the concentration of the ionic crosslinking
agent results in a more rigid sheet that is formed faster on
extrusion of the mixture.
[0010] The acrylic polymers employed in the present invention
primarily are based on monounsaturated esters of acrylic or
methacrylic acid. The esters are derived from an alcohol having up
to six carbon atoms although the preferred esters are methyl and
ethyl acrylate or methacrylate and butyl acrylate. In addition the
acrylic polymers employed in the present invention contain from 1
to 10% by weight of the polymer of acrylic or methacrylic acid
copolymerized with the esters. In further addition the polymers of
the present invention have copolymerized di- or polyethylenically
unsaturated acrylic or methacrylic esters in sufficient
concentration to achieve the desired covalent crosslinking of the
matrix resin. Such covalent acrylic crosslinking monomers include
ethylene glycol di(meth)acrylate, polyethylene glycol
di(meth)acrylate, propylene glycol di(meth)acrylate, 1,3-butylene
glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate,
polybutylene glycol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, dimethylolethane di(meth)acrylate, 1,1
dimethylpropane di(meth)acrylate, 2,2-dimethylolpropane
di(meth)acrylate, trimethylolethane tri(meth)acrylate,
trimethylolpropane tri(meth)acrylate, tetramethylolmethane
tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, and
neopentyl glycol di(meth)acrylate. The acrylic polymer is generally
employed in the form of a syrup of the polymer in a liquid
crosslinking acrylic monomer. Any acrylic monomer that is liquid at
room temperatures can be employed as the crosslinking monomer but
usually is either the acrylate or methacrylate ester of methanol or
ethanol. In accordance with the present invention the crosslinking
monomer may also contain other polymeric ingredients such as epoxy
resins.
[0011] The concentration of the polymer in the syrup can be varied
from about 25% to 45% by weight of the syrup. The molecular weight
of the acrylic polymer is generally in the range of about 20,000 to
100,000. The described acrylate polymer is employed in a
concentration of about 15 to 20% by weight of the engineered stone
composition.
[0012] The mineral particulates employed in the engineered stone
composition of the present invention are those normally used in
engineered stone composition and include marble, granite, quartz,
sand, and colored glass. The mineral particulate is employed in
sizes ranging from about 325 to 2 mesh (0.04 mm to 10.3 mm in
greatest average dimension).
[0013] In a preferred form the mineral particulate comprises a
mixture of varying particle sizes and in varying amounts of any
given size. The engineered stone compositions of the present
invention contain greater than 80% by weight and preferably from
about 80 to 85% of the mineral particulate based on the weight of
the total composition. The mineral particulate is generally used in
combination with a bonding agent to promote the adhesion of the
acrylic copolymer to the mineral particulate, Such bonding agents
have been described in the art and are preferably silanes such as
acryloylpropyltrimethoxysilane, commercially available as A174, and
vinyltrimethoxysilane, commercially available as A171.
[0014] The ionic crosslinking agents that are admixed with the
acrylic syrup and the mineral particulate are divalent metal oxides
and hydroxides capable of reacting with the carboxylic acid groups
of the acrylic resin in the syrup. The physical effect of the ionic
crosslinking is a viscosity increase of the composite of acrylic
syrup and particulate. Preferred metal oxides are calcium and
magnesium oxides and hydroxides. The metal oxides and hydroxides
are added to the syrup and mineral particulate mixture in finely
divided powder form in a concentration sufficient to cause an
increase in the viscosity of a sheet formed from the mixture so
that it can be handled as a flexible, rubbery solid. Concentrations
required to obtain the mixture of syrup and particulate in the
desired solid form vary from 0.5 to 5% by-weight of the mixture.
The ionic crosslinking occurs at room temperatures and requires
about 25 to 30 minutes for a formed sheet to reach a solid state
through increasing viscosities.
[0015] The moldable engineered stone compositions also include a
free radical polymerization initiator to initiate the crosslinking
of the formed and preferably extruded composite during the molding
step. Suitable initiators for the acrylic syrups are known in the
art and include benazyl peroxide, di-(4-tert-butyl-cyclohexyl)
peroxydicarbonate, 2,5- dimethyl-2,5-di-(2-ethylhexyanoylperoxy)
hexane, tert-amyl peroxy-2-ethylhexanoate, butyl
peroxy-2-ethylhexanoate, 1,1-
di-(tert-butylperoxy)-3,5,5-trimethylcyclohexane, and
1,1-di-(tert-butylperoxy) cyclohexane. The initiator concentration
can be varied although it is generally in the range of 0.01 to 2.5%
by weight of the matrix resin.
[0016] Other additives include pigments to provide desired color
variations such as titanium dioxide, carbon black, iron oxides, and
copper oxides. It is generally also desirable to add an antioxidant
or UV stabilizer if the final product is exposed to strong
sunlight. Similarly mold release agents may be added to the
composite mixture for easier removal of delicate shapes.
[0017] The molding process to obtain the engineered stone products
of the present invention involves two steps, where in the first
step a moldable sheet is formed, and in the second step, where the
moldable sheet is covalently crosslinked at elevated temperatures
in a mold to form the final cured product. Although the moldable
sheet can be formed from the composite through standard mixing and
casting processes, it is preferably formed using a mixing extruder,
the advantage being that the ionically crosslinked sheet can be
formed on a continuous basis. The extrusion should be conducted at
temperatures below which covalent crosslinking is initiated and
generally is done at ambient temperatures. All of the ingredients
are added to the mixing extruder and thoroughly blended by the
screw in the extruder. The extrudate from the extruder is formed
into a sheet with a thickness of preferably 0.2 to 2 inches and
exposed to ambient conditions on a flat surface such as a moving
belt for sufficient time for the ionic crosslinking to take place
and form a solid flexible sheet. Solidification of the sheet varies
with the concentration of carboxylic acid groups and metal oxide or
hydroxide present in the mixture, but generally varies from 15 to
45 minutes. Further exposure may increase the rigidity of the sheet
if desired. On completion of the ionic crosslinking, the resulting
rubbery sheet can be lifted off the flat surface and cut to the
desired dimensions to be placed in a mold and compression molded to
the final shape and allowed to cure through covalent crosslinking
at elevated temperatures. Curing temperatures generally vary from
150 to 300.degree. F. depending on the initiator used and the
length of the molding cycle.
[0018] The invention is further illustrated by the following
examples wherein the parts listed are by weight.
Example
[0019] Acrylic syrup preparation.
[0020] Into a reaction vessel with a stirrer, a thermometer, a
nitrogen introduction tube and a cooler were added 160 parts of
methyl methacrylate, 35 parts butyl methacrylate, 5 parts of
methacrylic acid, 3 parts of ethylene glycol dimethacrylate and 1
part of parafin wax. The mixture was heated under nitrogen to
180-200.degree. F. and 0.03 parts of azobisisobutyronitrile as a
polymerization initiator and 0.5 parts of n-dodecyl mercaptan as a
chain transfer agent were added with continuous agitation. Bulk
polymerization was continued for about 30 minutes after which the
reaction mixture was rapidly cooled . The viscosity of the
resulting acrylic resin syrup was 7 poises at room temperature and
had 25% polymer content.
[0021] Molded sheet preparation.
[0022] In preparing the syrup for blending with the mineral
particulate as the matrix resin, the foregoing syrup is further
modified by adding 1% based on the weight of the syrup of zinc
stereate as a mold release agent, 1% based on the weight of the
syrup of Dow Corning silane A-174, 1% by weight of the syrup of
Akzo Nobel Trigonox 141 crosslinking catalyst, to a mixing extruder
with a 4' mixing screw and separate ports for the matrix resin, the
particulate, and the ionic crosslinking agent. These components are
added through such ports: 80 parts of a particulate, 20 parts of
the described matrix resin, and 0.5 parts of magnesium oxide as the
ionic crosslinking agent. The particulate of comminuted quartz
comprised 40% by weight of the total particulate passing a 325 mesh
screen, 20% of the particulate passing a 72 but not a 100 mesh
screen, 20% passing a 20 but not a 70 mesh screen, and 20% passing
a 6 but not a 10 mesh screen. The extrusion was carried out at room
temperature. At the extrusion nozzle the extrudate was spread into
the confined section of a 50' long extrusion belt providing a flat
surface approximately 50'' wide and then passed through a set of
three rollers that spread the extrudate to a uniform sheet 6 mm
thick. The extruded sheet rapidly increased in viscosity and
solidified as a result of the ionic crosslinking as it moved the
length of the belt over a period of 30 minutes. At the end of that
time the sheets was a rubbery solid that could easily be lifted
from the belt. The sheet as formed can be directly placed in the
mold for the final step of molding the sheet into a covalently
crosslinked, cured solid but is preferably allowed to further form
ionic bonds for a period up to 12 hours. The sheet is then placed
in a mold and compression molded at a temperature of 230.degree. F.
and a pressure of 25 kg/cm.sup.2. The resulting molded piece has a
smooth stone like appearance.
* * * * *