Note: Descriptions are shown in the official language in which they were submitted.
C? I ~Sq38 , ~83PU505097
CONSTRUCTIOH ADHESIVE COMPOSITIOH
FIELD OF THE INVENTION
The present inYention relates to aqueous-based construction
mastics for bonding wood to wood and other substrates.
BACKGROUND OF THE INVENTION
Construction mastics are used for making field-gllled plywood-to-
wood framing joints. Traditional adhesive compositions used by the
construction industry in making these construction mastics, specifically
those meeting American Plywood Association Specification AFG-01, are
based on solutions of elastomeric materials in organic ~olvents.
Environmental concerns are driving the industry to replace these with
water-based products. However, to attain adequate performance, the
water carried products have been formulated at unacceptably high cost.
Existing water-based construction adhesives meeting AFG-01 and
other specifications are based on polymer latices filled with mineral
dust such as calcium carbonate and clay. To attain appropriate
adhesion, relatively high polymer leYels must be used, l~aking the
compositions expensive.
There is a need to provide a water-based construction mastic with
perfonmance meeting the AFG-01 specifications and which have adhesive
characteristics of traditional solvent-based technology.
EP O 534 393 A discloses a contact adhesive containing
thermoplastic hollow microspheres.
U.S. Application Serial No. 986,957 filed 8 Decem~er 1992
discloses a water-based construction adhesive composition containing an
aqueous emulsion polymer binder which comprises a blend, based on 100
weight parts of polymer solids, of 25 to 75 parts aqueous emulsion Yinyl
acetate/ethylene copolymer and 75 to 2~ parts aqueous emulsion vinyl
acetate homopolymer.
SUMMARY OF THE IHVENTION
The present il... ~ provides a ~vater-based C~ adhesive c~ lposilion Co...p~isillg an
ac~l F_ - '1 11 of an 8'~ polymer and having a ~ ranging from 200,000 to ~ 00 mPa
as measured by Brookfield viscometer fitted with TD spindle opc.~ted at 2.5 rpm, at room te...~ lul~; of
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appr~ el~ 23C The -'~- h_ c~ contalns 0.1 to 5 wt%, thermoplastic hollow mh~ )h~lcs,
based on 8'~ e cc.- ~ solids.
The incorporation of low density thermoplastic hollow microspheres
provides a significantly lower cost formulation on a volume basis, while
maintaining good adhesive characteristics.
Another embodiment of the invention provides a method for joining
two substrates, preferably wood substrates, which comprises applying the
above aqueous construction adhesive to a surface of one of the
substrates and joining the adhesive-containing surface of the substrate
with a surface of the second substrate, preferably under application of
pressure.
DETA~LED DESCRIPTION OF THE INYENTION
Construction adhesives (mastics) are sold by volume, typically in
a cartridge. Also, the functioning of the adhesive is directly related
to the dried volume, not the weight of the adhesive in ':he glue line.
When a specified volume of adhesive, typically a quarte,-inch diameter
bead, is applied to a substrate, it must dry to fill the gap in the
closed glue line without leaving any voids. The ratio of the dried
volume to the wet volume is the volume solids. The volilme solids is a
function of weight composition and the density of the indiYidual
ingredients used in the adhesive and can be calculated if the properties
of the individual ingredients are known.
The ~ - e d c~ ~ mastic ~ ling to the present i~ t _ comprises an
aqueous medium c~ g 20 to 80 wt% 2~ cn~p - (solid basis) and d~ g a
ranging from 200,000 to 2,(~01),(W mPa, preferably 600,000 to 800,000 mPa, as measured
by Brookfield ~ r Stted with TD spindle op~ at 2.5 rpm, at room tempc.alul~ of
app.-~ 23C.
Any of a number of adhesive polymer emulsions well known in the
mastics art and based upon, for example, vinyl acetate (VAc), vinyl
acetate-ethylene (VAE), acrylic, styrene-acrylic, styrene-butadiene
(random or block copolymer), styrene-isoprene-styrene or chloroprene
polymers may be used in the adhesive component of the construction
mastic.
The preferred aqueous adhesive component comprises a blend of 25-
75 wt% aqueous VAE copolymer emulsion and 75-25 wt% aqueous VAc
homopolymer emulsion, based on emulsion solids (polymer binder),
preferably a 50/50 wt% blend. Optionally, a plasticiz~r at 5 to 15
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3 --
parts per hundred parts polymer binder (pphp) is added to the emulsion
blend to i~prove freeze-thaw stability and enhance flexibility.
Suitable VAE copolymer emulsions would comprise 50 to 70% solids
with the copolymer consisting essentially of 70 to 85 wt% vinyl acetate
and 15 to 30 wt% ethylene, preferably 77 to 81 wt% vinyl acetate and 19
to 23 wt% ethylene. It is preferred that the VAE copolymer emulsion be
prepared using polyvinyl alcohol (PVOH) as a stabilizing agent, i.e.,
part or all of the stabilizing system. It is especially preferred that
the emulsion be high solids, i.e. 60 to 67 wt% solids, and that the
copolymer have a Tg ranging from -10 to 0C. Methods for making
suitable VAE copolymer emulsions are well known in the art. See U.S.
4,921,898 for making the preferred high solids, PVOH/surfactant
stabilized VAE emulsion. Such a suitable high solids, PVOH/surfactant
stabilized VAE emulsion is marketed by Air Products and Chemicals, Inc.
as Airflex~ 465 emulsion.
Suitable YAc homopolymer emulsions contain 50 to 60 wt% solids and
preferably are PVOH stabilized with the copolymer having a Tg of 30 to
40C. Methods for making the homopolymer emulsions are also well known
in the art and are similar to those used in making the VAE copolymer
emulsions except that the polymerization is performed under an inert gas
at atmospheric pressure. Useful VAc polymer emulsions include Vinac~
XX-210, XX-220, XX-230 and XX-240 emulsions marketed by Air Products and
Chemicals, Inc.
In general, suitable VAc and VAE polymer emulsions are marketed by
several manufacturers, including Air Products and Chemicals, Inc.,
National Starch and Chemicals, Inc., and Reichhold Chemicals, Inc.
Useful plasticizers would include any of those materials commonly
used in the art for VAE and VAc polymer emulsions such as esters of
phthalic or benzoic acids, e.g. butylbenzyl phthalate, but desirably
would be a water solublel volatile low molecular alcohol.
In addition to the adhesive component which comprises the
optionally plasticized polymer binder emulsion blend, construction
mastics typically contain numerous other ingredients such as (a) filler,
(b) thickener, and optionally, but desirably, (c) tackifying resin
(e.g., hydrocarbon, rosin and its derivatiYes, rosin esters, C5/Cg
copolymers, coumarin-indene resins and the like) to improve adhesive
strength to wood substrates and water resistance.
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The level of wzter in the overall composition is based on the
quantity and type of thickener and fillers added and is adjusted to meet
performance requirement of AFG-01 specification.
In addition, the pigment (filler) to binder (polymer + plasticizer
+ resin) level is important in achieving the correct balance of strength
and open time.
Any filler well known to those in the art may be used, such as
calcium carbonate and clay. The calcium carbonate ideally has a
particle diameter of about 10 microns and is used at 50 to 135 pphp.
The clay is ideally water washed, hydrous clay having an oil absorption
of 20-40 and average particle diameter of about 0.1-1 microns. The clay
is used in an amount ranging from O to 90 pphp. It is preferred to use
an all calcium carbonate filler.
- Suitable adhesion enhancing hydrocarbon resins well known in the
art are present at 5 to 20 pphp and preferably should have a softening
point of 90 to 110C and be dispersed in water at about 50 wt%.
The polyacrylate thickener may be used at 10 to 15 pphp and
comprises an aqueous polyacrylic emulsion which is alkali swellable.
The polyacrylate thickener enhances the open time of the mastic
composition. Other thickeners may be used. Such thickeners include
inverse emulsions.
The adhesive most importantly contains 0.1 to 5 wt% (solids
basis), preferably 1 to 2 wt%, of resilient thermoplastic hollow
microspheres having a dry density of 0.01 to 0.1 g/cm3, preferably 0.02
to 0.06 g/cm3. These thermoplastic hollow microspheres, also known as
expandable thermoplastic beads or microballoons, for example
poly(vinylidene chloride-acrylonitrile), polystyrene or
poly(styrene-acrylonitrile) beads, are produced commercially in a
suspension polymerization process where a liquid monomer or mixture of
monomers is dispersed in an aqùeous medium containing one or more
suspension agents, a volatile liquid hydrocarbon blowing agent and a
polymerization initiator. The beads are produced as a slurry in the
aqueous medium remaining after the polymerization.
In the initial state of such a process, the monomers and the
blowing agent form a droplet with a single phase. Then as the
polymerization proceeds, the blowing agent forms a separate phase as
small inclusions in the formed thermoplastic droplet because it has been
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soluble in the thermoplastic droplet. Thus the obtained beads comprise
thermoplastic shells containing the 1iquid, volatile blowing agent.
The beads may be expanded by being heated to a temperature both
above the boiling point of the blowing agent and above the softening
point of the thermoplastic, for example at about 70C for
poly(vinylidene chloride- acrylonitrile) beads.
Especially preferred microspheres are polymeric microspheres, such
as those described in U.S. 3,61~,972; 4,075,238 and 4,287,308. The
microspheres are available from Pierce ~ Stevens Company under the
trademark ~MICROLITE~ in unexpanded form and ''MIRALITEU in expanded
fonm. Similar microspheres are available from Kema Nord Plastics under
the trademark "EXPANCEL" and from Matsumoto Yushi Seiyaku under the
trademark ~MICROPEARL~. In expanded form, the microspheres have a
specific density of approximately 0.02-0.036 g/cm3. It is preferred to
mix the expanded microspheres into the aqueous adhesive polymer emulsion
of the adhesive component. Polymeric microspheres having an average
diameter of 10 to 200 micrometers may be blended into the mastic.
Desirable aqueous construction mastics based on aqueous polyvinyl
acetate and VAE copolymer emulsions would contain as the adhesive
component solids the following ingredients in the indicated parts per
hundred parts polymer binder (pphp), i.e., pphp of the polyvinyl acetate
and VAE copolymer solids. The polyvinyl acetate and VAE copolymer
binders are given in parts by weight based on polymer solids in the
polymer emulsion.
comPonent Broad Range Preferred
Airflex 465a 75-25 50
Vinac XX-210b 25-75 50
Nopco 8034C 1-2
Propylene Glycol 5-10 5
Pycal 94d 5-15 10
a Airflex 465 YAE emulsion (66% solids; Tg= C)
b Vinac XX-210 polyvinyl acetate emulsion (55% solids; Tg= 32C)
35c Nopco 834 defoamer
d Pycal 94 plasticizer -- ICI
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Such adhesive component is commercially available from Air
Products and Chemicals, Inc. as AIRBOND~ ACP411 emulsion.
The following Table 1 shows a standard aqueous construction mastic
containing the above adhesive component, a construction mastic according
to the present invention and broad, preferred and most preferred
inventive mastics. The ingredients listed in Table 1 are in parts by
weight (pbw) wet.
TABLE 1
Inventive Mastic*
10Standard Inventive Most
Component Mastic* Mastic Broad Preferred Preferred
Airbond ACP411 53.92 51.04 30-70 40-50 46.5
HCRE Resin Oispersiona 5.28 5.00 0-10 4-5 4.6
Expancel 551 WEb 0 5.33 0.5-35 4-10 5.5
Calcium Carbonate 21.11 . 19.99 1-40 9-15 12.3
Clay 7.04 6.66 1-40 3-5 4.1
Ammonium Hydroxide 0.28 0.27 0.1-1 0.2-0.5 O.Z
~ater 8.13 7.70 3-135 18-41 23.0
Acrysol TT-615C 3.24 3.06 0.5-5 1-3 2.8
Water (for adjustment) 1.01 0.95as needed as needed 1.0
a Tackifier -- Polysat Corp.
b Thermoplastic Poly(vinylidene-acrylonitrile) microspheres (15~ solids)
cAcrylic thickener
*pbw wet
The construction mastic can be applied to any wood substrate
surface and will firmly bond such wood substrates. In practice in the
field, a bead of the aqueous construction mastic is applied to a surface
of one of the wood substrates to be joined and then the adhesive coated
surface is joined together with the other wood substrate, preferably
under pressure. Curing conditions are variable ranging from hot/dry to
cool/damp to frozen. Specification allows for Z8 days curing.
In the following Examples the terms ~dry~, Uwetu, Ufrozenn, and
~moisture" refer to the test specifications for dry lumber, wet lumber,
frozen lumber and moisture-resistance testing, respectively, as detailed
in the American Plywood Association AFG-01 specification. Performance
data is peak lap shear strength reported as Ne~tons, the force re~uired
to break a standard test block (3.81 x 2.54 cm). Moisture resistance ,s
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reported as cycles passed and lap shear strength if three cycles were
passed.
EXAMPLE 1
This Example compares the performance of the prior art standard
mastic with the mastic composition according to the invention as tested
by AFG-01 protocol along with some fundamental calculated properties of
the blends as shown in Table 2. The data in Table 2 shows that the
simple addition of the thermoplastic microspheres resulted in comparable
performance with reduction in density of the mastic.
TABLE 2
Calculated ProDerties Standard Mastic Invention Mastic
Wt. Solids (%) 63.8 61.2
15Vol. Solids (%) 53.7 63.1
Density (kg/l) 1.28 0.95
Pigment to binder ratio 0.78 0.80
PVCa 24.87 55.0
20Measured Properties AFG-01
(Newtons) Specification
Wet 2580 5605 1001
Dry 5485 4551 1001
Frozen 3527 2433 667
25Room Temp 4399 5587 not specified
Open Time (min) ~30 >10 10
a Pigment Volume Concentration - Yol Fillers/Total Dry Vol X 100
EXAMPLE 2
In this Example three mastic formulations containing hollow glass
microspheres were compared to formulations containing thenmoplastic
microspheres. This was done to compare the thermoplastic microsphere
effects to the use of hollow glass microspheres as taught in the prior
art for adhesive compositions. The base formulation is shown in
Table 3.
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TABLE 3
Component Wt (parts)
Airbond ACP411 90.1
HRCE Resin Dispersion 8.8
5 Ammonium Hydroxide 0.5
Expancel 551WEa as shown
Extendospheres SF-10b as shown
Calcium Carbonate 16.1
Clay 5.4
Others 0.6
as needed to attain
Water volume solids
as needed to attain
Acrysol TT-615 viscosity of 800,000 mPa
a Thermoplastic hollow poly(vinylidene-acrylonitrile) microspheres
from Kem Norda Plastics.
b Glass hollow microspheres from PQ Corp.
The addition weights of the thermoplastic microspheres (Expancel
551WE) or the hollow glass microspheres (Extendospheres SF-10) along
with calculated fundamental parameters are shown in Table 4. Because of
the differences in the densities of the thermoplastic and hollow glass
microspheres, more glass microspheres are needed to attain the the same
PVC (Pigment Volume Concentration). Performance against the AFG-Ol
specification is shown in Table 5.
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g
TABLE 4
LevelWt Sol ids Vol ~ensi ty
RunMicrospheres ~ry Wt %* Solids %* kg/l PYC %
1THERMOPlASTIC 3.21 28 44 0.78 68.4
2THERMOPLASTIC 3.21 33 49 0.75 68.4
3THERMOPLASTIC 3.21 37 54 0.73 68.4
4 GLASS 3.21 60 54 l.lS 18.7
GLASS 80.50 43 44 0.98 68.4
6 GLASS 80.50 53 54 ~.98 68.4
CONTROLNONE 0.00 64 54 1.28 24.87
* Mastic composition
TABLE 5
Run Dry (N) Wet (N) Frozen (N) Moisture (MPa)
1 4386 1624 2451 pass 2 cycles
2 3648 2193 2491 0.98
3 4008 2571 2117 1.44
4 3852 2229 1850 1.69
2660 716 1557 pass 1 cycle
6 2447 178 0 pass 1 cycle
CONTROL 2491 2122 4003 1.79
The data in Tables 4 and 5 show that at the same PVC value the
aqueous construction mastic compositions containing the thermoplastic
microspheres demonstrated far superior bonding strengths than those
containing the glass microspheres.
STATEMENT OF INDUSTRIAL APPLICATION
The present invention provides an aqueous construction adhesive
for bonding wood to wood surfaces and to other surfaces.
-ML0460.APP
