Note: Descriptions are shown in the official language in which they were submitted.
2~3~3;~
POLYURETHANE ADHESIVE FOR PVC/WOOD LAMINATING
Laminates are commonly used substitutes for hard wood where durability,
machinability, water resistance, cost and/or other factors dictate against the
use of raw wood surfaces. Thus, laminates are formed into furniture, door or
window frames and Bills, kitchen cabinets, desk tops, display cases and the like.
In general, such laminates are formed from wood or board substrates to which
polyvinyl chloride or other plastic substrate i9 bonded using an adhesive
ccating. In addition to the normal adhesive and cohesive requirements associated
with theae laminates, the nature and configuration of the base substrate often
places additional stringent requirements on the adhesive composition per se.
Thus, many of the laminates are formed by bonding the plastic substrate to a
curved or irregularly shaped substrate, a factor which put~ greater stress on the
adhesive bond. Further, the base substrates utilized in the laminate production
often contain irregularities such as gaps on their surfaces. It i9 therefore
desirable to utilize an adhesive which will serve a~ a gap filler or will
otherwise compensate for the irregularities of the surface in the final laminate
construction. Moreover, the resulting laminate is often utilized in environments
which are exposed to severe changes in temperature and consequently the adhesive
must be able to accommodate such cyclical temperature fluctuations.
The present invention relates to a heat resistant laminate wherein a wood
ba~e or other substrate member is directly adhered to a decorative plastic film
using a ~pecific polyurethane as well as to the polyurethane adhesive composition
therefor. In more detail, the polyurethane adhesive of the present invention
consist~ essentially of 30 to 36% by weight diphenylmethane diibocyanate (MDI);
13.5 to 19.5% by weight ethylene oxide capped polypropylene oxide diol; 32.5 to
3 ~ ~
41.5~ by weight neopentyl adipate ester diol, 8 to 17~ by weight hydroxyl
terminated polybutadiene, 0.5 to 2.5~, preferably 0.8 to 1.2~, by welght diethylmalonato and 0.035 to 0.050~ dibutyl tin dilaurate. Higher levels of dibutyl tindilaurate, e.g. up to about 0.5~ by weight, may be used but no advantage i~
achleved thereby. The resulting adhesive is characterized by lmproved ~trength
on aging, even when expofled to fluctuating temperature condition~. Moreover, the
adhe~ive, when applied, serve~ as a gap filler to accommodate any irregularitie~in the substrate thereby producing a final laminate of excellent quality.
The polyurethane adhenive compo~ition disclo~ed herein as prepared in a
conventional manner by the reaction of an ethylene oxide capped polypropylene
oxide diol having an average molecular weLght ~number average~) of about 4000
(e.g. Poly G 55-28 from Olin Chemicals), neopentyl adipate ester diol having an
average molecular weight of about 1000 ~e.g. Ruccoflex S-107-110 from Ruco
Polymer Corp.) and a hydroxyl terminated polybutadiene having an average
molecular weight of about 2800 ~e.g. Poly ~D R-45 HT from sartomer) with an
excess of the diphenylmethane diisocyante (e.g. Mondur M from Mobay) to form a
branched polymer having a slight excess of free isocyanate groups. Subsequently,the diethyl malonate and then the dibutyl tin d$1aurate are admixed with the
re~ulting polymer.
It is generally recognized in the urethane art to react the
diisocyanate and hydroxylic reagent~ in a dry inert atmo~phere such as dry
nitrogen in the presence of a cataly~t. Catalysts for this reaction are well
known in the art and include numerous organometallic compounds such as heavy
metal carboxylates (e.g. dibutyl tin dilaurate, stannou~ octoate, lead octoate,
mercuric succinate), as well as amines and the ferric complex of acetoacetic
ester. In accordance with the pre~ent invention, we have found that polyurethaneadhesives characterized by an unexpected superior balance of properties is
produced when dibutyl tin dilaurate as employed a~ the catalyst and i~ present
at a level of at least 0.035~ by weight. In contrast, polyurethane adhesives
formulated with lower amounts of the dibutyl tin dilaurate catalyst produce
substantially poorer performance characteristics when used in the production of
plastic/wood laminates.
The re~ulting polyurethane may be used directly in it~ solvent-free form or
may be diluted with conventional ~olvents such a~ methyl ethyl ketone, 1,1,1
- 2 -
2 ~
trichloroethane, methylene chloride, toluene, and the like, dependlng upon the
application equlpment utilized by the partlcular laminate manufacturer.
The substrate employed in the laminate produced with the adhesive previously
described can be chosen from a wide varLety of materials such as particle board,hard board, fiber board, lauan plywood, styrofoam, and the like. This rigid
substrate serves as a base to which a thin, pla~tic film is laminated to give tha
composite structure and the desired appearance. The plastic film is not
restricted to any particular plastic but polyvinyl chloride film is the most
commonly employed. The plastic film generally has a thickness of about 1 to 55
mils, preferably 30 to 50
mils, and the substrate is generally at least about five times thicker than the
plastic film. The plastic film is adhered to one or more surfaces of the
substrate through th~ use of the specific adhesive disclosed herein.
In forming the laminates according to the prevent invention, the selected
substrate is sanded and cleaned, if required, and the adhesive is coated on the
substrate surface and dried in the cases where solvent is employed. A polyvinyl
chloride film is then placed on the adhesive coated surface and lamination is
effected at ambient temperature under pressure. Although not required, moderate
heat may be used to further accelerate the curing process. Additionally, though
not essential, a protective coating may be applied on top of the thin plastic
film by spreading a liquid polymeric resin on the pla~tic film surface and then
converting the thermopla~tic resin to a strong infusible, clear, colorless solid.
Examl~les
In order to prepare the urethane adhesive of the invention, the
following procedure was utilized:
A clean and dry reactor was purged with nitrogen and initially charged with
179 part~ diphenylmethane diisocyanate. The contents were heated to melt
(between 120-180 P) whereupon 59.5 parts hydroxyl terminated polybutadiene were
added with agitation, followed by the slow addition of 208 parts of neopentyl
adipate ester diol over a period of 1 to 6 hours while the temperature was
maintained between 120-180 F. Then 89 parts Of ethylene oxide capped
polypropylene diol were added and the temperature brought to 110-120 F for a
period of 2-3 hours to insure complete reaction. Diethyl malonate, 5.21 parts,
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2 'i~ `J 4?~ '3
was then disaolved into the fluid polymer followed by the addition of 0.19 partadibutyl tin dllaurate. The reaultant adhe~lve wa~ de~ignated Adhuaive 1.
Uslng a simllar procedure, Adhesives 1-4 de~crlbed ln Table I were prepared.
Adhesives I and 2 are repreaentatlve of the inventlon whLle adhesives 3 and 4
5 represent compo~itions of the prior art prepared wlth lower levela of the dlbutyl
tin dilaurate catalyst.
TABLF I
Ingrodients
(bv wei~ht) 1 2 3 4
Diphenylmethane diiosyanate 33 33 33 33
Hydroxyl Terminated 11 11 11 11
Polybutadiene
Neopentyl Adipate ester diol 38.5 38.5 38.5 38.5
Ehtylene Oxide Capped
Polypropylene diol 16.5 16.5 16.5 16.5
Dlethyl Malonate 0.965 0.950 0.972 0.975
Dlbutyltin Dilaurate 0.035 0.050 0.025 0.028
Test Sam~le Pre~aration
A 3/8 lnch partlcle board substrate was coated with the urethane adhesive
to be tested. Thereafter, a 40 mil thick polyvinyl chloride film was laminated
to the adhesive coated surface using a hand roller and the laminates were stacked
and allowed to cure for the time indicated in Table II. The re~ulting laminates
were then tested Using the following testing procadures.
Peel Strencth Test Procedure
4 x 1 inch segments of PVC laminated wood prepared as above were cut for use
as test ~amples. The laminate was stripped back along the irst square inch and
a pair of locking pliers was gripped onto the laminate tab. A Hunter Force Gaugewas attached to the locking pliers and with even hand presaure the laminate was
peeled away from the wood at a 90 angle. The continuous peel strength wall read
directly from the gauge and the moda of failure recorded.
The resulta of the testing of Adheaives 1, 2 and 3 are presented in Table
II.
-- 4 --
t ~ 3! 3'~ ~ ~
Table II
Effect of Catalvst Concentration on Peel Strenath~1~
Adhesive 1 Adhe~lve 2 Adhe~lve 3
% Catalvst bv WtØ035% 0.050~ 0.025
5Cure Time
4 hrs @ 72 F 1.9 pli 1.9 pli 1.2 pli
8 hrs @ 72 F 11.7 pli 11.3 pli 5.5 pli
12 hrs @ 72 F 23.7 pli 23.7 pli 14.8 pli
24 hrs @ 72 F 26.0 pli 26.4 pli 18.8 pli
1048 hrs @ 72 F25.5 pli 27.9 pli 21.7 pli
(1) Peel strengths reported are an average of three samples.
The results of the peel strength testing illustrate the dramatic and
unexpected difference in performance between the specific adhesive compositions
of the invention ~Adhesives 1 and 2) which were prepared with 0.035% and 0.050$
of the dibutyl tin dilaurate catalyst as compared to the control adhesive
(Adhesive 3) prepared with 0.025% dibutyl tin dilaurate. The results of these
tests for the sample# prepared with 0.025 and 0.035% dibutyl tin dilaurate
(Adhesives 1 and 3) are also plotted in Figure I.
As is also seen from the results presented in Table III, amounts of the
catalyst in excess of 0.035% may be employed; however, little or no additional
benefit to be achieved thereby as contrasted with the level of improvement between
the Adhesive I of the invention and the control adhesive containing lower levelsof catalyst.
In a further test, sample laminates were prepared as previously described and
allowed to cure overnight. one set of samples were then conditioned for 24 hoursat 180 F and another set soaked for 24 hour~ in 74 F water. After conditioning,
ths uamples were equilibrated for 2 hours at 72 F and tested using the peel
strength procedure described above. The results of the testing are shown in Table
III.
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TAsL~ III
Peel Strength
Adhesive 1 Adhesive 4
Conditionin~
24 hours @ 180 F 26.0 pli 12.3 pli
24 hours @ 74 E~ water 20.6 pli 17.0 pli
Additionally, when 1aminates prepared as described above using Adhesive I
were exposed to repeated cycllcal temperature change~ varying between -20 and 180
F, the bonds withstood ~ubstantially more cycles than did the currently utilized
commercial adhesive Composition.
Various change~ and modifications can be made in the process and products of
this invention without departing from the spirit and ~cope thereof. The variou~
embodiment~ set forth herein were for the purpose of further illustrating the
invention but were not intended to limit it.
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