U.S. patent application number 10/290469 was filed with the patent office on 2003-05-15 for hybrid phenol-formaldehyde and polymeric isocyanate based adhesive and methods of synthesis and use.
Invention is credited to Creel, Lewis D., Detlefsen, William D., Miller, Todd R..
Application Number | 20030092855 10/290469 |
Document ID | / |
Family ID | 24653679 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030092855 |
Kind Code |
A1 |
Miller, Todd R. ; et
al. |
May 15, 2003 |
Hybrid phenol-formaldehyde and polymeric isocyanate based adhesive
and methods of synthesis and use
Abstract
Hybrid resins formed of an acylated phenol-formaldehyde (PF)
resin and a polymeric phenyl isocyanate (pMDI) resin have extended
shelf stability, yet cure at a rate faster than any of its
components when used in conventional flakeboard, strandboard or
other board making processes.
Inventors: |
Miller, Todd R.; (Eugene,
OR) ; Creel, Lewis D.; (Dexter, OR) ;
Detlefsen, William D.; (Springfield, OR) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, L.L.P.
Suite 850
1615 L Street, N.W.
Washington
DC
20036
US
|
Family ID: |
24653679 |
Appl. No.: |
10/290469 |
Filed: |
November 8, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10290469 |
Nov 8, 2002 |
|
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09661458 |
Sep 13, 2000 |
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6478998 |
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Current U.S.
Class: |
525/495 |
Current CPC
Class: |
C08G 18/542 20130101;
C08L 61/06 20130101; C08G 18/7664 20130101; B27N 3/002 20130101;
C08G 8/28 20130101; C08L 61/14 20130101; C08G 18/6492 20130101;
C08L 61/06 20130101; C08L 75/04 20130101; C08L 61/14 20130101; C08L
75/04 20130101 |
Class at
Publication: |
525/495 |
International
Class: |
C08L 061/00 |
Claims
We claim:
1. A hybrid resin comprising a protected phenol-formaldehyde resin
and a polymeric phenyl isocyanate.
2. The hybrid resin of claim 1, wherein said protected
phenol-formaldehyde resin comprises an acylated
phenol-formaldehyde.
3. The hybrid resin of claim 1, wherein the phenol-formaldehyde
resin is a resole.
4. The hybrid resin of claim 1, wherein the phenyl isocyanate is
4-4'methylene bis(phenyl isocanate).
5. The hybrid resin of claim 1, wherein the ratio of the protected
phenol formaldehyde to the polymeric phenyl isocyanate is an amount
of from about 10% to about 80% by weight and 90% to about 20% of
the polymeric phenyl isocyanate.
6. The hybrid resin of claim 5, wherein the ratio of the protected
phenol formaldehyde to the polymeric phenyl isocyanate is from
about 10 wt % - 40 wt % phenol formaldehyde to about 60 wt % - 90
wt % polymeric phenyl isocyanate.
7. The hybrid resin of claim 1 having a storage stability of at
least two weeks at room temperature.
8. A method of manufacturing board made of lignocellulosic
particles comprising mixing said particles with a hybrid resin
according to claim 1, forming the resulting mixture of
lignocellulosic particles and resin into a loose mat and
consolidating the mat under heat and pressure to deprotect the
phenol-formaldehyde and cure the resin.
9. The process of claim 8, wherein the deprotection occurs in the
presence of moisture carried by the lignocellulosic particles.
10. The process of claim 8, wherein the deprotection occurs by
reason of moisture provided by steam.
11. The process of claim 8, wherein the deprotected phenol
formaldehyde reacts with the NCO group of the polymeric phenyl
isocyanate at room temperature in excess of 120.degree. C.
12. The process of claim 8, wherein the cellulosic particles are
selected from the group consisting of wood flakes, wood fibers,
wood wafers, wood strips, wood strands, wood veneers and mixtures
thereof.
13. A method of synthesizing a hybrid resin comprising providing a
phenol formaldehyde resin, protecting the reactive oxygens of the
phenol formaldehyde resin, mixing the protected phenol formaldehyde
resin with a polymeric phenyl isocyanate having reactive NCO
groups, deprotecting the reactive oxygens and permitting the
reactive oxygens of the hydroxyl groups of the phenol formaldehyde
to react with the NCO groups, thereby obtaining a hardened
resin.
14. The method of claim 13, including mixing the hybrid resin with
cellulosic material before the deprotecting step.
15. The method of claim 13, wherein the hybrid resin is mixed with
particles before the deprotecting step.
16. The method of claim 13, wherein deprotecting is achieved under
conditions of elevated heat, elevated pressure and in the presence
of moisture.
17. The method of claim 13, including the step of storing the
mixture for up to two weeks at room temperature before said
deprotecting step.
18. The method of claim 13, wherein the mixing step comprises
mixing 10 wt % to 80 wt % of the protected phenol formaldehyde with
90 wt % to 20 wt % of the polymeric phenyl isocyanate.
19. The method of claim 13, wherein the phenol-formaldehyde is a
resole and the phenyl isocyanate is 4-4'methylene bis(phenyl
isocyanate).
20. The method of claim 13, wherein the mixing comprises mixing 10
wt % to 40 wt % of the protected phenol formaldehyde with 90 wt %
to 60 wt % of the polymeric phenyl isocyanate.
21. The method of claim 13, wherein the protecting step results in
an acylated phenol formaldehyde resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to the field of adhesives,
more particularly to adhesives useful in the area of forest
products, such as plywood, chipboard, waferboard, strandboard, etc.
Methods of synthesis, the resulting adhesive and methods of using
the adhesive are within the scope of the invention.
[0003] 2. Description of the Related Art
[0004] Forest products, especially products which are manufactured
into useful materials through the use of adhesives are generally
known. Chipboard, waferboard, strandboard, plywood and other
composites made through the addition of an adhesive to forest
products or byproducts is well established. Generally, the adhesive
comprises a phenol-formaldehyde (PF) resin. Another commonly used
resin is a liquid polymeric 4,4'-methylene-bis(phenyl isocyanate)
(pMDI). Although aqueous, alkaline phenol-formaldehyde resins show
good durability, relatively low cost and relatively low toxicity,
they are known to exhibit slower press times and, in general,
produce products with higher thickness swell properties than the
same products composed of a pMDI binder. Although isocyanate resins
can exhibit some enhanced performance, they are more costly than PF
resins.
[0005] An additional drawback to production in manufacturing plants
is the huge capital costs associated with the press and associated
equipment, including steam generation equipment which provides the
heat during the pressing process. Yet the press itself is a
bottleneck in the process because of the dwell time of the product
required in the press in order to cure the adhesive. Thus, any
manner of reducing dwell time would be of commercial importance to
the board making industry.
[0006] Thus, there exists a need for suitable adhesive compositions
for the manufacture of improved wood products, especially exterior
grade products, such as waferboard and oriented strandboard.
SUMMARY OF THE INVENTION
[0007] It is, therefore, an object of the invention to provide
novel adhesive systems which avoid the problems associated with the
known adhesives.
[0008] It is a further object of the invention to provide a hybrid
resin comprising the combination of a PF resin and pMDI that forms
a single phase liquid material, and which has both shelf stability,
and fast cure times when used in conventional board making
processes.
[0009] We have found that by combining a protected PF resin and
pMDI we can obtain a storage life of greater than 2 weeks at room
temperature..
[0010] The hybrid resin of the invention can be applied to forest
products by applying, e.g., by spraying, blending or otherwise
mixing the adhesive and lignocelluosic material, such as wood
flakes, wood fibers, wood particles, wood wafers, strips or
strands, or other comminuted lignocellulosic materials while the
materials are tumbled or agitated in a blender or similar
apparatus. Once blended, the materials are formed into a loose mat
which, optionally after orientation of the lignocellulosic
materials, is compressed between heated platens or plates to set
the binder and bond the flakes, strands, strips, pieces, etc.
together in densified form.
[0011] Conventional processes are carried out at elevated
temperatures of from about 120 to 225.degree. C., by using a source
of heat, such as steam, to heat the platens, or even to inject the
steam into the mat, to cure the resin.
[0012] Alternatively, the blended material may be fed to molds for
the purpose of forming molded articles in which the resin and
particles are bonded under heat and pressure. However,
notwithstanding the particular shaping process employed, the resin
of the invention has a faster cure time than any of its
components.
[0013] The adhesive of the invention has other utilities, such as
being coated upon veneers or strips of wood, laminates, etc. by
roll coating, knife coating, curtain coating or spraying the
adhesive onto the veneer surface(s). A plurality of veneers are
then laid-up to form sheets of the required thickness and subjected
to heat and pressure to effect consolidation and curing of the
materials into a board.
[0014] Synthesis of the novel adhesives of the invention are also
disclosed in more detail in connection with the description of the
preferred embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Phenol-formaldehyde resins are generally well known to fall
into two classes depending upon the phenol to formaldehyde ratio
and being generally termed "novolacs" or "novolaks" (which are
thermoplastic) and "resoles" (which are thermosetting).
[0016] On the other hand, pMDI resins used to bond cellulosic
materials are also reported in the prior art; See, U.S. Pat. Nos.
3,666,953; 5,008,359; 5,140,086; 5,143,768; and 5,204,176, the
entire disclosures of which are herein incorporated by
reference.
[0017] To mediate the undesirable properties of PF and pMDI, the
inventors thought to combine the two resin systems. However, the
physical combination of the two binders is problematic because of
differences in polarity and incompatible chemical functional
groups. A strategy to produce a hybrid resin by emulsification of
the pMDI in PF resin and chemical modification of the NCO
functional group of the pMDI proved not to give a satisfactory
combination of storage life and performance. Thus, the inventors
conceived of the invention by modifying the PF resin.
[0018] The inventors protected the functional group of the PF
resin, e.g., by acylating the PF resin, and found that the
esterfication of the phenolic oxygen greatly diminished the
reactivity of the PF portion of the mixture when combined with pMDI
to form a single phase liquid material with a storage life of
greater than 2 weeks at room temperature.
[0019] The diminished reactivity of the PF portion is well
illustrated by its gel time in excess of 350 hours at 125.degree.
C. The gel time of the pMDI alone, or with added water to mimic the
conditions needed to cure the hybrid resin is in excess of 100 min.
at 121.degree. C. However the gel time with added water of the
acylated PF/pMDI system is about 10 min.
[0020] The acyl PF resin can be produced by any known method of
hydroxyl group acylation, to yield an organic-soluble anhydrous
clear liquid. The acylated PF resin can than be added to any
commercially available pMDI resin, or a pMDI resin synthesized to
customer's specifications.
[0021] When the acyl group is a carboxylic ester, it acts as a
protecting group that permits reactivity of the hydroxyl oxygens
with the NCO functionality of the pMDI resin. Under conditions of
temperature and moisture encountered during manufacture of boards,
such as strandboard, the PF portion is deprotected and the PF and
pMDI can react with one another.
[0022] There is a wide combination of phenolic resins and acyl
groups that can be employed to render the PF resin inactive toward
reaction with isocyanate groups as disclosed in U.S. Pat. Nos.
5,051,454 and 5,340,888, the entire disclosures of which are herein
incorporated by reference.
[0023] Because of the inherent protecting nature of the acyl
groups, the acyl PF resin can be used in combination with any pMDI
resin that is useful in commercial panel production.
[0024] We have found that the two resins may be combined in amounts
of from 10-80 wt % PF resin based on the weight of the whole
system. However, we have also found that hybrid resins comprised of
10-35 wt % PF exhibit better lack of viscosity advancement over a
period of four weeks. With the addition of water in acetone, a 30
wt % PF/pMDI hybrid resin will react at 121.degree. C. to form a
gel, which hardens to form a single phase material. We have also
found that strandboard panels produced with a 40 wt % PF/60 wt %
pMDI hybrid resin exhibit cure speeds that appear much faster than
either of its two components above. This synergistic effect was not
expected by us.
[0025] The advantages of the invention will become apparent by
reference to the following examples:
EXAMPLE 1
[0026] Phenyl acetate and aniline were combined in a reaction
vessel in approximately equimolar amounts. The temperature was
raised to 121.degree. C. for 5 minutes to simulate the interior of
a strandboard panel during hot pressing. Acetanilide, the product
of actuation by aniline was identified as a major reaction product
demonstrating that, under these conditions, the PF portion would be
deprotected and, therefore, activated toward condensation and
reaction with NCO.
EXAMPLE 2
[0027] An acetylated PF resin prepared from the treatment of a
commercially available PF resin (sold under the description
AcmeFlow.RTM.2012) with acetyl chloride and triethylamine was
combined with a commercial pMDI resin (sold under the description
MondurMR.RTM. from Bayer Co.). Combinations in the weight ratios of
10%, 25% and 33% acyl PF produced clear homogeneous solutions that
did not advance in viscosity noticeably over the test period of two
weeks.
EXAMPLE 3
[0028] A mixture of 30 wt % PF/pMDI with 0.25 mol. eq. of water/NCO
was heated at 121.degree. C. Samples are collected after 5 min. and
8 min. at which point the mixture was a soft gelatinous material.
The material was removed from the heat source and after 2-3
minutes, the sample appeared to be a single phase hard solid. This
example is consistent with the co-reactivity of the two resins.
EXAMPLE 4
[0029] A resin composition of 40 wt % acyl PF/60 wt % pMDI with an
intrinsic viscosity of 75 cps at 25.degree. C. and 300 cps at
40.degree. C. was applied to wood particles using the standard
procedure for making composite panels. The following resins were
compared to determine how the performance of the hybrid resin
compared to that of a commercially available pMDI (MondurMR.RTM.)
resin.
1 Resin Description 1 Mondur MR .RTM. wood moisture = 2.7 wt % 2
Acyl PF/Mondur 40 wt %:60 wt %; wood moisture = 2.7 wt % MR .RTM. 3
Acyl PF/Mondur 40 wt %:60 wt %; wood moisture = 5.6 wt % MR
.RTM.
[0030] Results of thickness swell and internal bond
2 Resin (press time in minutes) % Thickness Swell Internal Bond
(psi) 1 (5.75) 4.5 87 1 (5.50) 5.5 69 1 (5.25) 4.5 79 2 (5.75) 5.6
73 2 (5.25) 8.9 60 2 (5.00) 8.4 67 3 (5.50) 9.3 56 3 (5.25) 11.0 61
3 (5.00) 12.0 51
[0031] The results of the board study demonstrate that the resin of
the invention is capable of producing a panel with acceptable
thickness swell properties and internal bond strengths within press
times that are commercially viable. One of the surprising features
is that the same process used to provide greater room temperature
stability in the hybrid resin appears to also offer faster cure
speed in board production. The cure speed of the hybrid (mixed)
resin appears to be faster than that of either component. Past
experience with PF resoles indicates that they are always slower
than pMDI in cure time. The acylated PF resins are even slower than
ordinary PF resoles. Yet, when used in combination with pMDI, the
result is a faster cure time. This attribute has great commercial
advantage in reducing the dwell time in the consolidating press,
thereby making the board making process more productive. This
greatly improves the production for a fixed capital investment in
press apparatus and related equipment.
[0032] While it will be apparent to those skilled in the art that
various modifications and other embodiments of the invention can be
made upon review of the foregoing disclosure, such modifications
and embodiments do not depart from the spirit or scope of the
invention as defined in the appended claims.
* * * * *