U.S. patent application number 11/440660 was filed with the patent office on 2006-09-21 for method of coupling wireless portable communications device to electronicmail server by public wireless communications network when out of communication with private wireless communications.
Invention is credited to Greg Griffith, Charles M. II Link.
Application Number | 20060208858 11/440660 |
Document ID | / |
Family ID | 34710012 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060208858 |
Kind Code |
A1 |
Griffith; Greg ; et
al. |
September 21, 2006 |
Method of coupling wireless portable communications device to
electronicmail server by public wireless communications network
when out of communication with private wireless communications
Abstract
One-component adhesives/sealants comprising surface-deactivated
solid polyisocyanates and, optionally, isocyanate-reactive, liquid
binders can be rapidly cured below the conventional thickening
temperature by irradiating with microwaves, for example microwaves
of at least 2 wavelengths. This process is particularly suitable
for adhesively joining plastic substrates.
Inventors: |
Griffith; Greg; (Atlanta,
GA) ; Link; Charles M. II; (Roswell, GA) |
Correspondence
Address: |
WITHERS & KEYS FOR BELL SOUTH
P. O. BOX 71355
MARIETTA
GA
30007-1355
US
|
Family ID: |
34710012 |
Appl. No.: |
11/440660 |
Filed: |
May 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11119576 |
May 2, 2005 |
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11440660 |
May 24, 2006 |
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09474404 |
Dec 29, 1999 |
6917280 |
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11119576 |
May 2, 2005 |
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Current U.S.
Class: |
340/7.29 |
Current CPC
Class: |
H04W 80/10 20130101;
G06F 1/1632 20130101; H04W 80/04 20130101 |
Class at
Publication: |
340/007.29 |
International
Class: |
H04Q 7/14 20060101
H04Q007/14 |
Claims
1. A process for curing a one-component adhesive/sealant comprising
at least one surface-deactivated solid polyisocyanate, said process
comprising exposing the adhesive/sealant to microwave radiation,
wherein the adhesive/sealant is heated to a material temperature
below the thickening temperature.
2. A process according to claim 1, wherein immediately after the
end of the microwave irradiation, the adhesive/sealant has a
material temperature between 40.degree. C. and 120.degree. C.
3. A process according to claim 1, wherein immediately after the
end of the microwave irradiation, the adhesive/sealant has a
material temperature between 50.degree. C. and 70.degree. C.
4. A process according to claim 1, wherein the adhesive/sealant is
simultaneously irradiated with microwaves of at least two
wavelengths.
5. A process according to claim 4, wherein the at least two
wavelengths of the microwaves are generated by switching on
microwave producing microwave sources.
6. A process according to claim 5, wherein the switching on is
periodic.
7. A process according to claim 1, wherein the energy of the
microwaves is controlled as a function of the resulting
adhesive/sealant temperature and/or the state of cure of the
adhesive/sealant.
8. A process according to claim 1, wherein the adhesive/sealant is
on a substrate and the substrate is successively conveyed through a
plurality of zones that are irradiated with microwaves having an
identical fundamental frequency and which are modulated with at
least two different modulation frequencies.
9. A process in accordance with claim 8, wherein said identical
fundamental frequency is about 2.5 Gigahertz.
10. A process in accordance with claim 8, wherein said at least two
different modulation frequencies are selected from the group
consisting of about 1.2 Gigahertz, about 1.6 Gigahertz, about 1.9
Gigahertz, about 2.1 Gigahertz, about 2.5 Gigahertz and about 3
Gigahertz.
11. A process according to claim 1, wherein the at least one
surface-deactivated polyisocyanate has a melting point above
40.degree. C.
12. A process according to claim 1, wherein the polyisocyanate is
selected from diphenylmethane-4,4'-diisocyanate (MDI),
naphthalene-1,5-diisocyanate (NDI),
3,3'-dimethyl-biphenyl-4,4'-diisocyanate (TODI), dimeric
1-methyl-2,4-phenylene diisocyanate (TDI-U),
3,3'-diisocyanato-4,4'-dimethyl-N,N'-diphenylurea (TDIH), the
isocyanurate of IPDI (IPDI-T) or the addition product of 2 moles
1-methyl-2,4-phenylene diisocyanate with 1 mole 1,2-ethanediol,
1,4-butanediol, 1,4-cyclohexanedimethanol or ethanolamine.
13. A process according to claim 1, wherein the at least one
surface-deactivated polyisocyanate is produced by dispersing a
powdered polyisocyanate in a solution or dispersion of at least one
deactivation agent.
14. A process according to claim 13, wherein at least one low
molecular weight liquid polyamine, polyamidoamine,
polyoxyalkyleneamine, aminoalkyl alkoxysilane is employed as said
at least one deactivation agent.
15. A process according to claim 1, wherein the adhesive/sealant is
additionally comprised of at least one hydroxy-functional natural
oil and/or hydroxy-functional polyene selected from
hydroxy-functional polybutadienes, hydroxy-functional
polyisoprenes, hydroxy-functional copolymers of butadiene, isoprene
and styrene, or hydrogenated products thereof.
16. A process in accordance with claim 1, wherein said at least one
surface-deactivated polyisocyanate is in the form of a powder
having an average particle size of 10 .mu.m or less.
17. A process in accordance with claim 1, wherein said
adhesive/sealant is additionally comprised of at least one polyol
selected from the group consisting of polyether polyols, polyester
polyols, polyacrylate polyols, polyolefin polyols and polyether
ester polyols.
18. A process in accordance with claim 1, wherein said
adhesive/sealant is additionally comprised of at least one amine
selected from the group consisting of polyether amines and
substituted aromatic diamines.
19. A process for adhesively joining a first plastic substrate and
a second plastic substrate using a one-component adhesive/sealant
comprising at least one surface-deactivated solid polyisocyanate,
said process comprising curing the adhesive/sealant by exposing the
adhesive/sealant to microwave radiation, wherein the
adhesive/sealant is heated to a material temperature below the
thickening temperature.
20. A process in accordance with claim 19, wherein the first
plastic substrate and second plastic substrate are headlight
components.
21. A process in accordance with claim 19, wherein said
adhesive/sealant is dispensed onto a surface of at least one of
said first plastic substrate or said second plastic substrate using
a dispensing device conveyed on an arm of a robot and wherein a
microwave emitter conveyed on said arm of said robot is used as a
source of the microwave radiation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. Section 119
to German application DE 10200517912.6, filed 18 Apr. 2005.
FIELD OF THE INVENTION
[0002] The subject of the invention is a process for curing
one-component adhesives/sealants comprising surface-deactivated
solid polyisocyanates by means of microwave radiation, as well as
the use of this process for adhesively joining plastic
substrates
DISCUSSION OF THE RELATED ART
[0003] In modern industrial production, there is often the need to
bond plastic substrates together by adhesion. More and more
frequently, especially in the automobile industry, parts and
modules, such as lamp housings or automobile headlights, are
manufactured from plastics. For this, older joining processes are
known, in which a headlight housing has a U-shaped sealing bed on a
first side wall into which a second part, for example a closure or
a covering device of glass having a second side wall, is inserted
such that both parts are sealed and joined together. Nowadays,
lenses of plastic substrates, for example of polymethyl
methacrylate (PMMA) or polycarbonate (PC), are frequently used
instead of glass closures or covering lenses or also headlight
lenses.
[0004] Today, plastics are often bonded together by means of
2-component products that cure at room temperature. This is often
due to the fact that the substrates suffer thermal damage at high
temperatures and consequently cannot tolerate adhesives that
imperatively require these temperatures to reach their final
strength. At room temperature, the curing is indeed
substrate-friendly, but takes much longer than high temperature
curing. This problem can be mitigated by using 2-component products
with a short pot-life. However, this advantage is achieved at an
additional cost to the application (more frequent changes of static
mixers or/and cleaning out mixed material). A further advantage can
be obtained if, after application, at least a handling strength can
be achieved by means of an energy input, e.g. by thermal energy in
a circulating-air oven or by the use of hot-air techniques or even
by radiation energy (e.g., infra-red heating). These measures only
partially solve the problem, however, and require the use of
expensive equipment. A one-component product that is
substrate-friendly at relatively low temperatures and which almost
reaches its complete final strength in a relatively short time
would be a favorable solution to the problem.
[0005] One-component polyurethanes based on microencapsulated
isocyanate have been known for about 20 years and have been
introduced in the market in the form of various adhesives and
sealants for automobiles and commercial vehicles. In this field,
the state of the art for curing these products is by means of
thermal energy, e.g., in a circulating-air oven, through which the
automobile bodies in any case must transit to dry/cure the priming
coat, fillers or paints. In particular cases--mostly for mounted
parts--the hot air method can be used, whereby the hot air is only
blown onto the area of e.g. glue lines.
[0006] A process for bonding moldings with heat-curable adhesives
by irradiating the adhesive joint with electromagnetic radiation is
described in WO 03/076167. The adhesive joint should be such that
in the region of the adhesive joint, at least one of the moldings
of the substrate is transparent to electromagnet radiation,
particularly infrared radiation. The mass of the adhesive in the
adhesive joint should then be irradiated with energy-rich infrared
radiation (near infrared (NIR)). Heat curable adhesives, based on a
non-aqueous dispersion, which comprise one polyisocyanate that is
deactivated only on the surface and at least one polymer that is
reactive to isocyanate are proposed as the adhesive. A disadvantage
of this process is that the adhesive joint should be such that at
least one of the moldings to be joined is transparent to
IR-radiation in the region of the adhesive joint. A further
disadvantage is that the IR-radiation not only heats the adhesive,
but very frequently also the region of the mounted part close to
the adhesive.
[0007] Apart from these conventional methods, microwave curing of
polyurethanes has proven to be particularly advantageous when raw
materials that are suitable for microwave cure are used together
with conditions for this method that are favorable to highly active
catalysts. In this case it is also possible to realize good and
durable adhesion on critical primer coatings that, due to their low
surface tension, are difficult to wet.
[0008] Accordingly, there was the need to provide further processes
to bond plastic molded parts, enabling a rapid adhesion and
production process leading to a durable bond of the mounted parts,
and which are less dependent on special constructive limitations in
relation to the transparency to activating radiation.
[0009] The use of microwave irradiation for curing sealants and
adhesives is understood in principle, thus a process to at least
partially cure sealants and adhesives, particularly in connection
with the direct glazing of motor vehicles, is described in EP
318542 B1, the sealant and adhesive being heated by irradiation
with microwave energy. For this, the application of the microwave
energy should be localized and the microwave energy should be
applied in a pulse-like manner in a first and at least a further
group, the amplitude of each group being lower at the end than at
the start of the group, and continuous microwave energy is applied
for a period between the impulse groups. The constituents of the
binding agent comprise isocyanate-functional reaction products from
a stoichiometric excess of aromatic isocyanates with a polyol.
Complexed amines, particularly the complex of methylenedianiline
and common salt, are proposed as the heat-activatable crosslinking
agents. In this document, microencapsulated polyamino or
polyhydroxy functional compounds, which are consequently
unavailable for reaction with the isocyanate prepolymers at room
temperature, are proposed as additional crosslinking agents. These
types of crosslinking agent need material temperatures above
100.degree. C., advantageously between 120 and 160.degree. C., to
initiate the crosslinking reaction.
[0010] A method of dispensing adhesives onto a substrate, wherein
the adhesive is heated by microwave energy immediately before being
dispensed onto the substrate, is described in U.S. Pat. No.
5,948,194. For this, the material is conveyed under pressure
through a dispensing tube that is transparent to microwave energy.
The dispensing tube is located within a microwave resonant chamber.
The microwave energy is channeled from a microwave-generating
source along a waveguide to the microwave resonant chamber, wherein
the adhesive, on passing though the resonance chamber, undergoes
negligible heating at the radial boundaries of the dispensing tube.
The adhesive is subsequently dispensed onto the component along a
predetermined path. The material has to be heated to different
temperatures along the applied adhesive trail. General information
on the compositions of adhesives that are suitable for this process
is not available from this document.
[0011] A method of facilitating the adhesive bonding of various
components with variable frequency microwave energy is disclosed in
U.S. Pat. No. 5,804,801 A. According to this document, the time
required to cure a polymeric adhesive is decreased by placing
components to be bonded by the adhesive in a microwave heating
apparatus having a multimode cavity and irradiated with microwaves
of varying frequencies. This method provides uniform heating for
various articles comprising conductive fibers. Microwave energy may
be selectively oriented to enter an edge portion of an article
comprising conductive fibers. Other edge portions of an article can
be selectively shielded from the microwaves. Epoxy resin adhesives
are disclosed as useable adhesives.
[0012] Liquid, reactive, heat-curable compositions from a
polyepoxide, a di or polycarboxylic acid, together with a catalyst
that effects a rapid polymerization of the epoxide and anhydride
mixture under microwave irradiation are described in EP 0720995
B1.
[0013] A method of accelerating adhesive curing by the use of
adhesive compositions that comprise nano-particles having
ferromagnetic, ferrimagnetic, super paramagnetic or piezoelectric
properties, that under the influence of an electric or magnetic or
electromagnetic alternating field are heated up in such a way that
the binding agent matrix in reactive adhesives is heated to a
temperature that effects the crosslinking of the binding agent
matrix through the reactive groups of the binding agent, is
described in WO 02/12405. In this document, low frequency regions
from about 50 kHz up to about 100 kHz are proposed as the
electromagnetic radiation for heating the adhesive composition by
the nano-particles.
[0014] A method and a device for curing, crosslinking and/or drying
coating materials and/or substrates, and a novel use of a microwave
oven that is characterized by the use of microwaves with at least
two wavelengths, is described in EP 1327844 A2.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention provides a process for curing
one-component adhesive/sealing compositions that cure by means of
microwave radiation. More specifically, the subject of the present
invention relates to a process for curing one-component
adhesives/sealants comprising surface-deactivated polyisocyanates
that are solid at room temperature by means of microwave radiation,
and which is furnished in such a way that the adhesive/sealant
composition is macroscopically heated only to a temperature below
the thickening temperature.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION
[0016] In the context of this invention, the "thickening
temperature" is the temperature to which a room temperature, shelf
stable composition that comprises a surface deactivated isocyanate
must be heated for a short time, that is up to an hour, in order to
produce a polyaddition reaction and hence crosslinking. The
polyaddition reaction and/or crosslinking is recognized by a
significant "thickening", i.e., by the solidification of the
material. In the context of this invention, the thickening
temperature can be determined by placing the composition to be
tested in an oven at a predetermined temperature and measuring the
consistency of the composition as a function of time and
temperature. A further possibility is to apply a trail of material
onto a Kofler heating plate, i.e., a surface that exhibits a
specified temperature gradient. In this way, the thickening
temperature can be defined as the frontier between pasty and
crosslinked material. The simplest method of determination is a
viscosity measurement at defined increasing temperatures of the
measurement plate. In this case the thickening temperature is
defined as the value that can be read after initiation of the
curing reaction by extending the almost vertically rising branch of
the viscosity curve onto the temperature axis.
[0017] The "material temperature" of the adhesive/sealant
composition that is heated by microwave radiation according to the
inventive process is understood to mean the temperature measured at
the surface of the composition of the horizontal adhesive trails (1
cm wide, 0.5 cm high) immediately after they have left the
microwave radiation.
[0018] In a preferred embodiment of the process according to the
invention, the microwave radiation impinging on the adhesive
composition is controlled such that, in the sense of the above
definition, material temperatures between 40.degree. C. and
120.degree. C. are attained, the material temperature being
preferably between 50 and 70.degree. C.
[0019] In the context of this invention, "microwaves" are
understood to mean electromagnetic radiation in the frequency range
between 300 MHz and 300 GHz, i.e., electromagnetic rays between the
high frequency region of radio waves and infrared radiation. In
particular, the "microwave radiation" region in the context of this
invention includes the regions of decimeter waves with frequencies
between 300 MHz and 3 GHz and the centimeter waves with frequencies
between 3 GHz and 30 GHz and may, however, also include the region
of millimeter waves between 30 GHz and 300 GHz.
[0020] In preferred embodiments of the process according to the
invention, it is preferred to irradiate the adhesive/sealant
composition with microwaves with at least two wavelengths, wherein
the at least two wavelengths of the microwaves are generated by
switching on microwave-producing microwave sources, the switching
on being optionally periodic, and the energy of the radiating
microwaves is preferably controlled as a function of the resulting
adhesive/sealant temperature and/or the state of cure of the
polyurethane binding agent system.
[0021] With advancing curing of the binding agent system, the
quantity of microwave energy reflected from the irradiated adhesive
joint increases, such that the irradiated energy must be reduced by
means of a suitable feedback control system, so as to avoid
overheating. In order to obtain the most complete cure possible of
the adhesive/sealant in the adhesive joint under the mildest
possible conditions, it has to be ensured that the emittance of the
microwave energy takes place in such a way that the microwave
energy reaches the total volume of the adhesive so that the
crosslinking reaction can be initiated.
[0022] For this, the substrate provided with the adhesive/sealant
can be successively conveyed through zones that are irradiated with
microwaves having an identical fundamental frequency, preferably
about 2.5 GHz, and which are modulated with different modulation
frequencies, preferably with about 900 MHz, about 1.2 GHz, about
1.6 GHz, about 1.9 GHz, about 2.2 GHz, about 2.5 GHz and/or about 3
GHz.
[0023] Devices that are suitable for the inventive process of
adhering plastic components with the use of one-component
adhesives/sealants comprising surface deactivated solid
polyisocyanates are described, for example, in EP 1327844 A2. The
disclosure of this document in relation to the design of the device
is expressly incorporated as a component of the present
process.
[0024] For small components or for low surface area adhesive
joints, the devices for the inventive process to adhere plastic
components can be set up in such a way that the microwave emitter,
together with a dispensing device, is conveyed on an arm of a robot
along the region of the substrate provided with adhesive and to be
joined, such that the process can be extensively automated.
[0025] The solid, surface deactivated polyisocyanates which are
used in the adhesive/sealants according to the inventive process
preferably have a melting point above 40.degree. C. The
polyisocyanates listed below are particularly suitable:
Diphenylmethane-4,4'-diisocyanate (MDI),
naphthalene-1,5-diisocyanate (NDI),
3,3'-dimethyl-biphenyl-4,4'-diisocyanate (TODI), dimeric
1-methyl-2,4-phenylene diisocyanate (TDI-U),
3,3'-diisocyanato-4,4'dimethyl-N,N'-diphenylurea (TDIH), the
isocyanurate of IPDI (IPDI-T) or the addition product of 2 moles
1-methyl-2,4-phenylene diisocyanate with 1 mole 1,2-ethanediol,
1,4-butanediol, 1,4-cyclohexane dimethanol or ethanolamine.
[0026] The surface deactivation of these solid powdered
polyisocyanates is carried out by the known method of dispersing
the powdered polyisocyanates in a solution or dispersion of a
deactivating agent.
[0027] The solid polyisocyanates should preferably be in powder
form with an average particle size diameter of less than or equal
to 10 .mu.m (weight average). As a rule, they occur as a powder
having the required particle sizes of 10 .mu.m or less from their
synthesis; in other cases the solid polyisocyanates have to be
converted (prior to deactivation) to the inventive particle size
range by milling processes and/or sieving processes. The processes
are state of the art.
[0028] Alternatively, the powdered polyisocyanates can be converted
to an average particle size of equal to or less than 10 .mu.m by a
wet milling and fine dispersion subsequent to the surface
deactivation. Dispersion equipment of the rotor-stator type,
agitator ball mills, bead and sand mills, ball mills and friction
mills are suitable. According to the polyisocyanate and usage, the
grinding of the deactivated polyisocyanate may occur in the
presence of the deactivator or in non-reactive dispersing agents
followed by deactivation. The ground and surface-stabilized
polyisocyanate is also separated from the grinding dispersion and
optionally dried. The process is described in EP 204 970.
[0029] The surface deactivation reaction can be carried out in
various ways: [0030] By dispersing the powdered isocyanate in a
solution of the deactivator. [0031] By incorporating a melt of a
low-melting polyisocyanate into a solution of the deactivator in a
non-dissolving liquid dispersant. [0032] By adding the deactivator
or a solution of it to the dispersion of the solid, finely divided
isocyanate.
[0033] The solid polyisocyanates are preferably deactivated by the
action of primary and secondary aliphatic mono-, di- or polyamines,
hydrazine derivatives, amidines, and/or guanidines.
Ethylenediamine, 1,3-propylenediamine, diethylenetriamine,
triethylenetetramine, 2,5-dimethylpiperazine,
3,3'-dimethyl-4,4'-diamino-dicyclohexylmethane,
methylnonanediamine, isophoronediamine,
4,4'-diaminodicyclohexylmethane, diamino and triaminopolypropylene
ethers, polyamidoamines (also known as polyaminoamides), and
mixtures of mono-, di- and polyamines have proved their worth.
Aminoalkyl alkoxysilanes, such as for example the 3-aminopropyl
triethoxysilane or the corresponding alkyl dialkyloxysilanes or
other aminoalkyl alkoxysilanes as well as aminofunctional
polybutadienes or polyisoprenes are also suitable. The above amino
terminated polypropylene glycols, polyethylene glycols or
copolymers of propylene glycol and ethylene glycol are quite
particularly preferred. Mixtures of the above deactivators may also
be used.
[0034] The concentration of the deactivator should be 0.1 to 20,
preferably 0.5 to 8 equivalent percent, based on the total number
of isocyanate groups.
[0035] Accordingly, the binding agent of the microwave-curable
adhesive/sealant comprises polyols such as, e.g., polyether
polyols, polyester polyols, polyacrylate polyols, polyolefin
polyols and/or polyether ester polyols, polyether amines,
substituted aromatic diamines and a finely divided solid di- or
polyisocyanate that is surface deactivated during the dispersion in
the polyol/polyamine mixture.
[0036] In addition to the abovementioned constituents, typically
the adhesive/sealant comprises fillers, an optionally powdered
molecular sieve or other water-binding components, and/or
catalysts.
[0037] A large number of higher molecular weight polyhydroxy
compounds can be used as polyols. Room temperature-liquid
polyethers having two or three hydroxyl groups per molecule and in
the molecular weight range of 400 to 30,000, preferably in the
range 1000 to 15,000, are advantageously suitable as polyols.
Examples are di and/or trifunctional polypropylene glycols; also
statistical and/or block copolymers of ethylene oxide and propylene
oxide may be used. A further group of advantageously usable
polyethers are the polytetramethylene glycols
(poly(oxytetramethylene) glycols, poly-THF), which, e.g., are
prepared by acidic polymerization of tetrahydrofuran. In this case
the molecular weight range of the polytetramethylene glycols is
between 200 and 6000, preferably in the range 800 to 5000. Further
suitable polyols are the liquid, glassy amorphous or crystalline
polyesters that can be manufactured by condensing di or
tricarboxylic acids, such as, e.g., adipic acid, sebacic acid,
glutaric acid, azelaic acid, cork acid, undecanedioic acid,
dodecanedioic acid, 3,3-dimethylglutaric acid, terephthalic acid,
isophthalic acid, hexahydrophthalic acid, dimer fatty acids or
their mixtures with diols or triols such as, e.g., ethylene glycol,
propylene glycol, diethylene glycol, triethylene glycol,
dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol,
1,10-decanediol, 1,12-dodecanediol, dimer fatty alcohols, glycerin,
trimethylolpropane or their mixtures. A further group of
inventively applicable polyols is the polyesters based on
E-caprolactone, also known as "polycaprolactones". However,
polyester polyols of oleochemical origin may also be used. Such
types of polyester polyols can be manufactured by the total ring
opening of epoxidized triglycerides of a fat mixture comprising at
least partially olefinically unsaturated fatty acids with one or
more alcohols having 1 to 12 carbon atoms and subsequently
partially transesterifying the triglyceride derivatives to alkyl
ester polyols having 1 to 12 carbon atoms in the alkyl group.
Further suitable polyols that are used as polyols are polycarbonate
polyols and dimer diols (Henkel) as well as advantageously castor
oil and its derivatives and/or hydroxy-functional polybutadienes as
are obtainable under the trade name "Poly-bd". Besides the
abovementioned hydroxy-functional polybutadienes,
hydroxy-functional polyisoprenes, as well as the corresponding
hydroxy-functional copolymers of butadiene or isoprene with
styrene, as well as the hydrogenated products of hydroxy-functional
polybutadienes, polyisoprenes or their copolymers may also be
used.
[0038] In addition, linear and/or weakly branched acrylic ester
copolymer polyols that can be manufactured, for example, by the
radical copolymerization of acrylic acid esters or methacrylic acid
esters with hydroxy-functional acrylic acid- and/or methacrylic
acid compounds, such as hydroxyethyl methacrylate or hydroxypropyl
(meth)acrylate, are also suitable as the polyols. Due to their
manufacturing process, the hydroxyl groups in these polyols are
usually statistically distributed, so that they are either linear
or weakly branched polyols with an average OH functionality. The
hydroxy-functional binding agent component can also comprise
mixtures of one or a plurality of the abovementioned polyols. Amino
terminated polyalkylene glycols, particularly the difunctional
amino terminated polypropylene glycols, polyethylene glycols or
copolymers of propylene glycol and ethylene glycol can be
preferably added as the di or trifunctional amino terminated
polymers. They are also known by the name "Jeffamine" (trade name
of the Huntsman Petrochemical Corporation). In addition, the
difunctional amino terminated polyoxytetramethylene glycols, also
called poly-THF, are suitable. The difunctional amino terminated
polybutadiene compounds are also suitable building blocks, together
with aminobenzoic acid esters of polypropylene glycols,
polyethylene glycols or poly-THF (known under the trade name
"Versalink oligomeric diamines" of Air Products & Chemicals,
Inc.). The molecular weights of the amino terminated polyalkylene
glycols or polybutadienes are typically between 400 and 6000.
[0039] Similarly, substituted aromatic diamines, which are known
under the trade names Lonzacure (Lonza) or Unilink (UOP), can also
be used.
[0040] Chalks, natural, ground or precipitated calcium carbonates,
calcium magnesium carbonates (Dolomite), silicates such as, e.g.,
aluminum silicates, barites or magnesium aluminum silicates or also
talc are preferably used as the fillers. In addition, other
fillers, in particular reinforcing fillers like carbon blacks,
selected from the group of flame blacks, channel blacks, gas blacks
or furnace blacks or their mixtures can be optionally used with the
above fillers. The adhesives/sealants according to the present
invention can additionally comprise plasticizers or plasticizer
mixtures as well as catalysts, stabilizers and other auxiliaries
and additives.
[0041] Tertiary amines, particularly aliphatic cyclic amines, are
suitable catalysts. Under the tertiary amines, those that are also
suitable, carry additional groups, particularly hydroxyl and/or
amino groups, which are reactive towards isocyanates. Practical
examples are: dimethylmonoethanolamine, diethylmonoethanolamine,
methylethylmonoethanolamine, triethanolamine, trimethanolamine,
tripropanolamine, tributanolamine, trihexanolamine,
tripentanolamine, tricyclohexanolamine, diethanolmethylamine,
diethanolethylamine, diethanolpropylamine, diethanolbutylamine,
diethanolpentylamine, diethanolhexylamine,
diethanolcyclohexylamine, diethanolphenylamine as well as their
ethoxylation and propoxylation products, diaza-bicyclo-octane
(DABCO), triethylamine, dimethylbenzylamine (DESMORAPID DB, Bayer),
bis-dimethylaminoethyl ether (catalyst A 1, UCC),
tetramethylguanidine, bis-dimethylaminomethylphenol,
2-(2-dimethylaminoethoxy)ethanol,
2-dimethylaminoethyl-3-dimethylaminopropyl ether,
bis(2-dimethylaminoethyl) ether, N,N-dimethylpiperazine,
N-(2-hydroxyethoxyethyl)-2-azanorbornane, or also unsaturated
bicyclic amines, e.g. diazabicycloundecene (DBU) as well as TEXACAT
DP-914 (Texaco Chemical), N,N,N,N-tetramethylbutane-1,3-diamine,
N,N,N,N-tetramethylpropane-1,3-diamine and
N,N,N,N-tetramethylhexane-1,6-diamine.
[0042] The organometallic compounds commonly known in polyurethane
chemistry can also be used as catalysts, such as, for example iron
or also particularly tin or bismuth compounds. Specific examples of
them are 1,3-dicarbonyl compounds of iron, like iron (III)
acetylacetonate, as well as in particular the organotin compounds
of 2- or 4-valent tin, in particular the Sn(II) carboxylates or the
dialkylSn(IV) dicarboxylates or the corresponding dialkoxylates
such as, e.g., dibutyltin dilaurate, dibutyltin diacetate,
dimethyltin dineodecanoate, dioctyltin diacetate, dibutyltin
maleate, tin(II) octoate, tin(II) phenolate or also the
acetylacetonates of 2- or 4-valent tin. Optionally, mixtures of the
abovementioned tertiary amines with the organometallic compounds
can also be added as catalysts.
[0043] Lightweight fillers can also be used pro rata to manufacture
specific low-density adhesives/sealants, for example one can
utilize plastic microspheres, preferably in pre-expanded form.
These types of microspheres can either be added directly to the
adhesive/sealant in the prefoamed form or the microspheres in the
non-foamed form are added as a finely dispersed powder to the
adhesive/sealant. These microspheres comprise an aliphatic
hydrocarbon or fluorohydrocarbon-based liquid blowing agent as the
core and a skin of a copolymer of acrylonitrile with vinylidene
chloride and/or methyl methacrylate and/or methacrylonitrile. The
addition of such non-foamed microspheres results in their expansion
and consequently a foaming during the curing process of the
adhesive/sealant. The method results in a very uniform and fine
porous foaming. The use of this type of microspheres is described,
for example, in EP-A-559254. These types of microspheres are
commercially available, e.g., under the trade name "Expancel" from
Nobel Industries or under the trade name "Dualite" from Pierce
& Stevens Company (now part of Henkel Corporation).
[0044] In addition, additives for regulating the flow behavior can
also be added, for example urea derivatives, fibrillated or pulped
short fibers, pyrogenic silicas and the like.
[0045] Although the inventively used adhesives/sealants preferably
do not comprise plasticizers, sometimes it may be necessary to also
use known plasticizers. Dialkyl phthalates, dialkyl adipates,
dialkyl sebacates, alkylaryl phthalates, alkyl benzoates,
dibenzoates of polyols, like ethylene glycol, propylene glycol or
the lower polyoxypropylene- or polyoxyethylene compounds can be
used here. Further suitable plasticizers, alkyl phosphates, aryl
phosphates or alkyl aryl phosphates as well as allylsulfonic acid
esters of phenol or also paraffinic or naphthenic oils or
dearomatized hydrocarbons can be used as thinners. It is important
when using plasticizers as co-agents that they be selected such
that they will not attack the deactivating surface layer of the
deactivated finely dispersed polyisocyanates during storage of the
adhesive/sealant, as this would provoke a premature curing of the
adhesive/sealant.
[0046] The inventive choice of suitable radiation frequencies
enables various advantages to be achieved. [0047] 1. Radiation
energy is preferably or exclusively absorbed by the adhesive. The
substrates are only indirectly heated by thermal conduction and
therefore remain significantly cooler than in the case of oven
curing. [0048] 2. With the complete absorption of the emitted
energy directly in the adhesive, there results a markedly faster
curing than in the oven, particularly if the adhesive must be cured
between 2 substrates. Curing times of less than 10 minutes in an
oven are barely achievable. Under favorable conditions, less than
two, in the ideal case less than one minute are required for
microwave curing.
[0049] Surprisingly, it was moreover discovered that the curing
temperatures for the polyurethanes lie significantly lower than in
oven curing. Differences of 10.degree. C. and more in the surface
temperature were found when the values were determined immediately
after leaving the energy source. The values measured after
switching off the microwave field were also markedly lower than
those laboratory values determined by measuring the thickening
temperature.
[0050] The inventive process for curing one-component
adhesives/sealants is particularly suitable for adhesively joining
plastic substrates. Particularly preferably, this process for
adhesively joining plastic components can be employed in the
automobile industry, for example for attached parts and mounted
parts such as roof modules, trunk lids, door parts as well as
headlight components.
[0051] The inventive process is described below in more detail
using several examples.
EXAMPLES
Example 1
[0052] Castor oil (10 g), 220 g of OH-terminated polybutadiene
(e.g., LIQUIFLEX H), and 264 g of a process oil (e.g., NYTEX 840)
are mixed in a stirred vessel. Subsequently, the following
additives are stirred in:
[0053] Aminopropyl trimethoxysilane, 1 g;
[0054] Dimethyltin carboxylate (FOMREZ UL-28), 1 g;
[0055] 2-Methyl-2-azanorbornane (DABCO AN10) 1.5 g; and
[0056] Polyoxypropylenetriamine (JEFFAMINE T403), 2.5 g.
[0057] The following solids are then dispersed into the
above-described mixture under vacuum:
[0058] Powdered molecular sieve, 30 g,
[0059] Silica, 15 g,
[0060] Coloring carbon black, 5 g,
[0061] Surface-treated chalk, 410 g.
[0062] In the last step, 40 g of dimeric toluylene diisocyanate
(METALINK U) are stirred in, under vacuum, to homogeneity. A pasty
mass with a thickening temperature of ca. 80.degree. C. is
obtained.
[0063] The product was tested for suitability in adhesively joining
headlight substrates. Test pieces of polypropylene and
polycarbonate were used, a trail of adhesive according to example 1
was dispensed onto the polypropylene part and the polycarbonate was
added onto it. The pieces were then conveyed through a microwave
tunnel in which was a low energy microwave fundamental radiation of
2.45 GHz with an available second frequency of 1.6 GHz modulated
onto it. The curing between both the plastic pieces (adhesion of PP
to PC) was completed after ca. 2 minutes.
[0064] The surface temperature was determined by curing
freestanding trails under the same conditions. The temperature,
measured immediately after leaving the microwave tunnel, was
68.degree. C. In the oven, the product was cured after 15 minutes
at 78.degree. C.; at lower temperatures, the mass remained
pasty.
* * * * *