U.S. patent application number 12/161354 was filed with the patent office on 2010-09-02 for foams based on thermoplastic polyurethanes.
This patent application is currently assigned to BASF SE. Invention is credited to Frank Braun, Frank Prissok.
Application Number | 20100222442 12/161354 |
Document ID | / |
Family ID | 37944927 |
Filed Date | 2010-09-02 |
United States Patent
Application |
20100222442 |
Kind Code |
A1 |
Prissok; Frank ; et
al. |
September 2, 2010 |
FOAMS BASED ON THERMOPLASTIC POLYURETHANES
Abstract
Expandable thermoplastic polyurethane comprising blowing agent,
wherein the Shore hardness of the thermoplastic polyurethane is
from A 44 to A 84.
Inventors: |
Prissok; Frank; (Lemfoerde,
DE) ; Braun; Frank; (Ludwigshafen, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
37944927 |
Appl. No.: |
12/161354 |
Filed: |
January 12, 2007 |
PCT Filed: |
January 12, 2007 |
PCT NO: |
PCT/EP2007/050274 |
371 Date: |
July 18, 2008 |
Current U.S.
Class: |
521/60 ; 264/54;
521/56 |
Current CPC
Class: |
C08J 2201/03 20130101;
C08J 2375/04 20130101; A43B 13/187 20130101; B29B 9/065 20130101;
A43B 17/14 20130101; B29B 9/12 20130101; C08G 2101/00 20130101;
C08J 9/16 20130101; C08J 2375/08 20130101; C08J 3/12 20130101; C08J
9/141 20130101; A43B 13/04 20130101; C08G 18/10 20130101; C08J
9/232 20130101; A43B 13/023 20130101; C08G 18/48 20130101; C08K
3/32 20130101; C08G 18/4854 20130101; B29B 9/16 20130101; C08J 9/18
20130101; C08J 2203/14 20130101; B29B 9/14 20130101; C08G 18/7657
20130101; C08G 2410/00 20130101; C08L 75/04 20130101 |
Class at
Publication: |
521/60 ; 521/56;
264/54 |
International
Class: |
C08J 9/18 20060101
C08J009/18; C08G 71/04 20060101 C08G071/04; C08J 9/14 20060101
C08J009/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2006 |
EP |
06100506.2 |
Claims
1. An expandable thermoplastic polyurethane comprising a blowing
agent, wherein the thermoplastic polyurethane exhibits a Shore
hardness that ranges from A 44 to A 84.
2. The expandable thermoplastic polyurethane according to claim 1,
wherein the thermoplastic polyurethane exhibits a melting range,
measured by DSC using a heating rate of 20 K/min, that starts below
130.degree. C., and the thermoplastic polyurethane has at most a
melt flow rate of 250 g/10 min at 190.degree. C. with an applied
weight of 21.6 kg to DIN EN ISO 1133.
3. The expandable thermoplastic polyurethane according to claim 1,
wherein the thermoplastic polyurethane is based on a
polytetrahydrofuran of a molar mass that ranges from 600 g/mol to
2500 g/mol.
4. The expandable thermoplastic polyurethane according to claim 1,
wherein the thermoplastic polyurethane is based on a polyester
alcohol of a molar mass that ranges from 600 g/mol to 900
g/mol.
5. The expandable thermoplastic polyurethane according to claim 1,
wherein the thermoplastic polyurethane has an average diameter that
ranges from 0.2 to 10 mm.
6. The expandable thermoplastic polyurethane according to claim 1,
further comprising from 5 to 80% by weight of an organic filler, an
inorganic filler, or a combination thereof, based on the total
weight of the thermoplastic polyurethane.
7. A process for producing an expandable thermoplastic polyurethane
comprising a blowing agent, which comprises: (i) extruding a
thermoplastic polyurethane exhibiting a Shore hardness that ranges
from A 44 to A 84, if appropriate together with additives, to give
pellets with an average diameter that ranges from 0.2 to 10 mm,
(ii) impregnating the pellets with from 0.1 to 40% by weight, based
on the total weight of the pellets, of a blowing agent in aqueous
suspension under pressure at temperatures in the range from 100 to
150.degree. C., (iii) cooling the suspension comprising the
thermoplastic polyurethanes to from 20 to 95.degree. C., and (iv)
depressurizing the thermoplastic polyurethane.
8. A process for producing an expandable thermoplastic polyurethane
comprising a blowing agent, which comprises: (i) melting a
thermoplastic polyurethane exhibiting a Shore hardness that ranges
from A 44 to A 84 together with from 0.1 to 40% by weight, based on
the total weight of pellets, of a blowing agent and, if appropriate
with additives, in an extruder to form a melt, and (ii) pelletizing
the melt under water at a pressure that ranges from 2 bar to 20 bar
and a temperature that ranges from 5.degree. C. to 95.degree.
C.
9. A process for producing a foam based on a thermoplastic
polyurethane, which comprises foaming the expandable thermoplastic
polyurethane according to claim 1 at a temperature that ranges from
100.degree. C. to 140.degree. C.
10. A foam based on thermoplastic polyurethane obtained by the
process according to claim 9.
11. A process for producing an expanded thermoplastic polyurethane,
which comprises: (i) extruding a thermoplastic polyurethane
exhibiting a Shore hardness that ranges from A 44 to A 84, if
appropriate together with additives, to give pellets with an
average diameter that ranges from 0.2 to 10 mm, (ii) impregnating
the pellets with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a blowing agent, under pressure at
temperatures in the range from 100 to 150.degree. C., and (iii)
depressurizing said expandable thermoplastic polyurethane.
12. A process for producing an expanded thermoplastic polyurethane,
which comprises: (i) melting a thermoplastic polyurethane
exhibiting a Shore hardness that ranges from A 44 to A 84, together
with from 0.1 to 40% by weight, based on the total weight of
pellets, of a blowing agent, if appropriate with additives, in an
extruder to form a melt, and (ii) pelletizing the melt without
devices which inhibit foaming.
13. An expanded thermoplastic polyurethane obtained by a process
according to claim 11.
14. The expanded thermoplastic polyurethane according to claim 13,
wherein the thermoplastic polyurethane comprises, based on the
total weight of the thermoplastic polyurethane, from 5 to 80% by
weight of an organic filler, an inorganic filler, or a combination
thereof.
15. A process for production of foam based on thermoplastic
polyurethane, which comprises using steam with a temperature of
from 100.degree. C. to 140.degree. C. to fuse expanded
thermoplastic polyurethane according to claim 13 to give a molding.
Description
[0001] The invention relates to expandable thermoplastic
polyurethane, preferably in bead form, comprising blowing agent,
where the Shore hardness of the thermoplastic polyurethane is from
A 44 to A 84, preferably from A 62 to A 82, particularly preferably
from A 62 to A 80. The Shore hardness of the TPU here is measured
on the compact, i.e. unexpanded, TPU. The invention moreover
relates to processes for production of expandable thermoplastic
polyurethane, preferably in bead form, comprising blowing agent.
The invention also relates to processes for production of expanded
thermoplastic polyurethane, and to processes for production of foam
based on thermoplastic polyurethane, and to foams or expanded
thermoplastic polyurethanes thus obtainable.
[0002] Foams, and this particularly applies to moldable foams, have
been known for a long time and are widely described in the
literature, e.g. in Ullmann's "Encyklopadie der technischen Chemie"
[Encyclopedia of Industrial Chemistry], 4th edition, Volume 20, pp.
416 et seq.
[0003] DE 4015714 A1 mentions glass fiber-reinforced TPU foams
which are produced in an injection-molding machine. The examples
state densities of 800 g/L and greater. These are foamed TPU
sheets, not moldable foams.
[0004] Moldable foams based on thermoplastic polyurethane, also
termed TPU in this specification, have been disclosed in WO
94/20568. A disadvantage of the TPU foams described in WO 94/20568
is the high energy consumption during production and processing. A
steam pressure of from 4.5 bar to 7 bar is used, i.e. a temperature
of from 145.degree. C. to 165.degree. C.
[0005] WO 94/20568 also describes expanded, i.e. foamed, TPU beads
which can be processed to give moldings. These TPU foam beads are
produced at temperatures of 150.degree. C. and higher and in the
examples have a bulk density of from 55 to 180 g/L, with resultant
disadvantage in transport and storage of these beads due to the
increased space required.
[0006] The object of the present invention therefore consists in
developing a moldable TPU foam which can be produced at low
temperatures and simultaneously has good performance in relation to
elasticity and to temperature variation. A further object was to
develop expandable TPU beads and expanded TPU foam beads, and
processes for their production, these being beads which can be
produced and processed at low temperatures.
[0007] These objects have been achieved via expandable
thermoplastic polyurethane, preferably in bead form, comprising
blowing agent, where the Shore hardness of the thermoplastic
polyurethane is from A 44 to A 84, preferably from A 62 to A 82,
particularly preferably from A 62 to A 80. The Shore hardness of
the TPU here is measured on the compact, i.e. unexpanded, TPU.
[0008] The advantage of the present invention is that it uses TPU
with lower hardness, lower melting point, and better flowability.
The result is that temperatures and pressures can be kept lower
during the production of the expanded TPU beads. Specifically when
steam is used, it is advantageous to be able to operate at lower
temperatures. Furthermore, the softness makes adhesive-bonding of
the foam beads more effective.
[0009] According to the invention, preferred TPUs are those in
which the melting range measured by DSC with a heating rate of 20
K/min starts below 130.degree. C., more preferably below
120.degree. C., and the thermoplastic polyurethane has at most a
melt flow rate (MFR) of 250 g/10 min, particularly preferably
smaller than 200 g/10 min at 190.degree. C. with an applied weight
of 21.6 kg to DIN EN ISO 1133.
[0010] Another advantage of the inventive thermoplastic
polyurethanes consists in their better feel.
[0011] The inventive TPUs are preferably based on polyether
alcohol, particularly preferably polyetherdiol. Polytetrahydrofuran
can particularly preferably be used here. It is particularly
preferable that the TPU is based on polytefrahydrofuran whose molar
mass is from 600 g/mol to 2500 g/mol. The polyether alcohols can be
used either individually or else in a mixture with one another.
[0012] As an alternative, good results were achieved with TPU based
on polyester alcohol, preferably polyesterdiol, particularly
preferably derived from adipic acid and 1,4-butanediol, with a
molar mass of from 600 g/mol to 900 g/mol.
[0013] Thermoplastic polyurethanes and processes for their
production are well known. By way of example, TPUs can be produced
via reaction of (a) isocyanates with (b) compounds reactive toward
isocyanates and having a molar mass of from 500 to 10000 and, if
appropriate, (c) chain extenders having a molar mass of from 50 to
499, if appropriate in the presence of (d) catalysts and/or of (e)
conventional auxiliaries and/or conventional additives.
[0014] The starting components and processes for production of the
preferred polyurethanes will be described by way of example below.
The components (a), (b), and also, if appropriate, (c), (d) and/or
(e) usually used in production of the polyurethanes will be
described by way of example below: [0015] a) Organic isocyanates
(a) which may be used are well-known aliphatic, cycloaliphatic,
araliphatic, and/or aromatic isocyanates, preferably diisocyanates,
for example tri-, tetra-, penta-, hexa-, hepta- and/or
octamethylene diisocyanate, 2-methylpentamethylene
1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate, pentamethylene
1,5-diisocyanate, butylene 1,4-diisocyanate,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane
(isophorone diisocyanate, IPDI), 1,4- and/or
1,3-bis(isocyanatomethyl)cyclohexane (HXDI), cyclohexane
1,4-diisocyanate, 1-methylcyclohexane 2,4- and/or 2,6-diisocyanate,
and/or dicyclohexylmethane 4,4'-, 2,4'- and 2,2'-diisocyanate,
diphenylmethane 2,2'-, 2,4'- and/or 4,4'-diisocyanate (MDI),
naphthylene 1,5-diisocyanate (NDI), tolylene 2,4- and/or
2,6-diisocyanate (TDI), diphenylmethane diisocyanate,
3,3'-dimethylbiphenyl diisocyanate, 1,2-diphenylethane
diisocyanate, and/or phenylene diisocyanate. [0016] b) Compounds
(b) which may be used and are reactive toward isocyanates are the
well-known compounds reactive toward isocyanates, for example
polyesterols, polyetherols, and/or polycarbonatediols, these
usually also being combined under the term "polyols", having molar
masses of from 500 to 8000, preferably from 600 to 6000, in
particular from 800 to 4000, and preferably having an average
functionality of from 1.8 to 2.3, preferably from 1.9 to 2.2, in
particular 2. [0017] c) Chain extenders (c) that may be used
comprise well-known aliphatic, araliphatic, aromatic and/or
cycloaliphatic compounds having a molar mass of from 50 to 499,
preferably difunctional compounds, such as diamines and/or
alkanediols having from 2 to 10 carbon atoms in the alkylene
radical, in particular 1,4-butanediol, 1,6-hexanediol, and/or di-,
tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- and/or
decaalkylene glycols having from 3 to 8 carbon atoms, and
preferably corresponding oligo- and/or polypropylene glycols, and
use may also be made of a mixture of the chain extenders. [0018] d)
Suitable catalysts which in particular accelerate the reaction
between the NCO groups of the diisocyanates (a) and the hydroxy
groups of the structural components (b) and (c) are the
conventional tertiary amines known from the prior art, e.g.
triethylamine, dimethylcyclohexylamine, N-methylmorpholine,
N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol,
diazabicyclo-[2.2.2]octane and the like, and also in particular
organometallic compounds, such as titanic esters, iron compounds,
e.g. ferric acetylacetonate, tin compounds, e.g. stannous
diacetate, stannous dioctoate, stannous dilaurate, or the
dialkyltin salts of aliphatic carboxylic acids, e.g. dibutyltin
diacetate, dibutyltin dilaurate, or the like. The amounts usually
used of the catalysts are from 0.0001 to 0.1 part by weight per 100
parts by weight of polyhydroxy compound (b). [0019] e) Alongside
catalysts (d), conventional auxiliaries and/or additives (e) may
also be added to the structural components (a) to (c). By way of
example, mention may be made of blowing agents, surface-active
substances, fillers, flame retardants, nucleating agents,
antioxidants, lubricants and mold-release agents, dyes and
pigments, further stabilizers if appropriate in addition to the
inventive stabilizer mixture, e.g. with respect to hydrolysis,
light, heat or discoloration, inorganic and/or organic fillers,
reinforcing agents, and plasticizers. In one preferred embodiment,
component (e) also includes hydrolysis stabilizers, such as
polymeric and low-molecular-weight carbodiimides. In another
embodiment, the TPU can comprise a phosphorus compound. In one
preferred embodiment, phosphorus compounds used are
organophosphorus compounds of trivalent phosphorus, examples being
phosphites and phosphonites. Examples of suitable phosphorus
compounds are triphenyl phosphate, diphenyl alkyl phosphate, phenyl
dialkyl phosphite, tris(nonylphenyl)phosphite, trilauryl phosphite,
trioctadecyl phosphite, distearyl pentaerythritol diphosphite,
tris(2,4-di-tert-butylphenyl)phosphite, diisodecyl pentaerythritol
diphosphite, di(2,4-di-tert-butylphenyl)pentaerythritol
diphosphite, tristearyl sorbitol triphosphite,
tetrakis(2,4-di-tert-butylphenyl) 4,4'-diphenylenediphosphonite,
trisisodecyl phosphite, diisodecyl phenyl phosphite, and diphenyl
isodecyl phosphite, or a mixture thereof. [0020] The phosphorus
compounds are particularly suitable when they are difficult to
hydrolyze, since the hydrolysis of a phosphorus compound to give
the corresponding acid can lead to degradation of the polyurethane,
in particular of the polyester urethane. Accordingly, the
phosphorus compounds particularly suitable for polyester urethanes
are those which are particularly difficult to hydrolyze. Examples
of these phosphorus compounds are dipolypropylene glycol phenyl
phosphite, triisodecyl phosphite, triphenyl monodecyl phosphite,
trisisononyl phosphite, tris(2,4-di-tert-butylphenyl)phosphite,
tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylylene diphosphonite,
and di(2,4-di-tert-butylphenyl)-pentaerythritol diphosphite, or a
mixture thereof. [0021] Fillers that can be used are organic and
inorganic powders or fibrous materials, or else a mixture thereof.
Examples of organic fillers that can be used are wood flour,
starch, flax fibers, hemp fibers, ramie fibers, jute fibers, sisal
fibers, cotton fibers, cellulose fibers, or aramid fibers. Examples
of inorganic fillers that can be used are silicates, barite, glass
beads, zeolite, metals or metal oxides. It is preferable to use
pulverulent inorganic substances, such as talc, chalk, kaolin,
(Al.sub.2(Si.sub.2O.sub.5)(OH).sub.4), aluminum hydroxide,
magnesium hydroxide, aluminum nitrite, aluminum silicate, barium
sulfate, calcium carbonate, calcium sulfate, silica, powdered
quartz, Aerosil, alumina, mica, or wollastonite, or inorganic
substances in the form of beads or fibers, e.g. iron powder, glass
beads, glass fibers, or carbon fibers. The average particle
diameters or, in the case of fillers in the form of fibers, the
length should be in the region of the cell size or smaller.
Preference is given to an average particle diameter in the range
from 0.1 to 100 .mu.m, preferably in the range from 1 to 50 .mu.m.
Preference is given to expandable, thermoplastic polyurethanes
comprising blowing agent and comprising from 5 to 80% by weight of
organic and/or inorganic fillers, based on the total weight of the
thermoplastic polyurethane comprising blowing agent. Further
preference is given to expanded thermoplastic polyurethanes which
comprise from 5 to 80% by weight of organic and/or inorganic
fillers, based on the total weight of the thermoplastic
polyurethane.
[0022] Besides the components a) and b) mentioned, and if
appropriate, c), d) and e), it is also possible to use chain
regulators, usually with molar mass of from 31 to 499. These chain
regulators are compounds which have only one functional group
reactive toward isocyanates, examples being monohydric alcohols,
monobasic amines, and/or monohydric polyols. These chain regulators
can give precise control of flow behavior, in particular in the
case of TPUs. The amount of chain regulators which may generally be
used is from 0 to 5 parts by weight, preferably from 0.1 to 1 part
by weight, based on 100 parts by weight of component b), and the
chain regulators are defined as part of component (c).
[0023] All of the molar masses mentioned in this specification have
the unit [g/mol].
[0024] To adjust the hardness of the TPUs, the molar ratios of the
structural components (b) and (c) may be varied relatively widely.
Successful molar ratios of component (b) to the entire amount of
chain extenders (c) to be used are from 10:1 to 1:10, in particular
from 1:1 to 1:4, and the hardness of the TPUs here rises as content
of (c) increases.
[0025] It is preferable that chain extenders (c) are also used for
production of the TPUs.
[0026] The reaction can take place at conventional indices,
preferably with an index of from 60 to 120, particularly preferably
at an index of from 80 to 110. The index is defined via the ratio
of the total number of isocyanate groups used during the reaction
in component (a) to the number of groups reactive toward
isocyanates, i.e. to the active hydrogen atoms, in components (b)
and (c). If the index is 100, there is one active hydrogen atom,
i.e. one function reactive toward isocyanates, in components (b)
and (c) for each isocyanate group in component (a). If indices are
above 100, there are more isocyanate groups than OH groups
present.
[0027] The TPUs can be produced by the known processes
continuously, for example using reactive extruders, or the belt
process, by the one-shot method or the prepolymer method, or
batchwise by the known prepolymer process. The components (a), (b)
and, if appropriate, (c), (d), and/or (e) reacting in these
processes can be mixed with one another in succession or
simultaneously, whereupon the reaction immediately begins.
[0028] In the extruder process, structural components (a), (b),
and, if appropriate, (c), (d), and/or (e) are introduced
individually or in the form of a mixture into the extruder, e.g. at
temperatures of from 100 to 280.degree. C., preferably from 140 to
250.degree. C., and reacted, and the resultant TPU is extruded,
cooled, and pelletized. It can, if appropriate, be advisable to
heat-condition the resultant TPU prior to further processing at
from 80 to 120.degree. C., preferably from 100 to 110.degree. C.,
for a period of from 1 to 24 hours.
[0029] According to the invention, the inventive TPUs described at
the outset are used for production of the expandable thermoplastic
polyurethanes, preferably in bead form, comprising blowing agent,
for production of expanded thermoplastic polyurethane, and for
production of foam based on thermoplastic polyurethane. The
production of these materials from the inventive TPUs is described
below.
[0030] In principle, the inventive expanded TPU beads can be
produced via suspension or extrusion processes directly or
indirectly by way of expandable TPU beads and foaming in a pressure
prefoamer with steam or hot air.
[0031] In the suspension process, the TPU in the form of pellets is
heated with water, with a suspending agent, and with the blowing
agent in a closed reactor to above the softening point of the
pellets. The polymer beads are thereby impregnated by the blowing
agent. It is then possible either to cool the hot suspension,
whereupon the particles solidify with inclusion of the blowing
agent, and to depressurize the reactor. The (expandable) beads
comprising blowing agent and obtained in this way are foamed via
heating to give the expanded beads. As an alternative, it is
possible to depressurize the hot suspension suddenly, without
cooling (explosion-expansion process), whereupon the softened beads
comprising blowing agent immediately foam to give the expanded
beads, see, for example, WO 94/20568.
[0032] In the extrusion process, the TPU is mixed, with melting, in
an extruder with a blowing agent which is introduced into the
extruder. Either the mixture comprising blowing agent is extruded
and pelletized under conditions of pressure and temperature such
that the TPU pellets do not foam (expand), an example of a method
being used for this purpose being underwater pelletization, which
is operated with a water pressure of more than 2 bar. This gives
expandable beads comprising blowing agent, which are then foamed
via subsequent heating to give the expanded beads. Or the mixture
can also be extruded and pelletized at atmospheric pressure. In
this process, the melt extrudate foams and the product obtained via
pelletization is the expanded beads.
[0033] The TPU can be used in the form of commercially available
pellets, powder, granules, or in any other form. It is advantageous
to use pellets. An example of a suitable form is what are known as
minipellets whose preferred average diameter is from 0.2 to 10 mm,
in particular from 0.5 to 5 mm. These mostly cylindrical or round
minipellets are produced via extrusion of the TPU and, if
appropriate, of other additives, discharged from the extruder, and
if appropriate cooling, and pelletization. In the case of
cylindrical minipellets, the length is preferably from 0.2 to 10
mm, in particular from 0.5 to 5 mm. The pellets can also have a
lamellar shape. The average diameter of the thermoplastic
polyurethane comprising blowing agent is preferably from 0.2 to 10
mm.
[0034] The expandable TPU beads of the invention can be produced by
the suspension process or by the extrusion process.
[0035] As a function of the process used, the preferred blowing
agents can vary if appropriate. In the case of the suspension
process, the blowing agent used preferably comprises organic
liquids or inorganic gases, or a mixture thereof. Liquids that can
be used comprise halogenated hydrocarbons, but preference is given
to saturated, aliphatic hydrocarbons, in particular those having
from 3 to 8 carbon atoms. Suitable inorganic gases are nitrogen,
air, ammonia, or carbon dioxide.
[0036] In production via an extrusion process, the blowing agent
used preferably comprises volatile organic compounds whose boiling
point at atmospheric pressure of 1013 mbar is from -25 to
150.degree. C., in particular from -10 to 125.degree. C.
Hydrocarbons (preferably halogen-free) have good suitability, in
particular C.sub.4-10-alkanes, for example the isomers of butane,
of pentane, of hexane, of heptane, and of octane, particularly
preferably sec-pentane. Other suitable blowing agents are bulkier
compounds, examples being alcohols, ketones, esters, ethers, and
organic carbonates.
[0037] It is also possible to use halogenated hydrocarbons, but the
blowing agent is preferably halogen-free. Very small proportions of
halogen-containing blowing agents in the blowing agent mixture are
however not to be excluded. It is, of course, also possible to use
mixtures of the blowing agents mentioned.
[0038] The amount of blowing agent is preferably from 0.1 to 40
parts by weight, in particular from 0.5 to 35 parts by weight, and
particularly preferably from 1 to 30 parts by weight, based on 100
parts by weight of TPU used.
[0039] In the suspension process, operations are generally carried
out batchwise in an impregnator, e.g. in a stirred-tank reactor.
The TPU is fed, e.g. in the form of minipellets, into the reactor,
as also is water or another suspension medium, and the blowing
agent and, if appropriate, a suspending agent. Water-insoluble
inorganic stabilizers are suitable as suspending agent, examples
being tricalcium phosphate, magnesium pyrophosphate, and metal
carbonates; and also polyvinyl alcohol and surfactants, such as
sodium dodecylarylsulfonate. The amounts usually used of these are
from 0.05 to 10% by weight, based on the TPU.
[0040] The reactor is then sealed, and the reactor contents are
heated to an impregnation temperature which is usually at least
100.degree. C. The blowing agent here can be added prior to,
during, or after heating of the reactor contents. The impregnation
temperature should be in the vicinity of the softening point of the
TPU. Impregnation temperatures of from 100 to 150.degree. C., in
particular from 110 to 145.degree. C., are preferred.
[0041] As a function of the amount and nature of the blowing agent,
and also of the temperature, a pressure (impregnation pressure)
becomes established in the sealed reactor and is generally from 2
to 100 bar (absolute). The pressure can, if necessary, be regulated
via a pressure-control valve or via introduction of further blowing
agent under pressure. At the elevated temperature and
superatmospheric pressure provided by the impregnation conditions,
blowing agent diffuses into the polymer pellets. The impregnation
time is generally from 0.5 to 10 hours.
[0042] In one embodiment of the suspension process, cooling of the
heated suspension, usually to below 100.degree. C., takes place
after the impregnation process, the result being re-solidification
of the TPU and inclusion of the blowing agent. The material is then
depressurized. The product is expandable TPU beads which finally
are conventionally isolated from the suspension. Adherent water is
generally removed via drying, e.g. in a pneumatic dryer.
Subsequently or previously, if necessary, adherent suspending agent
can be removed by treating the beads with a suitable reagent. By
way of example, treatment with an acid, such as nitric acid,
hydrochloric acid, or sulfuric acid, can be used in order to remove
acid-soluble suspending agents, e.g. metal carbonates or tricalcium
phosphate.
[0043] In the extrusion process, it is preferable that the TPU, the
blowing agent and, if appropriate, additives are introduced
together (in the form of a mixture) or separately from one another
at one or various locations of the extruder. The possibility, but
not a requirement, here is to prepare a mixture in advance from the
solid components. By way of example, it is possible to begin by
mixing TPU and, if appropriate, additives, and to introduce the
mixture into the extruder, and then introduce the blowing agent
into the extruder, so that the extruder mixes the blowing agent
into to polymer melt. It is also possible to introduce a mixture of
blowing agent and additives into the extruder, i.e. to premix the
additives with the blowing agent.
[0044] In the extruder, the starting materials mentioned are mixed,
with melting of the TPU. Any of the conventional screw-based
machines can be used as extruder, in particular single-screw and
twin-screw extruders (e.g. Werner & Pfleiderer ZSK machines),
co-kneaders, Kombiplast machines, MPC kneading mixers, FCM mixers,
KEX kneading screw extruders, and shear-roll extruders, as
described by way of example in Saechtling (ed.),
Kunststoff-Taschenbuch [Plastics handbook], 27th edition,
Hanser-Verlag Munich 1998, chapter 3.2.1 and 3.2.4. The extruder is
usually operated at a temperature at which the TPU is present in
the form of a melt, for example at from 150 to 250.degree. C., in
particular from 180 to 210.degree. C.
[0045] The rotation, length, diameter, and design of the extruder
screw(s), amounts introduced, and extruder throughput, are selected
in a known manner in such a way as to give uniform distribution of
the additives in the extruded TPU.
[0046] In one embodiment of the extrusion process, expandable beads
are produced. To prevent premature foaming of the melt comprising
blowing agent on discharge from the extruder, the melt extrudate is
discharged from the extruder and pelletized under conditions of
temperature and pressure such that practically no foaming
(expansion) occurs. These conditions can vary as a function of the
type and amount of the polymers, of the additives, and in
particular of the blowing agent. The ideal conditions can easily be
determined via preliminary experiments.
[0047] One industrially advantageous method is underwater
pelletization in a waterbath whose temperature is below 100.degree.
C. and which is subject to a pressure of at least 2 bar (absolute).
Excessively low temperature has to be avoided, because otherwise
the melt hardens on the die plate, and excessively high temperature
has to be avoided since otherwise the melt expands. As the boiling
point of the blowing agent increases and the amount of the blowing
agent becomes smaller, the permissible water temperature becomes
higher and the permissible water pressure becomes lower. In the
case of the particularly preferred blowing agent sec-pentane, the
ideal waterbath temperature is from 30 to 60.degree. C. and the
ideal water pressure is from 8 to 12 bar (absolute). It is also
possible to use other suitable coolants instead of water. It is
also possible to use water-cooled die-face pelletization. In this
process, encapsulation of the cutting chamber is such as to permit
operation of the pelletizing apparatus under pressure.
[0048] The product is expandable TPU beads, which are then isolated
from the water and, if appropriate, dried. They are then foamed as
described at a later stage below, to give expanded TPU beads.
[0049] A preferred process for production of expandable TPU beads
comprising blowing agent comprises the following stages: [0050] i)
melting of TPU, if appropriate with additives, and extrusion to
give pellets whose average diameter is from 0.2 to 10 mm, [0051]
ii) impregnation of the pellets with from 0.1 to 40% by weight,
based on the total weight of the pellets, of a volatile blowing
agent in aqueous suspension under pressure, preferably at a
pressure of from 5 to 100 bar, at temperatures in the range from
100 to 150.degree. C., [0052] iii) cooling of the suspension to
from 20 to 95.degree. C., [0053] iv) then depressurizing.
[0054] Via cooling, the blowing agent becomes included within the
polymer, and the product does not foam. If the tank is
depressurized directly at high temperatures in step ii), the
blowing agent escapes, and the polymer, which is soft at these
temperatures, expands.
[0055] Another preferred process for production of expandable TPU
beads comprising blowing agent comprises the following stages:
[0056] i) melting of TPU together with from 0.1 to 40% by weight,
based on the total weight of the pellets, of a volatile blowing
agent and, if appropriate, with additives, in an extruder, [0057]
ii) discharge of the melt from the extruder and underwater
pelletization of the melt extrudate at pressures of from 2 bar to
20 bar and temperatures of from 5.degree. C. to 95.degree. C.
[0058] This process uses pelletization under water against
superatmospheric pressure to avoid escape of the blowing agent and
foaming of the polymer.
[0059] The invention therefore also provides, and this is
particularly preferred, a process for production of expandable
thermoplastic polyurethane, preferably in bead form, comprising
blowing agent, where a thermoplastic polyurethane whose Shore
hardness is from A 44 to A 84, preferably from A 62 to A 80, is
extruded, if appropriate together with additives, to give pellets
whose average diameter is from 0.2 to 10 mm, the pellets are
impregnated with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a preferably volatile blowing agent in
aqueous suspension under pressure, preferably at a pressure of from
5 to 100 bar, at temperatures in the range from 100 to 150.degree.
C., the suspension comprising the thermoplastic polyurethanes
comprising blowing agent is cooled to from 20 to 95.degree. C., and
then the thermoplastic polyurethanes comprising blowing agent are
depressurized.
[0060] The invention therefore also provides, and this is
particularly preferred, a process for production of expandable
thermoplastic polyurethane, preferably in bead form, comprising
blowing agent, where a thermoplastic polyurethane whose Shore
hardness is from A 44 to A 84, preferably from A 62 to A 80, is
melted together with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a preferably volatile blowing agent and,
if appropriate, with additives, in an extruder, and the melt is
pelletized under water at pressures of from 2 bar to 20 bar and
temperatures of from 5.degree. C. to 95.degree. C.
[0061] To the extent that expandable beads are obtained, these can
be foamed in a known manner, whereupon the inventive expanded TPU
beads are produced. The foaming generally takes place via heating
of the expandable beads in conventional foaming apparatuses, e.g.
with hot air or superheated steam in what is known as a pressure
prefoamer, for example of the type usually used for processing of
expandable polystyrene (EPS). It is preferable to foam the beads at
a temperature at which they soften (softening range), particularly
preferably at temperatures of from 100 to 140.degree. C.
[0062] The present invention therefore also provides a process for
production of foams based on thermoplastic polyurethane, where the
inventive expandable thermoplastic polyurethane, preferably in bead
form, comprising blowing agent is foamed at a temperature of from
100.degree. C. to 140.degree. C. The present invention also
provides foams thus obtainable and based on thermoplastic
polyurethane.
[0063] If steam is used for foaming, the steam pressure is usually,
as a function of the nature and amount of TPU and blowing agent,
and of the desired density of the foam to be produced, from 1 to 4
bar (absolute), preferably from 1.5 to 3.5 bar (absolute). As the
pressures increase here the densities of the foamed TPU product
become smaller, i.e. steam pressure can be used to set the desired
density. The foaming time is usually from 1 to 300 sec, preferably
from 1 to 30 sec. Foaming is followed by depressurization and
cooling. The expansion factor during foaming is preferably from 2
to 50.
[0064] In one embodiment of the suspension process for production
of the expanded TPU beads, the heated suspension is not cooled, but
depressurized suddenly while hot, without cooling. During
depressurization, the blowing agent which has previously diffused
into the TPU beads expands "explosively" and foams the softened
beads. Expanded TPU beads are obtained.
[0065] The suspension is usually depressurized via a die, a valve,
or another suitable apparatus. The suspension can be directly
depressurized to atmospheric pressure, such as 1013 mbar. However,
it is preferable to depressurize in an intermediate container whose
pressure is sufficient for foaming of the TPU beads but can be
above atmospheric pressure. A suitable method depressurizes to a
pressure of, for example, from 0.5 to 5 bar (absolute), in
particular from 1 to 3 bar (absolute). During the depressurization
process, the impregnation pressure in the impregnation container
can be kept constant, by introducing further blowing agent under
pressure. The method generally used comprises cooling of the
suspension after depressurization, isolation of the expanded TPU
beads conventionally from the suspension, and, before that or after
that, if appropriate, removal of adherent suspending agent, as
described above, and finally washing and drying of the beads.
[0066] In one embodiment of the extrusion process for production of
the expanded TPU beads, the melt comprising blowing agent is
discharged from the extruder and pelletized without underwater
pelletization, water-cooled die-face pelletization or other
precautions which inhibit foaming. By way of example, extrusion can
take place directly into the atmosphere. The melt extrudate
discharged from the extruder foams during this process, and
expanded TPU beads are obtained via pelletization of the foamed
extrudate.
[0067] A preferred process for production of expanded TPU beads
comprises the following stages [0068] i) melting of TPU, if
appropriate with additives, and extrusion to give minipellets whose
average diameter is from 0.2 to 10 mm, [0069] ii) impregnation of
the minipellets with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a volatile blowing agent in aqueous
suspension under pressure, preferably at a pressure of from 5 to
100 bar, at temperatures in the range from 100 to 150.degree. C.,
and [0070] iii) then depressurization.
[0071] Another preferred process for expansion of expanded TPU
beads comprises the following stages: [0072] i) melting of TPU
together with from 0.1 to 40% by weight, based on the total weight
of the pellets, of a volatile blowing agent and, if appropriate,
with additives, in an extruder, [0073] ii) discharge of the melt
from the extruder and pelletization of the melt extrudate without
apparatuses which inhibit foaming.
[0074] The invention also provides, and this is particularly
preferred, a process for production of expanded thermoplastic
polyurethane, where a thermoplastic polyurethane whose Shore
hardness is from A 44 to A 84, preferably from A 62 to A 80, is
extruded, if appropriate together with additives, to give pellets
whose average diameter is from 0.2 to 10 mm, the pellets are
impregnated with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a preferably volatile blowing agent,
preferably in aqueous suspension under pressure, preferably at a
pressure of from 5 to 100 bar, at temperatures in the range from
100 to 150.degree. C., and then are depressurized.
[0075] The invention also provides, and this is particularly
preferred, a process for production of expanded thermoplastic
polyurethane, where a thermoplastic polyurethane whose Shore
hardness is from A 44 to A 84, preferably from A 62 to A 80, is
melted together with from 0.1 to 40% by weight, based on the total
weight of the pellets, of a preferably volatile blowing agent, if
appropriate with additives, in an extruder, and the melt is
pelletized without apparatuses which inhibit foaming.
[0076] The present invention also provides expanded thermoplastic
polyurethanes obtainable via these process.
[0077] The TPU beads can be provided, prior to and/or after the
foaming process, with an antiblocking agent. Examples of suitable
antiblocking agents are talc, metal compounds, such as tricalcium
phosphate, calcium carbonate, silicas, in particular fumed silicas,
such as Aerosil.RTM. from Degussa, salts of long-chain (e.g.
C.sub.10-22) carboxylic acids, for example stearic salts, such as
calcium stearate, esters of long-chain carboxylic acids, e.g.
glycerol esters, such as the glycerol stearates, and silicone oils.
The antiblocking agent is generally applied to the beads via
mixing, spray application, drum application, or other conventional
processes. It is usually used in amounts of from 0.01 to 20 parts
by weight, preferably from 0.1 to 10 parts by weight, particularly
preferably from 0.5 to 6 parts by weight, based on 100 parts by
weight of the TPU.
[0078] In all cases the product is expanded TPU beads. Preferred
densities are from 5 to 600 g/l, and particularly preferably from
10 to 300 g/l.
[0079] The expanded beads are generally at least approximately
spherical and their diameter is usually from 0.2 to 20 mm,
preferably from 0.5 to 15 mm, and in particular from 1 to 12 mm. In
the case of non-spherical, e.g. elongate or cylindrical, beads,
diameter means the longest dimension.
[0080] Foams can be produced from the inventive expanded TPU beads,
for example by fusing them to one another in a closed mold with
exposure to heat. For this, the beads are charged to the mold and,
once the mold has been closed, steam or hot air is supplied, thus
further expanding the beads and fusing them to one another to give
foam, whose density is preferably in the range from 8 to 600 g/l.
The foams can be semifinished products, for example sheets,
profiles, or webs, or finished moldings with simple or complicated
geometry. The expression TPU foam therefore includes semifinished
foam products and includes foam moldings.
[0081] The temperature during the fusion of the expanded TPU beads
is preferably from 100.degree. C. to 140.degree. C. The present
invention therefore also provides processes for production of foam
based on thermoplastic polyurethane, where the inventive expanded
thermoplastic polyurethane is fused by means of steam at a
temperature of from 100.degree. C. to 140.degree. C., to give a
molding.
[0082] The invention also provides for the use of the expanded TPU
beads for production of TPU foams, and provides TPU foams
obtainable from the expanded TPU beads.
[0083] The inventive foams can be recycled by a thermoplastic route
without difficulty. For this, the foamed TPUs are extruded, using a
vented extruder, and there can be mechanical comminution prior to
this extrusion process. They can then be processed again to give
foams in the manner described above.
[0084] The inventive foams are preferably used in energy-absorbing
moldings and in moldings for automobile interiors.
[0085] Particular preference is therefore also given to the
following products comprising the inventive foams: helmet shells,
knee protectors, elbow protectors, shoe soles, midsoles, insoles,
and the following parts which comprise the inventive foams:
steering wheel parts, door side parts, and foot well parts.
[0086] The examples below are intended for further illustration of
the invention:
TABLE-US-00001 TABLE 1 Soft phase Thermoplastic polyurethane
Composition [mol] Composition [mol] 1,4- Molar 1,4- Shore Adipic
Butane- Poly- mass Soft Butane- 4,4'- hard- TPU acid diol THF
[g/mol] phase diol MDI ness A 1 1 -- 800 1.00 0.44 1.44 A78 B -- --
1 1333 1.00 0.97 1.97 A72
[0087] The Shore hardness of the PU elastomers was determined to
DIN 53 505.
EXAMPLE 1
[0088] Foam Bead Production
[0089] 100 parts of the TPUs stated in Table 1 in the form of
pellets each weighing about 2 mg, 250 parts by weight of water, 6.7
parts of tricalcium phosphate, and 20 parts of n-butane were
introduced, with stirring, into an autoclave and heated to the
temperature stated in Table 2. The contents of the pressure vessel
were then discharged through a basal valve and depressurized, while
the pressure in the tank was kept constant by introducing, under
pressure, nitrogen or the blowing agent used. The foam beads were
freed from adherent residues of auxiliaries via washing with nitric
acid and water and were air-dried at 50.degree. C.
[0090] The impregnation conditions and the resultant bulk densities
of the expanded beads are found in Table 2.
TABLE-US-00002 TABLE 2 TPU of n-Butane [parts by Table 1 weight]
Temperature [.degree. C.] Bulk density [g/L] A 20 112 300 A 20 114
170 B 20 119 240 B 20 120 190 B 20 122 140 B 20 125 120
EXAMPLE 2
[0091] Production of Moldings
[0092] The foam beads produced in Example 1 were charged into a
preheated mold, with pressure and compaction. The mold was heated
by steam at from 1.0 to 4.0 bar, i.e. at temperatures of from
100.degree. C. to 140.degree. C., on alternate sides.
[0093] The mold was then depressurized and cooled with water and,
respectively, air, and opened, and the mechanically stable molding
was removed.
* * * * *