U.S. patent application number 12/278400 was filed with the patent office on 2010-11-18 for fiber adhesive.
This patent application is currently assigned to BASF SE. Invention is credited to Konrad Knoll, Norbert Niessner, Dieter Urban, Bernd-Steffen Von Bernstorff.
Application Number | 20100291383 12/278400 |
Document ID | / |
Family ID | 37983537 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100291383 |
Kind Code |
A1 |
Urban; Dieter ; et
al. |
November 18, 2010 |
FIBER ADHESIVE
Abstract
Tacky polymeric fibers having a nontacky core and a tacky outer
shell.
Inventors: |
Urban; Dieter; (Speyer,
DE) ; Niessner; Norbert; (Singapore, SG) ; Von
Bernstorff; Bernd-Steffen; (Wachenheim, DE) ; Knoll;
Konrad; (Mannheim, 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: |
37983537 |
Appl. No.: |
12/278400 |
Filed: |
January 30, 2007 |
PCT Filed: |
January 30, 2007 |
PCT NO: |
PCT/EP2007/050858 |
371 Date: |
January 21, 2009 |
Current U.S.
Class: |
428/373 ;
264/172.15; 977/742 |
Current CPC
Class: |
B01D 39/1623 20130101;
D01F 8/10 20130101; D01F 8/06 20130101; Y10T 428/2929 20150115 |
Class at
Publication: |
428/373 ;
264/172.15; 977/742 |
International
Class: |
D02G 3/36 20060101
D02G003/36; D01D 5/34 20060101 D01D005/34 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2006 |
EP |
06101383.5 |
Claims
1. A tacky polymeric fiber having a nontacky core and a tacky outer
shell.
2. The tacky polymeric fiber according to claim 1, wherein the core
comprises a polymer (referred to below for short as core polymer)
which at 21.degree. C. has a breaking strength of between 5 and 60
Mpa and a breaking extension of between 2% and 1500% (by ISO 527
tensile test).
3. The tacky polymeric fiber according to claim 1, wherein the core
polymer is a thermoplastic or is a thermoplastic which has been
modified with an elastomer (thermoplastic elastomer).
4. The tacky polymeric fiber according to claim 1, wherein the core
polymer is a styrene copolymer.
5. The tacky polymeric fiber according to claim 1, wherein the core
is composed of more than 90% by weight of the core polymer and may
further comprise additives which may be stabilizers, fillers,
carbon nanotubes, pigments, dyes.
6. The tacky polymeric fiber according to claim 1, wherein the
outer shell is composed of a permanently tacky adhesive, of a
pressure-sensitive adhesive.
7. The tacky polymeric fiber according to claim 6, wherein the
adhesive is a permanently tacky hotmelt adhesive.
8. The tacky polymeric fiber according to claim 1, wherein the
adhesive, or hotmelt adhesive, at 21.degree. C. has a peel strength
of at least 1 N/2.5 cm.
9. The tacky polymeric fiber according to claim 1, wherein the
hotmelt adhesive comprises as binder a polymer (referred to below
as adhesive polymer) which is obtainable by free-radical
polymerization of ethylenically unsaturated compounds.
10. The tacky polymeric fiber according to claim 9, wherein the
adhesive polymer is a UV-crosslinkable polymer.
11. The tacky polymeric fiber according to claim 1, wherein the
adhesive is composed of more than 40% by weight of the adhesive
polymer and if appropriate may further comprise additives, which
may be tackifying resins, plasticizers, UV blockers, antioxidants,
dyes or fillers.
12. The tacky polymeric fiber according to claim 1, wherein the
polymeric fiber has a diameter of 8 .mu.m to 500 .mu.m.
13. The tacky polymeric fiber according to claim 12, wherein the
core has a diameter of 5 .mu.m to 497 .mu.m.
14. The tacky polymeric fiber according to claim 13, wherein the
outer shell has a layer thickness of 3 .mu.m to 100 .mu.m.
15. A process for producing the tacky polymeric fiber according to
claim 1, which comprises coextruding the core material and the
material for the outer shell.
16. The process according to claim 15, wherein the core material is
heated to temperatures between 150 and 300.degree. C. and the
material of the outer shell is heated to temperatures between 80
and 200.degree. C. and the coextrusion takes place at these
temperatures.
17. The process according to claim 16, wherein the polymeric fiber
obtained is additionally drawn immediately after coextrusion, the
length increase (degree of drawing) being preferably 10% to
300%.
18. The method of using the polymeric fiber according to claim 1
for producing permeable layers, which may be permeable nonwovens,
membranes, textile sheet structures.
19. The method of using the polymeric fiber according to claim 17
for binding, immobilizing or strengthening small piece goods.
20. The method of using the polymeric fiber according to claim 17
for producing gas-permeable sheet structures with a large adhesion
area, for producing dust filters or particle filters for
example.
21. The method of using the polymeric fiber according to claim 17
for producing elastic sheet structures which at application
temperature are tacky and/or detachable, for transporting and/or
sorting goods.
22. The method of using the polymeric fiber according to claim 17
for producing permeable sheet structures with a large adhesion area
for removing dispersed or emulsified particles from liquid or
gaseous media.
Description
[0001] The invention relates to a tacky polymeric fiber having a
nontacky core and a tacky outer shell.
[0002] In the case of adhesives, and particularly in the case of
pressure-sensitive adhesives as well, there is a desire both for
effective cling to the substrate to be bonded (good adhesion) and
for a sufficient internal strength within the adhesive layer
(cohesion). Adhesion and cohesion are mutually opposed performance
properties. Measures which produce an improvement in adhesion
generally lead to a deterioration in cohesion.
[0003] New adhesives or adhesive systems ought as far as possible
to have better performance properties than the existing adhesives,
and in particular both the adhesion and the cohesion ought to be
good.
[0004] In addition to this there is a desire for adhesive systems
having new performance properties. For adhesives of such kind there
are then, correspondingly, completely new application possibilities
available.
[0005] An object of the invention, therefore, were adhesive systems
having improved and innovative properties.
[0006] In accordance with this object the polymeric fibers defined
at the outset have been found. Also found have been processes for
producing and for using these polymeric fibers.
[0007] The polymeric fiber of the invention is composed essentially
of a nontacky core and of a tacky outer shell.
The Core
[0008] The core comprises a polymer (referred to below for short as
core polymer) which is thermoplastically deformable.
[0009] This polymer is in particular a thermoplastic or is an
elastomer-modified thermoplastic (thermoplastic elastomer). The
term "core polymer" also comprehends, in particular, mixtures of
polymers, known as polymer blends. Polymer blends modify properties
of different polymers; in particular the reversibility of the
deformation of thermoplastic polymers is increased through the
addition of elastomers.
[0010] The core polymer has at 21.degree. C. preferably a breaking
strength of between 5 and 60 MPa, more preferably from 20 to 60
MPa, and preferably a breaking extension of between 2% and 1500%,
more preferably between 300 and 700% (measured by ISO 527 tensile
test).
[0011] If a high reversibility in the deformation of the fiber
adhesive is desired, repetitions of the tensile test ought to
achieve extension values in the range of 20% and 100%, preferably
between 60% and 90% of the value measured in the 1st pass
(recovery).
[0012] Suitable core polymers are polymers obtainable by
free-radical polymerization (vinyl polymers), examples being
polyolefins, such as polyethylene, polypropylene, polycondensates,
examples being polyesters, polyamides, or polyadducts, examples
being polyurethanes.
[0013] Preferred core polymers are polyamide, polyamide copolymers
with more than 20% by weight polyamide fractions, polypropylene,
polyesters, such as polyethylene terephthalate, styrene
homopolymers or copolymers, especially styrene-butadiene
copolymers.
[0014] Preference is given in particular to thermoplastic styrene
copolymers. Styrene copolymers of this kind are composed preferably
of 5% to 99% by weight, more preferably of 10% to 85% by weight, of
styrene.
[0015] Particular preference is given to styrene-butadiene
copolymers, especially block copolymers.
[0016] Preferred block copolymers are those with a hard/soft/hard
block sequence or star block copolymers with external hard blocks
and internal soft blocks.
[0017] The weight fraction of the soft blocks ought preferably to
be greater than 50% by weight, more preferably 60% to 90% by
weight, with particular preference 65% to 85% by weight.
[0018] The hard blocks are composed preferably of pure polystyrene
or of copolymers of styrene with alpha-methylstyrene,
ring-hydrogenated styrene, para-methylstyrene,
paratertiary-butylstyrene or 1,1 diphenyl ether.
[0019] The soft phase is preferably composed of a polymer having a
glass transition temperature of less than or equal to 20.degree.
C., in particular less than 0.degree. C., more preferably less than
-20.degree. C. Soft phases may be composed of polybutadiene,
polyisoprene or subsequently hydrogenated polymers thereof,
polyisobutene, random copolymers of styrene and butadiene, styrene
and isoprene, and also combinations of these monomers.
[0020] The soft phase may also have a monomer composition which
changes along the polymer chain.
[0021] The block sequences (hard/soft).sub.n+1 and
(hard/soft/hard).sub.n+1 are also provided by the invention, with n
being a natural number (n=0, 1, 2, . . . ).
[0022] Particular preference is given to linear styrene-butadiene
block copolymers of the general structure S-(S/B)-S with one or
more (S/B) random blocks located between the two S blocks and
having a static styrene/butadiene distribution. Block copolymers of
this kind are obtainable by anionic polymerization in a nonpolar
solvent with the addition of a polar cosolvent or a potassium salt,
as described for example in WO 95/35335 or WO 97/40079.
[0023] The vinyl content is understood to be the relative fraction
of 1,2 linkages of the diene units, relative to the total of the
1,2,1,4-cis, and 1,4-trans linkages. The 1,2-vinyl content of the
styrene-butadiene copolymer block (S/B) is preferably below 20%, in
particular in the range from 10% to 18%, with particular preference
in the range of 12%-16%.
[0024] Particularly suitable styrene-butadiene copolymers are
available for example under the trade name Styroflex.RTM. from
BASF.
[0025] The nontacky core may comprise, besides the core polymer,
further constituents, examples being additives such as stabilizers,
e.g. UV stabilizers and heat stabilizers, fillers, pigments, e.g.
TiO2, dye pigments, carbon black, carbon nanotubes, glass, carbon
fibers, phyllosilicates, and dyes. With preference the core is
composed of more than 90% by weight of the core polymer.
The Outer Shell
[0026] The outer shell is composed of a permanently tacky adhesive,
i.e., of a pressure-sensitive adhesive. The adhesive in question is
in particular a pressure-sensitive adhesive which can be detached
again without residue when subsequently bonded.
[0027] In particular the adhesive in question is a permanently
tacky hotmelt adhesive (i.e., an adhesive which is processed
without water or solvent).
[0028] The adhesive has at 21.degree. C. preferably a peel strength
(as a measure of the adhesion) of at least 1 N/2.5 cm by the
measurement method below. The peel strength is preferably 1 to 25,
more preferably 2 to 20, very preferably 3 to 15 N/2.5 cm.
[0029] The shear strength, as a measure of the cohesion, is
preferably greater than 10 minutes by the measurement method below.
The shear strength is preferably 10 to 1440 minutes, more
preferably 100 to 1000 minutes, very preferably 200 to 500
minutes.
The Test Methods
[0030] The adhesive is coated at 20 g/m2 (solids) onto polyethylene
film and dried at 90.degree. C. for 3 minutes.
[0031] For the determination of the peel strength (adhesion) a test
strip 2.5 cm wide is adhered to a chromed V2A stainless steel test
plate and rolled on once using a roller weighing 1 kg. It is then
clamped by one end into the upper jaws of a tension/extension
testing apparatus. The adhesive strip is removed from the test
surface (V2A stainless steel) at 300 mm/min and at an angle of
180.degree.; that is, the adhesive strip was bent around and
removed parallel to the test plate, and the force required to
accomplish this was measured. The measure of the peel strength is
the force in N/2.5 cm which results as the average value from five
measurements (corresponding to AFERA standard method). The peel
strength is determined 24 hours after bonding.
[0032] For the determination of the shear strength the test strips
are adhered with a bonded area of 25 mm.sup.2 to a chromed V2A
stainless steel test plate, rolled on once using a roller weighing
1 kg, stored for 10 minutes (under standard conditions, 1 bar,
21.degree. C.), and then loaded in suspension with a 0.5 kg weight
(under standard conditions, 1 bar, 21.degree. C.). The measure of
the shear strength was the time which elapsed before the weight
fell down, in minutes; the average is calculated in each case from
five measurements (corresponding to PSTC standard method).
[0033] The adhesive comprises as an essential constituent at least
one binder and if appropriate further additives.
[0034] The binder may in particular be a synthetic polymer
(referred to below as adhesive polymer). The term "adhesive
polymer" is also intended to comprehend mixtures of different
polymers; in particular, such mixtures may be mixtures of nontacky
polymers with tacky polymers or with other polymers which produce
tack in the mixture.
[0035] Suitable adhesive polymers include free-radically
polymerized polymers, polyesters or polyadducts. Where the polymers
concerned are not tacky, the above tack (peel strength) is set by
addition of tackifying resins or plasticizers.
[0036] Mention may be made, for example, of styrene copolymers,
especially styrene-butadiene copolymers, ethylene vinyl acetate
copolymers, polyurethanes, polyisobutylenes, and noncrystalline
polyolefins, comprising an appropriate amount of plasticizers or
tackifying resins.
[0037] Also suitable in particular are block copolymers.
[0038] In the case of styrene block copolymers it is possible for
example to use free-radically polymerized styrene-butadiene
copolymers which have a butadiene content of greater than or equal
to 50% by weight, preferably greater than or equal to 60% by
weight, more preferably greater than or equal to 80% by weight.
[0039] Styrene-butadiene copolymers may for example be diblock,
triblock or multiblock copolymers, whose soft-phase fraction is
preferably greater than or equal to 60% by weight.
[0040] Preference is given in particular to diblock copolymers and
to mixtures thereof with triblock, multiblock or star block
copolymers.
[0041] Where plasticizers are used in the outer shell, plasticizers
are used (i.e., blended with the polymers) which have little or no
influence on the properties of the core polymer. Particular
preference is given to combinations of a polar soft phase in the
fiber core and a nonpolar soft phase in the tacky shell, or vice
versa.
[0042] In particular the adhesive polymer is composed of
free-radically polymerizable compounds (monomers). Preferably it is
composed of at least 40% by weight, more preferably at least 60% by
weight, and very preferably at least 80% by weight of what are
called principal monomers.
[0043] The principal monomers are selected from C1-C20 alkyl
(meth)acrylates, vinyl esters of carboxylic acids comprising up to
20 carbon atoms, vinylaromatics having up to 20 carbon atoms,
ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of
alcohols comprising 1 to 10 carbon atoms, aliphatic hydrocarbons
having 2 to 8 carbon atoms and 1 or 2 double bonds, or mixtures of
these monomers.
[0044] Examples include (meth)acrylic acid alkyl esters having a
C1-C10 alkyl radical, such as methyl methacrylate, methyl acrylate,
n-butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate.
[0045] In particular, mixtures of the (meth)acrylic acid alkyl
esters are also suitable.
[0046] Vinyl esters of carboxylic acids having 1 to 20 carbon atoms
are for example vinyl laurate, vinyl stearate, vinyl propionate,
Versatic acid vinyl esters, and vinyl acetate.
[0047] Suitable vinylaromatic compounds include vinyltoluene a- and
p-methylstyrene, a-butylstyrene, 4-n-butylstyrene,
4-n-decylstyrene, and, preferably, styrene. Examples of nitriles
are acrylonitrile and methacrylonitrile.
[0048] The vinyl halides are ethylenically unsaturated compounds
substituted by chlorine, fluorine or bromine, preferably vinyl
chloride and vinylidene chloride.
[0049] Examples of vinyl ethers include vinyl methyl ether or vinyl
isobutyl ether. Preference is given to vinyl ethers of alcohols
comprising 1 to 4 carbon atoms.
[0050] As hydrocarbons having 2 to 8 carbon atoms and one or two
olefinic double bonds mention may be made of butadiene, isoprene
and chloroprene, ethylene or propylene. Polymers or copolymers
obtained from butadiene or isoprene can also be hydrogenated
subsequently.
[0051] Preferred principal monomers are the C1 to C10 alkyl
acrylates and methacrylates, especially C1 to C8 alkyl acrylates
and methacrylates, the acrylates in each case being particularly
preferred.
[0052] Very particular preference is given to methyl acrylate,
ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, octyl acrylate,
and 2-ethylhexyl acrylate, and mixtures of these monomers.
[0053] Besides the principal monomers the polymer may comprise
further monomers, e.g., monomers having carboxylic acid, sulfonic
acid or phosphonic acid groups. Carboxylic acid groups are
preferred. Mention may be made, for example, of acrylic acid,
methacrylic acid, itaconic acid, maleic acid or fumaric acid.
[0054] Further monomers include, for example, monomers comprising
hydroxyl groups, especially C1-C10 hydroxyalkyl (meth)acrylates,
(meth)acrylamide, and monomers comprising ureido groups, such as
ureido (meth)acrylates.
[0055] Further monomers that may be mentioned include, moreover,
phenyloxyethyl glycol mono(meth)acrylate, glycidyl acrylate,
glycidyl methacrylate, and amino (meth)acrylates such as
2-aminoethyl (meth)acrylate.
[0056] Monomers which in addition to the double bond carry further
functional groups as well, e.g., isocyanato-, amino-, hydroxy-,
amide- or glycidyl-, may have the effect, for example, of improving
the substrate adhesion. Those suitable include, in particular,
cyclic lactams such as N-vinylpyrrolidone or
N-vinylcaprolactam.
[0057] The polymer is preferably synthesized from at least 40% by
weight, preferably at least 60% by weight and very preferably at
least 80% by weight of C1-C20 alkyl (meth)acrylates, especially the
abovementioned alkyl (meth)acrylates, and is therefore a
polyacrylate.
[0058] Particular preference is given to adhesives whose adhesive
properties can be adjusted by photochemical crosslinking, such as
by irradiation with electron beams or UV light.
[0059] Preferably the adhesive polymer, therefore, is a polymer
which is crosslinkable by irradiation with high-energy light, such
as electron beams or, preferably, UV light.
[0060] The polymer is crosslinkable thus if, for example, hydrogen
protons can be detached from the main chain of the polymer
photochemically, including in particular through the use of a
photoinitiator or as a result of electron beams, thereby producing
a free radical which is able to enter into further chemical
reactions.
[0061] The adhesive preferably comprises a photoinitiator.
[0062] The photoinitiator may comprise, for example, what are
called .alpha.-splitters--that is, photoinitiators in which a
chemical bond is cleaved to form 2 free radicals which initiate the
further crosslinking or polymerization reactions.
[0063] Examples that may be mentioned include acylphosphine oxides
(Lucirin.RTM. products from BASF), hydroxyalkylphenones (e.g.,
Irgacure.RTM. 184), benzoin derivatives, benzil derivatives, and
dialkyloxyacetophenones.
[0064] In particular the compounds in question may be what are
called H abstractors, which detach a hydrogen atom from the polymer
chain; these are, for example, photoinitiators having a carbonyl
group. This carbonyl group is inserted into a C--H bond to form a
C--C--O--H moiety.
[0065] Here mention may be made in particular of acetophenone,
benzophenone, and derivatives thereof.
[0066] It is possible to use both classes of photoinitiators alone
or else in a mixture. Preference as photoinitiator is given to H
abstractors.
[0067] In one particular embodiment the photoinitiator or at least
one of the photoinitiators, if a mixture is used, is attached to
the adhesive polymer.
[0068] With particular preference the photoinitiator in question is
a photoinitiator which is incorporated into the polymer chain by
means of free-radical copolymerization. For that purpose the
photoinitiator preferably comprises an acrylic or (meth)acrylic
group.
[0069] Suitable copolymerizable photoinitiators are acetophenone
derivatives or benzophenone derivatives which comprise at least
one, preferably one, ethylenically unsaturated group. The
ethylenically unsaturated group is preferably an acrylic or
methacrylic group.
[0070] The ethylenically unsaturated group may be attached directly
to the phenyl ring of the acetophenone derivative or benzophenone
derivative. In general there is a spacer group located between the
phenyl ring and ethylenically unsaturated group.
[0071] The spacer group may comprise, for example, up to 100 carbon
atoms.
[0072] Suitable acetophenone derivatives or benzophenone
derivatives are described, for example, in EP-A-346 734,
EP-A-377199 (1st claim), DE-A-40 37 079 (1st claim) and DE-A-38 44
444 (1st claim) and by this reference are also disclosed in the
present application. Preferred acetophenone derivatives and
benzophenone derivatives are those of the formula
##STR00001##
in which R.sup.1 stands for an organic radical having up to 30
carbon atoms, R.sup.2 for a hydrogen atom or a methyl group, and
R.sup.3 for an optionally substituted phenyl group or a C1-C4 alkyl
group.
[0073] R.sup.1 stands with particular preference for an alkylene
group, especially for a C2-C8 alkylene group.
[0074] R.sup.3 stands with particular preference for a methyl group
or a phenyl group.
[0075] The adhesive comprises preferably 0.0001 to 0.5 mol, more
preferably 0.0002 to 0.1, very preferably 0.003 to 0.01 mol of the
photoinitiator, or of the molecule group which is active as a
photoinitiator and is attached to the polymer, per 100 g of
adhesive polymer.
[0076] Suitable UV-crosslinkable polymers are available under the
trade name acResin.RTM. from BASF.
[0077] The glass transition temperature (Tg) of the adhesive
polymer is preferably -65 to +10.degree. C., more preferably -65 to
0.degree. C., very preferably -65 to -10.degree. C., or -65 to
-20.degree. C.; in one very particularly preferred embodiment the
glass transition temperature is -55 to -30.degree. C., or -50 to
-40.degree. C.
[0078] The glass transition temperature of the polymer can be
determined in accordance with customary methods such as
differential thermoanalysis or differential scanning calorimetry
(see, e.g., ASTM 3418/82, midpoint temperature).
[0079] Adhesive polymers can be prepared by copolymerizing the
monomer with the use of the customary polymerization initiators and
also, if appropriate, of regulators, polymerization taking place at
the customary temperatures in bulk, in emulsion, e.g., in water or
liquid hydrocarbons, or in solution. The polymerization, bulk
polymerization for example, may also be carried out in an
extruder.
[0080] The polymers are preferably prepared by polymerizing the
monomers in solvents (solution polymerization).
[0081] The adhesive is preferably a hotmelt adhesive which
comprises water or other solvents, examples being those from the
solution polymerization, only in small amounts if at all. Solvent
from the solution polymerization is therefore preferably separated
off.
[0082] The adhesive preferably comprises less than 5 parts by
weight, in particular less than 2 parts or 1 part by weight of
water and/or solvent per 100 parts by weight of adhesive polymer.
With particular preference the adhesive is substantially free from
water and other solvents.
[0083] The adhesive preferably comprises at least one
photoinitiator (see above). Where the photoinitiator in question is
not a photoinitiator attached to the adhesive polymer, the
photoinitiator may be added to the adhesive polymer at any
time.
[0084] Where the adhesive polymer comprises blends, a suitable
blend component comprises what are referred to as tackifying resins
(tackifiers).
[0085] Tackifiers are, for example, natural resins, such as rosins
and their derivatives formed by disproportionation or
isomerization, polymerization, dimerization or hydrogenation. They
may be in their salt form (with monovalent or polyvalent
counterions (cations), for example) or, preferably, in their
esterified form. Alcohols which are used for the esterification may
be monohydric or polyhydric. Examples are methanol, ethanediol,
diethylene glycol, triethylene glycol, 1,2,3-propanethiol and
pentaerythritol.
[0086] Preferred tackifiers are natural or chemically modified
rosins. Rosins are composed predominantly of abietic acid or
derivatives of abietic acid.
[0087] Further additives which may be added to the adhesive are,
for example, antioxidants, fillers, dyes, flow control
assistants.
[0088] The pressure-sensitive adhesive or hotmelt adhesive is
composed in particular of more than 40% by weight, with particular
preference of more than 60% by weight, and with very particular
preference of more than 80% by weight of the adhesive polymer,
which is intended to include also mixtures of different polymers
(see above).
The Fiber Adhesive in General
[0089] The fiber adhesive has the form of a fiber. The tacky outer
shell is attached to the core. The fiber as a whole is extensible
over a wide temperature range without the outer shell becoming
detached.
[0090] The polymeric fiber preferably has a diameter of 8 .mu.m to
500 .mu.m, more preferably of 10 to 100 .mu.m.
[0091] The diameter of the core is preferably 5 .mu.m to 497 .mu.m,
more preferably 7 to 97 .mu.m.
[0092] The layer thickness of the outer shell is preferably 3 .mu.m
to 100 .mu.m, more preferably 5 to 50 .mu.m, with very particular
preference 10 to 40 .mu.m.
[0093] The length of the fiber is arbitrary. The fiber may be in
the form of short fiber sections, with a length for example of 0.1
mm to 10 cm; alternatively the fiber may be in the form of
continuous fiber, depending on the desired further processing.
Production Processes
[0094] The fiber can be produced by standard methods. For example,
the core material can be extruded as a fiber and the outer shell
can be applied by customary coating techniques.
[0095] One particularly simple process is the coextrusion of core
material and of the material for the outer shell.
[0096] For the coextrusion the core material is heated preferably
to temperatures between 150 and 300.degree. C. and the material of
the outer shell to temperatures between 80 and 200.degree. C., more
preferably between 100 and 180.degree. C., very preferably between
110 and 150.degree. C., and then coextrusion too takes place at
these temperatures.
[0097] The polymeric fiber obtained is preferably drawn
additionally immediately after coextrusion, the length increase
(degree of drawing) being preferably 10% and 300%, more preferably
50% to 250%, and with very particular preference 100% to 200%.
[0098] Where the adhesive polymer is a UV-crosslinkable polymer,
production of the fiber is followed by irradiation with high-energy
light, in order thus to set the desired adhesive properties.
[0099] The radiation energy can amount for example to 10 mJ/cm2 to
1500 mJ/cm2 of irradiated area.
Use of the Polymeric Fiber
[0100] The polymeric fiber can be used for any of a very wide
variety of purposes. Through combination of the adhesive properties
with the mechanical properties of a fiber, in particular a high
elasticity and breaking strength, entirely new applications are
opened up.
[0101] The fiber may be used, for example, for producing a
sheetlike structure, a nonwoven fiber web for example. Sheetlike
structures of this kind are tacky but at the same time also possess
a high elasticity. The sheetlike structures can be designed in
terms of their dimensions and distances between the fibers in such
a way that they are permeable, for example, to gases and liquids,
while unwanted constituents are retained and cling to the
fibers.
[0102] The polymeric fiber is therefore suitable for producing
permeable layers, examples being permeable nonwovens, membranes, or
other textile sheetlike structures, which can be used as filters
for separating off any of a very wide variety of materials.
Suitable examples include dust filters or other sheetlike
structures for removing dispersed or emulsified particles from
liquid or gaseous media.
[0103] In addition the polymeric fiber can be used for binding,
immobilizing or strengthening small piece goods. Sheetlike
structures made from the fiber can be used for transporting or
sorting goods.
* * * * *