U.S. patent application number 10/588720 was filed with the patent office on 2008-09-04 for electrically conductive glass yarn and constructions including same.
This patent application is currently assigned to Saint- Gobain Vetrotex France S.A.. Invention is credited to Claire Ceugniet, Patrick Moireau.
Application Number | 20080213560 10/588720 |
Document ID | / |
Family ID | 34803326 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080213560 |
Kind Code |
A1 |
Moireau; Patrick ; et
al. |
September 4, 2008 |
Electrically Conductive Glass Yarn and Constructions Including
Same
Abstract
The invention relates to glass strands and glass strand
structures coated with an electrically conducting coating
composition which comprises (as % by weight of solid matter): 6 to
50% of a film-forming agent, preferably 6 to 45%, 5 to 40% of at
least one compound chosen from plasticizing agents, surface-active
agents and/or dispersing agents, 20 to 75% of electrically
conducting particles, 0 to 10% of a doping agent, 0 to 10% of a
thickening agent, 0 to 15% of additives. The invention also relates
to the electrically conducting coating composition used to coat the
said strands and strand structures, to their process of manufacture
and to the composite materials including these strands or strand
structures. Application to the preparation of structures and
composite materials which can be heated by the Joule effect or
which can be used for electromagnetic shielding.
Inventors: |
Moireau; Patrick; (Curienne,
FR) ; Ceugniet; Claire; (F-Saint-Ours, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Saint- Gobain Vetrotex France
S.A.
Chambery
FR
|
Family ID: |
34803326 |
Appl. No.: |
10/588720 |
Filed: |
February 11, 2005 |
PCT Filed: |
February 11, 2005 |
PCT NO: |
PCT/FR05/50087 |
371 Date: |
January 10, 2007 |
Current U.S.
Class: |
428/222 ;
252/500; 252/502; 427/372.2; 428/292.1; 428/294.7; 428/300.1;
428/368; 428/378 |
Current CPC
Class: |
Y10T 428/249924
20150401; Y10T 428/249948 20150401; C03C 25/44 20130101; C03C 25/47
20180101; Y10T 428/292 20150115; C09D 5/24 20130101; Y10T
428/249922 20150401; Y10T 428/2938 20150115; C03C 25/24 20130101;
Y10T 428/249932 20150401 |
Class at
Publication: |
428/222 ;
428/378; 428/368; 252/500; 252/502; 427/372.2; 428/292.1;
428/294.7; 428/300.1 |
International
Class: |
B32B 7/04 20060101
B32B007/04; B32B 17/02 20060101 B32B017/02; B32B 5/02 20060101
B32B005/02; B32B 27/04 20060101 B32B027/04; H01B 1/04 20060101
H01B001/04; H01B 1/00 20060101 H01B001/00; B05D 3/00 20060101
B05D003/00; B32B 13/02 20060101 B32B013/02; B32B 5/16 20060101
B32B005/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2004 |
FR |
0401426 |
Claims
1. Glass strand or glass strand structure coated with an
electrically conducting coating composition which comprises (as %
by weight of solid matter): 6 to 50% of a film-forming agent,
preferably 6 to 45%, 5 to 40% of at least one compound chosen from
plasticizing agents, surface-active agents and/or dispersing
agents, 20 to 75% of electrically conducting particles, 0 to 10% of
a doping agent, 0 to 10% of a thickening agent, 0 to 15% of
additives.
2. Strand or structure according to claim 1, characterized in that
the film-forming agent is a polymer.
3. Strand or structure according to claim 2, characterized in that
the film-forming agent is chosen from polyvinylpyrrolidones,
poly(vinyl alcohol)s, polyacrylics, styrene polymers, poly(vinyl
chloride)s, polyurethanes and the blends of these polymers.
4. Strand or structure according to claim 1, characterized in that
the plasticizing, surface-active and/or dispersing agent is chosen
from optionally halogenated, aliphatic or aromatic, polyalkoxylated
compounds, from polyalkoxylated fatty acid esters, from amino
compounds, from silica derivatives and from the blends of these
compounds.
5. Strand or structure according to claim 1 characterized in that
the conducting particles are based on carbon.
6. Strand or structure according to claim 5, characterized in that
the size of the particles does not exceed 250 .mu.m.
7. Strand or structure according to claim 6, characterized in that
30 to 60% of the particles have an aspect ratio which varies from 5
to 20.
8. Strand or structure according to claim 6, characterized in that
at least 15% of the particles have a flake or needle shape.
9. Electrically conducting aqueous coating composition for a glass
strand or glass strand structure, characterized in that it
comprises: 6 to 50% of a film-forming agent, 5 to 40% of at least
one compound chosen from plasticizing agents, surface-active agents
and/or dispersing agents, 20 to 75% of electrically conducting
particles, 0 to 10% of a doping agent, 0 to 10% of a thickening
agent, 0 to 15% of additives.
10. Composition according to claim 9, characterized in that it
exhibits a viscosity of greater than or equal to 190 mPas.
11. Composition according to claim 10, characterized in that it
comprises: 2.5 to 45% of graphite particles having a size of
between 10 and 100 .mu.m, at least 5% by weight of these particles
being provided in the form of flakes or needles with an aspect
ratio of greater than or equal to 5, 0 to 45%, of graphite
particles with a size of less than 10 .mu.m, 2.5 to 45%, of carbon
black particles having a size of less than 1 .mu.m.
12. Process for the preparation of a glass strand or of a glass
strand structure according to claim 1 which comprises the stages
consisting in coating a glass strand or a glass strand structure
with the conducting coating composition according to claims 1, and
heating the said coated strand or the said coated structure at a
temperature sufficient to remove the water and to strengthen the
conducting coating.
13. Process according to claim 12, characterized in that the
coating is carried out by immersion in a bath of the conducting
coating composition.
14. Process according to claim 12, characterized in that the
heating is carried out at a temperature of greater than
approximately 105.degree. C. and less than approximately
220.degree. C.
15. Glass strand structure according to claim 1, characterized in
that it is provided in the form of an assemblage of intertwined
strands or nonintertwined strands.
16. Structure according to claim 15, characterized in that it
exhibits an electromagnetic shielding value of between 5 and 50 dB,
preferably between 5 and 35 dB, measured between 100 MHz and 2.7
GHz.
17. Composite material comprising a matrix reinforced by glass
strands or a glass strand structure according to claim 1.
18. Material according to claim 17, characterized in that the
matrix is a thermoplastic or thermosetting polymer or a cementing
material.
Description
[0001] The present invention relates to glass strands comprising an
electrically conducting coating.
[0002] It also relates to the electrically conducting coating
composition used to coat the said strands, to the process for the
manufacture of these strands, to the reinforcing structures formed
from these strands and to the composite materials including these
strands.
[0003] Reinforcing glass strands are conventionally prepared by
mechanically drawing molten glass streams flowing by gravity from
the multiple orifices of bushings filled with molten glass, to form
filaments which are gathered together into base strands, which
strands are then collected.
[0004] During the drawing, and before they are gathered together
into strands, the glass filaments are coated with a sizing
composition, generally an aqueous sizing composition, by passing
over a sizing member.
[0005] The role of the size is essential in two respects.
[0006] During the manufacture of the strands, it protects the
filaments from the abrasion resulting from the rubbing of the
latter at high speed over the members of the process, acting as a
lubricant. It also makes it possible to remove the electrostatic
charges generating during this rubbing. Finally, it gives cohesion
to the strand by providing bonding of the filaments to one
another.
[0007] During the use for the purpose of producing composite
materials, the size improves the wetting of the glass and the
impregnation of the strand by the matrix to be reinforced and it
promotes the adhesion between the glass and the said matrix, thus
resulting in composite materials with improved mechanical
properties.
[0008] The glass strands in their various forms (continuous,
chopped or milled strands, mats, grids, fabrics, and the like) are
commonly used to effectively reinforce matrices of varied natures,
for example thermoplastic or thermosetting materials and
cement.
[0009] Generally, the glass strands are rendered conducting by the
application of a coating based on particles capable of conducting
the electrical current. The coating is obtained by depositing, on
the strands coated with the size, the conducting particles in
dispersion or in suspension in an aqueous medium and by removing
the water by heating at an appropriate temperature.
[0010] The compositions known for the preparation of the
abovementioned coating use, as conducting particles, graphite,
carbon black or organometallic compounds capable of decomposing to
give metals under the action of heat, if appropriate by introducing
a carbon-comprising compound capable of giving carbon by thermal
decomposition into the composition (U.S. Pat. No. 3,269,883) or
into the size (U.S. Pat. No. 3,247,020).
[0011] In U.S. Pat. No. 4,090,984, use is made of a semi-conducting
coating composition comprising at least one polyacrylate emulsion,
one carbon black dispersion and one thixotropic gelling agent. The
carbon black dispersion represents 20 to 40 parts per 100 parts of
the composition. In example 1, the content of carbon black is equal
to 11.9% by weight of the solid matter present in the
composition.
[0012] In U.S. Pat. No. 4,209,425, the coating composition
comprises conducting particles, in particular made of graphite or
of carbon, at least one surfactant, one thixotrophic gelling agent
and optionally one organosilane coupling agent and/or one
antifoaming agent. The content of conducting particles in the
composition is between 5 and 15% by weight of solid matter of the
composition.
[0013] With the compositions which have just been mentioned, the
content of conducting particles in the final coating remains low,
resulting for this reason in a low level of electrical
conductivity.
[0014] Recent times have seen the appearance of novel materials
incorporating glass strands which exhibit high electrical
conductivity properties and which can for this reason be heated by
the Joule effect. These materials include in particular composite
materials with an organic matrix, of the thermoplastic or
thermosetting polymer type, or cement matrix, in which materials
the abovementioned strands also play a reinforcing role.
[0015] The improvement in the electrical conductivity must not be
made at the expense of the other properties. As regards the
composite materials, it must in particular be kept in mind that the
strands are above all intended to reinforce matrices and
consequently they must exhibit all the qualities for this.
[0016] In particular, the conducting coating must: [0017] provide
bonding of the filaments to one another and also bond the strands
so as to obtain acceptable or improved mechanical properties when
composite materials are concerned, [0018] protect the glass strands
from the mechanical assaults which occur when the reinforcing
structures are employed on building sites, [0019] protect the glass
strands from chemical corrosion and from assaults related to the
environment, so as to provide satisfactory durability, and [0020]
provide good bonding with the polymer matrix to be reinforced, that
is to say render the strands and the matrix compatible.
[0021] A subject-matter of the present invention is glass strands
and structures incorporating glass strands provided with a coating
which exhibits a high electrical conductivity and which are in
addition capable of meeting the requirements related to
reinforcement which are mentioned above.
[0022] Another subject-matter of the invention is the electrically
conducting aqueous coating composition used to coat the
abovementioned glass strands and structures.
[0023] Another subject-matter of the invention is a process for the
manufacture of the glass strands and glass strand structures
capable of conducting the electrical current.
[0024] A further subject-matter of the invention is the composite
materials comprising a matrix reinforced by the abovementioned
strands or structures capable of conducting electricity.
[0025] The glass strands and the glass strand structures in
accordance with the invention are coated with an electrically
conducting coating composition which comprises (as % by weight of
solid matter): [0026] 6 to 50% of a film-forming agent, preferably
6 to 45%, [0027] 5 to 40% of at least one compound chosen from
plasticizing agents, surface-active agents and/or dispersing
agents, [0028] 20 to 75% of electrically conducting particles,
[0029] 0 to 10% of a doping agent, [0030] 0 to 10% of a thickening
agent, [0031] 0 to 15% of additives.
[0032] In the context of the invention, the term "glass strands" is
understood to mean both the base strands obtained by gathering
together, without twisting, a multitude of filaments under the
bushing, and the assemblages of these strands, in particular in the
form of rovings, and the strands which have been subjected to a
twisting operation, and the assemblages of these strands. In the
glass strands in accordance with the invention, the filaments are
coated with a sizing composition compatible in particular with the
film-forming agent of the conducting coating. The electrically
conducting coating will thus be superimposed on the size already
present on the strand, which means that the application of this
coating can be likened to a coating operation.
[0033] Still in the same context, the term "strand structures" is
understood to mean structures obtained by gathering together
intertwined strands, for example fabrics, or nonintertwined
strands, for example nonwovens, in the form of a mat or veil of
continuous strands, and grids.
[0034] The film-forming agent in accordance with the invention
plays several roles: it confers mechanical cohesion on the coating
by causing the conducting particles to adhere to the glass strand
and by providing bonding of these particles to one another, if
appropriate with the material to be reinforced; it contributes to
bonding the filaments to one another; finally, it protects the
strands against mechanical damage and chemical and environmental
assaults.
[0035] The film-forming agent is generally a polymer, preferably
with an elastomeric nature, so as to give flexibility to the
strands. Flexible strands prove to be particularly advantageous in
the production of structures which can be collected in the form of
a wound package and which are highly "conformable", that is to say
which are capable of matching virtually perfectly the most diverse
shapes.
[0036] The film-forming agent can, for example, be chosen from
polyvinylpyrrolidones, poly(vinyl alcohol)s, polyacrylics
(homopolymers or copolymers), styrene polymers, for example of the
styrene-butadiene (SBR) type, poly(vinyl chloride)s (in particular
in the latex or plastisol form), polyurethanes and the blends of
these polymers. Generally, thermoplastic polyolefins are avoided as
a result of their electrically insulating nature and their high
creep capability.
[0037] The choice of the polymer also depends on the nature of the
matrix to be reinforced. As regards cementing materials,
polyacrylics, styrene polymers and poly(vinyl chloride)s are
preferred.
[0038] When the content of film-forming agent is less than 6% by
weight of solid materials, the cohesion of the coating is
inadequate. Above 50%, in particular 45%, the amount of conducting
particles to be introduced is too low to achieve a satisfactory
level of electrical conductivity. Preferably, the amount of
film-forming agent in the coating represents 10 to 35% by weight of
the solid matter and better still 15 to 35%.
[0039] The plasticizing agent makes it possible to lower the glass
transition temperature of the film-forming agent to a value of the
order of 20.degree. C., which makes the coating more flexible, and
also makes it possible to limit the shrinkage after the heat
treatment. The polymers obtained by copolymerization of butadiene
and of an acrylic monomer are preferred.
[0040] The amount of plasticizing agent in the coating generally
represents 0 to 15% by weight of the solid matter, preferably 0 to
10% and better still 3 to 10%.
[0041] The surface-active agents improve the suspension and the
dispersion of the conducting particles and promote compatibility
between the other constituents and the water. It is preferable to
use cationic or nonionic surfactants, in order to avoid problems of
stability of the coating composition and of nonhomogeneous
dispersion of the particles.
[0042] The amount of surface-active agent in the coating generally
represents less than 10% by weight of the solid matter, preferably
0.5 to 10%.
[0043] The dispersing agents help in dispersing the conducting
particles in the water and reduce their separation on settling.
[0044] The amount of dispersing agent in the coating generally
represents 2 to 20% by weight of the solid matter, preferably 3 to
10%.
[0045] The plasticizing, surface-active and dispersing agents can
have one or more of the functions specific to each of the
categories mentioned above. The choice of these agents and of the
amount to be used depends on the film-forming agents and on the
conducting particles.
[0046] These agents can in particular be chosen from: [0047]
organic compounds, in particular [0048] optionally halogenated,
aliphatic or aromatic, polyalkoxylated compounds, such as
ethoxylated/propoxylated alkylphenols, preferably including 1 to 30
ethylene oxide groups and 0 to 15 propylene oxide groups,
ethoxylated/propoxylated bisphenols, preferably including 1 to 40
ethylene oxide groups and 0 to 20 propylene oxide groups, or
ethoxylated/propoxylated fatty alcohols, the alkyl chain of which
preferably comprises 8 to 20 carbon atoms and including 2 to 50
ethylene oxide groups and up to 20 propylene oxide groups. These
polyalkoxylated compounds can be block or random copolymers, [0049]
polyalkoxylated fatty acid esters, for example polyethylene glycol
fatty acid esters, the alkyl chain of which preferably comprises 8
to 20 carbon atoms including 2 to 50 ethylene oxide groups and up
to 20 propylene oxide groups, [0050] amino compounds, for example
amines, which are optionally alkoxylated, amine oxides or
alkylamides, sodium, potassium or ammonium succinates and taurates,
sugar derivatives, in particular sorbitan derivatives, sodium,
potassium or ammonium alkyl sulphates and alkyl phosphates, and
polyether phosphates, [0051] inorganic compounds, for example
silica derivatives, it being possible for these compounds to be
used alone or as a blend with the above-mentioned organic
compounds.
[0052] If the total amount of plasticizing, surface-active and
dispersing agents is less than 5%, poor dispersion of the
conducting particles (presence of aggregates) and/or phase
separation is/are observed. When the content exceeds 40%, a serious
decline in the mechanical performance occurs.
[0053] The electrically conducting particles make it possible to
confer electrical conductivity on the glass strands. In accordance
with the invention, these are carbon-based particles, in particular
graphite and/or carbon black particles.
[0054] Whether the graphite is natural or synthetic in origin has
no effect on the electrical conductivity. It is thus possible to
use without distinction either type of graphite, alone or as a
mixture.
[0055] The particles can have any shape, for example the shape of a
sphere, flake or needle. Nevertheless, it has been found that the
electrical conductivity of a mixture of particles of different
shapes is improved with respect to the same amount of particles of
identical shape. Preferably, 30 to 60% of the conducting particles
have a high aspect ratio (defined by the ratio of the greatest
dimension to the smallest dimension) preferably varying from 5 to
20, in particular of the order of 10, and advantageously at least
15% of the particles are provided in the flake or needle shape.
[0056] As well as the shape, the size of the particles is an
important parameter from the viewpoint of the electrical
conductivity. As a general rule, the size of the particles, taken
in their greatest dimension, does not exceed 250 .mu.m, preferably
100 .mu.m.
[0057] Advantageously, the abovementioned particles, generally made
of graphite, are combined with an electrically conducting carbon
black powder with a particle size of less than or equal to 1 .mu.m,
preferably exhibiting a mean size of between 50 and 100 nm. The
carbon black particles, as a result of their small size, make it
possible to create contact points between the graphite particles,
which makes it possible to further improve the electrical
conductivity.
[0058] Preferably, the conducting coating composition comprises (as
% by weight of solid matter): [0059] 2.5 to 45% and better still 15
to 40% of graphite particles having a size of between 10 and 100
.mu.m, at least 5% by weight of these particles being provided in
the form of flakes or needles with an aspect ratio of greater than
or equal to 5, [0060] 0 to 45%, preferably 5 to 25%, of graphite
particles with a size of less than 10 .mu.m, preferably having a
mean size of the order of 4 .mu.m, [0061] 2.5 to 45%, preferably 15
to 40%, of carbon black particles having a size of less than 1
.mu.m.
[0062] As already indicated, the amount of conducting particles
represents 20 to 75% of the weight of the solid matter of the
coating. If the content is less than 20%, there is no electrical
conduction as the percolation threshold is not reached. When the
content exceeds 75%, a portion of the particles no longer adheres
to the glass strand.
[0063] The doping agent makes it possible to increase the
conductivity by contributing free electrons or by promoting
delocalization of the electrons.
[0064] The doping agent is chosen from organic salts, such as
ammonium crotonate, lithium dodecyl sulphate and copper
acetylacetonate, or inorganic salts, such as ammonium
polyphosphate, titanium chloride or zinc chloride. Preferably,
ammonium crotonate is used.
[0065] The doping agent advantageously represents less than 5% of
the weight of solid matter of the coating. Nevertheless, owing to
the fact that the increase in conductivity remains low with respect
to the amount introduced and that problems of resistance to ageing
may occur, it is preferable to limit the content of doping agent to
1%. In the majority of cases, no doping agent is added.
[0066] The thickening agent makes it possible to adjust the
viscosity of the coating composition to the conditions of
application to the strand by stabilizing the dispersion of the
particles so as to prevent them from settling on standing, thus
making possible the deposition of the desired amount on the
strand.
[0067] The thickening agent is chosen from strongly hydrophilic
compounds, such as carboxymethylcelluloses, gums, for example guar
or xanthan gums, alginates, polyacrylics, polyamides and the blends
of these compounds.
[0068] The amount of thickening agent, when it is used, varies
according to the nature of the compound (the grade, in the case of
the carboxymethyl-celluloses).
[0069] Preferably, the content of thickening agent is less than 10%
by weight of the solid matter of the coating.
[0070] The conducting coating can also comprise the usual additives
for glass strands, in particular adhesion promoters, which make it
possible to improve the coupling between the glass and the material
to be reinforced, such as silanes, lubricating and/or antifoaming
agents, such as mineral oils, fatty esters, for example isopropyl
palmitate and butyl stearate, or organic polymers, or complexing
agents, such as derivatives of EDTA or of gallic acid.
[0071] Preferably, the total amount of additives is less than 10%
by weight of the solid matter of the coating.
[0072] The conducting coating composition capable of coating the
glass strands in accordance with the invention comprises
abovementioned constituents and water.
[0073] The content of water in the coating composition depends on
the conditions of application, in particular on the viscosity and
on the content of conducting particles to be deposited. As a
general rule, the amount of water is determined so as to obtain a
viscosity of greater than or equal to 190 mPas, preferably of less
than 40 000 mPas, advantageously of less than 20 000 mPas, better
still of less than 10 000 mPas, in particular of less than or equal
to 5400 mPas.
[0074] The composition is prepared conventionally by introducing
the various constituents in the aqueous medium, preferably
individually, with sufficient stirring to keep the conducting
particles in dispersion or in suspension.
[0075] When a thickening agent is used, it is introduced first in
the form of an aqueous solution, preferably heated to approximately
80.degree. C. in order to dissolve better.
[0076] Generally, the coating composition is used virtually
immediately after having been prepared but it can also be used
after a storage period of approximately six months at a temperature
of 20 to 25.degree. C. If appropriate, vigorous stirring makes it
possible to redisperse the particles which have separated by
settling, without this affecting the qualities of the
composition.
[0077] In accordance with the invention, the process for the
manufacture of the glass strands and of the strand structures
coated with the electrically conducting coating comprises the
stages consisting in: [0078] coating glass strands or glass strand
structures with the abovementioned conducting coating composition,
and [0079] heating the said strands or the said structures, thus
coated, at a temperature sufficient to remove the water and to
strengthen the conducting coating.
[0080] The composition is applied to glass strands at various
stages of the process after fiberizing, preferably to strands
originating from wound packages, for example rovings, or to
structures in which the strands are gathered together in various
ways: by superimposition of continuous strands deposited in a
random manner (mat or veil) or ordered manner (grid) or by weaving
with intertwining of the strands.
[0081] According to a preferred embodiment, the coating of the
strand or of the strand structure is carried out by immersion in a
bath of the conducting coating composition. In the bath, the strand
or the structure passes into a device which makes it possible to
control the amount of coating composition to be deposited.
[0082] In the case of strands, the device can be a bushing
positioned in the bath, preferably a conical bushing, the angle of
the cone of which is defined so that the strand entering via the
biggest opening can be coated by the composition in a uniform way
over the whole of its surface.
[0083] As regards strand structures, the device can be a padding
machine, of the type used in the textile industry, positioned at
the outlet of the bath.
[0084] Optionally, before passing through the bushing or over the
padding machine, the strand or the structure can pass over a device
targeted at "opening" the strands and making possible better
impregnation of the filaments. This device can be composed of one
or more series of bars forming turn rolls, in the case of the
treatment of the strand, or of a series of rollers, for the
treatment of strand structures.
[0085] At the outlet of the bath, the strand or the structure is
treated thermally to remove the water and to strengthen the
coating. As a general rule, the treatment temperature is greater
than approximately 105.degree. C. and less than approximately
220.degree. C., preferably less than 160.degree. C. To prevent
blistering of the coating brought about by rapid removal of the
water, it is preferable to heat the strand or the structure at a
temperature close to the minimum temperature indicated, if need be
while increasing the duration of treatment, or to carry out the
treatment continuously over the complete temperature range in
successive stationary phases or with a temperature gradient.
Preferably, the maximum temperature remains less than approximately
150.degree. C., and better still less than 130.degree. C.
[0086] Any appropriate heating device can be used for this, for
example an infrared oven or a device which makes it possible to
heat the strand or the structure by contact, for example a device
composed of one or more rotary heating drums.
[0087] The temperature and the duration of the treatment are chosen
according to the type of device used so as to obtain a strengthened
coating. By way of indication, the treatment in an oven can be
carried out satisfactorily at a temperature of the order of
105.degree. C. for a time which generally does not exceed 3
hours.
[0088] After the heat treatment, the glass strand is collected, for
example in the form of wound packages, or else it is deposited on a
translationally moving receiving support to form a mat.
[0089] The glass strand and the strand structure in accordance with
the invention are characterized in that they have electrical
conduction properties while having the qualities specific to
providing a reinforcing function. The strand and the structure are
noteworthy in that the amount of conducting coating can represent
up to 200% of their total weight, more generally of the order of 20
to 60%, and that this relatively high content of conducting
particles confers thereon an altogether advantageous level of
performance. An assessment of this level is given by the value of
the volume electrical resistivity (equal to the inverse of the
volume electrical conductivity), which is a standard reference term
in the field of conducting strands. The volume electrical
resistivity of the strand according to the invention is less than
1000 .OMEGA.cm, preferably 100 .OMEGA.cm, advantageously 10
.OMEGA.cm and better still 1 .OMEGA.cm. The strands and the
structures exhibiting a volume electrical resistivity varying from
10 to 100 .OMEGA.cm can be used for Joule effect heating. Those for
which the said resistivity is less than or equal to 1 .OMEGA.cm are
more particularly suitable for electromagnetic shielding.
[0090] The conducting strand and the strands which are constituents
of the structure in accordance with the invention can be made of
any kind of glass, for example E-, C-, R- and AR-glass. E-glass is
preferred.
[0091] The diameter of the glass filaments constituting the strands
can vary to a large extent, for example from 5 to 30 .mu.m. In the
same way, large variations can occur in the weight per unit length
of the strand, which can range from 68 to 2400 tex according to the
applications targeted.
[0092] The conducting glass strand and the conducting structures in
accordance with the invention can be used to reinforce various
materials and thus to form conducting composite materials capable
in particular of being heated by the Joule effect. As has already
been said, such composite materials can be used for the heating of
buildings or the de-icing of roads, bridges or landing runways.
[0093] The structures can, as such, act as electromagnetic
shielding or heating elements applied at the surface or
incorporated in wall faces or the ground.
[0094] As shielding elements, the purpose of the structures is to
weaken electromagnetic waves harmful to the satisfactory operation
of electronic devices or to limit, indeed even prevent, the use of
portable telephones in certain public or private places (hospitals,
cinemas, prisons, and the like).
[0095] Structures in the form of grids can be incorporated in
particular in structures, for example bridges, to limit battery
effects related to the presence of metal components which increase
the risks of corrosion.
[0096] The examples given below make it possible to illustrate the
invention without, however, limiting it.
[0097] In these examples, the following methods are used: [0098]
The loss on ignition is measured in the following way: a
predetermined amount (approximately 1 gram) of cut strands is
introduced into a porcelain crucible (weight W1). The crucible is
heated in an oven at 105.degree. C. for 1 hour to evaporate the
adsorbed water. On removal from the oven and after cooling, the
crucible is weighed (weight W2) and is then heated in an oven at
700.degree. C. for 5 hours. The crucible is weighed on removal from
the oven after cooling under anhydrous conditions (weight W3).
[0099] The loss on ignition is equal to: W2-W3/W2-W1. [0100] The
tensile strength of the strands is measured under the following
conditions.
[0101] The ends of a roving of a 2000 tex base strand, with a
length of 240 mm, are placed between flat clamping jaws lined with
Vulcolan.RTM. over a distance of 70 mm. The roving is drawn at the
rate of 100 mm/min until it breaks. The strength is expressed in
MPa. [0102] The volume resistivity is obtained by the calculation
from the relationship:
[0102] .rho.=R.times.S/l [0103] in which [0104] .rho. is the
resistivity in .OMEGA.cm, [0105] R is the resistance in Q, [0106] S
is the cross section of the strand in cm.sup.2, [0107] l is the
length of the fibre in cm.
[0108] The resistance R is measured using an ohmmeter, the distance
between the two electrodes being 20 cm. [0109] The electromagnetic
shielding, in dB, is measured under the conditions of Standard
MIL-STD-285 (27 Jun. 1956) between 100 MHz and 2.7 GHz.
EXAMPLE 1
a) Preparation of the Coating Composition
[0110] A composition is prepared comprising (as % by weight of
solid matter):
TABLE-US-00001 film-forming agent: polyvinylpyrrolidone.sup.(1) 20
thickening agent: carboxymethycellulose.sup.(2) 2 plasticizers:
bisphenol A bis(polyethylene glycol) 16.5 ether.sup.(3)
octylphenoxypoly(ethyleneoxy)ethanol.sup.(4) 8.5 cationic
dispersant.sup.(5) 3 conducting particles natural graphite
powder.sup.(6) (mean size of 30 the particles: 3 .mu.m) expanded
synthetic graphite.sup.(7) in the 10 form of flakes (size of the
particles: 10-50 .mu.m) natural graphite powder.sup.(8) (mean size
of 10 the particles: 5 .mu.m)
[0111] The composition is prepared by addition of the constituents
to a receptacle containing water at 80.degree. C. which is kept
vigorously stirred, the thickening agent being introduced first and
the conducting particles last.
[0112] The viscosity of the composition is 3800 mPas at 20.degree.
C.
b) Production of the Glass Strand
[0113] A glass strand composed of 4000 filaments with a diameter of
15.8 .mu.m (weight per unit length: 2000 tex) unwound from a roving
is immersed in a bath of the composition obtained under a). The
strand enters the bath via a strand guide at the rate of 2.5 m/min,
subsequently passes through a conical bushing (small diameter: 2.2
mm) and, at the outlet of the bath, is wound onto a frame rotating
around an axis. The frame is placed in an oven heated at
105.degree. C. for 3 hours.
[0114] The strand exhibits the following characteristics: [0115]
Loss on ignition: 21.0%> [0116] Resistivity: 7.8 .OMEGA.cm
(standard deviation: 2.3) [0117] Tensile strength: 863 MPa
(standard deviation: 23)
EXAMPLE 2
[0118] The operation is carried out under the conditions of Example
1, the conducting coating composition comprising (in % by weight of
solid matter):
TABLE-US-00002 film-forming agent: polyvinylpyrrolidone.sup.(1) 20
thickening agent: carboxymethylcellulose.sup.(2) 2 plasticizers:
bisphenol A bis(polyethylene glycol) 16 ether.sup.(3)
octylphenoxypoly(ethyleneoxy)ethanol.sup.(4) 7 cationic
dispersant.sup.(5) 5 conducting particles natural graphite
powder.sup.(6) (mean size 25 of the particles: 3 .mu.m) expanded
synthetic graphite.sup.(7) in the form 15 of flakes (size of
particles: 10-50 .mu.m) synthetic graphite powder.sup.(9) (mean
size of 10 the particles: 10 .mu.m)
[0119] The viscosity of the composition is 5400 mPas at 20.degree.
C.
[0120] The strand exhibits a loss on ignition of 20.0%.
[0121] The resistivity and tensile strength measurements of the
strand before and after accelerated ageing are as follows (the
standard deviation is given in brackets):
TABLE-US-00003 Time (days) t = 0 t = 1 t = 14 Resistivity (.OMEGA.
cm) 1.55 (0.4) 1.7 (0.2) 1.8 (0.2) Tensile strength (MPa) 1130 (62)
1044 (50) 950 (78)
[0122] After ageing for 14 days, the resistivity is substantially
unchanged and the tensile strength is equal to 84% of its initial
value.
EXAMPLES 3 AND 4
[0123] These examples illustrate the effect of amount of conducting
particles of high aspect ratio on the resistivity.
[0124] The operation is carried out under the conditions of Example
1, modified in that the following compositions are used (in % by
weight of solid matter):
TABLE-US-00004 film-forming agent: polyvinyl- 20.0
pyrrolidone.sup.(1) thickening agent: carboxymethyl- 2.00
cellulose.sup.(2) plasticizers: bisphenol A bis(polyethylene
glycol) 10.25 ether.sup.(3) octylphenoxypoly(ethyleneoxy) 10.25
ethanol.sup.(4) cationic dispersant.sup.(5) 7.50 conducting
particles Ex. 3 Ex. 4 graphite powder.sup.(10) in the form of 2.5
15.0 flakes (size of the particles: 10-50 .mu.m) synthetic graphite
powder.sup.(9) (mean 47.5 35.0 size of the particles: 10 .mu.m)
[0125] The viscosities of the compositions are 4900 mPas and 5400
mPas respectively at 20.degree. C.
[0126] The strands obtained exhibit the following characteristics
(the standard deviation is given in brackets):
TABLE-US-00005 Ex. 3 Ex. 4 Loss on ignition (%) 20.4 19.8
Resistivity (.OMEGA. cm) 2.9 (0.8) 2.3 (0.3) Tensile strength (MPa)
1320 (115) 1348 (58)
[0127] It is found that an increase in the relative proportion of
particles in the form of flakes, at an equivalent total amount of
particles, makes it possible to reduce the resistivity and thus to
increase the electrical conductivity.
EXAMPLE 5
[0128] The operation is carried out under the conditions of Example
1, modified in that the strand is composed of 800 filaments with a
diameter of 13.6 .mu.m (weight per unit length: 300 tex), that the
small diameter of the bushing is equal to 1.2 mm and that the
conducting coating composition comprises (as % by weight of solid
matter):
TABLE-US-00006 film-forming agent: polyvinylpyrrolidone.sup.(1)
20.0 thickening agent: carboxymethylcellulose.sup.(2) 2.0
plasticizers: bisphenol A bis(polyethylene glycol) 17.0
ether.sup.(3) octylphenoxypoly(ethyleneoxy)ethanol.sup.(4) 6.0
nonionic dispersant.sup.(11) 5.0 conducting particles expanded
synthetic graphite.sup.(7) in the form 25.0 of flakes (size of the
particles: 10-50 .mu.m) carbon black powder.sup.(12) (mean size of
the 25.0 particles: 50 nm)
[0129] The viscosity of the composition is 4800 mPas at 20.degree.
C.
[0130] The strand exhibits the following characteristics (the
standard deviation is given in brackets): [0131] Loss on ignition:
14.4%> [0132] Resistivity: 0.3 .OMEGA.cm (0.04); identical after
storing at 20.degree. C. for 15 weeks [0133] Tensile strength: 1361
(93) MPa.
EXAMPLE 6
[0134] The operation is carried out under the conditions of Example
1, the conducting coating composition comprising (as % by weight of
solid matter):
TABLE-US-00007 film-forming agents: acrylic polymer.sup.(13) 33.8
acrylic copolymer.sup.(14) 10.0 surfactants:
2,4,7,9-tetramethyl-5-decyn-4,7-diol.sup.(15) 0.2 10 EO
C.sub.12-C.sub.14 alcohol.sup.(16) 1.0 nonionic dispersant.sup.(11)
5.0 conducting particles expanded synthetic graphite.sup.(7) in the
20.0 form of flakes (size of the particles: 10-50 .mu.m) synthetic
graphite powder.sup.(17) (size of 10.0 the particles: 1-10 .mu.m)
carbon black powder.sup.(12) (mean size of 20.0 the particles: 50
nm)
[0135] The viscosity of the composition is 590 MPas at 20.degree.
C.
[0136] The strand exhibits a loss on ignition of 42.1%.
[0137] The resistivity and the tensile strength of the strand,
before and after accelerated ageing, are given below (the standard
deviation appears in brackets):
TABLE-US-00008 Time (days) t = 0 t = 1 t = 3 Resistivity (.OMEGA.
cm) 0.18 (0.01) 0.18 (0.03) 0.18 (0.01) Tensile strength 1876 (115)
1695 (78) 1565 (43) (MPa) Time (days) t = 7 t = 14 Resistivity
(.OMEGA. cm) 0.17 (0.02) 0.15 (0.01) Tensile strength (MPa) 1503
(158) 1697 (38)
[0138] The resistance of the strands under the accelerated ageing
conditions is excellent: the high level of performance, in
particular of the tensile strength, is maintained over time.
EXAMPLE 7
[0139] The operation is carried out under the conditions of Example
1, the conducting coating composition comprising (as % by weight of
solid matter):
TABLE-US-00009 film-forming agents: acrylic polymer.sup.(13) 38.9
acrylic copolymer.sup.(14) 11.5 surfactants:
2,4,7,9-tetramethyl-5-decyn-4,7-diol.sup.(15) 0.2 10 EO
C.sub.12-C.sub.14 alcohol.sup.(16) 1.0 nonionic dispersant.sup.(11)
4.4 conducting particles expanded synthetic graphite.sup.(7) in the
22.0 form of flakes (size of the particles: 10-50 .mu.m) carbon
black powder.sup.(12) (mean size of 22.0 the particles: 50 nm)
[0140] carbon black powder.sup.(12) (mean size of 22.0 the
particles: 50 nm)
[0141] The viscosity of the composition is 1820 mPas at 20.degree.
C.
[0142] The strand exhibits the following characteristics: [0143]
Loss on ignition: 39.8%> [0144] Resistivity [0145] t=0 days:
0.17 .OMEGA.cm (standard deviation: 0.01) [0146] t=14 days: 0.16
.OMEGA.cm (standard deviation: 0.03) [0147] Tensile strength:
[0148] t=0 days: 1864 MPa (standard deviation: 50) [0149] t=14
days: 1648 MPa (standard deviation: 72)
EXAMPLE 8
[0150] The operation is carried out under the conditions of Example
1, the conducting coating composition comprising (as % by weight of
solid matter):
TABLE-US-00010 film-forming agents: acrylic polymer.sup.(13) 23.8
acrylic copolymer.sup.(14) 20.0 plasticizers/surfactants: nonionic
surfactant.sup.(15) 0.2 ethoxylated fatty alcohol.sup.(16) 1.0
cationic dispersant.sup.(5) 5.0 conducting particles expanded
synthetic graphite.sup.(10) in the form 20.0 of flakes (size of the
particles: 10-50 .mu.m) synthetic graphite powder.sup.(17) (size of
10.0 the particles: 1-10 .mu.m) carbon black powder.sup.(12) (size
of the 20.0 particles: 50 nm)
[0151] The viscosity of the composition is 190 mPas at 20.degree.
C.
[0152] The strand exhibits the following characteristics: [0153]
Loss on ignition: 39.51%> [0154] Resistivity: 0.17 .OMEGA.cm
[0155] Tensile strength: 1673.3 MPa
EXAMPLE 9
[0156] This example illustrates the influence of the amount of
coating on the electrical conductivity and the mechanical
properties of the strand.
[0157] a) Preparation of the Coating Composition
[0158] A composition is prepared comprising (as % by weight of
solid matter):
TABLE-US-00011 film-forming agent: styrene-butadiene
copolymer.sup.(18) 46.5 nonionic dispersant.sup.(11) 6.0
antifoaming agent.sup.(19) 1.0 conducting particles expanded
synthetic graphite.sup.(7) in the form 18.6 of flakes (size of the
particles: 10-50 .mu.m) synthetic graphite powder.sup.(17) (size of
the 9.3 particles: 1-10 .mu.m) carbon black powder.sup.(12) (size
of the 18.6 particles: 50 nm)
[0159] The composition is prepared by addition of the constituents
to a receptacle containing water at ambient temperature
(approximately 25.degree. C.) with vigorous stirring, the
conducting particles being introduced last.
[0160] The composition exhibits a viscosity of 800 mPas at
20.degree. C.
[0161] b) Production of the Glass Strand
[0162] The operation is carried out under the conditions of Example
1, modified in that the glass strand is composed of 800 filaments
with a diameter of 13 .mu.m (weight per unit length: 275 tex).
[0163] A variable amount of conducting coating composition is
deposited on the glass strand (Tests 1 to 3).
TABLE-US-00012 Test 1 Test 2 Test 3 Loss on ignition (%) 21.9 30.6
45.7 Volume resistivity (.OMEGA. cm) 0.23 0.16 0.14 Tensile
strength (MPa) 2035 2045 2059
[0164] It is found that the volume resistivity decreases as a
function of the amount of coating composition deposited on the
strand, which means that the electrical conductivity is increased.
At the same time, the tensile strength level is virtually unchanged
(the increase observed not being significant).
EXAMPLE 10
[0165] The operation is carried out under the conditions of Example
9 while varying the ratio by weight of the conducting particles (P)
to the sum of the conducting particles (P) and of the film-forming
agent (F). The loss on ignition is between 21 and 23%.
TABLE-US-00013 Test P/P + F (%) Volume resistivity (.OMEGA. cm) 1
25 4.11 2 30 1.14 3 35 0.75 4 40 0.42 5 50 0.23 6 60 0.24
[0166] For these values, it is deduced that the percolation
threshold (corresponding to the P/P+F ratio starting from which the
strand exhibits a satisfactory conductivity) is between 30 and
35%.
EXAMPLE 11
a) Preparation of the Coating Composition
[0167] The operation is carried out under the conditions of Example
9, the coating composition comprising (as % by weight of solid
matter):
TABLE-US-00014 film-forming agent: styrene-butadiene
copolymer.sup.(20) 46.5 nonionic dispersant.sup.(11) 6.0
antifoaming agent.sup.(19) 1.0 conducting particles expanded
synthetic graphite.sup.(7) in the form 18.6 of flakes (size of the
particles: 10-50 .mu.m) synthetic graphite powder.sup.(17) (size of
the 9.3 particles: 1-10 .mu.m) carbon black powder.sup.(12) (size
of the 18.6 particles: 50 nm)
[0168] The composition exhibits a viscosity of 230 mPas at
20.degree. C.
b) Production of the Glass Fabric
[0169] A glass fabric (weight per unit area: 165 g/m.sup.2)
exhibiting a square mesh of 35 mm and a thickness of 0.4 mm is
immersed in a vat with a width of 300 mm filled with the
composition obtained under a). At the outlet of the vat, the fabric
is squeezed by passing between the two rolls of a calendar
(pressure: 0.6 bar; speed of rotation: 0.5 m/min) and then it
passes into an air oven comprising 4 compartments heated at
90.degree. C., 130.degree. C., 150.degree. C. and 90.degree. C.
respectively. The residence time in each compartment is 2
minutes.
[0170] Various tests were carried out with a level of coating
(weight of coating/weight of uncoated fabric) of 30% (Test 1), 60%
(Test 2) and 115% (Test 3). Several passes through the impregnation
bath were carried out in order to obtain the highest levels (Tests
2 and 3).
[0171] The curve of the electromagnetic shielding as a function of
the frequency is given in FIG. 1.
[0172] The fabric according to the invention exhibits a shielding
value of greater than 5 dB and of less than 25 dB depending on the
level of coating, over the entire frequency range examined.
[0173] It is specified that a shielding value of 10 dB corresponds
to a weakening in the strength of the electrical field by a factor
of 3, a value of 20 dB corresponds to a weakening by a factor of 10
and a value of 30 dB corresponds to a weakening by a factor of
30.
[0174] Tests 1 to 3 exhibit values of the same order of magnitude
as the available fabrics which are suitable for electromagnetic
shielding. In particular, the level of performance of Test 2 is
comparable with that which is obtained with a fabric based on
copper wires and on glass strands which are comingled and provided
with a conducting coating and which are arranged in weft and in
warp. However, this fabric is not entirely satisfactory as, on the
one hand, the contact of the copper wires at the crossing points is
not always assured and, on the other hand, the copper has a
tendency to oxidize to form an insulating surface layer which
results in a reduction in the electrical conductivity.
EXAMPLE 12
[0175] The operation is carried out under the conditions of Example
11, modified in that the coating composition comprises (as % by
weight of solid matter):
TABLE-US-00015 film-forming agent: styrene-butadiene
copolymer.sup.(20) 37.0 nonionic dispersant.sup.(11) 7.0
antifoaming agent.sup.(19) 1.0 conducting particles expanded
synthetic graphite.sup.(7) 22.0 synthetic graphite powder.sup.(17)
11.0 carbon black powder.sup.(12) 22.0
[0176] The composition exhibits a viscosity of 545 mPas at
20.degree. C.
[0177] The fabric was impregnated with a level of coating of 32%
(Test 1), 64% (Test 2) and 160% (Test 3).
[0178] The curve of the electromagnetic shielding as a function of
the frequency is given in FIG. 2.
[0179] It is observed that Tests 1 to 3 exhibit improved levels of
performance in comparison with those of Example 11. [0180] (1) Sold
under the reference "Luviskol K 90" by BASF [0181] (2) Sold under
the reference "Blanose.RTM. 7 MC" by Aqualon [0182] (3) Sold under
the reference "Simulsol BPPE" by SEPPIC [0183] (4) Sold under the
reference "Antarox CA 630 by Rhodia HPCII [0184] (5) Sold under the
reference "Solsperse 20000" by Avecia [0185] (6) Sold under the
reference "GK UF2 96/97" by Kropfmulh [0186] (7) Sold under the
reference "Grafpower TG 407" by Ucar [0187] (8) Sold under the
reference "GK UF4 96/97" by Kropfmulh [0188] (9) Sold under the
reference "SPF 16" by Ucar [0189] (10) Sold under the reference
"Grafpower TG 40" by Ucar [0190] (11) Sold under the reference
"Solsperse 27000" by Avecia [0191] (12) Sold under the reference
"Vulcan XC 72R" by Cabot S.A. [0192] (13) Sold under the reference
"Latex 651" by Ucar [0193] (14) Sold under the reference "Carboset
514 W" by Noveon [0194] (15) Sold under the reference "Surfynol
104-PA" by Air Products [0195] (16) Sold under the reference
"Simulsol P10" by SEPPIC [0196] (17) Sold under the reference "SPF
17" by Ucar [0197] (18) Sold under the reference "Styronal ND430"
by BASF [0198] (19) Sold under the reference "Tego Foamex 830" by
Degussa [0199] (20) Sold under the reference "Styronal D517" by
BASF
* * * * *