U.S. patent number RE30,860 [Application Number 05/663,196] was granted by the patent office on 1982-02-02 for process for treating cellulosic material with formaldehyde in liquid phase and sulfur dioxide.
This patent grant is currently assigned to Cotton, Incorporated. Invention is credited to Ronald Swidler, Katherine W. Wilson.
United States Patent |
RE30,860 |
Swidler , et al. |
* February 2, 1982 |
Process for treating cellulosic material with formaldehyde in
liquid phase and sulfur dioxide
Abstract
The dimensional stability, crease retention, wrinkle resistance
and smooth drying characteristics of a cellulose fiber-containing
material such as a cotton fabric are improved by impregnating the
material with an aqueous formaldehyde phase and curing the
formaldehyde-containing material at high temperature in the
presence of catalyst-forming sulfur dioxide while governing the
amount of water in the system to provide a self-limiting reaction
system, water being the limiting factor in the reaction by which an
acid curing catalyst is formed from formaldehyde, sulfur dioxide
and water. The aqueous formaldehyde phase may be applied to the
material as such, or it may be formed in the material by exposing
the latter in a humidified state to formaldehyde vapor. Sulfur
dioxide may be introduced into the system either in the course of
the aqueous impregnation step or in the curing step.
Inventors: |
Swidler; Ronald (Palo Alto,
CA), Wilson; Katherine W. (San Diego, CA) |
Assignee: |
Cotton, Incorporated (New York,
NY)
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[*] Notice: |
The portion of the term of this patent
subsequent to December 19, 1989 has been disclaimed. |
Family
ID: |
27498569 |
Appl.
No.: |
05/663,196 |
Filed: |
March 2, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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237056 |
Mar 22, 1972 |
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706792 |
Feb 20, 1968 |
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239361 |
Mar 29, 1972 |
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Reissue of: |
332332 |
Feb 14, 1973 |
03841832 |
Oct 15, 1974 |
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Current U.S.
Class: |
8/116.4; 8/125;
8/149.2 |
Current CPC
Class: |
D06M
13/127 (20130101); D06M 11/54 (20130101) |
Current International
Class: |
D06M
11/00 (20060101); D06M 11/54 (20060101); D06M
013/12 () |
Field of
Search: |
;8/116.4,125,149.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Michl; Paul R.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Parent Case Text
CROSS REFERENCE
This application is a continuation-in-part of Ser. No. 237,056,
filed Mar. 22, 1972 and now abandoned, which in turn is a
continuation-in-part of Ser. No. 706,792, filed Feb. 20, 1968 and
now abandoned; this application is also a continuation-in-part of
application Ser. No. 239,361, filed Mar. 29, 1972 and now
abandoned, which in turn is also a continuation of said Ser. No.
706,792.
Claims
What is claimed is:
1. A process for improving the dimensional stability, wrinkle
resistance and smooth drying characteristics of a cellulose
fiber-containing fabric which comprises:
a. depositing water and formaldehyde in the fabric to provide
therein an aqueous phase comprising formaldehyde and conditioning
the fabric to give the cellulose fibers a moisture content of
between about 4 and 20 percent based on dry weight of
cellulose;
b. heating the conditioned moisture-containing and
formaldehyde-containing fabric in the presence of catalyst-forming
sulfur dioxide and water vapor in a reaction zone at a temperature
above about 65.degree. C. for a time of between about 10 seconds
and 2 hours until formaldehyde in an amount equal to at least 0.3
percent by weight of said cellulose fibers is durably deposited in
the fabric and the cellulose fibers become effectively crosslinked,
said heating being conducted while governing the amount of water in
the system to control the amount of moisture in said fabric and
thereby regulate the amount of strong acid catalyst formed therein
by the reaction of formaldehyde and sulfur dioxide, a reaction in
which water is the limiting factor, to provide a self-limiting
reaction system; and
c. heating the thus crosslinked fabric to dissipate water vapor,
residual catalyst and unbound formaldehyde therefrom.
2. A process according to claim 1 wherein the fabric is heated in
step (b) to a temperature between about 80.degree. and about
150.degree. C. and is dried and unbound formaldehyde is vaporized
therefrom by heating it in step (c), thereby directly producing a
dry, crosslinked, essentially neutral fabric.
3. A process according to claim 1 wherein the fabric is treated
prior to the formaldehyde crosslinking step with a compound
containing an active hydrogen and selected from the group consistng
of polyhydric alcohols, ureas, amides and carbamates.
4. A process according to claim 1 wherein the conditioned
moisture-containing fabric is treated with sulfur dioxide gas
before being heated in said reaction zone in step (b).
5. A process according to claim 1 wherein the fabric is one
containing at least 35 percent by weight of cotton and wherein the
aqueous formaldehyde solution contains between about 1 and 40
percent by weight of formaldehyde.
6. A process for improving the dimensional stability, wrinkle
resistance and smooth drying characteristics of cotton containing
fabrics which comprises:
a. applying to the fabric an aqueous solution containing about 2 to
40 percent by weight of formaldehyde and conditioning the fabric to
give the cotton a moisture content of between about 4 to 20 percent
based on dry weight of cotton;
b. heating the conditioned moisture-containing and
formaldehyde-containing fabric to a temperature of between about
80.degree. and about 150.degree. C. in the presence of sulfur
dioxide in an atmosphere containing water vapor in a reaction zone
for a time of between about 10 seconds and 2 hours until
formaldehyde in an amount equal to at least 0.3 percent by weight
of said cotton is durably fixed in the fabric and the cotton fibers
are effectively crosslinked, said heating being conducted while
governing the amount of water in the reaction zone to control the
amount of moisture in said fabric and thereby regulate the amount
of strong acid catalyst formed therein by the reaction of
formaldehyde and sulfur dioxide, a reaction in which water is the
limiting factor, to provide a self-limiting reaction system;
and
c. at the end of said crosslinking step (b) removing residual
catalyst and unbound formaldehyde from the fabric by heating it in
an inert gaseous atmosphere, thereby directly producing a dry,
crosslinked, essential neutral fabric.
7. A process according to claim 6 wherein steam is injected into
the reaction zone in step (b) to adjust the water vapor
concentration therein at between about 10 and 70 percent by volume
and thereby to retard evaporation of moisture from the conditioned
fabric and control the crosslinking reaction.
8. A process for improving the dimensional stability, wrinkle
resistance and smooth drying characteristics of cotton-containing
fabrics which comprises:
impregnating in the fabric an aqueous solution containing about 10
to 30 percent formaldehyde;
drying and conditioning the impregnated fabric to a moisture
content of between about 4 to 20 percent;
heating the moisture-containing and formaldehyde-containing fabric
in a reactive gaseous atmosphere comprising water vapor and about
0.1 to 30 volume percent sulfur dioxide at a temperature between
about 90.degree. and about 150.degree. C. for a time of from about
10 seconds to about 2 hours until formaldehyde in an amount equal
to at least 0.3 percent by weight of said cotton fibers is durably
fixed in the fabric and the cotton fibers are effectively
crosslinked, said heating being conducted while governing the
amount of water vapor in said atmosphere to control the amount of
moisture in said fabric and thereby regulate the amount of strong
acid catalyst formed by the reaction of formaldehyde and sulfur
dioxide, a reaction in which water is the limiting factor, to
provide a self-limiting reaction system; and
drying the thus crosslinked fabric.
9. A process according to claim 8 wherein the fabric is treated in
a pad bath containing an amide prior to moisture conditioning.
10. A process according to claim 8 wherein urea or thiourea is
applied to the fabric together with the formaldehyde solution.
11. A process according to claim 10 in which the fabric being
treated is a flat fabric and the crosslinked fabric is washed to
remove residual reactants therefrom, and the washed, crosslinked
fabric is dried. .Iadd. 12. A process using formaldehyde and sulfur
dioxide vapors for treating cellulosic fabric-containing material
to impart a durable press thereto comprising conveying said
material through a first zone to introduce moisture thereinto,
conveying the material then through a second zone to subject it to
formaldehyde and sulfur dioxide vapors, and conveying said material
next through a third zone to effect a drying thereof and to subject
the material to a curing temperature of between 120.degree. C. and
160.degree. C. .Iaddend. .Iadd. 13. A process for treating
cellulosic fabric-containing material to impart a durable press
thereto comprising conveying said material through a first zone to
introduce moisture thereinto, conveying the material then through a
subsequent treatment zone to subject it to sulfur dioxide vapors,
thereafter conveying said material through a subsequent curing zone
to subject the material to a curing temperature of above about
65.degree. C., and wherein prior to conveying said material through
said curing zone, and prior to or during said treatment with sulfur
dioxide vapors, conveying said material through a zone to
impregnate it with formaldehyde. .Iaddend. .Iadd. 14. A process
according to claim 13 wherein said material is impregnated with
formaldehyde in said first zone..Iaddend.
Description
BACKGROUND OF THE INVENTION
In recent years various methods have been devised for treating
cellulosic fiber-containing products, such as cloth made of cotton
or cotton blends, in order to impart durable crease retention,
wrinkle resistance and smooth drying characteristics thereto. For
example, cellulosic materials have been crosslinked with
formaldehyde, giving durable crosslinks having good resistance to
repeated laundering and also to various acids and alkalis, and
chlorine bleaches. These formaldehyde treated cellulosic materials
are resistant to discoloration and yellowing, and are less likely
to produce a rash or other sensitization on the wearer than
cellulosic materials treated with resins or precondensates of the
urea-formaldehyde or substituted urea-formaldehyde types which may
decompose and release formaldehyde while in use.
However, while formaldehyde has made a significant contribution to
the cotton finishing art, the results have been far from perfect.
For instance, in some cases the formaldehyde crosslinking treatment
has tended to lack reproducibility, since control of the
formaldehyde crosslinking reaction heretofore has been difficult.
When high curing temperatures were used with an acid or potential
acid catalyst, overreaction and degradation of the cotton often
happened which considerably impaired its strength. On the other
hand, when attempts were made to achieve reproducibility at
temperatures of 50.degree. C. or less, much longer reaction or
finishing times were usually required, rendering the process
economically relatively unattractive. This has been particularly
true when sulfur dioxide was used as a catalyst in the previously
known processes such as that disclosed in U.S. Pat. No. 3,663,974
or the corresponding British Pat. No. 980,980. In other cases,
formaldehyde cross-linking has not been able to meet commercial
standards with respect to dry wrinkle recovery. For these and
similar reasons efforts have been continuing to develop new and
better finishing processes for cotton and other cellulose fiber
materials.
For the sake of completeness it may also be mentioned that it has
been previously suggested in U.S. Pat. No. 2,870,041 that
formaldehyde odors in fibrous material which has been treated with
a urea-formaldehyde or melamine-formaldehyde type crosslinking
resin can be prevented by treating such material with an aqueous
solution of sodium meta bisulfite or of some sulfite or bisulfite
salt which supplies HSO.sub.3.sup.- ions to the system and forms a
stable addition product with formaldehyde.
However, in such a system formaldehyde is not used as the
creaseproofing agent and the "stabilization" of the formaldehyde in
the system does not serve to creaseproof it. On the contrary, a
customary dry high temperature cure of the material containing the
melamine-formaldehyde or other crosslinking resin in the presence
of a latent curing catalyst is required, which in turn requires
removal of the salt catalyst from the cured fabric by washing. The
possibility of using sulfur dioxide in aqueous solution as the
formaldehyde-binding agent is also suggested in said U.S. Pat. No.
2,870,041. However, as only an unstable hydroxy methyl sulfonic
acid is formed from formaldehyde and sulfur dioxide in the presence
of water and this acid reverts to formaldehyde and sulfur dioxide
on drying, it is evident that this previously suggested use of
aqueous sulfur dioxide can not serve as an effective means either
for the permanent removal of formaldehyde odors nor for any other
significant improvement of the resin-treated material.
DESCRIPTION OF THE INVENTION
A primary object of the present invention is to provide a practical
process for treating cellulose fiber-containing materials with
formaldehyde to improve their shape holding properties while
avoiding or alleviating the problems mentioned above.
A more specific object has been to develop a process for
crosslinking cotton-containing fabrics with the aid of formaldehyde
which is deposited in the fabric in aqueous phase, forming the
required strong acid catalyst in the process substantially in the
amount needed by reaction with sulfur dioxide under controlled and
self-limiting conditions, thereby keeping acid injury to the fiber
to a minimum while avoiding the need for after-washing.
These and other objects, as well as the scope, nature, and
utilization of the invention will become more clearly apparent from
the following more detailed description. Unless otherwise
indicated, all proportions and percentages of materials or
compounds are expressed on a weight basis throughout this
specification and appended claims.
In accordance with the present invention, a process is provided for
treating a cellulose fiber-containing material to improve its
dimensional stability, crease retention, wrinkle resistance, and
smooth drying characteristics by treating the material with
formaldehyde in aqueous phase in the presence of sulfur dioxide
under controlled moisture conditions at a temperature between about
65.degree. and 150.degree. C. or higher, e.g., in a chamber heated
to between about 80.degree. and 170.degree. C.
The process, which is applicable to flat fabrics as well as
completed garments, requires relatively short reaction times, gives
high wrinkle recoveries and at the same time produces satisfactory
tensile and tear strengths without requiring an after-wash of the
treated fabric.
According to the invention claimed herein the cotton or other
cellulose-containing fabric such as a cotton-polyester blend is
impregnated with a liquid solution containing about 2 to 40
percent, preferably 10 to 30 percent, formaldehyde in water or
similar liquid solvent to give a wet pick-up of between about 50
and 110 percent based on dry cotton weight. The fabric is then
conditioned or dried to a moisture content of between about 4 and
20 percent, preferably between about 10 or 12 and 18 percent,
passed into or placed in an atmosphere containing sulfur dioxide
gas in a concentration which may range from as little as 0.1 volume
percent on up, for instance, 5 to 30 volume percent sulfur dioxide,
and maintained in the presence of sulfur dioxide under controlled
moisture conditions at a temperature between about 80.degree. and
150.degree. C. or higher, for a time of between about 10 seconds
and 2 hours, for instance, 30 seconds to 5 minutes, until the
proper amount of formaldehyde is durably deposited or fixed in the
fabric. Satisfactory durable wrinkle recovery and tear strength are
obtained when formaldehyde is durably fixed in the fabric in an
amount which may range from about 0.3 percent on upward, e.g.,
between 0.3 and 5 percent, based on the weight of the cellulose
fibers in the fabric. When the vapor treatment is performed
batchwise rather than by passing a stream of sulfur dioxide gas
through the treating chamber, very small concentrations of SO.sub.2
gas, e.g., as little as 0.1 volume percent, are sufficient to
produce the required amount of catalyst because the reactive
SO.sub. 2 gas tends to be absorbed in the moist fabric and thus
builds up a suitable effective concentration therein.
The optimum reaction time under any given set of reaction
conditions is one which is just long enough to effect the desired
degree of crosslinking without unnecessarily overexposing the
fabric to the acid catalyst. Increasing the reaction temperature
or, surprisingly, increasing the moisture content of the reactive
atmosphere or of the fabric permits reducing the reaction time
under otherwise comparable conditions, and vice versa.
The moisture content of the fabric to be treated is important in
this invention. Water is the limiting factor in the reaction of
sulfur dioxide and formaldehyde which forms the required strong
acid catalyst and which determines the extent of crosslinking of
the cellulose by reaction with formaldehyde. Removal or
displacement of water from the reaction system causes the system to
be self-limiting and readily controllable. The strong but unstable
catalyst makes the process fast as well as easy to control in a
reproducible fashion. Initial moisture in the fabric serves to
swell the cellulose fibers and to hold therein the formaldehyde,
the sulfur dioxide and the resulting acid catalyst in an aqueous
phase, but has only a relatively small effect on the total amount
of formaldehyde which is incorporated into the fabric in both fixed
and unfixed form. Nevertheless, because of its role in the
formation of the acid curing catalyst and in swelling the cellulose
fibers, such initial moisture and its subsequent evaporation have a
significant effect on wrinkle recovery and flex abrasion
characteristics of the cured fabric. Wet wrinkle recovery
improvement is produced principally when the fibers are crosslinked
while in a water swollen state whereas dry wrinkle recovery
improvement is produced in the process principally after most of
the initial moisture has evaporated from the fibers and they are
crosslinked in a near-dry, collapsed state.
Generally speaking, too little initial moisture gives low wrinkle
recovery values while too much moisture can cause excessive
degradation of the fabric because of hydrolysis of the cellulose by
the strong acid catalyst formed in the process. The amount of acid
catalyst formed in the presence of water also affects the
proportion of formaldehyde which actually forms durable crosslinks
in the fabric as against that which is merely present as
formaldehyde polymer.
For optimum control, the moisture content of the treating
atmosphere is desirably maintained between about 10 and 70 volume
percent, whereby evaporation of moisture from the fabric is
retarded and the cellulose crosslinking reaction proceeds at a high
rate while the cellulose fibers are in a water swollen condition.
When the initial moisture content of the fabric introduced into the
curing chamber is low such that the fabric dries rapidly on heating
and the amount of acid catalyst formed is insufficient for assuring
that the formaldehyde crosslinking reaction proceeds to the desired
extent, one can make up for this by injecting steam into the
reaction chamber and thereby increase the humidity of the system to
the desired level as needed, as originally disclosed in our parent
application Ser. No. 706,792, now abandoned, and our copending Ser.
No. 239,361, now abandoned.
Because of its chemical function in this process, water plays an
unusual role here in that the crosslinking reaction automatically
tends to come to a stop when water evaporates from the fabric to a
point where insufficient acid catalyst is formed or present to
promote the crosslinking reaction. Whereas previous formaldehyde
crosslinking processes were difficult to control, the decomposition
of the catalyst upon drying makes the present process self-limiting
in a desirable manner and makes it possible to produce a dry,
crosslinked fabric which is essentially neutral upon removal from
the high temperature treatment because dissipation of moisture from
the hot fabric automatically results in the removal of any residual
catalyst therefrom. Moreover, such formaldehyde polymer as is left
on the treated fabric at the end of the curing or crosslinking step
can be easily and permanently removed therefrom by simple heating,
for instance, by heating the cured fabric in a stream of air or a
mixture of air and high temperature steam or other nonreactive gas
at a temperature above 100.degree. C., preferably between
100.degree. and 150.degree. C. Such heating and stripping causes
drying and decomposition of the acid catalyst as well as
depolymerization and removal of unreacted formaldehyde from the
cured fabric. This precludes liberation of irritating formaldehyde
from the fabric during subsequent use and is in contrast to the
behavior of urea-formaldehyde or melamine-formaldehyde crosslinking
resins, which tend to decompose slowly and release formaldehyde
odors gradually from treated fabrics during service.
The fabric can be conditioned to give the desired initial moisture
content by any suitable method, such as by padding the fabric with
aqueous formaldehyde and partially drying or by holding a dried
fabric for a time at a suitable temperature and relative humidity
until it reaches the desired moisture regain.
Instead of impregnating the fabric directly with an aqueous
formaldehyde solution, it is possible to provide such a solution in
the fabric by first steaming or otherwise humidifying it to give it
an appropriate moisture content, e.g., 10 to 15 percent regain, and
then releasing formaldehyde vapors in a chamber where the
humidified fabric is held at or near ambient temperature, e.g.,
between 15.degree. and 45.degree. C., preliminary to the eventual
heating and curing step. As a result, the formaldehyde vapors
condense and dissolve in the moisture held in the fabric during
such a preliminary impregnation step, prior to the curing step. The
impregnation with aqueous formaldehyde solution and the subsequent
curing in the controlled presence of moisture and added sulfur
dioxide can be carried out consecutively in the same chamber, or
separately in consecutive chambers.
Furthermore, it is possible to release not only formaldehyde vapor
but also sulfur dioxide gas in such a preliminary impregnation step
and thus dissolve both the required formaldehyde and the required
sulfur dioxide in the conditioned or humidified fabric which is at
ambient or relatively low temperature. In such a case no sulfur
dioxide need to be added in the subsequent high temperature curing
step.
Other, optional features of the invention include the addition of
various monomeric or polymeric additives which serve to alter
fabric properties. For instance, treatment of the cloth prior to
the SO.sub.2 treatment with a compound having an active hydrogen,
and particularly with a hydroxyl compound such as ethylene glycol,
triethylene or tetraethylene glycol dimethyl ether, glycerine,
glycidol and the like, surprisingly results in a substantially
greater increase in wet wrinkle recovery than dry wrinkle recovery,
and can be used for this purpose when such an effect is desired.
Other useful additives having an active hydrogen compound include
amides such as urea proper or other ureas, e.g., cyclic
ethyleneurea, allylurea and thiourea, acetamide, malonamide and
acrylamide as well as sulfonamides such as methanesulfonamide;
carbamates such as ethylcarbamate or hydroxyethylcarbamate; and so
on. When such monomers which contain an active hydrogen are treated
with formaldehyde in accordance with the present invention, they
become fixed on the fabric so that they do not wash out. At dry
add-ons of about 5 percent, e.g., between 5 percent and 20 percent
pretreatment with the amides, and especially with urea, they tend
to lead to unusually high tensile and tear strength retentions.
They also add crispness to the fabric after being fixed thereon by
the formaldehyde.
Moreover, pretreatment of the cloth, prior to the SO.sub.2
treatment, with polymeric resinous additives that form soft films,
such as conventional dispersions or latexes, can result in an
unusually great incremental improvement in wrinkle recovery as
compared with similar effects when such additives are used in
conjunction with more conventional crosslinking treatments.
Polymers can also improve the flex abrasion resistance and tear
strength, or alter the ratio of dry wrinkle recovery to wet wrinkle
recovery, or in some instances shorten the reaction time needed to
produce an acceptable durable press fabric. Polymeric additives
suitable for such purposes are, in most cases, available
commercially in concentrated aqueous latex form, and it is
desirable to dilute these to a concentration of 1 to 3 percent
polymer before padding onto the fabric. Suitable polymeric
additives include solid resinous or rubbery acrylonitrilebutadiene
copolymers and mixtures containing the same with various vinyl
resins; polyethylene; deacetylated copolymers of ethylene and vinyl
acetate; polyurethanes; and various polymers of alkyl acrylates,
other polyesters and polyamides. Coating of the fabrics with such
polymers subsequent to the formaldehyde treatment may also be used
to give similar results.
The present invention is useful for treating various natural or
artificial cellulosic fibers alone or as mixtures with each other
in various proportions or as mixtures with other fibers. Such
natural cellulosic fibers include cotton, linen and hemp, and
regenerated or artificial cellulosic fibers useful herein include,
for example, viscose rayon and cuprammonium rayon. Other fibers
which may be used in blends with one or more of the above mentioned
cellulosic fibers are, for example, cellulose acetate, polyamides,
polyesters, polyacrylonitrile, polyolefins, polyvinyl chloride,
polyvinylidene chloride and polyvinyl alcohol fibers. Such blends
preferably include at least 15 or 20 percent by weight and most
preferably at least 35 or 40 percent by weight, of cotton or
natural cellulose fibers. Blends containing 50 to 80 percent cotton
and correspondingly 50 to 20 percent polyester fiber are eminently
suited for treatment according to this invention.
The fabric may be knit, woven or non-woven, or be any otherwise
constructed fabric. The fabric may be flat, creased, pleated,
hemmed, or sewn or otherwise formed to produce an article such as a
garment of any desired shape prior to curing. After processing, the
formed crosslinked fabric will maintain substantially the original
configuration for the life of the article, that is, a wash-wear or
durable press fabric will be produced.
When treating with gaseous sulfur dioxide the conditioned fabric is
passed into a treating atmosphere containing sulfur dioxide which
may be obtained from any convenient source. In addition to the
sulfur dioxide and water vapor, the treating atmosphere may contain
inert gases such as air, nitrogen, carbon dioxide, helium, and the
like. Since sulfur dioxide forms the required strong acid catalyst
by reacting with formaldehyde and water in the fabric, sulfur
dioxide as such need not be supplied to or present in the process
over the entire duration of the crosslinking reaction, but its
supply may be discontinued after the first minute or two or when an
adequate supply of sulfur dioxide has been absorbed by the fabric.
To take advantage of the self-limiting feature of this process, it
can be advantageous to pass the fabric being treated through zones
of progressively lower humidity. Obviously, a comparable
self-limiting effect is not obtainable when the more common
catalysts such as HCl, ammonium chloride or zinc nitrate are
used.
To contact the fabric with the gaseous sulfur dioxide any suitable
means may be employed. For example, a batch system utilizing a
closed chamber or tube containing the gaseous sulfur dioxide may be
used in which the conditioned, moisture-containing fabric may be
placed and there exposed to the treating atmosphere for the
appropriate time. As indicated earlier herein, the vapor treatment
may be carried out either in the same chamber in which the
impregnated fabric is actually cured or the vapor treatment and the
hot curing step may be carried out consecutively in separate
chambers. In the alternative, a dynamic or continuous system can be
used containing a series of more or less distinct zones for
conducting the desired combination of impregnation and
conditioning, curing and purging steps through which the
appropriate gases and the fabric or garments being treated are
passed at appropriate rates relative to each other.
DESCRIPTION OF SPECIFIC EMBODIMENTS
The present invention is further illustrated by the following
examples.
EXAMPLE 1
This is an illustrative example of sulfur dioxide catalyzed,
formaldehyde solution treatment of cotton printcloth in accordance
with the present invention.
A glass tubular reactor approximately 8 cm. in diameter and 40 cm.
in length, wrapped with heating tape and mounted horizontally, was
heated to the desired temperature. Sulfur dioxide was metered into
the reactor from a storage tank to give a sulfur dioxide
concentration in the reactor atmosphere of 10 volume percent, the
remainder being ambient air.
A piece of conditioned cotton printcloth was then introduced into
the reactor. The conditioned printcloth was mercerized cotton
printcloth which had been padded with an aqueous solution of
polyethylene, polyacrylate and formaldehyde, and then conditioned
to give the fabric a moisture content of 10 percent. After
treatment in the reactor the printcloth was taken out, rinsed with
hot water, washed in a household washer to which 25 ml. of
commercial alkylbenzene sulfonate household detergent powder (Vel)
was added, and tumble dried in a household dryer. Table I gives
data and results for three runs where temperature as well as
duration of treatment were varied. As can be seen, operating at
higher temperatures significantly improves the crease recoveries of
the fabric while permitting shorter reaction times, which is
commercially desirable.
TABLE I ______________________________________ Run 1 Run 2 Run 3
______________________________________ Formaldehyde in pad bath 13%
13% 13% Polyethylene in pad bath 2% 2% 2% emulsion emulsion
emulsion Polyacrylate in pad bath 2% 2% 2% emulsion emulsion
emulsion Fabric moisture content 10% 10% 10% Sulfur dioxide
concentration 10% 10% 10% Temperature 48.degree. C. 80.degree. C.
80.degree. C. Duration of treatment 20 min. 20 min. 10 min.
Wash-wear rating (AATCC 88A-1964T) 3.5 4.0 3.5 Wrinkle Recovery
(AATCC 66-1959T) Dry 273 306 312 (W + F) Wet 297 297 304 Elmendorf
Tearing Strength (ASTM D-1424-59) 725 grams 630 grams 640 grams
Stoll Flex Abrasion Resistance (ASTM D-1175-61T) (using head and
tension loads of 1/2 and 2 pounds respectively) 490 280 430
______________________________________
EXAMPLE 2
Table II shows the data for a series of samples of print-cloth
treated in accordance with this invention. First the samples were
padded with various aqueous solutions containing from 5 to 20
percent formaldehyde, which in each case also included 3 percent
softener in the form of finely dispersed acrylic polymer (Rhoplex
K-87 Latex). In addition, in the case of Sample II-16 the pad bath
included 66 percent aqueous isopropanol instead of water as the
aqueous solvent; in the case of Sample II-17, the pad bath further
included 5 percent tripropylene glycol monomethyl ether as a
humectant; and in the case of Sample II-18, 5 percent "Span 20"
sorbitan monolaurate. Excess solution was expressed from the
samples on a pad roll to leave about 65 percent wet pick-up based
on the weight of the fabric and the samples were then cured by
being exposed for various times to a stream of hot vapors of
SO.sub.2 at widely different conditions in a 100 liter cylindrical
aluminum reactor such as the one described in U.S. Pat. No.
3,706,526 at column 7, lines 30-38.
In the case of Samples II-5, II-6 and II-7, the padded fabrics were
dried in an air oven at 75.degree. C. for 3 minutes, 4 minutes and
3 minutes, respectively, before exposure to the hot SO.sub.2 vapors
in the reaction chambers; all the other samples were placed in the
reaction chamber without pre-drying. Of course, the samples
progressively dry out in the reaction chamber in any event as the
hot treating gas is passed over them.
TABLE II
__________________________________________________________________________
PRINTCLOTH FABRICS TREATED WITH AQUEOUS FORMALDEHYDE AND CROSSLINKS
BY HEATING IN PRESENCE OF SULFUR DIOXIDE
__________________________________________________________________________
Wrinkle Recovery Angle.sup.b SO.sub.2 Air Reaction (W + F)
Tearing.sup.b Sample Pad Bath Flow Rate.sup.a Flow Rate Temp. Time
Dry Wet Strength No. (% CH.sub.2 O) (cc/min) (cc/min) (.degree.C.)
(min) (degrees) (degrees) (grams)
__________________________________________________________________________
II-1 5 4 400 80 7 303 294 440 II-2 5 4 400 80 5 248 257 660 II-3 10
8 400 80 5 300 296 470 II-4 10 8 400 80 10 295 292 400 II-5 10 8
400 80 5 293 286 400 II-6 10 8 400 80 5 266 269 540 II-7 10 8 400
80 4 303 284 400 II-8 10 24 200 100 5 323 289 350 II-9 10 24 200
100 4 263 254 790 II-10 10 200 0 105 5 332 320 220 II-11 10 200 0
105 4 328 313 240 II-12 20 200 0 120 3 346 338 280 II-13 20 200 0
120 2 329 317 380 II-14 5 4 200 120 2 314 297 410 II-15 5 4 200 120
3 315 295 400 II-16 10 4 400 120 5 302 309 420 II-17 1 4 400 140 5
316 283 420 II-18 1 4 400 140 5 304 286 300 Untreated Control n.a.
n.a. n.a. n.a. n.a. 166 129 750
__________________________________________________________________________
Properties After 10 Laundering Cycles (W + F) Wrinkle Recovery
Angle Tearing Sample Dry Wet Strength No. (degrees) (degrees)
(grams)
__________________________________________________________________________
II-1 272 272 400 II-2 225 260 600 II-3 300 285 380 II-4 284 287 390
II-5 308 283 400 II-6 -- -- -- II-7 303 281 410 II-8 -- -- -- II-9
-- -- -- II-10 -- -- -- II-11 -- -- -- II-12 -- -- -- II-13 334 311
300 II-14 320 284 450 II-15 315 281 460 II-16 306 280 400 II-17 304
281 340
__________________________________________________________________________
n.a. not applicable .sup.a The exact concentration of SO.sub.2 in
the reactor was not determined. .sup.b After 1 laundering cycle
Upon conclusion of the treatment the essentially dry and neutral
samples were removed from the reactor and washed and tumble dried
so that their durable press ratings could be determined. These
ratings were determined after one such laundering-drying cycle and
after 10 such cycles.
As can be seen from Table II, high degrees of dry and wet recovery
could be obtained under a wide variety of treating conditions, with
formaldehyde concentrations in the pad bath ranging from as little
as 1 percent up to 20 percent.
At high SO.sub.2 concentrations ad at a temperature of 120.degree.
C. (Samples II-10, II-11, II-12 and II-13), the crosslinking
reaction proceeds very rapidly such that very high degrees of
wrinkle recovery are achieved in 2 minutes or less, whereas at
longer reaction times the fabric becomes progressively weaker due
to exposure to the large amount of strong acid formed in the
process.
If the fabric is dried to a relatively low initial moisture content
prior to heating in the presence of catalyst-forming SO.sub.2,
lower wrinkle recoveries are obtained in this system than when the
reaction is initiated at a relatively higher moisture content under
otherwise similar conditions. (Compare Samples II-6 with Samples
II-5 and II-7.)
At relatively high initial moisture contents and relatively low
reaction temperatures, higher wrinkle recoveries may be obtained by
increasing the reaction time or the SO.sub.2 concentration in the
treating atmosphere. Compare Sample II-2 with Samples II-1 and
II-3, and Sample II-9 with Samples II-8 and II-11.
EXAMPLE 3
In this series of tests, samples of twist twill cotton fabric of
7.8 oz./sq. yd. weight were padded with an aqueous solution
containing 7.5 percent formaldehyde and 10 percent "Rhoplex K-87"
finely dispersed acrylic polymer, excess solution was expressed
from the samples on a pad roll to leave about 65 percent wet pickup
based on the weight of the fabric, the samples were then exposed
for 1 to 5 minutes (as shown in Table III) to a stream of SO.sub.2
gas at a temperature of 20.degree. C. in the reactor described in
Example 2 and then (except in the case of Samples III-8 and III-9,
which were not further treated) the fabrics containing formaldehyde
and SO.sub.2 absorbed therein were cured for 5 minutes in an oven
which had been preheated to 150.degree. C.
In the case of Samples III-1, III-2 and III-3, the padded fabrics
were partially dried in air at room temperature to an estimated
moisture content of about 10 percent on weight of fabric before
being placed in the reactor and exposed to the SO.sub.2 gas.
Samples III-4, III-5, III-6, III-8 and III-9 were partially dried
for 5 minutes in an air oven at 80.degree. C. to reduce their
moisture before exposure to the SO.sub.2 gas; and Sample III-7 was
exposed to the SO.sub.2 wet, without any significant drying between
padding and exposure to the SO.sub.2 gas. Samples III-1 through
III-7 were washed and tumble dried after their high temperature
cure while Samples III-8 and III-9 were washed and tumble dried
directly after the SO.sub.2 treatment before the durable press
properties of these samples were determined. The results are shown
in Table III.
TABLE III
__________________________________________________________________________
TWILL COTTEN FABRICS TREATED WITH AQUEOUS FORMALDEHYDE AND SULFUR
DIOXIDE AND THEN HEATED
__________________________________________________________________________
Stoll Flex (degrees) Wrinkle Recovery Angle Abrasion Sample
SO.sub.2 Exposure Postheating Time Dry Wet Warp No. Time (min) at
150.degree. C. (min) Warp Fill Warp Fill (cycles)
__________________________________________________________________________
III-1 1 5 156 144 151 136 248 III-2 3 5 161 152 155 148 132 III-3 5
5 167 148 164 151 90 III-4 1 5 123 120 134 130 843 III-5 3 5 154
132 149 132 704 III-6 5 5 162 140 154 134 221 III-7 1 5 167 150 170
162 48 III-8 1 0 84 90 82 84 1202 III-9 5 0 92 82 88 86 1748
Untreated Control -- -- 80 74 76 72 505
__________________________________________________________________________
Tensile Properties Warp Fill Work-to Extension Breaking Work-to
Extension Breaking Sample Rupture at Break Strength Rupture at
Break Strength No. (in-lb) (%) (lb) (in-lb) (%) (lb)
__________________________________________________________________________
III-1 9.1 9.0 87.1 1.9 13.2 21.8 III-2 6.1 8.0 70.7 1.6 9.9 16.0
III-3 6.0 8.2 69.6 1.6 10.2 16.5 III-4 18.4 13.6 120.0 2.5 12.0
24.6 III-5 12.1 10.6 99.2 3.0 12.2 27.6 III-6 7.9 8.9 79.5 2.6 12.3
24.6 III-7 2.5 6.4 48.0 1.1 9.2 10.6 III-8 36.6 22.1 163.1 12.1
19.1 66.1 III-9 34.8 21.8 158.3 11.9 20.0 67.2 Untreated Control
30.5 13.4 171.0 11.2 17.2 66.7
__________________________________________________________________________
Samples III-1 through III-7, which had the SO.sub.2 gas applied
thereto at room temperature and were then oven cured, all exhibited
a high degree of wrinkle recovery. (In comparing Tables II and III,
it should be noted that in Table II the reported wrinkle recovery
angles are the sum of the values measured in the warp and in the
fill directions, whereas in Table III each of these two values is
reported separately.)
Sample III-7, which was not conditioned prior to exposure to the
SO.sub.2 gas, evidently underwent the highest degree of
crosslinking, as indicated by the high wrinkle recovery angles.
However, its tensile properties also were the lowest among those
reported, because of fabric degradation due to the relatively large
amount of strong acid present in the hot cure in this case.
At the other extreme, Samples III-8 and III-9 which were not heat
cured after treatment with the SO.sub.2 gas at room temperature
showed only an insignificant improvement in durable press
properties and only comparatively minor changes in tensile
properties as compared with the untreated control, although the
increase in tearing strength obtained as a result of the cool
SO.sub.2 treatment is worth noting.
In the absence of a final high temperature cure, little difference
is observed between the oven dried Sample III-8 which was exposed
to SO.sub.2 gas for 1 minutes and the similarly dried Sample III-9
which was exposed to SO.sub.2 gas for 5 minutes. On the other hand,
a comparison between Samples III-4, III-5 and III-6 shows that the
extent of formaldehyde crosslinking of the fibers increases with an
increase in time of the SO.sub.2 pretreatment. This is reflected
both in the increasingly high recovery angles and in the decreasing
tearing strengths. Evidently, more acid catalyst is present in the
high temperature cure as the duration of the SO.sub.2 pretreatment
of the moist fabric is increased. A similar effect is observed when
Samples III-1, III-2 and III-3 are compared with each other.
An increased intensity of treatment is also observed when one
compares Sample III-1 against III-4, III-2 against III-5, and III-3
against III-6. Evidently, more moisture and therefore more acid
catalyst is present in the samples which were conditioned in air at
room temperature prior to the SO.sub.2 treatment than in those
which were conditioned by being partially dried at 80.degree. C.
for a short time.
No attempt was made in this series of tests to optimize either the
initial moisture conditioning or the final curing conditions.
However, the tests demonstrate that SO.sub.2 can be absorbed in the
formaldehyde-containing aqueous phase in the fabric at relatively
low temperature prior to curing the fabric at an elevated
temperature.
EXAMPLE 4
Still another procedure was used in this series of tests in
depositing an aqueous phase containing formaldehyde and SO.sub.2 in
samples of the twist twill fabric described in Example 3 prior to a
final curing step. In this series the fabrics were padded with a
bath containing 3 percent acrylic polymer solids (Rhoplex K-87
Latex), partially dried in an air oven for 5 minutes at 80.degree.
C., exposed to formaldehyde-sulfur dioxide vapors at 120.degree. C.
for 1 minute in the reactor described in Example 2 above, removed
from the reactor and then immediately post-cured by being placed
for 5 minutes in an air oven which had been preheated to a specific
temperature between 120.degree. and 160.degree. C., as indicated in
Table IV. The cured samples were finally washed and tumble dried as
usual before determining their durable press and tensile
properties. For control purposes, in the case of Sample IV-11 the
final post-curing step was omitted.
To test their durable press and tensile properties, the treated
samples were washed in detergent and tumble dried and their wrinkle
recovery angles, wash-wear ratings and tensile properties were
measured in the conventional manner.
As can be seen from Table IV, very high crease recoveries were
obtained in the case of all samples with the exception of Sample
IV-11 which was not post-cured. In the latter case, the 1 minute
treatment with formaldehyde and SO.sub.2 vapors at 120.degree. C.
in the absence of any added steam was insufficient to permit
crosslinking of the cellulose with formaldehyde to proceed to the
desired extent. On the other hand, in all the other cases the heat
soaking step immediately following the formaldehyde-SO.sub.2 vapor
treatment of the moist fabric produced a good balance of durable
press and tensile properties. This shows that exposure of a moist
fabric to
TABLE IV
__________________________________________________________________________
CONDITIONED TWIST TWILL FABRICS EXPOSED TO FORMALDEHYDE - SULFUR
DIOXIDE FOR ONE MINUTE AND THEN HEAT SOAKED AT
120.degree.-160.degree. C.
__________________________________________________________________________
Properties After 1 Washing Wrinkle Recovery Angle Stoll Flex
(degrees) Abrasion Sample Heat-Soaking Temp Warp Fill Wash-Wear
Warp No. (.degree.C.) Dry Wet Dry Wet Rating (cycles)
__________________________________________________________________________
IV-1 160 143 145 122 126 3.6 270 IV-2 160 144 149 130 136 4.3 460
IV-3 150 150 148 128 122 4.2 440 IV-4 150 150 145 138 130 4.0 430
IV-5 140 150 146 130 125 4.0 300 IV-6 140 156 147 132 133 4.2 380
IV-7 130 162 166 138 144 4.1 380 IV-8 130 155 154 141 126 4.3 220
IV-9 120 150 144 122 128 4.2 510 IV-10 120 141 140 133 130 4.0 670
IV-11 (Not Cured) 97 104 104 107 2.5 1190 Properties After 25
Washings IV-1 160 120 130 111 114 3.2 370 IV-2 160 131 140 120 122
3.8 350 IV-3 150 136 135 117 110 3.8 270 IV-4 150 146 143 131 123
4.0 330 IV-5 140 140 140 120 116 3.9 340 IV-6 140 140 140 124 122
4.0 340 IV-7 130 144 150 130 130 3.7 250 IV-8 130 140 138 128 126
4.0 260 IV-9 120 108 131 106 108 4.0 460 IV-10 120 126 138 118 118
3.9 610 IV-11 (Not Cured) 96 97 86 95 2.0 1240 Untreated Control
n.a. 96 74 86 75 n.a. 870
__________________________________________________________________________
Properties After 1 Washing Tensile Properties Warp Fill Work-to-
Extension Tensile Work-to- Extension Tensile Sample Rupture at
Break Strength Rupture at Break Strength No. (in.-lb) (%) (lb)
(in.-lb) (%) (lb)
__________________________________________________________________________
IV-1 11.7 14.4 91 3.7 12.8 33 IV-2 10.8 14.0 83 3.3 13.4 32 IV-3
10.5 13.6 87 4.1 14.6 38 IV-4 12.2 15.6 92 3.1 14.4 30 IV-5 10.0
13.6 84 3.7 14.4 34 IV-6 10.5 14.2 84 2.9 12.7 30 IV-7 11.8 14.3 92
2.6 20.0 28 IV-8 10.2 14.0 84 3.1 12.6 32 IV-9 12.5 14.8 94 4.1
13.1 38 IV-10 17.1 16.8 106 3.2 12.4 31 IV-11 34.7 21.2 152 9.5
16.8 61 Properties After 25 Washings IV-1 10.0 14.1 82 4.6 13.4 43
IV-2 11.3 15.8 86 2.5 11.4 30 IV-3 10.7 15.6 86 3.1 12.5 32 IV-4
10.5 15.3 82 2.6 12.6 30 IV-5 11.8 15.2 92 3.1 12.8 32 IV-6 14.2
17.2 98 2.6 12.4 30 IV-7 11.9 16.0 92 2.8 13.2 31 IV-8 8.7 14.1 78
3.2 12.9 34 IV-9 14.4 16.3 99 3.9 12.2 39 IV-10 13.5 15.9 99 3.4
13.2 34 IV-11 40.8 26.6 147 8.7 16.0 60 Untreated Control 14.0 21.1
162 10.6 19.1 64
__________________________________________________________________________
formaldehyde and SO.sub.2 vapors under mild conditions which are
insufficient to impart the desired durable press properties to the
fabric can in fact form a catalyzed reactive aqueous formaldehyde
phase in the fabric such that the latter, having a proper initial
moisture content, can be subsequently crosslinked to the desired
extent by further heat treatment without adding any more SO.sub.2
or formaldehyde to the system.
It should be understood, of course, that even in the case of a
vapor treatment such as that used in preparing Sample IV-11
satisfactory durable press properties can be obtained directly by a
proper control of treating conditions as disclosed in our U.S. Pat.
No. 3,706,526, without any separate post-cure, e.g., by applying
the vapor treatment to the initially moist fabric at a higher
temperature or for a longer time or under more moist conditions, as
by reducing the rate of vapor flow through the reactor or by adding
stream to such vapors, or by a combination of these factors.
A procedure of this type, involving chemical pretreatment under
relatively mild conditions followed by a separate heat soaking step
of the pretreated, preconditioned fabric in hot air or a hot
air-steam mixture under controlled moisture conditions may be
particularly advantageous in the continuous processing of flat
fabrics.
The effects of moisture content, of amount of formaldehyde durably
fixed in the fabric and of additive pretreatments are similar in
this system wherein formaldehyde is applied in liquid phase, as in
the vapor phase system described in parent application Ser. No.
706,792 filed Feb. 20, 1968 and now abandoned, and in U.S. Pat. No.
3,706,526 which was filed as a continuation-in-part of the
former.
While all of the above runs were conducted at atmospheric pressure,
sub- or superatmospheric pressures may be used but are not
necessary.
The essential principles, as well as the preferred embodiments and
modes of operating of the present invention have been described in
the foregoing specification. However, the invention which is
intended to be protected herein may be practiced otherwise than as
described without departing from the scope of the appended
claims.
* * * * *