Gas phase radical polymerization for fabric treatment

The present invention relates to a process of modifying a fabric by conducting gas-phase polymerization in the presence of the fabric, fabrics obtainable by such process, the use of the fabrics and the use of specific polymer mixtures for the modification of fabrics.

In order to improve or modify the properties of fabrics, a tremendous amount of effort has been made. In the field of textile finishing, polymer coating has been of great importance as a tool for surface modification, for example to impart fabrics with water repellency and soil releasing characteristics.

While the finishing with a perfluoroalkylated polymer is useful to prevent a fabric from soiling, it is still unavoidable for the fabric to be more or less soiled. When the soiled fabric is immersed in water for laundering, the water/soil repellent finish works adversely. The preference of the treated fabric surface for oily soils, compared to water-borne soils, is stronger in water, resulting in poor soil releasing properties (Sharman, P.O. et al. Textile Research Journal 1969, 39, 449-459). In order to solve this problem, incorporation of hydrophilic moieties to the perfluoroalkylated polymer has been intended. For example, a block copolymer consisting of fluorine-containing segments and poly(alkylene oxide) segments has been proposed for soil releasing, in which the block copolymer changes its conformation. The hydrophobic fluorine-containing segments and the hydrophilic poly(alkylene oxide) segments are reversibly oriented outward in the air and aqueous environments, respectively (Sharman, P.O. et al. Textile Research Journal 1969, 39, 449- 459).

Hydrophilic treatment of polyester fabrics has been a matter of importance to the textile industry as soil-release and/or antistatic finish. Polyethyleneterephthalate (PET) itself is basically hydrophobic, it behaves similarly to water/soil repellent finishing in that it repels water and water-borne soil like dust, dirt, beverages, etc., but it tends to be stained by oily materials, which means once it is stained, it is hard to wash off the soil by laundry. Therefore, PET fabrics commonly undergo hydrophilic treatment to impart them with soil releasing as well as antistatic properties.

To take water repellent finishing as an example, the finishing agents typically contain a

perfluoroalkylated polymer as a main ingredient. Perfluoroalkylated polymers have excellent water repellency properties resulting from very low surface free energy attributed to the perfluoroalkyl moiety (I. Holme in Textile Finishing, D Heywood, Ed (Bradford, West Yorkshire, UK: Society of Dyers and Colourists, 2003) 166-198). Fluorinated polymers, however, have two major drawbacks. First, adhesion to a fabric is very poor and lacks laundry durability, and secondly, the treated fabric tends to lose its softness. In order to enhance the durability, functional groups or a cross-linking agent is usually incorporated in the polymer for internal cross-linking and/or grafting to the textile, which more or less results in further deterioration of the softness. Silicone softeners are conveniently used to compensate the softness, but they tend to weaken the water repellency generated by the fluorinated polymer.

Since water repellents are usually used in the form of emulsions, additional problems arise. First, commercial water repellents usually contain organic solvents and surfactants to stabilize the emulsion, as well as ingredients for processing aid and other purposes, and these chemicals usually have adverse effects on the repellency and in wastewater treatment. Secondly, the emulsion bath for padding tends to be contaminated during operation with chemicals such as dyes used in the preceding processes. Another issue is associated with the particle size in the emulsion. The particles formed in emulsion polymerization have an average size of about 0.1 micrometer, which limits the minimum thickness of the coating and, in turn, the utilization efficiency of the polymer. These disadvantages can be anticipated with not only water-repellent treatment but also soil releasing, as long as the treatment is carried out in a polymer emulsion or solution.

Liquid-phase graft polymerization in the presence of a substrate is also a known technique for surface treatment, for example in emulsion, solution, and bulk polymerization. In the case of textile finishing, emulsion polymerization is not applicable because it is impossible to emulsify a fabric. Solution and bulk polymerization are also problematic because most of the initiator or catalyst molecules are in the liquid phase away from the fabric surface and a lot of free polymer is formed in vain. In order to decrease the amount of the non- deposited polymer, immobilization of the initiator or catalyst on the fabric surface may sometimes be possible but requires additional processing steps and is costly.

In order to avoid the above-mentioned disadvantages associated with liquid phase processing, gas-phase treatments seem to be promising. Direct deposition of coating

material on a substrate and in situ polymerization are known techniques. As a means for textile finishing, included in this category are plasma polymerization, and catalytic or photo-catalytic polymerization in the gas/vapor phase.

Much work on plasma treatment has been done to impart hydrophilic (Masuoka, T. et al. Nippon Kagaku Kaishi 1995, (2) 144-149) or hydrophobic (WO 00/14296) properties to a textile. Although plasma polymerization on the surface of an organic substrate usually leads to durable coatings because of grafting reactions, the reaction involves a variety of active species, resulting in poor control of the architecture of the polymer. Plasma treatments have usually to be carried out under a pressure typically lower than 100 Pa, which is another disadvantage of plasma coating.

The catalytic or photo-catalytic gas-phase polymerization of vinyl monomers in the presence of a solid substrate including fabrics has also been investigated to modify the surface properties of the substrate. From a practical point of view, the effect of modification must be able to last for a long period of time. Naturally, grafting of the polymer chains onto the substrate is thought to be favorable to enhance the durability, as is the case with liquid-phase in situ polymerization. For example, K. Hayakawa et al. reported that acrylic esters were radically graft polymerized on a cotton swatch by UV or gamma-ray irradiation without an initiator, resulting in water repellency (Hayakawa, T. et al. in Textile Research Journal 1971 , 41 , 461-462).

It should be noted that cellulosic materials are generally more reactive than noncellulosic materials like polyesters, and grafting onto cotton can more easily occur, while graft polymerization onto non-cellulosic materials was rarely successfully achieved by gas- phase radical polymerization of vinyl monomers by using a conventional initiator or initiating system.

In EP 138224 A2 gas-phase graft polymerization without immobilization of an initiator is described. This document teaches a method of gas-phase graft polymerization, which is applicable to a wide variety of polymeric substrates including PET, as long as the substrate is capable of forming initiation sites upon attack of free radicals derived from a radical polymerization initiator. In other words, the applicable substrates according to EP 138224 A2 are limited to polymeric materials susceptible to the attack of free radicals ("susceptible substrates"). In reality, as shown in Examples 1 and 2 of the present

invention, it is considerably difficult to induce grafting onto non-cellulosic materials, for example PET, even though it is exemplified as an applicable substrate in EP 138224 A2.

Thus, treatment method with a long-lasting effect is required that is applicable not only to "susceptible substrates" but also "non-susceptible substrates".

In particular, there is a need to provide a process in which coating of a fabric with a polymer emulsion by dip and nip padding is avoided in order to eliminate or lessen disadvantages associated with an aqueous bath, contamination control of the liquor and wastewater treatment. To the contrary a solvent-free treatment throughout the whole process is highly appreciable.

Another aim is to increase efficiency of utilizing initiators and monomers for fabric coating. In the case of liquid-phase polymerization, the use of an initiator chemically bound to the fabric is effective to increase the monomer utilization, but the immobilization is costly.

Further it should become possible to control the polymer structure to optimize the modification and to use not only reactive fabric materials but also inert or less reactive materials in a modification process.

According to the present invention there is provided a process making use of a specific monomer mixture to be polymerized in a gas-phase deposition polymerization, imparting various functions to a fabric, like water repellency, soil releasing and the like, combined with excellent durability, and even humidity dependant property control of some fabrics, as for example in case of cellulosic fabrics.

Therefore the present invention provides a process of modifying a fabric, comprising the steps of

1) contacting a fabric with a radical polymerization initiator,

2) heating the fabric and/or exposing the fabric to ultraviolet light, while the fabric comes in contact with a mixture of ethylenically unsaturated monomers in the gaseous state, where the mixture of ethylenically unsaturated monomers contains at least one monomer having at least two ethylenically unsaturated groups and at least one monomer having one ethylenically unsaturated group,

whereby the mixture of ethylenically unsaturated monomers is deposited on the fabric by thermally and/or photochemically induced radical polymerization.

The steps of the present invention can be described in more detail as follows.

Step 1): Contacting the fabric with the initiator can e.g. be effected by impregnation, adsorption, absorption or a combination thereof. For instance a swatch of fabric can be soaked in a solution containing a radical polymerization initiator. Subsequently the solvent can be eliminated completely in vacuo at room temperature. In another possible embodiment a swatch can be placed in a chamber filled with a vaporized initiator for a prescribed period of time at an elevated temperature.

Generally speaking, an initiator is non-covalently and/or covalently deposited on a fabric in gas phase or liquid phase in the present invention, depending on the susceptibility of the substrate.

In the context of the present invention the term "in gas phase" means that the initiator contacts the substrate directly from gas phase without interaction in liquid phase. This does, however, not mean that the gas phase in the process according to the present invention must be completely free from micro-droplets or particles. It is also within the scope of the present invention that the gas phase contains microdroplets or particles of the initiators that can be spread in the gas phase by a carrier gas, depending on the method of introducing the initiator. It is, however, preferred that the gas phase according to the present invention is essentially or truly free of such micro-droplets or particles.

Contacting the fabric with the initiator through the gas phase can be carried out using a carrier gas. A carrier gas is a substance that is in the gaseous state at the operating conditions of the present invention. Preferably a substance is used as the carrier gas that is in the gaseous state below 100 ⁰ C, more preferably below 40 ⁰ C under normal pressure. Suitable carrier gases are essentially inert toward the initiators, monomers and substrates under the reaction conditions, and thus do not take part in the reaction itself. Gases like He, Ne, Ar, N ₂ , CO ₂ , H ₂ O and the like can be used.

The adsorption of the initiator takes place in a vessel of any shape or size as long as it can host the fabric. Suitable vessels can preferably be tightly sealed against the

surrounding atmosphere.

In case of gas-phase adsorption or absorption, initiators are introduced into the vessel in the gaseous state. This can generally be done by any method known to the skilled person, like evaporation under reduced pressure and gasification in a carrier gas flow, using a bubbler or spray. The initiator and the monomers are usually fed to the vessel separately and stepwise because preferred operating conditions for the initiator adsorption/absorption are not necessarily the same as those for polymerization. However, simultaneous feeding of the initiator and the monomers is possible.

The adsorption of the initiator can generally be performed at a temperature of from about - 80 to about 200 ⁰ C, depending on the thermal stability of the initiator and the fabric material. In a preferred embodiment the temperature ranges from about 0 ⁰ C to about 150 ⁰ C, more preferably from about 20 to about 100 ⁰ C.

Generally, the time required for contacting the initiator with the fabric can vary in a wide range, e.g., from about 1 minute to about 5 days, depending on the vapor pressure of the initiator, the affinity between the initiator and the substrate, and the quantity of the initiator to be deposited. In a preferred embodiment of the present invention, the deposition time ranges from about 1 minute to about 10 hours, preferably from about 10 minutes to about 1 hour. The deposition can be performed either batchwise or continuously.

The impregnation of the substrate with the initiator can also be achieved in liquid phase, by contacting a solvent or solvent mixture containing the initiator with the substrate by means of a method known to those skilled in the art, for example, padding, spraying, etc.

Basically, any kind of fabric can be used as a substrate in the present invention as long as it has enough affinity with an initiator. In the context of the present invention, the term "fabrics" includes woven and non-woven fabrics, knitted or crocheted fabrics, textiles, yarns, filaments, staples, fibers, and the like made of or consisting of natural fibers and/or man-made fibers.

Natural fibers comprise fibers grown in nature, like vegetable fibers, animal fibers or mineral fibers. Examples for vegetable fibers are e.g. polysaccharide fibers like cotton, flax or hemp, whereby cotton is most preferred in the present invention. Animal fibers are

e.g. wool or silk, while examples of mineral fibers comprise asbestos.

Man-made fibers are for example fibers derived from natural polymers, synthetic polymers or inorganic fibers, by means of controlled chemical reactions in a chemical-technical way. Man-made fibers derived from natural polymers or natural fibers comprise for example regenerated cellulose or cellulose acetates. Examples of man-made mineral fibers comprise glass fibers, ceramic fibers, carbon fibers, silicate fibers and metallic fibers.

However the most preferred man-made fibers of the present invention are synthetic polymers obtained as polycondensation, polymerization or polyaddition products. Examples for polycondensation products comprise polyesters, polyamides, polycarbonates, polycarbamides and mixed poly-co-condensates of these polymers. As polyadducts polyurethanes are to be mentioned, while polymerization products e.g. comprise polyolefines, like polyethylenes and polypropylenes, polydienes, polyvinylidenes and polyvinylic polymers like polyvinylchloride, polyvinyl alcohols, polystyrene, polyacrylonitrile and mixed polymerization products of the aforementioned products.

Any radical initiator known to those skilled in the art can be used as the initiator according to the present invention. In the case of an adsorption or absorption from the gas-phase, the initiator should have enough vapor pressure at the operation temperature. Suitable for the gas-phase adsorption are, for example, peroxides, like tert-butyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl cumyl peroxide, 2,2'-bis(tert-butylperoxy) butane, tert-butyl peroxyacetate, tert-butyl peroxybenzoate and OO-tert-butyl O-isopropyl peroxycarbonate, 2-hydroxy-2-methylpropiophenone, benzoin isobutyl ether, methyl benzoylformate, 2,2'- azobis(2-methyl butyronitrile), dimethyl 2,2'-azobis(isobutyrate), diethyl 2,2'- azobis(isobutyrate) and the like. Preferred initiators are those that are liquid and have a higher vapor pressure at the operating temperature, like di-tert-butyl peroxide. Light- sensitive initiators, for example, 2-hydroxy-2-methylpropiophenone, are also preferably used in combination with UV irradiation.

In the case of adsorption from liquid phase, a wider variety of initiators can be used compared with gas phase adsorption, without limitation regarding the vapor pressure.

In the present invention, initiators can be used alone or in combination of two or more.

Further photosensitizers, for example, benzophenone and anthraquinone may be used together with the initiators.

The amount of the initiator on the substrate preferably ranges from 0.1 to 5000 micromol/g-substrate, more preferably from 10 to 500 micromol/g-substrate.

Step 2): Heating the fabric and/or exposing the fabric to ultraviolet light, while the fabric comes in contact with the monomer mixture of the present invention can for example be carried out in a reactor filled with such mixture of gaseous/vaporized ethylenically unsaturated monomers and the fabric from step 1. The reactor can be heated up to a prescribed temperature, preferably ranging from 20 to 150 ⁰ C and/or the fabric is irradiated by UV light having a wavelength of preferably 200 to 400 nm under the atmosphere of the monomer gas/vapor. Thus, gas phase radical polymerization in the presence of a fabric is effected.

In the context of the present invention the term "gas phase radical polymerization" means radical polymerization where the monomers contact the substrate directly from gas phase without interaction in liquid phase. This does, however, not mean that the gas phase in the process according to the present invention must be completely free from micro-droplets or particles. It is also within the scope of the present invention that the gas phase contains microdroplets or particles of the monomers that can be spread in the gas phase by a carrier gas, depending on the method of introducing the monomers. It is, however, preferred that the gas phase according to the present invention is essentially or truly free of such micro-droplets or particles.

The contact of the monomers with the substrate through the gas phase can be carried out using a carrier gas. A carrier gas is a substance that is in the gaseous state at the operating conditions of the present invention. Preferably a substance is used as the carrier gas that is in the gaseous state below 100 ⁰ C, more preferably below 40 ⁰ C under normal pressure. Suitable carrier gases are essentially inert toward the initiators, monomers and substrates under the reaction conditions, and thus do not take part in the reaction itself. Gases like He, Ne ₁ Ar, N ₂ , CO ₂ , H ₂ O and the like can be used.

The contact of the monomers with the fabric takes place in a reactor of any shape or size

as long as it can host the fabric. Suitable reactors can preferably be tightly sealed against the surrounding atmosphere. Preferably the polymerization reaction is carried out in the same vessel used for the gas-phase initiator impregnation in step 1.

The monomers are introduced into the reactor in the gaseous state. This can generally be done by any method known to the skilled person, like evaporation under reduced pressure and gasification in a carrier gas flow, using a bubbler or spray. The monomers are usually fed to the reactor after the initiator is ad/absorbed. However, simultaneous feeding of the initiator and the monomers is possible.

The monomers can be fed to the reactor successively or simultaneously in combination of two or more in order to yield a crosslinked copolymer. Since the gas-phase polymerization according to the present invention has the nature of a living polymerization, the monomer having at least two ethylenically unsaturated groups does not have to be introduced to the reactor simultaneously with the co-monomers.

Any radically polymerizable monomer can be used according to the present invention as long as it has enough vapor pressure for polymerization. Preferred monomers are those that have a vapor pressure of higher than 2 kPa at 150 ⁰ C, more preferably higher than 5 kPa at 120 ⁰ C from an industrial point of view. Even if one or more of the polymerizable monomers have low vapor pressure values, it might be possible to vaporize those monomers, e. g. by azeotropic vaporization with one or more of the other radically polymerizable monomers having higher vapor pressure values.

Monomers having only one ethylenically unsaturated group, preferably one vinyl group are chosen depending on what kind of properties are required from the end product. As for a water-, oil- or soil-repellent finish, fluorine-containing monomers, like 2,2,3,3,3- pentafluoropropyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 2- (perfluoroalkyl)ethyl acrylates are preferred. On the other hand, hydrophilic monomers such as N-vinyl-2-pyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid and methacrylic acid are preferable in obtaining hydrophilic coatings. Further, e.g. 2-(tert-butylamino)ethyl methacrylate and its analogues may be used. The latter one and its analogues possess an antimicrobial effect employable to manufacture a fabric with an antimicrobial finishing. However, any of the monomers having only one ethylenically unsaturated group or having at least two ethylenically unsaturated groups can be chosen

among monomers showing antimicrobial effects, as long as they fulfill the essential features of the present invention.

The presence of monomers having at least two ethylenically unsaturated groups, preferably vinyl groups, is indispensable for the purpose of the present invention. Suitable multifunctional monomers include, for example, polyolesters of acrylic acid and methacrylic acid like, in particular di(meth) acrylic and tri(meth)acrylic esters of a polyol as for example ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, 1 ,3-butylene glycol dimethacrylate, di(ethylene glycol) diacrylate, di(ethylene glycol) dimethacrylate, etc. Also N.N'-methylene bisacrylamide and divinyl benzenes can conveniently be used.

The molar feeding ratio of monomers having one ethylenically unsaturated group to the monomers having at least two ethylenically unsaturated groups ranges preferably from 1 : 100 to 100: 1 , more preferably from 1 : 10 to 10: 1.

In case the fabric consists of a "non-susceptible substrate", i.e. a substrate that is not susceptible to the attack of free radicals, depending on the ratio of the monomers in the monomer mixture as well as the kind of monomers, a variety of modifications of the fabrics can be achieved.

As an example, a PET fabric treated with acrylic acid (hydrophilic monomer with one ethylenically unsaturated group) and ethylene glycol dimethacrylate (monomer having two ethylenically unsaturated groups) according to the method of the present invention shows hydrophilicity, which withstands repeated washing, while another one treated with acrylic acid only, lacks durability.

The reason why the treatment according to the present invention brings about the laundry resistance has not fully understood yet, but a possible reason is crosslinking, which makes the deposited polymer insoluble. Possibly interpenetrating polymer networks (IPN) or IPN-like structures are formed; some of the monomers and the initiating radicals generated by decomposition of the initiator diffuse into nanometer-sized spaces between polymer chains of the substrate in amorphous parts and polymerize in the spaces, resulting in the IPN or IPN-like structures composed of the newly formed polymer chains and the substrate polymer chains. The monomer having at least two ethylenically

unsaturated groups, may cause branching and/or crosslinking, which may help to maintain the tangled structure. Thus, grafting, i.e. covalent bond of the polymer formed during the polymerization reaction of the monomers, is not necessary to achieve a long-lasting finish.

In the case of natural fibers, in particular polysaccharide fibers like cotton, incorporating the monomer having at least two ethylenically unsaturated groups brings about an unexpected phenomenon in addition to durability. As illustrated in Example 3 later, a cotton fabric treated by gas-phase copolymerization of 2- hydroxyethylmethacrylate and ethylene glycol dimethacrylate shows hydrophilic/hydrophobic switching property according to the humidity of the environment. The cotton fabric thus treated is useful as a water-repellent and soil-releasing material for clothes and others.

Therefore a further object of the present invention is a fabric onto which a product of a radical polymerization of a mixture of ethylenically unsaturated monomers is covalently and/or non-covalently deposited, whereby this mixture comprises at least one monomer having at least two ethylenically unsaturated groups and at least one monomer having one ethylenically unsaturated group.

In a preferred embodiment of the present invention, the fabric onto which the product of the radical polymerization is essentially non-covalently deposited, is made of a synthetic polymer selected from the group comprising polycondensation products, addition polymerization products and polyaddition products as described for the process of the present invention.

Most preferably such polycondensation products are selected from the group comprising polyesters, polyamides, polycarbonates, polycarbamides and mixed poly-co-condensates of these polymers.

However, in yet another embodiment of the present invention the fabric onto which the product of the radical polymerization is deposited may consists of or be made of a natural fiber, preferably a polysaccharide fiber.

The mixture of ethylenically unsaturated monomers being covalently and/or non- covalently deposited onto the fabric by a radical polymerization reaction are preferably selected from acrylic acid esters, acrylic acid, methacrylic acid esters, methacrylic acid,

acrylamides, methacrylamides, N-vinyl-2-pyrrolidone, styrene and its derivatives, and the fluorinated and perfluorinated derivatives thereof in case of the monomers having one ethylenically unsaturated group. In case of the monomers having at least two ethylenically unsaturated groups, the monomers are preferably selected from the polyol esters of acrylic acid and methacrylic acid, and divinylbenzenes.

It is especially preferred, when the molar feeding ratio of the at least one monomer having one ethylenically unsaturated group to the at least one monomer having at least two ethylenically unsaturated groups is from 1 :10 to 10:1.

In yet another embodiment of the present invention the fabric according to the present invention possesses a static contact angle of water after drying the fabric at 110 ⁰ C for 30 min of at least 90°, preferably at least 100°, most preferably at least 120 °, measured 2 min after placing a water droplet of 20 μl_ onto the fabric. Such fabrics are further apt to absorb a water droplet of 20 μl_ placed onto the fabric, after being stored for 24 h at 23 ⁰ C and a relative humidity of 90%, within less than preferably 5 minutes, more preferably less than 2 minutes and most preferably less than 1 minute. The fabric used for this embodiment is preferably selected from the group of natural fibers. Most preferably polysaccharide fibers like cotton are used. However, any hydrophilic fiber with some susceptibility to the initiator is preferable. In this embodiment of the present invention it is preferred that the polymer built during the radical polymerization reaction is covalently bound to the fabric via graft polymerization.

The fabrics of the present invention are obtainable by the process of the present invention.

A further object of the present invention is the use of the fabrics of the present invention or obtained by the process of the present invention in the manufacture of, for example, clothing, socks and hosiery, shoes, upholstery, curtains and draperies, carpets, bedclothes, outdoor and indoor furniture, and industrial textile items.

Yet another object of the present invention is the use of a mixture of ethylenically unsaturated monomers in the gaseous state, where the mixture of ethylenically unsaturated monomers contains at least one monomer having at least two ethylenically unsaturated groups and at least one monomer having one ethylenically unsaturated group

for modifying fabrics by covalently or non-covalently depositinga polymer obtained through thermally and/or photochemically induced radical polymerization of the mixture of ethylenically unsaturated monomers onto a fabric. The conditions for an exemplified use of the invention are described in detail for the process of the present invention.

In the following the present invention is exemplified by examples.

EXAMPLES:

Example 1 (Hydrophobic treatment for aramid fabrics)

(A) Copolymerization

An aramid fabric (Nomex®, poly-meta-phenylene isophthalamide, 3cm x 3cm) was soaked for 20 minutes in 2OmM 2,2'-azobisisobutyronitrile (AIBN) in acetone, air dried for about 30 minutes, and then completely dried for about 30 minutes in vacuo at room temperature.

Gas phase copolymerization of 2,2,3,3,3-pentafluoropropylmethacrylate (FMA) and ethylene glycol dimethacrylate (EGDMA) was carried out in an H-shaped glass tube reactor, which comprised three parts, i.e. a thick leg (diameter 70 mm, height 70 mm) to accommodate the fabric, with a quartz plate cap on top of it; a thin leg (diameter 25 mm, height 70 mm) as the liquid monomer reservoir, equipped with a vacuum stopcock on top of it; and a bridge (diameter 20 mm, length 40mm), or a passage for vaporized monomer gas to diffuse from the liquid monomer reservoir to the fabric housing.

The aramid fabric was placed in the fabric housing, and a monomer mixture of FMA (1 ml_; approx. 5.85 mmol) and EGDMA (1 ml_, approx. 5.31 mmol) was introduced to the monomer reservoir. After three times of freeze-pump-thaw cycle to eliminate oxygen, the reactor was sealed in vacuo. Then, the reactor was settled in an oven kept at 8O ⁰ C for 12 hours. Thus, gas-phase copolymerization was effected.

After the polymerization, the fabric was set in a vacuum chamber for 5 hours at room temperature to eliminate adsorbed monomers.

The fabric product was subjected to measurement of static contact angles to a water droplet of 20 μl_, using an optical goniometer (model DropMaster 500, Kyowa Interface Science Co., Ltd.). The contact angle was observed at room temperature over a period of 10 minutes. The measurement was repeated 4 times at different points of the fabric and the average value was employed.

After measuring the contact angles, the fabric was subjected to extraction by tetrahydrofuran (THF) for 13 hours using a Soxhlet's extractor. Then, contact angles were

measured again in the same manner as above to see laundry and dry cleaning resistance.

(B) FMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 ml. of FMA was introduced to the monomer reservoir instead of the monomer mixture.

(C) EGDMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 ml. of EGDMA was introduced to the monomer reservoir instead of the monomer mixture.

The contact angles observed in (A), (B), and (C) are summarized in Table 1.

Table !

Static water contact angles of meta-aramid fabrics treated by gas-phase in-situ polymerization

Note 1 : Original aramid fabric absorbed a water droplet within 1 minute. Therefore, the contact angle was unstable and cannot be measured.

Note 2: The contact angle values are those observed 10 minutes after placing a water droplet on the fabric.

Treatment (A), copolymerization of FMA and EGDMA, resulted in water repellency even after the extraction. Treatment (B), FMA homopolymerization, also resulted in water repellency but the fabric lost the repellency after the extraction, meaning the treatment would not withstand washing and dry cleaning. Treatment (C), EGDMA homopolymerization showed little water repellency even before the extraction.

Example 2 (Hydrophilic treatment for polyester fabrics)

(A) Copolymerization

The H-shaped glass tube reactor used in Example 1 was also used for the treatment of

polyethyleneterephthalate fabrics, Monofiber (l)-8, JIS L 0803 (standard adjacent polyester fabric for staining of color fastness test, obtained from Japanese Standards Association).

The polyester fabric (3cm x 4cm) was placed in the fabric housing part, and 1 mL of an initiator (2-hydroxy-2-methylpropiophenone, HMPP) was introduced to the reservoir part. While the reservoir was cooled by liquid nitrogen, the reactor was evacuated by a vacuum pump, and then sealed in vacuo. The reactor was settled in an oven kept at 80 ⁰ C for 1 hour. Thus, the fabric was impregnated with HMPP from gas phase.

After the initiator impregnation, the remaining initiator in the bottom of the reservoir was replaced with a monomer mixture of 1 mL (approx. 14.57 mmol) of acrylic acid (AA) and 1 mL (approx. 5.31 mmol) of ethylene glycol dimethacrylate (EGDMA).

After three times of freeze-pump-thaw cycle to eliminate oxygen, the reactor was sealed in vacuo. Then, the reactor was settled in an oven kept at 40 ⁰ C for 1 hour, while the fabric was exposed to UV light through the cap plate made of quartz. The light source was a 500W high-pressure mercury-xenon lamp in Universal Arc Lamp Housing Model 66901 from Oriel Instrument, which was set at a distance of 5 cm from the fabric surface. Thus, gas-phase copolymerization was effected.

After the polymerization, the fabric was set in a vacuum chamber for 5 hours at room temperature to eliminate adsorbed monomers.

The fabric product was subjected to measurement of static contact angles to a water droplet of 20 μL in the same manner as Example 1. The contact angle was observed over a period of 6 minutes. The measurement was repeated 4 times at different points of the fabric and the average value was employed.

After measuring the contact angles, the fabric was subjected to laundry, in which the fabric was stirred for 1 hour in 3 L of tap water containing 2.3g of Attack®, a commercial home laundry detergent supplied by Kao Corporation, followed by 3 times of rinse in 3L of tap water, each. The laundry was repeated up to 10 times. The fabric was air dried for 24 hours, and then subjected to measurement of contact angles again in the same manner as the above to see laundry resistance.

(B) AA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 mL of AA was introduced to the monomer reservoir instead of the monomer mixture.

(C) EGDMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 mL of EGDMA was introduced to the monomer reservoir instead of the monomer mixture.

The contact angles observed in (A), (B), and (C) are summarized together with those of a non-treated polyester fabric in Table 2.

Table 2

Static water contact angles of polyester fabrics treated by gas-phase in-situ polymerization

Monomer Before laundry After 3 times laundry After 10 times laundry

(A) AA + EGDMA absorbed within absorbed within 0.5 absorbed within 0.5 0.5 min min min

(B) AA absorbed within 0.5 absorbed within 2 absorbed within 5 min min min

(C) EGDMA 85° 85° 45°

Ref. No treatment 85° 85° 35°

Note: The contact angle values are those observed 6 minutes after placing a water droplet on the fabric.

As shown in Table 2, Treatment (A), copolymerization of AA and EGDMA resulted in good hydrophilicity even after 10 times of laundry. In the case of Treatment (B), in which only AA was used for polymerization, the fabric gradually lost hydrophilicity along with repeated laundry. Treatment (C), homopolymerization of EGDMA showed little hydrophilicity; the treated fabric was as hydrophobic as the original polyester fabric.

Example 3 (Switchable hydrophilic/hydrophobic treatment for cotton fabrics)

(A) Copolymerization

The H-shaped glass tube reactor used in Example 1 was also used for the treatment of cotton fabrics (Monofiber (I) 3, JIS L 0803 (standard adjacent cotton fabric for staining of color fastness test, obtained from Japanese Standards Association)).

The cotton fabric (35mm x 55mm) was placed in the fabric housing part, and 1 ml. of an initiator (benzoin isobutyl ether, BIBE) was introduced to the reservoir part. While the reservoir was cooled by liquid nitrogen, the reactor was evacuated by a vacuum pump, and then sealed in vacuo. The reactor was settled in an oven kept at 80 ⁰ C for 1 hour. Thus, the fabric was impregnated with BIBE from gas phase.

After the initiator impregnation, the remaining initiator in the bottom of the reservoir was replaced with a monomer mixture of 1 ml. (approx. 8.24 mmol) of 2- hydroxyethylmethacrylate (2-HEMA) and 1 mL (approx. 5.31 mmol) of ethylene glycol dimethacrylate (EGDMA).

After three times of freeze-pump-thaw cycle to eliminate oxygen, the reactor was sealed in vacuo. Then, the reactor was settled in an oven kept at 40 ⁰ C for 2 hours, while the fabric was exposed to UV light through the cap plate made of quartz. The light source was a 500W high-pressure mercury-xenon lamp in Universal Arc Lamp Housing Model 66901 from Oriel Instrument, which was set at a distance of 10 cm from the fabric surface. Thus, gas-phase copolymerization was effected.

After the polymerization, the fabric was set in a vacuum chamber for 24 hours at room temperature to eliminate adsorbed monomers.

The fabric product was put for 30 minutes under "dry conditions", meaning that a fabric was put in an oven kept at 110 ⁰ C. Then, after cooling down in a desiccator, the fabric was subjected to measurement of static contact angles to a water droplet of 20 μl_ in the same manner as Example 1. The measurement was repeated 4 times at different points of the fabric and the average value was employed.

After measuring the contact angles of the dry fabric, the fabric was put for 24 hours under "humid conditions", 23 ⁰ C and relative humidity higher than 90 %. Then, the fabric was

subjected to measurement of static contact angles to a water droplet.

(B) 2-HEMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 2 mL of 2- HEMA were introduced to the monomer reservoir instead of the monomer mixture.

(C) EGDMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 2 mL of EGDMA were introduced to the monomer reservoir instead of the monomer mixture. The contact angles observed in (A), (B), and (C) are summarized together with those of a non-treated cotton fabric in Table 3.1.

Table 3.1

Static water contact angles of cotton fabrics treated by gas-phase in-situ polymerization

Note: The contact angle values are those observed 2 minutes after placing a water droplet on the fabric

As shown in Table 3.1 , Treatment (A), copolymerization of 2-HEMA and EGDMA resulted in either hydrophobicity or hydrophilicity according to humidity of the environment. Treatment (B), in which only 2-HEMA was used for polymerization, resulted in quick absorption of water droplets; no water repellency was observed. On the other hand, Treatment (C), homopolymerization of EGDMA did not bring about water repellency; the water droplets were retained for more than 10 minutes on the fabric surface.

In order to confirm the hydrophobicity/hydrophilicity switchability of the cotton fabric (A) in Table 3.1 , which was treated by gas-phase copolymerization of 2HEMA and EGDMA, the fabric was subjected to "dry conditions" and "humid conditions" three times alternately, and the contact angles to a water droplet were measured each time. The results are shown in Table 3.2 below.

Table 3.2 Static water contact angle of (A) after repeated drying and humidifying

Note: Water contact angle values are those observed 10 minutes after placing a water droplet on the fabric

Thus, the fabric (A) repeatedly became hydrophobic every time when subjected to "dry conditions", and retained the hydrophobicity at least for 10 minutes.

Example 4 (Hydrophobic treatment for aramid fabrics)

(A) Copolymerization

Exactly the same experiment as the case (A) of Example 1 was carried out, except that 0.5 ml. (approx. 2.93 mmol), instead of 1.0 ml_, of EGDMA was introduced to the monomer reservoir, and extraction by THF was carried out for 24 hours instead of 13 hours.

(B) FMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 mL of FMA was introduced to the monomer reservoir instead of the monomer mixture.

(C) EGDMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 mL of EGDMA was introduced to the monomer reservoir instead of the monomer mixture.

The contact angles observed in (A), (B), and (C) are summarized in Table 4.

Table 4

Static water contact angles of meta-aramid fabrics treated by gas-phase in-situ polymerization

Note 1 : original aramid fabric absorbed a water droplet within 1 minute. Therefore, the contact angle was unstable and cannot be measured.

Note 2: The contact angle values are those observed 10 minutes after placing a water droplet on the fabric.

The effect of copolymerizing EGDMA, a multifunctional monomer, was also observed as Example 1 , although the concentration of EGDMA in the gas-phase is lower than Example 1.

Example 5 (Hydrophobic treatment for aramid fabrics)

(A) Copolymerization

Exactly the same experiment as the case (A) of Example 1 was carried out, except that Twaron® (poly-para-phenylene terephthalamide) instead of Nomex® (poly-meta- phenylene isophthalamide) was used as a substrate fabric, 16 mg of N ₁ N'- methylenebisacrylamide (NMBA) instead of 1.0 ml_, of EGDMA was introduced to the monomer reservoir, and extraction by THF was carried out for 24 hours instead of 13 hours.

(B) FMA homopolymerization

Exactly the same experiment as the case (A) was carried out, except that only 1 mL of FMA was introduced to the monomer reservoir instead of the monomer mixture.

The contact angles observed in (A) and (B) are summarized in Table 5.

Table 5

Static water contact angles of para-aramid fabrics treated by gas- phase in-situ polymerization

Note 1 : original aramid fabric absorbed a water droplet within 5 seconds. Therefore, the contact angle was unstable and cannot be measured properly.

Note 2: The contact angle values are those observed 10 minutes after placing a water droplet on the fabric.

The effect of copolymerizing NMBA, a multifunctional monomer, was observed.