Process For Improving The Antistatic Properties Of Hydrophobic Synthetic Fibers

Abstract

The antistatic properties of hydrophobic synthetic fibers are improved by treatment with an aqueous mixture containing at least one copolymer prepared by copolymerization of a mixture of (I) monoester selected from alkoxy-polyalkyleneglycol-acrylates or alkoxy-polyalkylene-glycol-methacrylates and (II) diester selected from diacrylates and dimethacrylates of polyols. An improvement in the treatment is made by addition of (III) acrylonitrile or vinyl esters of alkyl-alcohols with more than 8 carbon atoms to the copolymerization mixture in order to increase the durability of the antistatic properties of the fibers as a result of laundering and dry cleaning, and to improve the handling qualities.

Parent Case Text

This is a continuation-in-part of our copending U.S. application Ser. No. 812,418, filed on Apr. 1, 1969 now abandoned.

Description

BACKGROUND OF THE INVENTION

The present invention relates to antistatic agents and process usable for treatment of hydrophobic synthetic fibers.

Synthetic fibers such as fibers manufactured from polyethylene-terephthalate, polyacrylonitrile or polyamide are used independently or in various combinations with natural fibers for numerous applications. As these synthetic fibers are generally hydrophobic, they have a tendency to become electrostatically charged when they are used for clothing or floor coverings. The static charge causes clothing made from these synthetic fibers to cling to the body of the wearer, makes the clothing more susceptible to soiling, and produces a sound as it discharges when the clothing is removed. Static charge is produced when fibers, filaments or fabric repeatedly rub together which prevents normal spinning, drawing, twisting, weaving and knitting operations.

Various methods for preventing the occurrence of static and antistatic agents for removing the static producing properties of such hydrophobic synthetic fibers are known. For commercial use, an antistatic agent is required to possess a strong antistatic property, high durability against laundering and dry cleaning, and the ability to improve, or at least not degrade, the handling qualities of the fabric on which it is used. However, it has been very difficult to obtain an antistatic agent which satisfies these requirements. For example, the antistatic agent disclosed in British Patent No. 852,399 having the general formula

has a high antistatic effect but is easily removed by laundering and dry cleaning. Certain other antistatic agents degrade the handling quality or the coloring of the fibers considerably.

In order to overcome these defects, methods are known of using copolymers of the aforementioned compounds and a linking functional group such as a compound containing a methylol group or an epoxy group, or acrylonitrile. However, the former has the following limitations:

1. Insufficient stability of the dispersing liquid

2. Curing must be carried out

3. The fibers discolor on curing

4. Durability is insufficient

Also, durability is not sufficient in the latter case.

SUMMARY OF THE INVENTION

The object of this invention is to provide antistatic agents and a process for antistatic treatment which bestows superior antistatic property to hydrophobic fibers.

Another object of this invention is to provide antistatic agents and a process for antistatic treatment which bestows a durable antistatic property to hydrophobic fibers.

A further object of this invention is to provide antistatic agents and a process for improving the handling quality of hydrophobic fibers without discoloring them.

It has been discovered that antistatic compounds which bestow superior antistatic properties to hydrophobic fibers can be obtained by copolymerizing a mixture of (I) alkoxy-polyalkylene-glycol-acrylate or alkoxy-polyalkyleneglycol-methacrylate and (II) a diester which is a diacrylate or dimethacrylate of a polyol.

Fabric having a combination of desirable properties including antistatic characteristics with high durability against both laundering and dry cleaning and excellent handling qualities is readily obtained by treatment of the fabric with a mixture of components I and II in such proportion that the gelating concentration of the mixture is in the range of about 14 to 30 percent.

DESCRIPTION OF THE INVENTION

Component (I) of the antistatic agent of the present invention is a compound which has the general formula

wherein R.sub.1 is selected from the group consisting of H, CH.sub.3 and C.sub.2 H.sub.5, R.sub.2 is selected from the group consisting of OH, alkoxy radicals having not more than 18 carbon atoms, halogen, alkyl-sulfide radicals having not more than 18 carbon atoms, a mono- or dialkylamine containing not more than 18 carbon atoms, phenoxy radicals and naphthoxy radicals, and l and m are satisfied with the formulas 10 .ltoreq. l .ltoreq. 100 and 0 .ltoreq. m < l.

Component (I) is prepared by reacting a lower-alkyl monoether of polyalkyleneglycol and an acid chloride of acrylic or methacrylic acid in the presence of pyridine. It is important that the value of l be 10 or above and up to 100 and more preferably above 20 and below 70. The antistatic properties of a copolymer with the value of l below 10 are ineffective. Also, when the value of l exceeds 100, polymerizability is low and durability is insufficient. Component (I) is hydrophilic and provides the antistatic properties in the resultant copolymer.

Component (II) is selected from diacrylates or dimethacrylates of polyols such as ethylene glycol, propylene glycol, polyethyleneglycol and polypropyleneglycol. Component (II) acts as a linking agent to provide three-dimensional structure to the copolymer thereby improving its durability during laundering and dry cleaning.

Polymerization of components (I) and (II) is carried out by the conventional methods. That is, the two components are heated in water in the presence of a free radical polymerization catalyst such as a potassium, sodium and ammonium persulfate and hydrogen peroxide, or a redox polymerization catalyst such as a mixture of the aforementioned oxidizing agent as the free radical catalyst and a reducing agent such as sodium sulfite, sodium hydrogen sulfite, sodium thiosulfate, oxalic acid and ferrous sulfate.

A characteristic of the copolymer of the present invention is that it can be obtained by carrying out the copolymerization reaction in water. When the copolymerization is carried out in organic solvents such as dimethyl sulfoxide, dimethyl-formamide or dimethyl acetamide, it is necessary to add a dispersing agent in order to disperse the copolymer in the fiber-treating solution. When fibers are treated by a copolymer obtained from a reaction carried out in an organic solvent, the handling property of the fiber is degraded, i.e., the texture becomes undesirably hard.

The treating temperature is generally determined by the activity of the catalyst used. The copolymerization is carried out in the range of room temperature of 100.degree.C., preferably in the range of 30.degree.-60.degree.C. It is necessary to prevent gelation in the above-mentioned two component copolymerization reaction. For this purpose, the copolymerization temperature must be controlled very carefully.

Gelation in this copolymerization system is related to the kind of components used and their relative proportions. The gelating concentration of the copolymerization system in this specification is defined as the minimum concentration, with respect to the weight of the total copolymerization system, required to cause gelation, of a mixture of about 20 c.c. of a mixture of components (I) and (II) dissolved in dimethyl sulfoxide to which 0.2 g./l. of sulfuric acid and 0.02 mol/l. of azobisisobutylnitrile are added when heated for 24 hours at 55.degree.C. The entire mixture is sealed in an ampule of 18 m.m. inside diameter and about 120 m.m. length, and copolymerization is carried out for 24 hours at 55.degree.C. in a rotating hot bath at 4 r.p.m.

It is necessary to maintain the gelating concentration of the copolymerization system in a range of 14-30 percent by weight in order to obtain the copolymer of the present invention. The copolymerization system is very unstable when the gelating concentration is below 14 percent and the process is difficult to carry out commercially. When the gelating concentration is above 30 percent, the copolymer obtained is very soluble in water and as a result it is easily removed by operations such as scouring, dyeing and laundering. A copolymer obtained by a copolymerization system with the gelating concentration in a range of 14 - 30 percent has a desirable three-dimensional structure; it is insoluble in water and organic solvents and, furthermore, it has suitable dispersing properties and superior adhesive properties toward fibers. Consequently, the antistatic property of textile products treated with such a copolymer has excellent durability against laundering and dry cleaning. A copolymer having superior permanency can be obtained from a copolymer system having a gelating concentration in a range of 17 - 27 percent.

The copolymer of the present invention can be further improved by using acrylonitrile or a vinyl ester of higher alcohols having more than eight carbon atoms as component (III). This improves the handling quality and durability of the treated fiber.

A copolymer containing acrylonitrile is obtained by means of the same method as that described above with a composition of 5 - 45 percent by weight relative to the total polymer weight. A copolymer containing a vinyl ester of a higher alcohol is prepared in an emulsion copolymerization system with a composition of 20 - 60 percent. The specific viscosity of a copolymer containing acrylonitrile is in the range of 0.3 - 1.0. It is desirable that the optical transmittance of a 1 percent dispersion in a solvent be greater than 45 percent.

The specific viscosity of the copolymer dispersion is determined in the following way. The relative viscosity of the dispersion containing the copolymer in an amount of 1 percent by weight based on the weight of the dispersion is measured by means of an Ostwald's viscometer at a temperature of 30.degree.C., and then the specific viscosity is calculated from the value of the relative viscosity.

Also, transmittance of the copolymer dispersion is obtained as follows; the copolymer is dispersed in water with a mixture of Nonipol 70 (Trademark of Sanyo Chemical Co. in Japan) and Sunmorine OT-70 (Trademark of Sanyo Chemical Co. in Japan) in a proportion 6:1, so that the copolymer and the mixture is contained in the dispersion in an amount of 0.25 and 0.025 percent by weight based on the weight of the dispersion, respectively. The dispersion of the copolymer is charged in a quartz cell with a measurement width of 10 m.m., and then transmittance of the dispersion in the cell is measured by way of Hitachi-Perkin-Elmer 139 UV-VIS Spectrophotometer.

The vinyl ester suitable for the copolymer of the present invention is selected from vinyl esters of higher alcohols which have more than 8 carbon atoms, such as the acrylates and methacrylates of octyl, decyl, undecyl, dodecyl, palmityl or stearyl alcohol, i.e., preferably alcohols containing 8 - 18 carbon atoms.

If the number of carbon atoms is less than eight, the copolymer obtained has a tendency to make the handling quality of the synthetic fiber hard and the durability against laundering is insufficient.

The application of the copolymer of the present invention to a synthetic fiber is carried out by preparing a water-dispersion of the copolymer, dipping the synthetic fiber in this water dispersion, removing excess moisture by squeezing and then drying the fiber. This water-dispersion contains 0.1 - 6 percent copolymer by weight based on the weight of the dispersion.

It is desirable to allow the copolymer in an amount of 0.1 - 8 percent by weight based on the weight of the fiber, preferably 0.2 - 2 percent, to remain on the textile product, which has been dipped in the copolymer-dispersion after squeezing. If the remaining quantity of the copolymer exceeds 8 percent o.w.f., the handling quality of the fiber becomes undesirable or the fibers adhere to each other. On the other hand, if the remaining quantity is less than 0.1 percent, the antistatic property is insufficient.

It is desirable to carry out drying of the squeezed goods at a temperature in a range of 80.degree. - 200.degree.C. It is not necessary to carry out curing after drying because the copolymer of the present invention has a three-dimensional structure. Also, there is no possibility of discoloring of the fibers by heating at a high temperature.

Synthetic fibers which can be treated by the process of the present invention include polyacrylonitrile fibers, polyamide fibers, polyester fibers, polyvinyl alcohol fibers and polypropylene fibers, and these may be used independently or as a mixture with rayon or natural fibers such as cotton or wool. Synthetic fibers which are particularly suitable for the process of the present invention are polyacrylonitrile fiber and acrylonitrile copolymer fiber, such as a copolymer of acrylonitrile and at least one copolymer component such as methyl acrylate, methyl methacrylate, sodium styrene sulfonate, sodium methacrylate sulfonate, sodium acryl sulfonate, 2-methyl-5-vinyl pyridine, vinyl chloride and vinylidene chloride. Such polyacrylonitrile fiber is manufactured by the wet-spinning process. That is, acrylonitrile polymer dissolved in an organic solvent such as dimethyl sulfoxide, dimethyl acetamide, dimethyl formamide and sodium thiocyanate is extruded from a spinneret into a coagulation solution, drawn and then washed with water. This water-washed fiber is an aquagel swollen by water and has a relatively large internal surface area. It is desirable for the polyacrylonitrile fiber on which the process of the present invention is applied to be an aquagel having an internal surface area from 35 to 160 m.sup.2 /g. The internal surface area is measured by the following method. The fiber is dipped in liquid nitrogen to freeze the fiber and fix its structure and then vacuum dried slowly at about -5.degree.C. This dried fiber is used as the sample for measuring by the BET method, that is, the method developed by Brunnaer-Emmett-Teller which utilizes physical absorption of gas on the substance to be determined.

Substance absorbed nitrogen Cross-section of absorbed molecule 1.62 = 10.sup.-.sup.9 m.sup.2 /molecule Absorption temperature -195.3.degree.C.

generally, polyacrylonitrile fiber aquagel has an internal surface area from 20 to 300 m.sup.2 /g. When the swollen acrylonitrile fiber is dried, the fiber structure becomes dense and the internal surface area becomes small, and, when this area value becomes larger than 160 m.sup.2 /g., it is difficult for the antistatic polymer to diffuse into the interior of the fiber; as a result, the durability of the antistatic effect is reduced. Also, the strength of fibers with an internal surface area below 3.5 m.sup.2 /g. is insufficient and cannot be put to practical use. One improvement of the process of the present invention is that the polyacrylonitrile fiber which has been impregnated with a dispersion containing the copolymer is then subjected to steaming at a temperature of at least 90.degree.C., preferably above, and dried. As a result of steaming, the copolymer adheres strongly to the fiber and removal of the copolymer from the treated fiber in the spinning and winding processes is prevented.

The objects, composition and effects of the present invention are further explained with reference to the following examples which, except for the reference examples included for purposes of comparison, illustrate the best mode currently contemplated for carrying out the invention but which must not be construed as limiting the invention in any manner.

EXAMPLE 1

Methoxy-polyoxyethyleneglycol-methacrylate (PEGM) was prepared from methacrylyl chloride in an amount of 1.2 moles and methoxy-polyethyleneglycol having an average molecular weight 1100 in an amount of 1.0 mole in the presence of pyridine as the catalyst. Polyethyleneglycol-dimethacrylate (PEGDM) was prepared from methacrylyl chloride in an amount of 3 moles and methoxy-polyethyleneglycol having an average molecular weight 100 in an amount of 1.0 mole in the presence of sulfuric acid as the catalyst. The gelating concentration of the methoxy-polyethylene-glycol-methacrylate obtained was 32 percent by weight and that of poly-ethylene-glycol-dimethacrylate was 4 percent. Six different mixtures, M.sub.1 to M.sub.6, shown in Table 1, were prepared from this methoxy-polyoxyethyleneglycol-methacrylate and polyethyleneglycol-dimethacryl-ate. The mixing ratios and the gelating concentrations of these are shown in Table 1.

TABLE 1

Mixture PEGM PEGDM Gelation No. (Wt. %) (Wt. %) Concentration (%) __________________________________________________________________________

M.sub.1 100 0 32 M.sub.2 96.5 3.5 26 M.sub.3 94 6 22 M.sub.4 92 8 19 M.sub.5 90 10 16 M.sub.6 82 18 12 __________________________________________________________________________

next, 10 parts by weight of acrylonitrile and 90 parts by weight of the mixture shown in Table 1 were dissolved in 90 parts by weight of water purified by ion-exchange, 0.3 part by weight of potassium persulfate and 0.1 part by weight of sodium hydrogensulfite were added to this solution while stirring at 200 r.p.m. and the copolymerization carried out at a temperature of 40.degree.C. for 4 hours. The six polymers obtained are designated A.sub.1 to A.sub.6, corresponding respectively to the six mixtures M.sub.1 to M.sub.6. However, 1300 parts by weight of ion-exchanged water was used for the polymer system using mixture M.sub.6 because the copolymerization system is unstable due to the low gelating concentration of the mixture M.sub.6. However, the gelation in the copolymerization system using the mixture M.sub.6 took place very easily and as a result, satisfactory copolymerization could not be carried out.

Next, an antistatic polyacrylonitrile type fiber with a fineness of 3 denier was manufactured according to the following process. Twenty-two parts by weight of a mixture containing 94.5 mole percent of acrylonitrile 5 mole percent of sodium styrene sulfonate, 0.3 part by weight of azo-bis-isobutylonitrile-dodecyl-mercaptan, one part by weight of water and 0.06 part by weight of dodecylmercaptan were dissolved in 76 parts by weight of dimethyl sulfoxide within a polymerization vessel and adjusted to pH of 4 by adding sulfuric acid. Polymerization of this mixture was carried out by heating at a temperature of 50.degree.C. for 40 hours with mechanical agitation. The polymer content of the polymer solution thus obtained was 20.2 percent by weight. This polymer solution was extruded through a spinneret orifice having a diameter of 0.07 mm. solidified in an aqueous solution of 50 percent by weight of dimethyl sulfoxide. This was drawn to 6 times in an aqueous solution containing 30 percent by weight of dimethyl sulfoxide at a temperature of 98.degree.C. The fibers thus obtained were next washed with water. The washed fibers in the aquagel condition were dipped respectively in the aforementioned 5 polymer solutions, A.sub.1 to A.sub.5, (copolymer content 0.8 percent by weight percent), squeezed to 100 percent liquid content based on the weight of the fiber with squeezing rolls and dried for 3 minutes at 170.degree.C.

The five thus-treated acrylonitrile type fibers and the untreated fibers were knitted respectively into 6 knitted products K.sub.1 to K.sub.5 and K.sub.B, and laundered 5 times with an electric laundering machine under the following conditions:

Laundering solution 3 g./1 an ion surface active agent Liquor ratio 1 : 40 Temperature 40.degree.C. Time Laundering 40 minutes, rinsing 5 minutes.

The moisture content of the laundered, knitted products was adjusted for 72 hours in a conditioning chamber of 40 percent RH, 20.degree.C., and the frictional static voltage and half-value period were measured with a rotary static tester manufactured by Koa Shokai. The results are given in Table 2.

TABLE 2

Knitted Monomer Frictional Static Half-value Product Mixture Voltage (V) Period (sec.) No. No. K.sub.1 M.sub.1 4800 25.0 K.sub.2 M.sub.2 1900 5.2 K.sub.3 M.sub.3 1500 3.7 K.sub.4 M.sub.4 1300 3.5 K.sub.5 M.sub.5 1500 3.2 K.sub.B 8300 300<

Knitted product K.sub.1 was knitted with fibers treated with a polymer which does not contain diester of polyols, i.e., polyethyleneglycol-dimethacrylate, and knitted products K.sub.2 to K.sub.5 were treated with the polymers of the present invention containing methoxy-polyoxyethyleneglycol-methacrylate and polyethyleneglycol-dimethacrylate, while K.sub.B was knitted with fibers on which antistatic treatment had not been applied. Table 2 indicates that the frictional static voltage and the half-value period of knitted products K.sub.2, K.sub.3, K.sub.4 and K.sub.5 are less than those of knitted products K.sub.1 and K.sub.B, and consequently have superior antistatic property. It is therefore, clear that a copolymer containing polyethyleneglycol-dimethacrylate as a component has better antistatic effect and durability than that which does not contain it.

EXAMPLE 2

Methoxy-polyethyleneglycol-methacrylate prepared in Example 1 was mixed with the seven different divinyl compounds shown in Table 3 and each of the seven mixtures, M7 to M13, had a gelating concentration of 22 percent.

TABLE 3

Mixture Divinyl Compound No. __________________________________________________________________________ M.sub.7 Ethyleneglycol dimethacrylate M.sub.8 Propyleneglycol dimethacrylate M.sub.9 Polyethyleneglycol dimethacrylate M.sub.10 Divinyl sulfone M.sub.11 Divinyl carbitol M.sub.12 Divinyl ketone M.sub.13 Divinyl benzene __________________________________________________________________________

In case of mixtures M.sub.7 to M.sub.11, 90 parts by weight of the mixture and 10 parts by weight of acrylonitrile were dissolved in 900 parts by weight of purified water.

Each of the copolymers A.sub.7 to A.sub.11 corresponding to the mixtures M.sub.7 to M.sub.11 was prepared by the addition of 0.3 part by weight of potassium persulfate and 0.1 part by weight of sodium hydrogen sulfite to each of the mixtures with stirring and then each of the mixtures was subjected to copolymerization for 5 hours at a temperature of 40.degree.C.

In the case of mixtures M.sub.12 and M.sub.13, 90 parts by weight of the mixture and 10 parts by weight of acrylonitrile were dissolved in 830 parts by weight of dimethyl sulfoxide. To each of polymers A.sub.12 and A.sub.13 obtained from mixtures M.sub.12 and M.sub.13 were added 0.3 part by weight of azo-bis-isobutylonitrile with stirring and polymerized for 35 hours at 50.degree.C. Separately, mixture M.sub.9 was copolymerized using dimethyl sulfoxide, the same as in the cases of M.sub.12 and M.sub.13, to obtain polymer A.sub.14.

Copolymers A.sub.7 to A.sub.11 could be dispersed stably in water but the dispersed solutions of A.sub.12 to A.sub.14 were unstable.

The acrylic fiber, same as that used in Example 1, was treated with an aqueous dispersion of 0.8 percent by weight of each of copolymers A.sub.7 to A.sub.11 or an aqueous dispersion containing 0.8 percent by weight of each of copolymers A.sub.12 to A.sub.14 and Nonipole 78 (Trademark of Sanyo Chemical Co.) of 10 percent by weight based on the weight of the copolymer in the same manner shown in Example 1, and then the eight differently treated fibers having a fineness of 3 denier were obtained.

The eight fibers thus obtained were knitted and the eight knitted products thus obtained were laundered in accordance with the manner of Example 1 and the frictional static voltage and half-value period of static charge of the products were measured in the manner of Example 1. The results are shown in Table 4.

TABLE 4

Knitted Linking Frictional product mixture static Half-value no. no. Solvent voltage (V) period (sec) __________________________________________________________________________ K.sub.7 M.sub.7 1800 5.2 K.sub.8 M.sub.8 1900 7.2 K.sub.9 M.sub.9 water 1100 3.5 K.sub.10 M.sub.10 4500 34 K.sub.11 M.sub.11 4700 53 K.sub.12 M.sub.12 4200 42 K.sub.13 M.sub.13 DMSO 4300 39 K.sub.14 M.sub.14 2200 4.5 K.sub.B -- 8300 300< __________________________________________________________________________

table 4 provides the following facts:

1. Knitted products K.sub.7, K.sub.8 and K.sub.9 which were treated with copolymer containing diacrylate and dimethacrylate as the linking component monomer have better antistatic effects than in the case containing other divinyl compounds as the linking component.

2. Knitted product K.sub.9 treated with copolymer prepared in water as the solvent of the component monomers has better antistatic effects than the product K.sub.14 using dimethyl sulfoxide as the solvent.

3. Each of knitted products K.sub.12 to K.sub.14 treated with water dispersions of the polymers A.sub.12 to A.sub.14 copolymerized by using dimethyl sulfoxide as the solvent of the component monomers has poor qualities of softness and undesirable handling.

Consequently, it is desirable to use diacrylate and methacrylate of polyols as the linking component monomer of the copolymer. Also, it is necessary to use water as the solvent for the monomers.

EXAMPLE 3

Three mixtures M.sub.15 to M.sub.17 were prepared in accordance with the compositions shown in Table 5 with the same methoxy-polyoxyethyleneglycol-methacrylate described in Example 1, the vinyl monomer having a linking functional group, i.e., N-methylol acrylamide (N-MAM) or glycidyl methacrylate (GMA), and sodium styrene sulfonate (SSS).

TABLE 5

Mixture No. Composition (wt%) __________________________________________________________________________ M.sub.15 PEGM/N-MAM 85/15 M.sub.16 PEGM/N-MAM/SSS 70/10/20 M.sub.17 PEGM/GMA-SSS 55/10/35 M.sub.18 PEGM/PEGDM/AN 64/6/30 __________________________________________________________________________

also, M.sub.18 is a mixture of methoxy-polyoxyethyleneglycol-methacrylate, polyethyleneglycol-dimethacrylate and acrylonitrile (AN) as shown in Table 5. Each of the mixtures in an amount of 10 parts by weight was dissolved in water in an amount of 90 parts by weight together with potassium persulfate in an amount of 0.3 part by weight and sodium hydrogen sulfite in an amount of 0.1 part by weight and the solution was subjected to copolymerization at 40.degree.C. for 4 hours. In the case of mixture M.sub.17, glycerol mono-oleate of 1 percent by weight based on the weight of the mixture was added into the solution as the emulsifier for glycidyl methacrylate. Polymers A.sub.15 to A.sub.18 were obtained from mixtures M.sub.15 to M.sub.18 in the above-mentioned manner. However, in the case of copolymer A.sub.15 and A.sub.16, potassium persulfate of 5 percent by weight was used as a polymerization catalyst, and in the case of copolymer A.sub.7, dimethylaminomethylphenol of 5 percent by weight was used as a catalyst.

Next, the same polyacrylonitrile type fiber described in Example 1, was treated according to the manner of Example 1 using an aqueous dispersion of 0.8 percent by weight of the polymers A.sub.15 to A.sub.18 to obtain treated fibers with a fineness of 3 denier. The drying temperatures of the dipped fibers were 80.degree. and 150.degree.C. and the times were 15 minutes each. The four knitted products K.sub.15 to K.sub.18 prepared from these fibers were laundered in the manner of Example 1 and degree of coloration, frictional static voltage and half-value period of static charge of the knittings were measured. The results were shown in Table 6.

TABLE 6

Frictional static Drying Degree of voltage of Half tempera- Co- coloration laundered value Fiber ture polymer of treated knitted period No. (.degree.C.) No. fibers product (V) (sec) __________________________________________________________________________ F.sub.15 A.sub.15 7.5 3800 17 F.sub.16 A.sub.16 7.3 4000 20 F.sub.17 80 A.sub.17 8.4 4200 24 F.sub.18 A.sub.18 6.8 1500 3.7 F.sub.B Blank 6.2 8300 300< F.sub.15 A.sub.15 17.8 3200 12 F.sub.16 A.sub.16 17.2 3400 15 F.sub.17 150 A.sub.17 19.2 2800 8.7 F.sub.18 A.sub.18 13.9 1800 4.2 F.sub.B Blank 13.5 8300 300< __________________________________________________________________________

The degree of coloration was measured as follows: the treated fibers were carefully unravelled, the unravelled fibers were subjected to measurement of the reflection rates at 570 m.mu. and 430 m.mu. using Shimazu's Automatic Recording Spectrophotometer, and the difference between the values of the reflection rates indicates the degree of coloration. A larger degree of coloration indicates greater coloration and this value is agreeable with the result of observation to the naked eye.

The following were made clear by this experiment:

1. In the case of copolymers A.sub.15, A.sub.16 and A.sub.17 obtained by using vinyl monomer having a linking group as the copolymer component, it is necessary to carry out the curing of the treated knittings at a high temperature, such as 150.degree.C., in order to obtain sufficient boiling water durability, laundering durability and dry cleaning durability.

2. However, when treated at such a high temperature, the copolymers A.sub.15 to A.sub.17 accelerate coloration of the fibers due to decomposition of the polyethyleneglycol group contained in the copolymer.

3. Polymer A.sub.18 of the present invention exhibits sufficient antistatic property, boiling water durability and laundering durability and dry cleaning durability by drying at a relatively low temperature, such as 80.degree.C. the reason for this is that polymer A.sub.18 is a copolymer which has a three-dimensional structure. Consequently, it is not necessary to carry out the curing at a high temperature so that there is no coloration of fibers or decomposition of the polyethyleneglycol group.

The aqueous dispersion of polymer A.sub.18 of the present invention has a much better stability than polymers A.sub.15 to A.sub.17. The stability of the dispersion becomes particularly important in order to obtain a uniform treating effect when the dispersion is used continuously for a long time. Table 7 shows a comparison of the formation of agglomeration in the dispersion when a dispersion of 1.0 percent by weight of polymers A.sub.15 to A.sub.18 is recycled for 10 days with a pump.

TABLE 7

Optical Copolymer Recycling Agglomeration transmittance No. % __________________________________________________________________________ A Before non 88.4 After produced 69.2 A Before non 87.5 After produced 67.3 A Before non 75.3 After produced 51.8 A Before non 89.2 After produced 85.3 __________________________________________________________________________

The transmittance was indicated by the transmittance of 400 m.mu. light of a polymer dispersion (polymer content 10 percent by weight) in a 10 m.m. width quartz cell using Hitachi's Perkin-Ellmer 139UV-VIS Spectrophotometer. The smaller this value, the larger is the amount of agglomeration. Also, the relation between the storage time of the aforementioned dispersion of polymer A.sub.18 and the antistatic effect is shown in Table 8.

TABLE 8

Storage time Frictional static Half-value (days) voltage (V) period (sec) __________________________________________________________________________ 0 1500 3.7 10 1400 4.1 30 1500 3.8 100 1500 4.0 __________________________________________________________________________

Table 8 indicates that the dispersion of polymer A.sub.18 is very stable and there is no change in the antistatic effect even when stored for a long time, such as 100 days.

EXAMPLE 4

Acrylonitrile (AN), acrylic acid (AA), or acrylamide (AAm) was added further as a copolymer component to methoxy-polyoxyethyleneglycol-methacrylate and polyethyleneglycol-dimethacrylate of Example 1 with the mixing ratio indicated in Table 9 to prepare 7 different mixtures M.sub.19 to M.sub.25.

TABLE 9

Mixture Components Composition No. weight __________________________________________________________________________ % M.sub.19 PEGM/PEGDM 94/6 M.sub.20 PEGM/PEGDM/AN 84.6/5.4/10 M.sub.21 PEGM/PEGDM/AN 70.5/4.5/25 M.sub.22 PEGM/PEGDM/AN 56.4/3.6/4.0 M.sub.23 PEGM/PEGDM/AN 42.3/2.7/55 M.sub.24 PEGM/PEGDM/AA 70.5/4.5/25 M.sub.25 PEGM/PEGDM/AAm 70.5/4.5/25 __________________________________________________________________________

Each of these mixtures in an amount of 10 parts by weight dissolved in purified water of 90 parts by weight, potassium persulfate of 0.3 part by weight and sodium hydrogen-sulfite of 0.1 part by weight were added to this solution with agitation and the solution was subjected to copolymerization at 40.degree.C. for 4 hours to manufacture 7 kinds of copolymers A.sub.19 to A.sub.25 .

Among the polymers obtained, the particle size of copolymer A.sub.23 was large and its dispersion was unstable but the dispersion of the other copolymers were very stable.

At the same time, polyacrylonitrile type fiber with a fineness of 3 denier was manufactured according to the following method. Twenty-four parts by weight of a mixture of acrylonitrile of 94.6 percent by molar concentration, methyl acrylate of 5 percent by molar concentration and sodium arylsulfonate (SAS) of 0.4 percent by molar concentration, water in an amount of 1 part by weight, dodecylmercaptan in an amount of 0.05 part by weight, sulfuric acid in an amount of 0.01 part by weight and 0.1 part by weight of azo-bis-dimethyl valeronitrile were added to 76 parts by weight of dimethyl sulfoxide and this solution was heated at 50.degree.C. for 24 hours to effect copolymerization. The copolymer content of the copolymer-dispersion obtained was 21.7 percent by weight. This copolymer-dispersion was extruded through a 0.07 mm. diameter spinning orifice and coagulated in fiber form in an aqueous solution containing 50 percent by weight of dimethyl sulfoxide. This coagulated fiber was drawn to six times in a 30 percent by weight solution of dimethyl sulfoxide at 92.degree.C. and then rinsed with water. Next, the rinsed polyacrylonitrile type fibers were dipped in an 0.8 percent by weight dispersion of copolymer A.sub.19 to A.sub.25, squeezed with squeezing rolls to 100 percent liquid content based on the weight of the fiber and then dried at 170.degree.C. for 3 minutes. The dried polyacrylonitrile type fibers were dipped in a finishing oiling solution, crimped by means of a crimper, dried at 50.degree.C. and cut into staple fibers F.sub.19 to F.sub.25 of 51 mm. in length. Seven different spun yarns Y.sub.19 to Y.sub.25 of 48.sup.s were manufactured from the acrylic staple fibers F.sub.19 to F25. The lap licking tendency of each stable fiber in the spinning process was as shown in Table 10.

TABLE 10

Fiber Copolymer Breaking length of lap No. No. due to its weight __________________________________________________________________________ (cm.) F.sub.19 A.sub.19 85 F.sub.20 A.sub.20 126 F.sub.21 A.sub.21 145 F.sub.22 A.sub.22 168 F.sub.23 A.sub.23 190 F.sub.24 A.sub.24 109 F.sub.25 A.sub.25 98 F.sub.B Blank 155 __________________________________________________________________________

Breaking length of lap due to its weight is measured by a manner in that a lap without reinforcement cloth is conditioned for 24 hours, the conditioned lap is opened on the floor, an end of the opened lap is supported between two plates and vertically raised up from the floor until the lap is broken due to its weight, and then the height from the floor surface to the end of lap is indicated as breaking length of lap.

Table 10 indicates that the degrees of slip of F.sub.20, F.sub.21, F.sub.22 and F.sub.23 treated with polymers A.sub.20, A.sub.21, A.sub.22 and A.sub.23 of the present invention are lower than those of fibers F.sub.19, F.sub.24 and F.sub.25 and thus have superior spinning properties.

These acrylic fibers were knitted into seven different products K.sub.19 to K.sub.25, treated for 2 hours in boiling water and then laundered 10 times in the manner of Example 1. The antistatic properties of the laundered knitted products are shown in Table 11.

TABLE 11

Knitting Laundering Frictional static Half-value No. voltage (volt) period (second) __________________________________________________________________________ K.sub.19 Before 1500 2.7 After 3800 22 K.sub.20 Before 1600 3.1 After 1900 3.9 K.sub.21 Before 1500 3.5 After 1600 3.9 K.sub.22 Before 1900 6.7 After 2200 7.1 K.sub.23 Before 3700 11 After 3900 14 K.sub.24 Before 1700 5.2 After 3600 21 K.sub.25 Before 1600 3.9 After 3800 18 K.sub.B Before 6800 300< __________________________________________________________________________

Table 11 shows the following facts:

1. Copolymers containing acrylonitrile have better boiling water durability and laundering durability than copolymers containing acrylic acid or acrylamide as the copolymer component.

2. The aqueous dispersion of copolymer A.sub.23 obtained from a copolymerization system containing 55 percent acrylonitrile is unstable and its antistatic property is poor. It is therefore desirable that the proportion of acrylonitrile be below 45 percent. Table 12 shows the performances of polyacrylonitrile type fibers F.sub.20, F.sub.21, and F.sub.22 treated by copolymers A.sub.20, A.sub.21 and A.sub.22 of the present invention and also of untreated fibers.

TABLE 12

Fiber No. F.sub.20 F.sub.21 F.sub.22 Untreated __________________________________________________________________________ Fineness (d) 2.85 2.83 2.81 2.83 Dry tenacity 3.87 3.59 3.76 3.71 (g./d) Dry breaking 29.2 30.7 28.7 29.7 elongation % Knot strength 2.23 2.20 2.38 2.31 (g./d) Knot strength 76 61 63 62 ratio % Young's modulus 45.9 45.3 45.6 45.7 % __________________________________________________________________________

Table 12 clearly shows that the properties of polyacrylonitrile type fibers treated by the copolymers of the present invention are almost similar to those of the untreated fiber. The treated fibers F.sub.20, F.sub.21 and F.sub.22 were transparent, being the same as the untreated fiber and the dyeability of the treated fibers was similar to that of the untreated fiber. Consequently, the copolymers of the present invention can bestow superior antistatic property and spinnability to polyacrylonitrile type fibers without any deterioration of the characteristics of the fibers.

EXAMPLE 5

A compound in an amount of 65 percent by weight which is shown by the general formula

(where R.sub.1 and R.sub.2 are those indicated in Table 13 ) is mixed with 5 percent by weight of polyethylene-glycol-dimethacrylate, which is the same as used in Example 1 and 30 percent by weight of acrylonitrile, and then 10 different copolymers A.sub.26 to A.sub.35 were produced in the manner of Example 4.

TABLE 13

Radical Copolymer No. R.sub.1 R.sub.2 __________________________________________________________________________ A.sub.26 H OCH.sub.3 A.sub.27 CH.sub.3 OCH.sub.3 A.sub.28 CH.sub.3 OC.sub.3 H.sub.7 A.sub.29 CH.sub.3 SC.sub.12 H.sub.25 A.sub.30 CH.sub.3 N(C.sub.2 H.sub.5).sub.2 A.sub.31 CH.sub.3

a.sub.32 ch.sub.3 a.sub.33 ch.sub.3

a.sub.34 ch.sub.3 cl A.sub.35 C.sub.2 H.sub.5 OCH.sub.3 __________________________________________________________________________

polyacrylonitrile type fibers in the aquagel condition, the same as used in Example 4, were treated with a dispersion of 10 percent by weight of these copolymers and 10 different knitted products K.sub.26 to K.sub.35 were manufactured from these. The antistatic properties of these knitted products when laundered in the manner of Example 1 are shown in Table 14. All polymers of the present invention, A.sub.26 to A.sub.35, indicated superior antistatic properties.

TABLE 14

Knitting Frictional static Half-value No. voltage (V) period sec __________________________________________________________________________ K.sub.26 1600 4.5 K.sub.27 1500 4.3 K.sub.28 1600 4.8 K.sub.29 1700 5.6 K.sub.30 1800 6.2 K.sub.31 1700 5.8 K.sub.32 1700 5.8 K.sub.33 1800 6.3 K.sub.34 1600 5.3 K.sub.35 1600 5.6 K.sub.B 8300 300< __________________________________________________________________________

example 6

eight different polymers A.sub.36 to A.sub.43 were produced from mixtures composed of 5 percent by weight of polyethyleneglycol-dimethacrylate which is the same as used in Example 1, 30 percent by weight of acrylonitrile and 65 percent by weight of a compound which can be shown by the following general formula

(where the values of l and m are indicated in Table 15) and polyacrylonitrile type fibers in the aquagel condition of Example 4 were treated in the manner of Example 4 and knitted into 8 kinds of knitted products K.sub.36 to K.sub.43.

TABLE 15

Copolymer No. l m __________________________________________________________________________ A.sub.36 8 0 A.sub.37 15 0 A.sub.38 20 0 A.sub.39 50 0 A.sub.40 90 0 A.sub.41 150 0 A.sub.42 30 10 A.sub.43 30 20 __________________________________________________________________________

the antistatic properties of these knitted products after laundering in the manner of Example 1 are shown in Table 16, from which it can be seen that the antistatic properties of copolymers A.sub.37 to A.sub.40 are superior to those of copolymers A.sub.36 and A.sub.41.

TABLE 16

Knitting Frictional static Half-value No. voltage (V) period (sec) __________________________________________________________________________ K.sub.36 4000 28 K.sub.37 2800 8.5 K.sub.38 1600 3.5 K.sub.39 1700 4.2 K.sub.40 2700 5.3 K.sub.41 3500 7.2 K.sub.42 1800 4.2 K.sub.43 2300 5.9 K.sub.B 8300 300< __________________________________________________________________________

example 7

the concentration of a monomer mixture having the same mixing ratio as A.sub.20 indicated in Example 4 was varied as shown in Table 17 and copolymers A.sub.44 to A.sub.49 were produced. The specific viscosity .eta..sub.sp /C. and the antistatic property of the knitted products of acrylic fibers of Example 4 treated with these copolymers and laundered are as shown in Table 17.

TABLE 17

Monomer Frictional Half-value Knitting concen- static period No. tration voltage wt. (%) .eta..sub.sp /C. (V) (sec.) __________________________________________________________________________ K.sub.44 3 0.128 4800 53 K.sub.45 5 0.218 3800 36 K.sub.46 7 0.246 2800 21 K.sub.47 10 0.332 1800 4.8 K.sub.48 12 0.567 1500 3.7 K.sub.49 15 1.873 1400 3.2 K.sub.B -- -- 8300 300< __________________________________________________________________________

that is, the antistatic effect and durability of copolymers A.sub.47 to A.sub.49 are clearly better than those of copolymers A.sub.44 to A.sub.46 when the monomer concentration during copolymerization is below 10%.

However, the practical value of copolymer A.sub.47 is low because a solution of the copolymer A.sub.47 gels easily and the treated acrylic fibers tend to wind undesirably around the spinning roller frequently during spinning.

EXAMPLE 8

The relation between the copolymer content of the antistatic copolymer dispersion and the antistatic property of fibers treated with this dispersion has been clarified in the present example.

Polyacrylonitrile type fibers being the same as used in Example 4 were treated in the manner of Example 4 with 6 different dispersions L.sub.50 to L.sub.55 indicated in Table 18 containing the same copolymer as copolymer A.sub.21 used in Example 4. Knitted products made from the treated fibers were laundered in the manner of Example 1 and the antistatic property of the knitted products and the amount of copolymer adherence of the treated fibers are shown in Table 18.

TABLE 18

Content of copolymer Frictional Half- in treating Adhered static value Dispersion dispersion quantity voltage period No. (%) (% owf) (V) (sec) __________________________________________________________________________ L.sub.50 0.1 0.09 4200 58 L.sub.51 0.4 0.21 2400 12 L.sub.52 0.8 0.32 1500 3.5 L.sub.53 1.5 0.6 1200 3.2 L.sub.54 3.0 1.2 800 3.0 L.sub.55 5.0 2.6 600 2.8 __________________________________________________________________________

it is clear from Table 18 that the antistatic effect of the knitted products became larger, the larger the adhered quantity of the copolymer.

The adhered quantity of copolymers on fibers treated with treating dispersions L.sub.54 and L.sub.55 was 1.2 percent and 2.6 percent by weight based on the weight of the fiber, respectively, and although both antistatic property and durability of these were satisfactory, spinnability was poor. Consequently, an adhered quantity of copolymer A.sub.21 in a range of 0.25 - 1 percent by weight based on the weight of the fiber is desirable.

EXAMPLE 9

The acrylic fibers laundered and dried in the manner of Example 4 were treated with treating dispersion L.sub.51 to L.sub.55 in the manner of Example 8. The quantity of copolymer adhering to the treated fibers and the antistatic property of the knitted products made from the treated fibers and laundered in the manner of Example 1 are shown in Table 19. It is clear from Table 19 that the antistatic property is improved when the adhered quantity of copolymer A.sub.21 on the dried fiber increases and that an adherence rate of over 0.25 percent by weight based on the weight of the fiber is desirable.

TABLE 19

Rate of adherence Frictional static Half-value (%) voltage (V) period (sec.) __________________________________________________________________________ 0.12 4500 52 0.30 2300 12 0.8 1400 3.2 1.2 1000 3.2 2.5 800 3.0 __________________________________________________________________________

EXAMPLE 10

Twenty parts by weight of a mixture M.sub.50 obtained by mixing methoxy-polyoxyethyleneglycol-methacrylate and polyethyleneglycol-dimethacrylate same as used in Example 1, and octyl acrylate in a composition of 60 : 5 : 35 was dissolved in 90 parts by weight of water containing 0.15 part by weight of Sunmorine OT-70 (Trademark of Sanyo Chemical Co.) and 0.85 part by weight of Nonipole 75 (Trademark of Sanyo Chemical Co.). The gelating concentration of this mixture was 18 percent. Potassium persulfate in an amount of 0.27 part by weight and 0.1 part by weight of sodium hydrogen sulfide were added to this solution as the polymerization catalyst. This polymerization system was heated for 6 hours at 55.degree.C. The obtained dispersion of copolymer A.sub.51 was very stable.

The optical transmittance of this copolymer was 80 percent. The acrylonitrile type fibers in the same aquagel condition as used in Example 4 treated with a 1 percent dispersion of this copolymer was treated in the same manner as shown in Example 4.

The antistatic properties of the treated acrylonitrile type fibers are shown in Table 20.

TABLE 20

Frictional static Half-value period voltage __________________________________________________________________________ Before After Before After dry dry dry dry Fiber Polymer cleaning cleaning cleaning cleaning __________________________________________________________________________ F.sub.50 A.sub.50 1800 1900 3.7 4.2 F.sub.B -- 8000 8100 320 230 __________________________________________________________________________

dry cleaning was carried out by dry cleaning the samples 10 times under the following conditions. About 2 g. of the knitted material was placed in a container of over 450 cc. capacity of a Launder-meter testing machine together with 20 steel balls with a diameter of 0.64 mm. (14 inch) and a mixture containing 100 cc. at 30.degree..+-.2.degree.C. perchloroethylene, 1 g. of nonionic surface active agent, 1 g. of anion surface active agent and 0.1 cc. of water; the container was sealed, attached to the rotating shaft, and treated for 30 minutes while rotating at a rate of 42 .+-. 2 r.p.m.; then the samples were removed, rinsed with 100 cc. of perchloroethylene; the liquid removed and dried in a drier whose temperature was below 60.degree.C.

As shown in Table 20, the copolymer A.sub.50 of the present example had superior antistatic property and durability against dry cleaning.

EXAMPLE 11

A spun yarn of 40.sup.s was prepared from a blend of polyester fiber of 65 percent by weight and cotton fiber of 35 percent by weight. The blended yarn was dipped into the dispersion containing 1 percent by weight of the copolymer A.sub.3 obtained in Example 1, the excess moisture was removed so that the dispersion of 100 percent by weight based on the weight of the yarn remained on the yarn, and dried at a temperature of 170.degree.C. for 3 minutes. Then, the adhering quantity of the copolymer A.sub.3 on the treated yarn was about 1 percent by weight based on the weight of the yarn. The measurements were employed to frictional static voltage and half-value period of the treated yarn and the untreated yarn. The results are shown in Table 21.

TABLE 21

Yarn Frictional static Half-value voltage (V) period __________________________________________________________________________ (sec.) Treated yarn 450 2.8 Untreated yarn 8300< 300< __________________________________________________________________________

As shown in Table 21, the copolymer according to the present invention has an excellent antistatic effect with respect to polyester fiber.

EXAMPLE 12

A nylon fabric was dipped in the aqueous dispersion containing 1 percent by weight of the copolymer A.sub.3 obtained in Example 1, the excess moisture was removed so that the dispersion of 50 percent by weight based on the weight of the fabric remained on the fabric, and dried at a temperature of 150.degree.C. for 10 minutes. The adhering quantity of the copolymer A.sub.3 on the nylon fabric was 0.5 percent by weight based on the weight of the fabric. The frictional static voltage and half-value period of static charge of the treated nylon fabric and the untreated fabric were measured. The results are shown in Table 22.

TABLE 22

Fabric Frictional static Half-value voltage (V) period (sec.) __________________________________________________________________________ Treated 400 3.0 Untreated 8300< 300< __________________________________________________________________________

As shown in Table 22, the copolymer A.sub.3 develops an excellent antistatic effect on the nylon fabric.

Claims

What we claim as new and desire to secure by Letters Patent is:

1. A process of improving the antistatic property of hydrophobic synthetic fibers comprising impregnating said fibers with an aqueous liquid containing at least one copolymer which is prepared by copolymerizing, in water, a mixture of

I. a monoester of the formula

wherein

R.sub.1 is selected from the group consisting of H, CH.sub.3 and C.sub.2 H.sub.5,

R.sub.2 is selected from the group consisting of OH, alkoxy containing not more than 18 carbon atoms, halogen, alkyl sulfide containing not more than 18 carbon atoms, a mono- or dialkylamine containing not more than 18 carbon atoms, phenoxy and naphthoxy, and

l and m are satisfied with the formulas

10 .ltoreq. l .ltoreq. 100 and O .ltoreq. m <l and

Ii. a diester selected from diacrylates and dimethacrylates of polyols in a proportion such that the gelating concentration of said mixture is 14 to 30 percent, the gelating concentration being the minimum concentration with respect to the total weight of the copolymerization system required to cause gelation of a mixture of about 20 cc. of a combination of said monoester and said diester dissolved in dimethyl sulfoxide containing 0.2 g./l. of sulfuric acid and 0.02 g./l. of azobisisobutylnitrile when heated at 55.degree.C. for 24 hours.

2. A process according to claim 1 wherein said hydrophobic synthetic fiber is polyacrylonitrile fiber.

3. A process according to claim 1 wherein said polyacrylonitrile fiber is in an aquagel condition.

4. A process according to claim 1 wherein said impregnated fibers are steamed at a temperature above 90.degree.C. before said drying.

5. A process according to claim 1 wherein said dried fiber absorbs 0.1 to 8 percent of said copolymer based on the weight of said fiber.

6. A process according to claim 5 wherein said absorption of said copolymer is 0.2 to 2.0 percent based on the weight of said fiber.

7. A process according to claim 1 wherein the copolymerization mixture further contains 5 to 45 percent of acrylonitrile based on the total weight of said copolymerization mixture.

8. A process according to claim 1 wherein the copolymerization mixture contains 20 to 60 percent of at least one monomer selected from acrylic and methacrylic esters of a higher alkyl alcohol having more than 8 carbon atoms, based on the total weight of said copolymerization mixture.

9. A process according to claim 1 wherein said copolymer has a specific viscosity of 0.3 to 1.0 in a dispersion containing 0.1 percent by weight of said copolymer, said specific viscosity being determined at a temperature of 30.degree.C. by means of an Ostwald viscometer.

10. A process according to claim 1 wherein the copolymerization mixture contains 20 to 60 percent of at least one monomer selected from acrylic and methacrylic esters of a higher alkyl alcohol having from eight to 18 carbon atoms, based on the total weight of said copolymerization mixture.

11. A process according to claim 1 in which in the formula of said monoester, 20 < l < 70.

12. A hydrophobic fiber having improved antistatic properties which has been treated in accordance with the process defined in claim 1.

13. A hydrophobic fiber having improved antistatic properties which has been treated in accordance with the process in claim 7.

14. A hydrophobic fiber having improved antistatic properties which has been treated in accordance with the process defined in claim 8.