US3595854A - Acetate filaments of improved resistance to hydrothermal delustering and the process for preparation thereof - Google Patents

Abstract

CELLULOSE ACETATE FILAMENTS HAVING EXCELLENT RESISTANCE TO HYDROTHERMAL DELUSTERING IN HOT WATER OF 110*C. AND ABOVE, GOOD QUALITATIVE REPRODUCIBILITY AND PRACTICALLY SATISFACTORY FIBER STRENGTH, AND PROCESS FOR PRODUCING SUCH FILAMENTS BY USING CELLULOSE ACETATE FLAKES WHICH HAVE BEEN POST-TREATED UNTIL THEIR REFINED PARAMETER AT THE STABILITY OF 0.08% IS REDUCED TO NO HIGHER THAN 80.

Description

United Smtes Patent 3,595,854 Patented July 27, 1971 3,595,854 ACETATE FILAMENTS OF IMPROVED RESIST- AN CE T HY DROTHERMAL DELUSTERING AND THE PROCESS FOR PREPARATION THEREOF Masao Matsuzaki, Matsuyama-shi, Japan, assignor to Teijin Limited, Osaka, Japan No Drawing. Filed Nov. 26, 1968, Ser. No. 779,271 Claims priority, application Japan, Nov. 28, 1967, 42/ 76,632 Int. Cl. CllSb 3/22 US. Cl. 260-230 3 Claims ABSTRACT OF THE DISCLOSURE Cellulose acetate filaments having excellent resistance to hydrothermal delustering in hot water of 110 C. and above, good qualitative reproducibility and practically satisfactory fiber strength, and process for producing such filaments by using cellulose acetate flakes which have been post-treated until their refined parameter at the stability of 0.08% is reduced to no higher than 80.

This invention relates to a process for the preparation of acetate filaments having excellent resistance to hydrothermal delustering, with good reproducibility, in which the inherent deficiency of cellulose acetate, filaments, i.e., hydrothermal delustering, is conspicuously eliminated without detrimental effect on the filaments favorable properties such as silk-like hand, luster, clarity of dyed color and practical strength, etc., and also relates to such improved filaments. The filaments of the invention exhibit no appreciable delustering phenomenon, which subjected to, for example, a treatment with hot water of 110 C. under an elevated pressure.

More particularly, the invention relates to a process for the preparation of acetate filaments of which hydrothermal delustering property is improved, comprising dissolving acetone-soluble cellulose diacetate flakes in a solvent system composed chiefly of acetone, and spinning the solution into acetate filaments, the characteristic features residing in that the flakes are subjected to a heating posttreatment in a dilute aqueous acid solution until their refined parameter at the stability of 0.08% is reduced to no higher than 80, and then removed of the treating liquid by washing, followed by the said dissolving and spinning steps, and relates also to thus obtained cellulose acetate filaments.

Cellulose acetate filaments possess such favorable properties as silk-like hand, luster, clarity of dyed color, and

practically valuable tenacity, etc. On the other hand, they tend to deluster in hot water and change to milky White state. Degree of such delustering is intimately related to the temperature of hot water. That is, up to approximately C., little appreciable delustering takes place, but the delustering is considerable in boiling water. At temperatures exceeding C., it is markedly advanced, and the filaments turn milky White which is observable with naked eye. Thus, cellulose acetate filaments which show no appreciable delustering phenomenon in hot water exceeding 100 C. (under elevated pressure), for example, C. or higher, do not exist, and therefore the elimination of this delustering phenomenon was considered to be impossible.

Thus delustered filaments exhibits inconveniently remarkable abnormalities in their fiber properties, particularly reduction in strength and increase in elongation. Such tendency is more conspicuous at advanced degree of delustering. Thus this drawback incurs indeed heavy limitations on the utility of cellulose acetate filaments.

For example, recently various mixed or blended weaving techniques are under development, effectively utilizing both the favorable properties of cellulose diacetate such as elegant feeling, clarity of dyed color, etc. and the excellent strength property of synthetic fibers such as of polyester. Therefore novel type of cellulose diacetate filaments which do not deluster in hot water of the temperatures in the order of 110130 C., which are normally employed for dyeing of synthetic fibers, for example, polyester, have been in urgent demand. That demand, however, has not been met to date, and all the existing cellulose diacetate filaments completely lose luster under said temperature condition, and their color tone is markedly impaired. Furthermore, their favorable property such as the fine, elegant feeling also is destroyed.

We engaged in extensive research works in pursuit of cellulose acetate filaments which exhibit markedly improved resistance to the hydrothermal delustering without any sign of deterioration in their favorable properties, in order to meet the above demand. In the course of studies we discovered that the main cause of hydrothermal delustering of cellulose acetate filaments is not the forma tion of crazing in the surface structure of the filaments but of microvoids of the diameters in the order of 0.02-- 0.5 micron in the filaments, and that the degree of delustering advances not with the growth in size of the microvoids, but with the increase in number thereof. We also found that in cellulose acetate of high acetyl value, the number of such microvoids formed is remarkably less.

Whereas, when we tested the hydrothermal delustering of the filaments prepared in identical manner from various cellulose acetate flakes of high acetyl value and of same quality, under identical test conditions, the results were entirely unpredictable. That is, the degree of delustering of the specimens were very much dispersed. Therefore under a hypothesis that the hydrophilic impurities of cellulose acetate flakes such as ash content, trace of free acetic acid, etc. may provide the bases or points in the resulting acetate filaments to draw the water molecules in hot water, and assist the microvoids formation as they cause distortion in dry filament structure, we repeated the identical test using cellulose acetate flakes of identical impurities contents. The results were in no way changed.

Generally speaking, cellulose acetate flakes of high acetyl value and low hydrophilic impurities contents exhibit less tendency for delustering, compared with those of lower acetyl value of higher hydrophilic impurities contents. From this fact, those factors appear to be somewhat correlated with the degree of delustering. However, the results of our experiments, that the degrees of delustering were dispersed as to the specimens in which those factors were identical, indicates that the prediction of delustering phenomenon of cellulose acetate filaments using those factors as the sole norms is impossible. Furthermore, in hot water exceeding 100 C., the filaments were delustered and became useless for any practical purpose, irrelevantly to the factors.

We pursued our studies aiming at the development of cellulose acetate filaments having heretofore unknown excellent resistance to hydrothermal delustering with good reproducibility. Whereupon we came to know that if the conventional stabilizing means of cellulose acetate is applied to the cellulose acetate flakes as a post-treatment thereof under the conditions heretofore avoided in the stabilizing operation, until the refined parameter at the stability of 0.08% (this term will be precisely defined later in this specification) is reduced to no more than 80, the cellulose acetate filaments prepared from such flakes exhibit an entirely novel property, i.e., excellent resistance to hydrothermal delustering in hot Water of 110 C. and above (under elevated pressure), for example, as high as 140 C., and furthermore the sufficient strength for practical use.

Conventionally, such means as thorough washing with water and boiling in water or dilute acid are well known as the stabilizing treatments of cellulose acetate, in order to completely eliminate the residual free acid from the precipitated cellulose acetate. Also the treatment with dilute acid and aqueous sodium chlorite solution is known as a bleaching and stabilizing means of cellulose acetate.

On the other hand, it has been the accepted practice among the experts to complete this dilute acid treatment within a shortest period possible, normally about l-2 hours. Because, such dilute acid treatment, if continued for a long time, causes non-uniform. saponification decomposition of acetic acid radicals of cellulose acetate and degrades the solubility thereof to acetone. And, the decrease in the acety value tends to aggravate the hydrothermal delustering of cellulose acetate filaments as aforesaid. Therefore, the dilute acid treatment for a long period which invites decrease of acetyl value appears to be objectionable also in this respect.

Whereas, quite surprisingly it is found that when the treatment is continued for a much longer period than that conventionally employed for stabilizing purpose, i.e. until the aforesaid new parameter is satisfied, the so treated flakes provide novel type of cellulose acetate filaments having high resistance to hydrothermal delustering as described in the foregoing. It is furthermore discovered that the filaments of the strength quite satisfactory for practical purposes can be obtained by suitably selecting the acetyl value of the flakes before the dilute acid treatment.

Again, the cellulose acetate filaments prepared from the flakes which have been so post-treated until the specified parameter is satisfied, exhibit always excellent resistance to hydrothermal delustering and fully satisfy 4 the reproducibility of the high quality. Whereas, the measured values of the said parameter of commercially available cellulose acetate flakes are no less than 150, normally above 200.

Accordingly, the object of the invention is to provide novel cellulose acetate filaments having excellent resistance to hydrothermal delustering, good qualitative reproducibilty and practically satisfactory fiber strength, and a process for the preparation of such filaments.

Still many other objects and advantages of this invention will become apparent from the following descriptions.

In the invention, cellulose diacetate flakes (which may be hereafter referred to as acetate flakes) include all forms of dry cellulose diacetate used as the spinning material, for example, powder, granule, pellet, foil, short staple, etc.

According to the invention, the acetate flakes are subjected to a heating post-treatment in dilute aqueous acid solution, for example, dilute aqueous solution of a mineral acid such as sulfuric, nitric, phosphoric, and hydrochloric acids, or of a lower fatty acid such as acetic acid. It is permissible to perform the post-treatment in the concurrent presence of similarly dilute aqueous solution of bleaching agent, such as of sodium hypochlorite, hydrogen peroxide, potassium permanganate, etc. Or, the flakes may be treated with such bleaching or reduction bleaching agent, after the specified dilute acid post-treatment.

The concentration of acid in the dilute aqueous solution for the heating post-treatment may range from approximately 0.l% to approximately 0.001%, in case mineral acids are employed. The concentration can be suitably varied, depending on the type of acid, shape of flakes, heating temperature, etc. The preferred concentration is normally around ODS-0.005%, inter alia, approximately 0.040.0l%. Also when lower fatty acid is employed, it may range approximately 100.5%, preferably 60.8%, inter alia, in the order of 4-l%.

Normally the heating temperature ranges about 200 C. Preferred range is about 180 C., inter alia, in the order of 90-160 C. The temperature is suitably selected depending on such factors as heating time, type and concentration of acid, shape of flakes, etc.

The treatment can be performed batchwise or continuously. For instance, the flakes may be suspended in a tank filled with the aqueous acid solution, to be heattreated. Or heated aqueous acid solution may be caused to flow down through a column packed with the flakes. Also the flakes continuously supplied from the top portion of a treating column may be countercurrently contacted with the aqueous acid solution supplied from bottom portion of the column as an upward flow. Or, heated, dilute aqueous acid solution may be sprayed on the acetate flakes which are being transferred on a movable belt. in short any optional method can be employed, so far as the aqueous acid solution and the solid flakes can intimately and uniformly contact with each other.

The treatment can be performed under either atmospheric or elevated pressure. Also if desired, it is permissible to employ a slightly reduced pressure condition under which the aforesaid heating temperature can be maintained.

Duration of this post-treatment is suitably varied or selected according to such factors as type and concentration of the acid, shape and amount of the flakes, treating system, pressure condition, etc., but in all cases it must be long enough to satisfy the aforesaid parameter.

Any treatment not satisfying the parameter is not within the scope of subject process. The products fail to show the resistance to hydrothermal delustering at temperatures exceeding C., and qualitative reproducibility is impaired.

In the present invention, the acetate flakes must be post-treated, until their refined parameter at the stability of 0.08% is reduced to no more than 80.

After the post-treatment, the flakes are thoroughly washed to remove the treating liquid remaining thereon. Warm water shows better washing efficiency than cold water. For example, warm water of about 4095 C. can be advantageously used. Or a dilute alkaline aqueous solution can be used for the same purpose.

Thus treated acetate flakes are normally dried, and dissolved in a solvent system composed chiefly of acetone by the means known per se. The cellulose acetate filaments spun therefrom exhibit no appreciable delustering in hot water of above 100 C., for example, 110-150 C. (under elevated pressure). Such cellulose acetate filaments are never before produced, although very much wished for.

The filaments can be imparted with strength suflicient for practical purposes. In the present invention, it is particularly advantageous and desirable for imparting the resistance to hydrothermal delustering at high temperatures with good reproducibility to the filaments, that the relation expressed by the equation below is satisfied by the water content and acetyl value of the cellulose acetate dope to be precipitated to provide the material flakes, the dope having been already acetylated and aged:

Water content of dope (wt. percent =(213-3.5 acety1 value) :3.0

In the present invention, that the refined parameter at the stability of 0.08% is no more than 80 signifies that the numeral value measured and calculated by the following method is no more than 80.

METHOD OF MEASUREMENT AND CALCULATION OF REFINED PARAMETER (I) The sample flakes are pulverized and 2 g. of the resulting powder accurately weighed with chemical balance is placed in a heat-resistant hard glass (Pyrex by the trade name) test tube. After addition of further 2 cc. of pure water, the test tube is closed airtightly with a rubber plug which has been thoroughly cleaned in boiling pure water. While maintaining thus sealed state, the test tube is immersed in boiling water to be heated for 7 hours. Then the content is separated into the solid sample and solution by means of quantitative filter paper, and the solid component is washed with 150 cc. of boiling pure water. The foregoing solution and washing are combined, and quickly neutralization titrated with 0.01 N aqueous caustic soda solution, using phenol-phthalein as the indicator.

In that stage, the water obtained through the identical procedures as above except the addition of the sample is omitted is similarly quickly neutralization titrated by way of a blank test, and the first titration value is corrected by subtracting the blank titration value therefrom.

From thus corrected titration value, the percentile acetic acid content (A) per sample weight is calculated.

Separately, g. of the same sample is precisely weighed and is immersed in 100 cc. of pure water at room temperature for 3 hours and filtered. Then the solid component of the sample is washed with 50 cc. of pure water, and the filtrate and washing are combined. The liquid is also neutralization titrated with 0.01 N aqueous caustic soda solution, using phenolphthalein as the indicator. Separately a blank test is conducted. The percentile acetic acid content (B) per sample weight is then calculated.

The numeral value obtained by subtracting (B) from (A) is called stability in this specification.

(II) Separately, 10 g. of the same sample is put in a porcelain crucible, and first calcined by pre-heating, followed by burning in 800 C. electric oven. The solid component is dissolved in hydrochloric acid in accordance with the accepted practice, and using Eriochrome Black-T indicator, its calcium and magnesium contents are measured with EDTA (ethylenediaminetetraacetic acid 2-sodium). The result (converted to calcium) per sample weight is indicated by ppm. unit (which is referred to as alkalinity in this specification).

(III) Several groups of each g. of sample flakes are prepared, which are immersed in each 2 liters of water of various hardness (IIS K-0101), which has been prepared by adding calcium acetate to pure water, for 24 hours at room temperature, and thereafter withdrawn and dried. Thus obtained plural groups of dry samples are each determined of the stability (Y) and alkalinity (X) according to the procedures (I) and (II) above.

With reference to the perpendicularly crossing co-ordinates in which the ordinate denotes stability and abscissa denotes alkalinity, the set values of the above samples are plotted, and the points are connected with a smooth curve. Then the reading of alkalinity corresponding to the intersection of this curve with the level of 0.08% stability is determined. This reading (p.p.m.) is the refined parameter (SP) at the stability of 0.08%.

The hardness of the water for immersing the flakes can be suitably selected to secure the intersection of the said curve with the 0.08% stability level. That is, when the stability of the sample flakes is above the level of 0.0 8%, plural types of water having hardnesses exceeding 2.5 times of the alkalinity corresponding to that stability are selected. And, if the stability of the sample flakes is below the level of 0.08%, the hardnesses of less than 2.5 times the corresponding alkalinity are selected.

The curve showing the correlation of stability with alkalinity of the sample obtained as described in the foregoing resembles a hyperbola for which the axis of abscissa and a straight line perpendicularly crossing therewith are the asymptates. The location of the straight line perpendicularly intersecting with the axis of abscissa varies, depending on the composition of acetate flakes employed.

It is not yet perfectly clear why the SP value of the acetate flakes in accordance with the present invention provides a highly reliable, excellent parameter for prediction of hydrothermal delustering and qualitative reproducibility of the cellulose acetate filaments prepared from the same flakes. However, the filaments made from the flakes satisfying this parameter exhibit excellent resistance to hydrothermal delustering and high qualitative reproducibility. More specifically, the filaments show the degree of delustering (Whcih will be defined later) of no more than grade 1.5 in hot water of 110 C., for example, grade 0.3 or 0.2 which means substantially no appreciable delustering.

DEGREE OF HYDROTHERMAL DELUSTERING AT 110 C.

The sample cellulose acetate filaments of 100 deniers/ 25 filaments are mechanically wound onto a frame into six layers, over a width of 3 cm. without gaps. The frame is then immersed in hot water in an autoclave wherein the temperature is controlled to 95 C. The autoclave is immediately closed airtightly, and inside temperature thereof is raised to 110 C. during the following 30 minutes. After an additional hour of the immersion at that temperature, the frame is withdrawn and air-dried at room temperature for 30 minutes. Subsequently the filaments are dried in a constant temperature drying oven of C. The degree of delustering of the filaments is then graded in comparison with the standard samples.

When identical test is performed except the temperature is raised to 140 C. instead of C, the result is referred to as the degree of hydrothermal delustering at C. Similarly, when the testing temperature is 100 C., the result is the degree of hydrothermal delustering at 100 C.

The standard samples are prepared to have successively increased degree of delustering with rise in the numerical grade, starting from the grade zero denoting the status of filaments before the hydrothermal treatment, to enable 8 Degree of delustering: Factor Per one sample exceeding grade 1.5 to grade functional determination of the grade. .At the delustering 3.0 "a- +0.3 grade 5, the filaments are substantially milky white. -As Per one sample exceeding grade 3.0 to gra e referential values, the corresponding whiteness values (L- 5 5.0 +0.8 values) measured with the color-difference meter of Nip- Per one sample exceeding grade 5.0 P0 iDeIlShOkll Kogyo w which is designed to measure Hereinafter the several embodiments of the subject the tristimulus values of color, are given in the below. process will be explained with refergnce to ki exam- When the sample filaments are photo-irradiated at the P1es angle of 45 to the advancing direction of the wound fila- Examples 1 4 controls 1 2 ments on the frame and L-values of the reflected light are determined, the correspondence become as in the table o .h ndred (100) parts of cellulose Were pre-treated below. with 50 parts of acetic acid, and subjected to an acetylation reaction with 350 parts of acetic anhydride, 400 parts Hydrothermal delustering 15 of methylene chloride, and 1 part of sulfuric acid as the grade Lvalue 1 catalyst, under stirring at a temperature not higher than 0 C, After the reaction system became a hom g 35 solution and acquired the predetermined viscosity, 80 1.0 43 parts f water and 5 parts of sulfuric acid were added to 48 20 perform the aging reaction at temperatures below 50 C. 2.5 61 When the acetyl value reached 55.0%, the Sulfuric aci 30 66 was neutralized with equivalent amount of sodium car- 4.0 7 bonate dissolved in parts of Water, 10 terminate h 5.0 78 reaction. 1 Measured with color difference m t r, 25 Thereafter the reaction mixture was heated so that the most of methylene chloride in the dope was removed by The cellulose acetate filaments prepared in accordance evaporation The remaining system i i d i with the present invention, that is, the filaments prepared 18% aqueous acetic id solution. from the cellulose diacetate flakes which have been post- Th precipitated flake were washed with water. A treated until their refined parameter at 0.08% stability is 30 ti th f was d i d on-treated flake and the reduced 110 more than 80, y dissolving the flakes in a rest was divided. The specimens were boiled in 0.02% solvent system composed chiefly of acetone and spinning aqueous sulfuric acid solution, each 2, 4, 10, 20 and th am n accordance w accepted Practice, P088685 30 hours. Then the sulfuric acid was completely washed heretofore unknown high resistance to hydrothermal demi fro th specimens with water. Then SP parameter of lustering, such as the degree of hydrothermal delustering 35 each specimen was measured. They were subsequently at 110 C. of grade 1.5 or less. Also the grade shows exdissolved in acetone and spun in the accepted manner. cellent qualitative reproducibility of no less than As to the resultant filaments, degrees of hydrthermal denormally The qualitative reproducibility is callustering at 100 C., C., and C., and qualitaculated as follows: tive reproducibility were measured, with the results as The above-described hydrothermal delustering test at given in Table 1 below.

TABLE 1 SP at Degree of hydrothermal Qualitative 0.08% delustering (grade) at reproducstabllity, ibility, No. Flakes (p.p.m) 100 C. 110 0. 140 0. percent Control 1 Untreated flakes 215 3. 0 4. 0 5. 0 50 Control 2 Flakes treated (2 hours) 1. 5 2. 6 4. 0 30 Example 1 Flakes treated (4 hours)... 91 0 1. 5 3. 0 +95 Example 2. Flakes treated (10 hours) 78 0 0. 5 0. 6 +100 Example 3 Flakes treated (20 hours) 30 O 0.3 0. 4 +100 Example 4 Flakes treated (30 hours) 18 0 0 0. 2 +100 110 C. is given to 24 filament samples taken from the filaments made from identical flakes. The number of samples whose delustering grade exceeded 1.5 is counted, and the result plus the below-specified factor, P, is used as the base for calculating the qualitative reproducibility in accordance with the equation below:

Qualitative reproducibility (percent) 24 100 Examples 5-8, controls 3-9 TABLE 2 Post-treatment of flakes SP at 0.08% Hydrothermal delustering degree at 100 0. 110 0. 140 0.

Acid coneen- Treating tration, time percent (his) Treating temp. 0.)

Dope, percent Water Acetyl content value Acid used pr%sure) Control 4I Example 7 Control 5 Control 6 Control 7 Control 8. r Control 9 i The before treatment and after treatment respectively mean before and aiter the hot Water treatment of a skein yarn in the same manner as the measurement of hydrothermal delustering degree at 110 C. The strength is a dry strfingth both before and after treatment.

5 Commercial product (acety1valuo=54.9%; degree of polymerization-=182.

4 Under concurrent use of aqueous solution of sodium hypochlorlto.

I claim:

1. A process for the preparation of cellulose diacetate filaments which have a degree of hydrothermal delustcring at 110 C. of not more than grade 1.5 and a qualitative 5 reproducibility of 97-l00% which comprises:

(a) heat-treating cellulose acetate flakes in a dilute aqueous acid solution, wherein the acid is selected from sulfuric, nitric, phosphoric, hydrochloric and acetic acids, until the refined parameter at a stability 10 of 0.08% is reduced to no greater than 80; said heat treatment being conducted at a temperature ranging from the boiling point of said solution to 200 C.

(b) Washing said flakes to remove said aqueous acid solution therefrom;

1 (c) dissolving the flakes free of said aqueous acid solution in a solvent system consisting essentially of acctone; and

(d) thereafter spinning the solution of (c) into filaments.

2. The process of claim 1 wherein the concentration of acid in the dilute aqueous acid solution is 0.l-0.001% in the case of sulfuric, nitric, hydrochloric and phosphoric acids and 0.86% in the case of acetic acid.

3. The process set forth in claim 1, in which the flakes are those obtained by precipitating the aged dope of cellulose diacctate of which Water content and acetyl value satisfy the relation of:

Water content of dope =(213-3.5 acetyl value)i3.0

References Cited UNITED STATES PATENTS 1,286,172 11/1918 Dreyfus 260-230 1,824,877 9/1931 Dreyfus et al 260230 2,203,699 6/1940 Seymour et a1. 26 023 0 3,505,313 4/1970 Kato 260-230 FOREIGN PATENTS 68,001 9/1911 Switzerland 260--230 298,819 10/1928 Great Britain 260230 299,326 3/1930 Great Britain 260-230 312,232 1930 Great Britain 260-230 DONALD E. CZAJA, Primary Examiner R. W. GRIFFIN, Assistant Examiner US. Cl. X.R. l06---196, 198