US3124415A - hours - Google Patents

Description

March 10, 1964 MASAMITSU NAGANO ETAL 3,124,415

POLYVINYL ALCOHOL FIBERS HAVING HIGH CRYSTALLINITY AND KNOT STRENGTH Filed Sept. 2 1960 5 HOURS 3 HOURS I HOUR 2 OJOU m0 uummvuc TEMPERATURE INVENTORS MASAMITSU NAGANO BYHIDEO TOKUMITSU ATTORNEY United States. Patent 3 124 415 PGLYVINY L ALCQI-IbL FIBERS HAVING HIGH CRYSTALLY AND KNOT STRENGTH v Masamitsn Nagano and HideoTolrnmitsn, ()kayama City,

Japan, assignors to Knrashiki Rayon C0,, Ltd, Kuraslriki-shi, .lapan, a corporation of Japan Filed Sept. 2, 1960, Ser. No. 53,671

1 Claim. (Cl. 8-1301) This invention relates to the treatment of polyvinyl alcohol fibers and is more particularly concerned with the heat-treatment of such fibers.

Heat-treatment of polyvinyl alcohol fibers is carried out to increase the crystallization of the molecules of polyvinyl alcohol and to promote the water-resistance and elasticity of the fibers. However, in accordance with the conventional heat-treating method. The fibers are heated only at a temperature above the second transition point for a specified time and no consideration is given to the speed of cooling of the fibers after the heat treatment.

The mechanical properties of polyvinyl alcohol fibers will be influenced by the size and number of crystalline particles in the fibers. particles, the higher the strength and water-resistance of the fibers. When polyvinyl alcohol fibers are to be used for making fishing nets and the. like, wherein fibers of a high knot strength are required, it is necessary to provide fibers of large crystalline particles. However, there is danger that the fibers will harden. Accordingly, problems are present in the production of polyvinyl alcohol fibers having desired characteristics of the type indicated which are not solved by'conventional heat-treating operations.

It is an object of the present invention to provide a process of heat-treating polyvinyl alcohol fibers to impart to them a high percentagecrystallinity in the form of large crystal particles and high knot strength.

In accordance with the present invention, polyvinyl alcohol fibers are first heat-treated only for a short time at a temperature above the second transition point but below the melting point, e.g. at 200 to 225 C., in accordance with known practice, and thefibers are then cooled under controlled temperature and time conditions. When the time of cooling is long, the crystallinity will be increased but a portion of the polyvinyl alcohol molecules will be thermally decomposed and saturated or unsaturated carbonyl radicals will be produced and 'discoloration will occur. In accordance with the invention, discoloration is prevented, and crystallinity and knot strength are increased, by slowly cooling the fibers by maintaining them at a temperature above the second transition point (85 Q), but not above 100 C., for a period of time up to two hours, preferably /z to 2 hours, and then allowing them to cool at room temperature, i.e. about 25 C. until they are at room tempera-' ture. During the heatetreatment and during the controlled'cooling of the process of this invention, the fibers are maintained at constant length until left at room temperature.

The invention will be further understood by reference heated by immersion in a molten metal (lead) bath at 220 C. for 1.5 minutes and were then cooled by the following procedures, while under tension to maintain constant length.

Sample No. 1: In substantially saturated Na SO solu- Thus, the larger the crystalline tion (as used for wet spinning) at 30 C. for 5 minutes, then left at room temperature.

Sample No. 2: In substantially saturated Na SO solution at 10 C. for 5 minutes, then left at room temperature.

Sample No. 3: In an oven at 110 C. for 10 minutes, then left at room temperature.

Sample No. 4: In an oven at 110 C. for 1 minute, then left at room temperature.

Sample No. 5: Immediately left at room temperature.

Sample No. 6: Immersed for 1 minute in a mixture of solid carbon dioxide and acetone, then left at room temperature.

When the mechanical properties and the percentage crystallinity of the fibers treated as described above were determined, the values set forth in Table 1 were obtained:

Table 1 Softening point in water Dry strength a s! denier) Percentage Crystallinity Fineness (denier) Four samples of wet-spun polyvinyl alcohol fibers were heated by immersion in a molten metal (lead) bath at 225 C. for 1.5 minutes and were then cooled at various temperatures as described below.

Sample No. 1: In an oven at 100 C. for 1 hour, then left at room temperature.

Sample No. 2: In an oven at C. for 1 hour, then left at room temperature.

7 Sample No. 3: In an oven at 60 C. for 1 hour, then left at room temperature. Sample No. 4: Left at room temperature immediately.

The properties of the thus-treated fibers were found to be as follows:

' Table 2 Wet Wet knot Softening Sample No. Fmeness strength strength point in (denier) (granis/ (grams/ Water denier) denier) 0) These tests show that slow cooling at a temperature above the second transition point C.) is effective to increase the wet knot strength and other properties.

EXAMPLE 3 Five samples of wet-spun polyvinyl alcohol fibers were heat-treated at. 225 C. for 15 minutes as described in Example 2 and they were then further treated at 100 C. for various periods of time as described below.

Sample No. 1: Maintained in an oven at 100 C. for 2 hours, then left at room temperature.

The results of tests upon the thus-treated fibers are set forth in the following table:

Table 3 Wet Wet knot Fineness strength strength Sample N o. (diener) (grams/ (grams/ denier) denier) These results show that it is desirable to effect slow cooling as a type of annealing for a prolonged period of time. However, the relationship between the degree of discoloration of the fibers and the annealing time and temperature are shown in the accompanying drawing. At temperatures of up to about 100 C., even when the fibers were treated for hours, there was no discoloration.

As previously indicated, the process of this invention is applicable to all types of fibers derived from polyvinyl alcohol produced in conventional manner and subjected to conventional treatments and processing operations, such as acetalization, stretching, and the like. Such fibers are conventionally spun from spinning solutions by known wet and dry spinning techniques. Spinning techniques are described, for example, in Cline et al. US. Patent 2,610,360 and Osugi et a1. Patent 2,906,594. An especially preferred spinning technique is described in copending As previously mentioned, the heat treating step which is combined with the controlled cooling step of this invention is carried out in conventional manner at a temperature above the second transition point but below the melting point, e.g. at 200 to 225 C., for a short time, e.g. 1 to 2 minutes. Heat treatment is effected in a molten metal bath or in a hot salt bath or even in heated air in accordance with known practice. Such heat treatment, and subsequent controlled cooling, is effected while maintaining the fibers under tension at a constant length in accordance with conventional techniques.

It will be understood that the conditions and the relative relationships set forthabov e which are illustrative of the invention are those preferred in carrying'out the process of the invention but it will be understood that other conditions and relationships may be used within the scope of the invention.

It will, therefore, be further understood that various changes and modifications may be made in the embodiments of the invention herein described without departing from the scope of the invention as defined in the appended claim. It is intended, therefore, that all matter contained in the foregoing description and in the drawing shall be interpreted as illustrative only and not as limitative of the invention.

We claim:

Polyvinyl alcohol fibers having a high percentage of crystallinity and a high knot strength produced by heating polyvinyl alcohol fibers to a temperature above the second application Serial No. 336,166 of Tomonari et al., filed February 10, 1953. Typical processes of treating polypatents and applications.

transition point but below the melting point and effecting step-Wise cooling of said fibers by maintaining them at a temperature above the second transition point but at a maximum of about C. for a period of time up to 2 hours and then cooling the fibers to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,088 Pinsky July 4, 1950 2,732,592 Tunnicliif et a1. Jan. 31, 1956 2,878,519 Wolinski Mar. 24, 1959 2,906,594 Osugi Sept. 29, 1959

Images