JPS6017111A - Preparation of extremely thin yarn of polypropylene - Google Patents

Abstract

PURPOSE:To obtain the titled extremely thin yarn free from troubles during preparation of pellets and melt spinning, by blending a crystalline polypropylene with a specific molecular weight modifier, pelletizing it, subjecting it to melt spinning, drawing it. CONSTITUTION:A crystalline powdery polypropylene having 0.1-20g/10min melt flow rate at 230 deg.C is blended with 0.02-1.0wt% hydroperoxide such as 2,5-dimethylhexane-2,5-dihydroperoxide, etc. as a molecular weight modifier having >=250 deg.C decomposition temperature to provide 1min half-life. Then, the mixture is melted and extruded by a pelletizer at <=230 deg.C to give pellets, these pellets are subjected to melt spinning at >=250 deg.C, and draw to give the desired extremely thin yarn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ultrafine polypropylene fibers.

Ultrafine polypropylene fibers are used for nonwoven fabrics and separation membranes, but the MFR (melt flow rate) is low.
It is difficult to obtain ultrafine fibers of 2d (denier) or less with polypropylene of y/1o minute (hereinafter, the description of y/1o minute may be omitted) or less, and it is necessary to use polypropylene with an MFR of 100 or more. be.

Methods for producing polypropylene with an MFR of 100 or more include a method of introducing a large amount of H2 gas during propylene polymerization, or a method of decomposing the polypropylene obtained by polymerization with peroxide in an extrusion state. However, in order to feed polypropylene to a spinning machine, it is necessary to pelletize it, and all of these methods suffer from a significant decrease in the discharge amount due to backflow in the extrusion pelletization process and low melt viscoelasticity. This method is not practical as it causes many troubles in the field such as frequent cutting defects when cutting pellets.

To solve this problem, it is possible to use peroxide as it is, in combination with a dispersant, or by mixing it with pellets in the form of a masterbatch during spinning, and then decomposing it at high temperatures and spinning. Phenomena such as yarn breakage due to non-uniformity and melt sloshing at the spinning nozzle occurred.

The inventors completed this invention as a result of intensive studies to solve these problems.

That is, this invention has an MFR of 0.1 to 2 at 230°C.
The decomposition temperature required to obtain a half-life of 1 minute as a molecular weight reducer for crystalline polypropylene of 0 g/10 minutes is 250
Hydroperoxide with a temperature of 0.02~CO weight ratio is added and mixed, and the mixture is melt-extruded in a pellet molding machine at a temperature of 230°C or less to obtain pellets.
The present invention relates to a method for producing ultrafine polypropylene fibers, which is characterized by melt-spinning and drawing at a temperature of 20° C. or higher.

By the method of this invention, it has become possible to produce ultrafine fibers without any trouble during pellet production or melt spinning.

In other words, in the extrusion pelletizing process, molecular weight reduction or almost no molecular weight reduction occurs, and therefore pellets with good extrusion conditions and no cutting defects are obtained.Also, the peroxide added as a degrading agent is mostly undecomposed and pellets are formed. It is possible to achieve uniform decomposition in the ninth-order spinning machine.

The crystalline polypropylene used in the method of the present invention is a homopolymer having an MFR of 0.1 to 20 f710 minutes, and is usually used in the form of a powder.

If the MFR is lower than 0.1, excessive power is required during extrusion, which is not practical, and if the MFR is higher than 2o, the effect of the present invention will be reduced.

As additives, antioxidants, light stabilizers, ultraviolet absorbers, slip agents, etc. can be included.

In addition, the hydroperoxide having a decomposition temperature of 250°C or higher to obtain a half-life of 1 minute, which is used in the method of the present invention, is preferably 2,5-dimethylhexane 7-2.5
-dihydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide and the like.

These can be used as they are or after being dispersed and diluted with wollastonite powder, silica gel, etc.

The hydroperoxide is used as a degrading agent for crystalline polypropylene, and the amount thereof is 0.02 to 1.0% by weight, preferably 0.02% by weight, based on the crystalline polypropylene.
05 to 0.5% by weight. If the amount of the hydroperoxide is less than 0.022% by weight, the effect of the present invention will be reduced, and if the amount of the hydroperoxide is more than 1.0% by weight, the decomposition of the hydroperoxide in the spinning machine will not occur. This is not desirable as it may become complete.

In the method of the present invention, a known suitable mixing method is applied to first mix the crystalline polypropylene and the hydroperoxide in a specific proportion in a pellet molding machine at a temperature of 230°C or less, preferably 170°C or less. 210℃ (
The average residence time is preferably 1 to 15 minutes. ) to obtain pellets.

As the pellet molding machine, a screw extruder set pelletizing device is used.

If the temperature at which the crystalline polypropylene and hydroperoxide are melt-extruded is higher than the upper limit, the crystalline polypropylene will decompose and the extrusion state of the melt and the cutting state during pelletization will deteriorate, which is not preferable.

In the method of this invention, the pellets obtained as described above are heated at a temperature of 250°C or higher, preferably 250°C to 250°C.
The fibers are melt-spun at a temperature of 80° C. and drawn using a known appropriate drawing method to obtain ultrafine polypropylene fibers.

For the above-mentioned melt spinning, a known melt spinning machine equipped with a die, an IJ, and a complete extruder can be used.

If the temperature at which the pellets are melt-spun is lower than the lower limit, undecomposed hydroperoxide remains in the polypropylene fibers obtained by melt-spinning, and the strength of the resulting ultrafine polypropylene fibers decreases, which is not preferable.

Examples and comparative examples are shown below. On each side 1 part means part by weight, crystalline polypropylene MFRu:A
Measured according to STM D12 filter 8.

Example 1 For 100 parts of polypropylene powder with MFR 9.0 g/10 min ([ηJ = 2.1, Decalin 135°C), BITo, 05 parts, Ganox 1010o,
5g of calcium stearate, 1 part of calcium stearate, and 0.15 part of monobutyl hydroperoxide were added and blended in a Henschel mixer.
It was extruded at a vent (-1') and cut under water to obtain pellets.

The temperature setting of the extruder at this time is cylinder part 170-190.
℃, the die temperature is 200℃, and the resin temperature at the die exit is 2
05°C (average residence time above 170°C 6 minutes). The discharge amount is 2.
5 ton/hr, and the cutting condition is good.

[η] of the pellet was 2.0, with almost no decomposition occurring. This pellet was used to produce an undrawn yarn using a screw gear pump type spinning machine at a winding speed of 260°C + 1100 m/min, and the obtained undrawn yarn (4d) was
Hot drawing was carried out at 0° C. to obtain a drawn yarn of 0.8 d. This thing M
The FR is 125 g/10 minutes and [η] is 0.8. The strength was 7.0 y/, a, and the elongation was 20.6 y/.

Comparative Example 1 Powder having the same composition as in Example 1 was applied to ring parts 200 to 2.
Temperature set to 50℃, dice 260℃ Shidabe/1, attachment 25
0. Extruded using an extruder.

At a discharge rate of 1.9 ton/hr, resin was observed to flow out from the vent.

In addition, cutting was difficult, resulting in a large number of irregularly shaped pellets, and an increase in oversize.

The MFR of the pellet was 110 f/10 min.

Comparative Example 2 In place of t-butyl hydroperoxide in Example 1, 0.15 part of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was used.

The extrusion amount is 2. Oton/hr + MFR of pellets
Cutting was difficult at 98 f/10 min, and a large number of irregularly shaped pellets were produced.

Comparative Example 6 M F R9,0! 710 minutes! J Flopylene pellets (B HT o, os sound I engineering rganox
0.15 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (supported with silica) was blended with The fibers were spun at 260° C. and 1100 m/min using a screw gear pump type spinning machine.

Thread breakage occurred frequently.

Patent applicant: Ube Industries Co., Ltd.

Claims (1)

[Claims] For crystalline polypropylene with an MFR of 0.1 to 20 g/10 min at 230°C, 9 hydroperoxides with a decomposition temperature of 250°C or higher to obtain a half-life of 1 minute as a molecular weight reducer are used. A polypropylene microfiber characterized by adding and mixing 1.0% by weight and melt-extruding it in a pellet molding machine at a temperature of 260°C or lower to obtain pellets.Then, the pellets are melt-spun at a temperature of 250°C or higher and drawn. manufacturing method.