JPH051111A - Polypropylene pellet - Google Patents

Abstract

PURPOSE: To provide polypropylene pellets with improved processability such as spinnability, extrusion properties by adding a free radical prodegradant such as 2,5-dimethyl-2,5-bis(t-butyl-peroxy)hexyne-3 having a specific value of half-life into a polypropylene.

CONSTITUTION: Low melt index polypropylene leaves are prepared by polymerizing propylene in a polypropylene reactor and into this polypropylene, at least 0.01%, based on the weight of polymer, compound such as 2,5-dimethyl-2,5-bis(t- butylperoxy)hexyne-3, 3,6,6,9,9-pentamethyl-3-(ethylacetate)-1,2,4,5-tetraoxycyclo- nonane is added as a free radical prodegradant having a half-life at 190.6°C of over 0.5 minute and uniformly mixed. Then the resulting mixture is pelletized in a pelletizer operating at 190.6°C for a retention time of about 2 minutes to obtain the desired polypropylene pellets with improved processability.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

The present invention relates to polypropylene polymer pellets having improved processability such as spinnability and extrudability. A polypropylene polymer having good processability for processing into a fiber or film preferably has the following attributes. 1) Do not break when deliquescing from the molten state. A polymer having this property has a high production amount per unit time when processed into a fine filament or a thin film having a high strength as compared with an unrefined material. 2) Capable of being pumped through pipes and capillaries, and / or requiring a minimum amount of energy for defiberization into fibers and films. This property means that the melted polymer has low shear stress and draw viscosity.

It has been proved that this first attribute (high fineness) can be achieved by using a polypropylene polymer having a small molecular weight distribution (defined by the ratio of the weight average molecular weight to the number average molecular weight). The second attribute (low shear stress and low stretching viscosity) can be achieved by using a polymer having a low weight average molecular weight. When a fine fiber or thin film is produced using the Ziegler-Natta catalyst currently used in the production of polypropylene for commercial use, a polymer with an excessively large molecular weight distribution comes out from the polymerization reactor. Thus, the low weight average molecular weight polymers produced in such reactors have low viscosities which are favorable for processing, but the desired refinement cannot be achieved. Therefore, in the polypropylene manufacturing industry, a polymer having a very high weight average molecular weight is obtained after a random molecular fragmentation step (thermal decay or chemical collapse) that has an inherent effect of reducing the molecular weight distribution and simultaneously reducing the weight average molecular weight to a desired level. Required to be manufactured.

Polypropylene is chemically disintegrated by the addition of compounds that decompose to form free radicals. Chemical stabilizers added to increase the end use stability of polypropylene can interfere with the action of the free radical generator. However, some free radical generator-type chemicals, such as certain types of organic peroxides, such as those described in British Patent No. 1,442,681, are minimally affected by commonly used stabilizers, and It can be a preferable disintegration accelerator.

However, the extent to which polymers can be disintegrated is limited by the inability of polymer making machines to form pellets from very low viscosity polymers. Therefore, a polypropylene processing machine for producing films and fibers has a problem that polypropylene, which is not optimal for processing into films and fibers, must be used as a material. Thus, polymers with high viscosity properties for pelletizing and low viscosities for end use processing have been required.

When polymer manufacturers commercially pelletize low-viscosity polypropylene polymers, which are preferred by polymer processors, they inevitably result in excessive "stringing" (pellets with long tails), which results in manufacturers and processing. It was also the cause of squeezing the vendor's equipment. In order to increase the viscosity of the polymer in order to pelletize it, it has been proposed to operate the pelletizer at a temperature just above the melting point of the polypropylene polymer to improve the cutting properties of the pellet. This cannot be accomplished without lowering the unit yield to reduce the heat generated by shear stress in the pelletizer and / or cooling the molten polymer. However, both of these methods add cost to the process and further complicate the process.

It has also been proposed to additionally add a chemical disintegration promoter to polypropylene pellets before the polymer is formed into fibers or films in end-use processing to reduce the viscosity of the polymer. However, this method has some disadvantages. It is 1) These peroxide type disintegration accelerators require special handling processes and equipment because they are at risk of ignition and explosion. 2) For peroxides to work most effectively, they must be evenly dispersed in the polymer prior to decomposition and reaction. If this is not done, a polymer with uneven viscosity will be produced, and the molecular weight distribution will be even larger than that of the polymer before processing. Polymer manufacturers who can produce finer flakes rather than pellets in a reactor using specialized equipment are in very favorable conditions to achieve the above uniform distribution. 3) Processor equipment can be damaged by polymers with uneven viscosity. 4) If it is well dispersed in the polymer before the reaction, the peroxide functions more effectively as a disintegration promoter. 5) If the peroxide is simply added on top of the pellets rather than in the pellets, the peroxide will act as a lubricant in the feed section of the extruder, thus reducing the unit production for a given rpm. Resulting in.

It is also possible to reduce the molecular weight by thermally degrading polypropylene using very high temperatures in the processing step. However, if the temperature is raised to an abnormally high level, the following problems will occur. 1) The life of the device is shortened. 2) There is a limit to the amount of unit production because rapid cooling cannot be done freely. 3) It requires excessive energy consumption. 4) It becomes a dangerous process site because high temperature is used. 5) Other problems.

[0008] Other problems include the following problems. 1) Excessive disintegration occurs, requiring more additive to be added to the polymer than the final product requires. 2) Due to the limited range of additives that can be used, it is necessary to use more expensive or non-optimal additives. 3) Polymer is pumped through pipes and capillaries, or clogged with collapse products when applied to a die mold.

Further information is available from the following prior art patents. British Patent No. 1,442,681 describes a process for producing polypropylene which comprises the step of producing a polypropylene polymer having a small molecular weight distribution and disintegrated with a peroxide type disintegration accelerator. U.S. Pat. No. 3,867,534 describes the use of aliphatic peroxides as disintegration promoters for polypropylene and discusses the problems associated therewith, and as a solution to this problem. It is proposed to avoid unreacted disintegration promoters.
U.S. Pat. No. 3,144,436 describes a method of disintegrating stereoregular polymers which involves the use of free radical initiators.
One example describes a two-step process that controls the operation of injecting a disintegration promoter into the melting region of an extruder. U.S. Pat. No. 3,849,241 and U.S. Pat. No. 3,978,18
No. 5 describes an improved melt blowing method by controlling the disintegration of the polymer. Similarly, US Pat. No. 3,755,527 describes the advantages of polymer degradation.

The present invention comprises 1) a stepwise polymer disintegration comprising the step of first producing a polymer which is readily formed into pellets which upon heating further disintegrate produces a low viscosity polymer which can be conveniently processed into high quality films and fibers. And 2) a polypropylene polymer containing a disintegration promoter in the form of pellets or other shapes obtained by the method. According to the present invention, when a specific free radical generating chemical agent that acts as a disintegration accelerator for polypropylene is added to a polymer and the pelletizing apparatus is operated in a prescribed manner, a part of the above chemical agent ends the pelletizing step. However, it is based on the discovery that it remains unreacted. That is, after the extrusion step for forming pellets, when the reaction is interrupted and then extruded again, the remaining disintegration accelerator reacts to produce a polymer which can be processed into a transparent film or fiber which can be easily processed. . The exact residual rate of the disintegration promoter after pelletization in the manufacturing process depends on the pelletization temperature, the residence time of the disintegration promoter at the temperature, and the type of disintegrant. However, half to 90% of the amount initially added is preferred. Ideally, no disintegration should occur during pelletization, but in practice some disintegration promoter will react during pelletization. The amount of the disintegration accelerator that reacts in the initial stage is as small as about 10%, and since the viscosity of the polymer in the pelletizer is only slightly lowered, well-formed free-flowing pellets can be produced. After the pelletizing step, it is necessary that at least 0.01% of the disintegration promoter, based on the weight of the polymer, remain in order to obtain satisfactory results. Thus, the advantages of the two-step disintegration addition method described in connection with the prior art patents are retained and the disadvantages are substantially eliminated.

The present invention is applicable to the production and processing of polypropylene. The present invention is also applicable to processing waste polypropylene material for reuse in film and fiber formation. It will be apparent to those skilled in the art that optimum operating conditions and concentrations will, of course, depend on the properties of the polymer used and the extreme properties desired by the processor. The polypropylene produced generally has a high weight average molecular weight in the range of about 250M to 500M and a molecular weight distribution of about 10-15. Polypropylene for high speed spinning and fiber forming has a weight average molecular weight distribution of about 2.5 to 4.5.
However, when the molecular weight is reduced to 130 M or less, it becomes difficult to process the polypropylene resin into pellets on a commercial level. Poorly formed pellets that are difficult to transport and handle are produced with low viscosity polymers. Therefore, manufacturers tend to limit the disintegrating action of polypropylene prior to shipping so that the molecular weight does not fall below about 160M. Many disintegration promoters are used to achieve the above degree of disintegration in pelletizers. And almost all of these disintegration promoters react fully under conditions where the peroxide disintegrant decomposes at various rates depending on temperature and environment. The rate of degradation is defined by the half-life.

According to the present invention, a free radical source disintegration promoter having a half-life in polypropylene of greater than 30 seconds at 190.6 degrees Celsius is sufficient to provide the final polymer properties desired by the polymer processor. Only added to the flaky high molecular weight polypropylene polymer produced by the reactor. Use a disintegration promoter with a short half-life,
Alternatively, if it is necessary to leave a large amount of disintegration promoter unreacted throughout the pelletizing step, the disintegration promoter may be injected into the molten polymer stream. Since it is necessary to disperse the disintegration promoter uniformly to obtain the maximum effect, it is necessary to perform the mixing process after injecting the disintegration promoter. In general, disintegration promoters must not interfere with or conversely interfere with the commonly used polypropylene stabilizers, and also effectively generate free radicals that initiate the disintegration of polypropylene as it decomposes. Must be something that However, the disintegration promoter must have a sufficiently short half-life at the re-extrusion temperature at the polymer processor that it reacts substantially entirely before exiting the extruder. The half-life of the disintegration accelerator in polypropylene is 287.8 degrees Celsius.
It must be less than 9 seconds in degree so that at least 99% of the disintegration promoter in the pellets has reacted by the time the 1 minute extruder residence time at this temperature has elapsed. Such disintegration promoters include, by way of non-limiting example, the following compounds: That is, 2,5-dimethyl 2,5 bis- (t
-Butylperoxy) hexyne-3 and 4-methyl 4t-
Butyl peroxy-2 pentanone (eg Penwalt Corpor
Loopersol 130 and Loopersol 120) sold by Lucidol Division of ation, 3, 6, 6,
9,9-pentamethyl-3- (ethyl acetate) -1,2,
4,5-texitraoxycyclononane (Wifco Chemic
al., USP-138), 2,5-dimethyl-2,5 bis- (t-butylperoxy) hexane (e.g. Loopersol 101) and 1-3-bis- (tert-butylperoxyisopropyl) -benzene (Herc.
It is a Vulcup R) sold by ules, Inc. Among the above compounds, Wifco USP-138 and Looper Sol 13
0 is most preferred. The preferred concentration of free radical source decay accelerator is in the range of about 0.01% to 0.4% by weight of the polymer. Desirably, the pelletizer operates to retain at least 75% of the disintegration promoter added to the pellets. When the polymer user applies the polymer to the extruder, the temperature will cause the polymer to resume disintegration and proceed to the desired extent to react substantially completely in the re-extrusion process. Generally, such extruder temperatures are in the range of about 237.8 degrees Celsius to 287.8 degrees Celsius. These conditions can also be applied to the disintegration action in the extruder die assembly.

In the following examples, a melt index measuring device (A of weight 2160 g and operating at a temperature of 80.6 degrees Celsius) is used.
The melt index is determined using STM1238). The sample was heated for 5 minutes to reach equilibrium before testing. The melt index is 10 from a 2.1 mm diameter thin tube.
Expressed in g of quantity delivered per minute. Example 1 A polypropylene reactor was used to obtain flakes with melt index values lower than 1. 0.275
A weight percentage of Looper Sol 130 was added to the flakes to prepare a homogeneous blend. The formulation was pelletized by a pelletizer operating at 190.6 degrees Celsius with a residence time of about 2 minutes. Theoretically, about 22% of the peroxide has reacted. The pellet melt index was measured and found to have a melt index of about 55. The actual melt index of the pellets is believed to be in the range of 40 to 45 because about 10% of the disintegration promoter in the pellets reacted in the melt index meter. The polymer was easily pelletized. The resulting polymer pellets were comparable to ordinary commercial pellets.

Next, these pellets were subjected to a temperature of 237.8 degrees Celsius.
The extruder was subjected to a re-extrusion process with a residence time of about 3 minutes. The melt index of the extrudate was measured to be about 5
A value of 50 was obtained. The melt index was increased from 550 to 580 when the extrudate was re-extruded to demonstrate that the 237.8 degree Celsius extrusion step had no effect on the melt index. Thus, about 95% of the melt index increase was due to the disintegration promoter in the pellets and about 5% was due to the action of the extruder. (Example 2) The same thin section and apparatus as in Example 1 were used. However, the difference from Example 1 is that 0.3% looper sol 130 was added to the flakes. The melt index of the pellets was measured and found to be 45-50. The extrudate during the re-extrusion process was found to have a melt index of about 660. Similar to Example 1, the pellet cutting characteristics were commercially satisfactory. Example 3 Witco Chemical USP-138 was applied to flakes so that its concentration was 0.35 weight percent. This formulation was subjected to an extrusion process with a temperature of 190.6 degrees Celsius and an extruder residence time of about 2 minutes. The melt index of the extruded sample was measured and found to be about 15. When this sample was subjected to a re-extrusion process at a temperature of 251.7 ° C. and a residence time of 3 minutes, the melt index was 2
A value of 15 was measured. Flake processed by the above method without the addition of peroxide had a melt index of 1.7 measured. (Example 4) 2% looper sol 130 was applied to Hercules PC
It was compounded into a commercial polypropylene pellet called -973. This formulation was then subjected to an extrusion process with a temperature of 170 degrees Celsius and a residence time of 1 minute. Theoretically, 98% of the peroxide would remain unreacted in the extrudate.
The peroxide-concentrated extrudates were then compounded into polypropylene pellets in various proportions. A theoretical equivalent of pure peroxide was added to the other pellet. These "concentrate" / polypropylene blends and liquid peroxide / polypropylene blends were separately subjected to the extrusion process using a Brabender extruder at a temperature of 240.6 degrees Celsius and a residence time of 7 minutes. The viscosity of the pellet discharged from the tip of the extruder die was measured and the value is shown in FIG. It turns out that both are equivalent.

The present invention thus comprises a concentrate of non-disintegration promoters. A disintegration promoter with a concentration of up to 5% by weight can be easily formed, and a high-concentration disintegration promoter can be formed. Without limiting the invention to any particular theory,
The significance of the particular disintegration promoter characteristics can be postulated. From the calculation of the half-life, it can be seen that the half-life reaction rate coefficient approximately follows Arrhenius' law.

That is, lnK = -19,700 / T + 40.4 (looper sol 130) lnK = -19,700 / T + 41.6 (looper sol 101) where K = reaction rate coefficient per minute in polypropylene. T = absolute temperature. When K is obtained, the amount of the unreacted disintegration accelerator after a certain period of time can be obtained by the following formula.

C _A / C _B = e ^{-Kt, where} C _A = concentration of unreacted disintegrant. C _B = initial concentration of disintegration accelerator t = reaction time (min) For example, comparing unreacted rate after 1 minute at 210 degrees Celsius (absolute 483 degrees), Loopersol 101 has only 1
In the case of looper sol 130, it becomes 50% with respect to 0%.

In addition, it can be seen that the viscosity of the polymer exiting one device can be predicted by the formula: 1 / μ = 1 / μ _A + KC _{R where} μ = viscosity of polymer exiting the device after chemical disintegration.

Μ _A = Viscosity of the polymer exiting the device without chemical disintegration. K = chemical decay efficiency coefficient. C _R = amount of disintegration promoter that reacts upon exiting the device. Note for a C _R = C _B -C _A, Applying this formula to the above equation to obtain a _{1 / μ = 1 / μ A} + KC A (1-e -Kt).

Thus, considering a constant (KC _B ), the ultimate viscosity of the polymer is all the same after a long reaction time, regardless of the disintegration promoter used. However, the correlation between viscosity and time depends on the half-life reaction rate coefficient K. For example, the initial viscosity of the polymer when the FIG. 1 has implemented pelletizing / extrusion process by (a typical value for example Rupazoru 130 or Rupazoru 101) KC _A and C 201.7 ° 0.005 poise ^-1 1 is a graph showing the relationship of time out polypropylene polymer viscosity with time based on 10,000 Poise. This graph shows Looper Sol 1
The intrinsic viscosities of the 30 sample and the Looper sol 101 are almost the same, but the "pelletizing" viscosity at a normal pelletizing time in the range of 1 to 3 minutes is that the looper sol 130 is about twice as much as the looper sol 101. Has been proven.

When a disintegration accelerator having a short half-life is used, the viscosity of polypropylene at the time of leaving the pelletizer at a residence time of 1 minute at 201.7 ° C. is only 67% of that of Loopersol 101, and Loopersol 130. It is only 30% of the case of. Thus, Looper Sol 130 is most preferred. In the case of looper sol 130, about 50% of the disintegration promoter may remain after the pelletizing process, but the initial loading is so small that there is little danger in handling the polymer. In the re-extrusion process, the processing conditions are generally at least 237.8 degrees Celsius, and at this temperature, the half-life coefficient of the looper sol 130 exceeds 6 / min, so the residual amount of the disintegration accelerator after the re-extrusion process is Virtually nothing. With a device residence time of only 2.5 minutes, for example, only 0.000017% of the peroxide in the pellets remains in the extrudate. For example, if the polypropylene pellets sent by the manufacturer contain 0.2% looper sol 130, the processor's extrusion equipment is 237.8 degrees Celsius.
The extruder residence time is 2.5 minutes, and the concentration of looper sol 130 in the polymer exiting the extruder is below 1 ppb.

As described above, according to the present invention, the pellets can be easily pelletized by the polymer manufacturer, and at the same time, the pelletizing capability of the processor is significantly improved and the pellets are completely satisfied with the above objects and advantages. What is provided is a polymer composition that can improve the method of manufacture.

[Brief description of drawings]

FIG. 1 is a graph showing the correlation between the reaction time and the viscosity at the extrusion temperature of polypropylene using the examples of the two disintegration promoters according to the present invention.

Claims (2)

[Claims] 1. The half-life in polypropylene is 190.degree.
Polypropylene pellets containing a free radical source disintegration promoter having a value of over 0.5 minutes at a temperature of 6 degrees. 2. The disintegration accelerator is 2,5-dimethyl-
2,5 bis- (t-butylperoxy) hexyne-3 and 3,6,6,9,9-pentamethyl-3- (ethyl acetate) -1,2,4,5-texitraoxycyclononane and At least 0.0 based on weight of polymer
Polypropylene pellets according to claim 1, characterized in that they are present in an amount of 1%.