JPH0443924B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for obtaining polypropylene polymer pellets having improved processability such as spinnability and extrudability. Polypropylene polymers with good processability for processing into fibers and films preferably have the following attributes:

1. Do not break when turning from molten state to finesse. Polymers with this property have a higher yield per unit time when processed into fine filaments or thin films with higher strength than non-attenuated materials.

2. It can be pumped through piping or thin tubes, and/or the energy required to decompose it into fibers or films can be minimized. This property means that the shear stress and drawing viscosity of the molten polymer are low.

This first attribute (high fibrousness) is defined by the molecular weight distribution (defined as the ratio of weight average molecular weight to number average molecular weight)
It has been proven that this can be achieved using polypropylene polymers with low The second attribute (low shear stress and low drawing viscosity) can be achieved by using polymers with low weight average molecular weights.

If fine fibers or thin films are produced using the Ziegler-Natsuta catalyst, which is currently used in the production of commercially available polypropylene, a polymer with an excessive molecular weight distribution will come out of the polymerization reactor. Thus, while low weight average molecular weight polymers produced in such reactors have low viscosities that are desirable for processing, they are unable to achieve the desired fiberization. Therefore, the polypropylene manufacturing industry produces polymers with very high weight average molecular weights after a random molecular fragmentation process (thermal or chemical collapse) which has the inherent effect of narrowing the molecular weight distribution and simultaneously lowering the weight average molecular weight to the desired level. is required to be manufactured.

Polypropylene is chemically degraded by adding compounds that decompose to form free radicals.
Chemical stabilizers added to enhance the end-use stability of polypropylene can interfere with the action of free radical generators.

However, some free-radical-generating chemicals, such as the particular class of organic peroxides described in GB 1442681, are minimally affected by commonly used stabilizers and are therefore preferred decay promoters. It can be an agent.

However, the degree to which the polymer can be disintegrated is limited by the inability of polymer manufacturing machines to form pellets from very low viscosity polymers. Therefore, polypropylene processing machines for producing films and fibers have the problem of having to use polypropylene as a material, which is not optimal for processing into films and fibers. Thus, there has been a need for polymers with high viscosity properties for pelletizing and low viscosity for end-use processing.

When polymer manufacturers commercially pelletize low viscosity polypropylene polymers, which are desirable to polymer processors, they inevitably produce excessive "stringiness" (long-tailed pellets).
This also caused the equipment of manufacturers and processors to become clogged.

In order to increase the viscosity of the polymer for pelletizing it has been proposed to operate the pelletizer at a temperature slightly above the melting point of the polypropylene polymer to improve the cutting properties of the pellets. This cannot be achieved without lowering the unit production to reduce the heat generated by shear stress in the pelletizing equipment 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 add additional chemical disintegrators to polypropylene pellets to reduce the viscosity of the polymer before it is formed into fibers or films in end-use processing. However, this method has some disadvantages. 1. These peroxide-type disintegration accelerators require special handling processes and equipment due to the risk of ignition and explosion.

2. For peroxide to work most effectively, it must be uniformly dispersed in the polymer before it can be decomposed and reacted. Failure to do so will result in a polymer with uneven viscosity and a larger molecular weight distribution than the unprocessed polymer. Polymer manufacturers who are able to produce flakes, rather than pellets, in their reactors using specialized equipment are very well placed to achieve this uniform distribution.

3. Processor equipment is damaged by polymers with uneven viscosity.

4. If the peroxide is well dispersed in the polymer before the reaction, it will function more efficiently as a disintegration accelerator.

5. If peroxide is added simply onto the pellets rather than into them, the peroxide acts as a circulating lubricant in the feed section of the extruder, reducing unit production for a given revolutions per minute. I end up.

The molecular weight can also be reduced by thermally collapsing the polypropylene using very high temperatures during the processing process. However, if the temperature is raised to an abnormally high temperature, the following problems will occur.

1 The life of the device will be shortened.

2 Unit production is limited because rapid cooling is not possible.

3. Requires excessive energy consumption.

4. It becomes a dangerous process site because high temperatures are used.

5 Other issues.

Other issues include the following issues:

1. Excessive disintegration occurs, requiring more additives to be added to the polymer than the final product requires.

2. The range of additives that can be used is limited, requiring the use of more expensive or suboptimal additives.

3. Polymers and piping become clogged with decay products when they are pumped through thin tubes or applied to die molds.

Further information is available from the following prior patents: British Patent No. 1442681 describes a method for producing polypropylene which includes a step of disintegrating with a peroxide-type disintegration promoter to produce a polypropylene polymer with a narrow molecular weight distribution. US Patent No. 3867534
The issue describes the use of aliphatic peroxides as disintegration accelerators for polypropylene.
It also discusses the problems associated with this and further suggests the avoidance of unreacted disintegration promoters as a solution to this problem. US Patent No.
No. 3,144,436 describes a method for disintegrating stereoregular polymers that involves the use of free radical initiators. One embodiment describes a two-step process controlling the injection of disintegration promoter into the melt zone of an extruder. U.S. Patent No. 3,849,241 and U.S. Patent No.
No. 3,978,185 describes an improved melt blowing process by controlling polymer disintegration.
Similarly, US Pat. No. 3,755,527 describes the advantages of polymer disintegration.

The present invention provides a stepwise polymer disintegration process that includes 1) first producing a polymer that is readily formed into pellets that, upon heating and further disintegration, produce a low viscosity polymer that can be conveniently processed into high quality films and fibers; 2) It relates to pellets or other forms of disintegration accelerator-containing polypropylene polymers obtained by the method.

The present invention provides that when a specific free radical generating chemical agent is added to the polymer which acts as a disintegration accelerator for the polypropylene and the pelletizing equipment is operated in a specified manner, a portion of said chemical agent is added to the polymer until the pelletizing process is completed. It is based on the discovery that even when exposed to heat, it remains unresponsive. That is, after the extrusion step to form pellets,
When the reaction is stopped and extrusion is carried out again, the remaining disintegration promoter reacts to form a polymer that is easily processed and can be made into films and fibers with transparent properties. The exact residual rate of the disintegration accelerator after pelletization in the manufacturing process depends on the pelletizing temperature, the residence time of the disintegration accelerator at that 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 reality some of the disintegration accelerator reacts during pelletization. The amount of initially reacting disintegration accelerator is small, on the order of 10%, and only slightly reduces the viscosity of the polymer in the pelletizer, resulting in the production of well-formed, free-flowing pellets. After the pelletizing step, it is necessary that at least 0.01% of the disintegration promoter remain based on the weight of the polymer to obtain satisfactory results. Thus, the advantages of the two-step disintegration addition method described in connection with the prior patent are retained;
Moreover, the disadvantages are virtually eliminated.

The present invention is applicable to the production and processing of polypropylene. The present invention is also applicable to processing waste polypropylene materials for reuse in film and fiber formation. It will be appreciated by those skilled in the art that optimal operating conditions and concentrations will depend on the properties of the polymer used and the extreme properties desired by the processor.

The produced polypropylene is generally about 250M
It has a high weight average molecular weight in the range of 500M to 500M and a molecular weight distribution of about 10 to 15. Polypropylene for high speed spinning and fiber forming has a weight average molecular weight distribution of about 2.5 to 4.5. However, as the molecular weight decreases below 130M, it becomes difficult to process polypropylene resin into pellets at a commercial level. The use of low viscosity polymers produces poorly formed pellets that are difficult to transport and handle. Manufacturers therefore tend to limit the disintegration of polypropylene before shipping so that the molecular weight does not fall below about 160M. A number of disintegration promoters are used to achieve the above degrees of disintegration in pelletizers. And almost all of these disintegration accelerators fully react under conditions where the peroxide-type disintegrant decomposes at varying rates depending on temperature and surroundings. Degradation rate is defined by half-life.

According to the present invention, the half-life in polypropylene is
A free radical source decay accelerator having a value greater than 30 seconds at 190.6°C is added to the flaked high molecular weight polypropylene polymer produced by the reactor in an amount sufficient to produce the final polymer properties desired by the polymer processor. Added. If a disintegration accelerator with a short half-life is used, or if large amounts of disintegration accelerator need to remain unreacted throughout the pelletizing process, the disintegration accelerator can be injected into the molten polymer stream. good. After the disintegration accelerator is injected, a mixing step is required since the disintegration accelerator needs to be uniformly dispersed for maximum effectiveness. In general, disintegration accelerators should not interfere with or adversely interfere with commonly used polypropylene stabilizers and, upon decomposition, should effectively generate free radicals that initiate polypropylene disintegration. It must be something that does. However, the disintegration promoter must have a sufficiently short half-life at the re-extrusion temperature at the polymer processor so that it is substantially entirely reacted before exiting the extruder. The half-life of disintegration accelerator in polypropylene is 287.8℃
at less than 9 seconds so that at least 99% of the disintegration promoter in the pellets has reacted by the end of 1 minute extruder residence time at this temperature. Such disintegration promoters include, by way of non-limiting example, the following compounds: That is, 2,5
-dimethyl2,5bis-(t-butylperoxy)
Hexyne-3 and 4-methyl 4t-butylpexy-
2pentanone (e.g. from Penwalt Corporation)
Loupersol 130 and Loupersol 120 sold by Lucidol Division), 3, 6, 6, 9,
9-pentamethyl-3-(ethyl acetate)-1,2,
4,5-Texitroxy cyclononane (USP sold by Wifco Chemical corporation)
138), 2,5-dimethyl-2,5bis-(t-butylperoxy)hexane (e.g. Loupersol
101) and 1-3-bis-(tert-butylperoxyisopropyl)-benzene (Valkap®, sold by Hercules, Inc.). Among the above compounds Wifco USP-138 and Loupersol 130 are most preferred. The preferred concentration of free radical source decay promoter is in the range of about 0.01% to 0.4% based on the weight of the polymer. Preferably, the pelletizer operates to retain at least 75% of the disintegrant 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 degree until substantially complete reaction occurs in the re-extrusion step. Typically such extruder temperatures range from about 237.8°C to 287.8°C. These conditions are also applicable to the disintegration action in the extruder die assembly.

In the following examples, the melt index is determined using a melt index measuring device (ASTM1238) that weighs 2160 g and operates at a temperature of 80.6°C. Samples were heated for 5 minutes to reach equilibrium before testing. Melt index is 2.1 in diameter
It is expressed in g as the amount released from a mm tube in 10 minutes.

Example 1 Flakes with a melt index value of less than 1 were obtained in a polypropylene reactor. 0.275
A homogeneous blend was prepared by adding % by weight of Loupersol 130 to the flakes. This formulation was heated to 190.6℃.
The pellets were pelletized using a pelletizer operating at a residence time of about 2 minutes. Theoretically peroxide approx.
This means that 22% responded. As a result of measuring the melt index of the pellet, it was found that the pellet had a melt index of about 55. Approximately 10% of the disintegration accelerator in the pellet in the melt index meter
The actual melt index of the pellets is thought to be in the range of 40 to 45 because of the reaction. This polymer was easily pelletized. The resulting polymer pellets were comparable to normal commercially available pellets.

These pellets were then subjected to a re-extrusion step at a temperature of 237.8 DEG C. and an extruder residence time of about 3 minutes. The melt index of the extrudate was measured to be approx.
A value of 550 was obtained. To prove that the 237.8°C extrusion process had no effect on the melt index, the extrudate was re-extruded and the melt index increased from 550 to 580.
Therefore, about 95% of the increase in melt index was due to the disintegration promoter in the pellets and about 5% was due to the action of the extruder.

Example 2 Using the same flakes and equipment as Example 1. The only difference from Example 1 is that 0.3% Loupersol 130 was added to the flakes. The melt index of the pellets was found to be 45 to 50 as a result of measurement.
The extrudate during the re-extrusion process was found to have a melt index of approximately 660. As in Example 1, the cutting properties of the pellets were commercially satisfactory.

Example 3 Witco Chemical USP-138 at a concentration of 0.35
The weight percent was applied to the flakes. This formulation was subjected to an extrusion process at a temperature of 190.6°C and an extruder residence time of approximately 2 minutes. The melt index of the extruded sample was determined to be approximately 15. When this sample was re-extruded at a temperature of 251.7°C and a residence time of 3 minutes, a melt index value of 215 was measured. A melt index of 1.7 was measured for flakes processed by the above method without the addition of peroxide.

Example 4 2% Loopersol 130 was blended into commercially available polypropylene pellets called Hercuies PC-973. This formulation was then subjected to an extrusion process at a temperature of 170°C and a residence time of 1 minute. Theoretically, 98% of the peroxide would remain unreacted in the extrudate. The various peroxide-enriched extrudates were then blended into polypropylene pellets. A theoretical equivalent of pure peroxide was added to the other pellet. These "concentrates"/polypropylene blends and liquid peroxide/polypropylene blends were separately processed using a Brabender extruder at a temperature of 240.6
℃ and a residence time of 7 minutes. The viscosity of the pellets discharged from the tip of the die of the extruder was measured and the values are shown in FIG. It turns out that both are equivalent.

Thus, the present invention includes a concentrate of non-disintegration accelerators.
Concentrations of disintegration promoters up to 5% by weight can be easily formed, and formation of high concentrations of disintegration promoters is also possible.

Without limiting the invention to any particular theory, the significance of particular disintegration accelerator characteristics can be hypothesized. From calculations to determine the half-life, it can be seen that the half-life reaction rate coefficient approximately follows Arrhenius' law.

i.e. l _oK = -19700/T+40.4 (Loopersol 130) l _oK = -19700/T+41.6 (Loopersol 101) where K = half-life reaction rate coefficient per minute in polypropylene. T=absolute temperature Once K is determined, the amount of unreacted disintegration accelerator after a certain period of time can be determined by the following equation.

C _A /C _A゜=e ^-kt where C _A = concentration of unreacted disintegrant.

C _A゜ = Initial concentration of disintegration accelerator t = Reaction time (minutes) For example, comparing the unreacted rate after 1 minute at 210°C (483〓), Loupersol 101 is only 10%, while Loupersol 130 is 50%. %become.

In addition, it is found that the viscosity of the polymer exiting a single device can be predicted by the following equation:

1/μ=1/μ゜+KC _R where μ= viscosity of the polymer leaving the device after chemical breakdown.

μ゜ = viscosity of the polymer that leaves the device without chemical breakdown.

K = chemical decay efficiency coefficient.

C _R = amount of disintegration accelerator reacting on exiting the device.

Note that since C _R =C _A °-C _A , applying this equation to the above equation yields 1/μ=1/μ°+KC _A (1-e ^-kt ).

Therefore, considering a constant constant (KC _A °), the ultimate viscosity of the polymer will be the same after a long reaction time, regardless of the disintegration promoter used. However, the relationship between viscosity and time depends on the half-life reaction rate coefficient K. For example, Figure 1 shows 0.005poise _-1
Figure 2 shows the relationship of effluent polypropylene polymer viscosity versus time based on a KC _A of (typical values for example Loupersol 130 or Loupersol 101) and an initial polymer viscosity of 10000 poise when carrying out the pelletizing/extrusion process at 201.7°C. It is a graph.
This graph shows that the intrinsic viscosities of the samples of Looper Sol 130 and Looper Sol 101 are almost the same, but in terms of "pelletizing" viscosity at normal pelletizing times in the range of 1 to 3 minutes, Looper Sol 130 is about 2 times that of Looper Sol 101. It has been proven to double.

With short half-life disintegration accelerators, the viscosity of polypropylene leaving the pelletizer at 201.7°C after a residence time of 1 minute is only 67% of that of Loupersol 101 and only 30% of that of Loupersol 130. It is. Thus Loupersol
130 is most preferred.

For Loupersol 130, approximately 50% of the disintegration accelerator
may remain after the pelletizing process, but the amount initially added is so small that there is little danger when handling the polymer. In the re-extrusion process, the processing conditions are generally at least 237.8℃, and at this temperature, the half-life coefficient of Loopersol 130 exceeds 6/min, so the amount of disintegration accelerator remaining after the re-extrusion process is essentially There will be none. If the equipment residence time is, for example, only 2.5 minutes, only 0.000017% of the peroxide in the pellets will remain in the extrudate. For example, if the polypropylene pellets sent by the manufacturer contain 0.2% Loopersol 130, the processor's extrusion equipment operates at 237.8°C, the extruder residence time is 2.5 minutes, and the extruder The concentration of Loopersol 130 in the polymer exiting the machine is below 1 ppb.

Thus, in accordance with the present invention, there is provided a method for producing pellets that facilitates pelletization by polymer manufacturers, significantly improves pellet processing capabilities of processors, and fully satisfies the objects and advantages described above. is given.

[Brief explanation of drawings]

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

Claims (1)

[Scope of Claims] 1. A process for preparing a polypropylene having a high weight average molecular weight; and an accelerated decay of a free radical source having a half-life in the polypropylene of more than 0.5 minutes at a temperature of 375°F (190.6°C). and a pelletizing step of pelletizing the polymer, wherein the pelletizing step is such that at least about 0.01% by weight of the disintegration accelerator remains with respect to the polymer after pelletizing. A method for processing polypropylene, which is carried out under conditions that cause further disintegration. 2. The method of claim 1, wherein the polypropylene has a weight average molecular weight in the range of about 250,000 to 500,000 and a molecular weight distribution of about 10 to 15. 3 The free radical source decay accelerators are 2,5-dimethyl-2,5bis-(t-butylperoxy)hexyne-3 and 3,6,6,9,9-pentamethyl-3.
-(Ethyl acetate)-1,2,4,5-texitraoxycyclononane The method according to claim 1 or 2, characterized in that it is selected from -(ethyl acetate)-1,2,4,5-texitraoxycyclononane. 4. The method according to any one of claims 1 to 3, characterized in that in the addition step, about 0.01 to 0.7% of the free radical source decay accelerator based on the weight of the polymer is added. 5 Pelleting in the pelletizing step is as follows:
Any one of claims 1 to 4 is characterized in that the step is carried out under conditions in which at least about 75% (wt%) of the free radical source decay accelerator remains as an unreacted component after pelletizing. The method described in.