JP6310736B2 - Method for producing thermoplastic resin composition and thermoplastic resin composition - Google Patents

Description

  The present invention relates to a method for producing a thermoplastic resin composition in which carbon nanofibers are dispersed and a thermoplastic resin composition.

  According to the method for producing a carbon fiber composite material previously proposed by the present inventors, the use of an elastomer improves the dispersibility of the carbon nanofiber, which has been considered difficult so far, and makes the carbon nanofiber uniform in the elastomer. (See, for example, Patent Document 1).

  According to such a method for producing a carbon fiber composite material, an elastomer and carbon nanofibers are kneaded, and dispersibility of carbon nanofibers having high cohesiveness is improved by shearing force. More specifically, when the elastomer and the carbon nanofiber are mixed, the viscous elastomer penetrates into the carbon nanofiber, and a specific part of the elastomer has high activity of the carbon nanofiber due to chemical interaction. In this state, when a strong shearing force is applied to a mixture of an elastomer having high molecular mobility (elasticity) and carbon nanofibers, the carbon nanofibers are deformed as the elastomer is deformed. The fibers also moved, and the aggregated carbon nanofibers were separated and dispersed in the elastomer by the restoring force of the elastomer due to elasticity after shearing.

  Thus, by improving the dispersibility of the carbon nanofibers in the matrix, expensive carbon nanofibers can be used efficiently as fillers for composite materials.

  In addition, attempts have been made to produce a thermoplastic resin composition in which carbon nanofibers are combined with a thermoplastic resin.

  However, with a thermoplastic resin, it is difficult to disperse the carbon nanofibers due to elasticity like an elastomer, and many aggregates of carbon nanofibers remain in the thermoplastic resin composition. Such agglomerates of carbon nanofibers cause stress concentration in the thermoplastic resin composition, so they tend to be a starting point of fracture, and become a relatively brittle material despite being reinforced with carbon nanofibers. was there.

  Therefore, as a method for producing a thermoplastic resin composition containing carbon nanofibers, a method of further dispersing carbon nanofibers by mixing dispersion particles that promote the dispersion of carbon nanofibers into a thermoplastic resin has been proposed. (For example, refer to Patent Document 2).

  However, since the carbon nanofibers are uniformly dispersed throughout the carbon nanofibers, there is a reinforcing effect, but the carbon nanofiber aggregates remain. Therefore, the high ductility required for the thermoplastic resin has been lost.

Also, carbon nanofibers are uniformly dispersed in the elastomer using the elasticity of the elastomer to obtain a mixture, and then the mixture is further mixed with a thermoplastic resin and kneaded at a low temperature to disperse the carbon nanofibers. The manufacturing method of the thermoplastic resin composition was proposed (for example, refer patent document 3).

  However, most carbon nanofibers can be defibrated and dispersed in the elastomer, but it has been difficult to disperse the carbon nanofibers into the thermoplastic resin phase.

  In recent years, pellets in which carbon nanofibers are blended with a thermoplastic resin have been sold (for example, see Non-Patent Document 1), but these also have a large number of aggregates of carbon nanofibers in the material, Even when ordinary molding processing was performed using the material, the agglomerates remained almost as they were in the product. And when such a molded article performed the tensile test, even if the compounding quantity of carbon nanofiber was a trace amount, it fractured | ruptured with low distortion.

JP 2005-97525 A JP 2005-336235 A JP 2007-154157 A

“PLASTICYLTMPP2001” published on the website of Nanocyl (Belgium), [December 11, 2012 search], Internet <http://www.nanocyl.com/en/Products-Solutions/Products/PLASTICYL-Carbon-Nanotubes -Conductive-Masterbatches>

  An object of the present invention is to provide a method for producing a thermoplastic resin composition in which carbon nanofibers are dispersed and a thermoplastic resin composition.

The method for producing a thermoplastic resin composition according to the present invention includes:
A mixing step of kneading polyethylene and carbon nanofibers at a first temperature to obtain a first mixture;
A temperature reduction step of adjusting the temperature of the first mixture to a second temperature;
A low-temperature kneading step of kneading the first mixture containing a plurality of carbon nanofiber aggregates in polyethylene and at the second temperature at the second temperature;
Including
The first temperature is a temperature that is 25 ° C. or more higher than the melting point (Tm) of the polyethylene,
The second temperature is in a range from a temperature 5 ° C. lower than the melting point (Tm) of the polyethylene to a temperature lower than the melting point (Tm) by less than 25 ° C.

  According to the method for producing a thermoplastic resin composition of the present invention, aggregated carbon nanofibers can be loosened and dispersed in polyethylene while being separated from each other. Therefore, since the thermoplastic resin composition obtained by the method for producing a thermoplastic resin composition according to the present invention does not have aggregates of carbon nanofibers, the destruction due to stress concentration caused by the aggregates does not occur. It can have a high elastic modulus without sacrificing ductility.

In the method for producing a thermoplastic resin composition according to the present invention,
The second temperature may be 110 ° C. or higher and lower than 140 ° C.

In the method for producing a thermoplastic resin composition according to the present invention,
The carbon nanofiber has an average diameter of 2 nm or more and 110 nm or less,
In the first mixture, the carbon nanofiber may be 15 parts by mass or more and 55 parts by mass or less with respect to 100 parts by mass of the polyethylene.

In the method for producing a thermoplastic resin composition according to the present invention,
The low temperature step can be performed by taking out the first mixture from the kneader used in the mixing step.

The thermoplastic resin composition according to the present invention is:
A thermoplastic resin composition in which carbon nanofibers are dispersed in polyethylene,
There is no aggregate of carbon nanofibers,
Carbon nanofibers are dispersed throughout and separated from each other .
The storage elastic modulus (E ′) in the dynamic viscoelasticity test based on JIS K7244 with a measurement temperature of 20 to 300 ° C., a dynamic strain of ± 0.05%, and a frequency of 1 Hz increases in a temperature region where the measurement temperature exceeds 200 ° C. ,
The carbon nanofiber has an average diameter of 2 nm or more and 110 nm or less,
To the polyethylene 100 parts by weight, the carbon nanofibers 15 parts by mass or more, and wherein the der Rukoto than 55 parts by mass.

  According to the thermoplastic resin composition of the present invention, since there are no aggregates of carbon nanofibers, there is no breakage due to stress concentration in the aggregates, so that it has a high elastic modulus without sacrificing ductility. Can do.

It is a figure which shows typically the manufacturing method of the thermoplastic resin composition which concerns on one embodiment. It is a SS curve in the sample of Examples 1-3 and Comparative Examples 1-5. It is a graph which shows the DMA measurement result (temperature dependence of storage elastic modulus E ') in the sample of Examples 1-3 and Comparative Examples 1-5. It is a graph which shows the DMA measurement result (temperature dependence of loss tangent tan-delta) in the sample of Examples 1-3 and Comparative Examples 1-5. It is a SEM observation photograph of 100 times the frozen section of the sample of Example 2. 4 is an SEM observation photograph of 500 times the frozen section of the sample of Example 2. FIG. 4 is a SEM observation photograph of 2000 times the frozen section of the sample of Example 2. 4 is a SEM observation photograph of 20000 times the frozen section of the sample of Example 2. 10 is a SEM observation photograph of 100 times the frozen section of the sample of Comparative Example 4. 5 is an SEM observation photograph of 500 times the frozen section of the sample of Comparative Example 4. 4 is a SEM observation photograph of 2000 times the frozen section of the sample of Comparative Example 4. 6 is a SEM observation photograph of 20000 times the frozen section of the sample of Comparative Example 4. It is a SS curve in the samples of Examples 4 and 5 and Comparative Examples 1, 4 and 6. It is a graph which shows the DMA measurement result (temperature dependence of storage elastic modulus E ') in the samples of Examples 4 and 5 and Comparative Examples 1, 4 and 6. It is a graph which shows the DMA measurement result (temperature dependence of loss tangent tan-delta) in the samples of Examples 4 and 5 and Comparative Examples 1, 4 and 6. It is a graph explaining the decreasing rate of a storage elastic modulus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The method for producing a thermoplastic resin composition according to one embodiment of the present invention includes a mixing step of kneading polyethylene and carbon nanofibers at a first temperature to obtain a first mixture, and the first mixture. And a low-temperature kneading step of kneading the first mixture containing polyethylene agglomerates in a plurality of carbon nanofibers at the second temperature at the second temperature. The first temperature is a temperature that is 25 ° C. or more higher than the melting point (Tm) of the polyethylene, and the second temperature is 5 ° C. lower than the melting point (Tm) of the polyethylene. The temperature range is lower than 25 ° C.

A thermoplastic resin composition according to an embodiment of the present invention is a thermoplastic resin composition in which carbon nanofibers are dispersed in polyethylene, and there are no aggregates of carbon nanofibers. Is dispersed in the whole in a state of being separated from each other, and the storage elastic modulus (E ′) in the dynamic viscoelasticity test based on JIS K7244 at a measurement temperature of 20 to 300 ° C., a dynamic strain of ± 0.05%, and a frequency of 1 Hz is The carbon nanofibers have an average diameter of 2 nm or more and 110 nm or less, and the carbon nanofibers are 15 parts by mass or more with respect to 100 parts by mass of the polyethylene. characterized in der Rukoto than 55 parts by mass.

  A. First, the manufacturing method of the thermoplastic resin composition concerning this Embodiment is demonstrated.

  Drawing 1 is a figure showing typically the manufacturing method of the thermoplastic resin composition concerning one embodiment.

  First, before the low temperature kneading step, a mixing step of kneading polyethylene and carbon nanofibers at a first temperature to obtain a first mixture will be described. In this mixing step, it can be presumed that a material in which carbon nanofibers are blended in advance with polyethylene, for example, a commercially available pellet-shaped material, is the first mixture produced by this mixing step. In this case, carbon nanofibers are dispersed throughout the first mixture in the form of aggregates.

A-1. Mixing step In the mixing step, polyethylene and carbon nanofibers are kneaded at a first temperature to obtain a first mixture.

A-1-1. Kneader For the mixing step, for example, a kneader such as an open roll, a closed kneader, an extruder, or an injection molding machine can be used. As an open roll, a well-known 2 roll, 3 roll, etc. can be used. The closed kneader is a so-called internal mixer, and a known Banbury type, kneader type, or the like can be used. These kneaders used in the mixing step desirably have a heating device for heating the mixture being processed.

A-1-2. 1st temperature 1st temperature is temperature higher 25 degreeC or more than melting | fusing point (Tm) of polyethylene. The first temperature is the actual temperature of the polyethylene during the mixing process, not the temperature of the processing equipment. In general, the processing temperature of polyethylene is expressed by the set temperature of the heating cylinder in the case of an extruder or an injection molding machine of a processing apparatus. The temperature of the resin becomes high. Since the first temperature in the present embodiment is a temperature during processing, it is desirable to measure the actual surface temperature of the resin as much as possible. However, if the measurement is not possible, the resin immediately after taking out the first mixture from the processing apparatus is used. The surface temperature can be measured and taken as that temperature.

  The first temperature may be 140 ° C. or higher when the polyethylene has a melting point of 115 ° C. or higher, and may be 140 ° C. to 310 ° C.

  The first temperature is slightly lower in the case of processing in the mixing process using an open roll than in the case of carrying out with a general polyethylene processing apparatus in consideration of the winding property to the roll, for example, 20 ° C. or lower. This can be done by setting the roll temperature to the temperature.

  It is not common to process polyethylene with an open roll. However, in the case of an open roll, the viscosity of polyethylene is lower than that of the other processing devices because of the special property that the material must be wound around the roll. Processing becomes difficult at temperatures that are too high.

  When kneading with an open roll using polyethylene having a melting point of 110 ° C to 120 ° C, the first temperature can be set to 135 ° C to 180 ° C. The first temperature only needs to be able to melt polyethylene and mix the carbon nanofibers. Therefore, when processing with a closed kneader, an extruder, an injection molding machine, etc., the first temperature is a setting of the processing apparatus. The surface temperature of the resin when the temperature is 135 ° C. to 310 ° C. can be used.

A-1-3. Open Roll A method of using a two-roll open roll 2 as shown in FIG. 1 will be described. The first roll 10 and the second roll 20 in the open roll 2 are arranged at a predetermined interval d, for example, 0.5 mm to 1.5 mm, and are rotated forward at rotational speeds V1 and V2 in the directions indicated by the arrows. Or it rotates in reverse. The temperature of the first roll 10 and the second roll 20 can be adjusted by, for example, heating means provided therein, and is set to the first temperature.

  As shown in FIG. 1, a plurality of carbon nanofibers 80 can be put into a bank 34 of polyethylene 30 wound around the first roll 10 and kneaded to obtain a first mixture. In the mixing step, the carbon nanofibers 80 are dispersed in the polyethylene 30 and, for example, kneading is performed until there is no color unevenness. For this kneading step, the same step as a general kneading in which a compounding agent (such as carbon nanofiber) is blended with polyethylene can be employed.

  However, in this state, the carbon nanofibers 80 in the first mixture are present dispersed throughout the same aggregate as the raw material. Therefore, the first mixture has defects in the material. For example, when a tensile test or the like is performed, the elongation at break is significantly lower than that of the raw material polyethylene alone.

  When this first mixture was subjected to a dynamic viscoelasticity test (hereinafter referred to as DMA test), it was found that the behavior was different from that of the raw polyethylene. The raw polyethylene has a storage elastic modulus (E ′) that rapidly decreases around the melting point and flows. However, in the first mixture in which the carbon nanofibers 80 are mixed, the storage elastic modulus (E ′) hardly decreases even when the melting point is exceeded by dispersing a predetermined amount or more of the carbon nanofibers, that is, like an elastomer. It was found that a rubber elastic region was developed.

  In the method for producing a thermoplastic resin composition according to the present invention, utilizing this rubber elastic region, the agglomerated carbon nanofibers are disentangled so as to be loosened and dispersed in polyethylene. Therefore, in carrying out the present invention, a DMA test is performed in advance on a sample of the first mixture of the blend to confirm whether or not a rubber elastic region has developed, and the temperature region is used to determine thermoplasticity. A resin composition can be produced.

A-2. Low temperature process The low temperature process adjusts the temperature of the first mixture to the second temperature.

  Here, the second temperature will be described.

  The general processing set temperature in the mixing process, that is, the set temperature of the processing equipment, is higher than the recommended processing set temperature for polyethylene in order to melt the polyethylene sufficiently in a short time and process it quickly. is there. Therefore, polyethylene is not processed near its melting point. As described above, the surface temperature of polyethylene during processing is higher than such processing set temperature.

  In particular, when a filler such as carbon nanofiber is blended in polyethylene, the processing set temperature is usually higher than the general processing set temperature. Moreover, if the compounding quantity of carbon nanofiber increases, the temperature of the 1st mixture in a mixing process will rise rapidly by the heat_generation | fever by shearing.

  Therefore, in order to implement the low-temperature kneading step described in A-3 below using the rubber elastic region described in A-1-3, it is necessary to lower the temperature of the first mixture. Since the temperature of the first mixture rises when kneading is performed, it is usually difficult to lower the temperature while continuing kneading. Therefore, in the low temperature process, after kneading, the kneader can be stopped for a predetermined time, or the first mixture can be taken out from the kneader and allowed to cool to the second temperature. In addition, the first mixture can be actively cooled using a cooling device including a cooling mechanism such as a fan, a spot cooler, or a chiller. Processing time can be shortened by actively cooling.

  The second temperature ranges from a temperature 5 ° C. lower than the melting point (Tm) of polyethylene used in this production method to a temperature lower than the melting point (Tm) by less than 25 ° C. Furthermore, the second temperature can range from a temperature 5 ° C. below the melting point (Tm) of the polyethylene to a temperature 20 ° C. above the melting point (Tm), in particular from a temperature 5 ° C. below the melting point (Tm). It can be in the range up to 5 ° C. above the melting point (Tm).

  From the results of the DMA test, it is preferable that the second temperature is equal to or higher than the melting point (Tm) of polyethylene and is a temperature range indicating a rubber elastic region in the DMA test of the first mixture. It is difficult to measure the internal temperature of one mixture. Therefore, as will be described in A-3 below, the second temperature is the surface temperature of the resin. Therefore, the second temperature includes a temperature slightly lower than the temperature range indicating the rubber elastic region. That is, the second temperature, which is the surface temperature of the resin, is set so that the internal temperature of the first mixture during processing falls within a temperature range indicating the rubber elastic region. In the case of polyethylene, the second temperature can be processed to a range lower than the rubber elastic region, for example, 5 ° C. lower than the melting point (Tm).

  The rubber elastic region is a flat region when a DMA test result is created as a graph of temperature-storage elastic modulus. The rate of decrease in elastic modulus in the flat region can be 0.01 MPa / ° C. to 0.15 MPa / ° C., and can further be 0.04 MPa / ° C. to 0.13 MPa / ° C.

  At this second temperature, the carbon nanofibers can be moved utilizing the restoring force due to the elasticity of polyethylene. The second temperature is a temperature that is not adopted as the processing temperature of polyethylene, and in particular, is a low temperature range that has not been adopted so far as the processing temperature of the first mixture.

If the second temperature is 25 ° C. or higher than the melting point (Tm), it is considered that the aggregates of carbon nanofibers cannot be loosened in the low-temperature kneading step. For example, when the melting point of polyethylene is 115 ° C., the second temperature can be 110 ° C. or higher and lower than 140 ° C., and can be 110 ° C. or higher and 135 ° C. or lower, particularly 110 ° C. or higher and 120 ° C. or lower. Can be.

  In the present invention, “melting point (Tm)” refers to a value measured in accordance with JIS K7121 using differential scanning calorimetry (DSC).

  The first mixture whose temperature has been lowered to the second temperature can be placed, for example, in an oven set to the second temperature and maintained at a predetermined temperature within the range of the second temperature. The temperature of the first mixture taken out from the kneader is lowered, so that the processing quality is stabilized.

  Moreover, when using the pellet containing a commercially available carbon nanofiber as a 1st mixture, a reheating process is needed between a mixing process and a low temperature process. The reheating step can be performed by heating to a temperature higher than the melting temperature of polyethylene.

A-3. Low temperature kneading step The low temperature kneading step kneads the first mixture at the second temperature.

  As a 1st mixture, what was obtained by the mixing process of said A-1 can be used.

  The step of kneading the first mixture at the second temperature in the low-temperature kneading step uses an apparatus for melting and molding polyethylene, for example, an open roll, a closed kneader, an extruder, an injection molding machine, etc. Can do. Similar to the mixing step, a method using an open roll 2 as shown in FIG. 1 will be described.

  In this step, the roll interval d between the first roll 10 and the second roll 20 is set to, for example, 0.5 mm or less, more preferably an interval of 0 mm to 0.5 mm, and the first obtained in the mixing step. The mixture can be put into the open roll 2 and kneaded.

  When the surface speed of the first roll 10 is V1, and the surface speed of the second roll 20 is V2, the surface speed ratio (V1 / V2) of both in this step is 1.05 to 3.00. And can be 1.05-1.2. By using such a surface velocity ratio, a desired high shear force can be obtained. The first mixture extruded from between such narrow rolls has a resilience due to the elasticity of polyethylene because the second temperature is a temperature range in which a rubber elastic region appears and has an appropriate viscosity. The carbon nanofibers can move greatly with the deformation of the polyethylene.

  The second temperature is the surface temperature of the first mixture in the low-temperature kneading step, not the set temperature of the processing apparatus. As described for the first temperature, it is desirable to measure the surface temperature of the actual resin as much as possible for the second temperature, but if it cannot be measured, the surface temperature of the resin immediately after taking out the thermoplastic resin composition from the processing apparatus is determined. It can measure and it can be set as the 2nd temperature in process from the temperature.

  In the case of the open roll 2, as shown in FIG. 1, the surface temperature can be measured using a non-contact thermometer 40 for the first mixture wound around the first roll 10. The arrangement of the non-contact thermometer 40 may be other than the position immediately after passing through the nip, and is preferably above the first roll 10. Immediately after passing through the nip, the temperature of the first mixture is an unstable temperature at which the temperature rapidly changes.

  Further, when the surface temperature of the first mixture in the low temperature kneading step cannot be measured as in a closed kneader or an extruder, the thermoplastic resin composition immediately after taking out from the apparatus after kneading is used. The surface temperature can be measured and confirmed to be within the second temperature range.

  The low temperature kneading step can be, for example, 4 minutes to 20 minutes at the second temperature, and further can be 5 minutes to 20 minutes. By sufficiently taking the kneading time at the second temperature, the carbon nanofibers can be defibrated more reliably.

  The workability of the first mixture is lowered due to the incorporation of carbon nanofibers, and the temperature of the first mixture becomes higher than the set temperature of the apparatus due to shearing heat generated by kneading the carbon nanofibers. Therefore, in order to maintain the surface temperature of the first mixture in the second temperature range suitable for the low temperature kneading step, if the roll is an open roll, the temperature of the first mixture is not increased by adjusting the temperature of the roll. The temperature must be adjusted so that it is actively cooled. The same applies to a closed kneader, an extruder or an injection molding machine, and the surface temperature of the first mixture is kept constant within the second temperature range by adjusting the processing set temperature of the apparatus so as to be actively cooled. Can be maintained for hours. For example, in the extruder, in the vicinity of supplying the material, the set temperature of the heating cylinder is set to a temperature higher than the general processing temperature, the other zones are set to a temperature lower than the second temperature, and the resin being processed The surface temperature can be adjusted to the second temperature.

  The thermoplastic resin composition obtained by the low-temperature kneading step can be, for example, put into a mold and pressed, or, for example, further processed into pellets using an extruder, etc. It can be formed into a desired shape using a polyethylene processing method.

  The shearing force obtained in the low-temperature kneading step causes a high shearing force to act on the polyethylene, so that the aggregated carbon nanofibers are separated from each other so as to be pulled out one by one by the polyethylene molecules, and then defibrated. To be distributed. In particular, since polyethylene has elasticity in the second temperature range, viscosity, and chemical interaction with carbon nanofibers due to activation of polyethylene molecules in the kneading process, carbon nanofibers are defibrated. Can be dispersed. And the thermoplastic resin composition excellent in the dispersibility and dispersion stability of carbon nanofiber (it is hard to re-aggregate carbon nanofiber) can be obtained.

  In the method for producing a thermoplastic resin composition, the average diameter of the carbon nanofibers can be 2 nm or more and 110 nm or less, and in this case, the first mixture has a carbon nanofiber content of 100 parts by mass of polyethylene. It can be 15 parts by mass or more and 55 parts by mass or less. In the case of carbon nanofibers having an average diameter of 2 nm or more and 110 nm or less, when the compounding amount of the carbon nanofibers with respect to 100 parts by mass of polyethylene is 15 parts by mass or more, a rubber elastic region having a melting point or more appears in the DMA test of the first mixture. be able to. Moreover, when the compounding quantity of the carbon nanofiber with respect to 100 mass parts of polyethylene will be 55 mass parts or more, the process in a low temperature kneading process will become difficult.

  Furthermore, in the first mixture, the compounding amount of the carbon nanofiber with respect to 100 parts by mass of polyethylene can be 17 parts by mass or more and 45 parts by mass or less.

  The average diameter of the carbon nanofiber may be 9 nm or more and 30 nm or less.

According to the method for producing a thermoplastic resin composition according to the present embodiment, carbon nanofibers that existed as aggregates in polyethylene can be dispersed in a separated state. Therefore, since the thermoplastic resin composition obtained by the method for producing a thermoplastic resin composition does not have aggregates of carbon nanofibers, fracture due to stress concentration caused by the aggregates does not occur, so the ductility is sacrificed. Without having a high elastic modulus.

A-4. Second low-temperature kneading step In the method for producing the thermoplastic resin composition, the polyethylene in the first mixture is the first polyethylene, and the second polyethylene is further added to the second mixture obtained in the low-temperature kneading step. And a second low-temperature kneading step of kneading at a third temperature to obtain a third mixture.

  The second polyethylene can be the same type of polyethylene as the first polyethylene. Here, the same type of polyethylene means that the second polyethylene and the first polyethylene are at least the same main constituent monomer.

  The third temperature can be the same temperature range as the second temperature described in A-2.

  If the blending amount of the carbon nanofibers in the first mixture in A-1 is small, the rubber elastic region in the DMA test in the first mixture may not appear. In such a first mixture, the carbon nanofibers cannot be separated from each other even when the low-temperature kneading step is performed. Therefore, when it is desired to process a thermoplastic resin composition containing a relatively small amount of carbon nanofibers, an arbitrary amount of the second polyethylene is added by carrying out the second low-temperature kneading step in this way. Thereby, content of the carbon nanofiber in a thermoplastic resin composition can be decreased.

B. Raw materials Next, the raw materials used in the manufacturing method of the present embodiment will be described.

B-1. Polyethylene Examples of the polyethylene include high density polyethylene (HDPE) having a density of 0.941 g / cm ⁻³ or more, medium density polyethylene (MDPE) having a density of 0.926 g / cm ^{−3 to} 0.940 g / cm ⁻³ , A low density polyethylene (LDPE) of 0.910 g / cm ^{−3 to} 0.920 g / cm ⁻³ can be used.

  Examples of polyethylene that can be used include high-pressure polyethylene (HPPE) and low-pressure polyethylene.

  Furthermore, as polyethylene, linear low density polyethylene (LLDPE), branched low density polyethylene (BLDPE), etc. can be used, for example.

  Note that ultra high molecular weight polyethylene (UHMWPE) having a molecular weight of 1 million or more is not included in the polyethylene in the present invention because it is difficult to use a general molding method.

B-2. Carbon nanofibers Carbon nanofibers can have an average diameter (fiber diameter) of 0.4 nm to 230 nm, and carbon nanofibers can have an average diameter (fiber diameter) of 2 nm to 110 nm, In particular, it can be 9 nm or more and 30 nm or less, or more than 30 nm and 110 nm or less.

  Since carbon nanofibers have a small average diameter and a large specific surface area, polyethylene can be effectively reinforced by a small amount of carbon nanofibers when carbon nanofibers can be defibrated and dispersed throughout. . By using carbon nanofibers having an average diameter (fiber diameter) of 0.4 nm or more and 230 nm or less, polyethylene can be reinforced.

  The carbon nanofibers can be oxidized, for example, in order to improve the reactivity with polyethylene on the surface.

  In the detailed description of the present invention, the average diameter and the average length of the carbon nanofibers are, for example, 5,000 times or more from an electron microscope (the magnification can be appropriately changed depending on the size of the carbon nanofibers), and the diameters of 200 or more locations. And the length can be measured and calculated as the arithmetic average value.

  The compounding quantity of the carbon nanofiber in a thermoplastic resin composition can be mix | blended suitably according to a desired characteristic.

  In particular, by using the second low-temperature kneading step described in A-4 above, 0.1 part by mass or more of carbon nanofibers can be blended with 100 parts by mass of polyethylene.

  In addition to carbon nanofibers, the thermoplastic resin composition can be used in combination with fillers generally used for processing thermoplastic resin compositions.

  Here, “part by mass” indicates “phr” unless otherwise specified, and “phr” is an abbreviation for “parts per undred of resin or rubber”, and is used as an external hook for additives such as rubber and thermoplastic resin. It represents a percentage.

  The carbon nanofiber can be a so-called multi-wall carbon nanotube (MWNT: multi-wall carbon nanotube) having a cylindrical shape formed by winding one sheet of graphite (graphene sheet) having a carbon hexagonal mesh surface.

  Examples of carbon nanofibers having an average diameter of 9 nm or more and 30 nm or less include Baytubes C150P and C70P manufactured by Bayer MaterialScience and NC-7000 manufactured by Nanocyl, and the average diameter is 30 nm. Examples of carbon nanofibers exceeding 110 nm may include NT-7 manufactured by Hodogaya Chemical Co., Ltd.

  A carbon material partially having a carbon nanotube structure can also be used. In addition to the name “carbon nanotube”, it may be called “graphite fibril nanotube” or “vapor-grown carbon fiber”.

Carbon nanofibers can be obtained by a vapor deposition method. Vapor growth is also called catalytic chemical vapor deposition (CCVD), which is a method of producing carbon nanofibers by gas phase pyrolysis of hydrocarbons and other gases in the presence of a metal catalyst. is there. The vapor phase growth method will be described in more detail. For example, an organic compound such as benzene or toluene is used as a raw material, an organic transition metal compound such as ferrocene or nickelcene is used as a metal catalyst, and these are used together with a carrier gas at a high temperature such as 400 ° C. It is introduced into a reaction furnace set to a reaction temperature of 1000 ° C or less and floated on a ceramic substrate such as alumina or magnesium oxide. For example, a catalyst-supporting reaction method (Substrate Reaction Method) in which carbon-containing fibers are brought into contact with a carbon-containing compound at a high temperature to form carbon nanofibers on a substrate can be used.

  Carbon nanofibers having an average diameter of 9 nm to 30 nm can be obtained by a catalyst-supporting reaction method, and carbon nanofibers having an average diameter of more than 30 nm and not more than 110 nm can be obtained by a floating flow reaction method.

The diameter of the carbon nanofiber can be adjusted by, for example, the size of the metal-containing particles and the reaction time. Carbon nanofibers having an average diameter of 9 nm or more and 30 nm or less can have a nitrogen adsorption specific surface area of 10 m ² / g or more and 500 m ² / g or less, and can be 100 m ² / g or more and 350 m ² / g or less. In particular, it may be 150 m ² / g or more and 300 m ² / g or less.

C. Thermoplastic resin composition Finally, the thermoplastic resin composition obtained by this Embodiment is demonstrated.

  The thermoplastic resin composition according to the present embodiment is a thermoplastic resin composition in which carbon nanofibers are dispersed in polyethylene, and there are no aggregates of carbon nanofibers. It is characterized by being dispersed in the whole in a separated state.

  The absence of carbon nanofiber aggregates in the thermoplastic resin composition can be confirmed by observing an arbitrary cross section of the thermoplastic resin composition with an electron microscope. In the electron micrograph, carbon nanofibers that have been defibrated and separated from each other appear dispersed in the fractured surface.

  The agglomerates are carbon nanofibers that are entangled with each other in the thermoplastic resin composition as in the case of the raw material. In particular, in the agglomerates, the resin is not hollow between the carbon nanofibers and the carbon nanofibers. There are many parts. The absence of such agglomerates means that the aggregated carbon nanofibers are loosened, and the carbon nanofibers are dispersed in a state separated from each other. The state which mutually isolate | separated means that it exists in the state in which a hollow part does not exist between carbon nanofibers in a thermoplastic resin composition.

  According to the thermoplastic resin composition according to the present embodiment, since there is no aggregate of carbon nanofibers, there is no breakage due to stress concentration in the aggregate, so that high elasticity is obtained without sacrificing ductility. Can have a rate.

The thermoplastic resin composition has an average diameter of carbon nanofibers of 2 nm or more and 110 nm.
When it is below, carbon nanofiber is 15 mass parts or more and 55 mass parts or less with respect to 100 mass parts of polyethylene . Further, in the thermoplastic resin composition, when the average diameter of the carbon nanofibers is 2 nm or more and 110 nm or less, the carbon nanofibers may be 17 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of polyethylene. it can.

The thermoplastic resin composition produced by using the second low-temperature kneading step of A-3 is obtained by adding polyethylene using a thermoplastic resin composition in which carbon nanofibers are already dispersed as a master batch. The compounding ratio of the carbon nanofibers in the plastic resin composition can be reduced. Therefore, for example, the carbon nanofiber can be less than 15 parts by mass with respect to 100 parts by mass of polyethylene. In that case, the thermoplastic resin composition has 0 carbon nanofibers per 100 parts by mass of polyethylene.
. It can be 1 part by mass or more and 55 parts by mass or less.

  The thermoplastic resin composition is suitable for use in, for example, a film because it has a high tensile strength and is excellent in heat resistance while being excellent in elongation at break. Examples of the film include food packaging bags and agricultural films. Further, the thermoplastic resin composition can be formed into a film by using an inflation method, a T-die method, or the like.

  As described above, the embodiments of the present invention have been described in detail. However, it will be easily understood by those skilled in the art that many modifications can be made without departing from the novel matters and effects of the present invention. Accordingly, all such modifications are intended to be included in the scope of the present invention.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

(1) Test using an open roll (1-1) Preparation of samples of Examples 1 to 3 Mixing step: An open roll having a roll diameter of 6 inches (roll temperature 140 ° C. = processing set temperature) is shown in each table. 100 parts by mass (phr) of polyethylene was charged, melted, and wound on a roll. The temperature (first temperature) of the polyethylene fabric surface at this time was 140 ° C. As the open roll, a hot roll capable of heating the roll was used.

  Next, multilayer carbon nanofibers (indicated in each table as “CNT”) having a mass part (phr) shown in Table 1 were added as compounding agents. At this time, the roll gap was set to 1.5 mm. Thorough kneading was performed to disperse the multilayer carbon nanofibers, and the first mixture was taken out from the open roll. The surface temperature of the dough temperature was measured with a non-contact type infrared thermometer.

  Low temperature process: The first mixture is taken out from the open roll, allowed to cool until the surface temperature of the first mixture reaches 110 ° C. to 120 ° C., and the first mixture is placed in an oven and maintained at 110 ° C. to 120 ° C. did.

  Low-temperature kneading step: The first mixture was put again into the open roll, and the roll gap was narrowed from 1.5 mm to 0.3 mm for kneading. During this kneading, the temperature of the roll of the first mixture was adjusted so that the temperature of the dough surface (second temperature) was measured with a non-contact infrared thermometer and maintained at 110 ° C. to 120 ° C. After kneading sufficiently, the roll gap was changed from 0.3 mm to 1.5 mm, and the thermoplastic resin composition was taken out from the open roll.

  Pressing process: The thermoplastic resin composition taken out from the open roll was put in a mold and pressure-molded under vacuum to prepare a sample. In vacuum press molding, the mold is heated to 140 ° C., preheated for 2 minutes without load, and then press molded at 4 MPa (pressing against the mold) for 5 minutes, and the mold is moved to a cooling press. And it cooled to room temperature, pressurizing at 2 MPa (with respect to a metal mold | die).

In each table, “CNT” is a multi-walled carbon nanotube having an average diameter (value obtained by arithmetically averaging 200 or more measured values using a scanning electron microscope), and “PE” is a prime polymer. Company-made polyethylene (linear low density polyethylene (LLDPE), grade name: ULT-ZEX15150J, MFR: 15 g / 10 min (JIS K7210), density: 914 kg / cm ³ (JIS K7112), melting point 115 ° C. (JIS
K7121)).

(1-2) Preparation of Samples of Comparative Examples 1 to 5 Since Comparative Example 1 is a polyethylene simple substance, resin pellets were put into a mold and a pressing process was performed to obtain a sample of a thermoplastic resin composition.

  In Comparative Examples 2 and 3, samples of the thermoplastic resin composition were obtained in the same manner as in Examples 1 to 3.

  In Comparative Example 4, a sample of the thermoplastic resin composition was obtained by omitting the low temperature step and the low temperature kneading step of Examples 1 to 3.

  In Comparative Example 5, a sample of the thermoplastic resin composition was obtained in the same manner as in Example except that the second temperature in the low temperature kneading step in Examples 1 to 3 was adjusted to 140 ° C.

(1-3) Tensile test About the sample of an Example and a comparative example, about the test piece pierced to the dumbbell No. 1 shape of JISK-7113-1, using the tensile tester of Shimadzu Corporation autograph AG-X. , 23 ± 2 ° C., tensile speed 50 mm / min based on JIS K7127, tensile strength (TS (MPa)), elongation at break (Eb (%)) and yield point tensile stress (σy (MPa) )) Was measured. The measurement results are shown in Tables 1 to 3 and FIG.

  In FIG. 2, curves E1 to E3 correspond to Examples 1 to 3, respectively, and curves C1 to C5 correspond to Comparative Examples 1 to 4, respectively.

(1-4) DMA measurement About the sample of an Example and a comparative example, about the test piece cut out into the strip shape (40x1x2 (width) mm), using the dynamic viscoelasticity tester DMS6100 made from SII. A DMA test (dynamic viscoelasticity test) was performed based on JIS K7244 at a distance between chucks of 20 mm, a measurement temperature of 20 to 300 ° C., a dynamic strain of ± 0.05%, and a frequency of 1 Hz.

  From the test results, the storage elastic modulus (E ′) and loss tangent (tan δ) were measured at measurement temperatures of 25 ° C., 100 ° C., and 200 ° C. The storage elastic modulus is shown in Tables 1 to 3. In Tables 1 to 3, “E ′ (25 ° C.) (MPa)”, “E ′ (100 ° C.) (MPa)”, “E ′ (150 ° C.) (MPa)”, “E ′ (200 ° C.)” (MPa) ". In addition, the flow start temperature in the DMA test (described as “flow temperature” in each table) is also described in each table. In each table, a sample that did not flow up to 300 ° C. was described as “not flowing”, and a sample that did not break up to 300 ° C. was described as “not broken”.

  Further, the measurement results are shown in FIG. 3 as a graph showing the temperature dependence of the storage elastic modulus E ′, and shown in FIG. 4 as a graph showing the temperature dependence of the loss tangent (tan δ).

  3 and 4, curves E1 to E3 correspond to Examples 1 to 3, respectively, and curves C1 to C5 correspond to Comparative Examples 1 to 4, respectively.

(1-5) Measurement of average linear expansion coefficient About the sample of the Example and the comparative example, the average linear expansion coefficient in a measurement temperature range was measured. The measurement apparatus was TMASS manufactured by SII, the measurement sample shape was 1.5 mm × 1.0 mm × 10 mm, the side long load was 25 KPa, the measurement temperature was 20 ° C. to 80 ° C., and the temperature increase rate was 3 ° C./min. These results are shown in Tables 1 to 3.

  According to the results of the tensile tests in Tables 1 to 3 and FIG. 2, the thermoplastic resin composition samples of Examples 1 to 3 have improved tensile strength (TS) as compared with Comparative Example 1, and carbon nanofibers. The effect of reinforcement by was obtained. Moreover, the thermoplastic resin composition samples of Examples 1 to 3 had an elongation at break (Eb) larger than those of Comparative Examples 4 and 5. Furthermore, the thermoplastic resin composition samples of Examples 1 to 3 had higher yield strength (σy) than Comparative Examples 1 to 3. In Example 2, the values of tensile strength (TS) and elongation at break (Eb) were larger than those of Comparative Examples 4 and 5, which are the same amount of carbon nanofibers.

  According to the results of the DMA tests in Tables 1 to 3 and FIGS. 3 and 4, the thermoplastic resin composition samples of Examples 1 to 3 showed storage modulus (E ′) as the amount of carbon nanofiber added increased. ) Improved. The thermoplastic resin composition samples of Examples 1 to 3 had a high storage elastic modulus (E ′) particularly at a high temperature. The thermoplastic resin composition samples of Examples 1 to 3 did not flow up to 300 ° C., which is the upper limit of the measurement temperature, and the storage elastic modulus (E ′) was improved around 200 ° C. The thermoplastic resin composition samples of Examples 1 to 3 had a low loss tangent (tan δ) peak value. It was found that the thermoplastic resin composition samples of Examples 1 to 3 were excellent in heat resistance.

  According to the results of linear expansion coefficient measurement in Tables 1 to 3, the thermoplastic resin composition samples of Examples 1 to 3 had a lower average linear expansion coefficient than Comparative Examples 1 to 5.

(1-6) SEM Observation The frozen fracture sections of the sample of Example 2 and the sample of Comparative Example 4 were observed with a scanning electron microscope (hereinafter referred to as “SEM”).

  5 to 8 are SEM observation photographs of frozen fractured sections (100 times, 500 times, 2000 times, 20000 times) of the sample of Example 2. FIG. Agglomerates of carbon nanofibers could not be confirmed on the frozen fracture surface of the sample of Example 2. The white fibrous substance in FIGS. 7 and 8 is carbon nanofibers, and it was found that the carbon nanofibers were defibrated and dispersed in a state separated from each other.

  9 to 12 are SEM observation photographs of frozen fractured sections (100 times, 500 times, 2000 times, 20000 times) of the sample of Comparative Example 4. FIG. Many aggregates of carbon nanofibers were confirmed on the frozen fractured surface of the sample of Comparative Example 4. In FIGS. 9 to 11, aggregates 100, 101, and 102 of carbon nanofibers can be observed in the black circles. The maximum diameter of the aggregate 100 in FIG. 11 is about 90 μm. When the aggregate 100 is enlarged as shown in FIG. 12, it aggregates in a state close to the raw material of the carbon nanofiber, and between the carbon nanofiber and the carbon nanofiber. There were many hollow parts in which no resin entered.

(2) Test using closed kneader (2-1) Preparation of samples of Examples 4 and 5 Mixing step: Brabender (manufactured by Brabender, PLASTI-CORDER, capacity 350 ml, chamber temperature 140 ° C.) 100 parts by mass (phr) of polyethylene shown in each table was added and melted.

  Next, multilayer carbon nanofibers (described as “CNT” in each table) having a mass part (phr) shown in Table 1 were added and mixed as a compounding agent.

  Low temperature process: Take out the first mixture from the Brabender, let it cool until the surface temperature of the first mixture reaches 110 ° C-120 ° C, put the first mixture in the oven and maintain it at 110 ° C-120 ° C did.

  Low temperature kneading step: The first mixture was charged again into the Brabender and kneaded. During this kneading, the temperature of the dough surface of the first mixture (second temperature) was measured with a non-contact infrared thermometer, and the temperature of the chamber was adjusted so as to be maintained at 110 ° C. to 120 ° C. After kneading sufficiently, the thermoplastic resin composition was taken out from the open roll.

  Pressing process: The thermoplastic resin composition taken out from the Brabender was placed in a mold and pressure-molded under vacuum to prepare a sample. In vacuum press molding, the mold is heated to 140 ° C., preheated for 2 minutes without load, and then press molded at 4 MPa (pressing against the mold) for 5 minutes, and the mold is moved to a cooling press. And it cooled to room temperature, pressurizing at 2 MPa (with respect to a metal mold | die).

  Note that “CNT” and “PE” were the same as those in Example 1-3.

(2-2) Sample preparation of Comparative Example 6 In Comparative Example 6, a sample of a thermoplastic resin composition was obtained in the same manner as in Examples 1 to 3.

(2-3) Tensile test About the sample of an Example and a comparative example, a tensile test is done similarly to said (1-3), tensile strength (TS (MPa)), elongation at the time of cutting (Eb (%)), and The yield point tensile stress (σy (MPa)) was measured. The measurement results are shown in Tables 4 and 5 and FIG.

  In FIG. 13, curves E4 and E5 correspond to Examples 4 and 5, respectively, and curves C1, C4 and C6 represent Comparative Examples 1, 4 and 6 (see Tables 2 and 3 for Comparative Examples 1 and 4). It corresponds to each.

(2-4) DMA measurement The DMA test (dynamic viscoelasticity test) was performed on the samples of Examples and Comparative Examples in the same manner as in the above (1-4). The test results are shown in Tables 4 and 5 and FIGS.

  14 and 15, curves E4 and E5 correspond to Examples 4 and 5, respectively, and curves C1, C4 and C6 represent Comparative Examples 1, 4 and 6 (Tables 2 and 3 for Comparative Examples 1 and 4). Correspond to each).

(2-5) Measurement of average linear expansion coefficient For the samples of Examples and Comparative Examples, the average linear expansion coefficient in the measurement temperature range was measured in the same manner as in the above (1-5). These results are shown in Tables 4 and 5.

  According to the results of the tensile tests shown in Tables 4 and 5 and FIG. 13, the thermoplastic resin composition samples of Examples 4 and 5 have improved tensile strength (TS) as compared with Comparative Example 1, and carbon nanofibers. The effect of reinforcement by was obtained. Moreover, the thermoplastic resin composition samples of Examples 4 and 5 had a larger elongation at break (Eb) than Comparative Examples 4 and 5. Furthermore, the thermoplastic resin composition samples of Examples 4 and 5 had higher yield strength (σy) than Comparative Example 6.

  According to the results of the DMA tests shown in Tables 4 and 5 and FIGS. 14 and 15, the thermoplastic resin composition samples of Examples 4 and 5 showed storage modulus (E ′) as the amount of carbon nanofiber added increased. ) Improved. The thermoplastic resin composition samples of Examples 4 and 5 had a high storage elastic modulus (E ′) particularly at a high temperature. The thermoplastic resin composition samples of Examples 4 and 5 did not flow up to 300 ° C., which is the upper limit of the measurement temperature, and the storage elastic modulus (E ′) was improved around 200 ° C. The thermoplastic resin composition samples of Examples 4 and 5 had a lower peak value of loss tangent (tan δ) than that of Comparative Example 4. It was found that the thermoplastic resin composition samples of Examples 4 and 5 were excellent in heat resistance.

  According to the results of linear expansion coefficient measurement in Tables 4 and 5, the thermoplastic resin composition samples of Examples 4 and 5 had a lower average linear expansion coefficient than that of Comparative Example 6.

(3) Elastic modulus reduction rate Based on the DMA measurement results (FIGS. 3, 4, 14, and 15) in (1) and (2) above, the elastic modulus reduction rate (MPa / MPa) of the examples and comparative examples. And the elastic modulus reduction rate (MPa / ° C.) of the flat region was calculated and shown in Table 6.

  The elastic modulus decrease rate is a change rate at which the storage elastic modulus decreases from 100 MPa to 1 MPa. However, since the example does not reach 1 MPa as shown in FIG. 16, the reduction rate is up to the elastic modulus value at 200 ° C.

  The elastic modulus decrease rate in the flat region is a change rate of the storage elastic modulus that decreases from the flat region start temperature to 200 ° C. as shown in FIG.

  According to the results in Table 6, the thermoplastic resin composition samples of Examples 1 to 5 had a flat region start temperature in the vicinity of 122 ° C to 125 ° C. The second temperature of the first mixture of Examples 1 to 5 in the low temperature kneading step was a temperature range slightly lower than the flat region starting temperature, that is, the rubber elastic region.

  In addition, the thermoplastic resin composition samples of Examples 1 to 5 had a smaller elastic modulus reduction rate than Comparative Example 1.

  Furthermore, the thermoplastic resin composition samples of Examples 1 to 5 had an elastic modulus reduction rate of 0.04 MPa / ° C. to 0.13 MPa / ° C. in the flat region.

  2 Open roll, 10 1st roll, 20 2nd roll, 30 polyethylene, 34 bank, 40 non-contact thermometer, 80 carbon nanofiber, 100 agglomerate, d interval, V1, V2 rotational speed, C1-C6 comparison Examples 1-6, E1-E5 Examples 1-5

Claims (5)

A mixing step of kneading polyethylene and carbon nanofibers at a first temperature to obtain a first mixture;
A temperature reduction step of adjusting the temperature of the first mixture to a second temperature;
A low-temperature kneading step of kneading the first mixture containing a plurality of carbon nanofiber aggregates in polyethylene and at the second temperature at the second temperature;
Including
The first temperature is a temperature that is 25 ° C. or more higher than the melting point (Tm) of the polyethylene,
The method for producing a thermoplastic resin composition, wherein the second temperature ranges from a temperature 5 ° C. lower than the melting point (Tm) of the polyethylene to a temperature lower than 25 ° C. higher than the melting point (Tm). In claim 1,
The method for producing a thermoplastic resin composition, wherein the second temperature is 110 ° C. or higher and lower than 140 ° C. In claim 1 or 2,
The carbon nanofiber has an average diameter of 2 nm or more and 110 nm or less,
The said 1st mixture is a manufacturing method of the thermoplastic resin composition whose said carbon nanofiber is 15 mass parts or more and 55 mass parts or less with respect to 100 mass parts of said polyethylenes. In any one of Claims 1-3,
The said low temperature process is a manufacturing method of the thermoplastic resin composition performed by taking out the said 1st mixture from the kneader used for the said mixing process. A thermoplastic resin composition in which carbon nanofibers are dispersed in polyethylene,
There is no aggregate of carbon nanofibers,
Carbon nanofibers are dispersed throughout and separated from each other .
The storage elastic modulus (E ′) in the dynamic viscoelasticity test based on JIS K7244 with a measurement temperature of 20 to 300 ° C., a dynamic strain of ± 0.05%, and a frequency of 1 Hz increases in a temperature region where the measurement temperature exceeds 200 ° C. ,
The carbon nanofiber has an average diameter of 2 nm or more and 110 nm or less,
To the polyethylene 100 parts by weight, the carbon nanofibers 15 parts by mass or more, Ru der than 55 parts by weight, the thermoplastic resin composition.