JP6090844B2 - Method for producing polypropylene molded body - Google Patents

Description

The present invention relates to a method for producing a polypropylene molded article.

Polypropylene, particularly isotactic polypropylene, is used in a wide range of fields such as materials for automobiles, materials for electrical products, materials for daily goods, and packaging materials.
Conventionally, in a molded product of polypropylene, physical properties are sometimes improved by increasing the crystallinity by heat treatment.
For example, Patent Document 1 discloses that a molded body containing polypropylene is heat-treated at 155 to 170 ° C. to improve rigidity, heat resistance, and hardness.
In Patent Document 2, a molded body of an olefin resin cooled to a crystallization temperature or lower is heated at a temperature 2 to 10 ° C. higher than the melting point of the polyolefin resin for 1 to 1,800 seconds to improve scratch resistance. It is disclosed.
Patent Document 3 discloses that after forming a molded body precursor by shaping polypropylene, the molded body precursor is heated at 150 to 170 ° C. to improve rigidity and impact strength.
In Patent Document 4, a polyolefin resin sheet obtained by melt extrusion is cooled, and the cooled sheet is heated at a temperature in the range of the Vicat softening temperature of the polyolefin resin to the melting point of the polyolefin resin. Heating at a temperature ranging from the melting point of the resin to -60 ° C) to the melting point of the polyolefin resin is disclosed.
In Patent Document 5, a polypropylene preform having a melting peak temperature of Tm (° C.) is heated to a temperature in the range from Tm-10 (° C.) to Tm + 5 (° C.), and then from Tm-15 (° C.). A method is disclosed in which a polypropylene molded body is obtained by lowering the temperature to a temperature in the range up to Tm (° C.) and performing a heat treatment.

JP-A-62-279927 JP 2003-292649 A JP 2008-37102 A JP 2009-12225 A JP 2011-195830 A

Depending on the intended use of the polypropylene molded body, high rigidity and heat resistance may be required. However, in the methods described in Patent Documents 1 to 4, rigidity and heat resistance of the polypropylene molded body may be insufficient, and transparency may be deteriorated.
Further, in the method described in Patent Document 5, the homogeneity of the structure of polypropylene constituting the molded body is not necessarily high. Therefore, the obtained polypropylene molded body may become non-uniform.
An object of this invention is to provide the manufacturing method of the polypropylene molded object which was excellent in rigidity and heat resistance, was highly homogeneous, and maintained transparency.

That is, this invention has the following aspects.
[1] A polypropylene preform with a melting peak temperature of Tm (° C.) determined by a temperature increase rate of 20 ° C./min is raised to a temperature in the range from Tm (° C.) to Tm + 6 (° C.). A first heat treatment step for heating and heat treatment and a polypropylene preform heat treated by the first heat treatment step at 0.5 to a temperature in the range from Tm-30 (° C) to Tm-12 (° C). And a second heat treatment step in which the heat treatment is performed by heating for at least a minute, and the temperature lowering rate or the cooling rate at the time of shifting from the first heat treatment step to the second heat treatment step is 300 ° C./min or more. .
[2] The polypropylene molded article according to [1], wherein a difference (T ₁ −T ₂ ) between a peak temperature T ₁ in the first heat treatment step and an average heat treatment temperature T ₂ in the second heat treatment step is 10 ° C. or more. Production method.
The temperature here is the temperature of the portion where the preform is in direct or indirect contact with the heating device used in each heat treatment step.
Peak temperatures T ₁ in the first heat treatment step is the maximum value of the temperature in the first heat treatment step.
Average heat treatment temperature T ₂ of the second heat treatment step is a value determined by the following method.
That is, the time of the second heat treatment step is t (min), and 0.1 t (min), 0.2 t (min), 0.3 t (min), 0.4 t (min), 0 from the start of the second heat treatment. .5T (min), 0.6 t (min), 0.7 t (min), 0.8 t (min), reads the temperature chart heat treatment temperature _{T x} at a 0.9t (min). _Then, the average thermal treatment temperature values determined from equation _{(T 0.1t + T 0.2t + ···} + T 0.9t) / 9.
[3] The method for producing a polypropylene molded article according to [1] or [2], wherein a temperature increase rate or a heating rate in the first heat treatment step is set to 300 ° C./min or more.
[4] The method for producing a polypropylene molded body according to any one of [1] to [3], wherein the cooling is performed at a temperature decrease rate of less than 300 ° C./min after the second heat treatment step.
[5] The method for producing a polypropylene molded body according to any one of [1] to [4], wherein a sheet or film having a thickness of 300 μm or less is used as the preform.

  According to the method for producing a polypropylene molded body of the present invention, a polypropylene molded body having excellent rigidity and heat resistance, high homogeneity, and maintaining transparency can be easily produced.

An example of a method for producing a polypropylene molded body of the present invention (to a heating apparatus heated to the temperature of the second heat treatment step after heating the heating device equipped with the preform to T ₁ and performing the heat treatment of the first heat treatment step) It is a graph which shows the heat processing temperature pattern in the example which moves a molded object and heat-processes. It is an example of the melting curve of differential thermal analysis. It is an example of the wide angle X-ray scattering profile of a polypropylene molded object.

<Method for producing polypropylene molded article>
The method for producing a polypropylene molded body of the present invention is a method for subjecting a polypropylene preform to a heat treatment.
Examples of the polypropylene used in this production method include a propylene homopolymer, or a block copolymer or a random copolymer of propylene and another α-olefin (having at most 12 carbon atoms). Specific examples of the α-olefin include ethylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 4-dimethyl-1-pentene, and vinylcyclopentane. And vinylcyclohexane. Among them, ethylene and 1-butene are preferable.

It is preferable that the molecular weight distribution ( _Mw / _Mn ) of polypropylene is 2-40. If the molecular weight distribution ( _Mw / _Mn ) of polypropylene is 2 or more, the rigidity of the obtained molded body can be further increased. It should be noted that it is difficult to make the molecular weight distribution (M _w / M _n ) of polypropylene larger than 40 by a practical method.
The MFR, which is an indicator of the fluidity of polypropylene, is preferably 0.01 to 1,000 g / 10 minutes. Here, MFR is a value measured under conditions of a temperature of 230 ° C. and a load of 21.6 N in accordance with JIS K6921-2.

The method for molding the preform is not particularly limited, and for example, a known molding method such as extrusion molding, injection molding, compression molding, inflation molding or the like can be applied.
Examples of the shape of the preform include, but are not limited to, a sheet shape, a film shape, a pipe shape, or a three-dimensional shape according to the application, but a sheet shape or a film shape is preferable in that the shape can be easily maintained.
Furthermore, since the sheet-shaped or film-shaped preform can easily increase the temperature rising rate during heating and the temperature decreasing rate during cooling, it is preferable to make it thin, and specifically, the thickness is 300 μm or less. It is preferably 100 μm or less. However, since it will be easy to fracture | rupture when it is too thin, it is preferable that thickness is 1 micrometer or more.
Moreover, it is preferable that the preform is as small as possible. When the orientation is large, the melting peak temperature Tm of the preform is apparently increased, and it becomes difficult to determine an appropriate heat treatment temperature.

  In addition, the preform includes, for example, a nucleating agent, a filler, a hydrochloric acid absorbent, a heat stabilizer, a light stabilizer, an ultraviolet absorber, an internal lubricant, an external lubricant, an antistatic agent, a flame retardant, a pigment, a dye, Additives such as a dispersant, a copper damage inhibitor, a neutralizer, a plasticizer, a foaming agent, an anti-bubble agent, a crosslinking agent, and a peroxide may be included.

In the method for producing a polypropylene molded body of the present invention, a first heat treatment step in which a first heat treatment is performed on a polypropylene preform having a melting peak temperature of Tm (° C.) and a second heat treatment is performed on the molded body that has been subjected to the first heat treatment. A second heat treatment step.
Tm in the present invention is a melting peak temperature of differential thermal analysis (DSC) obtained at a heating rate of 20 ° C./min for the preform. Specifically, the Tm of the preform is determined by the following measurement method.
That is, using a heat-compensated DSC (Perkin Elmer Diamond DSC), the polypropylene preform is held at 30 ° C. for 5 minutes and heated to 230 ° C. at a temperature increase rate of 20 ° C./min. Tm is obtained from the peak position of the melting curve obtained at that time. Note that the Tm of the preform includes the effect of an increase in the melting point due to an increase in the thickness of the crystal lamella due to the annealing effect during the temperature rise.

In the first heat treatment step, the polypropylene preform is heated to a temperature in the range from Tm (° C.) to Tm + 6 (° C.) and heat treated (first heat treatment) (see FIG. 1). That is, the first heat treatment step is a range from the start of temperature increase until the temperature of the preform reaches a peak temperature and becomes less than Tm (° C.). In this manufacturing method, the heat treatment temperature does not exceed Tm + 6 (° C.) over the entire heat treatment.
In the first heat treatment step, it is preferable to raise the temperature to a temperature in the range from Tm + 1 (° C.) to Tm + 5 (° C.).
In the first heat treatment step, if the heat treatment temperature of the preform is less than the lower limit, the uniformity of the resulting molded product is lowered, and if it exceeds the upper limit, the rigidity is lowered.
As a heating method in the first heat treatment, for example, a method in which a preformed body is sandwiched between a pair of metal blocks, a heating method, a method in which a preformed body is sandwiched between a pair of metal blocks previously heated to a predetermined temperature, and preforming. Examples include a method of heating the body itself with hot air or infrared rays.

The heating rate or heating rate in the first heat treatment step is preferably 300 ° C./min or more. Heating rate, {(temperature after heating) - (elevated temperature before)} / (the time required for movement of the preform to a pre-heating device and heated to T _1), the heating rate, { (temperature after heating) - obtained in (elevated temperature before)} / (the time until the temperature of the heating apparatus equipped with a preform reaches T _1). Here, the “temperature before the temperature rise” means the temperature in the vicinity of the preform, or when preheating is performed, the preform is directly or indirectly used in the heating apparatus used in the preheating step. It is the temperature of the part which contacts. Further, "temperature after heating" is the peak temperature T ₁ of the first heat treatment step described above.
If the heating rate or heating rate is 300 ° C./min or more, the rise in melting point due to the annealing effect is suppressed, and melting and recrystallization are further promoted by heat treatment. As a result, the uniformity of the resulting molded body and the performance of the crystal seed Becomes higher. Moreover, since a temperature increase rate or a heating rate is easily realizable, it is preferable that it is 100,000 degrees C / min or less.
As a method of increasing the heating rate or the heating rate to 300 ° C./min or more, for example, preheating using a hot air heater or an infrared heater, and raising the temperature to near the lower limit of the heat treatment temperature, Then, the method of heating further is mentioned. The preheating in this heating method is preferably performed at a temperature that does not cause the annealing effect. Specifically, the preheating temperature is preferably 140 ° C. or lower.
Also, rapid heating can be realized by heating with laser light or heating with microwaves, and the rate of temperature rise can be increased. Furthermore, a method in which a preform is sandwiched between a pair of metal blocks heated to a predetermined temperature in advance is also preferable.

  The preform may be heated for a while at a temperature ranging from Tm (° C.) to Tm + 6 (° C.). The heating time, that is, the heat treatment time of the first heat treatment is preferably 0.5 minutes or more, more preferably 1 minute or more from the viewpoint of further improving rigidity, heat resistance and homogeneity. Minutes or less is preferable, and 5 minutes or less is more preferable.

In the second heat treatment step, the polypropylene preform after the first heat treatment step is cooled to a temperature in the range from Tm-30 (° C.) to Tm-12 (° C.) and heat treated (second heat treatment) (FIG. 1). reference). That is, the second heat treatment step is a range from when the preform temperature reaches Tm-12 (° C.) to when the preform temperature decreases and reaches Tm-30 (° C.). The heat treatment temperature in the second heat treatment step is preferably in the range from Tm-25 (° C.) to Tm-12 (° C.).
When the heating temperature in the second heat treatment step is less than the lower limit value, the rigidity of the resulting molded article may be reduced, and even when the heating temperature exceeds the upper limit value, the rigidity may be reduced.
As a method for lowering the temperature when shifting from the first heat treatment to the second heat treatment, for example, a method of lowering the temperature after sandwiching a preformed body between a pair of metal blocks, a preformed body on a pair of metal blocks adjusted to a predetermined temperature in advance. There are a method of lowering the temperature by sandwiching the temperature, a method of stopping the heating of the preform and leaving it to cool.

The temperature decreasing rate or cooling rate when shifting from the first heat treatment to the second heat treatment is 300 ° C./min or more, preferably 500 ° C./min or more. When the temperature lowering rate or cooling rate is less than 300 ° C./min, undesirable crystals may be formed, and the rigidity and heat resistance of the resulting molded product may be lowered. The rate of temperature decrease is determined by {(temperature before temperature decrease) − (temperature after temperature decrease)} / (time required for movement from the temperature region of the first heat treatment step to the temperature region of the second heat treatment step). Cooling rate, - until a {(temperature before cooling) (temperature after cooling)} / (the temperature of the heating device of the first heat treatment step of mounting the preform from T ₁ of the second heat treatment process temperature region Time). Here, the "temperature before cooling", the peak temperature T ₁ of the first heat treatment step described above, the "temperature after cooling" is the average thermal treatment temperature T ₂ of the second heat treatment step.
On the other hand, since it can be easily realized, it is preferable that the cooling rate or the cooling rate when shifting from the first heat treatment to the second heat treatment is 100,000 ° C./min or less.

In the second heat treatment step, heating is performed in the temperature range for a while. The heating time, that is, the heat treatment time of the second heat treatment is 0.5 minutes or more, preferably 1 minute or more, more preferably 2 minutes or more, since rigidity, heat resistance and homogeneity are higher, and 3 minutes. The above is most preferable.
However, from the viewpoint of productivity, it is preferable that the heating time is short, specifically, 10 minutes or less is preferable, and 5 minutes or less is more preferable.

In this manufacturing method, since the rigidity and heat resistance of the polypropylene molded product are higher, the difference (T ₁ −T ₂ ) between the peak temperature T ₁ in the first heat treatment step and the average heat treatment temperature T ₂ in the second heat treatment step. Is preferably 10 ° C. or higher. The temperature here is the temperature of the portion where the preform is in direct or indirect contact with the heating device used in each heat treatment step.
Peak temperatures T ₁ in the first heat treatment step, in the same manner as described above, the highest value of the temperature in the first heat treatment step.
Average heat treatment temperature T ₂ of the second heat treatment step in the present invention is determined as follows.
That is, the time of the second heat treatment is t (min), and 0.1 t (min), 0.2 t (min), 0.3 t (min), 0.4 t (min),. The heat treatment temperature Tx at 5 t (min), 0.6 t (min), 0.7 t (min), 0.8 t (min), and 0.9 t (min) is read from the temperature chart. _Then, the average thermal treatment temperature values determined from equation _{(T 0.1t + T 0.2t + ···} + T 0.9t) / 9.
On the other hand, (T ₁ -T ₂ ) is preferably 30 ° C. or less from the viewpoint that the temperature can be easily adjusted.

After the second heat treatment step, it is preferable to have a cooling step for cooling the molded body that has been subjected to the second heat treatment step. The cooling rate during the cooling step is preferably less than 300 ° C./min, and more preferably less than 100 ° C./min. Here, the rate of temperature decrease is obtained by {(temperature before temperature decrease) − (temperature after temperature decrease)} / (time required for temperature change). When the temperature lowering rate is less than 300 ° C./min, the homogeneity of the obtained molded body is higher.
On the other hand, the temperature lowering rate is preferably 0.1 ° C./min or more from the viewpoint of productivity, and is preferably less than 100 ° C./min since it can be easily realized.
The cooling method is not particularly limited, and a method of cooling the obtained molded body directly or indirectly using an organic solvent such as water or acetone as a refrigerant, a method of cooling the molded body by leaving it in the air, The method etc. which cool by applying cold air to a molded object are mentioned.

In the first heat treatment of the above manufacturing method, a seed of polypropylene crystals is formed, and in the second heat treatment, the seed functions as a nucleating agent for polypropylene, so that crystallization proceeds in a short time even at a relatively high temperature. Therefore, in the method for producing a polypropylene molded body, the crystallinity is increased and the rigidity is increased. Further, in the temperature region of the second heat treatment step, α2 type crystals are easily formed, and as will be described later, the content ratio of α2 type crystals increases and heat resistance increases.
Further, in the above-described method for producing a polypropylene molded body, by performing the heat treatment at a high temperature equal to or higher than Tm in the first heat treatment, the unmelted portion of the preformed body does not remain, so that the homogeneity is improved. In addition, as homogeneity increases, transparency tends to increase.

<Polypropylene molded body>
Polypropylene molded article obtained by the production method of the present invention is excellent in rigidity and heat resistance, moreover is sufficiently high homogeneity of the polypropylene.
The polypropylene molded body obtained by the production method of the present invention is higher than the melting peak temperature Tm (° C.) of the preform in the melting curve (see FIG. 2) of differential thermal analysis obtained at a heating rate of 20 ° C./min. It is preferable to have a melting peak temperature higher than 6 ° C. Furthermore, it is more preferable to have a melting peak temperature of 7 ° C. or more higher than the melting peak temperature Tm (° C.) of the preform, and it is most preferable to have a melting peak temperature of 8 ° C. or more.
Incidentally, components exhibiting a high melting peak temperature T _A be present in minor amounts in the melting curve of differential thermal analysis in Figure 2 corresponds to the crystal seed, higher melting point, higher effect as a nucleating agent. On the other hand, mainly polypropylene molded body is a component showing a melting peak temperature T _B of the low temperature side, the low-temperature side of the melting peak temperature T _B is higher than the melting peak temperature Tm of the preform, a higher heat resistance It will be a thing.

Moreover, the polypropylene which comprises the polypropylene molded object obtained by the said manufacturing method has an alpha type crystal structure as a main body. The α type crystal structure of polypropylene includes α1 type crystal and α2 type crystal, but the polypropylene molded product obtained by the above production method contains a lot of α2 type crystal. Here, in the α1 type crystal, the direction of the methyl group between adjacent polypropylene chains in the crystal is random, but in the α2 type crystal, there is order.
In general, it is considered that the formation of α2-type crystals is accompanied by an increase in the thickness of polypropylene lamella (a plate-like crystal having a thickness of 5 to 80 nm) (T. Miyoshi et al., Journal Physical Chemistry B, 114 (1 ), 92 (2010)). As the lamella thickness increases, rigidity and heat resistance tend to increase.
In the polypropylene molded product obtained by the production method of the present invention, the peak intensity I (α2) of -231 and -161 reflection based on α2 type crystal, and the peak intensity I (α1 + α2) of scattering based on both α1 and α2 type crystals. ) Ratio I (α2) / I (α1 + α2) is preferably 0.1 or more, more preferably 0.3 or more, and further preferably 0.5 or more. When I (α2) / I (α1 + α2) is equal to or greater than the lower limit, rigidity and heat resistance are further increased.
The presence of α2-type crystals can be confirmed by -231 and -161 reflections in X-ray diffraction (see M. Hikosaka and T. Seto, Polymer Journal, 5 (2), 111 (1973)).
The X-ray source used for obtaining the above peak intensity ratio is preferably one using synchrotron radiation. Since the intensity of the -231 and -161 reflections is weak, the S / N ratio can be increased by using synchrotron radiation having high luminance, and a highly accurate result can be obtained.

  Said polypropylene molded object can be used conveniently, for example as a material for motor vehicles, a material for electric products, a material for daily goods, a packaging material, etc.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to a following example.
The polypropylene resin composition used in the following examples was produced by the following method.
A polymer as a raw material for the polypropylene resin composition was obtained by polymerizing propylene using a phthalate-based solid catalyst. The solid catalyst used is obtained by the method described in EP 6749991. Specifically, it was manufactured as follows:
The solid catalyst used for the polymerization was prepared by the method described in Example 1 of EP 6749991. The solid catalyst is one in which Ti and diisobutyl phthalate as an internal donor are supported on MgCl ₂ by the method described in the above-mentioned patent publication.
Contact the above solid catalyst with TEAL and dicyclopentyldimethoxysilane (DCPMS) for 5 minutes at −5 ° C. in an amount such that the mass ratio of TEAL to the solid catalyst is 11 and the mass ratio of TEAL / DCPMS is 3. I let you. The resulting catalyst system was prepolymerized by holding it in liquid propylene in suspension for 5 minutes at 20 ° C. The obtained prepolymer was introduced into a polymerization reactor, 0.135 mol% of hydrogen and propylene were fed, and a polymerization pressure was adjusted at a polymerization temperature of 80 ° C. to obtain a propylene homopolymer.
The obtained polymer is blended with 0.2 parts by weight of B255 manufactured by BASF as an antioxidant and 0.05 parts by weight of calcium stearate manufactured by Tamnan Chemical Co., Ltd. as a neutralizing agent, and is mixed for 1 minute with a Henschel mixer. Stir and mix. The obtained mixture was melted and discharged from a die using a single screw extruder (manufactured by Nakatani Machinery Co., Ltd., NVC, screw diameter 50 mm) whose cylinder temperature was adjusted to 230 ° C. The strand thus obtained was cooled in water and then cut with a pelletizer to obtain a pellet-shaped polypropylene resin composition, which was used in the following examples.
The obtained polypropylene resin composition had stereoregularity (mmmm): 97.8 mol%, mass average molecular weight ( _Mw ): 362,000, and molecular weight distribution ( _Mw / _Mn ): 6.8. Moreover, MFR was 4.3 g / 10min.
In addition, mmmm of polypropylene is ¹³ C-NMR using JNM LA-400 ( ¹³ C resonance frequency 100 MHz) manufactured by JEOL Ltd. for a sample dissolved in a mixed solvent of 1,2,4-trichlorobenzene / deuterated benzene. From the spectrum measured by the method, the ratio of the intensity of the peak corresponding to a pentad in which four meso (m) bond sequences of the propylene monomer were continuously obtained was calculated as follows. It was determined according to the method described in Zambelli, Macromolecules, 6, 925 (1973).
The mass average molecular weight ( _Mw ) and molecular weight distribution ( _Mw / _Mn ) were measured by gel permeation chromatography (PL-GPC220 manufactured by Polymer Laboratories).

Example 1
A sheet obtained by simply hot-pressing a polypropylene resin composition is heated at 230 ° C. for 1 minute, and then kept at 115 ° C. for 5 minutes to crystallize. A molded body was obtained. The Tm of the preform was 162.7 ° C.
Next, the sheet-shaped preform at room temperature was sandwiched between two preheated heating blocks via a thin metal plate and subjected to a first heat treatment for 7 minutes. The temperature increase rate at that time was 34,600 ° C./min, and the first heat treatment peak temperature T ₁ was 166.8 ° C.
Next, the molded body subjected to the first heat treatment was sandwiched between two other preheated heating blocks with the metal plate attached thereto, and then subjected to the second heat treatment for 3 minutes. The temperature lowering rate when shifting from the first heat treatment to the second heat treatment was 8,900 ° C./min, and the average heat treatment temperature T ₂ was 149.8 ° C.
Thereafter, the molded body subjected to the second heat treatment was immersed in acetone at about −90 ° C. (near the melting point) with a metal plate attached, and rapidly cooled. After taking out to room temperature environment, it peeled from the metal plate and obtained the polypropylene molded object.

(Example 2)
Polypropylene in the same manner as in Example 1 except that the rate of temperature decrease during the transition from the first heat treatment to the second heat treatment was changed to 11,500 ° C./min and the average heat treatment temperature of the second heat treatment was changed to 144.8 ° C. A molded body was obtained.

(Example 3)
Polypropylene in the same manner as in Example 1 except that the rate of temperature decrease during the transition from the first heat treatment to the second heat treatment was 12,500 ° C./minute and the average heat treatment temperature of the second heat treatment was changed to 142.8 ° C. A molded body was obtained.

Example 4
Instead of quenching after the second heat treatment, a polypropylene molded body was obtained in the same manner as in Example 2 except that it was allowed to cool in a room temperature environment.

(Example 5)
A polypropylene molded body was obtained in the same manner as in Example 2 except that the treatment time for the first heat treatment was changed to 1 minute and the treatment time for the second heat treatment was changed to 9 minutes.

(Example 6)
Polypropylene in the same manner as in Example 5 except that the peak temperature of the first heat treatment was changed to 164.8 ° C., and the rate of temperature decrease during the transition from the first heat treatment to the second heat treatment was 10,400 ° C./min. A molded body was obtained.

(Example 7)
Polypropylene molded in the same manner as in Example 2 except that the preform formed between thin metal plates was heated at a heating rate of 10 ° C./min using a hot press and the treatment time of the first heat treatment was changed to 11 minutes. A molded body was obtained.

(Comparative Example 1)
The preformed body in Example 1 was used as a polypropylene molded body as it was. In addition, the melting peak temperature of the polypropylene molded body of Comparative Example 1 is Tm in each Example and each Comparative Example.

(Comparative Example 2)
The temperature increase rate of the first heat treatment is 32,700 ° C./min, the peak temperature of the first heat treatment is 159.8 ° C., the treatment time is 1 minute, and the temperature decrease rate when shifting from the first heat treatment to the second heat treatment is A polypropylene molded body was obtained in the same manner as in Example 1 except that the average heat treatment temperature of the second heat treatment was changed to 157.8 ° C. and the treatment time was changed to 2 minutes at 1,000 ° C./min.

(Comparative Example 3)
A polypropylene molded body was obtained in the same manner as in Example 1 except that the second heat treatment was omitted. In addition, since the molded object of the comparative example 3 is anticipated that the structural change during temperature rising is large, DSC measurement was not performed.

(Comparative Example 4)
A polypropylene molded body was obtained in the same manner as in Example 4 except that the second heat treatment was omitted.

(Comparative Example 5)
The temperature increase rate of the first heat treatment is 35,100 ° C./min, the peak temperature of the first heat treatment is 168.8 ° C., and the temperature decrease rate when shifting from the first heat treatment to the second heat treatment is 12,500 ° C./min. A polypropylene molded body was obtained in the same manner as in Example 2 except that the above was changed.

(Comparative Example 6)
The temperature increase rate of the first heat treatment is 32,900 ° C./min, the peak temperature of the first heat treatment is 160.8 ° C., and the temperature decrease rate when shifting from the first heat treatment to the second heat treatment is 8,300 ° C./min. A polypropylene molded body was obtained in the same manner as in Example 2 except that the above was changed.

(Comparative Example 7)
Polypropylene in the same manner as in Example 1 except that the average heat treatment temperature of the second heat treatment was changed to 157.8 ° C., and the temperature lowering rate when shifting from the first heat treatment to the second heat treatment was changed to 4,700 ° C./min. A molded body was obtained.

(Comparative Example 8)
Polypropylene in the same manner as in Comparative Example 2 except that the average heat treatment temperature of the second heat treatment was changed to 144.8 ° C. and the temperature lowering rate during the transition from the first heat treatment to the second heat treatment was changed to 7,800 ° C./min. A molded body was obtained.

<Evaluation>
With respect to the obtained polypropylene molded article, the transparency, homogeneity, rigidity, heat resistance, and ratio index of α2-type crystals were evaluated as follows. The evaluation results are shown in Table 1 (Examples) and Table 2 (Comparative Examples).

[Transparency / homogeneity] Using a visual transparency tester manufactured by Toyo Seiki Seisakusho, the diffuse transmitted light value (LSI value) and the transmitted light value at a narrow angle (NAS value) were measured. The smaller the LSI value and the NAS value, the higher the transparency. Moreover, the smaller the NAS value, the higher the homogeneity.

[Rigidity] The complex elastic modulus was determined at a measurement frequency of 110 Hz according to JIS K7198 using Leo Vibron DOV-II-EA manufactured by Toyo Baldwin. The higher the complex elastic modulus, the higher the rigidity.

[Heat resistance] Depending on the peak position of the melting curve obtained when using a diamond DSC manufactured by PerkinElmer, Inc. and holding the polypropylene molded body at 30 ° C. for 5 minutes and then heating to 230 ° C. at a temperature increase rate of 20 ° C./min. The melting peak temperature of the polypropylene molded body was obtained and used as an index of heat resistance. The higher the melting peak temperature, the better the heat resistance. However, even if the melting peak temperature is high, the heat resistance is low if the melting peak temperature is low.

[Proportion of α2-type crystal]
Wide angle X-ray scattering (WAXD) was measured under the conditions of a wavelength of 0.1 nm and an exposure time of 5 seconds using a BL03XU beam line of SPring-8 operated by the Research Center for High Brightness Optical Science. From the X-ray scattering profile (see FIG. 3), an index of the proportion of α2 type crystals can be obtained.
That is, in the wide-angle X-ray scattering profile, -231 and -161 reflection peak intensities I (α2) peculiar to α2 type crystals observed near 2θ = 20.0 degrees (2θ = 31 degrees for CuKα rays). And the peak intensity I (α1 + α2) of scattering based on both the α1 type crystal and the α2 type crystal observed in the vicinity of 2θ = 21.2 degrees. Then, I (α2) / I (α1 + α2) was determined and used as an index of the proportion of α2 type crystals. The peak intensity is the number of counts between the base line connecting the minimum values (2θ = 20 ° lower angle side and 2θ = 21.2 ° higher angle side) at which each scattering is eliminated to the peak maximum. It was. A larger value of I (α2) / I (α1 + α2) means that the proportion of α2 type crystals in all α type crystals (total of α1 type crystals and α2 type crystals) is larger. However, the obtained value does not indicate the ratio of the α2 type crystal itself but is an index correlated with the ratio of the α2 type crystal.

The polypropylene molded bodies of Examples 1 to 7 were excellent in rigidity and heat resistance because the polypropylene was α-type crystals and contained many α2-type crystals. In addition, transparency and homogeneity were maintained.
On the other hand, the polypropylene preform of Comparative Example 1 obtained by crystallization at 115 ° C. had low rigidity and heat resistance. Also, the homogeneity was insufficient.
The polypropylene molded body of Comparative Example 2 obtained by lowering the peak temperature of the first heat treatment below the predetermined range and increasing the average heat treatment temperature of the second heat treatment above the predetermined range had low homogeneity.
The polypropylene molded body of Comparative Example 3 obtained by omitting the second heat treatment and quenching was low in rigidity.
The polypropylene molded body of Comparative Example 4 obtained by omitting the second heat treatment and allowing to cool was poor in homogeneity and also not sufficiently improved in rigidity.
The polypropylene molded body of Comparative Example 5 obtained by making the peak temperature of the first heat treatment higher than the predetermined range had low rigidity and heat resistance.
The polypropylene molded body of Comparative Example 6 in which the peak temperature of the first heat treatment was lower than the predetermined range had low homogeneity.
Although the peak temperature of the first heat treatment satisfies the range of Claim 1, the average heat treatment temperature of the second heat treatment exceeds the range of Claim 1, and Comparative Example 7 is not sufficiently improved in rigidity and heat resistance.
In Comparative Example 8 in which the peak temperature of the first heat treatment was lower than the range of Claim 1, the average heat treatment temperature of the second heat treatment satisfied the range of Claim 1, but the rigidity was not sufficiently improved.

Claims (5)

A polypropylene preform having a melting peak temperature of Tm (° C.) determined by a temperature increase rate of 20 ° C./min is Tm (° C.) to a temperature in the range from Tm (° C.) to Tm + 6 (° C.), A first heat treatment step of heating and heat-treating;
A second heat treatment step of heat-treating the polypropylene preform formed by the first heat treatment step at a temperature ranging from Tm-30 (° C.) to Tm-12 (° C.) for 0.5 minutes or more. And
A method for producing a polypropylene molded body, wherein a temperature lowering rate or a cooling rate when shifting from the first heat treatment step to the second heat treatment step is 300 ° C./min or more. The method for producing a polypropylene molded body according to claim 1, wherein the difference (T ₁ -T ₂ ) between the peak temperature T ₁ in the first heat treatment step and the average heat treatment temperature T ₂ in the second heat treatment step is 10 ° C or higher.
The temperature here is the temperature of the portion where the preform is in direct or indirect contact with the heating device used in each heat treatment step.
Peak temperatures T ₁ in the first heat treatment step is the maximum value of the temperature in the first heat treatment step.
Average heat treatment temperature T ₂ of the second heat treatment step is a value determined by the following method.
That is, the time of the second heat treatment step is t (min), and 0.1 t (min), 0.2 t (min), 0.3 t (min), 0.4 t (min), 0 from the start of the second heat treatment. .5T (min), 0.6 t (min), 0.7 t (min), 0.8 t (min), reads the temperature chart heat treatment temperature _{T x} at a 0.9t (min). _Then, the average thermal treatment temperature values determined from equation _{(T 0.1t + T 0.2t + ···} + T 0.9t) / 9.   The manufacturing method of the polypropylene molded object of Claim 1 or 2 which makes the temperature increase rate or heating rate in a 1st heat treatment process 300 degrees C / min or more.   The manufacturing method of the polypropylene molded object as described in any one of Claims 1-3 which cools with the temperature-fall rate of less than 300 degrees C / min after a 2nd heat treatment process. A sheet or film having a thickness of 300 µm or less is used as the preform.
The method for producing a polypropylene molded body according to any one of 4.

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