JP2000128993A - Crystallization of polymeric resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of the crystallization for a crystalline polymeric resin with both high degree of crystallinity and heat resistance. SOLUTION: This method comprises the following procedure: a pelletized high-impact polypropylene sample S as a resin to be crystallized is placed in an autoclave 1 where the sample S is melted under heating to erase the heat history involved therein so far; subsequently, the autoclave 1 is filled with carbon dioxide gas from a cylinder 2 via valves V1 and V2 to dissolve the gas in the resin under a pressure of 15-60 atm followed by withdrawing the autoclave from the oil bath, and heat release of the autoclave in ambient air results in the cooling and recrystallization of the sample S. The crystal structure of the resin thus afforded represents entire α-phase, wherein, as the pressure inside the autoclave increases, rise in both the crystallinity and melting point of the resin is recognized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer material having improved crystallinity and heat resistance and a method for crystallizing a molded product.

[0002]

2. Description of the Related Art Crystalline resins, among which polyolefin resins, are polymer resins widely used as general-purpose resins. Usually, when an electric product member or an automobile member is made from such a resin, the resin is melted, poured into a mold or extruded, and then cooled to solidify the resin to obtain a product. At that time, depending on the cooling method (speed / temperature history), the crystal characteristics of the completed compact,
Melting point characteristics are significantly different. At present, only changing the cooling rate is used in order to adjust the crystallinity of the resin, and in order to increase the crystallinity of the molded product, the cooling rate must be suppressed and the molded product must be cooled slowly. Such a method of suppressing the cooling rate has significantly impeded the improvement of productivity. Therefore, in reality, the cooling rate is determined only from the viewpoint of preventing the improvement of the crystallinity of the resin and preventing the shrinkage of the external shape (shrinkage of the resin caused by cooling).

[0003] Scientifically, as a crystallization method for improving the crystallinity of a crystalline resin, a method of cooling and crystallizing under high pressure has been reported. However, in this method, for example, in order to raise the melting point by 1 ° C., it is necessary to apply pressure above 40 atm. In order to obtain a product having higher crystallinity or a product having a higher melting point, the operating pressure must be several hundred atmospheres. And there is a problem in device design.

[0004]

SUMMARY OF THE INVENTION The present invention has a high crystallinity and a melting point of, for example, 5 to 5 atm.
It is an object of the present invention to provide a method for producing a crystallized resin improved in the range of 10 ° C.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of crystallizing a crystalline polymer resin by cooling and crystallizing the polymer in an atmosphere of a gas having solubility in the resin. The present invention relates to a method for crystallizing a polymer resin capable of improving the property and increasing the melting point of the resin.

More specifically, in the method for crystallizing a polymer resin of the present invention, the crystalline polymer resin is exposed in a molten state to a pressurized atmosphere of a gas having solubility in the polymer resin, and the gas is exposed. Characterized by being dissolved in a resin and solidifying the resin by cooling in a pressurized gas atmosphere,
Crystallization method for polymer resin.

The reason why the crystallization method improves the crystallinity of the crystallized polymer resin has not been clarified scientifically, but is considered as follows. When low molecules such as carbon dioxide and nitrogen gas dissolve into the resin composed of the polymer chains, the interaction between the polymer chains is weakened, and the mobility (movability) of the polymer chains is increased. By cooling and solidifying the resin in a state where the polymer chains are easily movable, the arrangement of the polymer chains tends to reach a state with a higher ordered structure and a lower energy potential, so that a more crystalline solid A resin is obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. (1) Crystalline polymer resin The term “crystalline polymer resin” as used in the present invention refers to a polymer resin in which the molecular arrangement has considerable order and clear crystalline X-ray diffraction is observed. In general, as the side group of the polymer chain becomes bulkier, the crystallinity decreases as the arrangement becomes more disordered. Commercially available polyethylene and polypropylene are all crystalline polymers. Other crystalline polymer resins include isotactic polystyrene having uniform orientation of benzene groups, which are side groups, and polyethylene terephthalate (PET) used for soft drink containers. Specific examples include polyolefin resins such as a polyethylene polymer and a polypropylene polymer, and more specific examples include polyethylene, polypropylene, polyethylene terephthalate, and isotactic polystyrene.

(2) Dissolvable gas “Dissolving” with respect to a soluble gas means whether or not the gas dissolves in the polymer resin, academically, whether or not the free energy difference ΔG before and after mixing is negative. Is defined by In reality, the molten resin is exposed to gas in a closed system, and by measuring the change in the weight of the resin or the change in the pressure of the gas, the number of moles of the gas present in the resin with respect to the resin per unit weight is obtained. The value is defined as solubility (SolubiSolubility). A gas having a non-zero solubility in a resin is referred to herein as a soluble gas. The high solubility of the gas in the resin refers to the high solubility at the same temperature and the same pressure. It has been found that the solubility of carbon dioxide and nitrogen increases almost linearly in proportion to the gas pressurization pressure for the polyethylene and polypropylene resins targeted for this discovery. The solubility of carbon dioxide for resin is higher for polypropylene than for polyethylene. In the same polypropylene, carbon dioxide has higher solubility than nitrogen at any temperature and pressure. As long as the gas is soluble in the crystalline polymer resin, it can be used in principle for the crystallization method of the present invention. The higher the solubility of the gas, the greater the crystallization effect targeted by the present invention. Conventionally, fluorocarbon gas has been known as a highly soluble gas, but from the viewpoint of environmental problems, fluorocarbon gas is in the direction of total elimination, which is not preferable. Although solubility is lower than that of fluorocarbon gas, carbon dioxide and nitrogen are preferable from the viewpoint of environmental problems.

Since gas cannot be dissolved in the crystalline phase of the crystalline polymer resin, the gas dissolved in the resin in a molten state is
It does not remain in the crystallized resin part. In particular, in a polyolefin and carbon dioxide or nitrogen gas system, when the polyolefin resin is at normal pressure and normal temperature, almost no gas is dissolved in both the crystalline phase and the amorphous phase.

(3) Crystallizing Step According to the method for crystallizing a polymer resin of the present invention, the crystalline polymer resin is heated and melted, exposed to a molten gas in a pressurized gas atmosphere soluble in the resin, and cooled again. Crystallizes. The cooling / crystallization step is performed in the presence of a gas having solubility in the resin.

Melting Conditions In order to dissolve the resin, it is indispensable to increase the temperature by heating, but usually, when the temperature is increased, the amount of gas dissolved in the resin decreases. Therefore, the heating temperature of the resin is set slightly higher than the melting point of the raw resin. For example, in the case of polypropylene, it is around 170 ° C.
It should be around 60 ° C.

Cooling conditions The autoclave is taken out of the oil bath into the air and allowed to cool naturally, for example, for 4 hours. This corresponds to cooling at a rate of 0.52 ° C./min in terms of a cooling rate.

Pressurizing Conditions Setting of the pressurizing conditions of the gas is performed from the viewpoint of controlling the solubility of the gas in the resin and a problem in designing the apparatus. The solubility increases with polyethylene and polypropylene for both carbon dioxide and nitrogen with increasing pressure. By the way, in the set temperature range of 160 ° C. to 180 ° C., the solubility of carbon dioxide in propylene is 0 to 10 at 0 atm.
It is reported that the pressure increases linearly from 1.8 to 2.0 [mol-gas / kg-polymer] at 0 atm. Therefore, it is considered that the effect of crystallization aimed at by the present invention increases as the pressurizing pressure is increased. However, from the viewpoint of the apparatus, the effect is set to 2 to 60 atm and m.

More specifically, the degree of increase in the melting point of the cooled and solidified resin varies depending on the amount of gas dissolved in the molten resin. That is, if the pressure is increased, the amount of gas dissolved in the resin increases, and the melting point of the obtained crystallized resin increases. Normally, the carbon dioxide gas cylinder is set to a maximum of 60 atm, and if the carbon dioxide gas is melted in the molten resin using such a carbon dioxide gas cylinder, the effect of the present invention can be sufficiently obtained.

[0016]

The present invention will be further described below with reference to specific examples. Target resin High impact polypropylene (alias: block polypropylene) was used. High-impact polypropylene is produced by polymerizing a homopolymer in the first-stage polymerization reactor, and then mixing the homopolymer obtained in the first-stage reaction vessel with ethylene-propylene rubber in the second-stage polymerization reactor. It was done.

Physical Properties of Resin The physical properties of the polypropylene used in the experiment were MI (AST
(Melt index measured according to M-D12138) is 18 g / 10 min, the EPR component is 18%, and the ethylene component is about 8%. The initial shape of the high impact polypropylene was a bellet shape.

Experimental Apparatus An experiment was performed using the apparatus shown in FIG. In the experimental apparatus, a carbon dioxide cylinder 2 (purity of 99.9% or more) is connected to an autoclave-type pressurized cell 1 via valves V1 and V2,
The pressure cell 1 has a safety valve V3 and a gas release valve V4.
And the pressure gauge G are connected. The autoclave 1 is immersed in oil in an oil bath to be heated. The test sample S is arranged in the autoclave 1.

Experimental Procedure i) In an autoclave, a sample formed on a cylindrical or 2 cm square sheet having a diameter of about 1 cm was suspended in the air,
1atm ・ 180 ℃ (oil bath set temperature) pressure ・
Heat at temperature for 15 minutes. The sample is returned to the molten state by heating, and the heat history up to now is erased. After the heating, the inside of the autoclave is filled with the added gas for 4 hours, and the gas is dissolved in the resin. Thereafter, the autoclave is taken out of the oil bath, and the sample is cooled and recrystallized (solidified) by natural heat radiation.

Ii) The effect of the temperature treatment on the crystallinity of the recrystallized resin was analyzed by changing the pressurizing pressure with carbon dioxide. At the same temperature, the solubility of carbon dioxide increases with increasing pressure. Therefore, a change in the pressurizing pressure is equivalent to a change in the solubility in the resin.

Iii) For comparison, an experiment was performed in which the pressure was increased by 50 atm of nitrogen gas without changing the manner of the temperature treatment.
Nitrogen gas, compared to carbon dioxide, at the same temperature and pressure,
Low solubility in sample.

Iv) For further comparison, an experiment was conducted in which the temperature treatment was the same, and cooling and crystallization were performed while maintaining the air at 1 atm.

Evaluation method i) Melting point The melting point of the recrystallized sample was measured by a differential scanning calorimeter (DS).
According to C), the amount of heat absorbed was measured at a heating rate of 10 ° C./min from 35 ° C. and determined.

Ii) Crystal Structure 1 The crystal structure of the recrystallized sample was determined to have a CuEα type wavelength of 1.
The peak position and half width were measured by a 54 ° line diffraction (W °) apparatus.

Iii) Crystal structure 2 The crystal structure of the recrystallized sample was determined by using a transmission electron condyle microscope (TE).
M).

Results i) FIG. 2 shows the DSC measurement results of the sample obtained by recrystallization under the pressure of carbon dioxide of 15, 30, and 60 atm. The curve shifts to the high temperature side as the pressure increases.

Ii) The peak value of the DSC curve was determined as the melting point and plotted against the carbon dioxide pressure. It can be seen that the melting point increases as the pressure increases.

Iii) The melting point of the sample crystallized with 50 atm of nitrogen is plotted in FIG. It can be seen that the sample in which carbon dioxide is dissolved has a higher melting point than the sample in which nitrogen is dissolved. From this, it can be understood that the pressure pressure does not directly affect the crystallinity, but the solubility of the gas is a direct factor. In FIG. 3, the melting point indicated by a symbol of 1 atm is that of a sample recrystallized in air. From this result, it can be seen that the presence of the dissolved gas clearly affects the increase in the melting point of the recrystallized sample.

Iv) A sample recrystallized at 15 atm of carbon dioxide, a sample recrystallized at 30 atm, and 6
FIG. 4 shows a line diffraction pattern of the sample recrystallized at 0 atm.
The peak values of 2β in the lines were 13.8, 16.7,
18.4, 20.9, and 21.60, and all of the obtained crystal structures are in the α phase regardless of the presence or absence of carbon dioxide. On the other hand, the half width of each peak becomes gradually smaller as the pressure is increased. In other words, it can be said that the crystallinity increases as the pressure increases.

V) In order to confirm that the crystallinity was improved, the crystal structure of the sample recrystallized with 60 atm of carbon dioxide was observed with a stained TEM. The photograph is shown in FIG. It can be seen from the photograph that the thickness of the normal crystal lamella is several hundred mm.

[0031]

As described above, by using the crystallization method of the present invention, it is possible to obtain a molded article with further improved crystallinity of the crystalline polymer resin, and to improve the heat resistance with the increased melting point. Excellent molded product is obtained.

Since carbon dioxide can be used, it is also effective from an environmental point of view.

Since the crystallization is not promoted by the pressure but by the solubility of the gas, the use of a highly soluble gas is advantageous in terms of the production cost because the equipment can be realized at a low pressure.

[Brief description of the drawings]

FIG. 1 schematically shows an apparatus used for performing a method for crystallizing a crystalline polymer resin of the present invention.

FIG. 2 shows DSC measurement results of a sample obtained by recrystallization under a pressure of carbon dioxide of 15, 30, and 60 atm.

FIG. 3 is a graph obtained by determining a peak value of an absorption heat curve of DSC as a melting point and plotting the peak value against a carbon dioxide pressure.

FIG. 4 shows a sample recrystallized at 15 atm of carbon dioxide, a sample recrystallized at 30 atm, and 60 atm.
FIG. 3 shows a line diffraction diagram of the sample recrystallized in FIG.

FIG. 5 is a photograph obtained by observing the crystal structure of a sample recrystallized with 60 atm of carbon dioxide using a stained TEM.

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Claims (3)

[Claims] 1. Exposing a crystalline polymer resin in a molten state to a pressurized atmosphere of a gas having solubility in the polymer resin,
A method for crystallizing a polymer resin, comprising dissolving a gas in a resin and solidifying the resin by cooling in a pressurized gas atmosphere. 2. The method according to claim 1, wherein the gas is carbon dioxide or nitrogen. 3. The method according to claim 1, wherein the polymer resin is a polyethylene polymer or a propylene polymer.