JP2847169B2 - Method for pulverizing polymer - Google Patents

Description

The present invention relates to a method for pulverizing a polymer,
In particular, the present invention relates to a method for pulverizing a polymer by pulverizing a polytetrafluoroethylene resin or other degradable polymers by utilizing the disintegration effect of radiation.

[Prior Art] Polytetrafluoroethylene resin (hereinafter abbreviated as “PTFE”) is a polymer having a chemical structure in which all hydrogen atoms of polyethylene are replaced by fluorine atoms. This PFTE is nonflammable and thermoplastic and stable in all organic solvents, so it is used for mechanical parts, linings and other applications.

The PTFE mentioned here corresponds to a commercially available new PTFE, a PTFE generated from a processing step of a new PTFE, and a PTFE that is used as a product after molding and then collected as scrap.

The PTFE generated from the process of processing the above-mentioned new PTFE will be briefly described. That is, although PTFE is a thermoplastic resin, its melt viscosity is abnormally high and cannot be molded by a processing method such as injection molding used for ordinary resins. Therefore, new PTFE powder is once compressed, pre-molded, heated to a temperature equal to or higher than the melting point, fired, cooled, and subjected to a product dimensional adjustment process to produce the desired product. I have. What is generated from the PTFE processing step is cutting chips generated in the dimension adjusting step of the product.

The shape of the PTFE may be any shape such as cutting chips, powder, and a compact.

However, since such PTFE is extremely stable chemically, there is a problem in its disposal or regeneration. In processing such PTFE, the conventional technology is PT
FE has radiation, especially α-ray and β which are called ionizing radiation
Irradiation with rays, gamma rays, electron beams, and various other types of radiation has been performed. In other words, irradiating PTFE with radiation lowers the molecular weight of high molecular weight PTFE and makes it easier to pulverize,
Utilizing this phenomenon, PTFE is pulverized or pulverized.

Finely ground PTFE is used for lubricants, paints, plastics,
It is used for a wide range of applications, such as lubricants for rubber and printing inks, and oil and grease extreme pressure additives.

For example, JP-A-49-22449 discloses that PTFE is irradiated with radiation, heated in the presence of a halogenated methane and an oxygen component, and then subjected to mechanical pulverization. Japanese Patent Application Laid-Open No. 55-31506 discloses that PTFE is subjected to a heat treatment during or after irradiation with radiation to be finely pulverized. In these methods, irradiate radiation, further heat treatment, PTFE
It promotes the decomposition or reduction of the molecular weight, and focuses on the effect of heat treatment.

However, in any method, since the powder is pulverized to a predetermined particle size, the irradiation dose of the radiation is increased, which causes a problem in cost.

Furthermore, PTFE is used as a lubricant for inks and the like, as described above. Recently, however, the addition of this PTFE to engineering plastics such as polycarbonate has overcome the performance limitations of plastics as a raw material and has been improved. It is used extensively for quality purposes.

However, especially for engineering plastics, PT
When FE is used, the melting point of PTFE is very important. In other words, engineering plastics to which PTFE fine powder is added are molded and used as products for various applications, but when this molding process involves heat treatment, the melting point is lower than that of the original material, engineering plastics. When PTFE fine powder is used, there is a problem that defects such as bubbles occur in the manufactured product.

[Problems to be Solved by the Invention] The present invention has been made in view of the above problems, and in a step of irradiating PTFE or other polymer with radiation, by controlling the oxygen concentration in the irradiation atmosphere, An object of the present invention is to provide a method for pulverizing a polymer for the purpose of reducing the melting point, the particle size of a pulverized product, and reducing the irradiation dose.

[Means for Solving the Problems] That is, the present invention is a method for pulverizing a polymer, which comprises irradiating a polytetrafluoroethylene resin (PTFE) or other polymer with a radiation to pulverize the polymer. A method for pulverizing a polymer, comprising controlling the particle size of the polymer to be pulverized by controlling the oxygen concentration in an irradiation atmosphere gas surrounding the polymer.

In addition, as the polymer, not only the above-mentioned polytetrafluoroethylene resin, but also a radiation-degradable polymer such as polychlorinated ethylene trifluoride and polyisobutylene can be used. In addition, the present invention can also be applied to miniaturization of wood, straw, fir, paper or the like containing cellulose as a polymer. However, for flammable objects, it is necessary to limit the oxygen concentration.

 Hereinafter, the present invention will be described in more detail with reference to FIG.

FIG. 1 shows a radiation irradiation apparatus 1 for carrying out the present invention.
The radiation irradiation apparatus 1 includes an electron accelerator 2, an oxygen concentration control apparatus 3, and an irradiation container 4.
, A hydrogen fluoride removing device 5, an ozone decomposing device 6, a blower 7, and a stack 8.

The electron accelerator 2 irradiates the irradiation container 4 with a predetermined dose of an electron beam.

The oxygen concentration control device 3 supplies a predetermined concentration of oxygen into the irradiation container 4, receives a detection signal from the oxygen analyzer 9 via the signal line 10, and reduces the oxygen concentration in the irradiation container 4 by a certain amount. Is appropriately controlled so that
The oxygen supplied by the oxygen concentration control device 3 may be produced and supplied by PSA method (pressure fluctuation adsorption method) using air as a raw material, or may be supplied from a cylinder, a CE device or the like.

The irradiation container 4 is a container having a predetermined volume, and a gas controlled to a predetermined oxygen concentration is made of PTFE contained in the irradiation container 4.
What is necessary is just to supply so that it may contact 11 evenly. The irradiation container 4 may have any form such as a fixed bed, a moving bed, and a fluidized bed. The oxygen may be effectively used by returning a part of the outlet gas of the irradiation container 4 to the entrance of the irradiation container 4 via the blower 12.

The hydrogen fluoride removing device 5 treats hydrogen fluoride (HF) generated when the PTFE 11 is irradiated with electrons to reduce the molecular weight, and renders the harmless.

The ozone decomposer 6 treats a small amount of ozone generated by collision of oxygen in an irradiation atmosphere with an electron beam to render the ozone harmless.

The blower 7 sucks the gas discharged from the irradiation container 4. This gas is discharged into the atmosphere via the stack 8 after being processed in the hydrogen fluoride removing device 5 and the azo decomposition device 6.

The radiation is not limited to the electron beam, and radiation generally called ionizing radiation can be used.

As a method of irradiating the PTFE 11, the PTFE 11 is put into a wire net, cardboard, or another container instead of the irradiation container 4, or the PTFE 11 is put into a bag made of a plastic or metal film as it is, and then a predetermined concentration is applied. May be filled with oxygen gas, placed on a cart conveyor, and passed under the electron accelerator 2 for irradiation.

Although the decomposition mechanism of PTFE11 when the PTFE11 is irradiated with an electron beam is not clear, it is considered that the process proceeds as follows.

That is, even if the PTFE 11 is left in the air or in a high concentration of oxygen, it does not decompose. Further, when the PTFE 11 is irradiated with an electron beam in an atmosphere containing no oxygen, for example, in a nitrogen atmosphere, the PTFE 11 cannot be pulverized by an ordinary method, and
Decomposition is very slow.

On the other hand, when the PTFE 11 is irradiated with an electron beam in a gas containing oxygen, its decomposition proceeds significantly. That is, oxygen reacts with PTFE 11 under the action of an electron beam, and firstly, peroxide of PTFE 11 and the like are generated. This peroxide is HF, CO2, CO
And other trace amounts of COF2. This peroxide etc.
It is considered that the molecular weight of PTFE 11 is reduced when it is changed to CO2, CO, or the like.

Further, it is considered that the peroxide and the like are generated and remain in the irradiated PTFE 11 according to the oxygen concentration at the time of irradiation. It is considered that the generated and remaining peroxide and the like and the reduction in molecular weight at the time of irradiation contribute to fine pulverization.

That is, decomposition of PTFE 11 can be promoted by generating as much peroxide and the like of PTFE 11 as possible. Accordingly, it is possible to control the decomposition of PTFE 11 by controlling the oxygen concentration.

For example, when it is desired to carry out pulverization so as to have a predetermined particle size or a particle size, oxygen having a corresponding concentration may be supplied to the PTFE 11 in the irradiation container 4.

In addition, it was found that the melting point of PTZTE11 gradually decreased as the irradiation dose of the electron beam increased, but that the melting point of PTFE11 was the same regardless of the oxygen concentration at the same irradiation dose. In other words, it is considered that the above-mentioned peroxides do not act to lower the melting point of PTFE 11.

Thus, in the present invention, the irradiation dose of radiation can be reduced by controlling the oxygen concentration, and the particle size and melting point of PTFE or the like to be finely powdered can be reduced by appropriately selecting such irradiation dose. Can be set within the range. Furthermore, heat treatment can be performed if necessary, so that the time required for such heating can be reduced and the energy required for heating can be saved.

[Function] In the method of pulverizing a polymer according to the present invention, the radiation concentration is controlled when irradiating radiation to a polytetrafluoroethylene resin or other polymer. The size and melting point can be obtained.

[Example] Next, an example of the method for pulverizing a polymer according to the present invention will be described.

The PTFE 11 was irradiated with an electron beam by the radiation irradiation device 1 shown in FIG. Specifically, PTFE 11 is 3 mm long, 3 mm wide, and thickness
Thin chips made of small pieces of 0.05 mm are used.
The container was filled and stored in a stainless steel irradiation container 4 having a thickness of 397 mm, a depth of 397 mm, and a depth of 100 mm, and the upper irradiation surface was sealed with a stainless steel thin film having a thickness of 0.05 mm. Thereafter, the valves on both sides of the closed irradiation container 4 are opened, and a gas containing a predetermined concentration of oxygen and nitrogen is circulated from the gas mixer, that is, the oxygen concentration control device 3, so that the gas inside the container is sufficiently discharged. After replacement, the valve was closed and resealed.

The sealed irradiation container 4 in which the oxygen atmosphere of the predetermined concentration is set.
On a speed-adjustable cart (not shown).
Electron beam irradiation was performed from the electron accelerator 2 under the irradiation conditions of 5 MV and a current value of 10 mA so as to obtain a desired irradiation dose. In addition, a gas containing a predetermined concentration of oxygen was supplied from the oxygen concentration control device 3 to the sealed irradiation device 4 at every irradiation dose of several Mrad, so that the oxygen gas concentration in the inside became constant.

When the prescribed irradiation dose is reached, this irradiated PT
FE11 was pulverized with a laboratory jet grinder.

The melting point of the irradiated PTFE 11 was calculated using a thermal analyzer (not shown).

FIG. 2 is a graph showing the relationship between the irradiation dose and the melting point under the condition of oxygen concentration of 0 to 100%, and FIG. 3 is a graph showing the relationship between the oxygen concentration and the melting point under a certain irradiation dose. .

As can be seen from FIG. 2, the melting point decreases almost linearly with a predetermined gradient as the irradiation dose increases. Moreover, as shown in FIG. 3, it was found that the melting point was not changed at all even if the oxygen concentration in the irradiation atmosphere gas was changed if the irradiation dose was the same.

FIG. 4 is a graph showing the relationship between the irradiation dose under each oxygen concentration condition and the average particle size Dp50 after pulverization. It can be seen that the average particle size decreases as the irradiation dose increases, and that the average particle size decreases significantly by increasing the oxygen concentration in the irradiation atmosphere gas.

For example, to obtain fine particles having an average particle size of 5 μm,
The irradiation dose when the oxygen concentration is 21% is 90 Mrad. When the oxygen concentration is 60%, the irradiation dose is 70 Mrad. Oxygen concentration 100
The irradiation dose at% is 50 Mrad. The melting points at these irradiation doses are 313 ° C, 316.5 ° C, 31
9.5 ° C.

Also, when it is desired to obtain a fine powdered PTFE 11 having a desired melting point of 320 ° C., an oxygen concentration of 100% and an irradiation dose of 50 Mrad
It is possible to produce PTFE fine powder having desired physical properties such as particle diameter and melting point by combining the oxygen concentration and the irradiation dose.

[Effects of the Invention] As described above, according to the present invention, since the oxygen concentration is controlled together with the irradiation of radiation, it is possible to reduce the irradiation dose and to set the oxygen concentration to a predetermined value. And fine particles having any particle size and melting point can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of a radiation irradiation apparatus 1 for carrying out a method of pulverizing a polymer according to the present invention, and FIG. 2 shows a relationship between an irradiation dose and a melting point under conditions of an oxygen concentration of 0 to 100%. Graph, FIG. 3 is a graph showing the relationship between the oxygen concentration and the melting point under a certain irradiation dose condition, and FIG. 4 is a relationship between the irradiation dose under each oxygen concentration condition and the average particle size after pulverization Dp50. FIG. DESCRIPTION OF SYMBOLS 1 ... Radiation irradiation apparatus 2 ... Electron accelerator 3 ... Oxygen concentration control apparatus 4 ... Irradiation container 5 ... Hydrogen fluoride removal apparatus 6 ... Ozone decomposition apparatus 7 ... Blower 8 ... Stack 9 ... Oxygen analysis Total 10: Signal line 11: PTFE (polytetrafluoroethylene) 12: Blower

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Keisaburo Odagiri 63-30 Yuyugaoka, Hiratsuka-shi, Kanagawa Sumitomo Heavy Industries, Ltd. Inside Hiratsuka Research Laboratory (56) References JP-A-55-124612 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) C08J 3 / 12,3 / 28 C08L 1 / 00,27 / 18,9 / 00

Claims (1)

(57) [Claims] 1. A method for pulverizing a polymer, which comprises irradiating a polymer with radiation to pulverize the polymer, comprising controlling the oxygen concentration in an irradiation atmosphere gas surrounding the polymer. A method for pulverizing a polymer, comprising controlling the particle size of the polymer to be produced.