JP4013428B2 - Irradiation crosslinking method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of irradiating and crosslinking polymer materials such as rubber and plastic, which are widely used in various fields as industrial product materials, with ionizing radiation.
[0002]
[Prior art]
As one of means for improving the performance of polymer materials such as rubber and plastic, it is a common practice to reinforce interatomic bonds by causing a crosslinking reaction.
[0003]
The main cross-linking methods conventionally include a method of causing a cross-linking reaction using a drug (cross-linking agent), a method of causing a cross-linking reaction using a high-temperature gas or water vapor as a heat medium, and a method for generating radiation. There is a known method of irradiating a cross-linked product to cause a cross-linking reaction. In particular, radiation irradiation cross-linking methods require radiation generators and special equipment, but reduce the properties of the cross-linked product. Therefore, it is considered that it will become a mainstream of crosslinking treatment for polymer materials such as rubber and plastic in the future.
[0004]
By the way, such an irradiation crosslinking method is conventionally performed by irradiating ionizing radiation such as an electron beam in the air at room temperature. Therefore, when the object to be crosslinked is a crystalline polymer material, Crosslinking may occur in the amorphous part, and the cross-linking reaction may become non-uniform. As a result, there is a problem that the properties such as elongation are deteriorated or the crosslinking treatment efficiency is deteriorated. In addition, when this cross-linked product is a fluororesin such as tetraethylene fluoropolymer (hereinafter referred to as PTFE) having a wide range of uses, a decomposition reaction occurs conversely by irradiation with radiation, and good cross-linking can be performed. There was a problem that there was no.
[0005]
For this reason, it has been proposed that the crosslinking treatment can be satisfactorily achieved by irradiating these fluororesins such as PTFE with ionizing radiation under a specific gas atmosphere and a specific temperature.
[0006]
[Problems to be solved by the invention]
However, in the past, in order to form a specific gas atmosphere, an experimental scale such that degassing, gas replacement, heating, irradiation, and cooling are repeated each time a material to be crosslinked is taken in and out of the chamber for each crosslinking process. Since it is a crosslinking treatment method, the production efficiency is low and it is difficult to apply to industrial production.
[0007]
Therefore, the present invention has been devised in order to effectively solve such problems, and the object thereof is good even with crystalline polymer materials and fluororesins that have been difficult to crosslink with irradiation conventionally. The present invention provides a novel irradiation crosslinking method capable of performing a crosslinking treatment and exhibiting excellent productivity.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
A high-molecular material conveying device comprising any of polytetrafluoroethylene, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer and tetrafluoroethylene-hexafluoropropylene copolymer; An atmosphere gas fills the inside of a container provided with a heating zone for heating the molecular material to the melting point or higher, an irradiation zone for irradiating the polymer material heated in the heating zone with ionizing radiation, and a cooling zone. ,
The step of irradiating the ionizing radiation in the irradiation zone again in the irradiation zone is repeated a plurality of times by circulating the transport device in the container and again irradiating the polymeric material irradiated in the irradiation zone from the cooling zone through the heating zone. it is, at the irradiation ray amount of the polymer material that was 0.1 kGy ~10MGy.
[0009]
As a result, in addition to being able to crosslink well even with crystalline polymer materials and fluororesins that have been difficult to crosslink with irradiation in the past, continuous cross-linking treatment is performed in a single container for a large amount of cross-linked materials. Therefore, the number of pre-crosslinking treatments such as entry / exit of the cross-linked product, degassing, gas replacement, etc. is greatly reduced, and as a result, the crosslinking treatment efficiency can be greatly improved.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
[0011]
First, as the polymer material used in the present invention, a tetrafluoroethylene copolymer (hereinafter referred to as PTFE), a tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as PFA), or tetrafluoroethylene is used. Fluorine resins such as ethylene-hexafluoropropylene copolymer (hereinafter referred to as FEP) can be exemplified.
[0012]
Such cross-linking of the fluororesin is performed under an inert gas atmosphere with an oxygen concentration of 100 torr or less, preferably 10 ⁻⁶ torr to 100 torr, more preferably 10 ⁻⁶ torr to 40 torr (10 ⁻³ mol / g). In addition, it can be carried out by irradiating with ionizing radiation within the irradiation dose range of 0.1 kGy to 10 MGy while being heated to a melting point of fluorine or higher. Even if the ionizing radiation is irradiated in an inert gas atmosphere where the oxygen concentration does not reach 10 ⁻⁶ torr, the crosslinking reaction is not sufficiently performed. As a result, a sufficient dynamic elastic modulus cannot be realized, and the oxygen concentration exceeds 100 torr. And, since the decomposition is preceded and the cross-linking reaction is largely inhibited, various characteristics are deteriorated.
[0013]
When irradiating with ionizing radiation, it is necessary to heat the fluororesin above its melting point. For example, when PTFE is used as the fluororesin, it is necessary to irradiate the ionizing radiation while the fluororesin is heated to a temperature higher than 327 ° C. which is the melting point of this material, and PFA or FEP is used. In this case, irradiation is performed by heating to a temperature higher than the melting point specified by 310 ° C. for the former and 275 ° C. for the latter. Heating the fluororesin above its melting point activates the molecular motion of the main chain constituting the fluororesin, and as a result, the intermolecular cross-linking reaction can be efficiently promoted. However, excessive heating, on the contrary, leads to cleavage and decomposition of the molecular main chain, so that the heating temperature is 10-30 ° C. higher than the melting point of the fluororesin from the viewpoint of suppressing the occurrence of such depolymerization phenomenon. It should be kept within a high range.
[0014]
As ionizing radiation, γ rays, electron beams, X-rays, neutron rays, high energy ions, etc. are used. If the irradiation dose of ionizing radiation is less than 0.1 kGy, sufficient crosslinking effect cannot be achieved, and 10 MGy is achieved. Exceeding it causes a significant decrease in elongation.
[0015]
Next, FIG. 1 shows a front view showing an embodiment of an irradiation crosslinking apparatus (hereinafter abbreviated as a crosslinking apparatus) of an object to be crosslinked (polymer material) in order to realize the method of the present invention, FIG. 2 is a side view. As shown in the drawing, in a sealed container 1 arranged horizontally, a plurality of trays 2, 2,... ... Circulates with both end portions in the container 1 as turning points.
[0016]
Further, as shown in FIGS. 1 and 3, a plurality of processing zones I to VIII (eight processing zones in the present embodiment) are formed in the container 1 in the longitudinal direction and in the vertical direction. Yes. And as shown in the figure, the processing zones I, II, VII and VIII located in the left part in the container 1 are heating zones, and the cross-linked product R is not less than the melting point while passing through the heating zones. Heating is performed by an infrared heater 4 so that the temperature can be increased. Further, the zone III adjacent to the heating zone H is an irradiation zone S provided with the irradiation window 5 and the radiation irradiation means 6, and for each tray 2, 2... Passing through the heating zone H. From the upper part, ionizing radiation such as an electron beam is irradiated. Further, the zones IV, V, VI located next to the irradiation zone S and near the inner bottom of the container 1 are cooling zones C, and the bridged object R whose temperature has been increased by irradiation is cooled. ing. As the ionizing radiation emitted from the radiation irradiating means 6, it is preferable to use an electron beam that can be obtained industrially relatively easily.
[0017]
Further, as shown in FIG. 1, a vacuum evacuation means 7 including a vacuum pump and an atmospheric gas supply means 8 for supplying a specific atmospheric gas are provided at both ends of the container 1, respectively. After the air in the container 1 is degassed by the means 7 to form a low oxygen atmosphere, a specific atmosphere gas such as an inert gas or nitrogen gas is supplied from the atmosphere gas supply means 8 to fill the container 1. ing.
[0018]
In addition, for example, a titanium foil 9 having a thickness of about 10 to 200 μm is attached to the irradiation window 5 described above, so that the electron beam can be satisfactorily passed and the airtightness in the container 1 is maintained. Yes.
[0019]
Each of the processing zones I to VIII described above is not strictly partitioned by a partition wall or the like, but the trays 2, 2... Are movably connected to each other. , 2... Are continuously heated, irradiated and cooled. In the figure, reference numerals 10 and 10 denote guide rails positioned vertically and parallel along the length direction of the container 1, and the wheels 2 a and 2 a of the respective trays 2, 2. The container 1 is guided to run horizontally in the length direction of the container 1. Further, 11 and 11 in the figure are wheels for moving the container 1.
[0020]
Next, an example of the method of the present invention will be described using the cross-linking apparatus configured as described above.
[0021]
First, on the plurality of trays 2, 2... Provided on the conveyor 3 in the container 1, for example, a cross-linked object R processed into a sheet shape, for example, a sheet-like crystalline polymer material or a fluororesin such as PTFE. Each sheet is placed and sealed in the container 1 as shown in FIG. In addition, taking in / out of this to-be-crosslinked object R in the container 1 is performed sequentially from an inlet / outlet (not shown) provided in the vicinity of the processing zone V, for example, while the conveyor 3 is operated slowly.
[0022]
Next, as shown in FIG. 1, if the object to be crosslinked R is placed on each of the trays 2, 2... After filling with a specific atmospheric gas, for example, nitrogen gas having an oxygen concentration of 100 torr or less, the to-be-crosslinked objects R, R,... On the trays 2, 2,. For example, to the melting point or higher.
[0023]
Then, the to-be-bridged object R heated to a predetermined temperature in the heating zone H reaches the irradiation zone S side as the tray 2 moves on the upper guide rail 10 to the irradiation zone S side. By irradiation with an electron beam passing through the window 5, radiation irradiation crosslinking is performed at a predetermined temperature in an inert gas atmosphere having a low oxygen concentration.
[0024]
Here, since the crosslinking rate by radiation irradiation varies depending on the radiation dose and the irradiation time, good radiation crosslinking is performed by appropriately setting the passing speed of the conveyor 3 appropriately according to the radiation dose.
[0025]
Thereafter, the temperature of the article to be cross-linked R that has reached the irradiation zone S is further increased by radiation irradiation, but is then transported to the cooling zone C side where the distance is set to be relatively long and moved downstream. As a result, the temperature gradually decreases, and the crosslinking treatment is completed.
[0026]
In this way, the cross-linked objects R on all the trays 2, 2,. .
[0027]
As a result, a large amount of cross-linked material R can be continuously crosslinked by a single gas replacement, heating, and irradiation operation, so that excellent productivity can be exhibited, and industrial mass production. Is possible.
[0028]
In addition, when it is necessary to irradiate the object to be cross-linked R with a high irradiation dose, it is desirable not to apply a high dose at a time, but to irradiate several times intermittently. It is preferable that the cross-linked product R is again circulated from the cooling zone C side to the heating zone H side and irradiated multiple times.
[0029]
In the present embodiment, the processing zones I, II, VII, and VIII are set as the heating zone H, the processing zone III is set as the irradiation zone S, and the processing zones IV, V, and VI are set as the cooling zone C, respectively. However, it goes without saying that this setting may be appropriately changed according to the size of the container 1, the type of the object to be crosslinked R, the temperature and type of the atmospheric gas, the radiation dose, the installation position, and the like.
[0030]
4 to 6 are explanatory views of an embodiment in the case where a conveyor is arranged in the container as a transfer device, FIG. 4 is a front view, FIG. 5 is a plan view, and FIG. 6 is a side view. 12 is a conveyor made of a SUS mesh belt, and 13 is an infrared heater. The to-be-crosslinked object R is subjected to crosslinking treatment in the same manner as in the above-described embodiment except that the conveying means is changed from the tray to the conveyor 12. That is, after passing through the heating zone H, the article to be cross-linked R is subjected to crosslinking treatment in the irradiation zone S and then conveyed to the cooling zone C.
【The invention's effect】
In short, according to the present invention, an irradiated object made of a fluororesin or the like, which has been difficult in the prior art , can be continuously crosslinked in a uniform crosslinked state. Productivity is greatly improved compared to the method. As a result, it is possible to industrially produce a crosslinked product, and it is possible to exhibit excellent effects such as being able to provide a high-quality plastic material to the market at a low cost.
[Brief description of the drawings]
FIG. 1 is a front (partly cross-sectional) explanatory view of an embodiment of an irradiation crosslinking apparatus used in the method of the present invention.
FIG. 2 is an explanatory view of a side surface (partial cross section) of an embodiment of an irradiation crosslinking apparatus used in the method of the present invention.
FIG. 3 is an explanatory view showing an example of each processing zone formed in a container of an irradiation crosslinking apparatus used in the method of the present invention.
FIG. 4 is a front (partial cross-sectional) explanatory view of another embodiment of an irradiation crosslinking apparatus used in the method of the present invention.
FIG. 5 is an explanatory plan view of another embodiment of an irradiation crosslinking apparatus used in the method of the present invention.
FIG. 6 is an explanatory view of a side surface (partial cross section) of another embodiment of an irradiation crosslinking apparatus used in the method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Container 2 Tray 3 Conveying device 4 Infrared heater 5 Irradiation window 6 Radiation irradiation means 7 Vacuum drawing means 8 Atmospheric gas supply means 12 Conveyor 13 Infrared heater C Cooling zone H Heating zone S Irradiation zone R

Claims (5)

A high-molecular material conveying device comprising any of polytetrafluoroethylene, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer and tetrafluoroethylene-hexafluoropropylene copolymer; An atmosphere gas fills the inside of a container provided with a heating zone for heating the molecular material to the melting point or higher, an irradiation zone for irradiating the polymer material heated in the heating zone with ionizing radiation, and a cooling zone. ,
The step of irradiating the ionizing radiation in the irradiation zone again in the irradiation zone is repeated a plurality of times by circulating the transport device in the container and again irradiating the polymeric material irradiated in the irradiation zone from the cooling zone through the heating zone. it is, radiation crosslinking method is characterized in that the irradiation ray amount of the polymer material and 0.1 kGy ~10MGy.   2. The irradiation cross-linking method according to claim 1, wherein the transport device includes a plurality of trays, and the polymer material is placed on the tray and moves.   2. The irradiation cross-linking method according to claim 1, wherein the transfer device comprises a conveyor, and the polymer material is placed on the conveyor and moves.   2. The irradiation crosslinking method according to claim 1, wherein the atmospheric gas is an inert gas having an oxygen concentration of 100 torr or less.   The irradiation cross-linking method according to claim 1, wherein the container includes an irradiation window made of a titanium foil, and the polymer material is irradiated with ionizing radiation through the irradiation window.

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