JPH0149404B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing a low molecular weight fluorine-containing polymer, and more specifically, a method for producing a low molecular weight fluorine-containing polymer, and more specifically, a method for producing a fluorine-containing polymer such as a fluorine-containing polymer such as polytetrafluoroethylene, a molecular fluorine-containing polymer,
The present invention relates to a method for producing a low molecular weight compound (wax) which is subjected to a catalytic reaction with at least one of a halogenated fluoride and a rare gas fluoride.

Low molecular weight fluorine-containing polymers such as polytetrafluoroethylene (PTFE) have excellent lubrication performance and low surface energy properties, so they are widely used as lubricants and mold release agents.

(Prior art) Among them, low molecular weight PTFE is called tetrafluoroethylene (TFE) wax, and various manufacturing methods have been proposed.The method for manufacturing wax by telomerization of TFE has been known for a long time and has been used industrially. is also being implemented.

However, in many of the methods to date, it is difficult to control reaction conditions such as temperature because they use a compound that becomes a telogen as a reaction medium (for example, Japanese Patent Application Laid-Open No. 51-41085), and they require techniques to control molecular weight, etc. , problems remain in the separation of monomer and telogen. A method using an aqueous reaction medium is also known, but there are problems with the thermal stability of the wax produced and difficulty in separating the monomer and telomer after the reaction.

On the other hand, as a method of thermally decomposing PTFE to make it into low-molecular molecules, there is a method of thermally decomposing it at low temperatures in the presence of silicon, aluminum, magnesium, and graphite.
No. 25446). A method of thermal decomposition in the presence of air or a deterioration accelerator such as O ₂ , SO ₂ , NO _, etc.
Methods such as thermal decomposition in NaNO ₃ molten salt are known, but the raw material PTFE is expensive, making it difficult to use for purposes other than scrap, making it difficult to obtain a uniform product, and reducing the amount of toxic pyrolysis gas generated. There are problems to be solved, such as the difficulty of disposal.

In addition, a recently developed method is to irradiate PTFE with radiation (X-rays, gamma rays) and decompose it.
An improved method of increasing the efficiency of decomposition with a small amount of radiation by adding oxygen and hydrogen and irradiating it (Tokuko Sho)
56-8043) are also known. However, since radiation is generally difficult to handle and expensive, appropriate equipment is required to employ it as an industrial manufacturing method.

(Problems to be Solved by _the Invention) The present inventors have investigated various new production methods to overcome the drawbacks of the above-mentioned conventional methods. The present invention was achieved by discovering that a low molecular weight fluorine-containing polymer having a controlled molecular weight distribution can be obtained in high yield by carrying out a contact reaction with at least one fluoride of a rare gas.

(Means for solving the problem) In the specific implementation method of the present invention, reaction conditions vary depending on each polymer, but the reaction temperature is 250 to 250°C.
It is carried out at 550°C, preferably 350-500°C.
Below 250℃, contact reaction requires a long time, and 550℃
If the temperature is above 0.degree. C., a uniform product cannot be obtained, and in this temperature range, the reaction to lower the molecular weight easily proceeds in a short time, resulting in a wax-like product.

The present invention will be explained in detail below.

The raw material fluorine-containing polymer in the present invention is
PTFE, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), chlorotrifluoroethylene (CTFE)-tetrafluoroethylene copolymer (ETFE) and Any form of powder such as vinylidene fluoride (PvdF) or polyvinyl fluoride (PVF), pellets, sheet-like scraps, or filled materials can be used. The fluorinating agents to be supplied include molecular fluorine (F ₂ ), chlorine fluoride (ClF), chlorine trifluoride (ClF ₃ ), chlorine pentafluoride (ClF ₅ ), bromine fluoride (BrF), Bromine trifluoride (BrF ₃ ), bromine pentafluoride (BrF ₅ ), iodine trifluoride (IF ₃ ), iodine pentafluoride (IF ₅ ), iodine heptafluoride (IF ₇ ), xenon difluoride ( Examples include compounds such as XeF ₂ ), xenon tetrafluoride (XeF ₄ ), xenon hexafluoride (XeF ₆ ), and krypton fluoride (KrF ₂ ). The above-mentioned fluoride is a fluorinating agent that generates F radicals, which cleave the main chain of the fluorine-containing polymer and couple and stabilize the terminal radicals of the resulting polymer, thereby facilitating reaction control.

The amount of these fluorinating agents added depends on the type and shape of the fluorinated polymer, but
It is sufficient to supply (presence) F in an amount of 0.01 part by weight or more per 100 parts by weight, and wax cannot be formed if the amount is less than 0.01 part by weight. Note that if it is present in excess, it remains unreacted and can be recovered and reused, so no particular problem will occur, but it is desirable to select it within a range of approximately 10 parts by weight.

Any type of reactor can be used as long as it allows gas and solid to come into contact, but examples include forced circulation type reactors equipped with multiple reaction shelves, gas-solid contact reactors such as fluidized beds A reactor that can perform this well is preferred. The higher the gas pressure, the faster the reaction occurs, but the reaction rate is sufficient even at normal pressure. The fluorinating agent can of course be used in its pure form, but it can also be used diluted with an inert gas such as nitrogen, argon, helium, or carbon tetrafluoride.

In the reaction with the fluorinating agent in the present invention, compared to the large amount of unsaturated poisonous gas by-produced by thermal decomposition in the conventional method, the gas by-produced in the reaction is contained in the fluorinating agent which has a strong fluorinating ability. Due to the reaction, the amount of by-product gases is extremely small, including C ₃ F ₈ , C ₂ F ₆ , CF _{4 ,} etc., and depending on the fluorinating agent used, fluorocarbon compounds, rare gases such as Xe, Kr, etc. It is a safe and easy-to-handle compound.

As shown in the examples, the molecular weight distribution of the low molecular weight fluoride produced is on the order of hundreds of thousands to several thousand units depending on the reaction temperature and reaction time, and is roughly proportional to the height of the temperature and the length of the reaction time. The molecular weight can be controlled freely. That is, if the particle size of the fluorine-containing polymer is small, the amount of fluorinating agent added is large, and the process is carried out in a high temperature range, a low molecular weight product can be obtained. Note that the product is decomposed in the presence of active fluorine radicals, so the terminal
It is converted into _OF3 and is extremely stable. Furthermore, since no carbon precipitation occurs, an extremely pure white product can be obtained.

These products obtained in the present invention can be easily pulverized to an average particle size of 100 μm using a normal hammer-type pulverizer, and 0.1 to 10 μm using a jet mill. .

The present invention will be explained in more detail with reference to Examples below.

Example 1 3mm thick PTFE sheet (sintered molded product)
20 equipped with a fan and heater for forcibly stirring 500g of pellets cut into squares.
Pour into a nickel reactor and heat at 440℃ in _N2 gas.
After the temperature was raised to , part of the N ₂ gas was removed using a vacuum pump, and 3 g of F ₂ was introduced to cause a reaction. At the start of the reaction, the F ₂ concentration was 23% and the pressure was normal pressure.

When the reaction was carried out for 2 hours, F ₂ was consumed and small amounts of CF ₄ , C ₂ F ₆ and C ₃ F ₈ gases were produced as by-products, and 498 g of pure white molten wax was obtained. The solid content yield is
It was 99.6%. This wax has a melting point of 305℃,
The relationship between melting point and molecular weight shown in U.S. Patent No. 3,067,262 [molecular weight =
The molecular weight was calculated according to 200/685 [1/melting point (〓) - 1/600] and was 4,600. This wax was coarsely pulverized and then finely pulverized with a jet mill to obtain a fine powder with an average particle size of 5 μm.

Example 2 500 g of PTFE molding powder and 8 g of ClF ₃ were reacted in the same reactor as in Example 1 at 420° C. for 4 hours. Collecting the generated solids and gases
49 g (yield 99.6%) of wax-like PTFE and by-product gases such as CClF ₃ , CCl ₂ F ₂ , CCl ₃ F and small amounts of CF ₄ , C ₂ F ₆ , and C ₃ F ₈ were obtained. When this wax was pulverized, a fine powder with an average particle size of 7 μm was obtained. The melting point of this wax is 310℃, and the average molecular weight is
It was 6100.

Example 3 500 g of the same PTFE as in Example 2 and 12 g of XeF ₂ were reacted at 400° C. for 2 hours in the same reactor. When the generated solid and gas were collected, 497g (yield
99.4%) wax-like PTFE and Xe and CF ₄ , C ₂ F ₆ , C ₃ F ₈ as by-product gases were obtained. The melting point of this wax is 326℃, and the average molecular weight is
It was 105,000. Note that this material could be easily pulverized.

Example 4 When 500 g of pellets obtained by cutting a 3 mm thick FEP sheet into 5 mm squares and 10 g of PrF ₃ were similarly reacted at 420°C for 3 hours, 495 g (yield 99.0%) of wax and CBrF ₃ were produced as by-product gas. , CBr ₂ F ₂ ,
CBr ₃ F and small amounts of CF ₄ , C ₂ F ₆ and C ₃ F ₈ were obtained. The wax had a melting point of 240°C and could be easily crushed.

Example 5 PFA pellets (3mmφ×5mm) 500g and IF ₃ 8g
When reacted at 400℃ for 6 hours, 490g (yield
ClF ₃ and small amounts of CF ₄ , C ₂ F ₆ , and C ₃ F ₈ were obtained as by-product gases. The wax had a melting point of 250°C and could be easily crushed.

Example 6 When 500g of CTFE pipe (10mmφ) cut into 10mm length was reacted with 3g of _F2 gas at 400℃ for 2 hours, 480g (yield 96%) of wax and a small amount of by-product gas were produced. CF ₄ , C ₂ F ₆ , CF ₃ Cl
I got it. The wax had a melting point of 236°C and could be easily crushed.

Claims (1)

[Claims] 1. A low molecular weight product of a fluorine-containing resin, which is characterized in that a fluorine-containing polymer is subjected to a catalytic reaction at 250 to 550°C with at least one of molecular fluorine, a halogenated fluoride, and a rare gas fluoride. Production method.