JPH0149403B2 - - Google Patents

Description

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

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 disposing of the toxic pyrolysis gas generated. There are problems to be solved, such as the difficulty of processing.

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) In order to overcome the drawbacks of the above-mentioned conventional methods, the present inventors investigated various new and different production methods. The inventors have discovered that a low molecular weight fluorine-containing polymer with a controlled molecular weight distribution can be obtained in high yield by contact reaction with a compound, and have thus arrived at the present invention.

(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), ethylene-tetrafluoroethylene copolymer (ETFE), and Polyvinylidene fluoride (PvdF), polyvinyl fluoride (PVF)
It can be used in any form, such as powder, pellets, scrap sheets, or filled ones. The fluorine-containing fluorides to be supplied include nitrogen trifluoride (NF ₃ ), nitrogen difluoride (NF ₂ ), hydrazine tetrafluoride (N ₂ F ₄ ), diazine difluoride (N ₂ F ₂ ), In particular, NF compounds consisting of two elements such as azine fluoride (N ₃ F) are mentioned, and NF ₃ is a colorless stable gas at room temperature (melting point -
206.8℃, boiling point -129.1℃), it is a unique fluorinating agent that has strong oxidizing power at high temperatures and easily generates F radicals at temperatures above 300℃. It couples and stabilizes the terminal radical of , making it easier to control the reaction.

The amount of these fluorine-containing compounds added depends on the type and shape of the fluorine-containing polymer, but it should be supplied (present) in an amount of 0.01 part by weight or more as F per 100 parts by weight of the fluorine-containing polymer. If the amount is less than 0.01 part by weight, wax cannot be formed. In addition,
If it is present in excess, it will remain unreacted and can be recovered and reused, so no particular problem will occur. However, it is preferable 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 with each other. A reactor that can perform well is preferable. The higher the gas pressure, the faster the reaction occurs, but the reaction rate is sufficient even at normal pressure. Further, the nitrogen-containing fluorine compound 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 nitrogen-containing fluorine compound in the present invention, the gas produced by the reaction is a fluorinating agent that has a strong fluorinating ability, compared to the large amount of unsaturated poisonous gas by-product produced by thermal decomposition in the conventional method. In order to carry out the reaction inside the
Very few by-product gases include N ₂ , C ₃ F ₈ , C ₂ F ₆ ,
CF ₄ is a safe and easy-to-handle perfluorocarbon.

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 the fluorine-containing compound added is large, and the process is carried out in a high temperature range, a low molecular weight product can be obtained. Since the product is decomposed in the presence of active fluorine radicals, the terminal end is converted to _CF3 , making it 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 5mm thick 3mm thick PTFE sheet (sintered molded product)
20 equipped with a fan and heater for forcibly stirring 632g of pellets cut into squares with gas.
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 8 g of NF ₃ was introduced to cause a reaction. At the start of the reaction, the NF ₃ concentration was 33% and the pressure was normal pressure.

When reacted for 2 hours, NF ₃ was consumed and N ₂
A small amount of CF ₄ , C ₂ F ₆ , and C ₃ F ₆ gas was produced as by-products, and 626 g of pure white molten wax was obtained. The solid content yield was 99%. This wax has a melting point of 300℃,
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 3700. 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 PTFE molding powder 632g and NF ₃ 24g
was reacted for 16 hours in the same reactor as in Example 1. Collecting the generated solids and gases
629g (yield 99.5%) of wax-like PTFE and by-product gases include N ₂ and small amounts of CF ₄ , C ₂ F ₆ ,
_{C3F8 was} 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 was 318°C and the average molecular weight was 11,700.

Example 3 The same 50 g of PTFE as in Example 2 and 1 g of N ₂ F ₄ were reacted at 400° C. for 10 hours in the same reactor. When the generated solid and gas were collected, 49.5g (yield 99%) was collected.
%) as waxy PTFE and by-product gas
_N2 and _{CF4 , C2F6} , _C3F8 were obtained _. This wax had a melting point of 310°C and an average molecular weight of 6,100. Note that this material could be easily pulverized.

Example 4 When 620 g of pellets obtained by cutting a 3 mm thick FEP sheet into 5 mm squares and 8 g of NF ₃ were similarly reacted at 420°C for 3 hours, 615 g of wax (yield 99.2%) and N ₂ as by-product gas were produced. and a small amount of _CF4 ,
C ₂ F ₆ and C ₃ F ₈ were obtained. The wax had a melting point of 244°C and could be easily crushed.

Example 5 PFA pellets (3mmφ×5mm) 630g and NF ₃ 8
When the mixture was reacted at 450° C. for 2 hours, 620 g (yield: 98.4%) of wax, N ₂ 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 253°C and could be easily crushed.

Example 6 When 500g of CTFE pipe (10φ) cut into 10mm length was reacted with 8g of _NF3 gas at 400℃ for 2 hours, 450g of wax (yield 90%) and N as a by-product gas were produced. ₂ and small amounts of CF ₄ , C ₂ F ₆ ,
CF ₃ Cl was obtained. The wax had a melting point of 240°C and could be easily crushed.

Claims (1)

[Claims] 1. A method for producing a low-molecular-weight fluorine-containing resin, which comprises catalytically reacting a fluorine-containing polymer with a fluorine-containing compound at 250 to 550°C.