Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
2001-05-16
2002-08-13
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S242000, C528S244000
Reexamination Certificate
active
06433128
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an oxymethylene copolymer having high stiffness and tenacity and excellent heat stability at a high yield.
2. Prior Art
Oxymethylene polymers have excellent mechanical and thermal properties and have been used in an extremely wide variety of fields as typical engineering plastics in recent years. However, along with the expansion of the application field of the oxymethylene polymers, further improvement of the properties of the oxymethylene polymers as a material is desired. Currently, oxymethylene polymers available on the market are roughly divided into oxymethylene homopolymers and oxymethylene copolymers. The oxymethylene homopolymers have high mechanical strength and stiffness and excellent mechanical properties such as fatigue resistance and abrasion resistance but it is inferior in heat stability and hot water resistance. On the contrary, the oxymethylene copolymers are inferior in mechanical strength and stiffness but it is excellent in tenacity and flexibility and has high heat stability as it contains in the molecular chain a stable copolymerization unit which suppresses decomposition. An oxymethylene (co)polymer which has good balance among stiffness, tenacity and heat stability, making use of the characteristic properties of these two, has been desired.
To this end, it is conceivable to blend additives such as a reinforcing filler to improve the mechanical strength and stiffness of an oxymethylene copolymer. In this case, tenacity is greatly impaired. WO 98/29483 discloses an oxymethylene copolymer having high stiffness and such a structure that an oxyalkylene comonomer unit is inserted into a polymer chain consisting of an oxymethylene monomer unit at random in an amount of 0.01 to 1.0 mol based on 100 mols of the oxymethylene monomer unit. However, high stiffness is obtained with the above amount of the comonomer but a reduction in heat stability is large. Therefore, the above oxymethylene copolymer is still unsatisfactory in terms of balance between mechanical properties and heat stability.
JP-A 8-59767 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses that an oxymethylene copolymer produced from 1,3-dioxolan as a comonomer contains a smaller amount of an instable portion which is the cause of poor heat stability than an oxymethylene copolymer which contains ethylene oxide as a comonomer, the amount of the formed instable portion depends on the amount of 1,3-dioxolan and the amount of the catalyst used, and the amount of the catalyst must be reduced to a predetermined value or less to suppress the formation of the instable portion. However, heat stability is improved with the above amounts of 1,3-dioxolan and the catalyst but stiffness is not so improved.
Problems to be Solved by the Invention
It is known in the prior art that the means of improving polymerization yield is to increase the amount of a catalyst used but the formation of an instable portion is promoted simply by increasing the amount of the catalyst. However, the inventors of the present invention have studied the means and have found that an oxymethylene copolymer is obtained at a high yield without increasing the amount of a catalyst because the formation speed of the copolymer at the time of production is increased by using a certain amount or less of 1,3-dioxolan.
Further, as for the mechanical properties of an oxymethylene copolymer produced by using a specific amount of 1,3-dioxolan and a specific amount of a catalyst, stiffness as high as that of an oxymethylene homopolymer can be obtained and also tenacity as high as that of a conventional oxymethylene copolymer can be retained.
SUMMARY OF THE INVENTION
It is an object of the present invention to obtain at a high yield an oxymethylene copolymer having as high mechanical strength and stiffness as an oxymethylene homopolymer while retaining the tenacity and heat stability of an oxymethylene copolymer, making use of the characteristic properties of both the polyoxymethylene homopolymer and the oxymethylene copolymer.
Means for Solving the Problems
The inventors of the present invention have conducted intensive studies to attain the above object and have found that the above object can be obtained by using a specific amount of 1,3-dioxolan to be copolymerized with trioxan and a specific amount of a catalyst. The present invention has been accomplished based on this finding.
That is, according to the present invention, there is provided a process for producing an oxymethylene copolymer by polymerizing trioxan and 1,3-dioxolan in the presence of a cationically active catalyst, wherein (1) 1,3-dioxolan is used in an amount of 0.01 to 2.9 mol % based on trioxan and (2) the cationically active catalyst is used in an amount of 1×10
−7
to 1.2×10
−4
mol based on 1 mol of trioxan.
The process for producing an oxymethylene copolymer of the present invention will be described in further detail hereinunder.
Polymerization in the present invention is bulk polymerization or melt polymerization. Bulk polymerization which does not use a solvent substantially or quasi-bulk polymerization which uses a solvent in an amount of 20 wt % or less based on a monomer is preferred. This polymerization is used to polymerize the monomer in a molten state so as to obtain a bulk or powdered solid polymer along with the proceeding of polymerization.
The main raw material monomer in the present invention is trioxan which is a cyclic trimer of formaldehyde and 1,3-dioxolan is used as a comonomer. The amount of 1,3-dioxolan is 0.01 to 2.9 mol %, preferably 0.5 to 2.5 mol %, particularly 0. 5 to 2.0 mol % based on trioxan. When the amount of 1,3-dioxolan is larger than 2.9 mol %, polymerization yield lowers and when the amount is smaller than 0.01 mol %, heat stability lowers.
In the present invention, 1,3-dioxolan is used as a comonomer in a relatively small amount based on trioxan and the cationically active catalyst is used in a specific ratio based on trioxan to attain the object.
That is, the cationically active catalyst is used in an amount of 1×10
−7
to 1.2×10
−4
mol, preferably 1×10
−7
to 1×10
−4
mol based on 1 mol of trioxan.
When the amount of the cationically active catalyst is larger than 1.2×10
−4
mol, the heat stability of the obtained copolymer may lower and when the amount is smaller than 1×10
−7
mol, polymerization yield may drop.
The cationically active catalyst used in the process of the present invention is a Lewis acid or protonic acid.
Examples of the Lewis acid include halides of boron, tin, titanium, phosphorus, arsenic and antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride, antimony pentafluoride, and complex compounds and salts thereof. Examples of the protonic acid include esters of trifluoromethanesulfonic acid, perchloric acid and protonic acid, particularly esters of perchloric acid and lower fatty acid alcohols, and protonic anhydrides, particularly mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids. In addition, triethyloxonium hexafluorophosphate, triphenylmethyl hexafluoroarsenate, acetylhexafluoroborate, heteropolyacid and acidic salts thereof, and isopolyacid and acidic salts thereof may also be used. Boron trifluoride, boron trifluoride hydrates and coordination complex compounds are preferred, and boron trifluoride diethyl etherate and boron trifluoride dibutyl etherate which are coordination complexes with ethers are the most preferred.
For the polymerization of the present invention, an appropriate molecular weight modifier may be used as required to adjust the molecular weight of the oxymethylene copolymer. Examples of the molecular weight modifier include carboxylic acids, carboxylic anhydrides, esters, amides, imides, phenols and acetal compou
Furukawa Masanori
Maji Kazumasa
Masumoto Isamu
Nakamura Takahiro
Okamura Akira
Acquah Samuel A.
Mitsubishi Gas Chemical Co, Inc.
LandOfFree
Process for producing oxymethylene copolymer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing oxymethylene copolymer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing oxymethylene copolymer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2888161