JP7246282B2 - Cross-linking accelerator for fluorine-containing elastomer and composition for cross-linking fluorine-containing elastomer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cross-linking accelerator for fluorine-containing elastomers and a composition for cross-linking fluorine-containing elastomers.

Fields that require performance that combines elasticity, heat-resistant chemical stability, chemical resistance, and fuel oil resistance (for example, O-rings for automobile parts, general industrial machinery, semiconductors, chemical plants, etc.) oil seals, packings, gaskets, etc.), various types of fluorine-containing elastomers are used.

Fluorine-containing elastomers are more expensive than general-purpose elastomers, so their fields of application were limited. With respect to various characteristics, requirements for parts are increasing, and the application of fluorine-containing elastomer products is increasing.

1,8-Diaza-bicyclo(5,4,0)undecene-7 (1,8-Diaza-bicyclo(5,4 ,0) undecene-7, generally referred to as "DBU (registered trademark)", hereinafter sometimes simply referred to as "diazabicycloundecene") exhibits excellent cross-linking acceleration performance (Patent Document 1). However, cross-linked products (vulcanizates) of fluorine-containing elastomers obtained using diazabicycloundecene tend to have lower compression set.

In addition, a case has also been reported in which a salt of diazabicycloundecene and benzyl chloride (benzyl chloride) is used as a cross-linking accelerator (vulcanization accelerator) to exhibit excellent cross-linking acceleration performance (Patent Document 2). . However, even when these are used, the compression set tends to decrease.

JP-A-48-55231 JP 2010-24339 A

The present invention has been made in view of the above problems, and its object is to obtain a molded article having excellent compression set properties while maintaining the high cross-linking acceleration performance of diazabicycloundecene. An object of the present invention is to provide a cross-linking accelerator for a fluorine-containing elastomer and a composition for cross-linking a fluorine-containing elastomer.

In order to achieve the above object, a cross-linking accelerator for fluorine-containing elastomer according to one aspect of the present invention is a cross-linking accelerator for cross-linking a fluorine-containing elastomer that is used when cross-linking a fluorine-containing elastomer with a polyol-based cross-linking agent. ,
including a dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 represented by the following general formula (1),
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)
pH is less than 7.

Further, the fluoroelastomer cross-linking composition according to one aspect of the present invention comprises a fluoroelastomer,
a polyol-based cross-linking agent;
a crosslinking accelerator containing a dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 represented by the following general formula (1) and having a pH of less than 7;
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)
and the dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 is in the range of 0.01 to 0.1 parts by mass with respect to 100 parts by mass of the fluorine-containing elastomer be.

According to the present invention, a cross-linking accelerator for a fluorine-containing elastomer that enables obtaining a molded product having excellent compression set properties while maintaining the high cross-linking acceleration performance of diazabicycloundecene, and a fluorine-containing cross-linking accelerator. An elastomeric cross-linking composition can be provided.

The cross-linking accelerator for fluorine-containing elastomers and the composition for cross-linking fluorine-containing elastomers of the present invention will be described in detail below.

<Crosslinking accelerator for fluorine-containing elastomer>
The cross-linking accelerator for a fluorine-containing elastomer of the present invention is a cross-linking accelerator for cross-linking a fluorine-containing elastomer used when cross-linking a fluorine-containing elastomer with a polyol-based cross-linking agent (hereinafter sometimes simply referred to as "cross-linking accelerator". ) and
Dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 (diazabicycloundecene) represented by the following general formula (1) (hereinafter simply “dicarboxylic acid salt”) may be referred to as.), including
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)
pH is less than 7.

Diazabicycloundecene is known as a cross-linking (vulcanization) accelerator for cross-linking (vulcanization) of fluorine-containing elastomers, and is marketed by Sun-Apro under the trade name of "DBU" (registered trademark).

In the present invention, the dicarboxylic acid for converting diazabicycloundecene into a dicarboxylic acid salt is represented by general formula (1).
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)

R in general formula (1) is preferably a direct bond or —(CH ₂ ) _n — with n of 5 or less, and a direct bond or —(CH ₂ ) _n — with n of 4 or less. is more preferred. Specifically, for example, oxalic acid (R in general formula (1) is a direct bond) and adipic acid (R in general formula (1) is —(CH ₂ ) _n — and n is 4) are preferred. It can be exemplified as a dicarboxylic acid.

As a method of converting diazabicycloundecene into a dicarboxylic acid salt using a dicarboxylic acid, the two may be mixed in a solvent, heated to 40 to 50° C., and maintained for a certain period of time. After the reaction, the desired liquid cross-linking accelerator for fluorine-containing elastomer can be prepared by drying under vacuum to remove the solvent.

Usable solvents include alcohols such as methanol, ethanol and propanol. Among these, methanol and ethanol are preferred, and dehydration in advance is more desirable.

The holding temperature of the mixture of diazabicycloundecene and dicarboxylic acid is preferably in the range of 30°C to 60°C, more preferably in the range of 35°C to 45°C. The holding time of the mixture of diazabicycloundecene and dicarboxylic acid is preferably in the range of 30 minutes to 180 minutes, more preferably in the range of 30 minutes to 90 minutes.

However, if the holding temperature is raised, the holding time can be shortened, and if the holding temperature is low, the holding time should be kept long. The holding of the temperature may be ended when the reaction has sufficiently progressed, and it is not necessary to continue the holding time any longer.

If the mixing ratio (c/a) of the diazabicycloundecene (a) and the dicarboxylic acid (c) is set to 1 as a molar ratio, both will react without waste (almost neither excess nor deficiency). However, as will be described later, it is necessary to adjust the pH of the cross-linking accelerator for fluorine-containing elastomer to the acidic side. It may be desirable to add excess.

For example, when using oxalic acid as the dicarboxylic acid or one in which R is —(CH ₂ ) _n — and n is 4 or less in general formula (1), the molar ratio (c/a) is 0.5. A range of ~2 is preferred, and a range of 0.6 to 1.6 is more preferred.

Thus, the mixing ratio (c/a) of diazabicycloundecene (a) and dicarboxylic acid (c) can be appropriately selected for the purpose of adjusting the pH of the cross-linking accelerator for fluorine-containing elastomer.

In the present invention, the pH of the cross-linking accelerator for fluorine-containing elastomer needs to be adjusted to less than 7, preferably in the range of 4 or more and less than 7, and preferably in the range of 5 or more to 6 or less. is more preferred. If the pH is 7 or higher, the obtained dicarboxylic acid salt exhibits water absorption, which is not preferable. On the other hand, if the pH is too low, it functions as a strong acid and may deteriorate the cross-linking promoting function, so it is preferable not to lower it too much.

The resulting cross-linking accelerator of the present invention is used in the form of diazabicycloundecene dicarboxylate, or by adding it to the fluorine-containing elastomer together with other additives described below. The amount of the cross-linking accelerator for the fluoroelastomer to be added is preferably in the range of 0.01 to 0.2 parts by mass, preferably 0.02 to 0.2 parts by mass, as the amount of the dicarboxylic acid salt with respect to 100 parts by mass of the fluoroelastomer. It is more preferably in the range of 0.15 parts by mass, and even more preferably in the range of 0.06 to 0.1 parts by mass. If the amount of the dicarboxylate is too small, it will be difficult to obtain a sufficient effect of promoting crosslinking, and if the amount of the dicarboxylate is too large, the compression set of the obtained crosslinked product tends to decrease, both of which are not preferred.

The fluorine-containing elastomer to be used in the present invention, the polyol-based cross-linking agent to be used, other additives, etc. will be described in the next section of "Composite for Cross-linking of Fluorine-Containing Elastomer".

<Composition for cross-linking fluorine-containing elastomer>
The fluorine-containing elastomer cross-linking composition of the present invention comprises a fluorine-containing elastomer, a polyol-based cross-linking agent, and the above-described cross-linking accelerator of the present invention.

The fluorine-containing elastomer to be used is not particularly limited, but examples include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-per fluoroalkyl vinyl ether copolymers, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkyloxyalkyl vinyl ether copolymers, and the like.

The cross-linking accelerator of the present invention may be blended with the fluoroelastomer as it is and kneaded, or may be used as a masterbatch dispersion with the fluoroelastomer. In addition to the above components, the formulation contains conventionally known fillers or reinforcing agents (carbon black, silica, graphite, clay, talc, diatomaceous earth, barium sulfate, titanium oxide, wollastonite, etc.), plasticizers, Agents, lubricants, processing aids, pigments and the like can also be added as appropriate.

The fluorine-containing elastomer can be cured by a known method using a polyol-based cross-linking agent. Usable polyol-based cross-linking agents include 2,2-bis(4-hydroxyphenyl)propane [bisphenol A], 2,2-bis(4-hydroxyphenyl)perfluoropropane [bisphenol AF], hydroquinone, catechol, known polyhydroxyaromatic compounds such as resorcin, 4,4'-dihydro-terminated phenyl, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylsulfone, 2,2-bis(4-hydroxyphenyl)butane; Alternatively, their alkali metal salts or alkaline earth metal salts are used. These polyol-based cross-linking agents are preferably used in a proportion of about 0.5 to 10 parts by weight, more preferably in a proportion of about 1 to 5 parts by weight, per 100 parts by weight of the fluorine-containing elastomer.

The polyol cross-linking is preferably carried out in the presence of a divalent metal hydroxide and a divalent metal oxide acting as an acid acceptor. The amount of the divalent metal hydroxide and divalent gold oxide to be added is preferably in the range of 1 to 15 parts by mass, more preferably in the range of 3 to 6 parts by mass, with respect to 100 parts by mass of the fluorine-containing elastomer. is more preferable. Examples of divalent metal hydroxides and oxides include hydroxides and oxides of magnesium, calcium, zinc, lead, and the like.

Each of the above components can be kneaded by a roll, kneader, Banbury, or the like. The kneaded mixture (fluorine-containing elastomer cross-linking composition of the present invention) is generally molded by press cross-linking (press vulcanization, primary vulcanization) performed at about 100 to 250° C. for about 1 to 60 minutes, Preferably, oven cross-linking (oven vulcanization, secondary vulcanization) is further performed at about 150 to 300° C. for about 30 hours or less, followed by molding. As a molding method, injection molding is also possible.

In addition, those skilled in the art can appropriately modify the cross-linking accelerator for fluorine-containing elastomers and the composition for cross-linking fluorine-containing elastomers of the present invention according to conventionally known knowledge. As long as the configuration of the present invention is still provided even with such modification, it is, of course, included in the scope of the present invention.

[Synthesis of cross-linking accelerator]
<Synthesis example 1>
100 g of dehydrated methanol as a solvent and 15.2 g of 1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) (0 .10 mol), and after installing a dropping funnel and a reflux tube, the mixture was replaced with nitrogen again. The mixture was heated to 40° C. while continuing to reflux, and while stirring was maintained, a solution prepared by dissolving 9.0 g (0.10 mol) of oxalic acid in 200 g of dehydrated methanol in a dropping funnel was added at a rate of 10 g/min. was added at a drop rate of . Stirring was continued even after the dropwise addition was completed, and the mixture was kept at 40° C. for 1 hour. After that, it is vacuum-dried at 30° C. for 15 hours to remove methanol, so that the molar ratio (c/a) of oxalic acid (c) to diazabicycloundecene (a) is 1 (a:c is 1). : 1) cross-linking accelerator for fluorine-containing elastomer (diazabicycloundecene oxalate) was obtained. This oxalate had a pH of 5.4 and did not exhibit water absorbency. The yield of the oxalate was 92 mol%.

<Synthesis Example 2>
100 g of dehydrated methanol as a solvent and 12.2 g of 1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) (0 .08 mol), and after installing a dropping funnel and a reflux tube, the mixture was replaced with nitrogen again. The mixture was heated to 40° C. while continuing to reflux, and while stirring was maintained, a solution prepared by dissolving 10.8 g (0.11 mol) of oxalic acid in 200 g of dehydrated methanol in a dropping funnel was added at a rate of 10 g/min. was added at a drop rate of . Stirring was continued even after the dropwise addition was completed, and the mixture was kept at 40° C. for 1 hour. Then, it is vacuum-dried at 30° C. for 15 hours to remove methanol, and the molar ratio (c/a) of oxalic acid (c) to diazabicycloundecene (a) is 1.5 (a:c). and 2:3) for fluorine-containing elastomers (diazabicycloundecene oxalate). This oxalate had a pH of 4.3 and did not exhibit water absorbency. The yield of the oxalate was 94 mol%.

<Synthesis Example 3>
100 g of dehydrated methanol as a solvent and 18.2 g of 1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) (0 .12 mol), and after installing a dropping funnel and a reflux tube, the mixture was replaced with nitrogen again. The mixture was heated to 40° C. while continuing to reflux, and while stirring was maintained, a solution prepared by dissolving 7.2 g (0.08 mol) of oxalic acid in 150 g of dehydrated methanol in a dropping funnel was added at a rate of 10 g/min. was added at a drop rate of . Stirring was continued even after the dropwise addition was completed, and the mixture was kept at 40° C. for 1 hour. Then, it is vacuum-dried at 30° C. for 15 hours to remove methanol, and the molar ratio (c/a) of oxalic acid (c) to diazabicycloundecene (a) is 0.67 (a:c). and 3:2) cross-linking accelerator for fluorine-containing elastomer (diazabicycloundecene oxalate) was obtained. This oxalate was a liquid with a pH of 9.8 and exhibited water absorbency. The yield of the oxalate was 87mol%.

<Synthesis Example 4>
100 g of dehydrated methanol as a solvent and 1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) 15.2 g (0 .10 mol), and after installing a dropping funnel and a reflux tube, the mixture was replaced with nitrogen again. Warm to 40° C. with continued reflux and add 16. adipic acid to a dropping funnel while maintaining stirring. A solution obtained by dissolving 1 g (0.10 mol) in 400 g of dehydrated methanol was added at 10 g/min. was added at a drop rate of . Stirring was continued even after the dropwise addition was completed, and the mixture was kept at 40° C. for 1 hour. After that, it is vacuum-dried at 30° C. for 15 hours to remove methanol, so that the molar ratio (c/a) of adipic acid (c) to diazabicycloundecene (a) is 1 (1 when expressed as a:c). : 1) cross-linking accelerator for fluorine-containing elastomer (adipate of diazabicycloundecene) was obtained. This adipate had a pH of 5.9 and showed no water absorption. The yield of the adipate was 92 mol%.

<Synthesis Example 5>
100 g of dehydrated methanol as a solvent and 15.2 g of 1,8-diaza-bicyclo(5,4,0)undecene-7 (DBU) (0 .10 mol), and after installing a dropping funnel and a reflux tube, the mixture was replaced with nitrogen again. The mixture was heated to 40° C. while continuing to reflux, and while stirring was maintained, a solution prepared by dissolving 12.7 g (0.10 mol) of benzyl chloride in 200 g of dehydrated methanol in a dropping funnel was added at a rate of 10 g/min. was added at a drop rate of . Stirring was continued even after the dropwise addition was completed, and the mixture was kept at 40° C. for 1 hour. Thereafter, the mixture was vacuum-dried at 30° C. for 15 hours to remove methanol, thereby obtaining a cross-linking accelerator for fluorine-containing elastomer (benzyl chloride diazabicycloundecene, for comparison). This benzyl chloride salt had a pH of 9.9 and exhibited water absorption. The yield of the benzyl chloride salt was 93 mol%.

<Synthesis Example 6>
1,8-Diaza-bicyclo(5,4,0)undecene-7 (DBU) itself was used as a cross-linking accelerator for fluorine-containing elastomer in Synthesis Example 6 (for comparison).

[Water absorption test of cross-linking accelerator]
The cross-linking accelerators synthesized in Synthesis Examples 1 to 7 were tested for confirming water absorption. About 1.00 g of the cross-linking accelerator of each synthesis example was allowed to stand under environmental conditions of 23° C. and a relative humidity of 50%, and water absorption was confirmed by observing the standing time and weight change. The results are shown in Table 1 below.

In Table 1 above, reagent A is diazabicycloundecene-orthophthalate, and U-CAT SA102 manufactured by San-Apro Co., Ltd. was used. In reagent A, the molar ratio (op/a) of orthophthalic acid (op) to diazabicycloundecene (a) is 1 (1:1 when expressed as a:op).

In Table 1 above, reagent B is diazabicycloundecene-octylate, and U-CAT SA810 manufactured by San-Apro Co., Ltd. was used. In Reagent B, the molar ratio (ot/a) of octylic acid (ot) to diazabicycloundecene (a) is 1 (1:1 in terms of a:ot).

The numerical values in Table 1 are the amount of increase in weight when the weight of the dicarboxylic acid salt (or carboxylic acid salt) at the start of the test is taken as 100, and correspond to the amount of water absorption. As can be seen from Table 1, the aqueous solution of the crosslinking accelerator having a basic liquidity has water absorption, and the liquid having an acidity does not have water absorption. Since polyol cross-linking is promoted by water, the water absorption of the cross-linking accelerator makes it difficult to adjust the cross-linking speed of the polyol cross-linking and further causes scorch. Furthermore, it is preferable that there is no water absorption.

[Production of Composition for Crosslinking Fluorine-Containing Elastomer]
The cross-linking accelerators of Synthesis Examples 1-8 were used and mixed according to the formulations shown in Table 2 below to produce fluorine-containing elastomer cross-linking compositions of Examples 1-5 and Comparative Examples 1-17. After cross-linking, comparative tests were conducted on the cross-linking acceleration performance and the compression set of the obtained cross-linked product.

The fluorine-containing elastomers used in the tests are as follows.
Fluorine-containing elastomer A: vinylidene fluoride/hexafluoropropylene copolymer elastomer (copolymerization molar ratio = 80/20), Mooney viscosity = 45
Fluorine-containing elastomer B: vinylidene fluoride/hexafluoropropylene copolymer elastomer (copolymerization molar ratio = 75/25), Mooney viscosity = 35
Fluorine-containing elastomer C: vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer elastomer (copolymerization molar ratio = 75/10/15), Mooney viscosity = 20
The Mooney viscosities of these fluorine-containing elastomers were measured according to JIS K 6300-1 (ML1+10, 121° C.).

Specifically, first, the ingredients shown in Table 2 were mixed and kneaded for 30 minutes using a roll mill. Thereafter, press cross-linking was performed at 180° C. for 10 minutes as primary cross-linking, and then oven cross-linking was performed at 230° C. for 22 hours as secondary cross-linking to obtain respective cross-linked products.

In addition to these cross-linking reactions, using a movable die rheometer (MDR2000 manufactured by Monsanto), at a temperature of 180 ° C., tc10 (min.) And tc90 (min.) By measuring, each implementation Crosslinking rates were determined for the compositions of the Examples and Comparative Examples.

Here, tc10 (min.) and tc90 (min.) are defined as follows. That is, a vulcanization curve is drawn with vulcanization torque on the vertical axis and time on the horizontal axis. When the maximum vulcanization torque during the test is _MH (10) and the minimum torque is _ML , the distance between a straight line passing through _MH and a straight line passing through _ML and parallel to the horizontal axis is tc10 ( _min .) is the time indicated by the intersection of the vulcanization curve and a straight line parallel to the horizontal axis passing through ML + 10% _ME , and a straight line parallel to the horizontal axis passing through _{ML +} 90% _ME . and the time indicated by the intersection of the vulcanization curve is tc90 (min.).

The compression set was measured for each of the obtained crosslinked products of Examples and Comparative Examples. Each crosslinked product was compressed at 200° C. for 70 hours and measured according to ASTM D395 Method B.
Table 3 below summarizes the measurement results of the crosslinking rate and compression set of each example and comparative example. Table 3 also shows the results of the water absorption of the used cross-linking accelerator (diazabicycloundecene carboxylate).

As can be seen from Table 3, according to the fluorine-containing elastomer cross-linking composition of the present invention, the cross-linking acceleration effect of the cross-linking accelerator for fluorine-containing elastomer of the present invention is exhibited, and the cross-linking speed is high. It also has excellent compression set resistance. Furthermore, the cross-linking accelerator for fluorine-containing elastomers of the present invention does not exhibit water absorbency, thus facilitating the adjustment of the cross-linking speed and causing less scorching.

Claims (2)

A cross-linking accelerator for cross-linking a fluorine-containing elastomer used for cross-linking a fluorine-containing elastomer with a polyol-based cross-linking agent,
including a dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 represented by the following general formula (1),
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)
A cross-linking accelerator for fluorine-containing elastomers, which has a pH of less than 7. a fluorine-containing elastomer;
a polyol-based cross-linking agent;
a crosslinking accelerator containing a dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 represented by the following general formula (1) and having a pH of less than 7;
HOOC-R-COOH ... general formula (1)
(In general formula (1) above, R represents a direct bond or -(CH ₂ ) _n -, and n represents a natural number of 6 or less.)
and the dicarboxylic acid salt of 1,8-diaza-bicyclo(5,4,0)undecene-7 is in the range of 0.01 to 0.2 parts by mass with respect to 100 parts by mass of the fluorine-containing elastomer A fluorine-containing elastomer cross-linking composition.