JP2011057894A - Method for producing foamed polyurethane elastomer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a foamed polyurethane elastomer having improved durability at high temperature. <P>SOLUTION: The foamed polyurethane elastomer is produced such that a prepolymer containing a terminal isocyanate group, which is obtained by reacting a polyol having a number-average molecular weight Mn of 500-4,000 and an aromatic diisocyanate, is stirred and mixed with a foaming agent comprising a mixture consisting of water, a low molecular weight glycol having a molecular weight of 48-200, and a high molecular weight glycol having a number-average molecular weight Mn of 1,000-3,000, to effect a foaming reaction. The foaming reaction is carried out using a foaming agent containing 1,2-dimethylimidazole catalyst to produce a foamed polyurethane elastomer. 3,3'-Dimethylphenyl-4,4'-diisocyanate is preferably used as an aromatic diisocyanate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a foamed polyurethane elastomer. More specifically, the present invention relates to a method for producing a polyurethane foam elastomer that is effectively used as an automotive elastic body part such as an auxiliary spring (bump stopper) of an automobile suspension.

  Polyurethane elastomer with a fine cell structure is excellent in vibration control and shock absorption, and is often used as an auxiliary spring for automobile suspensions from the viewpoint of dynamic characteristics, durability and resistance to heavy loads under high loads. Has been. In particular, polyurethane foam elastomers based on 1,5-naphthalene diisocyanate (NDI) are excellent in bending fatigue resistance and are often used in auxiliary springs where high durability is required. However, NDI has a problem that it is difficult to handle because of its high raw material cost and high reactivity compared to other diisocyanate compounds.

  The failure mechanism of the auxiliary spring for automobiles is considered to be due to the fact that the material itself generates heat due to repeated bending deformation, the physical properties of the material are lowered by the temperature at that time, and local cracks are generated. Therefore, auxiliary spring materials with excellent durability must have the property that physical properties do not deteriorate even in high-temperature environments, and this requires a high-dimensional structure of polyurethane molecular chains with a strong cross-linked structure. It becomes.

  However, diisocyanate, high molecular weight diol and chain extender (low molecular weight diol) are mixed together (one-shot method), or high molecular weight diol is reacted with diisocyanate in advance to prepare a prepolymer, and then low molecular weight diol is used to extend the chain. In the conventional production method of performing (prepolymer method), a high-dimensional structure of a polyurethane molecular chain having such a strong crosslinked structure cannot be realized using an aromatic diisocyanate other than NDI (see Non-Patent Document 1). ).

WO 2008/026367 JP 2005-60552 A JP 2002-30129 A Japanese National Patent Publication No. 11-513719

Issued by Industrial Research Institute Encyclopedia Publishing Center “Encyclopedia of Functional Polymers for Plastics”, p.426 (2004) Published by Nikkan Kogyo Shimbun "Polyurethane resin handbook" 118-120 pages (issued September 25, 1987)

  The present applicant has previously proposed a polyol and 3,3 as a method of producing a foamed polyurethane elastomer that achieves high durability, particularly high durability under high load, while using an inexpensive and easy-to-handle diisocyanate compound. From a mixture of water, a low molecular weight glycol having a molecular weight of 48 to 200 and a high molecular weight glycol having a number average molecular weight Mn of 1000 to 3000, to a prepolymer containing a terminal isocyanate group obtained by reacting ′ -dimethylbiphenyl-4,4′-diisocyanate Patent Document 1 proposes a method for producing a foamed polyurethane elastomer by stirring and mixing the resulting foaming agent and performing a foaming reaction.

  An object of the present invention is to provide a method for producing a foamed polyurethane elastomer having improved high-temperature durability in the method for producing a foamed polyurethane elastomer.

  The object of the present invention is to provide a terminal isocyanate group-containing prepolymer obtained by reacting a polyol having a number average molecular weight Mn of 500 to 4000 and an aromatic diisocyanate with water, a low molecular weight glycol having a molecular weight of 48 to 200, and a number average molecular weight Mn. A foaming polyurethane elastomer is produced by stirring and mixing a foaming agent composed of a mixture of 1000 to 3000 high molecular weight glycols and performing a foaming reaction using a foaming agent containing a 1,2-dimethylimidazole catalyst. Achieved by the method. As the aromatic diisocyanate, 3,3′-dimethylphenyl-4,4′-diisocyanate is preferably used.

  The foamed polyurethane elastomer produced by using the method according to the present invention comprises 3,3′-dimethylbiphenyl-4,4′-diisocyanate (tolidine diisocyanate; TODI) as a diisocyanate compound which is inexpensive and easy to handle as an aromatic diisocyanate. Even in the foamed urethane elastomer obtained by using as a foamed urethane elastomer, an excellent effect is obtained in that a foamed urethane elastomer having physical properties equivalent to those of NDI based on a high raw material unit price can be obtained. In other words, even a polyurethane foam elastomer obtained by reacting an inexpensive diisocyanate compound other than NDI with a polyol can have excellent bending fatigue characteristics, and also in an environment where the material generates heat due to repeated compression. Therefore, it is used effectively as an elastic body part for automobiles such as an auxiliary spring of an automobile suspension part that maintains a strong rubber elasticity and requires high durability.

  As described above, the auxiliary spring material having excellent durability is indispensable in that the physical properties do not deteriorate even under a high temperature environment, and this greatly depends on the higher order structure of the polyurethane molecular chain. In order to take such a higher-order structure of the polyurethane molecular chain, it is necessary to have a stronger cross-linked structure. However, in the foam curing reaction in the method for producing a polyurethane elastomer of the present invention, the reactivity is the first. High water or low molecular weight glycol reacts with excess diisocyanate present in the urethane prepolymer, but in the presence of a catalyst with high urethanation activity such as 1,2-dimethylimidazole, A hard segment with a relatively high proportion grows, and then reacts with the diisocyanate group in which the low-reactivity high molecular weight glycol remains to form a soft segment. It is considered that the physical crosslinkability is increased by further proceeding.

  That is, the polyurethane elastomer obtained by the method of the present invention has a higher-order structure rich in physical cross-linking and a tough hard segment with a high proportion of urethane bonds. Has characteristics. For example, in a general rubber material tensile test method, the elongation at break when stored at 100 ° C for 1 hour and the elongation test at break under the same temperature atmosphere is the elongation at break in a normal temperature atmosphere. 80% or more of the rate is maintained, and the physical property is less deteriorated under a high temperature atmosphere.

Furthermore, in the method of the present invention, the foaming agent in which water that reacts with the diisocyanate component to form a rigid urea bond and glycol that forms a tough urethane bond coexist is formed by the foaming reaction of the TDI / water system. Addition of 1,2-dimethylimidazole, which is an amine catalyst with a ratio (2) / (1) of reaction constant (2) and reaction constant (1) of TDI / diethylene glycol gelation reaction of 1.30 × 10 ^-1 or less By using this, it is possible to activate the urethane formation reaction rather than the urea formation reaction. By using such a resination active catalyst, it is excellent in toughness and beneficial for the durability of the auxiliary spring. Thus, a polyurethane elastomer having a higher order structure that exhibits the properties can be obtained.

  The polyol is not particularly limited as long as the number average molecular weight Mn which is a long-chain glycol having terminal active hydrogen is 500 to 4000, preferably 1000 to 3000, and the hydroxyl value is 30 to 150, preferably 40 to 100. Polyester-based, polyether-based, polycarbonate-based, silicone-based, 1,4-polybutadiene-based, 1,2-polybutadiene-based, castor oil-based polyols, and mixtures thereof are used. In addition, the Mn of the polyol is defined as 500 to 4000. If the Mn is less than this, the flexibility of the foamed polyurethane elastomer is impaired and becomes brittle, while if the Mn is higher than that, the foamed polyurethane elastomer has a low hardness. This is because sufficient material strength cannot be obtained.

  As the diisocyanate to be reacted with the polyol, 3,3′-dimethylbiphenyl-4,4′-diisocyanate (TODI) is preferably used, but toluene diisocyanate (TDI) and 4,4′-diphenylmethane diisocyanate (MDI) are also used. Aromatic diisocyanates such as polymeric MDI and p-phenylene diisocyanate (PPDI) are also used. These aromatic diisocyanates are used in such a ratio that the isocyanate group is more than 1 equivalent and 5 equivalents or less, preferably 4 equivalents or less per OH equivalent of the polyol. When the diisocyanate component is used in a smaller amount, a terminal isocyanate group-containing prepolymer is not formed. On the other hand, when the diisocyanate component is used in a proportion higher than this, the hardness of the polyurethane foam elastomer increases, making it unsuitable for use as a buffer part.

  The polyol and diisocyanate are reacted at about 90 to 130 ° C. for about 15 minutes to about 1 hour to form a prepolymer.

  As a blowing agent-forming component, 0.1 to 5.0 parts by weight of water, preferably 0.2 to 3.0 parts by weight, and a molecular weight of 48 to 200, preferably 62 to 160, 0.1 to 5.0 per 100 parts by weight of the terminal isocyanate group-containing prepolymer Part by weight, preferably 0.2 to 3.0 parts by weight and number average molecular weight Mn 1000 to 3000, preferably 1000 to 2000 high molecular weight glycol 0.5 to 70 parts by weight, preferably 1 to 50 parts by weight are used. If low molecular weight glycol is not used, hard segments cannot be grown. Conversely, if high molecular weight glycol is not used, soft segments cannot be grown. Cannot be made long, and physical crosslinkability cannot be improved.

  As the low molecular weight glycol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-bis (2-hydroxyethoxy) benzene and the like, and as the high molecular weight glycol, preferably Of the categories used for forming the prepolymer, more preferably the same kind of polyol is used, and specifically, ethylene adipate polyester polyol, ethylene butylene adipate polyester polyol, polytetramethylene glycol, polypropylene glycol and the like are used. The reason why the Mn of high molecular weight glycol is defined as 1000 to 3000 is that if the Mn is less than this, a soft segment that requires flexibility cannot be formed, while if the Mn is higher than this, the foaming agent has a high viscosity. This is because it is difficult to handle and is not preferable.

In the method of the present invention, a foaming agent comprising a mixture of water, a low molecular weight glycol and a high molecular weight glycol is stirred and mixed in the prepolymer, and when performing the foaming reaction, the reaction constant (2) and TDI by the foaming reaction of the TDI / water system are used. Using a blowing agent containing 1,2-dimethylimidazole, which is an amine-based catalyst having a ratio (2) / (1) to a reaction constant (1) due to gelation reaction of diethylene glycol / (1) of 1.30 × 10 ⁻¹ or less, A foaming reaction takes place.

  The ratio (1) / (2) of the reaction constant (1) due to the gelation reaction of TDI / diethylene glycol to the reaction constant (2) due to the foaming reaction of the TDI / water system is one index indicating the reaction activity of the amine catalyst. Therefore, it is described in Non-Patent Document 2.

In general, in the industrial production of polyurethane, a competitive reaction of (A), (B) occurs,
R-NCO + R′-OH → R-NHCOO-R ′ (A)
2R-NCO + H ₂ O → R-NHCONH-R + CO ₂ (B)
The reaction constant (1) indicating the reaction activity of the resinification reaction (gelation reaction; urethane formation reaction) of (A) (1) and the reaction constant (2) indicating the reaction activity of the foaming reaction (urea formation reaction) of (B) An amine catalyst having a reaction activity ratio defined by the ratio (2) / (1) of 1.30 × 10 ⁻¹ or less is used in the present invention.

Specifically, amine catalysts having a reaction constant ratio of 1.30 × 10 ⁻¹ or less include 1,2-dimethylimidazole (0.77 × 10 ⁻¹ ), N · (N ′, N′-dimethylaminoethyl) morpholine. (0.81 × 10 ⁻¹ ), tetramethylguanidine (1.04 × 10 ⁻¹ ), dimethylaminoethanol (1.23 × 10 ⁻¹ ) and the like are known, but 1,2-dimethylimidazole is preferably used in the present invention. It is done.

  1,2-dimethylimidazole is used in a proportion of 0.02 to 0.7 parts by weight, preferably 0.05 to 0.5 parts by weight, per 100 parts by weight of the prepolymer having a terminal isocyanate group. If the proportion of 1,2-dimethylimidazole used is less than this, the curing reaction takes time and the molding cycle becomes longer. On the other hand, if it is used in a proportion higher than this, the curing / foaming reaction will occur. It becomes faster and it becomes difficult to cast using a mold.

On the other hand, when an amine-based catalyst having a reaction constant ratio larger than 1.30 × 10 ⁻¹ is used, the compression set, which is an evaluation item of high-temperature sag resistance, increases, that is, the shape of the auxiliary spring is maintained when the material sags. Because it is not possible, it becomes inferior in durability. In addition, when a reaction constant ratio of about 3 × 10 ⁻¹ is used, it is inevitable that the elongation high temperature retention ratio during cutting (elongation during cutting at 100 ° C./elongation during cutting at room temperature) is significantly reduced.

  In the production of foamed polyurethane elastomers, amine-based catalysts are generally used as the catalyst. For example, Patent Documents 2 to 4 list many examples of amine-based catalysts. -Dimethylimidazole is also exemplified, but this is merely illustrative.

  In addition to the foaming agent, a foam stabilizer such as a silicone foam stabilizer is generally used at a ratio of 0.1 to 3.0 parts by weight, preferably 0.2 to 2.0 parts by weight per 100 parts by weight of the prepolymer as a component for determining the cell structure. It is preferable. In addition to the above components, fillers, divalent metal oxides or hydroxides, lubricants, and the like can be appropriately blended as necessary.

  These amine-based catalyst-containing foaming agent and foam stabilizer are mixed with the produced prepolymer, and after the polyurethane formation reaction proceeds by casting using a predetermined volume of mold, Is subjected to secondary cross-linking (annealing) at about 80 to 150 ° C. for about 5 to 24 hours to obtain a foamed polyurethane elastomer molded article having high toughness, high cohesion of hard segments, and excellent bending fatigue resistance be able to.

Next, the present invention will be described with reference to examples. In each of the examples, comparative examples, and reference examples described herein, a polyurethane foam elastomer was used and molded under the following conditions.
Prepolymer temperature used for foaming urethanization reaction: approx. 70-80 ° C
Foaming agent temperature used for the urethane urethanization reaction: approx. 50-60 ° C
Mold temperature: about 50-60 ℃
Mold release time: about 15-20 minutes Secondary cross-linking: 120 ° C., 24 hours molding is molded as a sample for evaluation of sheet shape with molding density of 0.5 g / cm ³ and auxiliary spring shape for automobile suspension. Molding was performed by slicing a block molded to 60 × 150 × 30 mm into a size of 60 × 150 × 2 mm after secondary vulcanization.

Example 1
After melting 100 parts by weight of ethylene adipate polyester polyol having a number average molecular weight Mn of 2,000 and a hydroxyl value of 56 at 120 ° C, the mixture was charged into a reactor heated to 120 ° C in advance and stirred with TODI 40 parts by weight (NCO / OH equivalent) Ratio 3.0) was added and reacted for 30 minutes to obtain a urethane prepolymer. Separately, 3937 parts by weight of an ethylene adipate polyester polyol having a number average molecular weight Mn of 2,000 and a hydroxyl value of 56 melted at 60 ° C., 150 parts by weight of water, 150 parts by weight of 1,4-butanediol, 1,2- 40 parts by weight of dimethylimidazole (Tosoh product TOYOCAT-DM70; reaction constant ratio 0.77 × 10 ^-1 ) and 100 parts by weight of foam stabilizer (Toray Dow Corning silicone product SH193OIL) are added, and these are stirred and mixed for 2 hours. Got.

  Under the above temperature conditions, urethane prepolymer: foaming agent was mixed at a weight ratio of 100: 26.5, stirred to perform foaming reaction, molded, and then subjected to secondary crosslinking to obtain a sample for evaluation.

Comparative Example 1
In the examples, 10 parts by weight of triethylenediamine (Air Products Japan product DABCO; reaction constant ratio 1.34 × 10 ⁻¹ ) was used as the amine catalyst, and the urethane prepolymer: foaming agent weight ratio was changed to 100: 26.3. A foaming reaction and vulcanization were performed to obtain a sample for evaluation.

Comparative Example 2
In Examples, a foaming reaction and vulcanization were performed using 40 parts by weight of Tosoh product TOYOCAT D60; reaction constant ratio 3.00 × 10 ⁻¹ ) as an amine-based catalyst to obtain an evaluation sample.

Comparative Example 3
In Examples, the TODI amount of the urethane prepolymer component was changed to 30 parts by weight, and the ethylene adipate-based polyester polyol was not used in the blowing agent component, and the amount of 1,2-dimethylimidazole as an amine-based catalyst was 35 wt. Further, the urethane prepolymer: foaming agent weight ratio was changed to 100: 2.1, and the foaming reaction and vulcanization were performed to obtain a sample for evaluation.

Comparative Example 4
In Comparative Example 3, 8 parts by weight of triethylenediamine (DABCO) was used as an amine catalyst, and the urethane prepolymer: foaming agent weight ratio was changed to 100: 2.0 to perform a foaming reaction and vulcanization. Obtained.

Reference Example After melting 100 parts by weight of ethylene adipate-based polyester polyol having a number average molecular weight Mn of 2,000 and a hydroxyl value of 56 at 120 ° C., it was charged into a reactor heated to 120 ° C. in advance and stirred with 20 parts by weight of NDI (NCO / OH equivalent ratio 1.9) was added and reacted for 30 minutes to obtain a urethane prepolymer. Separately, 150 parts by weight of water, 150 parts by weight of 1,4-butanediol, 2 parts by weight of triethylenediamine (DABCO) and 100 parts by weight of a foam stabilizer (SH1930IL) were stirred and mixed for 2 hours to obtain a foaming agent.

  A urethane prepolymer: foaming agent was mixed at a weight ratio of 100: 1.5, subjected to foaming reaction and vulcanization, and a sample for evaluation was obtained.

Using the sample for evaluation of the sheet shape obtained in each of the above Examples, Comparative Examples and Reference Examples, the glass transition point, hardness, tensile strength at room temperature and 100 ° C, at break at room temperature and 100 ° C Elongation and compression set were measured, and auxiliary spring durability was measured using a sample for evaluation of auxiliary spring shape for automobile suspension.
Hardness: Spring type Asker C type Tensile strength, Elongation at break: Conforms to JIS K6261 corresponding to ASTM D412 (Sample shape: Dumbbell No. 3 type)
Compression set: JIS K6262 compliant with ASTM D395 (13 mm diameter, 3 mm thick sheet, 25% compression, 80 ° C x 70 hours)
Auxiliary spring durability: 10kN × 1Hz × Evaluated by cracks after compression 100,000 times
Evaluated as “No” for cracks and “No” for cracks.
Measure the number of compressions when cracks occur

  The obtained results are shown in the following table together with the mixing ratio. In addition, each component amount has shown the weight part number with respect to 100 weight part of adipate polyol components in a urethane prepolymer.

Incidentally, the weight parts of the blowing agent, the amine catalyst and the foam stabilizer are calculated as follows.
When the compounding amount of each component in the prepolymer X is xi, the compounding amount of each component in the foaming agent Y is yi, and the compounding ratio is X: Y = m: n, the number of parts by weight of the yi component with respect to 100 parts by weight of the xi component kii is calculated by the following equation.
kii ＝ (100 × n × yi × Σxi) / (m × xi × Σyi)

  For measured values, high temperature durability is indicated by the high temperature retention rate of elongation at break and compression set, which is related to product durability against breakage, and compression set is product durability against sag. Related to. For example, even if the material has a high elongation retention at high temperature and is not easily damaged in actual use in a high temperature environment, the shape of the auxiliary spring can be used if the material has a large compression set and is easy to sag. Can't keep up.

Looking at the measurement results for Examples and Comparative Examples, the effect of improving high-temperature properties by using the specific amine catalyst of the present invention is remarkable when a high molecular weight polyol is added during the foaming reaction ( Example-Comparative Example 1) When no high molecular weight polyol is added, only the high temperature retention rate is effective (Comparative Example 3-4).
table
Comparative example
Example 1 2 3 4 Reference Example [Composition]
Urethane polymer
Adipate polyol 100 100 100 100 100 100
TODI 40 40 40 30 30 −
NDI − − − − − 20
Blowing agent
Adipate polyol 33.37 33.37 33.37 − − −
H ₂ O 1.27 1.27 1.27 0.96 0.96 0.68
1,4-butanediol 1.27 1.27 1.27 0.96 0.96 0.68
Amine catalyst
Dimethylimidazole 0.34 − − 0.22 − −
Triethylenediamine − 0.08 − − 0.05 0.01
TOYOCAT D60 − − 0.34 − − −
Foam stabilizer 0.85 0.85 0.85 0.64 0.64 0.45
〔Measurement item〕
Glass transition temperature (℃) -39 -38 -39 -36 -36 -34
Tensile strength 74 75 74 74 75 73
Room temperature (MPa) (A) 5.6 5.5 5.2 5.3 5.4 6.2
100 ° C (MPa) (B) 1.6 1.5 1.6 1.3 1.2 1.7
Retention rate ([B] / [A];%) 29 27 31 25 22 27
Elongation at break Normal temperature (%) [C] 520 490 490 480 480 420
100 ° C (%) [D] 430 400 300 280 270 350
Maintenance rate ([D] / [C];%) 83 82 61 58 56 83
Compression set (%) 21 24 22 29 28 22
Auxiliary spring durability
(Compressed 100,000 times)
Damaged ○ ○ ○ × × ○
Crack occurrence (times) − − − 7000 7000 −

  The foamed polyurethane elastomer molded product obtained by the method of the present invention has a high-dimensional structure rich in physical crosslinkability, and therefore maintains strong rubber elasticity even in environments where the material generates heat due to repeated compression. Therefore, it is effectively used as an elastic body part for automobiles such as auxiliary spring materials for automobile suspension parts that require a high durability function.

  In addition to these applications, for example, casters, rolls, packing, sealing materials, anti-vibration parts, ball joints and other machinery / automobile / precision parts, shoe soles, ski boots, snow chains and other sports / leisure goods, conveyor belts, Examples include keyboard sheets, gaskets, electric wires such as automobile wiring, and rope coverings.

Claims (7)

  A terminal isocyanate group-containing prepolymer obtained by reacting a polyol having a number average molecular weight Mn of 500 to 4000 and an aromatic diisocyanate, water, a low molecular weight glycol having a molecular weight of 48 to 200, and a high molecular weight glycol having a number average molecular weight Mn of 1000 to 3000 A method for producing a foamed polyurethane elastomer, which comprises stirring and mixing a foaming agent comprising the above mixture and performing a foaming reaction using a foaming agent containing a 1,2-dimethylimidazole catalyst.   The process for producing a foamed polyurethane elastomer according to claim 1, wherein 3,3'-dimethylbiphenyl-4,4'-diisocyanate is used as the aromatic diisocyanate.   0.1 to 5.0 parts by weight of water, 0.1 to 5.0 parts by weight of low molecular weight glycol, 0.5 to 70 parts by weight of high molecular weight glycol, and 0.02 to 0.7 parts by weight of 1,2-dimethylimidazole per 100 parts by weight of prepolymer containing an isocyanate group The method for producing a polyurethane foam elastomer according to claim 1 or 2, wherein each part is used.   The method for producing a foamed polyurethane elastomer according to claim 3, wherein the foam stabilizer is used in an amount of 0.1 to 3.0 parts by weight.   A foamed polyurethane elastomer produced by the method according to claim 1 or 4.   The foamed polyurethane elastomer according to claim 5, which is used as an elastic body part for automobiles. The polyurethane foam elastomer according to claim 6, wherein the elastic member for automobile is an auxiliary spring of an automobile suspension.