JPS6131130B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyurethane elastomer by a reaction injection molding method,
In particular, the present invention relates to a method for producing a polyurethane elastomer with a small rate of dimensional change upon absorption of water. It is known to produce polyurethane elastomers such as microcellular elastomers or non-foamed elastomers by reaction injection molding using polyols, chain extenders, and organic polyisocyanates as main raw materials. The production of polyurethane elastomers by reaction injection molding is currently being used for molded products in automobile-related fields, including the outer shell of automobile bumpers. It is also being considered for use in automobile fenders, door panels, front panels, and other exterior panels. These exterior members for automobiles, including the outer shell of the bumper, are required to have greater water resistance than interior members. However, the polyurethane elastomer conventionally used for bumper outer shells has had problems with poor water resistance. The most problematic aspect of conventional polyurethane elastomers has been dimensional changes due to water absorption.
That is, the polyurethane elastomer easily absorbs water, and the dimensions change due to water absorption, which tends to cause deformation of the molded product. Conventionally, molded products have been made thicker to avoid dimensional changes due to water absorption. However, it is extremely uneconomical to increase the wall thickness of a molded article solely to respond to dimensional changes due to water absorption. In addition, the limitation to thick walls means that the degree of freedom regarding the shape and physical properties of the molded product is reduced. Therefore, in order to essentially solve this problem, it is considered necessary to lower the water absorption of the polyurethane elastomer. When we investigated the cause of the water absorbency of polyurethane elastomers, we found that it is due to the hydrophilicity of the oxyethylene groups in the high molecular weight polyoxyalkylene polyol that is the raw material. It is believed that the problem of water absorption can be solved if a polyoxyalkylene polyol containing no oxyethylene group can be used. However, on the other hand, the presence of an oxyethylene group is essential for a polyoxyalkylene polyol that can be applied to reaction injection molding. That is, the polyoxyalkylene polyol used in reaction injection molding must have high reactivity, and therefore the polyol must have a high proportion of primary hydroxyl groups. It is necessary that the terminal oxyalkylene group of the polyol is an oxyethylene group. Typical polyoxyalkylene polyols are polyoxyalkylene polyols with oxyethylene groups at the terminals obtained by adding ethylene oxide to polyoxyalkylene polyols that have substantially only oxypropylene groups or oxypropylene groups and oxybutylene groups as oxyalkylene groups. It is a polyoxyalkylene polyol having a proportion of primary hydroxyl groups. Therefore, in order to solve the problem of water absorption, it was considered necessary to use a polyoxyalkylene polyol with a reduced content of oxyethylene groups while maintaining a high proportion of primary hydroxyl groups. The average hydroxyl value of high molecular weight polyoxyalkylene polyols used in reaction injection molding is approximately 15~
In the range of 60. Conventionally, the proportion of primary hydroxyl groups,
That is, the number of primary hydroxyl groups relative to the total number of hydroxyl groups,
It was thought that at least 80% was necessary.
For example, if we take a polyether polyol with a primary hydroxyl group content of 85%, a polyoxyalkylene polyol with a hydroxyl value of 35 requires an oxyethylene group content of at least about 25% by weight; In some cases, at least about 20% by weight of oxyethylene groups are required. That is, as the hydroxyl value of the polyoxyalkylene polyol decreases (ie, as the molecular weight increases), the relatively necessary content of oxyethylene groups decreases. However, the hydroxyl group 1 of polyoxyalkylene polyol
Calculating the number of oxyethylene groups per hydroxyl group (hereinafter referred to as units), at least about 5.5 to 6.0 units of oxyethylene group per hydroxyl group are required to achieve a primary hydroxyl group ratio of 85% regardless of the hydroxyl value. It means that. Theoretically, if there is one unit of oxyethylene group per hydroxyl group, the proportion of primary hydroxyl groups should be 100%. The reason why this does not happen is that when ethylene oxide is added to a polyoxyalkylene polyol having secondary hydroxyl groups, the addition of ethylene oxide to the hydroxyl groups is uneven, and the primary hydroxyl groups converted by the addition of one molecule of ethylene oxide are It reacts more easily with ethylene oxide than secondary hydroxyl groups, and even if the number of added ethylene oxides increases, secondary
This is thought to be because the ratio of addition to class hydroxyl groups decreases. Therefore, for these reasons, reducing the proportion of oxyethylene groups in polyoxyalkylene polyols inevitably leads to a decrease in the proportion of primary hydroxyl groups, and it is difficult to obtain a proportion of primary hydroxyl groups high enough to be used in reaction injection molding. A polyoxyalkylene polyol having the following properties cannot be obtained. In fact, as shown in the comparative example below, the production of a polyurethane elastomer using a conventional polyoxyalkylene triol with a hydroxyl value of about 26 and an oxyethylene group content of about 8% by weight, )
is extremely long, and the physical properties of the resulting polyurethane elastomer are poor, making it completely impractical. The present inventor took on the challenge of the above-mentioned problem that was previously thought to be theoretically impossible, and as a result of various research studies, it was found that even if the proportion of primary hydroxyl groups in the polyether polyol is low, as long as certain conditions are met, It has been found that a good polyurethane elastomer can be produced in the same molding time as conventional methods. A certain condition is that the amount of unsaturated group-containing monool component contained in the high molecular weight polyoxyalkylene polyol is
The condition is that it is 0.085meq/g or less. The amount of unsaturated group-containing monool component in polyoxyalkylene polyols with a high proportion of primary hydroxyl groups used in conventional reaction injection molding is about 0.12 me when the content of oxypropylene groups is high.
It was about q/g or more. The inventors have conducted various studies on the reason why a good polyurethane elastomer can be obtained even with a low proportion of primary hydroxyl groups by setting this to 0.10 meq/g or less, but the clear reason is unclear ( The reasoning will be explained later). However, the effect of using the polyoxyalkylene polyol is significant. Therefore, since it is not necessary to maintain a high proportion of primary hydroxyl groups, not only can the content of oxyethylene groups in the polyoxyalkylene polyol be reduced, but even if the content of oxyethylene groups is high to some extent, , it is possible to obtain a polyurethane elastomer that is better than conventional polyoxyalkylene polyols having the same amount of oxyethylene group content. The present invention relates to a method for producing a polyurethane elastomer by a reaction injection molding method characterized by using the above-mentioned specific polyol, namely, a polyol component containing a high molecular weight polyol and a chain extender as essential components, and a polyisocyanate compound. By reaction injection molding using at least two isocyanate components having as an essential component,
In a method for producing a polyurethane elastomer by reaction injection molding for producing a non-foamed or microcellular polyurethane elastomer molded article, substantially the entire amount or at least 80% by weight of the high molecular weight polyol is composed of a polyoxyalkylene polyol; The polyoxyalkylene polyol has an average number of hydroxyl groups of 2.1 to 3.5, an average oxyethylene group content of less than 15% by weight, and at least 5% by weight of the oxyethylene group is present at the end of the oxyalkylene chain, and contains an average unsaturated group-containing monool component. Amount 0.085meq/g or less, and average hydroxyl value 20-40
A method for producing a polyurethane elastomer by a reaction injection molding method, characterized in that the polyoxyalkylene polyol is a single or mixed polyoxyalkylene polyol. The reason why unsaturated group-containing monool components exist in polyoxyalkylene polyols is thought to be due to side reactions in the production of oxypropylene groups by addition of propylene oxide, and the side reactions are thought to be as follows. . (A: initiator or residue obtained by removing one hydroxyl group from polyoxyalkylene polyol M ⁺ : catalytic residue such as alkali metal ion) Therefore, in polyoxyalkylene polyol, CH ₂ = CH-CH ₂ OH or It contains an unsaturated group-containing monol component (hereinafter simply referred to as monol) produced by adding alkylene oxide to the hydroxyl group. This monool has a relatively low molecular weight, and although its amount is small when expressed in equivalent weight in the polyoxyalkylene polyol, it is present in a relatively large amount when expressed in molar amount. It is thought that ethylene oxide has a high tendency to react selectively with monool. Therefore, it seems that oxyethylene groups, which were conventionally necessary to increase the proportion of primary hydroxyl groups, were often distributed to monools, and were not sufficiently distributed to polyoxyalkylene polyols. . Therefore, in conventional polyoxyalkylene polyols, the high proportion of primary hydroxyl groups takes into account the primary hydroxyl groups of this monol, and the proportion of primary hydroxyl groups in polyoxyalkylene polyols excluding monools is actually It is estimated that the proportion was lower than the apparent proportion. Therefore, it is considered that if the amount of monol is small, the reaction activity equivalent to that of conventional polyoxyalkylene polyols can be maintained even if the proportion of primary hydroxyl groups in polyoxyalkylene polyols is lower than that of conventional polyoxyalkylene polyols. In addition, when considering the molding time, that is, the time until demolding becomes possible, the molding time is theoretically considered to be in a parallel relationship with the time until the crosslinking of polyurethane has progressed to a certain level. . Therefore, as mentioned above, the hydroxyl group of the monool is the
Because the proportion of primary hydroxyl groups in conventional polyoxyalkylene polyols is high, the proportion of primary hydroxyl groups in polyoxyalkylene polyols is relatively low, and the monool has a low molecular weight and high reaction activity. It is presumed that the reaction between the hydroxyl group of the monool and the isocyanate group preceded the reaction between the monool and the isocyanate group. On the other hand, crosslinking does not proceed in the reaction between monools and polyisocyanate compounds, so in the case of conventional polyoxyalkylene polyols that contain a large amount of monools, their apparent reactivity must be sufficiently high in order to increase the crosslinking rate. It seems that a higher proportion of primary hydroxyl groups was required than expected.
Therefore, if the content of monol is reduced, the reaction between polyoxyalkylene polyol and polyisocyanate compound will proceed faster and crosslinking will proceed, and even if the proportion of primary hydroxyl groups is low, molding times equivalent to or longer than conventional ones can be achieved. It is thought that it is possible to do so. In addition, less monool allows for more complete crosslinking of the polyurethane elastomer within the molding time, and if after-cure is required, it can be completed in a shorter time. Moreover, the physical properties of the resulting polyurethane elastomer are better than those obtained using a polyoxyalkylene polyol containing a large amount of monool. In particular, the water absorption dimensional change rate of polyurethane elastomers obtained using polyoxyalkylene polyols with low oxyethylene group content can be reduced from the conventional approximately 1.1% to 0.8% or less. It became. In the present invention, the high molecular weight polyol consists essentially of the entire amount or at least 80% by weight of a polyoxyalkylene polyol, and the polyoxyalkylene polyol has an average hydroxyl value of 2.1 to 80% by weight.
3.5. The average content of oxyethylene groups is less than 15% by weight, and at least 5% by weight of the oxyethylene group is present at the end of the oxyalkylene chain, the average content of monool components containing unsaturated groups is 0.085 meq/g or less, and the average hydroxyl group content is 0.085 meq/g or less. Single or mixed polyoxyalkylene polyols having a value of 20 to 40. The average oxyethylene group content can be varied depending on the purpose. That is, when the primary purpose is to reduce the water absorption dimensional change rate of polyurethane elastomers, the average oxyethylene group content is less than 14% by weight, especially 13% by weight.
Preferably, it is less than % by weight. However, if the purpose is to improve other physical properties or reactivity,
The average oxyethylene group content can be increased to nearly 15% by weight. The lower limit for the average oxyethylene group content is 5% by weight, which is present in the terminal portion of the oxyalkyl groups. If the amount of oxyethylene groups in the terminal portion is lower than this, the reactivity as a polyoxyalkylene polyol for reaction injection molding will usually be insufficient. Preferably, substantially all or most of the oxyethylene groups in the polyoxyalkylene polyol are present at the terminal portions of the oxyalkylene chains. Although it is preferable that no oxyethylene group is present in the non-terminal portion of the oxyalkylene acid, a small amount of oxyethylene group may be present in some cases. For example, an oxylene group may be present in the oxyalkylene chain of the initiator portion or the non-terminal portion. In particular, polyoxyalkylene polyols obtained using polyethylene glycols such as ethylene glycol and diethylene glycol as initiators are useful. but,
The amount of oxyethylene groups in the non-terminal portion is preferably 5% by weight or less, particularly 3% by weight or less, of the total oxyalkylene groups of less than 15% by weight, and it is particularly preferable that the oxyethylene group is substantially absent as described above. preferable. The polyoxyalkylene polyols described below do not contain an oxyethylene group at the non-terminal portion of the oxyalkylene chain, unless otherwise specified. The polyoxyalkylene polyol is preferably a mixed polyoxyalkylene polyol containing polyoxypropylene/oxyethylene triol or polyoxypropylene/oxyethylene diol as a main component. Furthermore, as will be described later, a portion of the oxypropylene groups in this polyoxypropylene/oxyethylene tri(or di)ol may be substituted with oxybutylene groups. The most preferred mixed polyoxyalkylene polyol is one in which at least 70% by weight of the mixed polyoxyalkylene polyol has an oxyethylene group content of less than 10% by weight, an unsaturated group-containing monool component content of 0.085 meq/g or less, and a hydroxyl group. It is a mixed polyoxyalkylene polyol which is a polyoxypropylene/oxyethylene triol (hereinafter referred to as a) having a valence of 20 to 40. It is also preferable to use this polyoxypropylene/oxyethylene triol (a) alone, but it deviates from the above average number of hydroxyl groups, average oxyethylene group content, average unsaturated group-containing monool component content, and average hydroxyl value. It is more preferable to use the polyoxyalkylene polyol (hereinafter referred to as c) in combination with other polyoxyalkylene polyols (hereinafter referred to as c). The next preferred mixed polyoxyalkylene polyol has an oxyethylene group content of 5 to 12% by weight, an unsaturated group-containing monool component content of 0.085 meq/g or less, particularly 0.075 meq/g or less, and an average hydroxyl value of 20. It is a mixed polyoxyalkylene polyol whose main component is polyoxypropylene oxyethylene diol (hereinafter referred to as b) of 40 to 40. Although this polyoxypropylene/oxyethylene diol (b) can be used alone, it is more preferably used in combination with a trivalent or higher polyoxyalkylene polyol (hereinafter referred to as d). In this case as well, the combination of polyoxypropylene/oxyethylene diol (b) and polyoxyalkylene polyol (d) is based on the above-mentioned average number of hydroxyl groups, average oxyethylene group content, average unsaturated group-containing monool component content, and average It is necessary that the hydroxyl value is within the range. In addition, the ratio of polyoxypropylene/oxyethylene triol (a) and polyoxyalkylene polyol (c) is 70 to 70 for the former in mixed polyoxyalkylene polyol.
100% by weight, the latter preferably from 0 to 30% by weight. Similarly, the proportion of the combination of polyoxypropylene/oxyethylene diol (c) and polyoxyalkylene polyol (d) is 60 to 90% by weight of the former.
and the latter preferably in an amount of 10 to 40% by weight. The polyoxyalkylene polyol (c) in the above mixed polyoxyalkylene polyol has its own number of hydroxyl groups, oxyethylene group content, unsaturated monool component content, And the hydroxyl value is not limited. For example, the content of oxyethylene groups in the terminal portion may be as high as about 30% by weight, some or all of the oxyethylene groups may be present in the non-terminal portion, and furthermore, polyoxyethylene containing no oxyethylene groups may be present. It may also be an alkylene polyol. Of course, polyoxypropyleneoxyethylenediol (b) may also be used. A more preferable polyoxyalkylene polyol (c) is polyoxypropylene having a hydroxyl value of 15 to 60 and having an oxyethylene group content of 35% by weight or less, most of which is present at the terminal portion of the oxyalkylene chain.
It is oxyethylene diol. As with the polyoxyalkylene polyol (c), the conditions for the polyoxyalkylene polyol (d) are not particularly limited. However, it is preferable to use polyoxypropylene oxypropylene having a hydroxyl value of 15 to 60 and having a hydroxyl value of 15 to 60 and a valence of 3 or more, especially a valence of 3 to 4. Ethylene polyols, especially polyoxypropylene oxyethylene triols. In addition,
The mixed polyoxyalkylene polyol is 2 above.
It goes without saying that the combination of components is not limited, and a multi-component mixed polyoxyalkylene polyol may be used as long as the above conditions are satisfied. Polyoxyalkylene polyol is produced by adding alkylene oxide to a divalent or higher initiator. The initiator may be a mixture of two or more types of initiators. Initiators include polyhydric alcohols, alkanolamines, mono- or polyamines, polyhydric phenols, and others. Particularly preferred are dihydric to octavalent polyhydric alcohols, particularly divalent to tetrahydric polyhydric alcohols. Examples of initiators include the following compounds. Ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, glycerin, trimethylolpropane, hexanetriol, pentaerythritol, diglycerin,
Dextrose, sorbitol, sucrose, triethanolamine, diethanolamine, ethylenediamine, bisphenol A, bisphenol F The alkylene oxide is preferably an alkylene oxide having 2 to 4 carbon atoms. Further, other epoxides such as halogen-containing alkylene oxide, styrene oxide, glycidyl ether, glycidyl ester, etc. can also be used together with alkylene oxide. As the alkylene oxide, it is essential to use ethylene oxide as described above. The cause of the production of the monool is the use of propylene oxide, and it is thought that the above problem will not occur unless propylene oxide is used, so the use of propylene oxide is also essential. Therefore, as the alkylene oxide, a combination of substantially only two types of propylene oxide and ethylene oxide, or a combination of substantially only three types of propylene oxide, butylene oxide, and ethylene oxide is preferable. Particularly suitable are polyoxyalkylene polyols in which at least 60% by weight, more preferably at least 80% by weight, are oxypropylene groups, and from an economic point of view, the oxyalkylene groups are substantially oxypropylene groups and oxyethylene groups. Preferably, a polyoxyalkylene polyol consisting of only The oxyethylene group at the end portion of a polyoxyalkylene polyol can be obtained by adding ethylene oxide as a final step to a polyoxyalkylene polyol whose end portion is not an oxyethylene group. For the oxyethylene group in the non-terminal part, use an oxyethylene group-containing initiator, and add alkylene oxide to ethylene oxide and alkylene oxide sequentially (addition of ethylene oxide and alkylene oxide in the above final step immediately before addition of ethylene oxide) ), or addition of a mixture of ethylene oxide and other alkylene oxides (ethylene oxide has high reactivity, so it reacts relatively quickly and the terminal part rarely becomes an oxyethylene group), can be introduced into the polyoxyalkylene polyol by a combination of these steps. In addition, the polyoxyalkylene polyol (c) which may have a large amount of oxyethylene groups
In cases such as (d), ethylene oxide is added to the polyoxyalkylene polyol, and then a small amount of alkylene oxide other than ethylene oxide is added to convert some or all of the primary hydroxyl groups originating from the terminal oxyethylene groups into secondary hydroxyl groups. It is also possible to use polyoxyalkylene polyols in which hydroxyl groups have been changed. Of course, polyoxyalkylene polyol
If (c) or (d) does not have an oxyethylene group, addition of ethylene oxide is not necessary,
For example, it can be produced by adding only propylene oxide to the initiator. In the present invention, the production of polyoxyalkylene polyols with low unsaturation-containing monool components involves purification by selecting catalyst components, changing reaction conditions, or removing monool components in the production of ordinary polyoxyalkylene polyols, It can be done in other ways. For example, JP-A-54-30110
Publication No. 1983-44720, Japanese Patent Publication No. 1987-44720
38322, JP 56-43322, U.S. Patent No. 3427256, U.S. Patent No. 3427334, U.S. Patent No. 3427335, U.S. Patent No.
No. 3,393,243 and the like describe a method for producing polyoxyalkylene polyols containing a small amount of unsaturated group-containing monool components. Particularly useful is the selection of catalyst components and the production of polyoxyalkylene polyols under milder reaction conditions than conventional ones. Measurement of unsaturated group-containing monool components is based on JIS K 1557.
(1970) “Polyether journal method for polyurethane”
This is done by measuring the "total unsaturation degree" as described in . In the present invention, the unsaturated group-containing monool component content is used in the same meaning as the total degree of unsaturation. In the present invention, the high molecular weight polyol may consist essentially only of the polyoxyalkylene polyol described above, but may also contain up to 20% by weight of other high molecular weight polyols. Other high molecular weight polyols include high molecular weight polyols other than the polyoxyalkylene polyols mentioned above, such as polyester polyols, polyester ether polyols, polyether polyols such as polyoxytetramethylene polyols produced by methods other than the addition reaction of alkylene oxide, and hydroxyl group polyols. Examples include hydroxyl group-containing hydrocarbon hydroxyl polymers such as polybutadiene. In particular, in order to reduce the water absorption dimensional change rate of the polyurethane ethostomer, it is effective to use a hydroxyl group-containing hydrocarbon polymer, which is a hydrophobic polyol. As the hydroxyl group-containing hydrocarbon polymer, a butadiene homopolymer having hydroxyl groups at both ends, and a butadiene copolymer consisting of a copolymer of butadiene, acrylonitrile, styrene, or other vinyl monomer are suitable. Furthermore, a high molecular weight polyol obtained by adding a small amount of alkylene oxide to this hydroxyl group-containing hydrocarbon polymer may also be used. The chain extender consists of a low molecular weight polyol and/or polyamine compound with a molecular weight of 400 or less. In particular, low molecular weight polyols having a molecular weight of 200 or less are preferred. Suitable low molecular weight polyols include polyhydric alcohols and alkanolamines having 2 or more, especially 2 to 4, hydroxyl groups, and polyols obtained by adding a small amount of alkylene oxide to the above-mentioned polyvalent initiators. Particularly preferred low molecular weight polyols are dihydric alcohols having 2 to 4 carbon atoms. Suitable polyamines are aromatic diamines having alkyl substituents and/or halogens. Preferred specific chain extenders include ethylene glycol, 1,4-butanediol, propylene glycol, diethylene glycol, dipropylene glycol, glycerin, trimethylolpropane, diethanolamine, triethanolamine, and especially ethylene glycol and 1,4-butanediol. -Butanediol is preferred. The amount used is preferably 5 to 40% by weight, particularly 10 to 30% by weight based on the total amount with the high molecular weight polyol. It has been found that the use of a chain extender having an oxyethylene group such as ethylene glycol does not have any adverse effect on the water absorption dimensional change of the polyurethane elastomer. The reason is,
The chain extender reacts with the polyisocyanate compound to form a hard block of polyurethane elastomer, and this hard block has low water absorption even if oxyethylene groups are present, and even if it absorbs water, it is hard. Therefore, it is thought that this will not cause deformation. On the other hand, the oxyethylene group present at the end of the molecular chain of high molecular weight polyol is thought to exist adjacent to this hard block, but unlike the case where it is located within the hard block, the oxyethylene group in this part belonging to the soft block is It is thought that the presence of ethylene groups has a large influence on the change in water absorption dimensions. The polyisocyanate compound includes aromatic, alicyclic, aliphatic, and other polyisocyanate compounds having at least two isocyanate groups, and modified products thereof. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate,
Examples include xylylene diisocyanate, isophorone diisocyanate, methylene-bis(cyclohexyl isocyanate), and hexamethylene diisocyanate. In addition, as modified forms, dimers,
There are trimers, prepolymer type modified products, carbodiimide modified products, urea modified products, and others. Two or more of these polyisocyanate compounds may be used in combination. Particularly preferred polyisocyanate compounds are 4,4'-diphenylmethane diisocyanate,
and its carbodiimide-modified products and prepolymer-type modified products. The amount of polyisocyanate compound used is expressed in isocyanate indelax.
90-120, especially 95-110 is suitable. In the production of polyurethane elastomers using the reaction injection molding method, it is usually essential to use a catalyst in addition to the above-mentioned main raw materials, and it is also preferable to use a blowing agent. Catalysts include various tertiary amine catalysts and organometallic compounds such as organotin compounds, and both may be used alone or in combination. In the present invention, a blowing agent is not necessarily essential, and even without using a blowing agent, a slightly foamed elastomer can be obtained due to the presence of air and water dissolved in the raw material.
Moreover, by sufficiently removing these, a non-foamed elastomer can be obtained. However, it is preferable to use a small amount of blowing agent for reasons such as improving moldability. Air, water, etc. can be used as the blowing agent, but halogenated hydrocarbons with a low boiling point are preferably used. Specifically, trichlorofluoromethane, dichlorodifluoromethane, methylene chloride, etc. are suitable. The amount is 15 parts by weight or less, especially 2 to 100 parts by weight of the high molecular weight polyol and chain extender.
10 parts by weight is appropriate. Furthermore, various additives may be added as optional additive components. Examples include reinforcing fibers, fillers, colorants, ultraviolet absorbers, antioxidants, flame retardants, and internal mold release agents. In particular, blending reinforcing fibers has the effect of lowering the water absorption dimensional change rate. This seems to be to improve the rigidity and strength of the polyurethane elastomer. Suitable reinforcing fibers include glass fibers such as milled fibers, cut fibers, and wollastonite. The amount thereof is approximately 20% by weight or less based on the entire polyurethane elastomer to have a sufficient effect. These additives, including the catalysts and blowing agents mentioned above, are usually added to the polyol component containing the high molecular weight polyol and chain extender. However, additives which are inert towards isocyanate groups can also be added to the isocyanate component. The reaction injection molding method is usually carried out by rapidly mixing the polyol component and the isocyanate component, immediately injecting the mixture into a mold, allowing the mixture to react in the mold, and removing the mixture as a molded product after curing. In some cases, three or more components may be used by dividing the polyol component or isocyanate component into two or more, or by using a third component. Rapid mixing is usually achieved by collisional mixing of each component, and an after-mixing mechanism may be provided in the runner section to perform remixing. The present invention is used for molding exterior parts of automobiles, especially bumper shells. However, the present invention is not limited to this use, and can also be applied to molded products and other uses that require water resistance. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples. Examples and Comparative Examples A mixture of a high molecular weight polyol, a chain extender, etc. listed in Table 1 below was charged into a tank on the polyol component side of a high-pressure foaming machine, and a polyisocyanate compound was charged into a tank on the isocyanate component side. The discharge pressure of the high-pressure foaming machine is 150Kg/ ^cm2 , and the discharge amount is 60-120Kg/
The reaction injection molding was carried out by adjusting the liquid temperature of each component to 30 to 40°C. The size of the mold is 140mm x 120mm x 1400
A mold for forming the outer shell of an automobile bumper with a diameter of 3 mm and an inner thickness of 3 mm was used, and the mold temperature was adjusted to 60 to 70°C. A sample for measuring physical properties was cut out from the obtained molded product, and the physical properties listed in Table 1, including the water absorption dimensional change rate, were measured. The demolding time and physical properties described in Table 1 were measured by the following methods. Demolding time: The time from the completion of injection until the mold can be demolded (the molded product can be demolded without cracking, etc.). Density: method by water or alcohol displacement.
(ASTM-D792) Water absorption dimensional change rate: Molded product sample (100 x 200 x 3
mm) is boiled at 100°C for 3 hours.
The water absorption dimensional change rate, ΔL, where t is the length after immersion for 240 hours, is given by the following formula. ΔL=t-to/to×100 Flexural modulus: Based on ASTM-D790 method. Tensile strength: According to JIS-K6301, dumbbell No. 2. Elongation: According to JIS-K6301 dumbbell No. 2. The raw materials used were as follows. Polyoxyalkylene polyols The following polyols A to G are polyoxypropylene/oxyethylene polyols that have oxyethylene groups only at the ends, and their number of hydroxyl groups, oxyethylene group content, unsaturated monool content, and hydroxyl value are It is as follows.

[Table] The mixed polyoxyalkylene polyol used in the Examples and Comparative Examples is a mixture of the above polyols, and its composition ratio (weight) and average number of hydroxyl groups, etc. are shown below as in the above.

[Table] Other high molecular weight polyols PBd: Polybutadiene glycol polyisocyanate compound with an average molecular weight of approximately 3000 [The amount used is the amount that gives an isocyanate index of 105] Polyisocyanate A: Carbodiimide-modified diphenylmethane diisocyanate (NCO content 28.5%) Polyisocyanate B: Prepolymer type modified diphenylmethane diisocyanate (NCO content 26%) Other raw materials EG: Ethylene glycol Catalyst A: Triethylenediamine solution (trade name;
DABCO 33LV) Catalyst B: Dibutyltin dilaurate R-11: Trichlorofluoromethane MFB: Milled glass fiber with an average length of about 0.15 mm

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Claims (1)

[Claims] 1. A non-foamed or microcellular product made by reaction injection molding using at least two components: a polyol component containing a high molecular weight polyol and a chain extender as essential components, and an isocyanate component containing a polyisocyanate compound as an essential component. In a method for producing a polyurethane elastomer by reaction injection molding to produce a polyurethane elastomer molded article, substantially the entire amount or at least 80% by weight of the high molecular weight polyol consists of a polyoxyalkylene polyol, and the polyoxyalkylene polyol has an average The number of hydroxyl groups is 2.1 to 3.5, the average oxyethylene group content is less than 15% by weight, and at least 5% by weight of the terminal portion of the oxyalkylene chain is present, the average unsaturated group-containing monool component content is 0.085 neq/g or less , and average hydroxyl value 20-40
A method for producing a polyurethane elastomer by a reaction injection molding method, characterized in that polyoxyalkylene polyols are used alone or as a mixture of polyoxyalkylene polyols. 2 In the polyoxyalkylene polyol, substantially all of the oxyethylene groups are present at the terminal portion of the oxyalkylene chain, the oxyethylene group content is less than 10% by weight, and the content of unsaturated group-containing monool components is 0.085 meq/g or less , and polyoxypropylene/oxyethylene triol with a hydroxyl value of 20 to 40
70-100% by weight and 0-30% by weight of other polyoxypropylene/oxyethylene polyols. 3 In the polyoxyalkylene polyol, substantially all oxyethylene groups are present at the terminal portions of the oxyalkylene chains, the oxyethylene group content is 5 to 12% by weight, and the unsaturated group content monool component content is 0.085 meq/g Polyoxypropylene/oxyethylene diol 60 below and with a hydroxyl value of 20 to 40
~90% by weight of trivalent or higher polyoxypropylene
A method according to claim 1, characterized in that it consists of 10 to 40% by weight of oxyethylene polyol.