JPH0433288B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a urethane prepolymer capable of forming a urethane elastomer having high hardness and a high coefficient of friction, which is used, for example, in belts, rollers, sheets, and various molded products, and the urethane prepolymer. It relates to a urethane elastomer obtained by curing a polymer. (Prior Art) Polyurethane molded bodies such as belts, rollers, sheets, and various molded products are required to have various properties such as mechanical properties, abrasion resistance, and oil resistance. In particular, one of the above characteristics, the coefficient of friction, is particularly important for belts. For example, in a flat belt that mainly uses friction transmission, if the coefficient of friction is small, the friction between the pulley attached to the bearing and the flat belt is small, and the tension of the flat belt is required to obtain the transmission force. In order to maintain a large tension, the belt thickness must be increased.
Moreover, if the tension of the flat belt is increased, there is a drawback that the bearing loss of the bearing section increases. In addition, when used as a conveyor belt, if the friction coefficient of the belt surface is around 0.6, the conveyed object placed on the belt will easily slip, so the maximum tilt angle that can be conveyed can only be increased to around 20 degrees. There are drawbacks. Furthermore, when used as a transmission belt, the friction coefficient usually decreases over time during use, so if the friction coefficient is low before use, there is a risk that power transmission will deteriorate in practice. This has the disadvantage that the reliability of the belt decreases. The present inventors conducted research on a method for manufacturing a urethane elastomer suitable for the above-mentioned belt. A urethane prepolymer obtained by reacting tolylene diisocyanate and polytetramethylene ether glycol as raw materials,
For example, MOCA (4,4'-methylenebis-2-chloroaniline; manufactured by Dupont), which is a type of curing agent.
We investigated a method of producing urethane elastomer by curing the urethane elastomer. The urethane elastomer obtained by the above method was satisfactory as a urethane elastomer for belts in terms of properties such as abrasion resistance, oil resistance, hardness, tensile strength, tear strength, and elongation at break. Its coefficient of friction was as low as 0.6 to 0.7, making it unsatisfactory as a material for belts. Therefore, the inventors investigated the friction coefficient of urethane elastomer using methods proposed in the past.
For example, a method using high molecular weight polytetramethylene ether glycol as a starting material,
We investigated methods of reacting tolylene diisocyanate and polytetramethylene ether glycol by reducing the NCO/OH value, and methods of using curing agents such as 1,4-butanediol, trimethylolpropane, and isopropanolamine. . (Problems to be Solved by the Invention) However, in the above method, the hardness of the elastomer obtained by curing is low, and the friction coefficient of the obtained urethane elastomer is high, but the tensile strength, tear strength, etc. of the urethane elastomer are low. This resulted in a decrease in physical properties. Furthermore, in order to increase the friction coefficient of urethane elastomers, other polymers with high friction coefficients or adhesive additives are added to the urethane prepolymer, which results in a decrease in the inherent wear resistance of polyurethane. It became. The present invention solves the above-mentioned drawbacks, and its purpose is to provide polyurethane with a high coefficient of friction without deteriorating its inherent physical properties such as tensile strength, tear strength, hardness, and abrasion resistance. The object of the present invention is to provide a urethane prepolymer capable of forming a urethane elastomer, and a urethane elastomer obtained by curing this urethane prepolymer. (Means for Solving the Problems) The urethane prepolymer of the present invention is a urethane prepolymer obtained by reacting a polyol component and tolylene diisocyanate, wherein the polyol component is a polyester having an average molecular weight of 650 to 1100. Component A, which is tetramethylene ether glycol, has an average molecular weight of 300% higher than the molecular weight of component A.
and B component which is polytetramethylene ether glycol having a molecular weight of 50:50 to 25:75, and the weight ratio of the A component and B component is from 50:50 to 25:75, thereby achieving the above purpose. be done. The urethane elastomer of the present invention is obtained by curing the urethane prepolymer described above, thereby achieving the above object. The polyol component, which is the raw material for the urethane prepolymer of the present invention, consists of a relatively low molecular weight component A and a high molecular weight component B. The average molecular weight of component A is
650 to 1100, and the average molecular weight of component B is 300 or more larger than the molecular weight of component A used above.
and ranges up to 2100. The weight ratio of component A to component B is from 50:50 to 25:75. By using such polytetramethylene ether glycol, the friction coefficient of the urethane elastomer finally obtained becomes high. When the molecular weights of component A and component B and their weight ratio are outside the above range, the coefficient of friction decreases. The blending ratio of the polyol component and tolylene diisocyanate is such that the NOC/OH value of the mixture is 1.4.
It is preferable to set it to about 1.8.
The hardness of the urethane elastomer obtained by curing depends on the amount of tolylene diisocyanate charged during prepolymer preparation and the NOC/OH value of the mixture. The hardness of the obtained urethane elastomer is low, and when the NOC/OH value exceeds 1.8, a molded article with high hardness exceeding JIS hardness A93 can be obtained. The reaction between the polyol component and tolylene diisocyanate can be carried out by a conventional method, and a catalyst may be added if necessary. To obtain a urethane elastomer by curing the urethane prepolymer thus obtained,
This can be carried out by a conventional method using a general curing agent for urethane. The curing agent is e.g. MOCA
(4,4'-methylenebis-(2-chloroaniline); manufactured by DuPont), 4,4'-methylene dianiline, 3,3'-dichlorobenzidine, 4,4'-diaminodiphenyl ether, etc. Group diamines, as well as curing accelerators such as triethylene diamine, diethylene triamine, dibutyltin dilaurate, stannath octoate, cobalt naphthenate, lead naphthenate, adipic acid, etc., can be used in combination.MOCA is particularly useful for urethane elastomers. This is preferable in terms of improving mechanical properties and the like. For example, when producing a flat belt from the urethane prepolymer obtained in this way, the first
This can be carried out by a casting method using a mold 1 as shown in the figure. In the figure, 11 is an inner mold of the cylindrical mold 1, 12 is an outer mold disposed outside the inner mold 11 with a gap, and the outer mold 12 is configured to be divisible, and the inner mold It can be removed from the outside of 11 as appropriate. A molding space 13 is formed between the inner mold 11 and the outer mold 12. An inlet 14 is provided on one side of the lower part of the space 13, and a deaeration port 15 to which a deaeration valve 16 is attached is provided on the other side of the upper part of the space 13. The supply pipe 1 is connected to the inlet 14.
7 is fitted, and the supply pipe 17
A reactor 18 equipped with a lid 18a is connected to the other end. In manufacturing a flat belt, first, the urethane prepolymer is heated in advance to 70 to 90°C, preferably 80°C, while the curing agent is heated to 120°C. A predetermined amount of the urethane prepolymer, a curing agent, and a catalyst if necessary are added, and after stirring and mixing these and degassing if necessary, the mixture is placed in the reactor 18, and the lid 18a is moved downward. By pressing and moving, the whole is 80
The mixture is poured into the mold 1 heated to ~120°C.
Thereafter, the urethane prepolymer is cured and molded under predetermined conditions such as temperature, time, and pressure to obtain a flat belt. For molding the urethane elastomer, since the urethane prepolymer is liquid, the casting method is generally convenient as described above, but centrifugal molding, pressure molding, etc. can also be used. Moreover, the urethane elastomer can also be applied to various rollers, sheets, molded products, etc. (Examples 1 to 6 and Comparative Examples 1 to 4) The present invention will be described in detail below based on Examples. <Preparation of urethane prepolymer> Component A and B of polytetramethylene ether glycol and component 2,
The amount (g) of 4-tolylene diisocyanate shown in Table 1 was added and mixed, and the mixture was reacted at 80° C. for the predetermined time shown in Table 1 under a nitrogen stream to obtain a urethane prepolymer. of the obtained urethane prepolymer
Table 1 shows the measurement results of NCO (%) and viscosity (cps/80°C). <Formation of cured product> Next, 400 g of the urethane prepolymer obtained as described above was heated, and the amount (g) of hardening agent MOCA shown in Table 1 was melted at 120°C and the two were mixed. , injected into a mold heated to 100℃, and heated to 16℃ at 100℃.
A sheet-like cured product was obtained by curing for a period of time. Using this sheet-shaped cured product, friction coefficient, abrasion resistance, hardness, tensile strength, tear strength, and elongation at break were measured. Separately, NCO of commercially available urethane prepolymer (trade name Takenate L-2705, Takeda Pharmaceutical Company Limited)
(%), and various physical properties of a sheet-like cured product obtained by curing this urethane prepolymer in the same manner as in the above example were also measured. The results of these measurements are shown in Table 1. The friction coefficient of urethane elastomer was measured using a Shimadzu tensile tester DSS-500.
It was calculated by measuring the sliding friction force. To explain the configuration of the testing machine, as shown in Fig. 2, the top surface of a fixed base 21 is covered with a stainless steel sliding face plate 22. The cut sample 23 of the cured material is mounted. 400g on the top surface of this sample 23
A load 24 of 24 is placed thereon. One end of a wire 25 is connected to the sample 23, and the wire 25 is extended upward by a pulley 26, and the other end is connected to a crosshead 27 which is movable upward at a set speed. A recording device 28 is connected to the crosshead 27 so that the frictional force acting on the crosshead 27 can be automatically recorded. Move this crosshead 27 at the set speed (50mm/
By moving sample 23 upward at
is moved while sliding its lower surface against the sliding face plate 22, and the frictional force at that time is applied to the crosshead 2.
7, and this frictional force is measured by the recording device 28. The measurement was performed three times for each sample, and the average frictional force was determined. The total load is the total weight of the sample 23 and the load 24, and is expressed by the formula:
The friction coefficient was calculated from friction coefficient x total load = friction force.

[Table] As shown in Table 1, the urethane prepolymers of Comparative Examples 1 to 3 were obtained by reacting polyol components in which the ratio of component A and component B exceeds the range of the present invention, and the resulting urethane prepolymers were It can be seen that the physical properties of the elastomer are that it has a low coefficient of friction. Furthermore, it can be seen that the urethane elastomer obtained by curing a commercially available urethane prepolymer also has a low coefficient of friction.
In contrast, the urethane elastomers obtained in Examples 1 to 6 have high friction coefficients without deteriorating other physical properties such as wear resistance, hardness, tensile strength, tear strength, and elongation at break. It can be seen that In addition, the hardness of each example is suitable for the belt.
It was JIS A75-93. NCO/ of each of the above examples
The OH value is approximately 1.4 to 1.8, and the OH value is approximately 1.4 to 1.8.
The NCO/OH value was 1.6. (Examples 7 and 8, Comparative Example 5) <Preparation of belt> The urethane prepolymers obtained in Examples 2 and 3 and Comparative Example 2 shown in Table 1 and a prescribed amount of curing agent
A flat belt was produced using MOCA and a mold 1 as shown in FIG. 1 in the following manner. The degassing valve 16 of the mold 1 is opened, and the reactor 18 is opened.
Then, a mixture of urethane prepolymer and curing agent is injected or pressurized into the mold 1 through the injection port 14. When a small amount of urethane prepolymer leaks out from the degassing port 15, the degassing valve 16 is closed and the lid 18a is pressed to further apply a higher pressure to the inlet 14 than during injection, and in this state, the prepolymer is heated to a specified temperature. The urethane prepolymer is cured under a predetermined pressure. Thereafter, the outer mold 12 was removed, the cylindrical cured product was taken out from the space 13 of the mold 1, and the cylindrical cured product was cut in the circumferential direction to obtain a belt having a desired width. In addition, Example 7 uses the urethane prepolymer of Example 2, Example 8 uses the urethane prepolymer of Example 3, and Comparative Example 5 uses the urethane prepolymer of Comparative Example 2. shall be. Next, a bending resistance test was conducted on each of the obtained belts, and the transmission force and friction coefficient before and after the test were measured. The results are shown in Table 2.

[Table] From the results in Table 2, it was confirmed that the belt made using the urethane prepolymer obtained in the example of the present invention had a high coefficient of friction and therefore a high retention rate of transmission force. It is known that when the coefficient of friction is high, for example, when it exceeds 1.0, the transmitted force increases rapidly. (Effects of the Invention) As described above, according to the present invention, a urethane prepolymer that can produce a urethane elastomer having a high coefficient of friction without reducing physical properties such as tensile strength, tear strength, hardness, and abrasion resistance. was gotten. Therefore, belts, rollers, and sheets are obtained as molded articles obtained by curing this urethane prepolymer, and among these, belts in particular have the following advantages. That is, by increasing the friction coefficient of the belt, the transmission force can be increased without increasing the tension of the friction-conducting belt. Therefore,
Since belt tension can be reduced while maintaining a specified transmission force, bearing loss is also reduced, and belt thickness can also be reduced, increasing transmission efficiency and reducing the energy required for power transmission. It is more economical. When used as a conveyor belt, conventional belts have a small coefficient of friction of around 0.6, so taking into account the slippage of conveyed objects, the maximum angle of inclination that can be conveyed is 20.
However, with the urethane elastomer of the present invention, it is possible to achieve a high friction coefficient of 1.0 or more, and therefore it is also possible to convey at an inclination angle of 30 degrees or more. It becomes possible. When used as a transmission belt, conventionally, because the absolute value of the friction coefficient at the time of manufacturing is low,
When the friction coefficient of the belt decreases with use, the transmission force decreases below a practically usable value, and the reliability of the flat belt product does not increase. However, since the urethane elastomer of the present invention has a high absolute value of the friction coefficient at the time of manufacture, even if the friction coefficient decreases to some extent due to use, no problem will arise in practice. Furthermore, the urethane prepolymer of the present invention uses two types of components A and B having different average molecular weights of polytetramethylene ether glycol,
Since it is obtained by reacting a polyol component with a set blending ratio of component B and tolylene diisocyanate, conventional manufacturing equipment can be used as is without major modification of the existing manufacturing equipment. No additional equipment costs are required.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a belt manufacturing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic view showing a friction coefficient measurement tester same as above.

Claims (1)

[Claims] 1. A method for producing a urethane elastomer, in which a urethane prepolymer obtained by reacting a polyol component and tolylene diisocyanate with an NCO/OH value in the range of 1.4 to 1.8 is cured using a curing agent. and the polyol component has an average molecular weight of 650 to 1100.
component A, which is polytetramethylene ether glycol, and component B, which is polytetramethylene ether glycol, whose average molecular weight is 300 or more larger than the molecular weight of component A, and up to 2100; Weight ratio of 50:50 to 25:75
A method for producing a urethane elastomer.