JP4629386B2 - Method for producing thermoplastic polyurethane tube - Google Patents

Description

The present invention relates to a method for producing a thermoplastic polyurethane tube having particularly improved fracture stress at high temperatures.

  Thermoplastic polyurethane tubes are flexible and convenient, and can be easily obtained by molding processes such as extrusion as with ordinary thermoplastic resins, so they are widely used for pneumatic tubes. ing. Thermoplastic polyurethane is generally produced using polyol, diisocyanate and low molecular diol as chain extender as raw materials, and a hard segment formed from diisocyanate and low molecular diol and a soft segment formed from polyol. One segment gives a high strength and flexible elastomer.

  Patent Document 1 describes a method for producing a thermoplastic polyurethane tube in which thermoplastic polyurethane is extruded at a specific preheating temperature and extrusion pressure.

  However, since ordinary thermoplastic polyurethane tubes have poor heat resistance, the usable temperature is limited, and in particular, they cannot be used for applications where the working pressure at high temperatures is high. For this reason, conventionally, nylon tubes are mainly used at high temperatures, but nylon tubes have high rigidity and poor flexibility.

In order to improve thermal properties such as heat resistance, various attempts have been made to change the molecular structure of the hard segment or soft segment of thermoplastic polyurethane (see, for example, Patent Document 2 below). However, since this method modifies the molecular structure of the thermoplastic polyurethane itself, the physical properties of the tube such as flexibility may be adversely affected.
JP-A-7-136278 Japanese Patent Laid-Open No. 7-113004

The subject of this invention is providing the manufacturing method of the thermoplastic polyurethane tube which heat resistance improved and enabled use at high temperature.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors succeeded in obtaining a thermoplastic polyurethane tube having improved heat resistance without impairing flexibility, and completed the present invention. .

That is, the method for producing a thermoplastic polyurethane tube according to the present invention comprises a molded product of a polyol, a low molecular weight diol, and a diisocyanate. The molded product that has been melt-molded and cooled and solidified at a temperature higher than the flow start temperature Tm A hard segment formed from diisocyanate at a temperature T2 below a temperature Tm and heated to a temperature T1 above the glass transition point Tg and then quickly lowered to a temperature T2 (where Tm>T1>T2>Tg); after the time structure in which a soft segment formed from a polyol and phase separation occurs is retained until after, characterized by cooling.

The thermoplastic polyurethane tube obtained by the present invention has an excellent characteristic not found in a nylon tube that is flexible, and it cannot be obtained by a conventional polyurethane tube that has a tube breaking stress at 80 ° C. of 3.6 MPa or more. Since it has a thermal property close to that of a nylon tube, there is an effect that it can be used at a high temperature where a thermoplastic polyurethane tube could not be used.

  The thermoplastic polyurethane used in the present invention is an addition polymer of a polyol having a molecular weight of 500 to 4000, a low molecular weight diol having a molecular weight of 500 or less, and a diisocyanate. Examples of the polyol include polyether polyols such as polyoxyalkylene polyol (PPG), modified polyether polyol, polytetramethylene ether glycol (PTMG); condensed polyester polyol (for example, adipate polyol), lactone polyester polyol, polycarbonate Examples include polyester polyols such as diols; acrylic polyols, polybutadiene-based polyols, polyolefin-based polyols, saponified EVA, flame-retardant polyols (phosphorus-containing polyols and halogen-containing polyols), and the like.

Examples of the diisocyanate include aromatic diisocyanates such as tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate (PPDI), and naphthylene diisocyanate (NDI), and hexamethylene diisocyanate (HDI). And aliphatic diisocyanates such as dicyclohexylmethane diisocyanate (HMDI) and isophorone diisocyanate (IPDI).
The low molecular weight diol is used as a chain extender, and examples thereof include 1,4-butanediol and bis (hydroxyethyl) hydroquinone.

  In the present invention, it is preferable to use a general-purpose thermoplastic polyurethane conventionally used for various applications as a thermoplastic elastomer. As a specific example, for example, a hard segment formed from 4,4′-diphenylmethane diisocyanate And a thermoplastic polyurethane comprising a soft segment formed from a polyol. The thermoplastic polyurethane may have a weight average molecular weight of about 100,000 to 1,000,000 and a number average molecular weight of about 20,000 to 100,000.

  The plastic polyurethane tube of the present invention has a difference between the temperature at which LogE ′ is 4.5 MPa and the peak temperature of tan δ in the dynamic viscoelasticity measurement from 190 to 225 ° C., preferably from 205 to 220 ° C. The difference is larger than that of the plastic polyurethane tube. This indicates that the higher-order structure or phase structure composed of the hard segment and soft segment of the thermoplastic polyurethane tube has changed as described above, and specifically, that the phase separation structure has occurred. Show. This improves the thermal properties of the molded product.

  In order to generate such a phase-separated structure, a thermoplastic polyurethane is melt-extruded at a temperature Tx equal to or higher than the flow start temperature Tm by a normal method to produce a tube. As shown in FIG. 1, the obtained thermoplastic polyurethane tube is heated to a temperature T1 that is equal to or lower than the flow start temperature Tm and is equal to or higher than the glass transition point Tg, and is then quickly dropped to a temperature T2 that is equal to or higher than the glass transition point Tg After holding until the time when the phase separation structure is formed, it is cooled to room temperature. The flow start temperature is such that when a constant load (usually 10 kg) is applied to the resin using a flow tester and the temperature is raised, the resin starts to flow out from the nozzle (usually 1 mm in diameter x 1 mm in length). It is determined by measuring the temperature.

  The temperature Tx may be a temperature at which the thermoplastic polyurethane can be melt-molded at a flow start temperature Tm or higher, and is usually 200 to 240 ° C. The melt molding means of the tube is not particularly limited, and melt extrusion molding can be mentioned. Further, the shape and size of the tube to be molded are not particularly limited, but generally a tube having an outer diameter of 3 to 16 mm and a wall thickness of 0.5 to 2 mm is exemplified.

  The temperature T1 is in the range of 175 to 190 ° C. If the temperature T1 is out of this range, the higher-order structure of the molded product may not be controlled. The holding time at the temperature T1 is 5 to 90 seconds, preferably 10 to 60 seconds.

  On the other hand, the temperature T2 is in the range of 155 to 165 ° C. If the temperature T2 is out of this range, the higher-order structure of the molded product may not be controlled. The holding time at the temperature T2 is at least until the time when the phase separation structure occurs, and is usually 30 seconds or longer, preferably 1 minute or longer. The upper limit of the holding time at the temperature T2 is not particularly limited, but is suitably 60 minutes or less.

  In the present invention, it is important to quickly drop the temperature from the temperature T1 to the temperature T2. If the temperature is not quickly lowered, the higher-order structure of the tube may not be controlled. After holding at temperature T2 for a predetermined time, it may be gradually cooled to room temperature or may be rapidly cooled. Here, the temperature drop from the temperature T1 to the temperature T2 is preferably a cooling rate of about 50 to 1000 ° C./min.

  In addition, the present invention requires uniform structure control with no unevenness throughout the tube, and in particular, if the temperature is uneven, the phase separation structure does not appear in a part of the tube, so the thermal properties at high temperatures can be improved. There is a risk of disappearing. An example of a structure control apparatus usable in the present invention is shown in FIG. As shown in the figure, the polyurethane tube 2 is heated by disposing a plurality of infrared heaters 1 in the circumferential direction of the polyurethane tube 2.

  As the infrared heater 1, any of a far infrared heater, a middle infrared heater, and a near infrared heater can be used. Here, although the mid-infrared heater is not as much as the near-infrared heater, it has high energy at a narrow wavelength and has high absorbability to plastic, so that precise heating is possible in a short time.

  The number of infrared heaters 1 arranged in the circumferential direction of the tube 2 is not particularly limited, but is suitably about 2 to 10 pieces. The infrared heater 1 is preferably arranged such that its length direction is parallel to the axial direction of the tube 2. Each infrared heater 1 is installed inside the reflector 3.

  In order to uniformly heat the polyurethane tube 2, it is preferable that the infrared heater 1 and the polyurethane tube 2 are relatively moved in the circumferential direction of the tube 2. Specifically, the infrared heater 1 or the polyurethane tube 2 is rotated in the circumferential direction of the tube 2. Thereby, it comes to be heated uniformly in the circumferential direction. The rotation speed is not particularly limited, but it is preferably about 10 to 300 rotations / minute for uniform heating.

  When processing a long polyurethane tube 2, for example, the infrared heater 1 is rotated in the circumferential direction of the tube 2 while moving the tube 2 or the infrared heater 1 surrounding the tube 2 at a constant speed in the length direction of the tube 2. You can do it.

  FIG. 3 shows an outline of a structure control device for a thermoplastic polyurethane tube. As shown in FIG. 3, this apparatus continuously draws the wound tube 2 with a take-up machine 4, and heats the polyurethane tube 2 to a temperature T1, and a first infrared heater heating area A, and the tube 2 to a temperature T2. A temperature drop region B that lowers the temperature to 2 °, a second infrared heater heating region C that heats the tube 2 to a temperature T2, and a cooling means D are arranged along the drawing direction of the tube 2.

  In the first infrared heater heating area A and the second infrared heater heating area C, a plurality of infrared heaters 1 are arranged in the circumferential direction of the tube 2 as shown in FIG. The temperature adjustment in each heating area A, C can be performed by adjusting the output of each infrared heater. The passage time of the tube 2 in each heating region A, C can be determined from the holding time of the tube 2 at each temperature T1, T2 and the length of each heating region A, C.

In the temperature drop region B, the temperature of the tube 2 is quickly lowered from the temperature T1 to T2 or the vicinity thereof by, for example, blowing cool air to the tube 2. The cooling means D is composed of, for example, a cooling water tank or the like, and cools the tube 2 to near room temperature. It is preferable that the temperature drop to the temperature T2 is performed uniformly over the entire circumferential direction of the tube.
The first infrared heater heating area A and the second infrared heater heating area C may be provided side by side without providing the temperature drop area B.
Further, the tube 2 is cooled while being extruded (for example, immersed in a water tank), and the first infrared heater heating area A, temperature drop area B, second infrared heater heating area C, and cooling means D are described. Heat treatment may be performed in the order of temperatures T1 and T2 and cooling by sequentially passing in order.

  In the thermoplastic polyurethane tube 2 of the present invention thus obtained, the peak temperature (that is, Tg) of tan δ in the dynamic viscoelasticity measurement is lower than that obtained by heating, melting, and solidifying ordinary thermoplastic polyurethane. 20-10 ° C. On the other hand, the temperature at which the Log E ′ becomes 4.5 MPa rises to 190 to 210 ° C. as compared with a temperature obtained by heating and melting ordinary thermoplastic polyurethane. As a result, as described above, the difference between the temperature at which LogE ′ becomes 4.5 MPa and the peak temperature of tan δ is 190 to 225 ° C.

As a result, thermoplastic polyurethane tube of the present invention is not impaired flexibility at room temperature, the tube breaking stress at 80 ° C. is more than 3.6M P a, improves working pressure at high temperature, further heat And cold resistance are also improved. By the way, the thermoplastic polyurethane tube of the present invention has substantially the same tube breaking stress at room temperature as a normal thermoplastic polyurethane tube.

  The thermoplastic polyurethane tube of the present invention whose structure is controlled as described above has almost the same properties as ordinary thermoplastic polyurethane tubes in mechanical properties and the like, in addition to the advantage that the breaking strength at high temperature is improved.

  In the above description, the infrared heater is used as the structure control means for manufacturing the thermoplastic polyurethane tube of the present invention, but the present invention is not limited to this. For example, (1) a heating furnace (hot air dryer or the like) having a temperature T1 and a heating furnace having a temperature T2 are arranged and the tubes are passed in this order. (2) A hollow metal tube is inserted into the tube, and the temperature T1 and The thermoplastic polyurethane tube of the present invention with improved breaking strength at high temperatures can also be obtained by passing two heating media (oil or the like) heated to T2 in this order.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited only to a following example.

[Reference example]
<Manufacture of thermoplastic polyurethane tube>
As the thermoplastic polyurethane, “Milactolane E394” manufactured by Nippon Polyurethane Co., Ltd. (flow start temperature Tm: about 190 ° C., glass transition point: about 0 ° C.) was used. This polyurethane uses MDI for the hard segment, PTMG for the soft segment, and 1,4-butanediol as the chain extender. This thermoplastic polyurethane was extruded, cooled to around room temperature, and solidified to obtain a thermoplastic polyurethane tube having an outer diameter of 8 mm and a wall thickness of 1.5 mm.

A near-infrared heater having a heater length of 80 mm is disposed as shown in FIG. 2, and the tube 2 obtained in the reference example is disposed in the center, and this is rotated at 200 rpm to heat the entire tube 2. . The temperature of each near infrared heater was adjusted by adjusting the output to the heater. That is, a thermocouple was installed on the surface of the tube 2, the temperature was measured, and the output of the heater was adjusted based on the data.
The structure of the tube 2 was controlled using the above apparatus. That is, the tube 2 was heated at 180 ° C. for 30 seconds, and then the heater output was quickly changed and heated at 160 ° C. for 180 seconds. At this time, the tube 2 was not deformed by heating.

(Optical microscope observation)
After slicing the tube surface to a thickness of 0.1 mm using a microtome, observation with a polarizing optical microscope was performed. As a result, a structure in which the hard segment and the soft segment are microphase-separated appears in the tube 2 subjected to the structure control process.

(Measurement of fracture stress at 80 ° C)
The breaking stress of the tube was measured by a tube breaking test using the apparatus shown in FIG. That is, as shown in FIG. 4, one end of the tube 5 was closed with a stopper 6, the other end was connected to a water supply port 7, and immersed in 80 ° C. warm water 8 placed in a water tank. After leaving in this state for 5 minutes, hot water at 80 ° C. is injected into the tube 5 from the water supply port 7 to apply water pressure (pressure increase rate: 0.12 MPa / second), and the pressure at which the tube 5 is broken is taken as the breaking pressure. The fracture stress was determined from the measurement according to the following formula.

  As a result, the fracture stress of the non-structure-controlled tube (control) was 2.89 MPa, whereas the fracture stress of the structure-controlled tube was improved to 3.60 MPa (approximately 24.6% strength). Improvement).

(Measurement of fracture stress at room temperature)
Fracture stress was measured in the same manner as in the case of 80 ° C., except that water at a temperature of 23 ° C. was placed in a water tank and the tube was immersed therein. As a result, the fracture stress of the tube without structure control (control) was 8.7 MPa, whereas the fracture stress of the tube with structure control was 8.9 MPa.

(Wide-angle X-ray (WAXD) measurement)
Wide-angle X-ray measurement was performed on the structure-controlled polyurethane tube obtained in Example 1 and the non-structure-controlled tube (control). The measurement was performed using “RNT-2000” manufactured by Rigaku Corporation under the conditions of a measurement range 2θ = 10 ° to 30 ° and a measurement rate of 0.2 °. The measurement results are shown in FIG. FIG. 5 shows that the polyurethane tube obtained in Example 1 has a high crystallinity.

(Dynamic viscoelasticity (DMS) measurement)
The dynamic viscoelasticity of the structure-controlled polyurethane tube obtained in Example 1 and the non-structure-controlled tube (control) were measured. The measurement conditions are as follows.
Measuring device: “DMS6100” manufactured by SII
Temperature condition: -100 ° C to + 250 ° C
Temperature increase rate: 5 ° C / min Measurement frequency: 1Hz
Sample size: width 5mm x length 20mm
The measurement results are shown in FIG. As apparent from FIG. 6, the increase in the drop temperature of LogE ′ and the decrease in the peak temperature of tan δ were observed in the tube of Example 1 as compared with the control tube without structure control. This indicates that the heat resistance and cold resistance of the polyurethane tube are improved.

(mechanical nature)
Using a polyurethane sheet (thickness 0.33 mm, width 5 mm) having the same composition as the above tube, heat it at 180 ° C. for 30 seconds as above, then quickly change the heater output and heat at 160 ° C. for 180 seconds. Structure control was performed.
The tensile strength at room temperature of the obtained sheet was measured according to JIS K 7161. As a control, a tensile strength was measured in the same manner using a polyurethane sheet which was not subjected to structural control. The result is shown in FIG. From the figure, it was found that the tube of Example 1 did not deteriorate in mechanical properties and had almost the same tensile strength as the control.

表１から明らかなように、構造制御した実施例１のウレタンチューブは対照チューブとキング半径がほぼ同等であるのに対して、ナイロンサンプルはキンク半径が大きく、柔軟性に劣っている。従って、構造制御ウレタンチューブはナイロンチューブと比べて、室温での柔軟性に優れていることがわかる。 (Flexibility)
The flexibility (bending strength) of the polyurethane tube obtained in Example 1 at room temperature was measured by the method shown in FIG. That is, in the measuring apparatus shown in FIG. 8, the tube 10 as a sample is bent and sandwiched between the two plates 11 and 12. The plates 11 and 12 are held on the rail 13 and are movable along the rail 13. A load cell 14 for measuring the stress when the tube is bent is located on the back side of the plate 12.
In this state, the plate 11 is slowly moved at a constant speed in the direction indicated by the arrow to measure the bending width and stress when the tube is bent. The point of maximum stress is the kink point of the tube, and half of the bending width at that time is the kink radius of the tube. In addition, the temperature at the time of a measurement is 23 degreeC, and the size of the tube 10 used for the test is 6 mm in outer diameter, 4 mm in inner diameter, and 220 mm in length.
For comparison, the same test was performed using a polyurethane tube (control) and a nylon tube (raw resin: nylon 6) that were not subjected to structural control. The results are shown in Table 1.

As is apparent from Table 1, the urethane tube of Example 1 with a controlled structure has a king radius almost equal to that of the control tube, whereas the nylon sample has a large kink radius and is inferior in flexibility. Therefore, it can be seen that the structure-controlled urethane tube is superior in flexibility at room temperature as compared with the nylon tube.

チューブには加熱による変形は認められなかった。また、実施例１と同様にして偏光光学顕微鏡観察を行なった結果、構造制御されたチューブには、ハードセグメントとソフトセグメントとがミクロ相分離した構造が出現していた。
さらに、８０℃での破壊応力を実施例１と同様にして測定した。その結果を表２に示す。表２から、構造制御されたチューブはいずれも対照に比べて、高い破壊応力を有していることがわかる。
As shown in FIG. 9, near-infrared heaters 51 and 52 having a heater length of 100 mm were arranged to face each other, and the tube 2 obtained in the reference example was arranged in the center between them. The outputs of the near infrared heaters 51 and 52 were made constant (300 ° C.), and the distances between the heaters 51 and 52 and the tube 2 were adjusted so that the surface of the tube 2 became a temperature necessary for structural control. That is, thermocouples 61 and 62 were installed on the surface of the tube 2, the temperature was measured, and the distance from the heater was adjusted based on the data. And the tube 2 was rotated at 200 rpm, and the whole tube 2 was heated.
The structure of the tube 2 was controlled using the above apparatus. That is, the tube 2 was heated at 180 ° C. for a predetermined time under the conditions shown in Table 2, and then the temperature was quickly changed to 160 ° C. and heated for a predetermined time.

The tube was not deformed by heating. Moreover, as a result of conducting the polarization optical microscope observation in the same manner as in Example 1, a structure in which the hard segment and the soft segment were microphase separated appeared in the structure-controlled tube.
Further, the breaking stress at 80 ° C. was measured in the same manner as in Example 1. The results are shown in Table 2 . From Table 2 , it can be seen that all the structurally controlled tubes have higher fracture stresses than the control.

It is a graph which shows the temperature control conditions in this invention. It is a top view which shows the outline of the apparatus for implementing temperature control. It is the schematic of a continuous temperature control apparatus. It is the schematic which shows a fracture stress measuring method. 2 is a graph showing wide-angle X-ray (WAXD) measurement results of Example 1 and a control. It is a graph which shows the measurement result of the dynamic viscoelasticity (DMS) of Example 1 and a control | contrast. 3 is a graph showing the measurement results of tensile strength in Example 1. It is the schematic which shows the apparatus which measures the softness | flexibility (bending strength) of a tube. It is a top view which shows the outline of the apparatus for implementing the temperature control used in Example 2. FIG.

Explanation of symbols

1 Infrared heater 2 Thermoplastic polyurethane tube

Claims (1)

The molded product comprising a molded product of polyol, low molecular weight diol and diisocyanate, melt-molded at a temperature not lower than the flow start temperature Tm and cooled and solidified is heated to a temperature T1 not higher than the flow start temperature Tm and not lower than the glass transition point Tg. Then, the temperature is quickly lowered to a temperature T2 (where Tm>T1>T2> Tg), and at this temperature T2, a structure in which a hard segment formed from diisocyanate and a soft segment formed from polyol are phase-separated occurs. after holding until the time has elapsed, method for producing a thermoplastic polyurethane tube, characterized in that the cooling.

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