JPH0125328B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a modified molding method for polyurethane resin, which maintains the hardness of the polyurethane resin and improves heat resistance, which is a drawback of thermoplastic polyurethane resin, when extrusion molding or injection molding the thermoplastic polyurethane resin. It is. Thermoplastic polyurethane resin is made by extrusion molding.
It is widely used by being molded into belts, tubes, electric wire cords, films, etc., and by injection molding into molded products such as shoe soles and ski boots. Polyurethane generally decomposes at temperatures above 230°C, so
Thermoplastic polyurethane resins used in extrusion molding and injection molding have a restriction that they must be melted at a temperature lower than the decomposition temperature of polyurethane.
Therefore, the heat resistance of molded products obtained from thermoplastic polyurethane resins is limited, and they have disadvantages such as being unable to be used in fields that require heat resistance. In particular, thermoplastic polyurethane resins with low hardness have poor heat resistance, and improvements have been desired. On the other hand, injection molding using thermoplastic polyurethane resin is considerably advantageous in terms of workability and productivity compared to cast polyurethane elastomer, but is inferior in terms of quality such as heat resistance and abrasion resistance. An object of the present invention is to provide a polyurethane molded article that maintains the hardness of the polyurethane resin and has excellent heat resistance, and another object of the present invention is to provide a method for producing such a polyurethane molded article in a stable and industrially advantageous manner. It is in. The method of the present invention is characterized in that when extrusion molding or injection molding a thermoplastic polyurethane resin, a polyisocyanate compound having a molecular weight of 300 or more is added to and mixed with the molten polyurethane resin, and is applicable to the present invention. The thermoplastic polyurethane resin is composed of a polyol with a molecular weight of 500 to 6000, such as bifunctional polyester, polyether, polycarbonate polyols, and block copolymers thereof, and an organic diisocyanate with a molecular weight of 500 or less, such as 4,4'-diphenylmethane. diisocyanate (MDI), tolylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate, naphthalene diisocyanate, etc., and a chain extender such as glycol, triol, diamine, hydrazine, water, etc. It is a polymer obtained by reaction. Among these polymers, those that are particularly suitable for extrusion molding and injection molding are polyols such as polyethylene adipate, polybutylene adipate, and polyhexamethylene diadipate, polycaprolactone polyol, polycarbonate polyol, and polytetramethylene ether. It is a polymer using glycol etc. Moreover, MDI is suitable as the organic diisocyanate. Glycols are preferred as chain extenders, with 1,4 butanediol (1.4BG) and bishydroxyethoxybenzene (BHEB) being particularly preferred. As a thermoplastic polyurethane resin used as a molding material in the present invention, in principle, a polymer synthesized without using a branching agent or a crosslinking agent is used. Therefore, the molding temperature can be kept at a low level, and thermal deterioration of polyurethane can be suppressed. Of course, polymers containing branching or crosslinking to the extent that the molding temperature does not become extremely high can also be used. The thermoplastic polyurethane used in the present invention can be synthesized using either the so-called prepolymer method in which a polyol and an organic diisocyanate are reacted in advance and then reacted with a chain extender, or the so-called one-shot method in which all reaction materials are mixed at once. can also be adopted. Polymerization methods include continuous production using an extruder or batch reaction to produce blocks,
A method of obtaining a flaky or powdery polymer is preferably used. The polyurethane resin used in the present invention is not only a completely thermoplastic polyurethane in which the urethanization reaction has been fully completed, but also a so-called incomplete thermoplastic elastomer, that is, flakes or pellets in which very few isocyanate groups remain, and are crosslinked after molding. It is also possible to use such polymers. However, since such pellets have the problem of being susceptible to deterioration due to humidity, temperature, etc. during storage, it is convenient to use fully reacted thermoplastic polyurethane resin. The polyisocyanate compound used in the present invention has two or more isocyanate groups in the molecule, preferably 2 to 4, particularly preferably 2, and a terminal having a molecular weight of 300 to about 6000, preferably 800 to 3000. It is a compound having an isocyanate group. The polyisocyanate compound also contains an NCO content of about 2 to about 29% by weight, preferably 3.4 to 22% by weight. The polyisocyanate compound can be synthesized by reacting at least one polyol with at least one organic polyisocyanate. The polyol has a molecular weight of 60 to 5000, preferably 300 to
2500, and is a polyol having two or more hydroxyl groups in the molecule. Examples of these polyols include polyether, polyester,
Mention may be made of those selected from the group consisting of polyesteramide and polycarbonate polyols. Particularly preferred polyols are polytetramethylene ether glycol and polycaprolactone and polybutylene adipate polyols. The organic polyisocyanate has a molecular weight of 500 or less, and suitable organic polyisocyanates include 4,4'-diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate, which are organic diisocyanates. Further, dimers, trimers, carbodiimide modified products, etc. of organic diisocyanates can also be used. As polyisocyanate compounds other than the above,
Trimers of organic diisocyanates, carbodiimide-modified polyisocyanates, and polyisocyanates obtained by reacting organic polyisocyanates with triols at an equivalent ratio (NCO/OH) of 2.0 or more can be used. Further, reaction products of glycols, triols, polyols, etc. and organic polyisocyanates, and mixtures of organic polyisocyanates can also be used. The molecular weight of the polyisocyanate compound applied to the present invention is expressed as the apparent molecular weight calculated from the isocyanate group weight measured by amine titration. If the molecular weight of the polyisocyanate compound is less than 300, the amount added will be small, and a slight increase or decrease in the amount added will likely cause variations in the physical properties of the molded product, making it impossible to stably improve heat resistance. On the other hand, if the molecular weight becomes too large, the percentage of the added amount becomes too large, and the plasticizing effect of the polyisocyanate compound becomes too large.
Molding becomes unstable. The amount of the polyisocyanate compound of the present invention added is 3 to 30% of the mixture of the thermoplastic polyurethane resin and the polyisocyanate compound to be used for molding.
(weight)%, particularly preferably 5 to 20%
(weight)%. The amount added depends on the polyisocyanate compound used.
Although it varies depending on the NCO content and type, if the amount added is small, the desired heat resistance improvement of the molded product will be insufficient. Also, if the amount added is too large, the mixture will be uneven, the molded product will be too soft immediately after molding, and when continuously molding belts, tubes, films, etc. by extrusion molding, the thickness and diameter will change easily and the product will be cut midway. This is undesirable because it is difficult to release the mold from the mold during injection molding, and workability decreases. The method for modifying a thermoplastic polyurethane resin of the present invention involves injection molding using a static mixing device so that a polyisocyanate compound is added to a portion where the resin is in a molten state during injection molding or extrusion molding of a thermoplastic polyurethane resin. Preferably, the process is carried out by being mounted on a machine or an extrusion molding machine. As such a static mixing device, a known device used for mixing pigments, dyes, plasticizers, modifiers, etc. can be used. When adding and mixing a polyisocyanate compound to a molten thermoplastic polyurethane resin, it is also possible to use a kneading device with a rotating part, but the viscosity difference between the molten polyurethane resin and the polyisocyanate compound in the same system Since the mixing ratio is large, mixing tends to be uneven, and in the case of a kneading device having a rotating part, there is a stagnation part, which is not preferable because there are parts that are locally susceptible to thermal deterioration. The shape and number of elements of the static kneading element vary depending on the conditions of use, but must be selected so that the molten polyurethane resin and polyisocyanate compound are sufficiently mixed. The method of carrying out the present invention will be explained below separately into an extrusion molding method and an injection molding method. [In the case of extrusion molding method] Thermoplastic polyurethane resin pellets are supplied from a hopper and heated and melted in an extruder. Although the melting temperature varies depending on the type of polyurethane, a range of 190 to 230°C is usually suitable. On the other hand, the polyisocyanate compound is melted at a temperature of 100°C or less in a supply tank and degassed. If the melting temperature is too high, the polyisocyanate compound is likely to undergo deterioration, so it is desirable that the melting temperature be as low as possible.
The molten polyisocyanate compound is measured by a metering pump, passed through a filter if necessary, and added to the molten polyurethane resin at a meeting point installed at the tip of the extruder. The molten polyurethane resin with the polyisocyanate compound is kneaded by a kneading device having a static kneading element, and is formed into a belt, tube, film, etc. through a die connected to the static kneading device. Immediately after molding, the strength may be relatively low, but the strength improves while left at room temperature. Strength can be improved in a short time by heating and aging after molding. [In the case of injection molding method] Thermoplastic polyurethane resin pellets are supplied from a hopper and heated and melted in an injection molding machine. Although the melting temperature varies depending on the type of polyurethane, a range of 190 to 230°C is usually suitable. On the other hand, the polyisocyanate compound is defoamed in the supply tank and melted at a temperature of 100°C or lower. Using a metering machine capable of supplying a fixed amount of molten polyisocyanate compound, the injection molding machine is automatically and intermittently fed into a kneading device with a static kneading element installed at the tip of the injection molding machine based on the screw position signal. After being dispensed in a fixed amount and kneaded, it is injected into a mold through a nozzle connected to a static kneading device and processed into a molded product. Immediately after molding, the strength may be relatively low, but the strength improves while left at room temperature. By heating and aging after molding, the strength can be improved in a short time. The method of the invention can also be applied to the production of polyurethane elastic yarns by melt spinning. The present invention will be explained below with reference to Examples. Parts and percentages in the examples are parts by weight and percentages by weight, respectively, unless otherwise specified. Examples 1-1 to 1-5 750 parts of dehydrated polybutylene adipate having a hydroxyl value of 150 and 500 parts of MDI were reacted at a temperature of 70 to 80°C for 1 hour to obtain a viscous polyisocyanate compound (A). The isocyanate group content of this product is 6.7
The molecular weight calculated from this in % was 1250. The polyisocyanate compound (A) thus obtained and paraprene 22SR (thermoplastic polyurethane resin manufactured by Nippon Polyurethane Industries, hardness JIS-A82)
was molded into a 2 mm thick belt using an extrusion molding machine equipped with a polyisocyanate compound supply device and a static kneading device. Table 1 shows the physical properties of belts extrusion molded with varying amounts of polyisocyanate compounds added. The extrusion molding machine is Hitachi Zosen SH-45 extruder (L/D
= 25, screw diameter 45 mm, non-vent type) and a stationary kneading element having 10 elements was used.

[Table] Comparative Examples 1-1 to 1-3 Using the same raw materials and equipment as in Example 1-1, a comparative test was conducted in which the polyisocyanate compound (A) was not added and the amount added was changed, and the physical property results were reported. It is shown in Table 1. In Comparative Examples 1-3, it was impossible to measure various physical properties due to poor molding.

[Table] The softening point of extrusion-molded belts without the addition of polyisocyanate compound (A) is as low as 105°C, but the softening point of belts with addition of polyisocyanate compound (A) is 20 to 30°C higher, and the hardness remains unchanged even with the addition of polyisocyanate compound. . As the amount of polyisocyanate compound (A) added increases, the plasticizing effect of (A) works and the resin viscosity after mixing decreases. In order to improve the shape, it is necessary to lower the die temperature as the amount added increases. If the amount added exceeds 30%, mold release properties during molding will deteriorate, resulting in poor moldability. Examples 2-1 to 2-4 Polyisocyanate compounds used in Example 1
(A) and Paraprene 26SR (thermoplastic polyurethane resin hardness JIS-A96 manufactured by Nippon Polyurethane Industries) are molded into a 2 mm thick sheet using an injection molding machine equipped with a polyisocyanate compound supply device and a static kneading device. did. Table 2 shows the physical properties of sheets injection molded with varying amounts of polyisocyanate compounds added. The injection molding machine used was Yamashiro Seiki's SAV-100B model, which was equipped with a static kneading element having 10 elements.

[Table] Comparative Examples 2-1, 2-2 Using the same raw materials and equipment as in Example 2-1, a comparison was made with no addition of polyisocyanate compound (A) and with an amount added outside the range, and the physical property results were obtained. are shown in Table 2.

【table】

[Table] As in the case of injection molding in Example 1, in injection molding in Example 2, it was possible to increase the softening point without changing the hardness of the polyurethane resin. On the other hand, the tensile strength and elongation set were improved. The abrasion resistance by filing also showed quite good values, and the drawback of hot melt abrasion resistance due to friction, which is characteristic of thermoplastic polyurethane resins, was significantly improved by the addition of the polyisocyanate compound. Examples 3-1 to 3-5 Dehydrated polyethylene adipate with a hydroxyl value of 56
Put 2000g and 1.4-BG180g into a kneader,
Dissolve while stirring and keep at a temperature of 85°C.
To this was added 766 g of MDI dissolved at 50°C, and the mixture was allowed to invert. As the reaction progressed, the temperature increased due to reaction heat, and the viscosity increased rapidly. The produced resin gradually solidified, and a block-shaped resin was obtained. This was pulverized into flakes using a granulator, and pelletized polyurethane resin () was obtained using an extruder. Using this polyurethane resin (2) and the polyisocyanate compounds shown in Table 3 as molding raw materials, a belt with a thickness of 2 mm was formed by extrusion molding in the same manner as in Example 1.

[Table] Table 5 shows the physical property results of belts extruded with different types of polyisocyanate compounds shown in Table 3.
It was shown to.

[Table] The amount of the polyisocyanate compound added was set so that the NCO content (%) of the polyisocyanate compound x the amount added (g) = 1.714 per 100 parts of the base polyurethane resin (a). The effect of adding isocyanate compounds was examined. The results are shown in Table 5. Comparative Examples 3-1 to 3-3 Comparative tests were conducted using the polyisocyanate compounds shown in Table 4 using the same raw materials and equipment as in Example 3-1. The results are shown in Table 5. In Comparative Examples 3-2 and 3-3, it was impossible to measure various physical properties due to poor molding.

【table】

[Table] As can be seen from the results in Table 3, polyisocyanate compounds B, C, and D have improved softening points. On the other hand, n = 500 indicated by symbols E, F, G, H
A polyisocyanate compound obtained by adding MDI to polyethylene adipate of ~1500 produced molded products with a high softening point without changing hardness, and had good elongation set, heat shrinkage rate, and abrasion resistance (file method). . In the case of the comparative example, foaming and surging occurred in moldability. Examples 4-1 to 4-4 1000 parts of dehydrated polytetramethylene ether glycol with a hydroxyl value of 112 and 500 parts of MDI were heated at 70 to 80°C.
The mixture was reacted at a temperature of 1 hour to obtain a viscous polyisocyanate compound (K). The isocyanate group content of this product was 5.60%, and the molecular weight calculated from this was 1500. Using the thus obtained polyisocyanate compound (K) and Paraprene-4319 (thermoplastic polyether-based polyurethane resin hardness JIS-A81 manufactured by Nippon Polyurethane Co., Ltd.) as molding raw materials, the same extrusion molding machine as in Example 1 was used. It was molded into a belt with a diameter of 2 mm. Table 6 shows the physical properties of belts extrusion molded with varying amounts of the polyisocyanate compound (K) added.

[Table]
Comparative Examples 4-1 to 4-3 Using the same raw materials and equipment as in Example 4-1, comparative tests were conducted with no addition of polyisocyanate compound (K) and with different amounts added, and the physical property results are shown in Table 6.
It was shown to. In Comparative Example 4-3, it was impossible to measure various physical properties due to poor moldability.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A method for modifying and molding a polyurethane resin, which comprises adding and mixing a polyisocyanate compound having a molecular weight of 300 or more to the polyurethane resin when thermoforming the thermoplastic polyurethane resin. 2 polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polycaprolactone, in which the polyol forming the thermoplastic polyurethane has a number average molecular weight of 500 to 6000;
The method according to claim 1, wherein the polyol contains at least one selected from polycarbonate polyols and polytetramethylene ether glycols. 3 The chain extender forming the thermoplastic polyurethane resin is a glycol, triol, or
The method according to claim 1, wherein the diamine is a diamine. 4. Claim 1, wherein the organic diisocyanate forming the thermoplastic polyurethane resin is selected from 4,4'-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.
The method described in section. 5. The method according to claim 1, wherein the polyisocyanate compound has a molecular weight of 800 or more. 6. The method according to claim 1, wherein the polyisocyanate compound is an organic diisocyanate derivative. 7 Organic diisocyanate derivative has a molecular weight of 60~
5,000 polyols, polyethers, polyesters, polyesteramides, and polycarbonates. Method. 8. The method according to claim 1, wherein the amount of the polyisocyanate compound added is 3 to 30% by weight based on the mixture of the thermoplastic polyurethane resin and the polyisocyanate compound. 9. The method according to claim 1, wherein the thermoplastic polyurethane resin and the polyisocyanate compound are mixed using an extrusion molding machine or an injection molding machine equipped with a static kneading element.