JP2007230124A - Manufacturing method of foam molding and foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable foaming molding of resins having so far being unsuitable for foaming molding, increase the foaming magnification of conventional resins and improve quality, in manufacturing methods of foam moldings which form foam moldings continuously by melting a thermoplastic resin in an extruder, injecting the molten resin into a mold and extruding the resin from the outlet of the mold while foaming the resin. <P>SOLUTION: The manufacturing method of foam moldings comprises introducing the thermoplastic resin molten in the extruder into a double- or multiple-walled tube type heat-exchange static mixer and extruding the resin having passed through the heat-exchange static mixer continuously from the outlet of the mold to form a foam molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a foam molded article used in the fields of building materials, industrial materials, etc., in particular, a thermoplastic resin is melted and kneaded by an extruder, and the molten and kneaded thermoplastic resin is passed through a mold. In addition, the present invention relates to a method for manufacturing a foam molded body, in which a foam molded body is continuously molded by extruding a resin from a mold outlet.

  The so-called chemical foaming method in which a thermoplastic resin is foamed and a foamed molded product is continuously obtained is charged into the extruder together with a decomposable foaming agent, decomposed and dispersed in the extruder, and extruded from the mold. In addition, a so-called physical foaming method in which a resin gas is melted in an extruder, a liquefied gas that is vaporized under normal temperature and normal pressure is injected, dispersed in the extruder, and then extruded from a mold is mainly used (for example, Patent Document 1). In any case, the foaming agent needs to be finely and uniformly dispersed in a liquefied state until it comes out of the mold, and in the case of chemical foaming, the foaming agent needs to be sufficiently decomposed. First, in order to prevent the foaming agent from evaporating in the mold, it is necessary to maintain the pressure in the mold. However, in a resin having a low melt viscosity, the pressure in the mold is low, so the foaming agent is easily vaporized and foams inside the mold. Therefore, good foam molding cannot be performed.

  In addition, even if foaming in the mold is not performed, if the melt viscosity or melt tension is low, the resin will come out of the mold, and when foaming proceeds under normal pressure, the cell will be broken and open bubbles will be formed. There is a problem that the mechanical strength is not obtained. Therefore, conventionally, a method of selecting a resin having a high melt viscosity suitable for foam molding, cross-linking the resin or mixing a polymer component as necessary, or using an additive having an effect of increasing the melt tension is used. Inevitably, there is a problem that the resin to be used can be restricted and the expansion ratio cannot be increased to the target expansion ratio. Furthermore, the obtained molded product also has problems such as poor recyclability and high cost due to crosslinking and additives.

The molding conditions are often set with the goal of relatively low temperature extrusion due to the higher melt viscosity of the thermoplastic resin at lower temperatures. There were many problems such as that the resin temperature did not decrease due to the increase in the temperature, the chemical foaming agent was poorly decomposed, and the resin melting point was delayed, resulting in poor dispersion of the foaming agent.
JP-A-10-146875

  An object of the present invention is to foam a resin that is not suitable for conventional foam molding, or to increase the foaming ratio and improve the quality of a resin that has been used for foam molding.

  In order to solve the problem, it is very effective to increase the melt viscosity and the melt tension by lowering the temperature of the resin while maintaining the state in which the foaming agent is sufficiently finely and homogeneously dispersed. If the resin temperature distribution in the extruder is lowered by changing the temperature setting or screw design setting, the melting end point in the extruder will move to the mold side, resulting in poor dispersion. Become. For this reason, in order to lower the temperature of the resin, it is first necessary to make the resin sufficiently reacted and dispersed by an extruder.

  In the present invention, the resin is cooled while maintaining homogeneity at a quality suitable for foaming extrusion, following an extruder for applying a sufficient amount of heat to the resin to efficiently and uniformly disperse the foaming agent. The above problem was solved by installing a heat exchange type static mixer of a double tube type or a multi-tube type.

  As described above, in the invention according to claim 1, the thermoplastic resin is melted by an extruder, the melted thermoplastic resin is passed through a mold, the thermoplastic resin is extruded from the mold outlet, and foamed. Thus, in the method for producing a foamed molded article that continuously molds the foamed molded article, the thermoplastic resin melted in the extruder is introduced into a double-pipe or multi-pipe heat exchange static mixer, The thermoplastic resin passed through the heat exchange type static mixer was continuously extruded from the mold outlet to form a foamed molded article.

  According to a second aspect of the present invention, a gear pump is provided between the extruder and the double-tube or multi-tube heat exchange static mixer, and the molten thermoplastic resin extruded by the extruder is a gear pump. Then, the foam-molding method is characterized by being introduced into the heat exchange static mixer.

  Further, in the invention according to claim 3, in the double-pipe heat exchange type static mixer, the inner diameter of the pipe through which the resin is passed is D, and the L / D is 5 from the length of the pipe being L. 100. The method for producing a foam according to claim 1 or 2, wherein the method is 100.

  According to a fourth aspect of the present invention, in the multitubular heat exchange type static mixer, the L / D is 3 to 70 when the inner diameter of the tube through which the resin passes is D and the length of the tube is L. The method for producing a foam according to claim 1 or 2, wherein the foam is produced.

  According to a fifth aspect of the present invention, there is provided a foamed molded article obtained by foaming and molding a thermoplastic resin using the foam production method according to any one of the first to fourth aspects. It was.

  In the present invention, a homogeneous and stable foam can be formed by using a double-tube or multi-tube heat exchange type static mixer. In particular, even in the molding of a resin that is suitable for extrusion in a temperature range where the foaming agent cannot be sufficiently decomposed in chemical foaming, the foaming agent is sufficiently decomposed by an extruder and then homogeneous to the target temperature range. Since it can be cooled while maintaining the temperature distribution and good dispersibility, it has become possible to perform good foam molding from thermoplastic resins that have not been suitable for foam molding to date, such as polyester resins.

  In addition, extrusion of polypropylene and other materials can be performed at a low temperature in a more homogeneous state, so existing methods such as cross-linking for foaming, incorporation of high molecular weight components, and addition of types that increase melt tension are particularly important. It became possible to make a good foam without using it. In addition, the improvement in dispersibility contributes to the reduction in the size of bubbles and the increase in mechanical properties due to the increase in the closed cell ratio.

  Further, it is possible to solve the problem that productivity is deteriorated because the number of revolutions of the extruder has to be reduced in order to perform extrusion at a temperature suitable for foaming.

  An object of the present invention is to foam-mold a resin that is not suitable for conventional foam molding, or to increase the expansion ratio and improve the quality of a resin that has been used for foam molding, and is used in the present invention. The thermoplastic resin is not particularly limited, and is suitably selected from polyolefin resins such as polyethylene and polypropylene, polystyrene resins, polyvinyl chloride resins, polymethyl methacrylate resins, polyethylene terephthalate resins, polyamide resins, polylactic acid, and the like. Selection is possible. These may be used alone, or may be used as a blend or a copolymer.

  Thermoplastic resins are heat stabilizers, acid neutralizers, UV absorbers, light stabilizers, colorants such as pigments and dyes, fillers, antistatic agents, lubricants, nucleating agents, flame retardants as necessary. An anti-blocking agent or the like can also be added.

  Among these additives, hindered phenols, sulfurs, phosphoruss, etc. as heat stabilizers, benzotriazoles, benzoates, benzophenones, triazines, etc. as ultraviolet absorbers, hindered amines as light stabilizers, etc. As the flame retardant, halogen flame retardant, phosphorus flame retardant, chlorine flame retardant, etc., fillers are calcium carbonate, silica, barium sulfate, zinc oxide, alumina, talc, mica, magnesium silicate, potassium titanate, There are magnesium sulfate, wollastonite, wood flour, and the like, and these additives can be used in any combination.

  In particular, by including wood flour as a wood-based filler in a thermoplastic resin, a wood resin foam molded article having a good wood texture and light weight can be obtained. These woody resin foam molded articles can be suitably used for applications such as building interior materials, flooring materials, joinery, and surface materials for home appliances.

  At this time, the amount of the wood-based filler can be appropriately selected from 10 parts by weight to 500 parts by weight with respect to 100 parts by weight of the thermoplastic resin. The filler is desirably 10 to 200 parts by weight, more preferably 15 to 150 parts by weight, based on 100 parts by weight of the thermoplastic resin.

  Any known method can be used for the foaming method. Generally, it can be classified into chemical foaming that generates gas by thermal decomposition or chemical reaction, and physical foaming that vaporizes by applying heat to a low boiling point liquid. Chemical foaming agents dispersed in the thermoplastic resin melt include inorganic sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, sodium borohydride, light metals, azide compounds, and organic foams. Any of azo, nitroso, hydrazide and the like can be used. In particular, physical foaming is mainly used as a foaming agent having a high foaming ratio exceeding 3 times, and carbon dioxide gas or aliphatic hydrocarbon is mainly used as a foam. These foaming agents may be used alone or in combination. For example, a chemical foaming agent can be used in combination with a physical foaming agent to adjust the cell shape of the foamed molded product.

  A foaming component such as a foaming agent and a foaming gas is added to the thermoplastic resin to obtain a foamed molded product. The method includes adding the foaming component to the thermoplastic resin before the thermoplastic resin is added to the extruder, and the former stage of the extruder. And a method of adding a foaming component in the middle of the latter stage. Further, among physical foaming, a supercritical foaming technique in which a supercritical foaming component is injected can also be used.

  Next, the manufacturing method of the foaming molding of this invention is described. In the present invention, a known foaming technique and equipment can be used as they are within the scope of the claims for the extrusion technique and equipment. In FIG. 1, the schematic of the manufacturing apparatus of the foaming molding of this invention was shown. The raw material thermoplastic resin 5 a is charged from the raw material charging port, and the thermoplastic resin is melted and kneaded in the extruder 1. The resin melted and kneaded by the extruder 1 is introduced into the static mixer 3. At this time, a gear pump 2 is provided between the extruder 1 and the static mixer 3 as necessary. In the static mixer 3, the thermoplastic resin is cooled to a temperature suitable for foam molding while maintaining homogeneity. Then, the thermoplastic resin that has passed through the static mixer and cooled to a temperature suitable for foam molding is introduced into the mold 4, subjected to foam molding, and continuously formed into a foam molded body 5 b.

  The extruder used in the present invention can be used as a single-screw extruder or a twin-screw extruder. In the twin-screw extruder, any combination of the same direction, different directions, conical, and parallel can be used. Similar to the known foaming technique, it is undesirable in terms of quality and stability that the foaming agent is vaporized in the extruder while maintaining a sufficient resin pressure near the exit of the extruder.

  The resin melted and kneaded by the extruder passes through a gear pump as required, and is introduced into a double-tube or multi-tube heat exchange type static mixer. The gear pump presses and extrudes the molten resin by rotating the gear, but a known pump can be used.

  The static mixer is also called a static mixer and has a tubular shape. An element for dividing, mixing, and stirring the resin is fixed inside the tube. As the element, a spiral element having a torsional blade portion can be used.

  In the present invention, a double-tube or multi-tube heat exchange type static mixer is used as the static mixer. This is a type mainly used as a heat exchanger. By flowing a fluid close to the target extrusion temperature through the outer peripheral pipe, it is possible to bring the temperature close to the target extrusion temperature while maintaining temperature uniformity.

  FIG. 2A shows an explanatory cross-sectional view of a double-tube heat exchange type static mixer, and FIG. 2B shows an explanatory cross-sectional view of a multi-tube type heat exchange type static mixer.

  In the double-tube heat exchange type static mixer, the pipe has a double structure, and the jacket pipe 12 has the heat transfer pipe 11 through which the thermoplastic resin passes. The heat transfer tube 11 has an element 13 fixed inside the tube. A coolant 15 having a constant temperature is passed through the jacket tube 12. When the thermoplastic resin 14 in the molten state passes through the heat transfer tube 11, heat exchange with the refrigerant is performed and the thermoplastic resin 14 is cooled.

  The multi-tube heat exchange type static mixer has a structure having a plurality of heat transfer tubes 11 in a jacket tube 12.

  A multi-tube heat exchange type static mixer has an excellent heat exchange rate, but the flow rate of each tube may vary. Although the double tube type has lower heat exchange efficiency than the multi-tube type, there is no variation in the flow rate of each tube, so it can be said that the versatility is high, but a longer effective length is required. Both the double-tube heat exchange type static mixer and the multi-tube type heat exchange type static mixer can quickly exchange heat between the molten thermoplastic resin and the refrigerant. At the static mixer outlet, It becomes possible to quickly cool the melting temperature of the thermoplastic resin to a temperature suitable for the foaming temperature of the thermoplastic resin.

  In the case of a double-tube static mixer, L / D is preferably 5 to 100 times, where D is the inner diameter of the tube through which the resin passes and L is the length of the tube. If the length is shorter than this range, a sufficient cooling effect cannot be obtained and it is difficult to achieve the object of the present invention. If the length is longer than this range, the pressure loss increases and becomes stable because extrusion is performed at a low temperature. It is difficult to continue feeding the resin.

  Similarly, in the case of a multi-tube heat exchange type static mixer, L / D is preferably 3 to 70 times, where D is the inner diameter of the tube through which resin passes and L is the length of the tube. . If the length is shorter than this range, a sufficient cooling effect cannot be obtained and it is difficult to achieve the object of the present invention. If the length is longer than this range, the pressure loss increases and becomes stable because extrusion is performed at a low temperature. It is difficult to continue feeding the resin.

  It is also possible to create a temperature gradient by dividing the zone through which the temperature-controlled fluid flows into several zones. If the pipe length is long and the pressure on the extruder side becomes too high, cooling may be performed in several stages, such as by installing a gear pump in the middle, and the pressure may be averaged.

  The extrusion foam molding technique is not particularly specified. The present invention can be applied to a technique capable of performing foam molding such as sheet molding, irregularly shaped, and blow molding. As the mold, T dice can be used in the case of sheet molding. For these facilities, adjustment and improvement are required as appropriate due to a decrease in cooling efficiency due to a higher expansion ratio and an increase in the pressure in the die due to low temperature extrusion.

  In the present invention, the temperature of the thermoplastic resin is lowered to a temperature suitable for foaming by passing the high-temperature thermoplastic resin extruded by the extruder through a heat exchange type static mixer. Therefore, since the load on the extruder becomes large, there is a case where sufficient discharge cannot be obtained or the extrusion itself may be difficult in an extruder with a small pressure increasing capacity or an extruder with a small screw torque. Raised. In addition, there is a concern that the residence time becomes long and excessive shearing occurs, causing problems such as heat generation and material deterioration. Further, in an extruder having a vent, so-called vent up in which the molten resin rises from the vent is likely to occur. In such a case, it is desirable to install a gear pump between the extruder and the heat exchange type static mixer. By having the gear pump, the feeding ability of the thermoplastic resin can be increased, and the above-described problems can be solved. In addition, in the extruder, if there is a margin in torque, it is possible to increase the feeding capacity of the thermoplastic resin by increasing the feeding capacity with a screw design.

  The gist of the present invention is that in the past, the resin must be produced in a temperature range that greatly exceeds the resin temperature that is originally desired to be extruded in order to melt the resin in the extruder, decompose the foaming agent, disperse, and increase the production efficiency. It is intended to produce a foamed molded article by cooling to a temperature suitable for extrusion, and there is no particular limitation on other moldings.

  Example 1 will be described. In Example 1, sheet molding was performed using a gear pump, a double tube heat exchange type static mixer, and a T die in order from the exit of the extruder. As the thermoplastic resin material, a mixture of 90% by weight of homopropylene (MFR = 7, melting point 160 ° C.) and 10% by weight of talc was used, and foaming was performed with carbon dioxide gas.

  At this time, the cylinder diameter of the used extruder is 65 mm, and the cylinder length L is 2340 mm (L / D = 36). The inner diameter D of the heat transfer tube of the double-tube heat exchange static mixer used is 65 mm, and the length L is 1300 mm (L / D = 20). Moreover, 130 degreeC oil was used as a refrigerant | coolant.

  At the time of producing the foamed molded product, the resin temperature at the exit of the extruder was 190 ° C., and the resin temperature at the exit of the heat exchange type static mixer was 150 ° C. to produce the foamed molded product. The obtained foamed molded product was a sheet-like foamed molded product having a thickness of 5 mm, and was a foamed molded product having a good foaming ratio having a closed cell structure at a foaming ratio of 15 times. By using the method for producing a foamed molded article of the present invention, foaming can be performed at a low temperature and in a homogeneous state, and a foamed molded article having a high foaming ratio can be produced.

  Example 2 will be described. In Example 1, sheet molding was performed using a gear pump, a double tube heat exchange type static mixer, and a T die in order from the exit of the extruder. As the thermoplastic resin material, a mixture of 90% by weight of polylactic acid (Lacia H400 (Mitsui Chemicals) / MFR = 3, melting point 166 ° C.) and 10% by weight of talc was used, and foaming was performed with sodium bicarbonate.

  At this time, the extruder used was the same as in the example, the cylinder diameter was 65 mm, and the cylinder length L was 2340 mm (L / D = 36). The inner diameter D of the heat transfer tube of the double-tube heat exchange static mixer used is 65 mm, and the length L is 1300 mm (L / D = 20). Moreover, 130 degreeC oil was used as a refrigerant | coolant.

  The number of heat transfer tubes of the used multi-tube heat exchange static mixer is 5, the inner diameter of the heat transfer tube is 25 mm, and the length L is 1000 mm (L / D = 40). Moreover, 110 degreeC oil was used as a refrigerant | coolant.

  At the time of manufacturing the foamed molded product, the resin temperature at the exit of the extruder was 175 ° C., and the resin temperature at the exit of the heat exchange type static mixer was 120 ° C. to manufacture the foamed molded product. The obtained foamed molded article was a sheet-like foamed molded article having a thickness of 5 mm, and was a foamed molded article having a good foaming ratio having an closed cell structure with a foaming ratio of 4.5 times. By using the method for producing a foamed molded article of the present invention, a resin material having a low melt viscosity can be cooled to a temperature suitable for foaming, and foaming can be performed at a low temperature. It became possible to produce a molded body.

It is the schematic of the manufacturing apparatus of the foaming molding of this invention. FIG. 2A is an explanatory cross-sectional view of a double-tube heat exchange type static mixer, and FIG. 2B is an explanatory cross-sectional view of a multi-tube type heat exchange type static mixer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extruder 2 Gear pump 3 Heat exchange type static mixer 4 Mold 5a Thermoplastic resin 5b Foam molding (thermoplastic resin)
11 Heat Transfer Tube 12 Jacket Tube 13 Element 14 Thermoplastic Resin 15 Refrigerant

Claims (5)

The thermoplastic resin is melted by an extruder, the molten thermoplastic resin is passed through a mold, the thermoplastic resin is extruded from the mold outlet, and foamed to continuously form a foam molded body. In the method for producing a foamed molded article,
The thermoplastic resin melted by the extruder is introduced into a double-tube or multi-tube heat exchange type static mixer, and the thermoplastic resin passed through the heat exchange type static mixer is continuously introduced from the mold outlet. A method for producing a foamed molded product, which comprises extruding the molded product into a foamed molded product.   A gear pump is provided between the extruder and the double-tube or multi-tube heat exchange static mixer, and after the molten thermoplastic resin extruded by the extruder passes through the gear pump, the heat exchange static mixer A foam molding method, which is introduced into the method.   The double-tube heat exchange type static mixer is characterized in that L / D is 5 to 100 when D is an inner diameter of a pipe through which resin passes and L is a length of the pipe. A process for producing a foam according to claim 1 or claim 2.   The multi-tube heat exchange type static mixer is characterized in that L / D is 3 to 70, where D is an inner diameter of a tube through which resin passes and L is a length of the tube. Or the manufacturing method of the foam of Claim 2.   A foamed molded article obtained by foaming and molding a thermoplastic resin using the method for producing a foam according to claim 1.

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