JP2007055122A - Multi-layer molding method of thermoplastic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer molding means of a thermoplastic resin friendly to environment capable of obtaining a multilayered molded product equipped with a foam layer having a desired foam density or foam diameter and a skin layer without producing a harmful decomposition product, discharging an environmental pollutant or an environmental disruption substance to the atmosphere and using a supercritical fluid producing and supplying device receiving legal control or complicated in introduction or handling. <P>SOLUTION: The thermoplastic resin is plasticized in an injection device and the plasticized thermoplastic resin is further mixed with a foamable gas to be injected and charged in the cavity of a clamped mold. After the injected and charged thermoplastic resin is integrally laminated to the skin material preset to the cavity, the volume of the cavity is expanded by a mold clamping device to foam the thermoplastic resin mixed with the foamable gas to obtain the multilayered molded product equipped with a skin layer comprising the skin material and the foam layer comprising the thermoplastic resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer molding method for obtaining a multilayer molded article comprising a skin layer made of a skin material and a foamed layer made of a thermoplastic resin.

  Multilayer molded articles (multilayer molded articles) including a skin layer made of a skin material and a foamed layer made of a thermoplastic resin have been used in various fields for a long time. Of the multilayer molded product, the foamed layer is excellent in lightness, heat insulation, sound absorption, and texture due to a large number of bubbles present inside the resin. On the other hand, the presence of a skin layer in a multilayer molded article can impart excellent appearance to the multilayer molded article. In recent years, in particular, in order to reduce the amount of resin used in a product and reduce the weight, means for foaming the resin has been adopted, and coupled with the fact that the weight reduction leads to cost reduction, the application field of multilayer molded products including a foam layer is Further spread.

  The method for obtaining the foamed layer in the multilayer molded article is classified into a physical foaming method and a chemical foaming method depending on the type of foaming agent mixed with the resin. In the physical foaming method, an inert gas such as nitrogen or carbon dioxide, or a vaporizable substance such as hydrocarbons or fluorocarbons, which is a physical foaming agent, is used. On the other hand, in the chemical foaming method, an organic foaming agent such as an azo compound or a nitroso compound, which is a chemical foaming agent, or an inorganic foaming agent such as sodium bicarbonate is used. According to the multilayer molding method, the molten resin in which the foaming agent and the resin material are mixed is injected and filled into the cavity of the mold, and separately, the molten resin made of the resin material not containing the foaming agent is injected into the mold cavity. It is possible to obtain a multilayer molded article including a foamed layer having a bubble diameter of about 80 to 300 μm and a non-foamed layer inside the layer by foaming a resin mixed with a foaming agent by injection filling inside. Is possible.

  As a method for obtaining a foamed molded product corresponding to the foamed layer of the multilayer molded product, for example, in Patent Document 1, a chemical foaming agent or a physical foaming agent is mixed with an olefin resin and melted, and the molded product is then obtained using a short shot method. A method of molding a foam molded product having bubbles inside is disclosed. According to the method disclosed in Patent Document 1, an inert gas such as nitrogen gas, or a volatile substance such as hydrocarbons or fluorocarbons, or a molding apparatus constituted by an extruder, an accumulator, and a mold, or Molten resin mixed with a chemical foaming agent and resin material is sent to an accumulator with an extruder, and then the molten resin sent to the accumulator is injected into the mold to foam the resin. It is possible to obtain a foamed molded product having the same.

  Further, for example, in Patent Document 2, as a method of obtaining a foamed molded product by using a physical foaming agent, air, other gas, or a vaporizable substance is added from the extruder hopper simultaneously with the supply of the resin material. A method is disclosed in which a resin material is melted and bubbles are contained and dispersed by a screw extruder while being supplied under pressure. According to the method disclosed in Patent Document 2, a sponge-like material molded article containing closed cells can be obtained by using polyethylene resin and supplying air under a pressure of about 0.69 to 0.78 MPa. I can do it.

  Furthermore, for example, in Patent Document 3, when carbon dioxide, which is an inert gas, is used as a foaming gas in a supercritical state, a conventional chemical foaming agent or physical foaming agent is used to form the molded product. Compared to the above, a method is disclosed in which the density of bubbles (the number of bubbles per unit volume) can be remarkably increased. According to the method disclosed in Patent Document 3, a system comprising a supercritical fluid booster and supply device and a gas cylinder is attached to a molding device, and carbon dioxide is injected in a supercritical state from a cylinder of the molding device. Resin molding that has a microporous property of less than 1 μm inside called microcell by dissolving the molten resin in the molten resin and injecting and filling the molten resin in which the injected carbon dioxide is dissolved into the mold. It is possible to obtain goods.

Japanese Patent Publication No. 44-6080 Japanese Patent Publication No.43-9913 JP-T 6-506724 Molding, 2001, No. 2, Volume 13

  However, when a multilayer molded article including a skin layer and a foamed layer is obtained, if the above-described conventional method for obtaining a foamed molded article is used to form a foamed layer of the multilayer molded article, the following problems occur. Realized.

  That is, when a means for supplying a resin and an organic chemical foaming agent (such as an azo compound or a nitroso compound) is employed (see Patent Document 1), corrosive ammonia, carbon monoxide, water vapor, etc. Gases, cyanic acid, isocyanic acid and the like are produced as decomposition products and released into the atmosphere, and the decomposition products remain in the foamed layer, causing discoloration of the skin material (skin layer). In addition, when sodium bicarbonate (inorganic foaming agent) is used as a foaming agent, a small amount of reaction residue containing an alkaline component discolors the foamed layer itself, and faces the problem that the weather resistance of the multilayer molded article is lowered.

  On the other hand, if a means for supplying vaporizable substances such as hydrocarbons or fluorocarbons, which are physical foaming agents that do not generate decomposition products, is adopted, emissions into the atmosphere are regulated as environmental pollution and environmental destruction substances. I faced the problem.

  In a means for supplying an inert gas such as nitrogen or air from a hopper of a resin extruder using a screw and kneading and molding under pressure simultaneously with the resin material (see Patent Document 2), gas is contained in the molten resin. In practice, there is a problem that it is quite difficult to form a foam layer having a desired cell density and cell diameter that is not finely dispersed.

  When means for dissolving carbon dioxide (foamable gas) in the molten resin in a supercritical state is employed (see Patent Document 3), there are the following problems. First, a supercritical fluid generator and supply device are required. These devices are subject to legal restrictions because they handle high-pressure gas, and the installation and handling of facilities is complicated. Next, there is a problem that the sealing mechanism of the foamable gas injected into the cylinder of the injection apparatus becomes complicated, and the apparatus becomes expensive. Next, when the sealing property of the foaming gas is increased, the plasticizing ability of the resin is lowered, and thus the productivity is also lowered. In addition, the injection control of the foaming gas has a problem that the control mechanism becomes complicated because the flow rate control is general. If the amount of foaming gas injected becomes excessive without optimal control, foaming gas is also ejected when the molten resin is injected and filled, causing damage to the skin material (skin layer) or permeation into the skin material. There is a problem.

  In addition, when a multi-layer molded product including a skin layer and a foam layer is obtained, if a skin insert molding method is used in which a skin material that becomes the skin layer is set in advance in the mold cavity, the pressure during injection filling of the molten resin is adopted. And the skin material was damaged by the heat of the molten resin, and the problem that the desired surface decoration expression could not be obtained became apparent.

  The present invention has been made in view of such circumstances. There is no generation of harmful decomposition products and no emission of environmental pollutants or environmentally destructive substances into the atmosphere. A multilayer molded article having a foam layer having a desired cell density and cell diameter and a skin layer expressing a desired surface decoration is obtained without using a complicated supercritical fluid generator and supply device. It is an object of the present invention to provide a multilayer molding means of an environmentally friendly thermoplastic resin. As a result of repeated research, it has been found that the above-mentioned object can be achieved by the means shown below.

  That is, first, according to the present invention, an injection device for plasticizing and injecting a thermoplastic resin as a molding material and a cavity that is a molding space filled with the thermoplastic resin injected from the injection device are provided. The mold is clamped on the mold and the mold clamping device capable of expanding and reducing the cavity volume by opening and closing the mold, and after setting the skin material in the mold cavity in advance, The mold is clamped by the clamping device, the thermoplastic resin is plasticized by the injection device, the plasticized thermoplastic resin is mixed with the foaming gas, and the foaming gas is mixed. The mold-clamping device is formed by injecting and filling the mold-filled thermoplastic resin into a mold-clamped mold cavity and integrally bonding the injection-filled thermoplastic resin and the skin material set in the cavity in advance. By cavity volume This is a multilayer molding method in which a thermoplastic resin mixed with foamable gas is foamed to obtain a multilayer molded article having a skin layer made of a skin material and a foamed layer made of a thermoplastic resin. The foaming gas is supplied to the injection device at a pressure of 0.1 MPa or more and less than 1.0 MPa, and a thermoplastic resin multilayer for mixing the thermoplastic resin plasticized by the injection device and the foaming gas is used. A molding method is provided (also referred to as a foaming gas mixing method).

  In the multilayer molding method of the thermoplastic resin of the present invention, after foaming the thermoplastic resin, the volume of the cavity is further expanded by a mold clamping device, and a gap is formed between the skin material and the surface forming the cavity of the mold. It is preferable to improve the texture of the skin material by generating the above.

  In the thermoplastic resin multilayer molding method of the present invention, it is more preferable that the pressure of the foaming gas supplied to the injection apparatus is 0.5 MPa or more and less than 1.0 MPa.

  In the thermoplastic resin multilayer molding method of the present invention, a bubble nucleation agent is previously included in the foamable gas before being supplied to the injection apparatus, and bubble nucleation is formed in the thermoplastic resin injected and filled into the mold cavity. It is preferable to contain an agent.

  In the thermoplastic resin multilayer molding method of the present invention, a cell nucleus forming agent is previously included in the thermoplastic resin as a molding material, and the cell nucleus forming agent is added to the thermoplastic resin injected and filled into the mold cavity. It is preferable to contain.

  In the thermoplastic resin multilayer molding method of the present invention, the cell nucleating agent is any one selected from the group consisting of iron oxide, calcium silicate, zinc stearate, magnesium stearate, organic acid, aluminum silicate, glass fiber, and talc. Or a mixture of two or more.

  In the thermoplastic resin multilayer molding method of the present invention, it is preferable that the foaming gas is supplied to the injection device by pressure control.

  In the thermoplastic resin multilayer molding method of the present invention, the supply destination of the foaming gas is in the hopper of the injection device corresponding to the thermoplastic resin inlet before being plasticized, or in the cylinder of the injection device that performs plasticization Among the thermoplastic resins after plasticization (after plasticization has started), it is preferable. That is, in the thermoplastic resin multilayer molding method of the present invention, the thermoplastic resin and the foamable gas may be brought into contact with each other in the injection device before the thermoplastic resin existing in the injection device is plasticized. The foamable gas may be blown into the thermoplastic resin in the injection device after the thermoplastic resin present in the injection device is plasticized.

  In the multilayer molding method of the thermoplastic resin of the present invention, the foamable gas is any one of the inorganic gas groups consisting of air, carbon dioxide and nitrogen, or an inorganic gas in which two or more are mixed. Is preferred.

  The thermoplastic resin used in the multilayer molding method of the thermoplastic resin according to the present invention is said to be styrene resin such as polystyrene, AS resin, ABS resin, olefin resin such as polyethylene, polypropylene, and engineering resin. Examples thereof include polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyamides, polyacetals, polycarbonates, modified polyphenylene ethers, and olefinic thermoplastic elastomers. These resins may be used as a mixture of two or more depending on the application and the like, and these thermoplastic resins may include plasticizers, mold release agents, antistatic agents, difficult additives as necessary. Various additives such as a flame retardant, various fillers for improving physical properties, glass fibers, carbon fibers, and the like, and further colorants, dyes, and the like may be mixed and used.

  In addition, as the foaming gas used in multilayer molding having a foam layer, carbon dioxide gas, nitrogen gas, air, or a mixed gas thereof may be mentioned, but in view of the properties of the resulting multilayer molded product, Air or carbon dioxide is preferred. In selecting these foamable gases, it is necessary to consider the oxidation resistance of the resin. It is preferable to use a gas other than air for a resin containing a group that is easily oxidized. For example, in the case of a resin such as polypropylene where oxidation resistance is not a problem, air is also preferably used in terms of availability. Cell nucleating agents include fine powders of inorganic substances such as iron oxide, calcium silicate, aluminum silicate, glass fiber, talc, sodium hydrogen carbonate (sodium bicarbonate), metal salts of organic acids such as zinc stearate and magnesium stearate, Examples thereof include organic acids such as acid and tartaric acid. Of course, these may be used as a mixture of, for example, a metal salt and an organic acid in consideration of the function as a bubble nucleating agent.

  The foamable gas used for forming the foamed layer is usually supplied to a predetermined portion of the injection molding apparatus under a pressure of 0.1 MPa to less than 1.0 MPa. By adopting this pressure, it is possible to simplify the gas sealing mechanism of the injection device, and as a result, it is possible to ensure a plasticizing ability exceeding a desired level. For example, in the case of a two-stage screw, the gas sealing performance of the injection device is usually ensured by narrowing the screw flight gap at the boundary between the first stage and the second stage, but the screw flight gap is too narrow. If too much, the passage of the molten resin is hindered, which may lead to a decrease in plasticizing ability. However, within the range of the above injection pressure, the screw flight gap can be set relatively large, and the plasticizing ability and the gas sealability can be satisfied at the same time. Also, by setting the pressure within the above range, the amount of foaming gas ejected from the resin tip during filling and injection can be suppressed to an appropriate level, so that the appearance of the desired multilayer molded product can be ensured. Is demonstrated. In addition, by controlling the injection amount of the foaming gas to pressure control, an optimum gas dissolution saturation amount for the resin to be used can be obtained regardless of the molding conditions. The gas injection amount is given as a pressure difference between the pressure of the decompression part (gas injection position) of the two-stage screw and the injection gas. Further, the amount of nitrogen gas dissolved in polystyrene (200 ° C.) is 0.4 mol / kg (1 MPa) to 0.6 mol / kg (10 MPa), and the difference in the amount of dissolution due to the pressure difference is small (see Non-Patent Document 1). Therefore, it can be said that the foamable gas amount necessary for foaming can be sufficiently ensured even within the pressure range of 0.1 MPa to less than 1.0 MPa. Therefore, even if the foaming gas is injected within the above-mentioned pressure range, sufficient foaming can be expected, and it can be said that there is substantially no influence on the properties of the obtained product.

  If the pressure is less than 0.1 MPa, it is not possible to obtain a foamed layer having a desired cell density and cell diameter in the desired multilayer molded product. A multilayer molded product having a desired cell density and cell diameter may be obtained, but sometimes there are abnormalities such as coarse foam cells or large differences in the expansion ratio depending on the part of the multilayer molded product. This is because the appearance of the multilayer molded product due to the swirl mark may be recognized and the surface state is not preferable. In addition, at higher pressures, it is necessary to provide molding equipment that can mold large-scale multilayer molded products such as automobile parts with a high degree of sealing performance. In addition to the difficulties involved, the facilities themselves need to have high pressure resistance, and it is not only a huge investment required to increase the pressure resistance of a house that accommodates large equipment. Even if you have it, you can't completely eliminate anxiety in order to be complete.

  The supply of the foaming gas to the injection device is from 0.1 MPa to less than 1.0 MPa, preferably from 0.2 MPa to 0.99 MPa, in view of the foamed state, appearance, soft feeling, etc. of the multilayer molded product. More preferably, it is preferably performed at a pressure of 0.5 MPa to 0.9 MPa. Since the supply of the foaming gas to the injection device is in the molten resin in the hopper or plasticizing cylinder that supplies the thermoplastic resin provided in the injection molding device described later, the foaming gas and the bubbles The nucleating agent can be sufficiently dispersed and mixed in the molten resin. In addition, since the screw of the injection device provided with the foaming gas supply in the plasticizing cylinder adopts a two-stage screw, the foaming gas and the cell nucleus forming agent are dispersed in the molten resin and mixed. It can be made. For the purpose of improving the mixing and dispersibility of the molten resin, the foamable gas, and the cell nucleating agent, a screw having a highly dispersible screw head is more preferable.

  The thermoplastic resin multilayer molding method according to the present invention is a method in which a thermoplastic resin mixed with a foaming gas is injected and filled into a cavity of a mold in which a skin material is previously set, and a skin layer made of a skin material and a thermoplastic resin A method for obtaining a multilayer molded article comprising a foam layer comprising: supplying foaming gas to an injection device at a pressure of 0.1 MPa or more and less than 1.0 MPa when mixing foaming gas with a thermoplastic resin In addition, since the plasticized thermoplastic resin and the foaming gas are mixed in the injection device, the desired bubble diameter can be obtained without using a foaming agent harmful to the environment or a supercritical fluid generator and supply device. It is possible to obtain a multilayer molded article of a thermoplastic resin having a foam layer having a bubble density and no harmful decomposition products remaining.

  Further, since the supply pressure of the foaming gas is 0.1 MPa or more and less than 1.0 MPa, the sealing mechanism of the foaming gas injected into the cylinder of the injection apparatus is simple and does not become complicated. A decrease in the plasticizing ability of the resin can be prevented. When the screw shape of the injection device is a two-stage screw, the gas seal performance is ensured by narrowing the gap between the screw flights at the boundary between the first stage and the second stage. If it is higher than 1.0 MPa, it is necessary to make the gap of the screw flight narrower in proportion to it, leading to a decrease in the plasticizing ability of the resin. However, according to the thermoplastic resin multilayer molding method of the present invention, since the supply pressure of the foaming gas is as described above, such a problem can be avoided.

  Furthermore, since the supply pressure of the foaming gas is 0.1 MPa or more and less than 1.0 MPa, the amount of foaming gas ejected from the resin during injection filling is more than that of 1.0 MPa or more. Therefore, the problem of damaging the skin material (skin layer) or soaking into the skin material and causing deterioration does not easily occur, and the appearance of the multilayer molded product (product) becomes better.

  In the thermoplastic resin multilayer molding method according to the present invention, the foaming gas supply pressure is set to 0.1 MPa or more because the desired bubble density and bubble diameter cannot be obtained at 0.1 MPa or less. is there. On the other hand, the reason why the supply pressure of the foaming gas is less than 1.0 MPa is that when it is 1.0 MPa or more, the foaming pressure becomes larger than the elongation viscosity of the thermoplastic resin, the bubble diameter becomes coarse, and the swirl mark This is because the appearance defect of the foamed layer (molded product) becomes prominent and the variation in the resin pressure in the initial filling stage and the latter half of the filling stage during injection filling is large. .

  More preferably, the foaming gas is supplied to the injection device at a pressure of 0.5 MPa or more and less than 1.0 MPa and under pressure control. A multilayer molded article having a foamed layer having a cell diameter can be obtained. In addition, since the supply of the foaming gas to the injection device is at a pressure of 0.1 MPa or more and less than 1.0 MPa, a conventional supercritical fluid generator and supply device using the foaming gas in a supercritical state is provided. do not need.

  In a preferred embodiment of the thermoplastic resin multilayer molding method according to the present invention, the supply destination of the foamable gas to the injection device is a hopper of the injection device corresponding to the thermoplastic resin inlet before plasticization, or plasticization Since the thermoplastic resin after being plasticized in the cylinder of the injection apparatus performing the above, the foamable gas can be sufficiently dispersed and mixed in the molten resin forming the foam layer. I can do it. In order to improve the mixing and dispersibility of the molten resin and the foamable gas, it is more preferable to use a screw provided with a highly dispersible screw head.

  In a preferred embodiment of the thermoplastic resin multilayer molding method according to the present invention, since the foaming gas injection control is pressure control, the optimal foaming gas dissolution for the thermoplastic resin to be used is not affected by molding conditions. A saturated amount can be obtained stably. For example, when a two-stage screw is used as the screw of the injection device, the difference in pressure between the pressure of the decompression part (foaming gas injection position) and the pressure of the foaming gas to be injected is the injection of the foaming gas. The amount of nitrogen gas dissolved in polystyrene resin is 0.4 mol / kg (1 MPa) to 0.6 mol / kg (10 MPa) at 200 ° C., and the difference in the amount of dissolution due to the pressure difference is small ( Non-patent document 1), a foaming gas in an amount necessary for foaming can be sufficiently secured at a pressure of 0.1 MPa or more and less than 1.0 MPa. Furthermore, if the pressure is in the range of 0.1 MPa or more and less than 1.0 MPa, it can be judged that the influence on the multilayer molded product (product) is small. In addition, since the amount of foaming gas injected does not become excessive due to optimal control, foaming gas is ejected during injection filling of the molten resin, and the skin material (skin layer) is damaged or penetrates into the skin material to cause deterioration. Is unlikely to occur.

  In a preferred embodiment of the thermoplastic resin multilayer molding method according to the present invention, after foaming the thermoplastic resin, the volume of the cavity is further expanded by a mold clamping device, and the surface material and the surface forming the mold cavity are formed. A gap is created between them. Therefore, the texture of the skin material once damaged by the pressure at the time of injection filling of the molten resin and the heat of the molten resin is recovered by itself, and a desired surface decoration expression by the skin material can be obtained.

  Hereinafter, embodiments of the present invention will be described with appropriate reference to the drawings, but the present invention should not be construed as being limited thereto. Various changes, modifications, improvements, and substitutions can be added based on the knowledge of those skilled in the art without departing from the scope of the present invention. For example, the drawings show preferred embodiments of the present invention, but the present invention is not limited by the modes shown in the drawings or the information shown in the drawings. In practicing or verifying the present invention, the same means as described in this specification or equivalent means can be applied, but preferred means are those described below.

  First, a multilayer molding apparatus suitable for carrying out the multilayer molding method for thermoplastic resins according to the present invention will be described. FIG. 1 is a diagram illustrating an example of a multilayer molding apparatus, and is an overall configuration diagram of a horizontal clamping type injection molding apparatus. As shown in FIG. 1, the injection molding apparatus 100 includes a mold 10, a mold clamping apparatus 20, an injection apparatus 30, a foaming gas supply means 40, and a control apparatus 70.

  The mold 10 includes a fixed mold 3 attached to the fixed platen 1 and a movable mold 4 attached to the movable platen 2. The fixed mold 3 and the movable mold 4 have a half-push structure. The surface of the fixed mold 3 that forms the cavity (cavity forming surface) and the surface of the movable mold 4 that forms the cavity (cavity forming surface) are combined in the fitted state. The cavity 11 of the mold 10 is formed. The fitting portion of the half-push structure is formed over the entire circumference of the cavity 11 of the mold 10, and even if the cavity 11 of the mold 10 is enlarged after injection filling, the resin filled in the cavity 11 of the mold 10 is mold. No leakage from 10. The mold clamping device 20 includes a mold clamping cylinder 22 that operates to open and close the mold 10. The movable mold 4 is guided by a tie bar (not shown) with respect to the fixed mold 3 to move forward and backward. It is configured to be able to.

  Note that the mold 10 is not limited to the mold having the half-push structure, and other molds having a flat push structure may be used as long as the mold 10 can be applied to foam molding. Further, instead of a horizontal mold clamping type injection molding apparatus having a direct pressure type mold clamping apparatus, a toggle type mold clamping apparatus, an electric servo motor type, or a vertical mold clamping type injection molding apparatus may be used.

  An injection device 30 shown in FIG. 1 includes a cylinder 31, a screw 32 that is built in the cylinder 31 and has a flight, and a hopper 35 that supplies a molding material into the cylinder 31, and further a screw that moves the screw 32 back and forth. A moving means 33 and a screw rotating means 34 for rotating the screw 32 are provided. A heater (not shown) is attached to the outer peripheral surface of the cylinder 31. In addition, after the injection device 30 is plasticized in the hopper 35 (the hopper port) of the injection device, which is the injection port of the thermoplastic resin before being plasticized, or in the cylinder 31 (after the plasticization has started) The foamable gas is supplied from the foamable gas supply means 40 into the thermoplastic resin.

  The injection device 30 is configured such that the pellet-shaped molding material is supplied from the hopper 35 into the cylinder 31 when the screw 32 is rotated by the screw rotating means 34, and the supplied pellet-shaped molding material is It is heated by a heater attached to the cylinder 31 and melted by receiving a kneading compression action by the rotation of the screw 32. At this time, since the foaming gas is supplied from the foaming gas supply means 40 to the injection device 30, the supplied pellet-shaped molding material (thermoplastic resin) is subjected to a kneading compression action, thereby generating a foaming gas. Are mixed, dispersed, melted, and sent to the front of the screw 32. The molten resin in which the foamable gas is kneaded and dispersed is injected and filled into the cavity 11 of the mold 10 from the nozzle 36 attached to the tip of the cylinder 31 by the screw 32 that is advanced by the screw moving means 33. The bubble nucleating agent is supplied to a suitable amount of bubble nucleating agent from the bubble nucleating agent supply device to be described later based on preset molding conditions and mixed with the thermoplastic resin. I can do it.

  In the injection device 30, the screw moving means 33 is a hydraulic cylinder and the screw rotating means 34 is a hydraulic motor, but may be a screw moving means or a screw rotating means using an electric servo motor. Moreover, it is good also as a screw pre-pull type injection apparatus which does not have the structure which has an in-line screw type injection device which performs plasticization and injection by one screw like the injection device 30, but performs plasticization and injection by separate mechanisms. . The shape of the screw is not a two-stage screw such as the injection device 30. For example, when the foaming gas supply destination is the hopper 35, the screw may be a single (single) stage screw.

  The foamable gas supply means 40 includes an air supply source 41, a carbon dioxide supply source 42, and a foamable gas supply device 43, and the air supply source 41 and the carbon dioxide supply source 42 are connected by a supply path. . Further, the foamable gas supply means 40 includes a foamable gas supply path to the foaming gas supply port provided in the cylinder 31 and the hopper 35 of the injection device 30, and is based on a command from the control device 70. A foaming gas is supplied to 30. In addition, bubble nucleating agent supply devices 61 and 62 for supplying a bubble nucleating agent are provided in the vicinity of the end of the supply path connected to the foaming gas supply device 43 and the injection device 30. Supply nucleating agent. In addition, the cell nucleating agent can be dry blended in advance to the molding material as a powder, or the cell nucleating agent can be added to the molding material as a master batch, or by kneading in advance during the production of the molding material, It can be contained in a thermoplastic resin.

  A control device 70 shown in FIG. 1 controls plasticization of a molding material (thermoplastic resin), supply of a foaming gas, supply of a cell nucleating agent, and injection of molten resin into the cavity 11 of the mold 10. Injection control unit 71, mold clamping control unit 72 for controlling opening and closing of the mold 10 and mold clamping force, a skin material supply device (not shown) for setting the skin material at a predetermined position of the cavity 11 of the mold 10, and a timer It consists of a variety of things. The mold clamping control unit 72 moves the position of the movable platen 2 so that the volume of the cavity 11 becomes a desired volume at the start of the resin foaming process for obtaining the foamed layer of the multilayer molded product. While having a setting part, the mold clamping which hold | maintains the position of the movable platen 2 until the completion of the foaming process can be controlled now. The foaming step includes a step of detecting that the resin has been filled into the cavity 11 of the mold 10 and reducing the mold clamping force, and a step of expanding the volume of the cavity 11 of the mold 10. A skin layer and bubble nuclei are formed during the pressure step-down process, and more bubble nuclei are formed as the pressure-lowering speed of the clamping force is higher. The expansion speed of the cavity 11 of the mold 10 is set based on the extension viscosity of the molding resin. Specifically, it is desirable to set the enlargement speed slow when the extensional viscosity is low, and to increase the enlargement speed when the extensional viscosity is high.

  Next, taking the case of using the multilayer molding apparatus shown in FIG. 1 as an example, the multilayer molding method for thermoplastic resin according to the present invention will be described with reference to FIG. 2 in addition to FIG. In the method for multilayer molding of thermoplastic resins according to the present invention, a molten resin containing a foaming agent is injected and filled into a mold cavity in which a skin material is previously set, and then the mold cavity is expanded to foam the resin. It is a method having a process, and is a suitable method for obtaining a multilayer molded article having a skin layer made of a skin material and a foamed layer made of a thermoplastic resin.

  FIG. 2 is a process diagram showing one embodiment of a thermoplastic resin multilayer molding method according to the present invention, which is composed of (a) to (f), and (a) to (e) in FIG. Only the mold 10 and the injection device 30 in FIG. 1 are depicted in a simplified manner. In performing multilayer molding to obtain a multilayer molded product having a skin layer made of a skin material and a foamed layer made of a thermoplastic resin, first, the mold 10 shown in FIG. 11 is set with a skin material 123 (skin insert method). Then, by supplying pressure oil to the piston head side of the clamping cylinder 22 and moving the piston rod forward, the movable platen 2 is moved in the direction of the fixed platen 1 and the mold 10 is clamped and held ( (See (a) of FIG. 2). The mold clamping force applied to the mold 10 is preferably set to a minimum value that does not open the mold 10 with the resin filling pressure at the time of resin filling from the viewpoint of the energy used and the life of the molding apparatus. In FIG. 2 (a), the mold is clamped, but the mold is desired after being injected and filled with the molten resin 124 or simultaneously with injection and filling in a mold open holding state with an appropriate gap. It is good also as operation which closes to a position. These are appropriately selected according to the type and characteristics of the skin material to be used.

  After completion of the mold clamping, the molten resin 124 containing the foaming gas and the cell nucleus forming agent is injected and filled into the cavity 11 of the mold 10 based on the preset injection filling amount, injection pressure, and injection speed (FIG. 2). (See (b)). Specifically, in the injection device 30 shown in FIG. 1, pressure oil is supplied to the screw rotating means 34 to rotate the screw 32. By this operation, the molding material (thermoplastic resin) supplied from the hopper 35 is heated by a heater (not shown) attached to the cylinder 31, is subjected to a kneading compression action by the rotation of the screw 32, melts, and has its own. The foaming gas and the cell nucleating agent are mixed and dispersed therein, and sent to the front of the screw 32. The molten resin 124 in which the foamable gas sent to the front of the screw 32 and the cell nucleating agent are mixed and dispersed is supplied with pressure oil to the screw moving means 33 to advance the screw 32, thereby causing the cavity of the mold 10. 11 is pushed and injected into the fixed platen 1 (fixed mold 3) side of the cavity 11 so that the skin material 123 set in advance in 11 is pushed in, and the skin material 123 set in advance in the cavity 11 is bonded together. (See (c) in FIG. 2).

  When the resin filling is completed, the pressure oil applied to the piston head side of the mold clamping cylinder 22 is then depressurized to lower the mold clamping force. Then, by supplying pressure oil to the piston rod side of the mold clamping cylinder 22 and moving the piston rod backward, the movable platen 2 is moved in the direction opposite to the fixed platen 1 and the mold 10 is opened. The volume of the cavity 11 of the mold 10 is expanded. The expansion control of the volume of the cavity 11 is performed based on the position for moving the position of the movable platen 2 provided in the mold clamping control unit 72 and the set value of the speed setting unit, and the movable platen 2 stops at a preset position. And hold that position.

  By expanding the volume of the cavity 11 in this way, the pressure in the cavity 11 begins to decrease, and at the same time, inside the molten resin 124 containing the foaming gas and the cell nucleus forming agent filled in the cavity 11. Foaming begins to occur. Further, the foamed layer 122 is molded (solidified) by holding and cooling the volume of the cavity 11 for a preset cooling time (see FIG. 2D). As shown in FIG. 2, even when the mold 10 is slightly opened, the fixed mold 3 and the movable mold 4 are fitted in the fitting portion, and the mold cavity The molten resin does not leak out of the mold 10.

  As described above, when the molten resin 124 containing the foamable gas and the bubble nucleating agent is injected and filled into the cavity 11 of the mold 10, the skin is caused by the pressure during the injection and filling of the molten resin 124 and the heat of the molten resin 124. The material may be damaged and the texture may deteriorate. On the other hand, it is possible to recover the texture of the skin material by re-opening the mold as follows.

  In order to restore the texture of the skin material, specifically, after the molten resin (thermoplastic resin) is foamed and molded as the foamed layer 122, pressure oil is supplied to the piston rod side of the mold clamping cylinder 22 to provide a piston. By moving the rod backward, the movable platen 2 is further moved in the direction opposite to the fixed platen 1, the mold 10 is opened, and the volume of the cavity 11 of the mold 10 is further expanded. What is necessary is just to produce a clearance gap between the cavity formation surfaces of the metal mold | die 10 (movable metal mold | die 4) (refer (e) of FIG. 2 and this process is also called remolding of a metal mold | die). The expansion control of the volume of the cavity 11 is performed based on the position for moving the position of the movable platen 2 provided in the mold clamping control unit 72 and the set value of the speed setting unit, and the movable platen 2 stops at a preset position. And hold that position.

  By further increasing the volume of the cavity 11 in this way, the pressure in the cavity 11 begins to decrease, and the texture of the skin material 123 preset in the cavity 11 is restored by itself, and the desired surface by the skin material 123 is recovered. It is possible to obtain a decorative expression. The re-opening of the mold is performed at a timing at which the foam layer 122 does not re-expand (secondary foaming) by the re-opening operation and is in a temperature state necessary to recover the texture of the skin material. It is important to start.

  When the texture of the skin material 123 is restored, the foamed layer 122 integrated with the skin material 123 is taken out of the mold 10 and cut by a cutting line 126 to remove the unnecessary skin material 123. A multilayer molded article provided with the skin layer 125 made of the material 123 can be obtained (see (f) of FIG. 2).

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

  (Example 1) A multi-layer molding method (foaming gas mixing) with a skin insert method shown in FIG. 2 using a horizontal toggle type injection molding machine (UBE-MD350 type injection molding machine manufactured by Ube Industries) as an injection molding apparatus. Method) was used to produce a two-layer molded product (multilayer molded product) composed of a skin layer made of a skin material and a foamed layer. In accordance with the method shown in FIG. 2, the mold was re-opened after foaming, and the skin material was recovered. Polypropylene resin (PP, automobile interior grade MFR = 35, manufactured by Mitsui Chemicals) was used as the resin material for the foam layer in order to achieve both weight reduction of the molded product (product) and the feel of the surface.

  A fine powder of talc was used as a bubble nucleating agent and was previously mixed with the resin material. Carbon dioxide was used as the foaming gas and was injected into the molten resin in the cylinder at a pressure of 0.9 MPa. As the screw, a two-stage screw with a mixing head attached to the screw tip was used, and the gas seal portion was adjusted according to the pressure of the foaming gas to be injected.

  The two-layer molded product was an automobile interior product (pillar garnish) of 600 × 180 mm, and the thickness of the two layers before foaming was 2.0 mm. The molding conditions were set at a resin temperature of 200 ° C. and a mold temperature of 30 ° C. The molded product was evaluated by visual observation of a foamed state, an appearance state, and a raised skin feeling. The results are shown in Table 1.

  (Examples 2, 4 to 6) A foamed gas was produced in the same manner as in Example 1 except that the foaming gas (foaming agent) used and the injection pressure of the foaming gas were changed. The appearance and the raised surface feeling were visually evaluated. The results are shown in Table 1 together with the foaming gas, the injection pressure, the thickness of the foamed layer before foaming and the thickness after foaming.

  (Example 3, Comparative Examples 1 and 2) Except that the foaming gas used (foaming agent), the injection pressure of the foaming gas was changed, and the mold was not re-opened after foaming. A two-layer molded product was produced in the same manner as in Example 1, and the foamed state, the appearance state, and the raised skin feeling were visually evaluated. The results are shown in Table 1 together with the foaming gas, the injection pressure, the thickness of the foamed layer before foaming and the thickness after foaming.

  (Comparative Example 3) A foam layer was formed using sodium bicarbonate (inorganic chemical foaming agent) without using a foaming gas, and the mold was not re-opened after foaming. In the same manner as in Example 1, a two-layer molded product was produced, and the foamed state, the appearance state, and the raised skin feeling were visually evaluated. The results are shown in Table 1.

  In Table 1, the foamed state indicates that A is good because an aggregate of fine bubbles is seen, and B is that coarse bubbles are mixed. In addition, the appearance state indicates that A is good with few swirl marks and silver streaks, B is (same) slightly more, C is (same) more, and D is (same) much. Furthermore, the feeling of raising the epidermis indicates that A is good, B is slightly fallen, and C is severely fallen and the texture of the epidermis is not good. The relative plasticizing ability values in Table 1 represent the relative values of the plasticizing ability when the plasticizing ability (kg / hr) of Comparative Example 3 is 1.0.

  From the results shown in Table 1, according to the multilayer molding method for thermoplastic resins according to the present invention, a molded product having good foamed state, appearance state, and skin raising feeling can be obtained without greatly reducing plasticizing ability. It was confirmed that it was possible to produce.

  The thermoplastic resin multilayer molding method of the present invention may be used as a molding means for all multilayer molded articles. In particular, it can be suitably used as a molding means for products that require both high quality maintenance and light weight for the appearance, such as motorcycle parts, automobile parts, home appliances, and housing equipment parts.

It is a whole block diagram which shows an example of a multilayer shaping | molding apparatus. (A)-(f) of FIG. 2 is process drawing which shows one Embodiment of the multilayer molding method of the thermoplastic resin which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed platen 2 Movable platen 3 Fixed metal mold 4 Movable metal mold 10 Mold 20 Clamping device 30 Injection device 31 Cylinder 32 Screw 35 Hopper 40 Foamable gas supply means 41 Air supply source 42 Carbon dioxide supply source 43 Foamable gas supply Device 61 Bubble nucleating agent supply device 62 Bubble nucleating agent supply device 70 Control device 100 Horizontal mold-clamping type injection molding device

Claims (9)

An injection device for plasticizing and injecting a thermoplastic resin as a molding material, a mold having a cavity that is a molding space filled with a thermoplastic resin injected from the injection device, and a mold for the mold A mold clamping device capable of performing clamping and expanding and reducing the volume of the cavity by opening and closing the mold,
After setting the skin material in the cavity of the mold in advance, the mold clamping is performed by the mold clamping device,
The injection device plasticizes the thermoplastic resin, mixes the plasticized thermoplastic resin and the foamable gas, and clamps the thermoplastic resin mixed with the foamable gas. After injection filling into the cavity of the mold, and integrally bonding the injection filled thermoplastic resin and the skin material previously set in the cavity,
The mold clamping device expands the volume of the cavity, and foams the thermoplastic resin mixed with the foamable gas to provide a skin layer made of a skin material and a foam layer made of a thermoplastic resin. A multilayer molding method for obtaining a multilayer molded article,
A thermoplastic resin that supplies the foamable gas to the injection apparatus at a pressure of 0.1 MPa or more and less than 1.0 MPa and mixes the thermoplastic resin plasticized by the injection apparatus and the foamable gas. Multi-layer molding method.   After foaming the thermoplastic resin, the volume of the cavity is further enlarged by the mold clamping device, and a gap is formed between the surface material and the surface forming the cavity of the mold, The multilayer molding method for thermoplastic resins according to claim 1, wherein the texture is restored.   The thermoplastic resin multilayer molding method according to claim 1 or 2, wherein the pressure of the foamable gas supplied to the injection apparatus is 0.5 MPa or more and less than 1.0 MPa.   The bubble nucleating agent is previously included in the foamable gas before being supplied to the injection apparatus, and the bubble nucleating agent is contained in the thermoplastic resin injected and filled into the cavity of the mold. A multilayer molding method for a thermoplastic resin according to claim 1.   The bubble nucleating agent is preliminarily included in the thermoplastic resin as the molding material, and the bubble nucleating agent is contained in the thermoplastic resin injected and filled into the cavity of the mold. A multilayer molding method of the thermoplastic resin as described.   The bubble nucleating agent is any one or a mixture of two or more of the group consisting of iron oxide, calcium silicate, zinc stearate, magnesium stearate, organic acid, aluminum silicate, glass fiber, and talc. A method for multilayer molding of a thermoplastic resin according to 4 or 5.   The thermoplastic resin multilayer molding method according to any one of claims 1 to 6, wherein supply of the foamable gas to the injection device is performed by pressure control.   The thermoplastic resin after plasticization in the hopper of the injection device, which is the inlet of the thermoplastic resin before plasticization, or the cylinder of the injection device that performs plasticization, is the supply destination of the foamable gas The method for multilayer molding of a thermoplastic resin according to any one of claims 1 to 7.   The said foamable gas is an inorganic gas of any one of an inorganic gas group consisting of air, carbon dioxide and nitrogen, or an inorganic gas in which two or more are mixed. A method for multilayer molding of thermoplastic resins.

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