JP5075506B2 - Manufacturing method of foam molded article - Google Patents

Description

  The present invention relates to a method for producing a foamed molded article by injection molding. More specifically, the present invention is capable of a higher foaming ratio than before, prevents molding defects that impair the surface appearance of molded articles such as swirl marks, and decomposes the foaming agent. The present invention relates to a method for producing a foamed molded article that suppresses generation of residues and the like and causes less mold contamination.

  Molded articles using thermoplastic resins are widely used in various fields such as automobile parts and household appliance parts. Among them, many products are foamed using a foaming agent for the purpose of reducing the weight of the parts and imparting flexibility. In recent years, many foam molded products by injection molding have been seen.

As a method of manufacturing a foam molded product by injection molding, an amount of foamable molten resin less than the volume of the cavity is injected into the mold, and the voids in the mold are foamed by the foaming pressure of the foamable molten resin. A short shot foaming method filled with resin is known.
This method can be easily implemented without the need for special equipment, but due to the characteristics of the method, the cavity is completely filled with the pressure of the foaming gas, so there is a limit to the filling rate of the gap, and the average foaming ratio However, the product weight reduction rate is not satisfactory. Further, the foamed cell diameter and cell density in the foam (near the gate and the filling end) are not uniform, and the required quality of the product has not been satisfied.

Therefore, a method of foaming while increasing the cavity volume is disclosed as a method for increasing the foaming ratio (see, for example, Patent Document 1). However, since the volume of the cavity is enlarged simultaneously with the injection, there is a problem that bubbles burst in the surface portion of the molded product, resulting in a problem that the appearance deteriorates. In addition, due to the characteristics of the construction method, there is a problem such as poor filling or insufficient foaming at the standing wall of the product because the wall thickness does not increase.
Also, it is known to use an organic or inorganic chemical foaming agent that generates an inert gas by thermal decomposition in foam molding. However, when the chemical foaming agent is decomposed, if a by-product is generated and the molding is continuously performed for a long time, there is a problem of so-called mold contamination in which the by-product is deposited on the mold surface. It was. As a result, a transfer failure of the deposited portion occurs, resulting in a defect that impairs the appearance of the molded product. In order to prevent this, periodic mold cleaning is required, and there is a problem that productivity is significantly impaired.
Furthermore, a method using a physical foaming agent in a supercritical state is also known as a method for improving the expansion ratio and preventing mold contamination. This technique is known as a microcellular foaming technique (see, for example, Patent Documents 2 and 3). However, in injection foam molding using such a supercritical state physical foaming agent, regardless of the amount of the supercritical state physical foaming agent to be introduced, as in the case of the molded product of the above-mentioned method, in which fine cells are not possible, There are problems such as uneven foam cell diameter and cell density, and the required quality of the product has not been fully satisfied. In addition, there are many restrictions on molding processing, and there is a problem that a large-scale high-pressure facility is required.

As an injection foaming method that solves these problems, an injection foaming method has been developed that enables the injection of a critical physical foaming agent into the cylinder of an injection molding machine at low pressure to obtain a product with a high expansion ratio and a good appearance. (See, for example, Patent Documents 4 and 5), but requires an expensive special device. Furthermore, there are problems such as generation of swirl marks on the surface of the foam and non-uniformity of the foam cell state as in the former.
JP-A-62-246710 US Pat. No. 5,158,986 US Pat. No. 4,473,665 JP 2000-84968 A JP 2002-79545 A

As described above, none of the techniques disclosed up to now can satisfy all the requirements for foamed molded products.
An object of the present invention is to provide a method for producing a foam-molded article having a high expansion ratio, which can be carried out simply, easily and efficiently, and has an excellent appearance, in view of the above-mentioned problems of the prior art.

  In order to achieve the above object, the present inventors have conducted intensive research, and as a result, when the thermoplastic resin composition containing the thermoplastic resin and the thermally expandable microcapsule is injection-molded, the inside of the mold has a negative pressure. It has been found that when the injection molding is performed in this state, a foamed molded product having an excellent appearance in which the foaming ratio of the molded product is increased and molding defects such as swirl marks are not generated can be obtained. The present invention has been completed based on these findings.

That is, according to the first invention of the present invention, a foamed thermoplastic resin composition in a molten or semi-molten state is injected into a cavity formed by closing a mold composed of a cavity mold and a core mold that can be opened and closed. A foamed molded article manufacturing method for filling and foaming and cooling and solidifying a foamable resin composition in a cavity, the foamable thermoplastic resin composition comprising a thermoplastic resin and a thermally expandable microcapsule, When injection filling the foamable thermoplastic resin composition , the pressure in the cavity at the start of injection filling is 150 to 700 hPa, and the pressure in the cavity at the completion of injection filling is 150 to 700 hPa. A method for producing a foamed molded article is provided.

According to a second aspect of the present invention, there is provided a method for producing a foam molded product according to the first aspect, wherein the thermoplastic resin is an olefinic thermoplastic resin.
Furthermore, according to the third invention of the present invention, in the first or second invention, the foamable thermoplastic resin composition may be thermally expanded microcapsules 0.5 to 100 parts by weight with respect to 100 parts by weight of the thermoplastic resin. A method for producing a foam-molded article comprising 20 parts by weight is provided.

According to a fourth invention of the present invention, in any one of the first to third inventions, the thermally expandable microcapsule has a volume average particle diameter of 5 to 50 μm and a maximum foaming temperature (Tmax) of 180 ° C. There is provided a method for producing a foam-molded article characterized by the above.
Furthermore, according to a fifth invention of the present invention, in any one of the first to fourth inventions, after completion of injection filling, the mold is opened by a predetermined amount to increase the cavity volume, A manufacturing method is provided.

  When the method for producing a foamed molded product of the present invention is used, a foamed molded product that is sufficiently foamed can be obtained without molding defects such as swirl marks. In addition, since there is no occurrence of decomposition residues and the like, there is no mold contamination, so there is no need for mold cleaning during production, and the productivity is greatly improved.

Hereinafter, the method for producing a foamed molded product of the present invention will be described in detail for each item.
In the method for producing a foamed molded article of the present invention, a foamed thermoplastic resin composition in a molten state or a semi-molten state is injected and filled into a cavity formed by closing a mold comprising a cavity mold and a core mold that can be opened and closed. , A foamed molded article manufacturing method for foaming and cooling and solidifying a foamable resin composition in a cavity, wherein the foamable thermoplastic resin composition includes a thermoplastic resin and a thermally expandable microcapsule, When injection filling the thermoplastic resin composition, the cavity internal pressure is set to a negative pressure.

1. Foam molding method The method for producing a foam molded article of the present invention comprises an injection unit capable of injecting and filling a molten or semi-molten resin into a cavity of a mold, and a cavity mold and a core mold that can be opened and closed relatively. It can be performed using an injection molding machine having a mold unit.
In the present invention, after foaming resin is injected and filled into a cavity formed by closing the mold, foaming and cooling and solidification of the molded product are performed after an appropriate time. Thereafter, the mold is opened and the foamed molded product is taken out. The opening and closing of the mold may be performed by moving either the cavity mold or the core mold, and both may be moved, but it is preferable to perform the opening and closing by moving the cavity mold.
As a foaming method, an amount of foamable molten resin less than the volume of the cavity is injected into a cavity formed by closing the mold, and the void in the mold is filled by the foaming pressure of the foamable molten resin. Examples include a short shot molding method, a mold development foam molding method in which a predetermined amount of the mold is opened to increase the cavity volume, and a foam molding method in which the volume shrinkage of the resin is expanded by foaming. A method combining these as much as possible may be used. For example, after injecting a foamable molten resin in an amount less than the volume of the cavity and filling the void in the mold by the foaming pressure of the foamable molten resin, the mold is opened by a predetermined amount to increase the cavity volume. And a method of further foaming.

In the injection molding of the present invention, it is important to set the pressure in the cavity during injection filling to a negative pressure. Negative pressure refers to a state where the pressure inside the cavity is lower than the pressure outside the cavity. Without negative pressure, the expansion ratio does not increase. Moreover, if cooling solidification progresses after injection filling, even if it carries out a negative pressure after that, there is only a little effect or it is not.
As a method of making the pressure in the cavity at the time of injection filling negative, the method of injecting and filling the resin after making the inside of the cavity negative, the method of making the negative pressure while injecting and filling the resin, the resin at the time of completion of injection filling The method of making it a negative pressure is mentioned. In the latter two methods, a buffer tank in a negative pressure state in which the inside of the cavity can be made sufficiently negative in advance is connected to the cavity via a valve, the valve is opened at a predetermined timing, and the inside of the cavity is quickly negatively charged. It is preferable to select a means for achieving a negative pressure so that foaming is effectively generated according to the progress of cooling and solidification of the molded product.

The minimum pressure in the cavity is preferably 800 hpa or less, more preferably 100 to 700 hpa. If the minimum pressure is less than 100 hpa, it takes a long time to achieve such a degree of vacuum, and the molding cycle is prolonged, and the thermally expandable microcapsule foams more than necessary, which causes appearance defects and the like. It is not preferable. On the other hand, when the minimum pressure exceeds 700 hpa, the promotion of foaming becomes insufficient. By obtaining a sufficient foaming promotion effect, improvement and uniformity of the foaming ratio of the entire molded product can be obtained, and a molded product that is lighter in weight can be obtained.
Here, the time of injection filling means from the start of injection to the completion of injection.
The minimum pressure is a pressure (P) at which Σ (P-Pi) ² is a minimum value by measuring a time (seconds) -pressure (hpa) profile from the start of injection to the completion of injection. There is no limit to the number of measurements, but three or more points including any one point at the start of injection, completion of injection, and injection filling excluding the two points are preferable.
As the definition of the negative pressure, it means from less than atmospheric pressure to around atmospheric pressure 0 (vacuum) around the molding machine for carrying out the contents of the present invention.

  In addition, in the injection molding according to the present invention, in addition to keeping the minimum pressure in the cavity at the time of injection filling to a negative pressure, the pressure in the cavity at the start of injection filling is preferably 100 to 700 hpa, More preferably, it is 150-600 hpa. By setting the pressure in the cavity at the start of injection filling within this range, there is an advantage that molding can be performed without sacrificing the molding cycle.

  Furthermore, in the injection molding according to the present invention, in addition to keeping the minimum pressure in the cavity at the time of injection filling to a negative pressure, the pressure in the cavity at the end of injection filling is preferably set to 100 to 700 hpa, More preferably, it is 150-600 hpa. By setting the pressure in the cavity at the end of injection filling to this range, there is an advantage that burrs are hardly formed on the molded product.

An example of the configuration of an injection mold that can be used in the present invention will be described with reference to FIG.
The injection mold 1 includes a core mold 2 that can be opened and closed and a cavity mold 3, and molten resin heated by a heating cylinder 11 is injected into the cavity 4 from a molten resin injection port 10. The mold 1 is connected to a vacuum apparatus via vacuum paths 7 and 8 provided in the cavity mold and the core mold so that the cavity 4 can be decompressed. The means for depressurizing the inside of the cavity 4 is not particularly limited, and a depressurization device may be incorporated in one or both of the cavity mold and the core mold, and the cavity mold, one or both of the core mold, or the parting surface between the cavity mold and the core mold It may be connected to a vacuum apparatus through a vacuum path provided in the above.
The vicinity of the cavities of the vacuum paths 7 and 8 is preferably formed of a porous body 9 having fine communicating voids. By using the porous body 9, it is possible to prevent the resin before cooling and solidification from flowing out into the vacuum path. Examples of the porous body include an aluminum porous body, a stainless metal powder porous body, and the like. The porous body is available as a porcelain made by Shinto Kogyo.

  Pressure reducing means such as a vacuum pump is connected to the tips of the vacuum paths 7 and 8. The vacuum path may be provided with a buffer tank (not shown), an openable / closable valve (not shown), and the like as necessary. The buffer tank is preferably installed because it can reduce a rapid pressure fluctuation during injection filling of the molten resin.

  The pressure in the cavity 4 can be measured by a pressure gauge installed in the cavity, or can be measured by a pressure gauge installed in the buffer tank. In the latter case, attention must be paid to the pressure loss in the vacuum path.

  Further, a sealing member 6 can be provided on the parting surface 5 in order to prevent or adjust air leakage from the parting surface 5 between the cavity mold 3 and the core mold 2. The seal member 6 may be provided so as to surround the cavity 4 or may be provided partially. Examples of the sealing member 6 include rubber packing.

  The molten resin inlet 10 may be provided with a shut-off function in order to prevent or adjust air leakage. The shut-off function may be provided on the mold 1 side or on the heating cylinder 11 side. When provided on the heating cylinder 11 side, it is preferable to provide a seal member at the nozzle touch portion.

The foam molded article of the present invention can be produced by an injection foam molding method in which foamable molten resin melt-kneaded by an injection foam molding machine is shaped and cooled by injection molding and foam-molded.
As a foaming method, a short amount of foamable molten resin less than the volume of the cavity is injected into a cavity formed by closing the mold, and the gap in the mold is filled by the foaming pressure of the foamable molten resin. Examples include a shot molding method, a mold development foam molding method in which a predetermined amount of mold is opened after short shot molding to increase the cavity volume, and a foam molding method in which the volume shrinkage of the resin is expanded by foaming.

In the present invention, the injection molding conditions will be described by taking an olefin resin composition as a preferable resin described later as an example. The injection pressure is 30 to 120 MPa, the injection time is 2 to 15 sec, the holding pressure is 0 to 12 MPa, and the holding time is By injection molding under the conditions of 0 to 30 sec, cooling time of 10 to 60 seconds, and resin temperature of 180 to 250 ° C., for example, an injection molded product of a polypropylene resin composition can be obtained.
In this case, in particular, the injection time and the pressure holding time can be shortened, and the molding cycle is shortened. By setting the injection pressure to 40 to 120 MPa, a desired molding machine can be used without being particularly limited by the scale of the molding machine. By setting the injection time to 2 to 15 seconds, it becomes possible to perform molding without being particularly limited by the size of the mold. Furthermore, by setting the holding pressure to 0 to 12 MPa, there is no particular limitation on the scale of the molding machine and the number of gates. Furthermore, the influence which it has on the external appearance of the molded object (polypropylene resin composition) by holding time is optimized by making holding time into 0-30 sec. Moreover, it becomes possible to raise production efficiency by making resin temperature into 180-250 degreeC. On the other hand, if the resin temperature is less than 180 ° C, insoluble defects of the polypropylene resin may occur. If the resin temperature exceeds 250 ° C, production efficiency decreases, gas burns, product sinks, etc. occur, which is not appropriate.

2. Foamable thermoplastic resin composition In the foamable thermoplastic resin composition according to the present invention, the usable resin is not particularly limited as long as it is a thermoplastic resin. Specifically, polyolefin resins such as polyethylene, polypropylene, poly 1-butene, poly 4-methyl-1-pentene, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6-naphthalate, nylon-6, Polyamide resins such as nylon-66, nylon-11 and nylon-12, polyether resins such as polyoxymethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid ester copolymer, ethylene / methacrylic acid ester copolymer Ethylene / unsaturated carboxylic acid ester copolymer resin, ethylene / acrylic acid copolymer and other ethylene / unsaturated carboxylic acid copolymer resin, and their metal ion cross-linked products (ionomer resin), polystyrene, ABS resin Etc. That.

Among these thermoplastic resins, polyolefin resins, particularly polyethylene and polypropylene are preferable from the viewpoint of mechanical strength, moldability, and cost. As the polyethylene, any of high density polyethylene, medium density polyethylene, linear low density polyethylene, and high pressure method low density polyethylene can be used.
A particularly suitable thermoplastic resin is polypropylene, which may be a homopolymer of propylene or a copolymer of propylene and other α-olefins. As the α-olefin, an olefin having 2 to 20 carbon atoms such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene can be used. preferable. The α-olefin content as a comonomer is 10 mol% or less, preferably 5 mol% or less. In the case of a copolymer, it may be a random copolymer of propylene and an α-olefin, or may be a block copolymer.

Polypropylene which can be preferably used in the present invention, the density is preferably 0.890~0.920g / cm ^3, more preferably 0.900~0.910g / cm ^3.
The melt flow rate (MFR) measured at 230 ° C. under a 2.16 kg load according to ASTM D-1238 is preferably 0.5 to 200 g / 10 minutes, more preferably 2 to 50 g / 10 minutes. is there.
When polypropylene having a broad molecular weight distribution and high stereoregularity is used, an injection molded product with higher rigidity can be obtained.

In the expandable thermoplastic resin composition according to the present invention, as a thermally expandable microcapsule that can be used, the maximum foaming temperature (Tmax) has a preferable lower limit of 180 ° C., and more preferably a lower limit of 200 ° C. By setting Tmax to 180 ° C. or higher, it is possible to reduce the sag of the thermally expandable microcapsule when the thermally expandable microcapsule is put into the cylinder. If the maximum foaming temperature (Tmax) is less than 180 ° C., the expansion of the thermally expandable microcapsule may occur in the cylinder, and the foaming ratio may be lowered.
In the present specification, the maximum foaming temperature is when the diameter of the thermally expandable microcapsule becomes maximum when the diameter is measured while heating the thermally expandable microcapsule from room temperature (maximum displacement). It means temperature.

  In addition, the volume-average particle diameter of the thermally expandable microcapsules has a preferable lower limit of 5 μm and a preferable upper limit of 50 μm. If the volume average particle size is less than 5 μm, the resulting molded article has too small bubbles, which may result in insufficient weight reduction of the molded article. On the other hand, if it exceeds 50 μm, the resulting molded article has bubbles. Since it becomes too large, it may become a problem in terms of strength and the like. A more preferred lower limit is 10 μm, and a more preferred upper limit is 40 μm.

  In the expandable thermoplastic resin composition according to the present invention, the amount of the thermally expandable microcapsule added is preferably 0 with respect to 100 parts by weight of the matrix resin, that is, 100 parts by weight of the thermoplastic resin. 0.5 part by weight, more preferred lower limit is 1.0 part by weight, while a preferred upper limit is 20 parts by weight, and a more preferred upper limit is 10 parts by weight. If the amount added is less than the lower limit part by weight, the resulting molded article has fewer bubbles, and it is difficult to exhibit various performances such as weight reduction. It may be a problem in terms of strength.

As such a thermally expandable microcapsule, for example, a nitrile monomer and methacrylic acid are contained as polymerization monomer components, and a monomer mixture in which the proportion of methacrylic acid in the monomer components is at least 10% by weight or more is polymerized. Inside the shell, a thermally expandable microcapsule encapsulating a volatile swelling agent as a core agent, having a maximum foaming temperature of 180 ° C. or higher and a volume average particle size of 30 μm or less, specifically, Sekisui Chemical “Advancell” (registered trademark) heat-resistant grade development product numbers “EMS-023” and “EMS-024” manufactured by Kogyo Co., Ltd., “EXPANCEL DU” manufactured by Nihon Philite Co., Ltd., and the like.
Moreover, when using the said heat | fever expansible microcapsule for injection molding, the pellet which carried out the masterbatch of the said heat | fever expansible microcapsule with base resins, such as polyethylene, can also be used.
Examples of such thermally expandable microcapsule pellets include “Advancell” (registered trademark) heat resistant grade developed product numbers “EMS-023MB” and “EMS-024MB” manufactured by Sekisui Chemical Co., Ltd.

The foamable thermoplastic resin composition according to the present invention or the thermoplastic resin can be used as a resin composition in which various additives are blended. For example, when an inorganic filler is contained, mechanical strength such as rigidity can be increased.
Inorganic fillers include talc, silica, mica, calcium carbonate, glass fiber, glass beads, barium sulfate, magnesium hydroxide, wollastonite, calcium silicate fiber, carbon fiber, magnesium oxysulfate fiber, potassium titanate fiber, titanium oxide, Examples thereof include calcium sulfite, white carbon, clay, and calcium sulfate.

Moreover, an elastomer can also be mix | blended with the foamable thermoplastic resin composition which concerns on this invention, and the said thermoplastic resin, and thereby mechanical strength, such as impact resistance, can be improved. A preferred elastomer is an olefin elastomer composed of a copolymer of α-olefin having 2 to 20 carbon atoms, preferably 2 to 10 carbon atoms. Examples of olefins include ethylene, propylene, 1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-tetradecene and 1-octadecene. Can do.
Specific examples of olefin elastomers include ethylene / propylene copolymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, ethylene / 1-octene copolymers, ethylene / 1-decene copolymers. Examples thereof include a polymer, a propylene / 1-butene copolymer, a propylene / 1-butene / ethylene copolymer, and an ethylene / propylene / diene copolymer. These elastomers can be used alone or in combination of two or more. The amount of the elastomer is preferably 1 to 30 parts by weight with respect to 100 parts by weight of the thermoplastic resin.

  In addition, the following additives can be blended with the foamable thermoplastic resin composition according to the present invention, if necessary, as long as the object of the present invention is not impaired. That is, antioxidants, heat stabilizers, weathering stabilizers, light stabilizers, UV absorbers, antistatic agents, nucleating agents, hydrochloric acid absorbers, slip agents, lubricants, flame retardants, pigments, dyes, dispersants, copper Examples thereof include harm prevention agents, neutralizing agents, foaming agents, plasticizers, bubble prevention agents, crosslinking agents, flowability improving agents such as peroxides, weld strength improving agents, natural oils, synthetic oils, waxes and the like.

3. Foam-molded article According to the method for producing a foam-molded article of the present invention, a foam-molded article having high rigidity, beautiful and excellent surface appearance can be obtained. Applications of such molded products are suitable for automotive interior parts such as instrument panels and door trims, automotive exterior parts such as bumpers and back doors, industrial parts such as toilet parts, washstands, toiletries, and other industrial parts. Can be used for

The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist.
The evaluation contents used in Examples and Comparative Examples are described below.

(I) Foaming ratio: In a predetermined molding method, the maximum foaming ratio that can reproduce the shape of the cavity was determined.
In the short shot method, the filling rate was changed, and the foaming ratio of the molded product obtained at the minimum filling rate at which the shape of the molded product could reproduce the cavity shape was used.
In the mold opening method, the mold opening amount was changed, and the foaming ratio of the molded product obtained at the time of the maximum mold opening amount that the shape of the molded product could reproduce the cavity shape was used.
Furthermore, in the combination of the short shot method and the mold opening method, the filling rate is fixed to the minimum filling rate that can reproduce the cavity shape, and the mold opening amount is changed by changing the mold opening amount. The foaming ratio of the molded product obtained at the time of the maximum mold opening amount that can reproduce the cavity shape.
The specific gravity (d _G , d _M ) of each test piece obtained by cutting from the gate part and the filling end part of the foam molded product is measured, and the average value (d _G-M ) and the specific gravity of the material for the foam molded product are measured. The ratio with (d ₁ ) was determined and (d ₁ / d _G−M ) = foaming ratio.

(Ii) Appearance of molded product: Visually judged according to the following evaluation criteria.
○: Specular gloss, very small swirl mark △: Surface fogging, low swirl mark ×: No gloss, many swirl marks

(Iii) Mold deposits: Judgment was made based on the following evaluation criteria.
○: Mold gloss maintenance, no adhesion ×: No gloss, adhesion

(Iv) Molding cycle: A molding time of 80 seconds / one cycle or less and a molded product obtained was indicated by ◯, and a molding product exceeding 80 seconds / 1 cycle was marked by ×.

[Example 1]
Polypropylene resin (Nippon Polypro Homopolypropylene MA06, hereinafter referred to as PP (A)) 100 parts by weight and thermally expandable microcapsule pellets (“Avancell EMS-023MB” manufactured by Sekisui Chemical, volume average particle size: 26 μm, Tmax: 210) C.) (mass ratio of base resin / thermally expandable microcapsule = 1/1) 2.5 parts by weight were dry blended to prepare a polypropylene resin composition.
The obtained resin composition was supplied to an injection molding machine in which a mold connected with a vacuum pump through a buffer tank and an opening / closing valve was set. The mold is provided with a film gate on one short side, and a vacuum path is provided near the other short side corresponding to the flow end of the molten resin. After closing the mold and reducing the pressure in the cavity to 400 hpa, an amount of resin composition corresponding to 87% of the cavity volume (104 cm ³ ) was added to a resin temperature: 210 ° C., resin pressure: 80 MPa, injection time: 2 Injection molding was performed in seconds. Two seconds after the start of injection (at the end of injection), the open / close valve was closed to shut off the vacuum path. The cooling time was 30 seconds. A flat plate of 300 × 100 × 4 mm was obtained. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank. The pressure after 2 seconds from the start of injection was 400 hpa, and the minimum pressure was 400 hpa.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.
Separately, when an amount of resin corresponding to 86% of the cavity capacity was injected and filled, the expansion ratio was 1.16 times, but insufficient filling was recognized.

[Example 2 (reference example) ]
100 parts by weight of polypropylene resin (PP (A): Nippon Polypro Homopolypropylene MA06) and thermally expandable microcapsule pellets (“Avancell EMS-023MB” manufactured by Sekisui Chemical, volume average particle size: 26 μm, Tmax: 210 ° C.) 2 0.0 parts by weight were dry blended to prepare a polypropylene resin composition.
After the mold was closed and the inside of the cavity was reduced to 100 hpa, injection molding was performed in the same manner as in Example 1 except that a resin composition corresponding to 91% of the cavity volume was injected. The pressure after 2 seconds from the start of injection was 100 hpa, and the minimum pressure was 100 hpa. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Example 3]
A polypropylene resin composition was prepared in the same manner as in Example 1.
The obtained resin composition was supplied to an injection molding machine in which a mold connected with a vacuum pump through a buffer tank and an opening / closing valve was set. The mold is provided with a film gate on one short side, and a vacuum path is provided near the other short side corresponding to the flow end of the molten resin. After closing the mold and reducing the pressure in the cavity to 400 hpa, an amount of resin composition corresponding to 87% of the cavity volume (104 cm ³ ) was added to a resin temperature: 210 ° C., resin pressure: 80 MPa, injection time: 2 Injection molding was performed in seconds. Two seconds after the start of injection (at the end of injection), the open / close valve was closed to shut off the vacuum path. Thereafter, the cavity mold was retracted by 3 mm to promote foaming to obtain a molded product having a thickness of 7 mm. The cooling time was 30 seconds. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank. The pressure after 2 seconds from the start of injection was 400 hpa, and the minimum pressure was 400 hpa.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Example 4]
In Example 3, “Advancel EMS-023MB” was changed to “Advancel EMS-024MB” (base resin / thermally expandable microcapsule mass ratio = 1/1) (volume average particle size: 27 μm, Tmax: 220 ° C.) The same operation as in Example 3 was performed except that.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Example 5]
Dry 100 parts by weight of ABS resin (Technopolymer 130) and 2.5 parts by weight of thermally expandable microcapsule pellets (“Advance EMS-023MB” manufactured by Sekisui Chemical, volume average particle size: 26 μm, Tmax: 210 ° C.) By blending, a resin composition was prepared.
Injection molding was performed in the same manner as in Example 1 except that the mold was closed and the inside of the cavity was decompressed to 300 hpa, and then an amount of the resin composition corresponding to 88% of the cavity volume was injected. The pressure 2 seconds after the start of injection was 300 hpa, and the minimum pressure was 300 hpa. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Comparative Example 1]
100 parts by weight of a polypropylene resin (PP (A): Nippon Polypro Homopolypropylene MA06) and 2.5 parts by weight of a chemical foaming agent (“Fine Blow S20N” manufactured by Nitto Kako Co., Ltd.) are dry blended to obtain a polypropylene resin composition. Was prepared.
After the mold was closed and the inside of the cavity was reduced to 600 hpa, injection molding was performed in the same manner as in Example 1 except that the resin composition was injected in an amount corresponding to 98% of the cavity volume. The pressure 2 seconds after the start of injection was 600 hpa, and the minimum pressure was 600 hpa. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Comparative Example 2]
100 parts by weight of a polypropylene resin (PP (A): Nippon Polypro Homopolypropylene MA06) and 2.5 parts by weight of a chemical foaming agent (“Fine Blow S20N” manufactured by Nitto Kako Co., Ltd.) are dry blended to obtain a polypropylene resin composition. Was prepared.
Injection molding was performed in the same manner as in Example 1 except that the mold was closed and the inside of the cavity was depressurized to 100 hpa, and then an amount of the resin composition corresponding to 100% of the cavity volume was injected. The pressure after 2 seconds from the start of injection was 100 hpa, and the minimum pressure was 100 hpa. The pressure in the cavity was measured with a pressure gauge installed in the buffer tank.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

[Comparative Example 3]
A polypropylene resin composition was prepared in the same manner as in Example 1.
Injection molding was performed in the same manner as in Example 1 except that the resin composition was injected in an amount corresponding to 98% of the cavity volume without closing the mold and reducing the pressure in the cavity.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured. The obtained results are shown in Table 1.

[Comparative Example 4]
100 parts by weight of a polypropylene resin (PP (A): Nippon Polypro Homopolypropylene MA06) and 2.5 parts by weight of a chemical foaming agent (“Fine Blow S20N” manufactured by Nitto Kako Co., Ltd.) are dry blended to obtain a polypropylene resin composition. Was prepared.
Injection molding was performed in the same manner as in Example 1 except that the resin composition was injected in an amount corresponding to 100% of the cavity capacity without closing the mold and reducing the pressure in the cavity. Thereafter, the cavity mold was retracted by 3 mm to promote foaming to obtain a molded product having a thickness of 7 mm.
The obtained flat plate-shaped molded article was not insufficiently filled and reproduced the cavity shape. The expansion ratio of the molded product was measured, and the appearance of the molded product, the deposit on the mold, and the molding cycle were evaluated. The obtained results are shown in Table 1.

  From the evaluation result of Table 1, in Examples 1-5, compared with Comparative Examples 1-4, there is no metal mold deposit and it is excellent in the appearance of the molded product. In particular, Examples 3 and 4 are highly foamed. It turns out that it is a magnification. On the other hand, in Comparative Examples 1 and 2, although the cavity internal pressure is negative, the chemical foaming agent is used as the foaming agent in the resin composition. Evaluation etc. are bad. Moreover, although the comparative example 3 contains the thermally expansible microcapsule in a resin composition, since the cavity internal pressure is atmospheric pressure, compared with Example 1, a foaming magnification is low and molded article external appearance evaluation is "". The surface is cloudy and the swirl mark is low. Furthermore, it can be seen that Comparative Example 4 has a bad cavity internal pressure and a chemical foaming agent as the foaming agent in the resin composition, and thus the molded product appearance and mold deposit evaluation are poor.

  According to the method for producing a foam-molded product of the present invention, a foam-molded product having a high expansion ratio that is highly rigid, beautiful and excellent in surface appearance can be obtained. Therefore, it should be used suitably for automotive interior parts such as instrument panels and door trims, automotive exterior parts such as bumpers and back doors, industrial parts such as toiletries, washstands, toiletries and other amenity parts. Can do.

It is a figure explaining an example of composition of an injection mold used for the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection mold 2 Core type 3 Cavity type 4 Cavity 5 Parting surface 6 Sealing member 7 Vacuum path 8 Vacuum path 9 Porous body 10 Resin injection port 11 Heating cylinder

Claims (5)

A mold formed of a cavity mold and a core mold that can be opened and closed is injected and filled with a foamed thermoplastic resin composition in a molten or semi-molten state, and the foamable resin composition is foamed in the cavity. And a method for producing a foam-molded product that is cooled and solidified,
The foamable thermoplastic resin composition includes a thermoplastic resin and a thermally expandable microcapsule. When the foamable thermoplastic resin composition is injected and filled , the pressure in the cavity at the start of injection filling is 150 to 700 hPa. And a pressure in the cavity at the completion of injection filling is 150 to 700 hPa .   The method for producing a foam molded article according to claim 1, wherein the thermoplastic resin is an olefin-based thermoplastic resin. The foamable thermoplastic resin composition according to claim 1 or 2 , wherein the foamable thermoplastic resin composition contains 0.5 to 20 parts by weight of thermally expandable microcapsules with respect to 100 parts by weight of the thermoplastic resin. Production method. The foam-molded article according to any one of claims 1 to 3 , wherein the thermally expandable microcapsule has a volume average particle diameter of 5 to 50 µm and a maximum foaming temperature (Tmax) of 180 ° C or higher. Manufacturing method. The method for producing a foam-molded article according to any one of claims 1 to 4 , wherein after completion of injection filling, the mold is opened by a predetermined amount to increase the cavity volume.

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