JP2013095043A - Mold for injection foam molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of occurrence of circular and elliptic recesses, so-called pitted surface, in injection foam molding, in which particularly a molding method using both of a counter-pressure manufacturing method and a heat and cool molding method suffers from frequent occurrence of the pitted surfaces although silver and swirl marks can be eliminated, and failure in appearance cannot be overcome at present.SOLUTION: A beautiful injection foam molded body can be obtained by eliminating pitted surface as a failure in appearance by forming a thin film having a dynamic friction coefficient (μk) relative to a thermoplastic resin of ≤0.25 as measured by a measuring method according to JIS K 7125 to the entire or part of the surfaces of a cavity and a core for injection foam molding.

Description

  The present invention relates to a mold for injection foam molding.

  In the injection foam molding field, as a method of foaming in the mold for the purpose of weight reduction and cost reduction, foaming is performed using a mold that consists of a fixed mold and a movable mold that can move forward and backward at any position. There is a so-called core back method (moving cavity method) in which a thermoplastic resin containing an agent is melted and the movable mold is moved backward after the injection is completed. It is widely known that if this method is used, a non-foamed layer is formed on the surface, and the foamed inner layer tends to become uniform bubbles at a high magnification, and it is easy to obtain an injection-foamed molded article that is light in weight and particularly excellent in appearance. ing.

  However, in current injection foam molding, appearance defects such as silver derived from foaming agents, swirl marks, avatars, etc. have occurred, but among these silver and swirl marks, the mold design surface is subjected to a textured process, resulting in poor appearance. A counter pressure manufacturing method in which the molten foamed resin material is injected into a mold that has been pressurized to a pressure that does not cause bubble breakage in the flow front of the previously melted foamed resin material, or the mold surface in advance. Has been improved by a heat and cool manufacturing method or the like in which a foamed resin material is injected into a mold adjusted to a temperature equal to or higher than the load deflection temperature of the resin used (conforming to JIS K 7191-2). In Patent Document 1, a thick film layer is provided in a mold cavity with a resin having high heat resistance such as silicone resin, fluorine resin, epoxy resin, polyimide resin, etc., and injection foam molding is performed by improving heat insulation. A technique for preventing the occurrence of swirl marks is disclosed.

  However, any of the production methods has a big problem that a circular or elliptical dent called “avatar” (also called “skin skin”) occurs. Here, as a mechanism of avatar generation, when the molten foam resin material is injected into the mold, the mold surface and the flow front come into contact with each other, and the molten foam resin material with a gas reservoir is in close contact with the mold. When the gas component is solidified and escapes, it remains as a circular or elliptical dent, and its size is about 0.5 to 10 mm in diameter. In particular, in the counter pressure manufacturing method, since the gas itself is injected into the mold, avatar tends to be easily generated between the mold and the molten foamed resin material.

  Similarly, in the heat and cool manufacturing method, since the foamed resin raw material is injected while the mold surface is heated, the skin layer is cored back in a thin or soft state, so that the foam is melted with the mold. The skin layer was pushed by the gas reservoir generated between the resin raw materials, and avatars were likely to be generated.

  Further, Patent Document 2 discloses a technique for eliminating the avatar by providing a vacuum device for forcibly discharging excess gas in the mold after injecting the molten foamed resin material in order to improve the avatar in the counter pressure manufacturing method. Has been. Certainly, this method can improve the avatar in the counter pressure manufacturing method, but it has the disadvantage that a special apparatus is required and it is difficult to set conditions for forcibly removing gas.

JP 2002-321246 A JP 2010-167667 A

  The present invention provides a mold capable of obtaining a beautiful molded body that eliminates an avatar at the time of injection foam molding without adding a special device to the mold unlike the improvement of silver and swirl marks. It is.

  In view of the above-described situation, the present inventors have filled the molten foamed resin raw material without closely adhering to the mold surface after the flow front has broken, so that a gas pool is formed between the mold and the skin layer. Is likely to remain and frequently occurs in molded products as avatars, and by improving the molds with a simple method, the occurrence of avatar peculiar to injection foam molding is greatly reduced, and a beautiful molded body is produced. It became possible to get.

  The present invention is as follows.

  1). A thin film having a dynamic friction coefficient (μk) with respect to a thermoplastic resin of 0.25 or less on the entire surface or a part of the mold cavity and the core surface by a dynamic friction coefficient (μk) according to JIS K 7125 A mold for injection foam molding in which is formed.

  2). 1. A mold for injection foam molding according to 1), wherein a thin film is formed of a fluororesin on the entire surface or part of the cavity and core surface of the mold in order to reduce the dynamic friction coefficient (μk).

  3). The injection foam molding die according to 1), wherein a thin film is formed of a silicone-based resin on the entire surface or a part of the cavity and the core surface in order to reduce the dynamic friction coefficient (μk).

  4). Injection foaming that performs foam molding by feeding the foamed resin raw material consisting of thermoplastic resin and foaming agent to an injection molding machine, melt-kneading, and then injecting the molten foamed resin raw material into the mold and then moving the movable side backward In molding, an injection foam molding method characterized by using any of the molds described in 1) to 3).

  5). Injection foaming performed with any of the molds described in 1) to 3) in a method of injecting a molten foamed resin raw material into a mold that has been previously pressurized to a pressure at which foaming does not occur at the flow front of the foamed resin raw material Molding method.

  6). In the production method of injecting a foamed resin raw material melted into a mold that has been adjusted to a temperature equal to or higher than the load deflection temperature (based on JIS K 7191-2) of the resin used on the mold surface in advance, 1) to 3) An injection foam molding method performed with any mold.

  7). 4. The injection foam molding method according to 4) to 6), wherein the thermoplastic resin is a thermoplastic elastomer resin.

  8). 4. The injection foam molding method according to 4) to 6), wherein the thermoplastic resin is a polypropylene resin.

  The metal mold | die of this invention is a metal mold | die which can eliminate the external appearance defect in injection foam molding, especially generation | occurrence | production of an avatar. The molded body obtained by injection foam molding with this mold can be suitably used for automobile interior members, building materials, housing materials, etc. without painting.

  Unlike the above-mentioned reference, the present invention is a measurement method in which the dynamic friction coefficient (μk) conforms to JIS K 7125 on the entire surface or a part of the mold cavity and the core surface. μk) is a mold for injection foam molding in which a thin film having a thickness of 0.25 or less is formed, and the dynamic friction coefficient between the mold and the molten foam resin material is reduced, that is, the lubricity between the melted foam resin material and the mold. It is possible to improve the appearance defect by improving. In the present invention, as a result of considering the current state at the time of occurrence of avatar at the time of injection foam molding, the range of estimation is not exceeded, but by improving the lubricity between the injected molten foam resin material and the mold surface, The idea has been reached that the foamed resin raw material is filled to the end of the mold without causing gas accumulation on the mold surface.

  In the present invention, the material of the mold is not particularly specified, and there is no problem as long as it is a material used for normal injection molding and injection foam molding. Also, there is no particular designation on the surface state of the mold, and the avatar can be eliminated for mirror surfaces and texture processing.

  In the present invention, the fluororesin includes polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride, polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (FPA), and tetrafluoroethylene. -Hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene (ECTFE), and the like. From the viewpoint of heat resistance, polytetrafluoroethylene (PEFE) ) Is preferable as the fluororesin.

  Examples of the silicone resin in the present invention include silicone resins (epoxy group and methoxy group addition type), polyorganosiloxane, polyorganosilsesquioxane cured product, dimethylpolysiloxane, and the like, which have a high effect of reducing the dynamic friction coefficient. Therefore, polyorganosiloxane is preferable as the silicone resin. The formation of the thin film in the present invention means that the fluororesin or the silicone resin is formed with a thickness of 5 to 200 μm on the fixed side, the movable side and a part of the injection foam molding die. Point to.

  The thin film may be formed by a general forming method performed by an injection mold, an injection foaming mold, a roll molding roller, or the like, and the dynamic coefficient of friction (μk) is 0.25 for the surface roughness. If it is below, there is no problem in particular. In forming a thin film, a commercially available adhesive tape based on a fluororesin and a silicone resin may be used. About the film thickness of a thin film, 5-200 micrometers is preferable, More preferably, it is 5-150 micrometers, Most preferably, it is 10-100 micrometers. When the film thickness is less than 5 μm, the thin film is easily peeled off by the pressure during injection foam molding, and when it is formed thicker than 200 μm, a heat insulating layer is formed on the mold. It is not preferable because the molded product cannot be cooled. As described above, when injection foam molding is performed with a mold in which a heat-resistant resin thick film is formed on the mold surface in Patent Document 1, the skin layer is difficult to cool due to the heat insulating effect, and a phenomenon similar to the heat and cool manufacturing method occurs. The possibility of the occurrence is very high, which is not preferable.

  The dynamic friction coefficient (μk) of a mold having a thin film formed of a fluororesin system and / or a silicone resin system is 0.25 or less, more preferably 0.2 or less, and most preferably 0.15 or less. When the dynamic friction coefficient (μk) is 0.25 or more, the dynamic friction coefficient of the die subjected to embossing without forming a thin film is in the range of more than 0.25 and 0.3 or less. In this state, the avatar cannot be eliminated. .

  In the injection foam molding using a mold according to the present invention, the avatar can be eliminated by combining a counter pressure manufacturing method and a heat and cool manufacturing method in which avatars are easily generated.

  The thermoplastic resin used in the present invention is preferably a thermoplastic elastomer or a polypropylene resin. Examples of the thermoplastic elastomer include olefin-based thermoplastic elastomers (TPO, TPV), styrene-based thermoplastic elastomers (TPS), vinyl chloride-based thermoplastic elastomers (TPVC), urethane-based elastomers (TPU), polyester-based thermoplastic elastomers ( TPEE), polyamide-based thermoplastic elastomer (TPAE), and the like. From the viewpoint of cost and touch, olefin-based thermoplastic elastomers (TPO, TPV) are particularly preferable. As the polypropylene resin, a polypropylene resin can be suitably used as long as it is a polyolefin resin containing propylene, more preferably a blend with a modified polypropylene resin.

  Among polypropylene resins, the melt flow rate is preferably 10 g / 10 min to 100 g / 10 min, more preferably 15 g / 10 min to 50 g / 10 min, and the melt tension is preferably 2 cN or less, more preferably A linear polypropylene resin having 1 cN or less is preferable.

  When the melt flow rate of the linear polypropylene resin is less than 10 g / 10 min, when producing an injection foamed molded article, a short shot is required in the injection foam molding in which the mold cavity clearance has a thin part of about 1 to 2 mm. In some cases, it is difficult to continuously and stably perform injection foam molding. When the melt flow rate exceeds 100 g / 10 min, bubbles are likely to be destroyed at the time of foaming, and a high foaming ratio cannot be obtained, or the rigidity of the injection foamed molded article may be lowered. On the other hand, when the melt tension exceeds 2 cN, the transferability to the mold surface tends to deteriorate, and it is difficult to obtain an injection-foamed molded article having a beautiful appearance.

  The melt flow rate is a value measured under a load of 2.16 kg at 230 ° C. in accordance with ASTM D-1238. The melt tension is a capillograph (manufactured by Toyo Seiki Seisakusho) with an attachment for measuring the melt tension. When a strand lowered at a piston descending speed of 10 mm / min is drawn at 1 m / min from a die having a hole of φ1 mm and a length of 10 mm at 230 ° C., and the take-up speed is increased at 40 m / min after stabilization. This refers to the take-up load of a pulley with a load cell when it breaks.

The linear polypropylene resin here is a polypropylene resin having a linear molecular structure, and is a normal polymerization method, for example, a catalyst system obtained from a transition metal compound and an organometallic compound supported on a carrier. (Eg, Ziegler-Natta catalyst) in the presence of polymerization. Specific examples include propylene homopolymers, block copolymers, and random copolymers, which are crystalline polymers. As a copolymer of propylene, a copolymer containing propylene in an amount of 75% by weight or more is preferable in that the crystallinity, rigidity, chemical resistance, etc., which are characteristics of the polypropylene resin, are maintained. The copolymerizable α-olefin is ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene. , 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, and the like, α-olefin having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene, tetracyclo [6,2,1 ^1,8 , 1 ^3,6 ] -4-dodecene and other cyclic olefins, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1,4-hexadiene, 7-methyl-1,6 -Diene such as octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, acrylic Butyl Le, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene. Among these, ethylene and 1-butene are preferable in terms of improving cold brittleness resistance and low cost.

  The mixing method of the linear polypropylene resin and the modified polypropylene resin is not particularly limited, and can be performed by a known method. For example, the pellet-shaped resin is dry-blended using a blender, a mixer, or the like, and melt-mixed. And a method of melting and mixing in a solvent. In the present invention, a method of dry blending and then subjecting to injection foam molding is preferable because it requires less heat history and decreases the melt tension.

  These thermoplastic resins may be used alone, but the melt flow rate is preferably 0.1 g / 10 min or more and less than 100 g / 10 min, more preferably 1.0 g / 10 min or more and 80 g / 10 min or less, It is preferably a blend with a modified polypropylene resin exhibiting strain hardening.

  The blending ratio of the thermoplastic resin and the modified polypropylene resin is preferably thermoplastic resin: modified polypropylene resin = 50 to 97% by weight: 3 to 50% by weight, and more preferably 55 to 95% by weight: 5 to 45%. It is preferable that the blending ratio is wt%, most preferably 60 to 95 wt%: 5 to 40 wt%. When the blending ratio of the modified polypropylene resin is within the above range, the composition has fluidity suitable for injection foam molding and melt tension for preventing bubble breakage, and is lightweight and has a high expansion ratio. An injection foam molded article having good transferability and excellent soft feeling can be obtained.

If the melt flow rate is less than 0.1 g / 10 min, the modified polypropylene resin may have poor dispersibility in the linear polypropylene resin, resulting in uneven foaming ratio and bubbles and poor surface properties. There is a case. When the melt flow rate is 100 g / 10 min or more, the concentration of the modified polypropylene resin on the surface of the injection-foamed molded article tends to be too high and it is difficult to obtain a beautiful surface appearance. On the other hand, the melt tension varies depending on the melt flow rate of the modified polypropylene,
(A) When the melt flow rate is 0.1 g / 10 min or more and less than 10 g / 10 min, the melt tension is 5 cN or more, preferably 7 cN or more.
(B) When the melt flow rate is 10 g / 10 min or more and less than 30 g / 10 min, the melt tension is 2 cN or more, preferably 3 cN or more.
(C) When the melt flow rate is 30 g / 10 min or more and less than 50 g / 10 min, the melt tension is 1 cN or more, preferably 1.5 cN or more.
(2) When the melt flow rate is 50 g / 10 min or more and 100 g / 10 min or less, the melt tension is 0.3 cN or more, preferably 0.6 cN or more.
Thus, when it is less than each numerical value, it is difficult to obtain an injection foam molded article having a foaming ratio of 2 times or more, and it is difficult to form uniform fine bubbles.

  Strain hardening here is defined as that the viscosity increases as the stretch strain of the melt increases, and is usually the method described in Japanese Patent Application Laid-Open No. 62-121704, that is, the elongation measured by a commercially available rheometer. This can be determined by plotting the relationship between viscosity and time. Further, for example, strain hardening can be determined from the breaking behavior of the molten strand at the time of melt tension measurement. That is, when the melt tension increases abruptly when the take-up speed is increased, strain hardening is exhibited. If the modified polypropylene-based resin does not exhibit strain-hardening properties, it is difficult to obtain an injection-foamed molded article having a high expansion ratio exceeding 2 times even when the melt tension is high.

  Examples of such a modified polypropylene resin include a branch obtained by irradiating a linear polypropylene resin with radiation, or by melting and mixing a linear polypropylene resin, a radical polymerization initiator, and a conjugated diene compound. A modified polypropylene resin containing a structure or a high molecular weight component may be mentioned. Among these, in the present invention, a modified polypropylene resin obtained by melt-mixing a linear polypropylene resin, a radical polymerization initiator and a conjugated diene compound is inexpensive because it does not require expensive radiation irradiation equipment. This is preferable because it can be manufactured. Examples of the raw material polypropylene resin used for the production of the modified polypropylene resin include the same as the linear polypropylene resin.

  Examples of the conjugated diene compound include butadiene, isoprene, 1,3-heptadiene, 2,3-dimethylbutadiene, 2,5-dimethyl-2,4-hexadiene, and these may be used alone or in combination. Good. Among these, butadiene and isoprene are particularly preferable because they are inexpensive and easy to handle and the reaction easily proceeds uniformly.

  The addition amount of the conjugated diene compound is preferably 0.01 parts by weight or more and 20 parts by weight or less, and more preferably 0.05 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. If the amount is less than 0.01 parts by weight, the effect of the modification may be difficult to obtain, and if the amount exceeds 20 parts by weight, the effect is saturated, which may not be economical.

  Monomers copolymerizable with the conjugated diene compounds, such as vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, metal acrylate Salt, metal methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, and other acrylic esters, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-methacrylic acid 2- Methacrylic acid esters such as ethylhexyl and stearyl methacrylate may be used in combination.

  The radical polymerization initiator generally includes peroxides, azo compounds, and the like, but those having a capability of extracting hydrogen from a polypropylene resin or the conjugated diene compound are preferable. Generally, ketone peroxides, peroxyketals, hydroperoxides are used. Organic peroxides such as oxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, and peroxyesters are listed. Of these, those having particularly high hydrogen abstraction ability are preferred, such as 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, Peroxyketals such as n-butyl 4,4-bis (t-butylperoxy) valerate, 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, 2,5-dimethyl-2,5 -Di (t-butylperoxy) hexane, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, di-t-butylperoxide, 2,5-dimethyl Diacyl peroxides such as dialkyl peroxides such as -2,5-di (t-butylperoxy) hexyne-3 and benzoyl peroxides Oxide, t-butyl peroxyoctate, t-butyl peroxyisobutyrate, t-butyl peroxylaurate, t-butyl peroxy 3,5,5-trimethylhexanoate, t-butyl peroxyisopropyl carbonate , 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butyl peroxyacetate, t-butyl peroxybenzoate, and peroxyesters such as di-t-butylperoxyisophthalate Or 2 or more types are mentioned.

  The addition amount of the radical polymerization initiator is preferably 0.01 parts by weight or more and 10 parts by weight or less, more preferably 0.05 parts by weight or more and 2 parts by weight or less with respect to 100 parts by weight of the linear polypropylene resin. If the amount is less than 0.01 part by weight, the effect of reforming may be difficult to obtain, and if the amount exceeds 10 parts by weight, the effect of reforming may be saturated and not economical.

  The apparatus for reacting the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator includes a roll, a kneader, a Banbury mixer, a Brabender, a single screw extruder, a kneader such as a twin screw extruder, a twin screw, etc. Examples of the surface renewal machine include a horizontal stirrer such as a biaxial multi-disk device, and a vertical stirrer such as a double helical ribbon stirrer. Among these, a kneader is preferably used, and an extruder is particularly preferable from the viewpoint of productivity.

There is no particular limitation on the order and method of mixing and kneading (stirring) the linear polypropylene resin, the conjugated diene compound, and the radical polymerization initiator. The linear polypropylene-based resin, the conjugated diene compound, and the radical polymerization initiator may be mixed and then melt-kneaded (stirred). After the polypropylene-based resin is melt-kneaded (stirred), the conjugated diene compound or the radical initiator may be mixed. They may be mixed simultaneously or separately, collectively or divided. The temperature of the kneading (stirring) machine is preferably 130 to 300 ° C. in that the linear polypropylene resin melts and does not thermally decompose. The time is generally preferably 1 to 60 minutes. In this way, a modified polypropylene resin can be produced. There is no restriction | limiting in the shape and magnitude | size of a polypropylene resin, A pellet form may be sufficient.

  The foaming agent that can be used in the present invention is not particularly limited as long as it can be usually used for injection foam molding, such as a chemical foaming agent and a physical foaming agent. The chemical foaming agent is mixed with the resin composition in advance and then supplied to the injection molding machine, and decomposes in the cylinder to generate a gas such as carbon dioxide. Examples of the chemical foaming agent include inorganic chemical foaming agents such as sodium bicarbonate and ammonium carbonate, and organic chemical foaming agents such as azodicarbonamide and N, N′-dinitrosopentatetramine. A physical foaming agent is injected into a molten resin in a cylinder of a molding machine as a gaseous or supercritical fluid, dispersed or dissolved, and functions as a foaming agent by being released from pressure after being injected into a mold. It is a thing. Physical foaming agents include aliphatic hydrocarbons such as propane and butane, alicyclic hydrocarbons such as cyclobutane and cyclopentane, halogenated hydrocarbons such as chlorodifluoromethane and dichloromethane, nitrogen, carbon dioxide, air, etc. Inorganic gas. You may use these individually or in mixture of 2 or more types.

  Among these foaming agents, an inorganic chemical foaming agent that can use a normal injection molding machine and easily obtain uniform fine bubbles is preferable. These inorganic chemical foaming agents include, for example, foaming aids such as organic acids such as citric acid and inorganic fine particles such as talc, in order to stably and uniformly make the bubbles in the foamed molded product. A nucleating agent such as may be added. Usually, the inorganic chemical foaming agent is preferably used as a masterbatch of a polyolefin resin having a concentration of 10 to 50% by weight from the viewpoints of handleability, storage stability, and dispersibility in a thermoplastic resin.

  The amount of the inorganic chemical foaming agent added varies depending on the type, concentration in the masterbatch and the desired expansion ratio, but is preferably 0.1 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin. Preferably it is used in the range of 0.5 to 20 parts by weight. By using in this range, it is easy to economically obtain an injection foam molded article having a foaming ratio of 2 times or more and uniform fine bubbles.

  Further, if necessary, as long as the effects of the present invention are not impaired, antioxidants, metal deactivators, phosphorus processing stabilizers, UV absorbers, UV stabilizers, fluorescent brighteners, metal soaps, antacid adsorption An additive such as a stabilizer such as an agent, a crosslinking agent, a chain transfer agent, a nucleating agent, a lubricant, a plasticizer, a filler, a reinforcing material, a pigment, a dye, a flame retardant, and an antistatic agent may be used in combination. These additives that are used as necessary are used in a range that does not impair the effects of the present invention, but preferably 0.01 parts by weight or more and 10 parts by weight or more with respect to 100 parts by weight of the thermoplastic resin. Less than parts by weight are used.

[Measurement of dynamic friction coefficient]
The dynamic friction coefficient in the present invention is measured using Shinto Seiki's HEIDON 14D-R according to JIS K 7125, and the mating material is cut out from a flat molded body using TPO M142E made by Prime Polymer. used. The measurement conditions of the dynamic friction coefficient (μk) in JIS K 7125 are as follows.
Measurement speed: 100 mm / min
Measuring load: 200g
Mating material size: 63mm x 63mm
Room temperature conditions during measurement: 23 ° C. × 50 ± 5% RH

[About expansion ratio]
The bottom face thickness in a mold described later was set to 2 mm, and after injection foaming molding, the center part of the bottom face was cut out with an ultrasonic cutter, measured with a digital thickness gauge, and the foaming ratio was calculated.

[Avatar evaluation method]
Only the aluminum plate described later was evaluated for avatar improvement evaluation. The judgment is as follows.
Avatars cannot be confirmed at all (0 avatars): ○
Local avatars are generated (1 to 3 avatars):
Avatar is generated on the entire surface of the plate (more than 4 avatars): ×
Specific examples are shown below, but the present invention is not limited to the following examples.

Example 1
A thin film (thickness: about 30 μm) was formed with polytetrafluoroethylene on an aluminum plate having dimensions of width 50 mm × length 150 mm × thickness 0.5 mm, and 30 ° taper at the end. The dynamic friction coefficient (μk) of this plate was 0.12. This plate was affixed to the cavity side of the mold (test box mold) with double-sided tape.

  Prime resin Prime TPO M142E and modified polypropylene resin (modified PP) were used as the base resin. The modified polypropylene resin is a mixture of 100 parts by weight of a polypropylene homopolymer having a melt flow rate of 45 g / 10 min as a linear polypropylene resin and 0.4 parts by weight of t-butylperoxyisopropyl carbonate as a radical polymerization initiator. It is supplied from a hopper of a 45 mmφ twin screw extruder (L / D = 40) at 70 kg / hour, 0.35 parts by weight of isoprene monomer is supplied from an introduction part provided in the middle using a metering pump, and the strand is water-cooled. The physical properties of the modified polypropylene resin obtained by chopping showed a melt flow rate of 60 g / 10 min, a melt tension of 1.1 cN, and a strain hardening property. The foaming agent is dry blended in the number of parts shown in Table 1, using Polyslen EE275F (27% foaming agent concentration) manufactured by Eiwa Kasei Kogyo Co., Ltd. and the colorant (CMB) PP-M 77255 Black manufactured by Dainichi Seika Co., Ltd. And put into an injection foam molding machine hopper.

  The mold is a test box type and has a built-in hot runner, and has a valve gate at the center of the molded body. Molded body dimensions: 200 mm × 200 mm, gate pin → cavity side / plane pin used, initial thickness 1.5 mm adjusted. The mold temperature was set to 35 ° C. on the cavity side and 30 ° C. on the core side.

The injection molding machine is an electric injection molding machine (manufactured by Ube Industries Co., Ltd.) having a mold back force of 350 t and a core back function and a shut-off nozzle. After melt-kneading at a cylinder temperature of 200 ° C. and a back pressure of 15 MPa, It is a test box type with a built-in hot runner consisting of a fixed type set at 35 ° C and a movable type set at 30 ° C that can move forward and backward, and a valve gate (φ2) in the center of the molded body It was injection-filled at an injection speed of 100 mm / sec with an initial thickness t ₀ = 2.0 mm of the bottom surface portion. After the injection filling was completed, the movable mold was retracted (core back) so that the bottom surface portion had a desired thickness (foaming ratio), and the resin in the cavity was foamed. After completion of foaming, the injection foamed molded article was taken out after cooling for 100 seconds.

(Example 2)
A polyorganosiloxane (TSF451-1000, manufactured by GE Toshiba Silicone) is applied by brush to an aluminum plate having a width of 50 mm, a length of 150 mm, and a thickness of 0.5 mm, and a taper of 30 ° at the end. The film was baked for 5 hours with a hot air drier kept at -5 ° C., and after removing the temperature, the excess was wiped off with gauze to form a thin film (film thickness of about 10 μm). The dynamic friction coefficient (μk) of this plate was 0.05. An injection foamed molded article was obtained in the same manner as in Example 1 except that this plate was attached to the cavity side of a mold (test box mold) with a double-sided tape.

(Example 3)
Nittolon tape (tape thickness 50 μ) manufactured by Nitto Denko Corporation was attached to the thin film forming portion of the aluminum plate. The dynamic friction coefficient (μk) was 0.07. An injection foamed molded article was obtained in the same manner as in Example 1 except that this plate was attached to the cavity side of a mold (test box mold) with a double-sided tape.

Example 4
An injection-foamed molded article was obtained in the same manner as in Example 1 except that Prime Polypro J708UG was used as the base resin formulation.

(Example 5)
An injection foamed molded article was obtained in the same manner as in Example 1 except that the molten foamed resin material was injected into a mold pressurized to 1 MPa in advance, and the pressure in the mold was released simultaneously with completion of the injection.

(Example 6)
In a cavity with the fixed side set at 120 ° C. and the movable side set at 110 ° C., the base resin formulation Prime Polymer Pro J708UG (load deflection temperature: 110 ° C.) made by Prime Polymer Co., Ltd. is used. An injection foamed molded article was obtained in the same manner as in Example 1 except that the injection was carried out, and the fixed side and the movable side were switched to a 30 ° C. cold water line 15 seconds after injection.

(Comparative Example 1)
Implemented except that an aluminum plate with a width of 50 mm x length of 150 mm x thickness of 0.5 mm and a taper of 30 ° at the end was attached to the cavity side of the mold (test box mold) with double-sided tape In the same manner as in Example 1, an injection foam molded article was obtained. The dynamic friction coefficient (μk) of this plate was 0.42.

(Comparative Example 2)
An aluminum plate with a width of 50 mm x length of 150 mm x thickness of 0.5 mm and a taper of 30 ° at the end is subjected to graining (skinning), and both sides are placed on the cavity side of the mold (test box mold). An injection foamed molded article was obtained in the same manner as in Example 1 except that it was affixed with a tape. The dynamic friction coefficient (μk) of this plate was 0.28.

(Comparative Example 3)
An injection foamed molded article was obtained in the same manner as in Comparative Example 1 except that the molten foamed resin material was injected into a mold pressurized to 1 MPa in advance, and the pressure in the mold was released simultaneously with completion of the injection.

(Comparative Example 4)
In a cavity with the fixed side set at 120 ° C. and the movable side set at 110 ° C., the base resin formulation Prime Polymer Pro J708UG (load deflection temperature: 110 ° C.) made by Prime Polymer Co., Ltd. is used. An injection foamed molded article was obtained in the same manner as in Comparative Example 1, except that the injection was carried out and the fixed side and the movable side were switched to a 30 ° C. cold water line 15 seconds after injection.

(Comparative Example 5)
Chrome plate is applied to the aluminum plate with dimensions of 50mm width x 150mm length x 0.5mm thickness and 30 ° taper at the end, and is attached to the cavity side of the mold (test box mold) with double-sided tape. An injection foamed molded article was obtained in the same manner as in Comparative Example 1 except that. The dynamic friction coefficient (μk) of this plate was 0.43.

Claims (8)

A thin film having a dynamic friction coefficient (μk) with respect to a thermoplastic resin of 0.25 or less on the entire surface or a part of the mold cavity and the core surface by a dynamic friction coefficient (μk) according to JIS K 7125 A mold for injection foam molding in which is formed. 2. The injection foam molding die according to claim 1, wherein a thin film is formed of a fluororesin on the whole surface or a part of the cavity and the core surface in order to reduce the dynamic friction coefficient (μk). The mold for injection foam molding according to claim 1, wherein a thin film is formed of a silicone-based resin on the whole surface or a part of the cavity and core surface of the mold in order to reduce a dynamic friction coefficient (µk). Injection foaming that performs foam molding by feeding the foamed resin raw material consisting of thermoplastic resin and foaming agent to an injection molding machine, melt-kneading, and then injecting the molten foamed resin raw material into the mold and then moving the movable side backward An injection foam molding method using the mold according to any one of claims 1 to 3 in molding. The injection foaming performed in the mold according to any one of claims 1 to 3, in a method of injecting a molten foamed resin raw material into a mold that has been previously pressurized to a pressure at which foaming does not occur in the flow front of the foamed resin raw material Molding method. In the manufacturing method which inject | pours the foamed resin raw material fuse | melted in the metal mold | die adjusted beforehand to the temperature more than the load deflection temperature (based on JISK7191-2) of the resin which a metal mold | die surface uses beforehand, An injection foam molding method performed with any mold. The injection foam molding method according to claim 4, wherein the thermoplastic resin is a thermoplastic elastomer resin. The injection foam molding method according to claim 4, wherein the thermoplastic resin is a polypropylene resin.