JP2010120335A - Method of manufacturing moisture-proof light-weighted resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a moisture-proof light-weighted molding of excellent appearance, usable in water or in a high-humidity environment. <P>SOLUTION: This method of manufacturing the moisture-proof light-weighted molding includes a process for melting a thermoplastic resin composition containing 100 pts.wt. of thermoplastic resin, 0.001-0.5 pt.wt. of chemical foaming agent comprising only an organic foaming agent, and 0.1-1.0 pt.wt. of inorganic foaming nucleus agent, using an injection molding machine having a two-stage compression screw, a process for supplying a physical foaming agent from a midway of a cylinder of the injection molding machine to the molten thermoplastic resin composition, and an injection foaming molding process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a moisture-resistant lightweight resin molding by injecting a thermoplastic resin composition into a mold cavity attached to an injection molding machine using at least two kinds of foaming agents. More specifically, the present invention relates to a method for producing a moisture-resistant lightweight resin molded article for exterior use that does not deteriorate in appearance even in water or in a humid environment.

  Injection molding is a highly productive molding method that can form high-precision products with complex shapes in a single process and can be produced continuously in a short cycle. Automotive, electronic / electric equipment, precision machinery, office work It is one of the excellent molding methods used in a wide range of fields such as machines, building materials, and daily necessities.

  In the above injection molding, a foamable thermoplastic resin composition in which a foaming agent is kneaded and dissolved in a thermoplastic resin is filled with less than the cavity volume in the mold cavity, and a molded body is molded with foaming force. A method, (2) a method of discharging and foaming an internal thermoplastic resin composition after filling into a mold cavity, and (3) a method of preventing sinking by foaming by volume shrinkage after filling into a mold cavity, (4) Various injection foam molding methods are known, such as foaming by filling the mold cavity and then moving the mold cavity. These injection foam moldings are effective means for preventing sinking, heat insulation, and weight reduction of injection foam moldings, and are used for armrests, grips, tableware, office equipment, home appliance parts, and the like.

  By the way, in recent years, injection foam molded articles have begun to be used for automobile interior parts such as door trims and backside trims in response to the demand for weight reduction against the need for carbon dioxide emission suppression and fuel efficiency improvement in the automobile industry (for example, patent documents). 1-6).

  However, injection-molded foams of propylene-based resins in the field related to automobiles are mostly used as interior parts, and are hardly used for exterior parts such as bumpers and moldings. Also, in the past publicly known literature, there is no specific injection-molded molded article of exterior propylene-based resin disclosed in the examples.

  The reason is that when automobile exterior parts are manufactured by the same injection foam molding method as that used to manufacture automobile interior parts, not only the molded body that is not painted, but also the molded body that has been painted is cloudy on the surface. This is because the swirl mark may occur.

  In addition, when an organic chemical foaming agent is used as the foaming agent, swirl marks are inherently generated in large quantities. Furthermore, when a large amount of an organic chemical foaming agent is added to obtain sufficient foaming, the cavity surface of the mold is corroded or a foaming agent residue adheres to the cavity surface. As a result, the appearance of the cavity may be deteriorated by transferring the cavity surface to which the corrosion or residue is adhered to the molded body. In addition, if the amount of the organic chemical foaming agent is sufficiently foamed, there is a concern that the molding environment may be deteriorated due to a gas odor generated during molding.

On the other hand, when an inorganic chemical foaming agent is used as the foaming agent, the mold is less contaminated and the swirl mark itself is less than the organic chemical foaming agent, which is advantageous in appearance. However, in order to obtain sufficient foaming, it is necessary to use a large amount of an inorganic chemical foaming agent. For this reason, not only the occurrence of swirl marks cannot be ignored, but there is a problem that blisters (blowing) occur in water or in a high humidity environment. In other words, not only the molded body that is not painted, but also the molded body that has been painted, blisters are generated so as to lift the painted surface,
There is a problem that the surface appearance of the molded body is remarkably impaired. In order to avoid this problem, when the amount of the inorganic chemical foaming agent is reduced, the foaming property is deteriorated, and it is difficult to form not only a predetermined expansion ratio but also a desired shape of the molded body. .

  For such a chemical foaming agent, there is a method of performing foam molding using only a physical foaming agent without using a chemical foaming agent. However, this method has a problem that foam cells tend to be enlarged, and as a result, irregularities are formed on the surface of the molded body and the appearance of the molded body is deteriorated. Further, the expansion ratio could not be sufficiently increased. To solve this problem, there is a method in which a foamed cell is made smaller by including a physical foaming agent in a supercritical state in a thermoplastic resin composition and foam-molding. Swirl marks, dimples, dents and the like were generated, and the appearance generally tended to deteriorate. For this reason, it could not be used as a molding method of a molded body that requires a good appearance.

  Patent Document 4 and Patent Document 5 propose that in an injection foam molding method, a chemical foaming agent and a physical foaming agent are used in combination to obtain a foam product having a good appearance. As a chemical foaming agent, It is described that it is preferable to use an organic foaming agent composed of a polycarboxylic acid such as citric acid and an inorganic foaming agent such as sodium hydrogen carbonate in combination.

  However, it has been found that when an organic foaming agent and an inorganic foaming agent are used in combination as chemical foaming agents, blisters are formed on the surface of the molded product when the resulting foam is placed under high humidity. Thus, conventionally, it has been very difficult to obtain a foamed molded product that requires a high appearance under water or in a high humidity environment.

In addition, as the weight is reduced, the thickness of the molded product tends to be thinner, and the resin temperature during molding is required to be 220 ° C. or higher. In such a case, the organic foaming agent is decomposed, and with only the organic foaming agent, foaming failure may occur during molding.
Japanese Patent Laid-Open No. 04-073142 JP-A-11-335414 JP 2000-226478 A JP 2002-079545 A JP 2004-189911 A JP 2004-195897 A

  The problem to be solved by the present invention is to provide a method for producing a moisture-resistant lightweight resin molded body having a high appearance that can be used in water or in a high humidity environment.

  The present inventors have intensively studied to solve the above-mentioned problems, and in the thermoplastic resin composition, the necessary minimum amount of an organic foaming agent that hardly reacts with water in water or in a high-humidity environment together with an inorganic foam nucleating agent. It has been found that the above-mentioned problems can be solved by containing and using a physical foaming agent together and injection molding.

  That is, the manufacturing method of the moisture-resistant lightweight resin form of the present invention uses a chemical foaming agent 0.001 consisting of 100 parts by weight of a thermoplastic resin and an organic foaming agent using an injection molding machine having a two-stage compression screw. A step of melting a thermoplastic resin composition comprising -0.5 parts by weight and 0.1-1.0 part by weight of an inorganic foam nucleating agent; and a physical foaming agent in the molten thermoplastic resin composition It includes a step of supplying from the middle of a cylinder of the injection molding machine and a step of injection foam molding.

  The inorganic foam nucleating agent is preferably silica. The physical foaming agent is preferably a gaseous physical foaming agent. The organic foaming agent is preferably azodicarbonamide.

The physical foaming agent is preferably supplied in an amount of 0.1 to 2.0% by weight with respect to the thermoplastic resin composition.
The moisture-resistant lightweight resin molded product is preferably a moisture-resistant lightweight polypropylene resin molded product having a density in the range of 0.4 to 0.8 g / cm ³ .

  It is preferable that the moisture-resistant lightweight resin shaped body is an automobile exterior material.

  The moisture-resistant lightweight resin molded article obtained by the production method of the present invention is a foam molded article having a smooth skin layer and an appearance that does not deteriorate even in water or in a humid environment, and is used in exterior parts such as outdoors. It can be applied to automotive exterior materials with opportunities.

Hereinafter, the manufacturing method of the moisture-resistant lightweight resin molding of this invention is demonstrated concretely.
The method for producing a moisture-resistant lightweight resin molded article of the present invention is a method for producing a moisture-resistant lightweight resin molded article using an injection molding machine having a two-stage compression screw, comprising 100 parts by weight of a thermoplastic resin, and an organic foam. A step of melting a thermoplastic resin composition containing 0.001 to 0.5 parts by weight of a chemical foaming agent consisting of only an agent and 0.1 to 1.0 parts by weight of an inorganic foam nucleating agent; It includes a step of supplying a physical foaming agent to a thermoplastic resin composition from the middle of a cylinder of an injection molding machine, and a step of injection foam molding.

  In the present invention, the moisture-resistant lightweight resin molded product is a molded product in which the specific gravity of the molded product is about 10 to 50% lighter than the original specific gravity of the molded product raw material (that is, the thermoplastic resin composition). It is defined as a compact that does not produce blisters on the surface when left in a wet environment or in water for a long time.

  Hereinafter, after describing the thermoplastic resin composition used as a raw material in the present invention, the method for producing the moisture-resistant lightweight resin molded body of the present invention will be described in detail.

<Thermoplastic resin>
The thermoplastic resin used in the method for producing the moisture-resistant lightweight resin molded body of the present invention is not particularly limited as long as it is a thermoplastic resin that can be subjected to normal injection molding, and various known thermoplastic resins can be used. Specifically, for example, polyolefin resins such as polyethylene resin, polypropylene resin, poly 1-butene, polymethylpentene; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene 2,6-naphthalate, polycarbonate; nylon 6, Polyamide resins such as nylon 66, nylon 11 and nylon 12; polyethers such as polyoxymethylene and polyphenylene ether; polyvinyl chloride; styrenic resins such as polystyrene, ABS and AES; ethylene / vinyl acetate copolymer; Examples thereof include ethylene / unsaturated carboxylic acid (ester) copolymers such as acrylic acid ester copolymers, ethylene / methacrylic acid ester copolymers, and ionomer copolymers.

  Of these thermoplastic resins, polyolefin resins are preferred, polyethylene resins and polypropylene resins are more preferred, and polypropylene resins are particularly preferred from the viewpoints of cost performance, mechanical strength, and moldability.

  As the polyethylene resin, any of high pressure method low density polyethylene (HP-LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), or high density polyethylene (HDPE) can be preferably used.

  Further, as the polypropylene resin, a homopolymer of propylene, a random copolymer of propylene and a small amount of ethylene, an α-olefin such as 1-butene, a homopolymer of propylene or a random copolymer, and amorphous or Any block copolymer comprising a low crystalline ethylene / propylene copolymer (containing a small amount of polyethylene depending on the production conditions) can be preferably used. In particular, by foam molding using a polypropylene resin as a raw material, a moisture-resistant lightweight resin molded body comprising a polypropylene resin molded body having a better appearance and having excellent foamed cells, and being light and rigid. It can be manufactured easily and efficiently.

<Chemical foaming agent>
The chemical foaming agent used in the method for producing the moisture-resistant lightweight resin molded article of the present invention consists only of an organic foaming agent.

Although the organic foaming agent used by this invention is not specifically limited, The following can be mentioned.
(A) N-nitroso compound: N, N′-dinitrosoterephthalamide, N, N′-dinitrosopentamethylenetetramine,
(B) azo compounds: azodicarbonamide _{(H 2 NOCN = NCONH 2)} , azobisisobutyronitrile, azo cyclohexyl nitrile, azo-diaminobenzene, barium azodicarboxylate,
(C) Sulphonyl hydrazide compound: benzene sulfonyl hydrazide, toluene sulfonyl hydrazide, p, p′-oxybis (benzene sulfonyl hydrazide), diphenyl sulphone-3,3′-disulfonyl hydrazide,
(D) Azide compound: calcium azide, 4,4′-diphenyldisulfonyl azide, p-toluenesulfonyl azide,
(E) Polycarboxylic acid: oxalic acid, citric acid, fumaric acid, malic acid, tartaric acid, cyclohexane 1,2 dicarboxylic acid, camphoric acid, ethylenediaminetetraacetic acid, triethylenetetramine hexaacetic acid, nitrilolic acid.

  Among these organic foaming agents, it is particularly preferable to use azodicarbonamide (ADCA) or citric acid. Moreover, these organic foaming agents may be used individually by 1 type, and may be used in combination of 2 or more type.

  That is, in the present invention, as the chemical foaming agent, only the organic foaming agent is used without using the inorganic foaming agent. As a result, the resulting moisture-resistant light-weight resin molded article hardly has the problem that blisters occur in water or in a high-humidity environment. The reason for this is that the present inventors do not use an inorganic foaming agent that easily reacts with moisture as the chemical foaming agent, and thus suppresses the occurrence of swirl marks on the surface of the molded body.

  The organic foaming agent functions to make the cell diameter contained in the moisture-resistant lightweight resin molded body obtained uniform. That is, in the foam molding method using only the physical foaming agent, the physical foaming agent dissolved in the thermoplastic resin is likely to be a cell generation nucleus in which a microscopically uneven portion is generated. When an organic foaming agent is used for the plastic resin, the cell diameter contained in the foamed molded product can be made uniform. That is, the organic foaming agent acts as a foam nucleating agent.

  The organic foaming agent is 0.001 to 0.5 parts by weight, preferably 0.03 to 0.5 parts by weight, more preferably 0.05 to 0.5 parts by weight, based on 100 parts by weight of the thermoplastic resin. Used. When the amount of the organic foaming agent is within the above range, the formation of bubbles in the foamed cells of the resulting moisture-resistant lightweight resin molded product can be remarkably improved, and problems such as generation of off-flavors and mold contamination do not occur. .

<Inorganic foam nucleating agent>
The inorganic foam nucleating agent used in the present invention can make the cell diameter contained in the foamed molded article uniform.

Examples of the inorganic foam nucleating agent include silica, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, barium sulfate, mica, clay, wollastonite, alumina, iron oxide, titanium oxide, magnesia, carbon black, and graphite. . These inorganic foam nucleating agents may be used alone or in combination of two or more.
Silica is preferably used as the inorganic foam nucleating agent.

  The inorganic foam nucleating agent is used in an amount of 0.1 to 1.0 part by weight, preferably 0.1 to 0.7 part by weight, based on 100 parts by weight of the thermoplastic resin. When the amount of the inorganic foam nucleating agent is within the above range, the specific gravity is not increased and the cell diameter contained in the foamed molded product can be made uniform without increasing the cost.

  The average particle diameter of the inorganic foam nucleating agent is preferably 0.5 μm to 10 μm. In addition, it is preferable that the inorganic foam nucleating agent is subjected to a hydrophobic surface treatment because it is further excellent in dispersibility in the resin.

<Other additives>
The thermoplastic resin composition used in the present invention includes various known rubbers / elastomers and inorganics in advance in accordance with the intended use of the moisture-resistant lightweight resin molded body, in addition to the above components, within a range that does not impair the purpose of the present invention. Fillers, additives and the like may be added.

  Specific examples of the rubber / elastomer include polybutylene, polyisobutylene, polybutadiene, natural rubber, thermoplastic polyurethane, polyisoprene, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, ethylene-propylene- Examples include diene rubber and chloroprene rubber.

  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 , Calcium sulfite, white carbon, clay, calcium sulfate and the like. These inorganic fillers may be used alone or in combination of two or more.

  Additives include crystallization nucleating agents, antioxidants, hydrochloric acid absorbents, heat stabilizers, weathering stabilizers, light stabilizers, UV absorbers, slip agents, antiblocking agents, antifogging agents, lubricants, antistatic agents , Flame retardants, pigments, dyes, dispersants, copper damage inhibitors, neutralizers, plasticizers, foam inhibitors, crosslinkers, flowability improvers such as peroxides, weld strength improvers, natural oils, synthetic oils And known additives such as wax.

<Thermoplastic resin composition>
The thermoplastic resin composition used in the present invention includes the thermoplastic resin, a chemical foaming agent composed only of the organic foaming agent, the inorganic foaming nucleating agent, and the other components as necessary. And an embodiment in which all the components including the organic foaming agent are mixed in advance before cylinder introduction, and before the cylinder introduction, components other than the organic foaming agent are mixed, There exists an aspect which inject | pours only the said organic type foaming agent from the middle of a cylinder. Mixing of the components before introducing the cylinder can be performed using a known mixing apparatus. Examples of the mixing device include a Banbury mixer, a kneader, and an extruder. When the organic foaming agent is injected from the middle of the cylinder, the organic foaming agent and other components are melted and mixed in the compression region of the cylinder.

  The organic foaming agent may be blended in advance with a foaming aid or the like and mixed with a material such as an elastomer or polyethylene having a low melting temperature to produce a masterbatch, which may be blended into a thermoplastic resin.

  The inorganic foam nucleating agent may be processed into a master batch based on a resin, wax, or rubber having a foam nucleating agent amount of 5 to 50% by weight and blended with a thermoplastic resin. When processed into a master batch, contamination of the molding machine hopper, adhesion of powder to the molding surface, and screw wear can be reduced.

≪Method for manufacturing moisture-resistant lightweight resin molding≫
The method for producing a moisture-resistant lightweight resin molded article of the present invention is a method for producing a moisture-resistant lightweight resin molded article using an injection molding machine having a two-stage compression screw,
(I) Heat including 100 parts by weight of a thermoplastic resin, 0.001 to 0.5 parts by weight of a chemical foaming agent composed only of an organic foaming agent, and 0.1 to 1.0 part by weight of an inorganic foaming nucleating agent Melting the plastic resin composition;
(Ii) supplying a physical foaming agent to the molten thermoplastic resin composition from the middle of a cylinder of the injection molding machine;
(Iii) a step of injection foam molding.

<Injection molding machine with two-stage compression screw>
An injection molding machine having a two-stage compression screw used in the present invention comprises a hopper for supplying the thermoplastic resin composition, and a plasticizing means comprising a cylinder for bringing the thermoplastic resin composition into a molten state, A physical foaming agent supplying and dissolving means for kneading and dissolving the physical foaming agent in the molten thermoplastic resin composition, provided with a gas supply port for supplying the physical foaming agent in the middle of the cylinder of the injection molding machine, and obtained The injection molding means is provided with a mold for obtaining a foamed molded product from the foamed gas-dissolved resin composition in a molten state, and a screw is provided in the cylinder. The gas supply port communicates with physical foaming agent storage means via a physical foaming agent supply pipe. Moreover, in the aspect which adds an organic type foaming agent in the middle of a cylinder and manufactures a thermoplastic resin composition, it has an organic type foaming agent supply port in the middle of a cylinder.

  Hereinafter, an example is given and demonstrated about the composition of a two-stage compression screw. The screw has supply / compression / metering areas in the first and second stages. The screw groove is deep in the compression region of the first stage, gradually becomes shallow toward the front of the first stage, suddenly deepens at the supply part of the second stage, and gradually toward the front of the second stage. It becomes shallower. The first stage screw has such a shape to feed the pellets forward and to remove air in the resin composition, and the groove suddenly becomes deeper in the second stage supply section. The cross-sectional area is increased because the physical foaming agent is easily supplied by lowering the pressure of the molten thermoplastic resin composition below the physical foaming agent supply pressure and bringing the molten resin composition close to starvation. This is to create a space in which gas can be injected in addition to the molten resin.

  The cylinder is preferably provided with a gas supply port for introducing a physical foaming agent at a position corresponding to the second-stage supply part of the two-stage compression screw, and any organic foaming agent supply port is compressed in two stages. Preferably, the screw is provided at a position corresponding to the first stage supply portion of the screw.

  The injection molding machine is preferably a molding machine capable of high-speed injection, and a molding machine capable of injection at an injection rate of usually 400 cc / second or more, preferably 600 cc / second or more, more preferably 800 cc / second or more is used. The injection rate is an index that is generally used as an index indicating the ability of the injection molding machine to inject, and is represented by a volume (cc / second) that can be injected by the molding machine per second. When this injection rate is used, the flow rate of the resin injected into the mold by the molding machine can be defined even if the size and type of the injection molding machine are different.

  It is preferable that a resin backflow prevention mechanism is provided at a gas supply port provided in the middle of the cylinder for supplying the physical foaming agent to the injection molding machine. Examples of the resin backflow prevention mechanism include a mechanism for opening and closing a physical foaming agent supply port, a mechanism having a fine port such as a sintered vent, a sintered metal obtained by compacting and sintering metal powder or overlapping a metal net, etc. A mechanism with can be used.

Examples of the physical foaming agent storage means include a cylinder and a tank.
Moreover, it is preferable that a heat retention mechanism is provided in the supply pipe for the physical foaming agent. By providing a heat retention mechanism, it becomes possible to always supply a physical foaming agent stably even if the surrounding environment (especially the environmental temperature) changes, preventing foaming unevenness, especially in mass production. To do. This can also prevent the production stability due to the season and time from deteriorating. Furthermore, this heat retention mechanism also has a function of preventing solidification of the backflow prevention mechanism for the foaming gas provided at the gas supply port. This heat retention mechanism preferably uses waste heat of the injection molding machine barrel.

<(I) 100 parts by weight of a thermoplastic resin, 0.001 to 0.5 parts by weight of a chemical foaming agent composed only of an organic foaming agent, and 0.1 to 1.0 part by weight of an inorganic foaming nucleating agent Process of melting thermoplastic resin composition>
First, a thermoplastic resin composition is supplied from a hopper, and the thermoplastic resin composition is plasticized and kneaded in a cylinder of an injection molding machine to be in a molten state (hereinafter also referred to as “molten resin”). .

  When the thermoplastic resin composition supplied from the hopper does not contain the organic foaming agent in advance, the organic foaming agent is thermoplastic in the middle of the cylinder, preferably in the first stage screw supply region. It may be added to a mixture of resin, inorganic foam nucleating agent and any other additives.

  As a specific example, a thermoplastic resin composition is supplied from a hopper in a first stage screw supply region, and the thermoplastic resin composition is melted, kneaded and / or plasticized in a compression region, and downstream of the thermoplastic resin composition. In the metering region, kneading is further performed to make the dispersion of the thermoplastic resin and the organic foaming agent contained in the thermoplastic resin composition uniform.

<(Ii) Step of supplying a physical foaming agent to the molten thermoplastic resin composition from the middle of the cylinder of the injection molding machine>
A physical foaming agent is supplied from the gas supply port to a molten resin containing a foaming gas generated from an organic foaming agent, and is kneaded and dissolved. This physical foaming agent is preferably supplied in the supply region of the second stage screw. Here, it is preferable to sharply lower the resin pressure by deepening the groove in the second-stage supply region as compared with the measurement region of the first-stage screw. Due to this reduced pressure, the molten resin becomes close to a starvation state, and the physical foaming agent can be easily supplied. Further, by increasing the pressure in the downstream direction from the supply region of the second stage screw to the compression region and the metering region, kneading and dissolution of the supplied physical foaming agent and the molten resin can be promoted.

  As a specific example, the pressure of the molten thermoplastic resin composition is lowered from the physical foaming agent supply pressure by enlarging the cross-sectional area of the groove at the second stage supply part of the screw, and then the physical supply from the gas supply part. The blowing agent is supplied, and the supplied physical blowing agent and the molten thermoplastic resin composition are kneaded and dissolved while increasing the pressure in the downstream direction, and the molten thermoplastic resin is further melted in the downstream measurement region. Improves the dispersibility of the physical foaming agent in the composition.

<Physical foaming agent>
The physical foaming agent used in the method for producing the moisture-resistant lightweight resin molded body of the present invention is not particularly limited as long as it is a normal physical foaming agent, and examples thereof include inert gases such as carbon dioxide, nitrogen, argon, helium, and neon. It is done. Among these, carbon dioxide, nitrogen, and argon are the best because they are inexpensive and have very little risk of environmental pollution and fire. The physical foaming agent can be used in any of a liquid state, a supercritical state, and a gas state, but it is preferable to use the physical foaming agent from the viewpoint of handling and safety.

The supply amount of the physical foaming agent in the present invention is selected according to the required physical properties of the obtained moisture-resistant lightweight resin molded product in consideration of a preferable foaming ratio, etc. The range of 0.1 to 2.0% by weight, preferably 0.1 to 1.0% by weight, more preferably 0.1 to 0.7% by weight, based on the thermoplastic resin composition containing the foaming agent. It is in. When the supply amount of the physical foaming agent exceeds the above range, the foaming ratio itself of the obtained molded product increases, but swirl marks and dimples may be generated in large quantities. For this reason, not only the unpainted molded product, even if it is painted, uneven gloss depending on the location may occur, the molded product may become cloudy, the appearance will deteriorate, and it may not be used as an actual product is there.
The supply amount of the physical foaming agent is calculated by measuring the physical foaming agent consumption per unit resin by measuring the weight of the cylinder.

<(Iii) Step of injection foam molding>
A molten resin in which a physical foaming agent is dissolved is injected into a mold cavity in a mold-clamped state attached to an injection molding machine and then foamed.

  The foaming method may be a foaming method such as short shot foaming or anti-sink foaming that does not change the cavity volume, but the foaming method (core back) that increases the cavity volume and foams is an injection foamed molded article with a high foaming ratio. Since it is obtained, it is preferable.

  In the method of foaming by increasing the cavity volume (core back), it is preferable to increase the cavity volume by placing an appropriate time after injecting the molten resin into the mold cavity. As a preferable method for increasing the cavity volume, a metal plate constituting the wall of the mold cavity is moved using a mechanism using a hydraulic cylinder, a pneumatic cylinder, or a motor, or a movable side mold of an injection molding machine. For example, there is a method of moving the mold mounting plate itself in the mold opening direction.

Note that the cavity space thickness (T ₀ ) at the start of injection is preferably 1.0 to 3.0 mm.
When the thickness is in the range of 1.0 to 2.5 mm, more preferably 1.0 to 2.0 mm, the appearance of the molded article becomes good. Further, the ratio (T ₁ / T ₀ ) between the cavity space thickness (T ₀ ) at the start of injection and the cavity space thickness (T ₁ ) after the movable mold retreats is preferably 1.2.
-3.0, more preferably 1.2-2.5, and still more preferably 1.3-2.0.

  In addition, by injecting molten resin at once into the mold cavity as described above, the surface of the molten resin in contact with the mold is solidified faster than the inside, and an unfoamed skin layer can be formed on the surface of the molded body. it can. As a result, a solid product shape can be formed and maintained, and a highly rigid molded body having a uniform internal foamed state can be obtained. Although the thickness of the said skin layer is not specifically limited, Preferably it is 0.1 mm or more, More preferably, it is 0.3 mm or more.

  The core back start timing for forming the skin layer varies depending on the type of thermoplastic resin, the type of organic foaming agent and physical foaming agent, the mold temperature, and the molten resin temperature. When a normal polypropylene resin is used as the thermoplastic resin, it is preferably about 0.5 to 4 seconds after completion of the injection. If the time from the completion of injection to the start of the core back is too short, the tip of the molten resin is still flowing, swirl marks appear at the tip of the flow, causing deterioration of the appearance, and a skin layer with sufficient thickness May not be formed. Further, if the time from the completion of injection to the start of the core back is too long, solidification of the molten resin proceeds, and a sufficient foaming ratio cannot be obtained even if the core is backed. However, in a normal injection molding machine, even if the time from the completion of injection to the start of the core back is set to 0 seconds, there is a time during which the mold clamping pressure at the time of injection is about 0.5 to 1 second. Therefore, in terms of setting, even if the mold is opened at the same time as the completion of injection, there is almost no problem of short shots or swirl marks.

  The core moving speed during core back also varies depending on the thickness of the molded product, the type of thermoplastic resin, the types of organic foaming agent and physical foaming agent, mold temperature and molten resin temperature. For example, carbon dioxide is used as the physical foaming agent. When a normal polypropylene resin is used as the thermoplastic resin, it is preferably about 0.01 to 50 mm / second. When the core moving speed is too slow, the molten resin is solidified in the middle of the core back, and a sufficient foaming ratio cannot be obtained. On the other hand, if the core moving speed is too high, the generation and growth of the foamed cells do not follow the core movement, and the foamed cells are destroyed and a good molded product cannot be obtained.

Further, the core back can be performed in several stages, whereby a molded body having highly foamed and finely foamed cells can be obtained.
Mold temperature is the same as the mold temperature normally used for molding the thermoplastic resin to be used. However, when obtaining a molded product with a thin thickness or a foam with a high expansion ratio, the mold temperature should be higher than the normal mold temperature. It is good to set. For example, when carbon dioxide is used as the physical foaming agent and a normal polypropylene resin is used as the thermoplastic resin, the mold temperature is preferably in the range of about 10 to 80 ° C, more preferably about 20 to 60 ° C.

  As for the mold temperature, when a crystalline resin is used as the thermoplastic resin, if the surface temperature of the mold cavity at the time of injection is between the crystallization temperature of the crystalline resin and the melting temperature, the molded body It is possible to obtain a high-foamed and highly-foamed molded body that does not exhibit swirl marks on its surface. Similarly, when an amorphous resin is used as the thermoplastic resin, the temperature between the softening point and the melting temperature of the amorphous resin is the swirl mark suppression temperature. However, if the surface temperature of the mold cavity is increased, cooling is hindered, and it is difficult to remove from the mold as a molded body unless the surface temperature of the molten resin in contact with the surface of the mold cavity is lowered below the crystallization temperature or the softening point. Become. For this reason, there exists a problem that a shaping | molding cycle becomes long or the temperature control apparatus which raises / lowers mold temperature during a shaping | molding cycle is required. In addition, the metal mold | die provided with the mechanism which raises / lowers such metal mold temperature can also be used for the manufacturing method of the molded object of this invention.

On the other hand, instead of raising or lowering the mold temperature, the periphery of the mold cavity is sealed with a rubber seal having various cross-sections such as circular, plate, tube, hose, rectangular or trapezoidal, and air is injected into the mold cavity. In addition, a method of molding using a counter pressure method, in which a gas such as carbon dioxide or nitrogen is injected and injection is applied, is also applicable to the method for producing a moisture-resistant lightweight resin molded body of the present invention. Can do.

The cooling time is a time provided for suppressing the swelling of the molded body caused by the internal gas pressure after taking out the molded body and for solidifying the surface of the molded body, and is generally about 5 to 40 seconds.
In the present invention, a hot runner, a shut-off nozzle, a valve gate, or the like used in normal injection molding can also be used. Hot runners, shut-off nozzles or valve gates not only suppress the generation of waste resin such as runners, but the thermoplastic resin composition containing a foaming agent leaks from the runner into the cavity, resulting in poor appearance of the foam molded product in the next cycle. It has the effect of preventing foaming defects.

<Moisture resistant lightweight resin molding>
According to the method for producing a moisture-resistant lightweight resin molded body of the present invention, even if some distribution occurs in the cell shape, cell density and / or foaming ratio inside the molded body, the smoothness, rigidity, and moisture resistance of the skin layer. Thus, a moisture-resistant lightweight resin molded article excellent in lightness and appearance can be obtained.

  In the production method of the present invention, the expansion ratio and appearance performance are the temperature of the injected molten resin, the injection speed, the waiting time from the end of injection to the start of core back, the core back amount, the core back speed and / or the core back. It can be appropriately controlled depending on the cooling time after completion.

  In the case where the moisture-resistant lightweight resin molded product is a product having closed cells, the average cell diameter is about 0.1 to 1.0 mm. Depending on the product shape and product application, the surface of the molded product may have irregularities due to the size of the internal cells or communication even if there are some cells with an average cell diameter of several millimeters and some of the cells communicating. If it does not occur and there is almost no change in thickness between the front surface and the back surface of the molded body when the molded body is curved to some extent, there will be no problem as a molded body.

  In the case of highly foamed products, the foamed cells are associated and communicated together, and the foamed product becomes a kind of hollow, but because there are struts stretched with resin as columns in the hollow, it is highly lightweight. Thus, it is possible to manufacture a product having strong rigidity. These highly foamed products are ideal for substitutes such as cardboard.

Density of the resulting moisture resistance lightweight resin molded article by the process of the present invention is usually in the range of 0.4 to 0.8 g / cm ^3, preferably in the range of 0.5~0.8g / cm ^3. Since the density of the moisture-resistant lightweight resin molded article obtained by the production method of the present invention is usually in the above range, it is lightweight and can be suitably used for exterior parts such as automobiles.

  The moisture-resistant lightweight resin molded product obtained by the production method of the present invention is a moisture-resistant lightweight resin molded product whose appearance does not deteriorate even in water or in a humid environment. For example, it can be applied to automobile exterior materials such as bumpers, moldings, and undercovers. It can also be applied to industrial applications such as pallets and containers, as well as water-related products such as kitchens, toilets, and bathrooms, such as washing machine wash tubs and lids, and bathroom chairs. Moreover, it can use suitably also as an automotive exterior material to which printing, painting, or a decoration process was added.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.
In addition, the evaluation method etc. of the moisture-resistant lightweight resin molding obtained by the manufacturing method of this invention are as follows.

[Density measurement method for moisture-resistant lightweight resin moldings]
The density of the moisture-resistant lightweight resin molded body was measured according to JIS K7222A. Those having a large variation in the plate thickness due to poor foaming were not evaluated because the density also varied.

[Appearance evaluation method]
The surface of the moisture-resistant lightweight resin molding was visually observed and judged according to the following criteria.

<Thickness>
Three plate thicknesses of the moisture-resistant lightweight resin molding were measured with a vernier caliper and averaged. Evaluations were not possible for foaming defects that caused large variations in plate thickness.

<Cell state>
○: Good, △: Slightly large cell but no effect on appearance, ×: Large cell and moisture-resistant, light-weight molded resin surface has unevenness or cell connection, cannot be evaluated: Poor foaming and large variation in foamed state

<Surface uneven dimple>
○: None, △: Occurred on the back surface, x: Occurred on both the front and back surfaces (including deformation due to poor foaming)

<Swirl mark>
○: Almost no confirmation, △: Slightly more, ×: Many

<Moisture resistant lightweight resin molding shape>
○: Good (none), ×: Deformed (dent, wrinkle, uneven thickness)

<Appearance after hot water resistance test>
The moisture-resistant lightweight resin molded body was cut out to 5 cm × 5 cm, and after being immersed in water under the conditions of 80 ° C. × 24 hours and 40 ° C. × 240 hours, appearance evaluation was performed to confirm occurrence of surface blisters.
○: Good, ×: Poor, unevaluable: Appearance is unsatisfactory due to poor appearance (large deformation of specimen or excessive swirl mark)

[Example 1]
100 parts by weight of a polypropylene resin (manufactured by Prime Polymer Co., Ltd., trade name: Prime Polypro TSOP-GP6B), and an organic foaming agent master batch (EE206E ADCA, manufactured by Eiwa Kasei Co., Ltd.) as the amount of the organic foaming agent is 0. .06 parts by weight, inorganic (silica) foam nucleating agent masterbatch (trade name: Prime Polypro MB401 (particle size: 2 μm) added as silica to 0.3 parts by weight, dry blended, thermoplastic resin composition A pellet was prepared.

The above resin composition pellets are supplied to the hopper of an injection molding machine (trade name: MD850S-III) manufactured by Ube Industries Co., Ltd. and melted, and the molten resin composition (molten resin) is physically processed from the middle of the cylinder. 0.2% by weight of CO ₂ was supplied as a foaming agent and dissolved and kneaded.

A mold cavity is produced by injecting a molten resin at 230 ° C. in which CO ₂ is kneaded and melted into a mold having a mold cavity space thickness (T ₀ ) of 1.8 mm and a surface temperature of 40 ° C. in 0.8 seconds. Filled in. The injection time was the time from the start of injection to the end of injection of the entire amount of molten resin.

The core back is started 0.5 seconds after the completion of the injection of the molten resin, the core moving speed is 20 mm / second, the space thickness (T ₁ ) of the mold cavity is 2.8 mm, the length is 50 cm, the width is 80 c.
A moisture-resistant lightweight resin molded product of m was obtained. The cooling time was 30 seconds. Table 1 shows the measured values of the thickness and density of the obtained moisture-resistant lightweight resin molded body and the observation results of the appearance.

[Example 2]
In Example 1, it implemented similarly to Example 1 except the quantity of a silica having been 0.5 weight part. Table 1 shows the measured values of the thickness and density of the obtained moisture-resistant lightweight resin molded body and the observation results of the appearance.

Example 3
In Example 1, it implemented like Example 1 except the quantity of an organic type foaming agent (ADCA) being 0.1 weight part, and the quantity of a silica being 0.5 weight part. Table 1 shows the measured values of the thickness and density of the obtained moisture-resistant lightweight resin molded body and the observation results of the appearance.

[Comparative Example 1]
In Example 3, it carried out similarly to Example 3 except having made the quantity of the inorganic type foam nucleating agent into 0. Table 1 shows the measured values of the thickness and density of the foamed molded article and the observation results of the appearance.

[Comparative Example 2]
In Example 3, it carried out similarly to Example 3 except having made the quantity of the inorganic type foam nucleating agent 0.01. Table 1 shows the measured values of the thickness and density of the foamed molded article and the observation results of the appearance.

[Comparative Example 3]
In Example 3, the amount of the inorganic foaming nucleating agent was 0, and the organic foaming agent composed of sodium hydrogen carbonate (sodium bicarbonate) instead of the organic foaming agent (ADCA) as the chemical foaming agent and the organic foaming agent composed of citric acid. This was carried out in the same manner as in Example 3 except that the mixed foaming agent consisting of Table 1 shows the measured values of the thickness and density of the foamed molded article and the observation results of the appearance.

Claims (7)

A method for producing a moisture-resistant lightweight resin molding using an injection molding machine having a two-stage compression screw,
A thermoplastic resin composition comprising 100 parts by weight of a thermoplastic resin, 0.001 to 0.5 parts by weight of a chemical foaming agent comprising only an organic foaming agent, and 0.1 to 1.0 part by weight of an inorganic foaming nucleating agent Melting the product,
Supplying a physical foaming agent from the middle of the cylinder of the injection molding machine to the molten thermoplastic resin composition;
A method for producing a moisture-resistant lightweight resin molded article, comprising a step of injection foam molding.   The method for producing a moisture-resistant lightweight resin molded article according to claim 1, wherein the inorganic foam nucleating agent is silica.   The method for producing a moisture-resistant lightweight resin molded article according to claim 1 or 2, wherein the physical foaming agent is a gaseous physical foaming agent.   The method for producing a moisture-resistant lightweight resin molded article according to any one of claims 1 to 3, wherein the organic foaming agent is azodicarbonamide.   The moisture-resistant lightweight resin molding according to any one of claims 1 to 4, wherein the physical foaming agent is supplied in an amount of 0.1 to 2.0% by weight based on the thermoplastic resin composition. Body manufacturing method. The moisture-resistant lightweight resin molded body is a moisture-resistant lightweight polypropylene resin molded body having a density in the range of 0.4 to 0.8 g / cm ³ . A method for producing a moisture-resistant lightweight resin molding.   The method for producing a moisture-resistant lightweight resin molded product according to any one of claims 1 to 6, wherein the moisture-resistant lightweight resin shaped product is an automobile exterior material.