WO2011013499A1

WO2011013499A1 - Method for producing foam molded body

Info

Publication number: WO2011013499A1
Application number: PCT/JP2010/061655
Authority: WO
Inventors: 徳村　幸子; 勝志三木; 北野　健一
Original assignee: 松本油脂製薬株式会社
Priority date: 2009-07-28
Filing date: 2010-07-09
Publication date: 2011-02-03
Also published as: JPWO2011013499A1

Abstract

Disclosed is a method for producing a lightweight foam molded body which has closed cells. Specifically disclosed is a method for producing a foam molded body, which comprises a mixing step in which a resin mixture that contains a foaming component and a resin component is kneaded within a cylinder so as to obtain a molten mixture, and a molding step in which the molten mixture is extrusion molded through a die. The foaming component essentially contains thermally expandable microspheres each of which is configured of a shell that is composed of a thermoplastic resin and an expansive agent that is contained within the shell and is evaporated when heated. The highest temperature of the cylinder is lower than the temperature of the die, and the temperature difference between the cylinder and the die is within the range of 10-150˚C.

Description

Method for producing foam molded article

The present invention relates to a method for producing a foam molded article. More specifically, the present invention relates to a method for producing a lightweight foamed molded article having closed cells by extrusion molding.

Various methods for adding a foaming agent to a thermoplastic resin or thermoplastic elastomer to obtain a foamed molded product have been studied. As a generally used foam molding method, a chemical foaming agent is mixed with a matrix resin (resin component), the chemical foaming agent is decomposed by heat at the time of melting the resin, and foamed by the gas generated at that time, Examples thereof include a physical foaming method in which a gas (physical foaming agent) such as water vapor, nitrogen gas or carbon dioxide gas is introduced into a melted matrix resin and foamed.
However, in these methods, since gas easily escapes to the outside of the resin, communication bubbles are easily formed, and the resulting molded article has a poor appearance. Moreover, since bubbles are not uniform, there is a problem that it is difficult to obtain a foamed molded article having uniform and fine bubbles. Further, in the foaming mechanism by these methods, it is necessary to control the melt tension and pressure of the resin. For this reason, the kind of resin from which a foaming molding can be obtained, and the molding conditions are limited.

Therefore, in recent years, by using thermally expandable microspheres having a structure in which a thermoplastic resin is used as an outer shell and an expander is enclosed therein as a foaming agent, a foam molded body having uniform and fine closed cells is obtained. A method has been proposed (see Patent Documents 1 to 3).
There are various methods for forming a foamed molded product. For example, in the case of extrusion molding using a chemical foaming agent or a physical foaming agent as the foaming agent, sufficient mixing and heating are performed in the compression zone in the middle of the cylinder to promote the melting of the matrix resin and the decomposition of the foaming agent. After that, a method of obtaining a foamed molded article by lowering the die temperature and suppressing gas expansion due to a rapid pressure drop when passing through the die is common.

In the method of obtaining a foamed molded article by adding thermally expandable microspheres as a foaming agent to the matrix resin instead of the chemical foaming agent or the physical foaming agent, the die temperature is not higher than the cylinder temperature as described above. (For example, see Patent Document 3). In this method, the thermally expandable microspheres are expanded at the temperature of the compression zone, the thermally expandable microspheres are expanded inside the cylinder, and then the temperature of the resin is lowered to increase the viscosity, thereby expanding the balloon into the resin. Therefore, fine closed cells are formed in the molded body. However, it has been difficult to obtain a foamed molded article that is lightweight, that is, has a high expansion ratio.

Japanese Unexamined Patent Publication No. 2000-17140 Japanese Laid-Open Patent Publication No. 11-043551 Japanese Unexamined Patent Publication No. 2001-97594

An object of the present invention is to provide a method for producing a lightweight foamed molded article having closed cells.

When heat-expandable microspheres are used as a foaming agent, when the heat-expandable microspheres expand, the expansion of the expander causes the surrounding heat to be lost and the temperature of the resin component to decrease. Since the die temperature is lower than the cylinder temperature in the conventional method for producing a foam molded article, the resin component is excessively cooled when passing through the die, and the expansion of the thermally expandable microspheres is hindered.
In order to alleviate or prevent this cooling, the inventors of the present invention solved the above-mentioned problem by performing extrusion molding by increasing the die temperature higher than the cylinder temperature, and further optimizing the temperature difference. Reached.

That is, the method for producing a foamed molded article according to the present invention includes a mixing step in which a resin mixture containing a foaming component and a resin component is kneaded in a cylinder to form a molten mixture, and molding in which the molten mixture is extruded through a die. The foaming component essentially comprises thermally expandable microspheres composed of an outer shell made of a thermoplastic resin and an expansion agent encapsulated therein and vaporized by heating, In this manufacturing method, the maximum temperature of the cylinder is lower than the temperature of the die, and the temperature difference is in the range of 10 to 150 ° C.
Preferably, the minimum temperature of the cylinder is equal to or higher than the melting temperature of the resin component, and the vapor pressure of the expansion agent is in the range of 0.1 to 5.0 MPa at the maximum temperature of the cylinder.

When an arbitrary point A in the cylinder and an arbitrary point B in the extrusion direction from the point A are selected and the temperatures are TA and TB, respectively, it is preferable that TA ≦ TB.
When the inside of the cylinder is divided into three sections of a feed zone, a compression zone, and a metering zone in order from the raw material supply port in the extrusion direction, and the temperatures of the respective sections are C1, C2, and C3, C1 ≦ C2 ≦ C3 Is preferable.

The weight ratio of the foaming component in the resin mixture is preferably in the range of 0.1 to 35% by weight with respect to 100% by weight of the resin component.
The weight ratio of the thermally expandable microspheres in the foaming component is preferably in the range of 40 to 100% by weight of the total foaming component.

The foamed molded product of the present invention is obtained by the above production method.
The foamed molded article preferably has at least one physical property of the following (1) to (3).
(1) The average cell diameter is 2 to 500 μm.
(2) The closed cell ratio is 50% or more.
(3) The b ^* value is 20 or less.

In the method for producing a foamed molded product of the present invention, a lightweight foamed molded product having closed cells can be produced.
Moreover, since the foaming molding of this invention is obtained by this manufacturing method, it has a closed cell and is lightweight.

It is the schematic which shows an example of the extrusion molding machine used with the manufacturing method of this invention.

The method for producing a foamed molded product of the present invention is a production method including a mixing step and a molding step.

[Mixing process]
A mixing process is a process performed in a cylinder and knead | mixing the resin mixture containing a foaming component and a resin component to make a molten mixture.
The foaming component is a component that essentially includes thermally expandable microspheres composed of an outer shell made of a thermoplastic resin and an expansion agent that is contained in the shell and vaporizes when heated.

Thermally expandable microspheres can be expanded at various temperatures depending on the combination of the thermoplastic resin constituting the outer shell and the encapsulated expansion agent, and can be appropriately selected depending on the melting temperature and molding temperature of the resin component. .
The thermoplastic resin constituting the outer shell of the thermally expandable microsphere is not particularly limited. For example, an unsaturated carboxylic acid copolymer such as a vinylidene chloride copolymer or a (meth) acrylic acid copolymer. , Unsaturated carboxylic ester copolymers such as (meth) acrylic ester copolymers, nitrile copolymers such as (meth) acrylonitrile copolymers, (meth) acrylic acid- (meth) acrylonitriles And unsaturated carboxylic acid-nitrile copolymers such as copolymers.

Examples of the polymerizable monomer used as a raw material for the thermoplastic resin include vinylidene chloride; vinyl chloride; vinyl acetate; nitrile monomers such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, fumaronitrile; acrylic acid, methacrylic acid, itaconic acid , Fumaric acid, maleic acid and unsaturated carboxylic acid (salt) monomers such as metal salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meta ) (Meth) acrylate monomers such as acrylate, glycidyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate; acrylamide, methacrylamide, substituted acrylic Amide monomers such as luamide and substituted methacrylamide; Imide monomers such as N-phenylmaleimide, N- (2-chlorophenyl) maleimide and N-cyclohexylmaleimide; Vinyl aromatics such as styrene, α-methylstyrene and chlorostyrene Monomer, isoprene, butadiene and the like. These polymerizable monomers may be used alone or in combination of two or more. Moreover, you may use together the monomer (crosslinking agent) which has 2 or more of polymerizable double bonds with the said polymerizable monomer as needed.
In the thermally expandable microsphere, if the thermoplastic resin constituting the outer shell is a nitrile copolymer (obtained by polymerizing a polymerizable monomer containing a nitrile monomer, for example), flexibility and heat resistance And the effects of the present invention are easily obtained. When the weight ratio of the nitrile monomer is preferably 70% by weight or more of the polymerizable monomer, more preferably 80% by weight or more, the gas barrier property of the outer shell is high, and a foamed molded article having a high foaming ratio is easily obtained. .

In the thermally expandable microsphere, the thermoplastic resin constituting the outer shell is unsaturated (obtained by polymerizing a polymerizable monomer including an unsaturated carboxylic acid (salt) monomer and a nitrile monomer, for example). A carboxylic acid-nitrile copolymer is preferred. When the total weight ratio of the nitrile monomer and the unsaturated carboxylic acid (salt) monomer is preferably 60% by weight or more of the polymerizable monomer, more preferably 70% by weight or more, and particularly preferably 80% by weight or more, the heat resistance is improved. It is high and can be suitably used in molding at 200 ° C. or higher. At this time, the mixing ratio of the unsaturated carboxylic acid (salt) monomer in the total of the nitrile monomer and the unsaturated carboxylic acid (salt) monomer is preferably 5 to 70% by weight, more preferably 10 to 60% by weight. It is.
The expansion agent is not particularly limited as long as it is encapsulated in the outer shell and is vaporized by heating. For example, propane, normal butane, isobutane, normal pentane, cyclopentane, isopentane, neopentane, normal hexane, isohexane, heptane , Hydrocarbons such as octane, isooctane, nonane, normal decane, isododecane, petroleum ether, chlorofluorocarbons, fluorine-containing compounds that do not contain chlorine or bromine atoms, and compounds that generate gas by thermal decomposition upon heating. . These swelling agents may be used alone or in combination of two or more.

Thermally expandable microspheres can be produced by a known method. For example, a method in which an oil phase containing the polymerizable monomer, an initiator, and the swelling agent is subjected to suspension polymerization in an aqueous phase suspension containing a dispersant and the like.
The dispersion stabilizer in the aqueous phase is not particularly limited. For example, colloidal silica, colloidal calcium carbonate, magnesium hydroxide, calcium phosphate, aluminum hydroxide, ferric hydroxide, calcium sulfate, sodium sulfate, calcium oxalate, carbonate Examples include calcium, barium carbonate, magnesium carbonate, and alumina sol. In addition, as dispersion stabilizers, condensation products of diethanolamine and fatty acid dicarboxylic acids, gelatin, polyvinylpyrrolidone, methylcellulose, polyethylene oxide, polypeptides, polyvinyl alcohol, and other polymer type dispersion stabilizers; alkyltrimethylammonium chloride, chloride And cationic surfactants such as dialkyldimethylammonium; anionic surfactants such as sodium alkyl sulfate; amphoteric surfactants such as alkyldimethylaminoacetic acid betaine and alkyldihydroxyethylaminoacetic acid betaine. In addition, a water-soluble compound such as a scale inhibitor may be added to the aqueous phase suspension in combination with the dispersion stabilizer.

The polymerization temperature is set appropriately depending on the type of polymerization initiator. The polymerization may be carried out under pressure. For example, the initial polymerization pressure is preferably in the range of 0 to 5.0 MPa.
Thermally expandable microspheres are also commercially available. As typical commercially available products of thermally expandable microspheres, Matsumoto Microsphere's Matsumoto Microsphere's product numbers of thermally expandable microspheres are listed. Can be mentioned.

The average particle diameter of the thermally expandable microspheres is preferably 1 to 60 μm. If it is smaller than 1 μm, uniform dispersion is difficult and the expansion ratio is low. Moreover, since the intensity | strength of the foaming molding obtained will become weak when larger than 60 micrometers, it is not desirable.
In the thermally expandable microspheres used in the present invention, it is preferable that the weight ratio of the expanding agent to the thermally expandable microspheres is 2 to 85% by weight because closed cells are easily formed. More preferably, it is 5 to 60% by weight, particularly preferably 7 to 55% by weight. If the weight ratio of the expansion agent to the heat-expandable microspheres is less than 2% by weight, the expansion ratio of the heat-expandable microspheres is small and it is difficult to obtain a lightweight foamed molded product. On the other hand, when the amount is more than 85% by weight, the thermally expandable microspheres are easily broken in the mixing step, and communication bubbles are easily formed.

The thermally expandable microsphere has a maximum expansion ratio of preferably 5 times or more, more preferably 10 times or more, and particularly preferably 20 times or more in volume. The upper limit of the expansion ratio is not particularly limited, but is usually 400 times or less. The volume expansion ratio can be calculated from the specific gravity before and after heating the thermally expandable microspheres with an oven or the like.
There are an expansion start temperature (Ts) and a maximum expansion temperature (Tmax) as indices indicating the thermal expansion characteristics of the thermally expandable microspheres. The expansion start temperature is defined as the temperature at which the thermally expandable microsphere expands when heated above that temperature, and the maximum expansion temperature is defined as the temperature at which the expansion of the thermally expandable microsphere is maximized. . The detailed measurement method of the expansion start temperature and the maximum expansion temperature will be described below. The expansion start temperature (Ts) is a temperature at which the thermally expandable microspheres are heated under a constant pressure, and expansion starts when the temperature is increased. It is. The maximum expansion temperature (Tmax) is a temperature at which the temperature is increased after the start and a displacement amount (maximum displacement amount; Dmax) at which the expansion is maximized is indicated.

The expansion start temperature (Ts) of the thermally expandable microsphere is preferably 100 ° C. or higher, more preferably 120 ° C. or higher. The maximum expansion temperature of the thermally expandable microsphere is preferably 150 ° C. or higher, more preferably 160 ° C. or higher. Here, when ΔT = Tmax−Ts, 10 ≦ ΔT ≦ 100 is preferable, 15 ≦ ΔT ≦ 90 is further preferable, and 20 ≦ ΔT ≦ 80 is particularly preferable.
Further, when a temperature (TD ₅₀ ) at which the displacement amount (D ₅₀ ) is 50% of the maximum displacement amount (Dmax) is obtained and R = (Tmax−TD ₅₀ ) / (Tmax−Ts), 0.2 ≦ R ≦ 0.9 is preferable, 0.3 ≦ R ≦ 0.8 is more preferable, and 0.35 ≦ R ≦ 0.75 is particularly preferable.

In the mixing step, it is preferable that the maximum expansion temperature of the heat-expandable microspheres is higher than the melting temperature of the resin component so that the heat-expandable microspheres are not excessively expanded. The temperature difference is preferably 10 ° C. or higher, more preferably 20 ° C. or higher, and particularly preferably 30 ° C. or higher. The upper limit of the temperature difference is 200 ° C.
The foaming component may further contain a chemical foaming agent, a physical foaming agent and the like. In the present invention, the temperature of the resin component is lowered due to the thermal expansion of the thermally expandable microspheres, and the viscosity thereof is increased. It is possible to obtain.

Examples of chemical blowing agents include inorganic blowing agents such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, ammonium nitrite, azide compounds, sodium borohydride; azodicarbonamide, azobisisobutyronitrile, barium azodi Carboxylate, dinitrosopentamethylenetetramine, 4,4'-oxybis (benzenesulfonylhydrazide), diazoaminobenzene, N, N'-dimethyl-N, N'-dinitrosotephthalamide, N, N'-dinitroso Pentamethylenetetramine, nitrourea, acetone-p-toluenesulfonylhydrazone, p-toluenesulfonylamide, 2,4-toluenedisulfonylhydrazide, trinitrosotrimethylenetriamine, p-methylurethanebenzenesulfonylhydrazide, p- Examples thereof include organic blowing agents such as toluenesulfonyl semicarbazide, oxalyl hydrazide, nitroguanidine, hydroazodicarbonamide, trihydrazinotriazine, 5-phenyltetrazole, and bistetrazole. Moreover, you may use a foaming adjuvant together with the said chemical foaming agent as needed. The foaming assistant is an additive that acts to lower the decomposition temperature of the foaming agent, accelerate the decomposition, and make the bubbles uniform, and examples thereof include zinc stearate, salicylic acid, and phthalic acid.
Examples of the physical foaming agent include butane, pentane, dichloromethane, water, nitrogen gas, carbon dioxide gas, and air.

By adjusting the weight ratio of thermally expandable microspheres in the foaming component according to the type of chemical foaming agent, physical foaming agent, etc. and the type of resin component described later, a lightweight molded body having closed cells is obtained. However, the weight proportion of the thermally expandable microspheres in the foaming component is preferably 40 to 100% by weight, more preferably 50 to 100% by weight, particularly preferably 60 to 100% by weight of the whole foaming component. It is. When the weight ratio of the thermally expandable microspheres is less than 40% by weight, the expansion pressure of the gas generated from the chemical foaming agent is superior to the increase in the viscosity of the resin component due to the thermal expansion of the thermally expandable microspheres. Bubbles are easily formed, which is not preferable.
The foaming component may be mixed with the resin component described later as it is to form a resin mixture, but as a wet product obtained by premixing the foaming component with a liquid such as oil, or a granulated product obtained by solidifying the foaming component with wax or the like Therefore, it may be mixed with a resin component to form a resin mixture. Also, a master batch containing a foaming component and a resin component is prepared in advance, and it may be mixed with the resin component to form a resin mixture. In these cases, the dispersibility of the foaming component in the molten mixture obtained by kneading the resin mixture in a cylinder is preferable.

The liquid material used for the moistened material is not particularly limited as long as the compatibility with the resin component is good, and examples thereof include mineral oil, fluid paraffin, silicone oil, and plasticizer. The weight ratio of the liquid is preferably from 0.1 to 60% by weight, more preferably from 0.2 to 50% by weight, particularly preferably from 0.5 to 40% by weight, based on the entire wetted product. When the weight ratio of the liquid material is less than 0.1% by weight, the humidification is not sufficient and the effect of enhancing the dispersibility of the foaming component is small. On the other hand, when the weight ratio of the liquid is more than 60% by weight, the stickiness is high and the workability is poor.
Examples of the wax used in the granulated product include fatty acids and paraffin waxes. The weight ratio of the wax is preferably 5 to 70% by weight, more preferably 10 to 60% by weight, and particularly preferably 15 to 50% by weight of the whole granulated product. If the weight ratio of the wax is less than 5% by weight, a granulated product cannot be formed. Moreover, when there are more weight ratios of a wax than 70 weight%, there exists a concern about the influence on the physical property of a resin component.

The resin component used in the masterbatch is not particularly limited as long as it is a resin component specifically exemplified below, but a melting temperature lower than the expansion start temperature of the thermally expandable microsphere and the decomposition temperature of the chemical foaming agent. It is preferable that the thermoplastic material has a masterbatch because the foaming performance is not impaired. The weight ratio of the resin component is preferably 25 to 95% by weight of the entire master batch, more preferably 30 to 90% by weight, and particularly preferably 35 to 80% by weight.
In the present invention, thermally expandable microspheres are used as the foaming component. For this reason, it is possible to foam a resin having a low melt tension, a filler-containing resin, or the like, and the resin component that can be used is not particularly limited.

Examples of the resin component include generally used thermoplastic resins and thermoplastic elastomers. For example, polyolefin resins such as polyethylene, polypropylene, polybutene, polymethylpentene, TPO, TPV, and olefin-based thermoplastic elastomers; Olefin resin copolymers such as vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene- (meth) acrylic acid (ester) copolymer, ionomer resin; polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate Polyvinyl resins such as polyvinyl alcohol; polyethylene terephthalate, polybutylene terephthalate, polytetramethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate, polyarylate, polycarbonate, TP Polyester resins such as E; acrylic resins such as poly (meth) methyl acrylate, poly (meth) ethyl acrylate, poly (meth) acrylate butyl, poly (meth) acrylonitrile; polystyrene, AS resin, ASA resin, Styrenic resins such as ABS resin; polyamide resins such as 6-nylon, 6,6-nylon and TPEA; biodegradable resins such as polylactic acid; fluororesins; polyurethane thermoplastic elastomers; liquid crystal polymers . These resin components may be used alone or in combination of two or more.
In addition to the foam component and resin component, the resin mixture can be variously used as necessary, such as lubricants, plasticizers, antioxidants, colorants, fillers, antistatic agents, flame retardants, wood flour, glass fibers, carbon fibers, etc. An additive may be contained. In that case, various additives may be mixed as the third component with respect to the foaming component and the resin component, and a molten mixture may be prepared using a resin component containing various additives in advance.

In the resin mixture, the weight ratio of the foaming component and the resin component is not particularly limited as long as it is a blending ratio capable of extruding a molten mixture obtained by kneading the resin mixture in a cylinder, but the foaming component in the resin mixture is not limited. The weight ratio is preferably 0.1 to 35% by weight, more preferably 0.3 to 25% by weight, and particularly preferably 0.5 to 15% by weight with respect to 100% by weight of the resin component. When the weight ratio of the foaming component is less than 0.1% by weight, the lightening effect is small. On the other hand, when the weight ratio of the foaming component is more than 35% by weight, the obtained foamed molded product becomes brittle.
The extruder used in the present invention is not particularly limited as long as it is generally used, and examples thereof include a single-axis or biaxial extruder and a co-extrusion machine.

As an example of an extruder used in the present invention, an extruder having a heater 2 and a thermocouple 3 in a cylinder 1 is shown in FIG. The number of heaters is not particularly limited in the present invention, but is three in FIG.
The cylinder 1 is equipped with a raw material supply port 5 for supplying a foaming component and a resin component (resin mixture 4) to the cylinder 1. Inside the cylinder 1, a screw 6 for moving the resin mixture 4 from the raw material supply port 5 in the extrusion direction while kneading is installed.

In FIG. 1, the inside of the cylinder 1 is divided into three sections of a feed zone 7, a compression zone 8, and a metering zone 9 corresponding to each position of the heater 2 in order from the raw material supply port 5 in the extrusion direction. Here, the temperatures of the respective sections are sequentially referred to as C1, C2, and C3.
In FIG. 1, the resin mixture 4 supplied to the cylinder 1 becomes a molten mixture 10 by the heating of the heater 2 and the rotation of the screw 6, and is extruded through a die 11 to obtain a foamed molded body 12.

In extrusion molding, the kneading state of resin components and additives is adjusted by the screw shape design. Therefore, in the conventional method, it was necessary to perform strong kneading mainly in the compression zone 8 and to further optimize the L / D (ratio between the length L and the diameter D) of the screw. However, in the present invention, the screw shape and L / D are not particularly limited, and known ones can be used. Furthermore, in the method of the present invention, since a lightweight foamed molded product can be obtained without requiring strong kneading, a screw shape with weak kneading can be used. In this case, the expansion of the thermally expandable microspheres in the cylinder can be suppressed, and the effect of the present invention can be easily obtained, which is preferable.
Moreover, it is preferable that the minimum temperature of the cylinder is equal to or higher than the melting temperature of the resin component because the shearing force applied to the thermally expandable microspheres is reduced. The temperature difference between the two is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and particularly preferably 15 ° C. or higher. The upper limit of the temperature difference is 200 ° C.

When the extruder is provided with a vent, it is desirable to perform molding with the vent closed. When the vent is opened, the molten mixture is extruded from the vent, and it may be difficult to obtain a lightweight foamed molded product.
Further, in extrusion molding, generally, a vacuum pump or the like is connected to a vent provided immediately before a die and exhausted to remove voids generated during kneading. However, in the present invention, when the molten mixture comes out of the die, the resin component is highly fluidized and the foaming due to the expansion of the thermally expandable microspheres is promoted. Therefore, even if there is no operation of removing a void with a vent, a lightweight foamed molded article without a void can be easily obtained.

Thermally expandable microspheres are greatly affected by pressure and shear once expanded. In the case where the inside of the cylinder described above is divided into three sections, molding is conventionally performed in a state where C2 is higher than C1 and C3 is not higher than C2 (C1 <C2 and C2 ≧ C3). Yes. In this case, in the metering zone 9, the pressure in the system increases and the shearing force increases as the resin temperature decreases and the viscosity increases, so that the thermally expandable microspheres that have once expanded in the compression zone are contracted or broken. For this reason, there is a problem that a highly foamed molded article cannot be obtained.
In order to solve this problem as well, in the cylinder 1 of the extruder, an arbitrary point A and an arbitrary point B in the extrusion direction from the point A are selected (not shown in FIG. 1), It is preferable that TA ≦ TB, where TA is the temperature at point A and TB is the temperature at point B. Here, in any case where the point A and the point B are selected, it is more preferable that TA ≦ TB. As described above, when the inside of the cylinder is divided into three sections, it is particularly preferable that C1 ≦ C2 ≦ C3. Thus, in the present invention, by preventing the temperature from decreasing in the direction of extrusion in the cylinder, the thermally expandable microspheres are gradually expanded, and the maximum expansion is induced in the die portion. It is possible to obtain a foamed molded article.

The temperature of C1, C2, and C3 is not particularly limited and is appropriately selected depending on the melting temperature of the resin component, but is preferably 80 to 300 ° C, more preferably 100 to 280 ° C, and 120 to 270 ° C. And particularly preferred.
When ΔC ₁₂ = C2-C1, 0 ≦ ΔC ₁₂ ≦ 40 is preferable, 0 ≦ ΔC ₁₂ ≦ 30 is more preferable, and 0 ≦ ΔC ₁₂ ≦ 20 is particularly preferable.
When ΔC ₂₃ = C3-C2, 0 ≦ ΔC ₂₃ ≦ 50 is preferable, 0 ≦ ΔC ₂₃ ≦ 40 is more preferable, and 0 ≦ ΔC ₂₃ ≦ 30 is particularly preferable.
The vapor pressure of the expansion agent contained in the thermally expandable microspheres at the maximum cylinder temperature is preferably 0.1 to 5.0 MPa, more preferably 0.5 to 4.5 MPa, and particularly preferably 1.0 to 4.0 MPa. If the vapor pressure is less than 0.1 MPa, the expansion rate of the thermally expandable microspheres is slow, and the die temperature does not sufficiently expand only with the die temperature. On the other hand, if the vapor pressure exceeds 5.0 MPa, the thermally expandable microspheres expand in the cylinder and the pressure in the system rises, so that the expansion is not sufficient.

[Molding process]
The molding step is a step of extruding and molding the molten mixture obtained in the mixing step through a die.
As the die used in the present invention, any molding die can be used according to the shape of the obtained foamed molded article. Examples of the die include a straight die, a cross head die, a flat die (T die), and a circular die.

In the heat-expandable microspheres contained in the molten mixture, the thermoplastic resin in the outer shell is softened by heating in the cylinder in the mixing step. Next, in the molding process, the resin is extruded while expanding toward the die outlet (pressure release port). Therefore, it is considered that by making the maximum temperature of the cylinder lower than the temperature of the die, the fluidity of the resin component is increased at the die portion and the molten mixture is easily foamed.
On the other hand, when the foaming component is only a chemical foaming agent or a physical foaming agent, the flowability of the resin component is increased and gas escape is likely to occur at the same time. It does not become a body. However, when the foaming component contains thermally expandable microspheres, there is no problem of outgassing, and by expanding the thermally expandable microspheres more, many bubbles can be introduced into the resin component, which is lightweight. Can be obtained.

In the present invention, the maximum cylinder temperature is lower than the die temperature. The temperature difference is usually in the range of 10 to 150 ° C., preferably 15 to 140 ° C., more preferably 20 to 130 ° C., particularly preferably 25 to 120 ° C., and most preferably 30 to 110 ° C. Due to this temperature difference, the expansion of the thermally expandable microspheres is promoted, and a highly foamed and lightweight foamed molded product can be obtained. However, if the temperature difference is less than 10 ° C., the heating in the die becomes insufficient, and the influence on the expandability due to the high die temperature may not be seen so much. On the other hand, when the temperature difference exceeds 150 ° C., the expansion of the thermally expandable microspheres in the cylinder is insufficient, and a lightweight foamed molded product cannot be obtained.
The time from when the resin mixture is introduced into the raw material supply port until it is extruded from the die can be adjusted by the number of rotations of the screw. The number of rotations of the screw may be set as appropriate depending on equipment and resin components, but the time (residence time) from when the resin mixture is introduced into the raw material supply port until it is extruded from the die is 0.2 to 30 minutes. It is preferable that it is 0.3, more preferably 0.3 to 20 minutes, and particularly preferably 0.5 to 15 minutes. If the residence time is shorter than 0.2 minutes, heating may be insufficient and a lightweight foamed molded product may not be obtained. On the other hand, if the residence time is longer than 30 minutes, the work efficiency may deteriorate and productivity may be problematic.
The foamed molded body extruded from the die is usually cooled by a cooling facility such as air cooling, water cooling, or a roll to obtain a desired molded body. In the present invention, equipment generally used as cooling equipment, take-up equipment, or the like can be used.

[Foamed molded product]
The foamed molded product of the present invention is manufactured by, for example, the above manufacturing method. This foam-molded product is a foam-molded product having closed cells, has little yellowing, has excellent whiteness, and has good surface properties.
The average cell diameter of the foamed molded article of the present invention is not particularly limited, but is preferably 2 to 500 μm, more preferably 3 to 400 μm, and particularly preferably 5 to 300 μm. If the average cell diameter is smaller than 2 μm, it may be difficult to obtain a lightweight foamed molded product. On the other hand, when the average cell diameter is larger than 500 μm, the strength of the obtained foamed molded product may be weak, which is not preferable.

The closed cell ratio of the foamed molded article of the present invention is not particularly limited, but is preferably 50% or more, more preferably 60% or more, particularly preferably 65% or more, and most preferably 80% or more. The upper limit of the closed cell ratio is 100%. If the closed cell ratio is less than 50%, the strength of the resulting foamed molded product is weak, and there is also a problem of water absorption due to open cells, which is not preferable. On the other hand, a foamed molded product having a high closed cell ratio is preferred because it is a foamed molded product having excellent strength and heat insulation.
The bubble diameter of the foam molded article can be easily adjusted by the particle diameter of the thermally expandable microsphere. If the thickness of the foamed molded product is thin or if the rigidity of the foamed molded product is required, select thermally expandable microspheres with a small particle diameter and increase the weight ratio of thermally expandable microspheres in the foam component. It is preferable. Further, when the flexibility of the foamed molded product is required, it is preferable to select thermally expandable microspheres having a large particle diameter or to reduce the weight ratio of thermally expandable microspheres in the foam component.

The foamed molded article of the present invention is excellent in dimensional stability. In the conventional molding method, a difference in foaming is likely to occur in the extrusion direction and the direction perpendicular thereto. For example, when a wide sheet or the like is produced, there is a difference in the degree of foaming between the central portion and the end portion. However, in the present invention, since the fluidity of the resin component is increased at the die portion, it is easy to foam uniformly and hardly cause a difference in foaming. In addition, when the resin mixture contains a third component, the third component is easily oriented uniformly and randomly, so that the difference in physical properties such as the degree of foaming in the extrusion direction and the vertical direction is small.
The b ^* value of the foamed molded product is not particularly limited, but is preferably 20 or less, more preferably 15 or less, and particularly preferably 10 or less. The lower limit of the b ^* value is zero. The b ^* value indicates the degree of yellow coloring, and the larger the value, the darker the color.

The b ^* value of a foamed molded product is generally greatly influenced by the type of foaming component. When the foaming component contains thermally expandable microspheres, the b ^* value varies depending on the type of thermally expandable microsphere. However, in the present invention, if the maximum temperature of the cylinder is lower than the temperature of the die, it is interesting that even if the same type of foaming component is used, foam molding with a smaller b ^* value than the conventional method. The body is obtained.
Since the foamed molded product according to the present invention has little yellowing and is excellent in whiteness, the color can be easily adjusted, and a light-colored molded product can be produced.

The foamed molded product thus obtained is lightweight and has heat insulation and cushioning properties, and is used for building materials, automobile materials, industrial materials, and the like. Further, according to the present invention, it is possible to obtain a highly foamed molded article without giving a cross-linked structure to the resin component, so that there is an advantage that the resin component is excellent in recyclability.

Examples of the present invention will be specifically described below. The present invention is not limited to these examples.
About the thermally expansible microsphere used below and the foaming molding manufactured by the Example and the comparative example, the physical property was evaluated in the following way. Thermally expandable microspheres are sometimes referred to simply as microspheres, and foamed molded articles are sometimes referred to simply as molded bodies.

[Ts and Tmax]
The expansion start temperature (Ts) and the maximum expansion temperature (Tmax) of the thermally expandable microspheres are measured using DMA (DMA Q800, manufactured by TA instruments). The heat-expandable microspheres are placed in an aluminum cup and heated from 20 ° C. to 300 ° C. at a rate of temperature increase of 10 ° C./min. The displacement amount (D) in the vertical direction was measured, the displacement start temperature in the positive direction was defined as the expansion start temperature (Ts), and the temperature when the maximum displacement amount (Dmax) was indicated was defined as the maximum expansion temperature (Tmax).
Further, the temperature (TD ₅₀ ) when the displacement amount (D ₅₀ ) is 50% of the maximum displacement amount (Dmax) is obtained, and (Tmax−TD ₅₀ ) / (Tmax−Ts) is calculated. R.

[Formability]
Judgment on shape retention and ease of manufacture of molded product based on the following evaluation criteria.
○: Good (Extruded for 1 hour, and the molded product can be recovered without changing the discharge amount and shape)
Δ: Slightly defective (Extrusion for 1 hour, discharge amount and shape change occasionally, adjustment is required)
×: Defect (The discharge amount and shape are not stable, and the molded product cannot be recovered)

〔specific gravity〕
The specific gravity of the obtained molded product was measured by a method based on JIS K-7112 A method (submerged replacement method).

(Bubble state)
Using an electron microscope (SEM) apparatus, the bubble state of the obtained molded body cross section was confirmed.
From the SEM photograph taken at a magnification of 30 times, the ratio of closed cells per unit area is calculated and determined based on the following evaluation criteria.
A: Uniform independent (closed cell ratio 80% or more)
○: Almost uniform independent (closed cell ratio of 50% or more and less than 80%)
X: non-uniform (closed cell ratio less than 50%)

[Average bubble diameter]
Calculated by a method according to ASTM D3576-77 from SEM photographs of a cross section of the resulting molded article taken at 100x magnification.

〔Surface condition〕
The surface of the obtained molded body was confirmed by visual observation and judged based on the following evaluation criteria.
○: Good (no surface roughness due to outgassing)
Δ: Slightly defective (state where irregularities due to outgassing are partly seen)
X: Defect (a state in which there are many irregularities due to outgassing as a whole, and the skin is crumpled)

[B ^* value]
The color of the obtained foamed molded product is measured with a spectrocolorimeter (SPECTROTOPOMETER CM-3600d, manufactured by KONICA MINOLTA), and the b ^* value is calculated.

The resin components and thermally expandable microspheres used in the following examples and comparative examples are shown in Tables 1 and 2. Prototype 1 in Table 2 was produced according to Production Example 1.
[Production Example 1]
A heat-expandable microsphere having a thermoplastic resin obtained by copolymerizing acrylonitrile, methacrylonitrile and methacrylic acid as an outer shell and encapsulating isobutane and isopentane as an expanding agent is prepared by a known method. (Prototype 1; see Table 2).

[Production Example 2]
50 parts by weight of thermally expandable microspheres 1 (see Table 2), 2 parts by weight of fluid paraffin oil (PW-200) and 48 parts by weight of ethylene vinyl acetate resin were blended with a ribbon mixer, and Laboplast mill (Toyo) Extruded into a strand having a diameter of 2 mm using Seiki ME-25; cylinder temperature and die temperature are all 100 ° C .; screw rotation speed is 30 rpm. After the obtained strand was air-cooled, it was converted into a 4 mm long rod-shaped pellet by a pelletizer, and a master batch 1 containing 50% by weight of thermally expandable microspheres 1 was obtained.
In the same manner as described above, master batches 2 to 4 were obtained using thermally expandable microspheres 2 to 4, respectively.

[Production Example 3]
80 parts by weight of thermally expandable microspheres 5 (see Table 2) and 20 parts by weight of fluid paraffin oil (PW-200) were blended with a ribbon mixer to obtain an oil moistened product 5 of thermally expandable microspheres 5. .

[Example 1]
Resin 1 shown in Table 1 and master batch 1 obtained in Production Example 2 were mixed at a weight ratio of 96: 4 to obtain a resin mixture. At this time, the mixing ratio of the resin component and the foamed component (thermally expandable microsphere 1) was 98: 2.
A lab plast mill (ME-25 manufactured by Toyo Seiki Co., Ltd.), which is an extrusion molding machine shown in FIG. 1, was prepared, and the resin mixture was supplied from the raw material supply port. The temperature of the cylinder is C1 = C2 = C3 = 160 ° C., the screw mixture is extruded at 40 rpm, the molten mixture is extruded, and a plate-like foamed molded article is formed at a die temperature of 200 ° C. using a T die (width 150 mm, lip thickness 1.7 mm). (Width 140 mm × thickness 1.5 mm) was obtained.

[Example 2]
Using the resin 2 shown in Table 1 and the master batch 2 obtained in Production Example 2, the cylinder temperature was C1 = C2 = C3 = 190 ° C. and the die temperature was 220 ° C. A plate-like foamed molded product was obtained.
Example 3
Using the resin 2 shown in Table 1 and the master batch 3 obtained in Production Example 2, the cylinder temperature was C1 = C2 = C3 = 180 ° C. and the die temperature was 220 ° C. A plate-like foamed molded product was obtained.

Example 4
Using the resin 2 shown in Table 1 and the master batch 4 obtained in Production Example 2, the cylinder temperature was C1 = C2 = C3 = 180 ° C. and the die temperature was 290 ° C. A plate-like foamed molded product was obtained.
[Comparative Example 1]
A plate-like foamed molded article was obtained in the same manner as in Example 1 except that the cylinder temperature was C1 = C2 = C3 = 170 ° C. and the die temperature was 170 ° C.

[Comparative Example 2]
A plate-like foamed molded article was obtained in the same manner as in Example 2 except that the cylinder temperature was C1 = C2 = C3 = 200 ° C. and the die temperature was 200 ° C.
[Comparative Example 3]
A plate-like foamed molded article was obtained in the same manner as in Example 3 except that the cylinder temperature was C1 = C2 = C3 = 200 ° C. and the die temperature was 200 ° C.
Table 3 shows the molding conditions and the physical property evaluation results of the obtained foamed molded products for Examples 1 to 4 and Comparative Examples 1 to 3.

When Example 1 and Comparative Example 1 were compared, the resin component and the foaming component used were the same, but in Example 1, the foamed molded article was lighter than Comparative Example 1. Similarly, when Example 2 and Comparative Example 2 and Example 3 and Comparative Example 3 are compared, the resin component and the foaming component used are the same, but in the example, the foamed molded article is lighter than the comparative example. It was.
In addition, the foamed molded products obtained in Examples 1 to 4 had fine closed cells, and the surface condition was good.

Example 5
The resin 3 shown in Table 1 and the oil wet product 5 obtained in Production Example 3 were mixed to obtain a resin mixture. Each mixing ratio was such that the resin 3 as a resin component was 100% by weight, and the microspheres 5 contained in the oil moistened product 5 were 1% by weight.
In the same manner as in Example 1, the resin mixture was supplied to the lab plast mill. Cylinder temperature is C1 = 160 ° C, C2 = C3 = 170 ° C, screw rotation is 30rpm, the molten mixture is extruded, and foam sheet with die temperature of 240 ° C using T die (width 150mm, lip thickness 0.5mm) (Width 140 mm × thickness 0.3 mm) was obtained.

Example 6
A foamed sheet was obtained in the same manner as in Example 5 except that the microspheres 5 were mixed at a ratio of 2% by weight.
[Comparative Example 4]
A foamed sheet was obtained in the same manner as in Example 5 except that the cylinder temperature was changed to C1 = 160 ° C., C2 = C3 = 220 ° C., and the die temperature was changed to 220 ° C.

[Comparative Example 5]
A foam sheet was obtained in the same manner as in Example 6 except that the cylinder temperature was changed to C1 = 160 ° C., C2 = C3 = 220 ° C., and the die temperature was changed to 220 ° C.
Table 4 shows the molding conditions and the physical property evaluation results of the obtained foamed molded articles for Examples 5 and 6 and Comparative Examples 4 and 5, respectively.

In Examples 5 and 6, as compared with Comparative Examples 4 and 5, it was possible to obtain a foamed molded article that was lighter in weight and less yellowing and excellent in whiteness.

Example 7
Resin 4 shown in Table 1 and master batch 4 obtained in Production Example 2 were mixed at a weight ratio of 110: 2 to obtain a resin mixture. At this time, the weight ratio of the foamed component (thermally expandable microsphere 4) was 1% by weight with respect to 100% by weight of the resin component.
In the same manner as in Example 1, the resin mixture was supplied to the lab plast mill. The temperature of the cylinder is C1 = 200 ° C., C2 = C3 = 210 ° C., the screw mixture is extruded at 40 rpm, the molten mixture is extruded, and a plate shape is formed at a die temperature of 240 ° C. using a T die (width 150 mm, lip thickness 1.7 mm). A foamed molded product (width 140 mm × thickness 1.5 mm) was obtained.

Example 8
The resin 4 shown in Table 1 and the master batch 4 obtained in Production Example 2 and ADCA master batch (50% azodicarbonamide-containing polyethylene master batch; commercial product) were mixed at a weight ratio of 110: 2: 0.6, A plate-like foamed molded article was obtained in the same manner as in Example 7 except that the resin mixture was used. At this time, the weight ratio of the foaming component was 1.3% by weight with respect to 100% by weight of the resin component.

[Comparative Example 6]
Resin 4 and ADCA masterbatch (polyethylene masterbatch containing 50% azodicarbonamide; commercial product) shown in Table 1 were mixed at a weight ratio of 110: 3 to obtain a resin mixture. At this time, the weight ratio of the foaming component was 1.5% by weight with respect to 100% by weight of the resin component. Using this resin mixture, a plate-like foamed molded article was obtained in the same manner as in Example 7 except that the die temperature was 200 ° C.

[Comparative Example 7]
Resin 4 shown in Table 1 and ADCA masterbatch (polyethylene masterbatch containing 50% azodicarbonamide; commercially available product) were mixed and mixed at a weight ratio of 110: 3 in the same manner as in Example 7 except that a resin mixture was obtained. Thus, a plate-like foamed molded product was obtained. At this time, the weight ratio of the foaming component was 1.5% by weight with respect to 100% by weight of the resin component.
Table 5 shows the molding conditions and the physical property evaluation results of the obtained foamed molded products for Examples 7 and 8 and Comparative Examples 6 and 7, respectively.

In Examples 7 and 8, a lightweight foamed molded article having closed cells could be obtained. On the other hand, although it was possible to reduce the weight a little in Comparative Example 6, the bubbles were continuous bubbles and the surface condition was not good. In Comparative Example 7, the weight could hardly be reduced.

[Production Example 4]
To 600 g of ion-exchanged water, 160 g of sodium chloride, 60 g of colloidal silica which is 20% by weight of silica active ingredient, 1 g of diethanolamine-adipic acid condensate and 0.1 g of ethylenediaminetetraacetic acid / 4Na salt are added, and the pH is adjusted to 2.8-3. To 2 to prepare an aqueous dispersion medium.
Separately, 150 g of acrylonitrile, 90 g of methacrylonitrile, 10 g of methyl methacrylate, 1 g of ethylene glycol dimethacrylate, 1 g of azobis (2,4-dimethylvaleronitrile) and 65 g of isopentane were mixed to prepare an oily mixture.
The aqueous dispersion medium and the oily mixture were mixed, and the obtained mixed liquid was dispersed with a homomixer (TK machine manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a suspension. The suspension was transferred to a pressure reactor having a capacity of 1.5 liters, and purged with nitrogen. Then, the initial reaction pressure was 0.5 MPa, and polymerization was performed at a polymerization temperature of 60 ° C. for 20 hours while stirring at 80 rpm. The polymer solution obtained after the polymerization was filtered and dried to obtain thermally expandable microspheres 6. Table 6 shows the physical properties of the thermally expandable microspheres 6 obtained.

[Production Examples 5 to 9]
Thermally expandable microspheres 7 to 11 were obtained in the same manner as in Production Example 4 except that the various components and amounts used in Production Example 4 were changed to those shown in Table 6. Table 6 shows the physical properties of the obtained heat-expandable microspheres 7 to 11.

[Production Example 10]
In the same manner as in Production Example 2, master batches 6 to 11 were obtained using thermally expandable microspheres 6 to 11, respectively.

Example 9
In Example 1, except that the master batch 1 was changed to the master batch 6 containing the thermally expandable microspheres 6 and changed to the molding conditions shown in Table 7, a plate-like foamed molded article was obtained in the same manner as in Example 1. Obtained. The physical properties were evaluated and the results are shown in Table 7.
[Examples 10 to 14, Comparative Examples 8 to 13]
In Example 9, the master batch 6 was changed to a master batch containing microspheres shown in Table 7 and the molding conditions were changed to the molding conditions shown in Table 7, respectively. Got. The physical properties were evaluated, and the results are shown in Table 7.

In Examples 9 to 14 and Comparative Examples 8 to 13, the resin component and the foaming component used were the same, but the examples and comparative examples having different molding methods were compared. The surface condition was generally good.

The method for producing a foamed molded article of the present invention can produce a lightweight foamed molded article having closed cells. Therefore, the obtained foamed molded product is a foamed molded product that is lightweight, excellent in heat insulation and compression properties, and has a good appearance, and is a machine part and interior / exterior material for automobiles, rollers and cable parts for household appliances, and construction. Widely used as a material.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Heater 3 Thermocouple 4 Resin mixture 5 Raw material supply port 6 Screw 7 Feed zone 8 Compression zone 9 Metering zone 10 Molten mixture 11 Die 12 Foam molding

Claims

A production method comprising a mixing step of kneading a resin mixture containing a foaming component and a resin component in a cylinder to form a molten mixture, and a molding step of extruding the molten mixture through a die,
The foaming component is essentially a thermally expandable microsphere composed of an outer shell made of a thermoplastic resin and an expansion agent encapsulated therein and vaporized by heating,
The maximum temperature of the cylinder is lower than the temperature of the die, and the temperature difference is in the range of 10 to 150 ° C .;
A method for producing a foam molded article.
The foam molded article according to claim 1, wherein the minimum temperature of the cylinder is equal to or higher than the melting temperature of the resin component, and the vapor pressure of the expansion agent is in the range of 0.1 to 5.0 MPa at the maximum temperature of the cylinder. Production method.
3. An arbitrary point A in the cylinder and an arbitrary point B in the extrusion direction from the point A are selected, and TA ≦ TB when the temperatures are TA and TB, respectively. The manufacturing method of the foaming molding of description.
When the inside of the cylinder is divided into three sections of a feed zone, a compression zone, and a metering zone in order from the raw material supply port in the extrusion direction, and the temperatures of the respective sections are C1, C2, and C3, C1 ≦ C2 ≦ C3 The method for producing a foam molded article according to any one of claims 1 to 3, wherein
The method for producing a foamed molded article according to any one of claims 1 to 4, wherein a weight ratio of the foaming component in the resin mixture is in a range of 0.1 to 35% by weight with respect to 100% by weight of the resin component.
The method for producing a foamed molded product according to any one of claims 1 to 5, wherein a weight ratio of the thermally expandable microspheres to the foaming component is in a range of 40 to 100% by weight of the whole foaming component.
A foam molded article obtained by the production method according to any one of claims 1 to 6.
The foam molded article according to claim 7, wherein the average cell diameter is 2 to 500 µm.
The foamed molded product according to claim 7 or 8, wherein the closed cell ratio is 50% or more.
The foam molded article according to any one of claims 7 to 9, wherein the b * value is 20 or less.