JP2002337186A - Method for supplying material to injection molding machine or extrusion machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for realizing a shortened molding cycle, when an extrusion/expansion molding process and an injection/expansion molding process are to be performed by injecting a physical expansion agent into the cylinder of an extrusion machine or an injection molding machine, with a two- stage screw. SOLUTION: This method for supplying a material comprises the steps to heat a thermoplastic resin at a temperature higher than an ambient temperature by 30 deg.C and higher than the melt point of the thermoplastic resin by 50 deg.C, and to supply the heated resin to the injection molding machine or the extrusion machine of such a structure that a two-stage compression screw is housed in the cylinder and the physical expansion agent is supplied halfway through the cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for feeding a material to an extruder or an injection molding machine having a two-stage screw. More specifically, the present invention relates to a method for supplying a material having a two-stage screw and capable of shortening a molding cycle in an extruder or an injection molding machine in which a physical foaming agent is injected from the middle of a cylinder.

[0002]

2. Description of the Related Art In recent years, a method has been proposed in which a supercritical fluid such as nitrogen or carbon dioxide is injected into a cylinder of an extruder or an injection molding machine to perform extrusion foaming and injection foaming. For example, Japanese Patent No. 2625776 may be mentioned.

In a specific proposal, as a method of injecting a supercritical fluid into an injection molding machine to obtain a foamed product, for example, Japanese Patent Application Laid-Open Nos. 11-34129 and 11-3413.
And WO 98/31521, and WO 98/08667 as a method of injecting a supercritical fluid into an extruder.

[0004] The screws used in these proposed extruders and injection molding machines are two-stage screws, in which the molding material is melted in the first full-flight portion, and then a supercritical fluid is injected. It is a mixed structure. Proposals have also been made to improve the mixing of the molten resin and the supercritical fluid by providing pins, irregularities, etc. in the second stage of the screw.

In the case of injection molding, the foam has good contact with the surface of the mold cavity and has a high cooling effect. In addition, since the viscosity of the molten resin impregnated with the supercritical fluid is reduced, the resin temperature and the mold temperature at the time of injection can be lowered, so that the cooling effect is further enhanced. Therefore, at that point, the cooling cycle can be shortened. However, since the material resin is brought into contact with the supercritical fluid after being melted, it is necessary to improve the plasticizing ability of the material resin in order to shorten the molding cycle.

[0006] In the two-stage screw, since the material resin is melted in the first stage, the screw area that can be used for plasticization, that is, the so-called plasticized portion of the screw is shortened.
The plasticization ability of the material resin is limited.

As a result, even if the cooling cycle can be shortened, the plasticizing ability of the raw material resin is inferior to that of a normal single-stage screw. Plasticization for injection is not completed. Forcibly injecting will result in the injection molding of the unmelted molding material, resulting in poor appearance of the injection foam product.

Therefore, even if the cooling time is shortened by the injection molding method using a supercritical fluid, the effect is not sufficiently obtained because the plasticizing time of the material resin is prolonged. .

Also, in the extrusion molding method, the material resin is melted only in the first stage of the two-stage screw as compared with the case of using a normal one-stage screw. Had led to a decline.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for extruding a foamed or injection-foamed mold by injecting a physical foaming agent into a cylinder of an extruder or an injection-molding machine having a two-stage screw. It is to provide a method for realizing a molding cycle. More specifically, when a physical foaming agent is injected into a cylinder of an extruder or an injection molding machine having a two-stage screw to carry out extrusion foaming and injection foaming, the first stage of the two-stage screw exhibits a high plasticizing ability. Is to provide.

[0011]

The present invention relates to an injection molding machine or an extruder having a two-stage compression screw in a cylinder and supplying a physical foaming agent from the middle of the cylinder.
A method for supplying a material by heating a thermoplastic resin to a temperature range from 30 ° C. higher than the ambient temperature to 50 ° C. higher than the melting point of the resin is provided.

[0012] The structure of the two-stage compression screw reduces the volume between the grooves in the cylinder in the injection direction, and compresses the resin and sends the resin in the injection direction to the first-stage portion, and the volume between the subsequent grooves once. The distribution of the length of the first and second stages measured from below the hopper is 0.
The method of supplying the material in the range of 5: 1.5 to 1.8: 0.2 is a preferred embodiment of the present invention.

The second stage of the screw has a shape of a full flight screw, the volume between the grooves of the screw is reduced in the injection direction, and the material is compressed and fed in the injection direction. The method is also a preferred embodiment of the present invention.

The method for supplying the material, wherein the second stage of the screw has at least partly an uneven structure, is also a preferred embodiment of the present invention.

[0015] The method for supplying the material in which the screw is a twin screw is a preferred embodiment of the present invention.

A preferred embodiment of the present invention is a method for supplying the above material, wherein the thermoplastic resin is heated by blowing hot air in a hopper in a temperature range of 30 ° C. higher than room temperature to 100 ° C. higher than the melting point of the resin in a hopper. It is.

[0017] A preferred embodiment of the present invention is a method for supplying the material, wherein the thermoplastic resin is heated in a storage tank or a shelf dryer.

The method for supplying the material, in which the physical blowing agent is supplied to the cylinder in a liquid state or a supercritical state, is a preferred embodiment of the present invention.

The method of supplying the material, in which the physical blowing agent is heated before supplying the physical blowing agent to the cylinder, is a preferred embodiment of the present invention.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The material supply method of the present invention will be described in detail below. The present invention relates to an injection molding machine or an extruder having a two-stage compression screw in a cylinder and supplying a physical foaming agent from the middle of the cylinder. This is a method for supplying a material that is heated and supplied to a temperature range up to 50 ° C. higher than the melting point.

The extruder or injection molding machine of the present invention has a structure in which a physical foaming agent is supplied into a cylinder from a hole in the middle of the cylinder. As the structure for supplying the physical foaming agent, an ordinary cylinder with holes is sufficient, and it is preferable to have a mechanism for stopping the supply when the resin pressure rises above the supply pressure. Such methods include:
A method of constantly measuring the resin pressure in the cylinder and increasing / decreasing the injection pressure of the physical foaming agent, and a method of intermittent injection are possible. Further, a check valve of resin may be attached so that the molten resin does not penetrate into the injection hole.

The screw structure of the injection molding machine or extruder of the present invention is preferably a two-stage compression screw structure. In the preferred structure of the two-stage compression screw, the volume between the grooves in the cylinder was reduced in the injection direction, and the first-stage portion for compressing and sending the resin in the injection direction and the volume between the subsequent grooves were once increased. It consists of the second stage.

The physical foaming agent has a structure that is continuously or intermittently supplied to the screw portion of the second stage at all times or at least temporarily.

In the screw according to the present invention, the length distribution of the first stage measured from below the hopper and the second stage in which the volume between the grooves is temporarily increased (preferably rapidly increased) is from 0.5: 1.5 to 1.5: 1.5.
It is preferably in the range of 1.8: 0.2. The distribution of the lengths of the first and second stages is a preferable range from the viewpoint of increasing the extrusion amount and shortening the plasticization time, and from the viewpoint of good mixing of the physical foaming agent and the molten resin in the second stage. .

In the screw of the present invention, the second stage of the screw has the shape of a full flight screw, reduces the volume between the grooves of the screw in the injection direction, compresses the resin, and sends the resin in the injection direction. Those having a structure are preferred embodiments. The second stage screw may have the shape of a full flight screw and a structure having pins between flights.

The second stage screw may have an uneven structure at least in part. These concavo-convex structures may be pin-shaped, or the concavo-convex structure may be a disk or an elliptical shape perpendicular to the axial direction of the screw. Examples of such a screw include a pineapple mixer structure and a cavity transfer mixer structure. The embodiment of the present invention in which the screw of the present invention is a twin screw is a preferable embodiment because the plasticizing ability of the resin, for example, the shortening of the plasticizing time and the increase of the plasticizing amount are possible.

A static mixer may be installed after the second screw, or a gear pump may be installed.

In the present invention, the thermoplastic resin is heated and supplied in a temperature range from 30 ° C. or more higher than the ambient temperature to a temperature not exceeding 50 ° C. of the melting point of the raw material resin. The term “ambient temperature” as used in the present invention refers to a temperature at a portion 100 cm away from the screw surface of an extruder or an injection molding machine, where no device such as a resin supply unit is present or where the device is not affected by radiant heat. The temperature at the time of supply in the present invention is a temperature in a hopper of an extruder or an injection molding machine. In the present invention, the melting point refers to an endothermic peak temperature measured by a differential scanning calorimeter (DSC) in the case of a crystalline resin, and a change caused by a change in specific heat due to melting in an amorphous resin. Say the tune.

If the temperature of the supply resin is too low, the heating by the heat radiation from the screw does not sufficiently raise the temperature of the material resin and comes into contact with the screw. It must be melted while the material resin is transported between them, and must be completely melted before it reaches the second stage, but it takes a long time to melt, which reduces the amount of extrusion and prolongs the plasticization time. . On the other hand, if the temperature of the supplied resin is too high, the resin melts before reaching the screw surface, causing blocking of resin pellets near the joint between the hopper and the cylinder.

In the present invention, the thermoplastic resin is added at an ambient temperature of 3%.
There is no particular limitation on the method of heating the thermoplastic resin in order to supply the resin at a temperature higher than 0 ° C. and not exceeding the melting point of the resin as a raw material by 50 ° C. or more. It is possible to use the equipment used for the above purpose as it is.

For example, a method in which pellets are put in a heating tank and transported to a hopper of an injection molding machine or an extruder by a hopper loader. Heating with a shelf-type oven / dryer and supplying it to the hopper, heating and circulating hot air inside the hopper, heating the hopper by applying ultrasonic waves to the inside of the hopper, heating screw inside the hopper And a method of heating. In the case of a resin that is easily blocked, it is effective to apply a vibration to the raw material resin to heat and supply while releasing the blocking state, and to force the heated resin pellets into the hopper with a gear mechanism and a push rod.

The physical foaming agent used in the present invention includes:
There is no particular limitation. For example, vapors of low-boiling organic solvents such as methanol, ethanol, propane, butane, and pentane; dichloromethane, chloroform, carbon tetrachloride, freon, and vapors of halogen-based inert solvents such as nitrogen trifluoride;
Inert gases such as carbon dioxide, nitrogen, argon, helium, neon, and astatine. Among these,
Carbon dioxide, nitrogen, and argon are the most excellent because they do not need to be heated to produce steam, are inexpensive, and have very low risk of environmental pollution and fire.

These physical foaming agents may be in any of a gas state, a liquid state and a supercritical state. When injecting into a cylinder of an extruder or an injection molding machine in a liquid state or a supercritical state, the resin temperature is lowered to cause an increase in the viscosity of the resin. The method of heating the physical foaming agent before supplying to the cylinder is effective in the present invention because there is a possibility that the extruding ability and the plasticizing ability may be reduced.

As a molding material that can be used in the present invention, a thermoplastic resin can be preferably mentioned. The thermoplastic resin in the present invention refers to a thermoplastic polymer that can be injection-molded, and any thermoplastic resin that can be injection-molded in a normal unfoamed state can be used without any particular problem. Examples of thermoplastic resins include low density polyethylene,
Linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultrahigh-molecular-weight polyethylene, polyethylene such as cyclic polyethylene, ethylene-styrene copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, ethylene -Ethylene copolymers such as vinyl acetate copolymer, homopolypropylene, ethylene,
Polyolefin resins such as polypropylene, polybutene, polymethylpentene, etc .; random copolymers of α-olefins such as butene, pentene, hexene, octene and propylene; ethylene-propylene block copolymers; polybutylene, polyisobutylene, polybutadiene, natural rubber And rubber elastomers such as thermoplastic polyurethane, isoprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, ethylene-propylene-diene rubber, and chloroprene rubber. In addition, even if it is a crosslinked rubber / elastomer, it is crosslinked to the extent that injection molding is possible, and even if it is a thermosetting resin, it is one that has not been cured by crosslinking or the like. can do.

The thermoplastic resin of the present invention may have improved fluidity by adding wax, polyethylene, polypropylene, mineral oil or the like.

Styrene resins such as polystyrene, AS resin and ABS resin are suitable as materials for obtaining highly foamed molded products. Amorphous resins such as polyvinyl chloride, high nitrile resin, polymethyl acrylate, and polymethyl methacrylate polycarbonate, and engineering plastics can also be used. Examples of these usable thermoplastic resins include polymethylpentene, polyphenylene ether, polyphenylene oxide, polyacetal, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polylactic acid, polyether ketone, polyether sulfone, nylon 6, nylon 11, Nylon 12, Nylon 66, Nylon 6
10, nylon 612, liquid crystal polymer, polyimide, poly-p-phenylene terephthalate, polysulfone, and the like.

A foam of a biodegradable resin obtained by mixing polylactic acid or starch with a polyolefin can be decomposed in a short time after disposal.

The material resin of the present invention may be a blended resin for improving moldability, mechanical properties, and the like. In particular, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-butene rubber, ethylene-octene rubber, rubber such as ethylene-propylene-diene rubber,
Blending with a polyolefin resin such as polyethylene or polypropylene is desirable because the cell diameter when foamed becomes uniform.

Further, recycled resins such as recycled pets, recycled polypropylene and recycled polystyrene can be used without any problem.

The material resin of the present invention may contain, if necessary, additives such as a heat stabilizer, a weathering agent, a lightproofing agent, a flame retardant, an antistatic agent, an antibacterial agent, carbon black, a pigment, talc, mica,
Calcium carbonate, barium magnesium whisker,
A filler such as potassium titanate whisker or glass fiber may be added.

The viscosity of the thermoplastic resin of the material in the present invention is an MFR (melt flow rate) as an index.
The measurement conditions are not constant because the measurement conditions are different for various resins, but there is no particular problem as long as they are sold and used as ordinary extrusion and injection grades.

For example, in the case of polypropylene, an MFR (according to ASTM D-1238: 230
° C, measured under a load of 2.16 Kg) is 0.1 to 10 g / 10
min is preferable, and 2 to 100 g / 10 mi for injection.
n is preferred. Further, if the polypropylene has a wide molecular weight distribution, even if the MFR is about 3 g / 10 min, the M
It exhibits fluidity corresponding to ordinary polypropylene having an FR of about 10 g / 10 min, and can be preferably used.

For the purpose of preventing blocking between resin pellets, talc, calcium carbonate, silicone resin, polyolefin powder, metal soap, etc. may be applied to the pellets to prevent blocking.

In the present invention, the addition of a foam nucleating agent has the effect of making the cell diameter of the foamed product uniform and enhancing the appearance of the product. The physical foaming agent dissolved in the resin tends to be a cell generation nucleus when a microscopically nonuniform portion is generated. As the foam nucleating agent that can be used, a particulate substance, a compound that generates a foam nucleating agent by reaction or decomposition, and the like can be used. As the particulate matter, as an inorganic substance,
Inorganic fillers such as talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, barium sulfate, mica, clay, wollastonite, silica, alumina, iron oxide, titanium oxide, magnesia, carbon black, graphite, etc. .

The average particle size of the inorganic fine particles is 0.5 to
Those having a diameter of 10 μm are preferred, and those having been subjected to a hydrophobic surface treatment to improve the dispersion in the resin are more excellent in the dispersibility. The addition amount is preferably 0.1 to 5% by weight based on the raw material resin. In consideration of contamination of the hopper of the molding machine, adhesion of powder to the product surface, and abrasion of the screw, for example, it is used after processing into a master batch containing 5 to 50% by weight of a resin, wax or rubber as a base material. You can also.

As a compound which generates a foam nucleating agent by reaction or decomposition, a chemical foaming agent can be used. The chemical blowing agent decomposes in the cylinder of the injection molding machine, and the foam residue can be a foam nucleating agent. Examples of the chemical foaming agent include azodicarboxylic acid amide, oxybisbenzenesulfonyl hydrazide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, and paratoluenesulfonyl hydrazide. Also, polycarboxylic acids such as citric acid, oxalic acid, fumaric acid, phthalic acid, malic acid, tartaric acid, cyclohexane 1,2-dicarboxylic acid, camphoric acid, ethylenediaminetetraacetic acid, triethylenetetraminehexaacetic acid, and nitrilic acid; Examples thereof include a mixture of an inorganic carbonate compound such as sodium, sodium aluminum hydrogen carbonate and potassium hydrogen carbonate, and a salt of a polycarboxylic acid such as sodium dihydrogen citrate and potassium oxalate.

For polyolefin, it is preferable to use a combination of a polycarboxylic acid and an inorganic carbonate compound. In particular, a combination of citric acid and sodium hydrogen carbonate has a microcellular effect, that is, an effect of forming a large amount of foam nuclei. , A good foamed product is obtained.

Also, the combined use of citric acid and sodium bicarbonate has a very good nucleating effect. For example, a polypropylene composition containing 10 to 30% by weight of talc can already obtain a sufficient nucleating effect. By further adding a combination of citric acid and sodium hydrogen carbonate, a higher microcellular effect can be obtained.

The addition amount of these chemical blowing agents is preferably 0.01 to 1% by weight based on the raw material resin. If the added amount is too large, the decomposed product may become eyes and contaminate the product. These chemical blowing agents have an average particle size of 1 to 100.
It can be processed into particles of μm and dusted on the raw material resin, but can be dusted on the material during injection molding. Further, it may be blended with auxiliaries such as urea, zinc hydroxide, zinc oxide, lead oxide, zinc stearate and calcium stearate. Further, in consideration of the contamination of the hopper of the molding machine and the adhesion of powder to the product surface, it can be processed and used as a master batch using a resin as a base material.

Further, after the chemical foaming agent is added to the resin of the material, the chemical foaming agent may be decomposed by pelletizing. The chemical foaming agent may be decomposed in advance, and the residue may be added to the resin. You may. The addition amount of the chemical foaming agent residue is preferably 0.01 to 1% by weight in terms of an undecomposed product.

As an injection molding method to which the present invention can be applied, a so-called short-circuiting method in which a foamed product is obtained by injecting an amount smaller than the cavity volume into a mold cavity and abruptly vaporizing the injected physical foaming agent. Molding method: a so-called counter pressure method in which the inside of the cavity is maintained at a pressure at which the physical foaming agent does not vaporize at the time of injection, and after the resin of the material is filled, the pressure in the cavity is rapidly reduced to cause foaming. Can be. In this way, silver, flash, etc. can be reduced or completely eliminated. It is also possible to incorporate an in-mold foaming mechanism such as a core-back method for increasing the volume of the cavity after completely filling the cavity in the mold.

In particular, in order to reduce or completely eliminate the appearance of the product which is a drawback of the core back method, for example, flash, silver, etc., the volume in the cavity is made smaller than the intended filling amount, and the injection is carried out. After filling the resin while opening the mold, a method of expanding the internal volume of the cavity at an appropriate time is recommended.

As a method of expanding, a method of moving a metal plate constituting a wall of the cavity (core back method) is suitable, and a method of moving the metal plate to the movable platen side of the mold mounting plate is the simplest. By filling the cavity with resin at once and forming a skin layer on the molded product surface,
A hard product shape can be obtained, and even if there is a part where the foaming state is uneven inside the product, or even if a bubble having a large cell diameter is generated, the appearance becomes inconspicuous. Therefore, it is not necessary to maintain the inside of the cavity at a high pressure unlike the counter pressure method, and the molding can be performed under the atmospheric pressure.

Thus, for example, US Pat. No. 4,473,665,
As in U.S. Pat. No. 5,334,536, WO 98/31521, there is no need to apply pressure so that the physical blowing agent used in the cavity does not vaporize. Therefore, it is not necessary to provide a rubber packing for maintaining pressure in the mold, and it is not necessary to seal the gap between the molds. Furthermore, if the mold is assembled from a plurality of metal plates, the air present in the cavity at the time of filling the resin freely escapes from the gap between the metal plates when the resin spreads into the cavity, and the air pools in the mold. It does not occur, and there is no fear of poor appearance due to air accumulation.

As the mold clamping mechanism of the injection molding machine used in the present invention, a direct pressure type, an electric type or the like is preferable because the speed at the time of core back can be precisely controlled. In addition, if it is a mold clamping mechanism such as a toggle type that core back is difficult,
After releasing the mold clamping force, it is also possible to make the core back by a mechanism such as a spring. Even when the core back is in the direction other than the movable platen direction, the core back can be performed by moving the metal plate on the side surface of the cavity using an appropriate oil pressure, electric device, spring, or the like. For example, when a gate is provided at the bottom with a box shape and core back is performed in the direction of the bottom, the side surface hardly foams.

In the case of such a product, when the core is backed in a direction perpendicular to the bottom surface, the remaining side surfaces 4 are almost simultaneously.
Foaming is possible in all five directions by core backing with the directions. For the core back in a direction other than the movable platen, a T-shaped or Y-shaped hydraulic cylinder can be used for the mold clamping cylinder. Even when the die metal plate is cored back in a complicated manner, mechanical design can be easily performed because counter pressure is not performed.

In the case of a box-like object such as a container,
It is also possible to form an assembly box after molding separately from the bottom and side surfaces with the core back only on the movable platen side, and the containers etc. manufactured in such a shape can be disassembled only after the transportation of luggage is completed Can be recovered at Also,
If it is a box shape, it can be injected into a shape as shown in a developed view, core-back molded on the movable platen side, and after taking out the product, it can be assembled and used when necessary.

When such a folded portion occurs,
While the resin does not completely solidify the linear part to be folded,
Using a mold ejection mechanism, crush the foamed part,
By adding the weaving habit, the assembling work is facilitated, and the strength of the bent portion is increased, so that a box that can withstand repeated use can be formed.

Further, a mold of a dough-shaped container is produced and attached, and after injecting while foaming with the mold opened,
After closing the mold and spreading the foam resin over the entire cavity,
By core-backing, the foamed resin turns around the wall of the container where the expansion ratio does not increase, and a donburi container with a foamed side surface is obtained. Since it is lightweight, it is most suitable for a container of an instant food.

In order to improve the molding cycle of injection molding, the temperature of the mold may be controlled by changing the temperature of water and oil for controlling the temperature of the mold so that the temperature is rapidly cooled after injection into the mold. It is also possible to mount an embedded heater and a cooling pipe in a mold and to inject or circulate cooling water or oil into the cooling pipe after injection to improve the cooling rate.

[0061]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Examples 1 to 3) Inner diameter 50 mm, L / D3
A single-screw extruder No. 7 (from below the hopper to the tip of the screw) was equipped with a two-stage full-flight screw having an outer diameter of 49.8 mm. The ratio of the length of the first stage to the second stage is 0.6: 0.4, and the depth of the first stage is evenly reduced from 6.3 mm below the hopper to 3.1 mm at the end of the first stage The second stage has a structure in which the groove depth at the connection portion with the first stage is 8 mm, and the groove depth is uniformly reduced to 2.5 mm at the tip end.

A physical foaming agent injection hole having an inner diameter of 2 mm was provided at a position 1D closer to the second stage than the connection between the first and second stages of the extruder, and a check valve was further provided outside the hole. From siphon liquefied carbon dioxide, by decipro pump
Liquefied carbon dioxide was injected into the extruder. The injection amount was adjusted to 3 to 5% using a flow meter. The injection pressure was 20 MPa. Under the hopper of the extruder, cooling water having a water temperature of 30 ° C. is passed through to cool the extruder, and the set temperature of the cylinder is adjusted to 170, 180, 190 (carbon dioxide injection section), 20 toward the extruder tip.
Set to 0,210 ° C, the temperature of the adapter and die should be 1
80 and 180 ° C were set.

Polypropylene (Grand Polymer Co., Ltd., Grand Polypro ^™ E101, MFR0.
(5 g / 10 min, melting point: 162 ° C.). The polypropylene material was heated at 90 ° C. for 2 hours using a shelf dryer before feeding. A thermocouple thermometer was installed at the center of the hopper, and the temperature inside the hopper was constantly measured. The temperature in the hopper during extrusion foaming was 50 ° C, and the ambient temperature of the extruder was 15 ° C. While changing the number of rotations of the screw, the extrusion amount, the carbon dioxide injection amount, and the expansion ratio were measured. Table 1 shows the results.

(Comparative Examples 1 to 3) The screw rotation speed, extrusion rate, carbon dioxide injection rate, and expansion ratio were measured in the same manner as in Example 1 except that the polypropylene material was not heated by a shelf dryer. Table 1 shows the results. The resin temperature in the hopper was 20 ° C., it took time to melt the material, the screw rotation speed could not be increased as compared with Examples 1 to 3, and the extrusion amount was low even at the same rotation speed.

[0066]

[Table 1]

(Examples 4 to 6) As an injection molding machine, Toshiba Machine IS-450GS-27A (mold clamping force 450 tons, direct pressure mold clamping system), L / D 27, screw outer diameter 6
9.8mm, the first stage compression part is 14D in L / D (9D from the bottom of the hopper is a flat part and the groove depth is 7.3mm, and in the following 5D, the groove depth is even from 7.3mm to 3.1mm) 13D (7D is a flat portion with a groove depth of 11 mm, and the subsequent 6D has a groove depth of 11D).
(equally reduced from 5 mm to 5 mm). The distance between the screw grooves was constant.
A physical foaming agent injection hole having an inner diameter of 2 mm was provided in a cylinder portion corresponding to the second-stage compression portion 2D portion when it advanced most in the injection direction, and a check valve was further provided outside the hole. A shut-off nozzle mechanism is provided at the tip of the cylinder. A mechanism capable of injecting into the cylinder through a pressure reducing valve and a check valve attached to the cylinder was provided using carbon dioxide provided by a commercially available cylinder as a physical foaming agent.

The pressure of the carbon dioxide cylinder is 7.2 MPa.
And the supply pressure to the injection molding machine by the pressure reducing valve is 3M
Pa was maintained. Carbon dioxide injection amount is 1% by weight based on resin
Met. The injection mold used had a cavity (product thickness) whose cavity (product thickness) could be finely adjusted by the hydraulic pressure of the molding machine, and had a product dimension of 95 mm × 340 mm (injected from the center of the product by a direct gate). This mold was attached to a molding machine, and the mold temperature, 50 ° C., mold cooling time 60 seconds, and cylinder set temperature were 180, 200, and 22 from the bottom of the hopper.
0, 230 and 230 ° C were set. As a molding material, a propylene block copolymer (Grand Polymer Co., Ltd., Grand Polypro ^™ J704ZA, MFR 5 g / 10 m
in melting point 162 ° C). The material was heated using a hopper dryer. A thermocouple type temperature system was installed at the center of the hopper, and the temperature inside the hopper was constantly measured.
The resin temperature in the hopper was 70 ° C, and the ambient temperature of the injection molding machine was 12 ° C. The period from the end of injection to the start of core back is 1 second, and the core back speed is 1 mm /
At the time of injection, the gap in the cavity of the mold at the time of injection was set to 2 mm, and after injection, the core was backed and the cavity interval was set to 4 mm for foaming. The plasticization time was measured after the injection was completed and the plasticizing was completed by the molding machine. Table 2 shows the plasticization time, the amount of carbon dioxide, and the expansion ratio.

(Comparative Examples 4 to 6) The same procedure as in Examples 4 to 6 was carried out except that the material polypropylene was not used with a hopper drier.
Injection molding was performed in the same manner as in No. 6. The resin temperature in the hopper was 22 ° C., and the plasticization time was longer than in Examples 4 to 6. Table 2 shows the plasticization time, the amount of carbon dioxide, and the expansion ratio.

[0070]

[Table 2]

(Examples 7 to 9) Nitrogen was used as a physical foaming agent, the pressure was increased using a pressurizing horn, and the pressure-resistant container having a volume of 200 ml was injected into the same injection molding machine as in Example 1 as a buffer tank. The pressure in the buffer tank varied between 20 and 50 MPa during the injection cycle. The molding material and the heating temperature were the same as in Examples 4 to 6, and the molding conditions were set similarly. The temperature around the molding machine is 18 ° C,
The temperature of the material in the hopper was 75 ° C. Table 3 shows the plasticization time, the amount of carbon dioxide, and the expansion ratio.

(Comparative Examples 7 to 9) The same procedure as in Examples 7 to 9 was carried out except that the polypropylene as the material was not used with a hopper drier.
Injection molding was performed in the same manner as in No. 9. The resin temperature in the hopper was 26 ° C., and the plasticization time was longer than in Examples 7 to 9. Table 3 shows the plasticization time, the amount of carbon dioxide, and the expansion ratio.

[0073]

[Table 3]

[0074]

According to the present invention, in a method of supplying and injecting a physical foaming agent into a cylinder of an extruder or an injection molding machine, since the material is heated and supplied, the time required for plasticization can be shortened. According to the present invention, since the time required for plasticization can be shortened, there is no need to lengthen the cylinder unnecessarily.For example, the current extruder, the cylinder of the injection molding machine is kept as it is, and only the screw is remodeled, and the physical Foaming is possible, and excessive investment can be avoided. Further, according to the present invention, since the extrusion amount can be increased and the molding cycle can be shortened, the production amount per unit time can be increased.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) B29C 47/56 B29C 47/56 47/80 47/80 // B29K 105: 04 B29K 105: 04 F-term (Reference) 4F206 AA11 AB02 AG20 AK01 AR067 JA07 JD01 JE06 JF04 JF12 JL02 JQ17 JQ22 4F207 AA11 AB02 AG20 AK01 AR06 KA01 KA11 KE06 KF04 KK13 KK23 KK28 KK34 KL04 KL23

Claims (15)

[Claims] 1. An injection molding machine or an extruder having a two-stage compression screw in a cylinder and supplying a physical foaming agent from the middle of the cylinder, feeds the thermoplastic resin from a temperature 30 ° C. higher than the ambient temperature to the resin. A method for supplying a material that is heated and supplied to a temperature range up to 50 ° C. higher than the melting point. 2. The structure of the two-stage compression screw reduces the volume between the grooves in the injection direction, and increases the first-stage portion for compressing and feeding the resin in the injection direction and the volume between the subsequent grooves once. It consists of a second stage, and the length distribution of the first stage and the second stage measured from below the hopper is 0.5: 1.5 to 1.8: 0.
2. The method according to claim 1, wherein the material is in the range of 2. 3. The method according to claim 1, wherein the second stage of the screw has a shape of a full flight screw, has a structure in which the volume between the grooves of the screw is reduced in the injection direction, and the resin is compressed and sent in the injection direction. The method for supplying a material according to claim 1 or 2, wherein the material is supplied. 4. The method according to claim 3, wherein the second stage screw has a shape of a full flight screw and has a pin between flights. 5. The method according to claim 1, wherein at least a part of the second screw has an uneven structure. 6. The method according to claim 5, wherein the second screw has a pineapple mixer structure. 7. The second stage screw has a cavity transfer mixer structure.
The method for supplying the material according to the above. 8. The method according to claim 5, wherein the uneven structure of the second screw is pin-shaped. 9. The method according to claim 5, wherein the concavo-convex structure of the second-stage screw has a disk or elliptical shape perpendicular to the axial direction of the screw. 10. The method according to claim 1, wherein the screw is a twin screw. 11. The method according to claim 1, wherein said thermoplastic resin is heated in a hopper by blowing hot air in a temperature range from 30 ° C. higher than room temperature to 100 ° C. higher than the melting point of said resin. 11. The method for supplying a material according to any one of items 10 to 10. 12. The method according to claim 1, wherein the thermoplastic resin is heated in a storage tank or a shelf dryer. 13. The method according to claim 1, wherein the physical blowing agent is supplied to the cylinder in a liquid state or a supercritical state.
Item 13. The method for supplying a material according to any one of Items 12 to 12. 14. The method according to claim 13, wherein the physical foaming agent contains at least one selected from nitrogen, argon, and carbon dioxide. 15. The method according to claim 1, wherein heating is performed before the physical blowing agent is supplied to the cylinder.