JP3866973B2 - Method for producing styrene resin foam - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing a styrene resin foam. In particular, the present invention relates to a method for producing a foam having good dimensional stability, which is uniformly foamed at a high magnification and has fine bubbles.
[0002]
[Prior art]
Styrenic resins can be foamed using various foaming agents, and the resulting foam is relatively tough and has physical properties suitable for general use, so it is widely used in various fields. ing.
[0003]
An extrusion foaming method is widely used to make a foam made of a styrene resin. The extrusion foaming method is a method in which a resin is put into an extruder, the resin is melted in the extruder to create a resin melt containing a foaming agent, and this is extruded from the extruder and simultaneously foamed to obtain a foam. It is.
[0004]
In order to extrude and foam a styrene-based resin, various types of foaming agents can be used. The foaming agents are roughly classified into the following three types. The first is a solid compound that decomposes and generates gas when heated to a temperature above the softening point of the resin, such as azodicarbonamide, dihydrosopentamethylenetetramine, sodium bicarbonate, and the like. . The second is a liquid that is vaporized when it is included in a resin under pressure and extruded into the atmosphere. Examples include propane, butane, benzene, methyl chloride, trichlorotrifluoroethane, acetone, ether, and the like. . The third is an inert gas dissolved in the resin under pressure, and examples thereof include carbon dioxide and nitrogen.
[0005]
Each of these blowing agents has advantages and disadvantages. That is, the first decomposable solid compound has an advantage that the amount added to the resin can be easily adjusted, but the magnification that can be foamed is low, and the residue after decomposition remains in the resin. It has the disadvantage of contaminating the foam. The second vaporizable liquid has the advantage of being easily impregnated into the resin and relatively easy to foam. However, the foaming agent has an adverse effect on the environment, or the foaming agent remains in the resin and gradually evaporates. Therefore, the third inert gas has the disadvantage of deteriorating the dimensional stability of the foam, the third inert gas has the advantage of not polluting the environment and giving a foam with good dimensional stability However, it has a drawback that the expansion ratio is low.
[0006]
Moreover, a foaming agent cooperates with the bubble regulator used together, and each specific bubble state appears. That is, the foaming agent and the air bubble adjusting agent change the distribution and size of the air bubbles generated in the foam depending on what is specifically used. For example, depending on the foaming agent, the bubble distribution may be uniform or non-uniform, the bubble size may be coarse or small, and the bubbles may be independent or open. It may be sex. Such a bubble state embodied by the foaming agent is difficult to predict and cannot be understood unless it is experimentally observed.
[0007]
This inventor does not pollute the environment because ether is familiar with the styrenic resin among the foaming agents belonging to the second vaporizable liquid and is composed of three elements of carbon, hydrogen and oxygen. In that respect, it was noted that it was excellent as a foaming agent. As a result of various experiments, it was found that dimethyl ether, among ethers, immediately evaporates from the styrenic resin after foaming, thus giving a foam with good dimensional stability.
[0008]
Examining the prior art, JP-A-60-145835 describes a method for obtaining a laminate by performing extrusion foaming by adding ether to a styrene resin as a foaming agent and adding talc as a foam regulator. Yes. JP 7-507087 uses a styrene resin, specifically, a styrene resin having a melt flow index of 4.5, and is added with dicumyl and talc as bubble size control agents, and is extruded and foamed. To obtain a foam with high compression resistance.
[0009]
However, depending on the methods taught in these publications, it is difficult to obtain a styrenic resin foam that is uniformly foamed with fine bubbles. That is, in JP-A-60-145835, a foam having coarse bubbles having an average cell diameter of 0.5 mm or more is obtained, as described in page 10, lower left column, lines 10-12. . In addition, Japanese Patent Publication No. 7-507087 does not describe what type of cellular foam is obtained. Therefore, the present inventor tried to make a follow-up test. However, in the embodiment of this publication, a dioctyl-unknown bubble size control agent is used, so that the test cannot be made. Therefore, it cannot be said that this publication teaches a method for obtaining a foam that is foamed uniformly and finely.
[0010]
Since dimethyl ether has a boiling point of −24.9 ° C., it is a gas under normal temperature and normal pressure, but it is liquefied immediately when a slight pressure is applied, and is usually handled as a liquid. Since dimethyl ether has a low boiling point compared to butane (boiling point -0.5 ° C) generally used as a blowing agent, it has a strong foaming force, and therefore it is difficult to control the foaming of the resin. Actually, Japanese Patent Application Laid-Open No. 11-158315 describes that an ether alone or an excessive ratio of ether is not preferable as a foaming agent for extrusion foaming of a styrene resin.
[0011]
[Problems to be solved by the invention]
This inventor tried to establish a method for uniformly and finely foaming a styrene-based resin at a high expansion ratio by using dimethyl ether as a foaming agent when extruding and foaming the styrene-based resin.
[0012]
[Means for solving problems]
This inventor uses a styrene-based resin having a relatively low degree of polymerization when dimethyl ether is used as a foaming agent for extrusion foaming of a styrene-based resin, and a fine powder of polytetrafluoroethylene resin as a bubble regulator. It has been found that the use of can make the styrenic resin foam in a uniform and fine bubble state. The present invention has been completed based on such knowledge.
[0013]
Here, the styrene resin having a relatively low degree of polymerization refers to a resin having a melt mass flow rate value in the range of 4.6 to 10 when the melt mass flow rate is measured according to the method defined by JIS K 7210. ing. The uniform fine bubble state refers to a state in which all the bubbles are 0.5 mm or less, and all the bubbles are uniform in size.
[0014]
In the present invention, a styrene resin having a melt mass flow rate measured in accordance with a method defined by JIS K 7210 within a range of 4.6 to 10 is put into an extruder together with a fine powder of polytetrafluoroethylene resin to melt the resin. Then, dimethyl ether is press-fitted into this, and after kneading, this is extruded from an extruder and foamed to provide a method for producing a styrenic resin foam.
[0015]
In the present invention, the reason why the styrene resin having a melt mass flow rate (hereinafter referred to as MFR) of 4.6 to 10 is selected is based on the experimental fact described below. That is, if the MFR of the styrenic resin is lower than 4.6, the melt viscosity of the styrenic resin becomes too high and the expansion ratio cannot be increased, and the extruded foam extends along the extrusion direction. This is because a good foam cannot be obtained due to streaking. In addition, if the MFR of the styrene resin is higher than 10, the melted styrene resin does not have viscoelasticity suitable for the foam, and thus cannot be foamed at a high expansion ratio. This is because a foam having a good appearance cannot be obtained.
[0016]
The selection and use of a styrene resin having a relatively low molecular weight as described above in the present invention has not been widely practiced by extrusion foaming until now. This is because, until now, it has been attempted to obtain a foam having high mechanical strength. This is because in order to obtain a foam having high mechanical strength, a styrene resin having a relatively high molecular weight must be used. Therefore, the selection of a relatively low molecular weight styrenic resin having an MFR of 4.6 to 10 in the present invention departs from the prior art.
[0017]
The styrenic resin used in the present invention must have a MFR value in the range of 4.6 to 10, preferably in the range of 4.8 to 9.5, More preferably, it is in the range of 5.0 to 9.0.
[0018]
The styrenic resin that can be used in the present invention contains a homopolymer and a copolymer of styrene. As the copolymer, a copolymer of styrene and methylstyrene, chlorostyrene, methyl methacrylate, butadiene, or acrylonitrile can be used. In the copolymer, styrene accounts for a majority amount.
[0019]
In the present invention, a polytetrafluoroethylene resin is used as a cell regulator when the styrene resin is extruded and foamed. Polytetrafluoroethylene resin is used as a fine powder. The particle diameter is preferably 1 to 50 μm, more preferably 2 to 40 μm, and particularly preferably 3 to 30 μm in terms of a 50% by weight average particle diameter by the light transmission method. The polytetrafluoroethylene resin preferably has a specific melt viscosity. For example, when polytetrafluoroethylene resin is melted by heating to 340 ° C. and extruded from a hole having an inner diameter of 2.1 mm and a length of 80 mm under a pressure of 20 kg / cm ² , 1. It is preferable to use one having a viscosity such that 0 g or more flows out.
[0020]
A finely powdered polytetrafluoroethylene resin having the above-described viscosity is commercially available. For example, it is sold as Aflon L150J, Aflon L169J, Aflon L170J, Aflon L172J, Aflon L173J, etc. from Asahi Glass Co., and as TLP10F-1, MP1100, MP1300, etc. from Mitsui / DuPont Fluorochemicals. In the present invention, these commercially available products can be used as they are.
[0021]
The amount of polytetrafluoroethylene resin added to the styrenic resin varies depending on the composition of the styrenic resin, the magnification to be foamed, the extruder used, and the mold attached to the tip of the extruder. Generally speaking, the polytetrafluoroethylene resin added to 100 parts by weight of the styrenic resin is suitably 0.05 to 2 parts by weight, and of these, 0.1 to 1.5 parts by weight. It is preferable to use 0.15 to 1.0 parts by weight.
[0022]
In the present invention, the polytetrafluoroethylene resin makes the bubbles generated in the styrene resin uniform and fine. In addition, the polytetrafluoroethylene resin is superior in foaming efficiency to styrene-based resins compared to other cell regulators. For this reason, when a polytetrafluoroethylene resin is used to obtain a foam having the same expansion ratio, it is sufficient to use a small amount of a foaming agent as compared with the use of other bubble regulators. . Further, the polytetrafluoroethylene resin can suppress the plastic effect when a foaming agent having a high plastic effect such as ether is used. In particular, when the polytetrafluoroethylene resin having the above-mentioned flow characteristics is used, the polytetrafluoroethylene resin has a property of being very uniformly dispersed in the melted styrene resin, and thus works more effectively as a bubble regulator.
[0023]
In the present invention, any of a single-screw extruder and a multi-screw extruder such as a twin-screw extruder can be used as the extruder. In addition, two or three extruders can be combined and used as a multistage extruder. In the multistage extruder, the foaming agent is press-fitted in the vicinity of the tip of the first stage extruder. The extruder must be capable of melting a styrene resin and kneading the polytetrafluoroethylene resin well therewith.
[0024]
In this invention, dimethyl ether is injected into a mixture of a styrene resin and a polytetrafluoroethylene resin in an extruder. The weight of the dimethyl ether to be injected varies depending on the expansion ratio of the foam to be obtained, but is usually in the range of 0.5 to 15 parts by weight with respect to 100 parts by weight of the styrene resin. Of these, the amount is preferably 1 to 10 parts by weight, more preferably 1.5 to 8 parts by weight.
[0025]
In this invention, not only dimethyl ether but also other blowing agents can be used in combination as the blowing agent. Other blowing agents include saturated aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane and hexane, aromatic hydrocarbons such as benzene, xylene and toluene, An inert gas such as carbon dioxide or nitrogen can be used. These other foaming agents need to be contained in a smaller amount than dimethyl ether and do not deteriorate the quality of the foam.
[0026]
In this invention, when dimethyl ether is injected as a blowing agent into a styrene resin melted in an extruder, it is preferable to keep the melted resin at or above the critical temperature and critical pressure of dimethyl ether. The critical temperature and pressure of dimethyl ether are 126.9 ° C. and 5.27 MPa, respectively. Therefore, the molten styrene resin in the extruder is preferably 127 ° C. or higher and 5.3 MPa or higher.
[0027]
Among them, a styrenic system having a temperature higher than 127 ° C. by 5 ° C. to 25 ° C., that is, a temperature of 132 ° C. to 152 ° C., and a pressure higher than 5.3 MPa by 1 MPa, that is, a pressure of 6.3 MPa or more. It is preferable to press-fit dimethyl ether into the molten resin. Under such temperature and pressure, dimethyl ether is placed under a critical temperature and a temperature and pressure higher than the critical pressure, so that it is uniformly dispersed in the styrenic resin. Therefore, it is possible to obtain a foam that is uniformly foamed at a high magnification.
[0028]
The temperature of the resin at the tip of the extruder before the molten polystyrene resin is introduced into the mold is 131.9 ° C. to 151.9 ° C., and the resin at the tip of the extruder before being introduced into the mold By setting the pressure at 6.3 MPa or more, the foaming agent in the molten resin can be maintained in a supercritical state even in the mold, and thus extrusion foaming can be stabilized. As a result, it is possible to stably produce a foam having uniform bubbles and a high expansion ratio.
[0029]
The temperature range of the preferred resin is 132.9 ° C to 146.9 ° C, more preferably 133.9 ° C to 141.9 ° C. On the other hand, the pressure of a preferable resin is 7.27 MPa or more, and particularly preferably 8.27 MPa or more.
[0030]
Although depending on the mold temperature and flow path, if the resin temperature is lower than 131.9 ° C., the dimethyl ether in the molten resin cannot be maintained in a supercritical state up to the tip of the mold, and foaming becomes unstable. On the other hand, when the temperature of the resin is higher than 151.9 ° C., the melt tension of the polystyrene-based resin is lowered, and internal foaming occurs in the mold, resulting in a foam having a poor appearance. When the resin pressure is lower than 6.3 MPa, dimethyl ether cannot be maintained in a supercritical state, and internal foaming occurs in the mold, resulting in a foam having a poor appearance.
[0031]
Moreover, when a styrene resin is extruded from an extruder under the above-mentioned temperature and pressure, a foam foamed at a high magnification can be stably obtained.
[0032]
In the present invention, extrusion foaming is performed by attaching a die having an appropriate opening to the tip of the extruder in accordance with the cross-sectional shape of the foam to be obtained. The mold can be a circular mold, a flat mold, a modified mold, a nozzle mold, a T-die, or the like. In order to obtain a plate-like foam, a circular mold is used, and the resin is tubularly extruded from the circular mold into the atmosphere. The resulting tubular foam is flattened between a pair of rolls, and the inner surface is melted. It is preferable to make it a board.
[0033]
In the present invention, an appropriate antistatic agent, pigment, ultraviolet ray inhibitor, heat deterioration inhibitor, flame retardant and the like can be added depending on the use of the foam.
[0034]
【The invention's effect】
According to the method of the present invention, a styrene resin having an MFR of 4.6 to 10 is selected and used, and a fine powder of a commercially available polytetrafluoroethylene resin is added thereto, and this is put into an extruder. Then, by melting the resin, press-fitting dimethyl ether as a foaming agent into the resin, kneading and extruding, it is possible to obtain a foam with good dimensional stability that is easily foamed uniformly and finely and at a high magnification. In addition, this method is suitable for current requirements because it does not generate anything that pollutes the environment. The present invention provides such benefits.
[0035]
Examples and comparative examples are given below to clarify the superiority of the method of the present invention.
[0036]
In Examples and Comparative Examples, the average cell diameter, residual gas amount and surface hardness in the obtained foams were measured. The measurement method is as follows.
[0037]
The average cell diameter was measured according to ASTM D-2842-69. Microscopic photography at that time was taken with a scanning electron microscope S-3000N (manufactured by Hitachi, Ltd.), and the average bubble diameter was determined by measuring the average chord length from the number of bubbles on a straight line (60 mm) of the cut surface. Was calculated by the following equation.
Average chord length = 60 / (number of bubbles × multiple of photographing), bubble diameter = average chord length / 0.616
The average bubble diameter was calculated from the arithmetic average of the obtained three bubble diameters (MD, TD, VD). When the average bubble diameter was less than 0.5 mm, the foam was a fine bubble.
[0038]
Residual gas amount About 30 mg of polystyrene resin foam was set in a heating furnace, and the residual gas amount was measured from the chromatographic curve obtained by the measurement.
Measuring apparatus: gas chromatograph GC-14B, pyrolysis furnace PYR-1A (manufactured by Shimadzu Corporation)
Column: Polapack Q (80/100) Ф 3mm x 1.5m
Detector: TCD
Measurement conditions: column temperature (100 ° C.), injection temperature (120 ° C.), detection temperature (120 ° C.), carrier gas (helium), helium flow rate (1 ml / min), furnace temperature (150 ° C.)
[0039]
Surface hardness The surface hardness was measured with an Asker rubber / plastic hardness meter CS type (manufactured by Kobunshi Keiki Co., Ltd.) (spring type hardness tester). The larger the measured value, the harder the surface.
[0040]
[Example 1]
Tandem type extruder consisting of 100 parts by weight of MFR 5.0 polystyrene resin and 0.5 parts by weight of polytetrafluoroethylene resin (average particle size 13 μm) consisting of a single screw extruder having a diameter of 50 mm and a single screw extruder having a diameter of 65 mm Supplied to the hopper. Further, dimethyl ether was injected at a rate of 5% by weight from the middle of the first stage extruder. At that time, the temperature of the dimethyl ether injection portion of the first stage extruder was 210 ° C., and the injection pressure was 15 MPa. The resin temperature at the tip of the first stage extruder was 205 ° C., and the resin pressure was 14 MPa or more. After the polytetrafluoroethylene resin and dimethyl ether are melted and mixed in the first and second stage extruders, the foam is removed from the mold (circular mold having a diameter of 70 mm) attached to the tip of the second stage extruder. While being extruded into a tubular shape, compressed air (gauge pressure 0.1 MPa) is sprayed onto the surface of the extruded tubular foam, and the deflection plate is narrowed as it moves away from the mold (maximum opening interval 300 mm, minimum opening interval 30 mm) The polystyrene resin plate-like foam was produced by adjusting the shape into a plate shape and passing between rolls while fusing the inner surface of the tubular foam. The resin pressure at the tip of the extruder at that time was 12 MPa, and the resin temperature was 138 ° C.
The obtained plate-like foam has uniform bubbles and a beautiful appearance with a thickness of 5 mm (minimum thickness 4.75 mm, maximum thickness 5.25 mm), an expansion ratio of 20 times, an average cell diameter of 0.40 mm, The fused surface was strongly fused. The plate-like foam had a residual dimethyl ether content of 0.74% by weight after 2 weeks and a surface hardness of 72, which was excellent in mechanical strength.
[0041]
[Example 2]
A polystyrene resin plate-like foam was produced in the same manner as in Example 1 except that the MFR of the polystyrene resin was 7.0 and the resin temperature was 134 ° C.
The obtained plate-like foam has uniform bubbles and a beautiful appearance with a thickness of 5 mm (minimum thickness 4.7 mm, maximum thickness 5.3 mm), an expansion ratio of 20 times, an average cell diameter of 0.37 mm, The fused surface was strongly fused. The plate-like foam had a residual dimethyl ether content of 0.81% by weight after 2 weeks and a surface hardness of 73, which was excellent in mechanical strength.
[0042]
[Comparative Example 1]
Except for using butane as the foaming agent, an attempt was made to produce a plate-like foam in the same manner as in Example 1, but the resin pressure at the tip of the second-stage extruder increased to 18 MPa, and fracture occurred in the mold. A good foam was not obtained.
[0043]
[Comparative Example 2]
Plate-like foaming is performed in the same manner as in Example 1 except that butane is used as a foaming agent, the cylinder temperature of the second stage extruder is increased, the resin temperature at the tip of the second stage extruder is 145 ° C., and the resin pressure is 12 MPa. Although an attempt was made to produce a body, stripes parallel to the flow direction on the surface of the foam occurred, the thickness in the width direction varied greatly, and only a plate-like foam having a poor appearance was obtained.
The obtained plate-like foam had a thickness of 5 mm (minimum thickness 4.5 mm, maximum thickness 5.5 mm) and a foaming ratio of 16 times, but streaks parallel to the flow direction of the foam surface occurred, and the average The bubble diameter was 0.52 mm and the bubble was coarse.
The amount of butane remaining after 2 weeks of the obtained foam was 2.5% by weight and the surface hardness was 66.
[0044]
[Comparative Example 3]
Except for using a polystyrene resin having an MFR of 3.7, an attempt was made to produce a plate-like foam in the same manner as in Example 1, but the resin pressure at the tip of the second-stage extruder rose to 17 MPa.
The obtained foam had a thickness of 5.0 mm (minimum thickness 4.5 mm, maximum thickness 5.5 mm) and a foaming ratio of 16 times, which was 20% lower than that of Example 1. Further, the obtained foam had streaks parallel to the flow direction, and the thickness in the width direction had a large variation.
[0045]
[Comparative Example 4]
An attempt was made to produce a plate-like foam in the same manner as in Example 1 except that a polystyrene resin having an MFR of 11.8 was used (however, the resin temperature at the tip of the second stage extruder was 138 ° C. and the resin pressure) However, streaks parallel to the flow direction occurred on the surface of the foam, and the thickness in the width direction varied greatly, and only a foam with a poor appearance was obtained. Further, the foaming ratio of the obtained foam was as low as 10 times.

Claims (4)

  A fine powder of polytetrafluoroethylene resin is added to a styrene resin having a melt mass flow rate measured by the method specified by JIS K 7210 within the range of 4.6 to 10, and this is put into an extruder. A method for producing a styrene-based resin foam, which comprises melting, press-fitting dimethyl ether as a foaming agent into the melt, kneading, and then extruding the foam from an extruder to cause foaming.   A fine powder of polytetrafluoroethylene resin is added to a styrene resin having a melt mass flow rate measured by the method specified by JIS K 7210 in the range of 4.6 to 10, and this is put into an extruder. The styrenic resin is melted at a temperature of 127 ° C. or higher and a pressure of 5.3 MPa or higher, dimethyl ether is injected as a foaming agent therein, kneaded, and then extruded from an extruder to be foamed. A method for producing a styrene resin foam. The method for producing a styrene resin foam according to claim 1 or 2, wherein 0.05 to 2 parts by weight of polytetrafluoroethylene resin is added to 100 parts by weight of the styrene resin.   The method for producing a styrene resin foam according to any one of claims 1 to 3, wherein dimethyl ether is press-fitted in an amount of 0.5 to 15 parts by weight with respect to 100 parts by weight of the styrene resin.