JP4263539B2 - Extrusion method of thermoplastic resin, extruded product - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for extrusion molding of a thermoplastic resin, and more particularly to an extrusion molding method for obtaining a foamed extruded product by adding a foaming agent to a thermoplastic resin.
[0002]
[Prior art]
Conventionally, long foamed extruded products have been used as various sealing materials to seal between the opening (opening) of automobiles and doors, bonnets, etc., and to prevent water leakage and sound leakage from the gaps. It has been.
[0003]
This type of foamed extruded product is manufactured by extrusion molding using a kneader (extruder). That is, after adding various foaming agents to the base thermoplastic resin, it is heated and kneaded to produce a product. It is extruded from a die having a required groove according to its shape, and is formed as a long molded product having a required cross section. At this time, when the base resin passes through the die and is released from the high pressure in the kneader, the foaming agent contained in the base resin foams in the base resin, so that the extruded product has many bubbles. It becomes a foam extrusion molding formed inside. The foamed extruded product thus formed is characterized by high flexibility and excellent shape recovery property against compression, and these physical properties are suitable as a sealing material.
[0004]
Conventionally, chemical foaming agents are mainly used for foam extrusion molding, and it is also known to use water foaming or foaming by thermal expansion microspheres as other methods.
[0005]
Chemical foaming agents are made of various organic and inorganic gases (NH_Three, NO_X, N₂, CO₂, H₂O or the like). In extrusion molding using a chemical foaming agent, a base resin blended with a chemical foaming agent is heated and kneaded with a screw in a cylinder of an extruder (kneading machine), and at this time, by heating to a predetermined decomposition temperature, Convert chemical blowing agents to gases such as nitrogen gas and carbon dioxide. The generated gas is restrained from expanding by maintaining the pressure of the resin at a high pressure until it reaches the vicinity of the exit (head, die) of the extruder. As a result, when the resin is released at the die outlet, the gas expands all at once. Bubbles can thereby be formed, thereby causing high foaming.
[0006]
Water foaming is a method in which water is used as a foaming agent instead of the above chemical foaming agent. In this method, water as a blowing agent is poured into a cylinder of an extruder and kneaded with a base material by rotating a screw. When the base resin is closer to the exit of the extruder, the pressure becomes higher, and the base resin is extruded from the outlet of the die. When the base resin is released to the atmospheric pressure, the water in the base material is instantly turned into gas and foaming is obtained.
[0007]
The thermal expansion microsphere is a small resin sphere having a structure in which a liquid gas is included in a polymer shell. When this thermal expansion microsphere is heated, the shell softens and the liquid gas inside the shell is vaporized, and the gas pressure increases, so that the volume increases dramatically and becomes hollow spherical particles. The foaming extrusion method using this thermal expansion microsphere is the same as the case of using a chemical foaming agent. The thermal expansion microsphere is heated and kneaded with the base material in the extruder cylinder, and heat is generated by the thermal energy at this time. The expanded microsphere is expanded to obtain a highly foamed molded product.
[0008]
[Patent Document 1]
JP 59-138420 (Japanese Patent Application No. 58-13060)
[Patent Document 2]
JP 7-246646 A (Japanese Patent Application No. 6-76275)
[Patent Document 3]
Japanese Patent Laid-Open No. 2001-121973 (Japanese Patent Application No. 11-346629)
[0009]
[Problems to be solved by the invention]
Among the above-described foaming extrusion molding methods, the method using water foaming forms bubbles having a relatively large diameter, and since the gas escapes from the surface, there are many pores on the surface, and a molded article with high hygroscopicity is obtained. There is a feature. However, when molding is performed by this method, relatively large-scale equipment such as equipment for introducing water to be injected into the base resin is required.
[0010]
In addition, the method using thermal expansion microspheres is characterized in that a foam in which completely closed cells are formed can be obtained because the thermal expansion microspheres expand as they are from the original shape due to heat. However, when a molded article having a high expansion ratio is formed by this method, thermal expansion microspheres expanded to a large diameter may be deposited on the surface of the molded article, thereby impairing the smoothness of the surface.
[0011]
On the other hand, in the method using a chemical foaming agent, after adding and kneading the chemical foaming agent to the plasticized base resin, the foam can be molded simply by molding using a normal extrusion molding machine. There is no need for capital investment as in the case of using water foaming. In addition, the resulting molded product has fine bubbles and a clean surface, and when it is attached to an automobile opening as a sealing material, it is flexible and has superiority such as excellent followability to a curved portion. It has been known.
[0012]
The present invention uses a chemical foaming agent that can be carried out with relatively simple equipment, and can obtain physical properties such as surface smoothness suitable as a sealing material, among foaming extrusion molding methods using these various foaming agents. The method is intended to be further improved.
[0013]
That is, when a foamed molded product is used as a sealing material, it is advantageous that the foamed molded product has high flexibility. For this reason, a soft material, particularly an elastomeric material, is used as the base resin, or the expansion ratio is reduced. It may be possible to increase it further. In such a case, in the conventional molding method using a chemical foaming agent, there is a problem that the physical characteristics of the molded product, in particular, the tear resistance is greatly reduced.
[0014]
As a result of investigations by the inventors, when the foaming agent is included in the base resin and extruded while foaming, bubbles formed by the foaming agent are elongated in the extrusion direction due to the influence of internal pressure on the material, Also, it tends to be aligned in a line in this direction, and moreover, a plurality of bubbles tend to communicate with each other. For this reason, a weak portion of the material is formed along the arrangement of the bubbles, and the sealing material is torn from this portion. I knew that it would be easier.
[0015]
Accordingly, an object of the present invention is to provide an extrusion molding method capable of improving physical properties of a molded product, particularly tear resistance, in an extrusion molding method mainly using a chemical foaming agent.
[0016]
[Means for Solving the Problems]
  In order to achieve the above object, the extrusion molding method of the present invention is such that a foaming agent added to a thermoplastic resin is heated and kneaded and extruded from a die, and the foaming agent foams in the extruded thermoplastic resin. In the extrusion molding method to obtain foamed extrusion molded products using, a chemical foaming agent that is converted into a gas by thermal decomposition and a thermal expansion microsphere containing a liquid gas in a polymer shell are added as a foaming agentThe extrusion conditions were set so that part of the thermally expanded microspheres expanded and some remained unexpanded.It is characterized by that.
[0017]
  According to this extrusion molding method, when a chemical foaming agent is added to a thermoplastic resin and extruded from a die, the foam formed by the chemical foaming agent tends to grow elongated in the extrusion direction and be aligned. Can be dispersed randomly by adding thermally expanded microspheres. In addition, the resin pressure balance in the die can be made uniform, and thereby the communication of bubbles can be suppressed.In this case, the unexpanded thermal expansion microsphere also works effectively to disperse the bubbles due to the chemical foaming agent, and the expanded thermal expansion microsphere is formed by leaving a part of the thermal expansion microsphere unexpanded. Can be prevented from precipitating on the surface of the molded product and impairing the smoothness of the surface.
[0018]
In the extrusion molding method of the present invention, the chemical foaming agent and the thermal expansion microsphere added to the thermoplastic resin are sufficiently dispersed and extruded so that the bubbles are dispersed and formed as described above. preferable.
[0020]
In order to effectively obtain the function of dispersing bubbles by the chemical foaming agent by the thermal expansion microsphere, the diameter B of the bubble formed by the expanded thermal expansion microsphere₁Is the diameter A of the bubbles formed by the chemical foaming agent.₁It is preferable to make it larger. In addition, in order to keep the surface smoothness of the molded product high, the diameter B of the bubbles formed by the unexpanded thermal expansion microspheres₀Is the bubble diameter A by the chemical foaming agent.₁It is preferable to make it smaller.
[0021]
In the present invention, the compounding amount of the chemical foaming agent to be added is preferably less than 10.0% by weight with respect to the thermoplastic resin, and the compounding amount of the thermal expansion microsphere is preferably less than 5.0%. The thermal expansion microsphere is added mainly for the purpose of dispersing bubbles due to the chemical foaming agent, and the blending amount thereof may be smaller than that of the chemical foaming agent.
[0022]
The extruded product of the present invention is formed by the above-described extrusion molding method. Therefore, this extrudate has a feature that bubbles formed by a chemical foaming agent and bubbles formed by thermal expansion microspheres are irregularly dispersed in a thermoplastic resin. ing.
[0023]
In this way, by forming the bubbles in a dispersed manner, the bubbles are elongated in one direction, and the strength of the molded product, particularly the tear strength, is increased compared to the case where the bubbles are formed in an array. Can do.
[0024]
In particular, the extruded product of the present invention can have a tear strength according to JIS-K6301 of 20 N / cm or more. Further, the tensile strength according to JIS-K6251 can be 2000 kPa or more.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the drawings.
[0026]
In the present embodiment, a method for producing an elongated predetermined-shaped member having high flexibility and excellent shape recovery property against compression by extrusion molding will be described. A long member produced by this extrusion molding method can be suitably used as a seal member for each part of an automobile by taking advantage of the above-described characteristics.
[0027]
FIG. 2 shows a cross-sectional view of such various sealing members of an automobile cut in a direction perpendicular to the longitudinal direction. FIGS. 2A, 2B, and 2C show a door opening trim 10, a hood seal 11, and a back door opening trim 12 that cover the edges of an opening to which a door, a hood, and a back door are attached, respectively. ing. Each member is attached in its longitudinal direction so as to extend along the edge of each opening of the automobile. Each member has hollow seal portions 10a, 11a, and 12a. The hollow seal portions 10a, 11a, and 12a are sandwiched between the edge of the opening of the automobile and the door, hood, and back door, respectively. By filling the gap between the two, it functions as a sealing member that keeps the confidentiality in the automobile.
[0028]
In the extrusion molding of this embodiment, as schematically shown in FIG. 1 (a), a base resin material 2 and a foaming agent are placed in a general extruder 1, heated and kneaded, and a die having a predetermined shape (not used) A molded product having a desired cross-sectional shape is formed by extrusion from the figure. At this time, as the foaming agent, the thermal expansion microsphere 4 is used in addition to the chemical foaming agent 3. As the die, a material adjusted so as to have a predetermined shape after the extruded material is expanded by foaming is used.
[0029]
The details of this extrusion molding method will be described below.
[0030]
(Material structure)
As the base resin material 2, an elastomer resin of a thermoplastic resin is suitable. Particularly, X121-60W228 (121-68W228, 201-68W228, etc.) (trade name) manufactured by AES Japan Co., Ltd. can be preferably used.
[0031]
As the chemical blowing agent 3, an organic gas (NH_Three, NO_X, N₂), Inorganic gas (CO₂, H₂Various known chemical foaming agents that convert to O) can be used, and those that expand in volume 100 to 250 times under a temperature condition of 150 to 230 ° C., and obtain bubbles having a diameter of 40 to 100 μm after expansion are suitable. In particular, EV405D, 8147 (trade name) manufactured by Eiwa Chemical Industry Co., Ltd. is suitable.
[0032]
The thermal expansion microsphere 4 which is a microsphere encapsulating a liquid gas in a thermoplastic resin shell has a diameter of less than 50 μm in an unexpanded state, and the volume expands 200 to 300 times under a temperature condition of 100 to 240 ° C. Those having a diameter after expansion of 100 μm or more are suitable. In particular, EXPELLCEL (grade 092RMB120, 092MB120, 098RMB120, 098MB120) (trade name) manufactured by Nippon Philite Co., Ltd., Matsumoto Microsphere (grade F100) (trade name) manufactured by Matsumoto Yushi Co., Ltd. are suitable.
[0033]
As a blending ratio, the blending ratio of the chemical foaming agent 3 is less than 10.0% and the blending ratio of the thermal expansion microsphere 4 is less than 5.0% with respect to 100% of the base resin material 2 in terms of weight ratio. .
[0034]
At this time, as a feature of the present invention, the blending amount of the microspheres 4 is set to a sufficiently small ratio with respect to the blending amount of the chemical foaming agent 3. In the present invention, as will be described later, the thermal expansion microsphere 4 mainly functions to disperse bubbles by the chemical foaming agent 3 and can sufficiently fulfill this role even if the amount is small. Further, by making the blending amount of the thermal expansion microsphere 4 very small, it is possible to prevent the expanded thermal expansion microsphere 4 from appearing on the surface of the molded product and disturbing the smoothness of the surface, and molding with excellent surface smoothness. Things can be formed.
[0035]
(Molding condition)
The base resin material 2, the chemical foaming agent 3, and the thermal expansion microsphere 4 as described above are charged into a kneading portion in the cylinder 1a of the known extruder 1 in a predetermined blending amount, and these materials are heated and kneaded. , Feed in the direction of the die cut the required slit, and extrude from the die. In the extruded base material 2, the expansion of the chemical foaming agent 3 and the expansion of the thermal expansion microsphere 4 occur immediately, and a foamed molding with a high expansion ratio (110 to 150%) is continuously extruded. Molded.
[0036]
As the specifications of the extruder 1, it is suitable that L / D is 20 or more and the rotational speed of the screw is 30 rpm or more. In this way, by sufficiently increasing the L / D and sufficiently increasing the screw rotation speed, the material can be kneaded well, and a sufficient resin pressure can be secured until the outlet of the die. The appearance can be improved and sufficient foaming can be obtained. In particular, the resin pressure can be maintained at 50 MPa between the vicinity of the outlet of the die, thereby suppressing the foaming until the extrusion from the die, and the foaming starts at the same time as the extrusion. Obtainable.
[0037]
As a screw (not shown) used for the extruder 1, a full flight type shape with a Murdoch mixing pin is most suitable. It is possible to use a general full-flight shape, but in order to sufficiently disperse the chemical foaming agent 3 and the thermal expansion microsphere 4, high-kneading and high-dispersion types such as Murdoch, Mixing Pin, Dalmage, etc. It is preferable to use a screw.
[0038]
As for the temperature condition in the cylinder 1a, the temperature is raised up to about 200 ° C. from the upstream to the outlet, and then lowered to about 160 ° C. near the mouth outlet so that a large internal pressure is applied to the base resin material 2. It is preferable to do this.
[0039]
This temperature condition (kneading condition) is such that the base resin material 2 (elastomer) is sufficiently plasticized, and the thermally expanded microspheres 4 expand to a sufficiently large diameter after foaming, and the small diameter that is almost unfoamed. It is suitable for the present invention to set so that what remains will coexist. At this time, it is suitable for the present invention that the ratio of foaming to a large diameter and that remaining unexpanded is 1:99 to 40:60, and that the unexpanded one is increased. That is, among the thermally expanded microspheres 4, unexpanded ones are not deposited on the surface of the molded product, but are formed with excellent surface smoothness and good appearance by reducing the ratio of those that expand to a large diameter. You can get things. At this time, even if the thermal expansion microsphere 4 is not expanded, it is considered that the thermal expansion microsphere 4 functions to disperse bubbles by the chemical foaming agent 3 as described later.
[0040]
FIG. 1C schematically shows the state of the longitudinal section of the molded product 5 that forms the door opening trim 10 as shown in FIG. 1B, which is formed by extrusion molding under the above conditions. Indicate. In the molded product 5, bubbles 5 a formed by the chemical foaming agent 3, bubbles 5 b due to the thermal expansion microsphere 4 expanded to a larger diameter, and bubbles due to the thermal expansion microsphere 4 remaining with a small diameter remain. 5c are randomly distributed.
[0041]
On the other hand, FIG. 4 is a schematic diagram showing an extrusion molding method corresponding to the prior art compared with the extrusion molding method of the present embodiment. In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals for the sake of convenience, and detailed description thereof is omitted.
[0042]
In this extrusion molding method corresponding to the prior art, as shown in FIG. 4 (a), as the foaming agent, except that only the chemical foaming agent 3 is added, the extrusion molding is performed in the same manner as in the above-described embodiment, As shown in FIG. 4B, a molded product 25 constituting the door opening trim 10 having the same appearance as that of the above-described embodiment is obtained. In this molded product 25, as schematically shown in FIG. 4 (c), the bubbles 25a by the chemical foaming agent are flattened into an elliptical shape elongated in the longitudinal direction of the extrusion molding, and are arranged in this one direction. There is a tendency that the formed bubbles 25a communicate with each other. In such a state, the strength is reduced at the portion where the bubbles 25a are formed side by side. For this reason, the molded product 25 is easily torn along the direction in which the bubbles 25a are arranged, that is, the longitudinal direction at the time of extrusion molding. As a result, the tear strength is lowered.
[0043]
On the other hand, in the molded product 5 formed by the extrusion molding method of the present embodiment, as described above, the bubbles 5a formed by the chemical foaming agent 3 are irregularly dispersed without being flattened. Is located. This is considered because the growth and arrangement of the bubbles 5a formed by the expansion of the chemical foaming agent 3 are disturbed by the bubbles 5b and 5c formed by the thermal expansion microspheres 4 dispersed in the base resin material 2. It is done. Further, the communication of the bubbles 5a, 5b, 5c can be suppressed. This is considered to be because the resin pressure balance in the die is made uniform.
[0044]
And the molded product 5 of this embodiment in which the bubbles 5a, 5b, and 5c are dispersed and thus positioned, as in the molded product 25 produced by the extrusion molding method corresponding to the above-described conventional technique, The strength does not decrease in a specific portion, and therefore, it can have higher strength, particularly tensile strength.
[0045]
Thus, according to this embodiment, the shape and arrangement of the formed bubbles can be improved, and a molded product having a higher strength than that of the prior art can be obtained. In addition, when forming a molded product having the same strength as the molded product obtained by the conventional technique, the foaming ratio can be increased compared to the conventional technique, which can contribute to the reduction in density and weight of the product. .
[0046]
In addition, as a result of repeated examination by the present inventors, in order to favorably disperse the bubbles 5a formed by the chemical foaming agent 3, the diameter B of the bubbles 5b formed by the expanded thermal expansion microspheres 4 is obtained.₁Is the diameter A of the bubble 5a by the chemical foaming agent 3.₁It has been found that it is preferable to make it larger. In order to maintain the surface smoothness of the molded product 5, the diameter B of the bubbles 5c formed by the unexpanded thermal expansion microspheres 4 is used.₀Is the diameter A of the bubble 5a by the chemical foaming agent 3.₁It has been found that it is preferable to make it smaller. That is, these diameters A₁, B₀, B₁Is B₀<A₁<B₁It is preferable to set so as to satisfy the relationship.
[0047]
Moreover, although the example which uses the chemical foaming agent 3 and the thermal expansion microsphere 4 as a foaming agent was shown in this embodiment, you may add water as a foaming agent in addition to these.
[0048]
【Example】
Next, a comparative example showing an example in which only a chemical foaming agent is used as a foaming agent as a method to be compared with an example showing an actual extrusion molding in accordance with the above-described embodiment, and A description will be given below together with the comparison results between the example and the comparative example.
[0049]
(Example)
The base resin material 2 is an olefin-based thermoplastic elastomer resin (trade name X121-60W228) manufactured by AES Japan Co., Ltd., and the chemical foaming agent 3 is an inorganic foaming agent manufactured by Eiwa Kasei Kogyo Co., Ltd. No. 8147, foaming temperature 150 ° C. to foaming ratio 180 times) is blended at a weight ratio of 4.0%, and further, as the thermal expansion microsphere 4, a microsphere manufactured by Nippon Philite Co., Ltd. (trade name 092RMB120, expansion temperature 130) C. to 200.times.) Was blended at a weight ratio of 0.5% and used for extrusion molding.
[0050]
As the extruder 1, a cylinder having a cylinder diameter of 40 mm and an L / D ratio of 30 and having a full flight-shaped screw with a Murdoch mixing pin was used. The screw rotation speed at the time of extrusion molding was 50 rpm, and the temperature conditions were 160 ° C. → 200 ° C. → 180 ° C. → 165 ° C. → 160 ° C. (head portion) in order from the upstream.
[0051]
Under these conditions, the molded product 5 has a tube shape, a thickness of 1.60 mm, and a density of 0.55 g / cm.^ThreeFormed.
[0052]
(Comparative example)
In the comparative example, the same base resin material as in the example was blended with the same chemical foaming agent as in the example at a weight ratio of 4.5% for extrusion molding. Thermally expanded microspheres were not blended.
[0053]
Extruder 1 was exactly the same as in the example, and the extrusion molding conditions, that is, the screw rotation speed and temperature conditions during extrusion molding were the same as in the example.
[0054]
Under these conditions, the wall thickness is 1.60 mm and the density is 0.55 g / cm.^ThreeA tube-shaped molded product was formed.
[0055]
(Evaluation method, results)
First, regarding the moldability, the appearance of the molded product was visually observed, and a cross-sectional photomicrograph was taken for comparative evaluation.
[0056]
As a result, looking at the appearance of the molded product, both the examples and comparative examples were finished smoothly, and no significant difference was observed in appearance.
[0057]
On the other hand, a micrograph of the cross section is shown in FIG. 3A shows a cross section of the molded product of the example cut along the extrusion direction, and FIG. 3B shows a similar cross section of the molded product of the comparative example. When the two are compared, there is a remarkable difference, that is, as shown in FIG. 3A, in the molded product of the example, bubbles are irregularly dispersed, whereas FIG. ), It can be seen that in the molded product of the comparative example, the bubbles are flattened in the extrusion direction and arranged in a line.
[0058]
Next, the strength was evaluated.
(1) Tear strength
The tear strength was compared by performing a tear test in accordance with the tear test method defined in JIS-K6301 on the molded products of Examples and Comparative Examples.
[0059]
As a result, the tear strength of the molded product of the comparative example was 14.0 N / cm, whereas the tear strength of the molded product of the example was 25.0 N / cm. According to the example, the tear strength was It was confirmed that the height was about 80% higher than that of the comparative example.
[0060]
(2) Tensile strength
Comparison of the tensile strength was carried out by conducting a tensile test according to the tensile test method defined in JIS-K6251 on the molded products of Examples and Comparative Examples.
[0061]
As a result, the tensile strength of the molded product of the comparative example was 1250 kPa, whereas the tensile strength of the molded product of the example was 2200 kPa. According to the example, the tensile strength was nearly 80% of the comparative example. It was confirmed that it was high.
[0062]
Next, as an evaluation of the sealing property when the molded product obtained by extrusion molding was used as a hollow seal member, the flexibility and shape following property of the molded product were evaluated. That is, when each molded product is used for the hollow seal portions 10a, 11a, 12a of various seal members as shown in FIG. 2, the hollow seal portions 10a, 11a, 12a It is preferable that the gap is satisfactorily deformed in accordance with this gap so as to cover the gap between them, and a certain repulsive force is generated, so that the gap is filled without generating a gap. Sealability is obtained. For this purpose, it is preferable that the molded articles constituting the hollow seal portions 10a, 11a, and 12a are flexible and have high shape followability, and have uniform flexibility and shape followability in all directions.
[0063]
The comparison of the sealing performance is a molded product according to the example and the comparative example, and a portion corresponding to the hollow seal portion 10a of the door opening trim 10 of FIG. 2 (a) is formed and softened when pressed under various conditions. This was carried out by confirming the property and the shape following property with tactile sensation. As a result, the example showed higher homogeneity of the molded product, finer and more flexible than the comparative example, and showed excellent shape followability against pressing from all directions.
[0064]
【The invention's effect】
As described above, according to the present invention, in the foaming extrusion molding method of a thermoplastic resin, a chemical foaming agent is formed by adding a small amount of thermal expansion microsphere in addition to the chemical foaming agent as a foaming agent. It is possible to irregularly disturb the growth and arrangement of the bubbles by the thermal expansion microspheres in the direction of extrusion, so that the bubbles are dispersed and formed, thereby forming a high strength, particularly a high tear strength. You can get things. In the present invention, the thermal expansion microsphere to be added is sufficient in a trace amount, and by suppressing the addition amount of the thermal expansion microsphere to a very small amount, the thermal expansion microsphere is prevented from being deposited on the surface of the molding, It is possible to prevent the appearance from being impaired and to obtain a molded article having a good appearance.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an extrusion molding method according to an embodiment of the present invention, FIG. 1 (a) is a schematic diagram showing a flow of extrusion molding, and FIG. 1 (b) is an example of a molded product to be formed. FIG. 1C is an external view, and is a cross-sectional view taken along the line AA in FIG.
FIG. 2 is a cross-sectional view taken along a direction perpendicular to the longitudinal direction of various seal members of an automobile suitable for being formed by an extrusion molding method according to an embodiment of the present invention.
FIG. 3 is a photomicrograph of a cross section cut in a direction perpendicular to the longitudinal direction of a molded product formed by an example of the present invention and a comparative example compared with the example.
4A and 4B are schematic diagrams showing an extrusion molding method corresponding to a conventional example compared with an embodiment of the present invention. FIG. 4A is a schematic diagram showing a flow of extrusion molding, and FIG. FIG. 4C is a cross-sectional view taken along the line BB of FIG. 4B.
[Explanation of symbols]
1 Extruder
1a cylinder
2 Base resin material
3 Chemical foaming agents
4 Thermal expansion microsphere
5,25 Molded product
5a, 5b, 5c, 25a Air bubbles
10 Door opening trim
10a, 11a, 12a Hollow seal part
11 Food seal
12 Back door opening trim

Claims (8)

In an extrusion molding method of obtaining a foamed extrusion molded article by utilizing the fact that a foaming agent is added to a thermoplastic resin and extruded from a die by heating and kneading, and the foaming agent foams in the extruded thermoplastic resin.
As the foaming agent, a chemical foaming agent that is converted into a gas by thermal decomposition and a thermal expansion microsphere containing a liquid gas in a polymer shell are added, and the thermal expansion microsphere is partially expanded and partially expanded Is an extrusion method characterized in that it remains unexpanded .   By dispersing the chemical foaming agent and the thermal expansion microsphere in the thermoplastic resin and extruding, the growth and arrangement of bubbles formed by the chemical foaming agent are irregularly disturbed by the thermal expansion microsphere. The extrusion molding method according to claim 1, wherein each bubble is dispersed and formed. The bubble diameter A ₁ formed by the chemical foaming agent, the bubble diameter B ₁ formed by the expanded thermal expansion microsphere, and the bubble diameter B ₀ formed by the unexpanded thermal expansion microsphere. DOO is, B ₀ <satisfy the relation of a ₁ <B _1, extrusion molding method according to claim 1 or 2. From the weight ratio, the chemical foaming agent is added in an amount of less than 10.0% with respect to 100% of the thermoplastic resin, and the thermal expansion microsphere is added in an amount of less than 5.0%. extrusion molding method according to any one of the three. An extrusion molded product produced by the extrusion molding method according to any one of claims 1 to 4 . 6. The extruded product according to claim 5, wherein the foam formed by the chemical foaming agent and the foam formed by the thermal expansion microsphere are irregularly dispersed in the thermoplastic resin. The extruded product according to claim 5 or 6 , wherein the tear strength according to JIS-K6301 is 20 N / cm or more. The extruded product according to any one of claims 5 to 7 , wherein the tensile strength according to JIS-K6251 is 2000 kPa or more.

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