JP4409889B2 - Resin foam manufacturing method and paper sheet multi-feed preventing member using the foam - Google Patents

Description

  The present invention relates to a method for producing a resin foam and a paper sheet multi-feed preventing member using the foam, and more specifically, by improving the method for producing a resin foam by extrusion gas foaming, the bubble diameter can be reduced, It improves the wear resistance of the resin foam.

  Conventionally, in a paper feeding mechanism in an ink jet printer, laser printer, electrostatic copying machine, plain paper facsimile machine, automatic deposit payment machine (ATM), etc., it is attached to the upper surface of a tray and sandwiches paper between paper feeding rollers. A paper sheet multi-feed preventing member such as a separation sheet to be conveyed is used.

The paper sheet multi-feed preventing member such as the separation sheet is required to have a high friction coefficient, but conventionally, since the load applied to the separation sheet is low, the amount of wear caused by contact with the paper is relatively small. Therefore, the wear resistance has not been required so much.
In recent years, there is a tendency to reduce the number of parts for cost reduction, and in order to make the paper feeding mechanism simpler, there is also a mechanism in which the paper feeding roller is idled for each paper feeding. In this case, the load applied to the separation sheet increases due to contact with the idling sheet feeding roller, and is required to have high strength and wear resistance.

  Conventionally, the paper sheet multi-feed preventing member is formed of a rubber material such as urethane rubber or acrylonitrile butadiene rubber (NBR). Separation sheets made of these rubber materials have a high coefficient of friction and excellent wear resistance, but wear resistance against the load applied to the separation sheet when the paper feed roller is idled for each sheet feeding. Is not enough. In addition, the separation sheet made of these rubber members has a disadvantage that an unpleasant vibration sound called “squeal” is likely to occur due to contact between the paper and the separation sheet when the sheet is passed.

  In response to the problem of “squeal”, the weight of the paper sheet is blended with a rubber chemical foaming agent, vulcanized to provide a foamed rubber body, and absorbs vibrations that generate “squeal” in the voids in the foamed rubber body. An anti-feed member is provided. However, since a vulcanization process is necessary, the cost is increased, and environmental considerations are necessary because a chemical foaming agent is used.

  In response to the above problems, instead of the method of blending a chemical foaming agent in a rubber material and vulcanizing to produce a foam, a foam is produced by a physical method of injecting a high pressure gas into a thermoplastic resin to cause gas foaming. Japanese Patent Laid-Open No. 2003-127201 (Patent Document 1) proposes a method for manufacturing the above. In the method for producing a thermoplastic elastomer foam of Patent Document 1, an inert gas, water, or a chemical foaming agent is mixed into the thermoplastic elastomer, and the pressure before the die (die) is maintained at 10 MPa or more to form an extruded bubble. Thus, a foamed thermoplastic elastomer having a surface irregularity of 10 μm or less is manufactured.

However, in the die outlet structure of Patent Document 1, the shape of the outlet portion of the die is the shape shown in FIGS. 6A and 6B in order to keep the pressure before the die at 10 MPa. Therefore, as shown in FIG. 6 (A), the portion continuing to the outlet tip 1 is a straight portion 1a and has the same cross section, so the pressure is not drastically dropped and the pressure gradient is gentle. There is a problem that it becomes large, easy to generate continuous bubbles, and it is difficult to reduce the bubble diameter. Therefore, there is a problem that the strength of the foam to be manufactured is lowered.
In addition, in the structure shown in FIG. 6B, a column 2 with a partially cut side surface is provided, and the column 2 is rotated to reduce the cross-sectional area. However, there is a problem that clogging is likely to occur at this portion. is there.
JP 2000-127201 A

  The present invention has been made in view of the above-described problems. The manufacturing method disclosed in Patent Document 1 has been improved to control the bubble diameter of the foam and effectively generate vibration noise in the voids generated by the bubbles. It is an object of the present invention to provide a method for producing a resin foam that can be suppressed to a low level and a paper sheet multi-feed preventing member produced by the production method.

In order to solve the above problems, the present invention provides a kneaded product of an ester-based thermoplastic elastomer having a melt temperature + 60 ° C melt viscosity B (B / A) of 0.1 to less than 1 with respect to a melt temperature + 10 ° C melt viscosity A. Is extruded into an extruder and extruded, and the kneaded product is dissolved by injecting carbon dioxide gas of 6 MPa or more and 10 MPa or less in the middle of the extrusion process,
The temperature of the carbon dioxide gas injection site of the extruder is set to −5 ° C. to + 40 ° C. of the melting temperature of the thermoplastic resin,
The residence time of the kneaded material in the extruder from the time when the thermoplastic resin kneaded material is introduced into the cylinder of the extruder to the time when it is extruded from the outlet is 3 minutes to 6 minutes,
The base attached to the tip of the extruder via a head is a tapered outlet having a diameter reduced toward the outlet opening, and the taper angle θ of the tapered outlet is 5 ° ≦ θ ≦ 20 ° with respect to the central axis of the outlet portion. And the range
The temperature of the head and the base is set to a melting temperature of the thermoplastic resin of −25 ° C. or higher and a melting temperature of + 15 ° C. or lower,
The resin pressure is suddenly raised before the outlet opening of the die, and bubbles are generated by a sudden pressure drop when the gas dispersed and dissolved in the kneaded product is pushed out from the outlet. A method for producing a resin foam is provided.

The present invention has been found by repeating the experiment with various changes in the pressure of the carbon dioxide gas, the temperature of the extruder, and the residence time for various thermoplastic resins. In addition, it is possible to obtain a resin foam having a small bubble diameter and uniform bubbles.
That is, the melt gas temperature + 10 ° C. melt viscosity A + 60 ° C. melt viscosity B (B / A) of 0.1 to less than 1 kneaded thermoplastic resin with carbon dioxide gas injected By setting the temperature of the extruder within the above range, the resin can be reliably plasticized.
Moreover, the pressure of resin in which carbon dioxide gas is dissolved can be increased by setting the temperature of the head and the die attached to the tip of the extruder within the above range.
Furthermore, by setting the residence time and the pressure of the carbon dioxide gas within the above ranges, the carbon dioxide gas is uniformly dissolved and dispersed in the resin kneaded material. In this way, if the resin pressure is suddenly increased before the outlet opening of the extruder and then extruded from the outlet opening, the pressure is released at the moment of extrusion, and a sudden pressure drop occurs at the outlet portion. The gas mixed in can uniformly generate bubbles having a small cell diameter, and a resin foam having a small cell diameter can be obtained.

The thermoplastic resin used in the present invention has a melting temperature + 60 ° C. melt viscosity B (B / A) of 0.1 or more, preferably 0.3 or more, and approaches 1 as much as possible. It is preferable. The upper limit is less than 1 because there is no thermoplastic resin that is 1 or more.
The reason why B / A is 0.1 or more as described above is that if the temperature dependence of the melt viscosity is large, the melt viscosity decreases when heated to a temperature higher than the melt temperature, and the bubbles become huge and bubble breakage occurs. It becomes easy. On the other hand, when the temperature is lowered, a sudden viscosity change occurs, so that the viscosity curing proceeds rapidly due to the temperature change at the outlet of the die and the temperature immediately after extrusion, and clogging tends to occur at the outlet opening and uniform foaming is realized. Hateful. However, when B / A is as low as 0.1 or more, the temperature dependency is not rapidly cured even if the temperature drops immediately after the outlet part of the die and the extrusion, and the curing proceeds slowly. Is promoted. For the reasons described above, it is desirable that the temperature dependence of the melt viscosity is small, and it is desirable that B / A is as small as 1.

The temperature of the extruder at the carbon dioxide injection site is set to a melting temperature of the thermoplastic resin of −5 ° C. or higher and a melting temperature of + 40 ° C. or lower, preferably a melting temperature of + 15 ° C. or higher and a melting temperature of + 35 ° C.
This is because if the melting temperature is lower than −5 ° C., the thermoplastic resin does not melt and the viscosity becomes very high, and the extruder stops because a large load is applied to the extruder when kneading. On the other hand, if it is higher than the melting temperature + 40 ° C., it approaches the melting temperature + 45 ° C., which is the decomposition temperature of the resin, so that the resin may be decomposed during extrusion of the kneaded product.

Further, the temperature of the head and the die attached to the tip of the extruder is set to the melting temperature of the thermoplastic resin of −25 ° C. or higher and the melting temperature of + 15 ° C. or lower, preferably the melting temperature of −25 ° C. or higher and the melting temperature of −5 ° C. or lower.
This is because if the melting temperature is lower than −25 ° C., solidification of the resin starts and the resin is clogged at the exit of the extruder. On the other hand, when the melting temperature is higher than + 15 ° C., the viscosity of the kneaded product of the resin is low, and the pressure is not suitable for foaming the gas dissolved at the exit of the extruder.

The residence time of the kneaded material in the extruder from the time when the resin kneaded material is injected into the cylinder to the time when the resin kneaded material is extruded from the outlet is set to 3 minutes to 6 minutes.
This is because if the residence time is shorter than 3 minutes, the injected carbon dioxide is pushed out before it is completely melted into the kneaded product, so that the undissolved gas forms large bubbles in the resin, and a uniform foam of bubbles is formed. By not being able to get. On the other hand, if it is longer than 6 minutes, the thermal deterioration due to the long residence time of the kneaded product proceeds in the extruder, so that the foamed state deteriorates and a good foam cannot be obtained.

The extruder comprises screw-type extrusion with a screw incorporated in a cylinder. In order to keep the kneaded product residence time within the above range, the screw rotation speed of the extruder is preferably 20 rpm or more and 40 rpm.
The reason is that when the cylinder diameter is φ30 and the amount of kneaded material charged into the cylinder is 50 g / min, when the screw rotation speed is 20 rpm, the residence time is 6 minutes, and when the screw rotation speed is 40 rpm, This is because the residence time is 3 minutes.

The flow rate of carbon dioxide injected into the kneaded material is preferably 50 g / h or more and 200 g / h or less.
This is because if the carbon dioxide gas flow rate is less than 50 g / h, the amount of dissolved carbon dioxide gas is small, so that a foam capable of sufficiently absorbing vibration cannot be obtained. This is because a uniform foam cannot be obtained.

The pressure of the carbon dioxide gas injected into the kneaded product is 6 MPa or more and 10 MPa or less, preferably 8 MPa or more and 10 MPa or less.
This is because if it is less than 6 MPa, the amount of carbon dioxide dissolved in the resin kneaded product is reduced, and a high foaming ratio cannot be obtained. On the other hand, if it is greater than 10 MPa, the saturated dissolution amount of the gas into the resin will be exceeded, and the undissolved gas will be released so as to explode at the exit of the extruder.

The outlet pressure of the outlet opening of the die of the extruder is preferably 7 to 10 MPa. By setting this range, the resin kneaded product is extruded from the extruder and the pressure suddenly increases immediately before the moment, and a sudden pressure drop occurs when the resin is extruded, so the carbon dioxide dissolved in the kneaded product is bubbled. This is because a good foam can be obtained.
That is, the resin pressure in front of the outlet opening is rapidly increased to 240% to 330% with respect to the resin pressure when the thermoplastic resin in the cylinder is plasticized.

Further, as described above, the base attached to the front end side of the extruder through the head is a tapered outlet having a diameter reduced toward the outlet opening, and the taper angle θ of the tapered outlet is the central axis of the outlet portion. In contrast, 5 ° ≦ θ ≦ 20 °, preferably 8 ° ≦ θ ≦ 15 °, and the tip of the outlet opening is the minimum area.
As described above, the taper angle θ of the tapered outlet is set to 5 ° ≦ θ ≦ 20 °. If the angle is smaller than 5 °, the pressure gradient becomes gradual and the resin pressure cannot be increased rapidly. This is because it is difficult to uniformly generate a gas dissolved in the resin when the bubbles inside are pushed out from the outlet of the die. On the other hand, when the angle is larger than 20 °, the pressure rises too rapidly and the extruder is overloaded.

Further, the tip opening of the tapered outlet has a width (lateral dimension) W (W / T) with respect to a thickness (vertical dimension) T of 30 or less, preferably 7 or less. This is because if W / T is greater than 30, the opening is small and very elongated, and the resin is likely to be clogged at the die outlet.
Furthermore, the cross-sectional area of the distal opening of the tapered outlet may preferably be 11 mm ² or less, and more preferably, 11 mm ² or less. This is because if the diameter is larger than 11 mm ² , the cross-sectional area of the mouthpiece outlet becomes large, so that the head pressure is not sufficiently high, gas is released from the outlet, and bubbles of the foam due to carbon dioxide gas become large, which may cause continuous bubbles. It is.

Without blending chemical blowing agent, preferably in a foam with only the extrusion gas foaming.
The ester-based thermoplastic elastomer has a relatively low melt viscosity dependency and can be obtained at a low cost, and can impart physical properties similar to those of an elastic rubber while being foamed by extrusion gas. In particular, those having a good balance between heat resistance and physical strength are preferably used. Ester-based thermoplastic elastomers have various grades depending on the ratio of hard segment component (polyester) and soft segment component (polyether), type of hard segment component, molecular weight, etc., but the melting temperature is not so low and low. An ester thermoplastic elastomer having a hardness is preferably used. Specifically, the ester-based thermoplastic elastomer having a hardness of 90 A, a specific gravity of 1.15, a melting temperature of 203 ° C., a melt viscosity of 205 Pa · s (10 ² sec ⁻¹ (240 ° C.)) and a B / A of 0.7. Is most preferably used.

  Further, by using carbon dioxide as the high-pressure gas, the cost can be reduced and the environment is taken into consideration.

  Furthermore, if a foam is obtained by injecting carbon dioxide gas without adding a chemical foaming agent and only by extrusion gas foaming, a foam can be obtained by using only the extrusion gas without using a chemical foaming agent that is undesirable for the environment. At the same time, when it is recycled, it does not contain anything other than carbon dioxide as bubbles, so it is environmentally friendly. Furthermore, since no chemical foaming agent is used, the manufacturing cost can be reduced.

It is preferable that the bubbles generated by the extrusion gas foaming are 200 μm or less on average and the expansion ratio is 2 or more.
When the expansion ratio is less than 2 times, since there are few bubbles and there are many resin matrices, the cell density becomes small and the foam does not function. The expansion ratio is preferably 3 times or more.
The foaming ratio is preferably 20 or less, and if it exceeds 20 times, the cell diameter increases and the strength decreases.
Moreover, the cell diameter of the bubbles of the resin foam is set to 200 μm or less on average. When the cell diameter is larger than 200 μm, the walls of the bubbles are broken at the growth stage, and two or more bubbles are combined to form one large void. It is because it becomes an open cell (open bubble). Preferably it is 100 micrometers or less.
When the cell diameter is as small as 200 μm or less and the bubbles are uniformly dispersed, the strength and wear resistance can be improved.
The average cell diameter of the bubbles is 50 μm or more, and this is because it is difficult to make it less than 50 μm in production.

Secondly, the present invention provides a resin foam produced by the above method.
Furthermore, the present invention thirdly provides a paper sheet multi-feed preventing member formed of the resin foam. In the paper sheet multi-feed prevention member, the strength and wear resistance are improved, so that the wear amount generated when the paper feed roller is idling is small and has durability, and there is a gap between bubbles generated by gas foaming. Generation of vibration sound called “squeal” can be suppressed.

As is clear from the above description, according to the present invention, carbon dioxide gas is injected into the ester-based thermoplastic elastomer , the temperature of the extruder where the carbon dioxide gas is injected, the temperature of the head and the base attached to the tip of the extruder. By extruding by controlling the pressure of carbon dioxide gas and the residence time of the kneaded product, a resin foam having uniform and small cell diameter bubbles can be produced.
According to the above method, since no chemical foaming agent is used, it is environmentally friendly and the manufacturing cost can be reduced.

  Furthermore, since it is a resin foam, it is excellent in strength and wear resistance as compared with a rubber foam, and is excellent in durability when molded as a paper sheet multi-feed prevention member. Further, since the vibration sound can be absorbed in the voids of the bubbles, it is possible to reduce or prevent “squeal” that is a problem in the paper sheet multi-feed preventing member.

Hereinafter, embodiments of the resin foam of the present invention will be described.
The resin foam of the present invention is formed by injecting carbon dioxide gas at a pressure of 9.8 MPa into an ester-based thermoplastic elastomer made of polyester and polyether and foaming the extruded gas.

The ester-based thermoplastic elastomer used in the present invention is TPEE-a and TPEE-b shown in FIG.
TPEE-a has a melting temperature of 200 ° C., 210 ° C. (melting temperature + 10 ° C.), a melt viscosity A of 2100 Pa · s, a melt viscosity B of 260 ° C. (melting temperature + 60 ° C.) of 1470 Pa · s, and a B / A of 0 .7.
TPEE-b has a melting temperature of 200 Pa, a melting viscosity A of 210 ° C. (melting temperature + 10 ° C.) of 3000 Pa · s, a melting viscosity B of 260 ° C. (melting temperature + 60 ° C.) of 900 Pa · s, and a B / A of 0.3.

  TPEE-c shown in FIG. 1 has a melting temperature of 160 ° C., a melt viscosity A of 170 ° C. (melting temperature + 10 ° C.) is 3700 Pa · s, and a melt viscosity B of 220 ° C. (melting temperature + 60 ° C.) is 260 Pa · s and B / A is 0.07, which is outside the scope of the present invention.

The ester thermoplastic elastomer (TPEE-a) is subjected to extrusion gas foaming by an extrusion apparatus shown in FIG.
As the extrusion device, a screw type single screw extruder 10 in which a screw is incorporated in a cylinder (φ30 in the present embodiment) arranged in a horizontal direction is provided, and a hopper 11 is provided at one end of the cylinder and a head 21 is provided at the other end. A base 12 is attached via

The raw material (the thermoplastic elastomer) is charged into the conveying space 10 a of the extruder 10 from the hopper 11. A screw (not shown) is mounted in the conveyance space 10a, and the raw material charged by the rotation of the screw is pushed out while being kneaded toward the outlet 10b. A carbon dioxide injection port 10c is provided at an intermediate position of the conveyance path of the conveyance space 10a, and carbon dioxide heated to a required temperature is injected from the carbon dioxide stable supply device 20 during kneading.
Further, nine temperature control heaters 30 are attached along the conveyance space including the cylinder, the head 21 and the base 12 of the extruder 10 to heat each part to a required temperature.

  The position of the carbon dioxide gas injection port 10c is between the time when carbon dioxide gas is supplied to the kneaded product in a sufficiently kneaded state and the gas is dispersed in the kneaded material after injection and is pushed out from the outlet of the base 12. The intermediate position is such that the gas can be sufficiently dissolved and dispersed throughout the entire kneaded product. This position is the shortest position (C4 in FIG. 2) that can be plasticized in order to make the melting time of carbon dioxide gas as long as possible.

Specifically, the present inventor has found through repeated experiments that, in resin extrusion gas foaming, the lower the temperature of the head 21 and the base 12, the smaller the cell diameter of the bubbles and the higher the expansion ratio.
In general, when the resin temperature is high, the solubility of carbon dioxide gas decreases, while the diffusion coefficient of carbon dioxide gas into the resin increases as the temperature increases.
From these points, the temperature of each part is adjusted by the nine heaters 30. In addition, carbon dioxide gas supplied to the resin in the conveying space 10a of the extruder 10 by controlling the temperature and the time from when the cylinder is charged until it is extruded at the die outlet (specified by the extrusion conveying distance and the screw rotation speed). Is sufficiently diffused, dissolved in the resin kneaded material, and extruded from the die outlet.

  Specifically, the temperature of C4 in FIG. 2 is 240 ° C. (melting temperature + 40 ° C.), the temperature of the head 21 and the base 12 is 180 ° C. (melting temperature −20 ° C.), and from when the cylinder is inserted until it is pushed out at the base outlet. The residence time of the kneaded product is 6 minutes.

  Further, as shown in FIG. 3A, the outlet structure of the base 12 is provided with a tapered outlet 12c that tapers from the land portion 12a of the outlet portion toward the outlet opening 12b, and the outlet opening 12b has a minimum area. The angle θ of the inner peripheral surface of the tapered outlet 12c is in the range of 5 ° ≦ θ ≦ 20 ° with respect to the central axis of the outlet, and is 10 ° in this embodiment.

Further, as shown in FIG. 3B, the outlet opening 12b having the minimum area is rectangular, and when the width of the outlet opening 12b is W and the thickness is T, W / T is 30 or less. However, the thickness is increased so that clogging does not occur at the outlet, and foaming can be promoted. In this embodiment, W is 7 mm, T is 1 mm, and W / T = 7. The cross-sectional area of the outlet opening 12b differs depending on the production amount, but if it is too large, there is a problem that the head pressure is lowered, so that it is 11 mm ² or less, preferably 7 mm ² or less.

Next, a process for producing a resin foam by foaming an ester-based thermoplastic elastomer by extrusion gas foaming using the above-described extrusion apparatus will be described.
The ester thermoplastic elastomer TPEE-a is put into a hopper 11 of a screw type single screw extruder 10, and the extruder 10 is extruded while rotating at 20 rpm and kneading. In the middle of the conveyance of the extruder, the high pressure gas stable supply device 20 injects the carbon dioxide gas kneaded material into the conveyance space 10a of the extruder 10 at a pressure of 9.8 MPa. Since the injected carbon dioxide gas has a high pressure, it is uniformly dispersed and dissolved in the kneaded product. After gas injection, it is pushed out to the outlet side in a short time, and the pressure is suddenly increased in front of the tapered outlet 12c of the base 12 attached to the outlet portion. Foam is produced by bubbling carbon dioxide gas.
In this embodiment, a single screw extruder is used, but the present invention is not limited to this, and a twin screw extruder may be used.

When the foam is produced, the outlet pressure of the outlet opening of the die becomes 8.8 MPa, and the pressure is suddenly reduced at the moment of being extruded from the extruder 10, so that the carbon dioxide dissolved in the kneaded material is bubbled and foamed. You can get a body.
The extrusion pressure in the cylinder is 3.0 Mpa, whereas the extrusion pressure at the outlet opening is 8.8 Mpa, which is increased rapidly by 290%.

  The resin foam produced by the above method is extruded at the outlet of the cap from the time when carbon dioxide gas is charged, the temperature of C4 is 240 ° C. (melting temperature + 40 ° C.), the temperature of the head 21 and the base 12 is 180 ° C. (melting temperature −20 ° C.). 6 minutes and the pressure of carbon dioxide gas is 9.8 MPa, the expansion ratio is 2 times or more (7.1 times in this embodiment), and the cell diameter is 200 μm or less on average (this embodiment) 97 μm), and a good foamed state in which small bubbles are uniformly dispersed is obtained.

Hereinafter, Examples 1-4 and Comparative Examples 1-16 of the resin foam of this invention are explained in full detail.
In Examples 1-4 and Comparative Examples 1-16, Perprene P47D, which is a polyester-based thermoplastic elastomer having a melting temperature + 60 ° C melt viscosity B (B / A) of 0.7 with respect to a melt temperature + 10 ° C melt viscosity A (Toyobo Co., Ltd.) was used as a material for the resin kneaded material.

Using a Φ30 single screw extruder (manufactured by SunNT Co., Ltd.) as an extruder, changing the screw of the extruder, rotating the material into the cylinder from the hopper, and kneading while heating And pushed out. At an intermediate position C4 in the extrusion process, carbon dioxide was injected into the kneaded product using a carbon dioxide stable supply device (manufactured by Showa Carbon Co., Ltd.).
In Examples 1 to 4 and Comparative Examples 1 to 16, as shown in Table 1, the temperature of C4 in the extruder is the extrusion condition (1) -1, the temperature of the head and the base is the extrusion condition (1) -2, Extrusion conditions (2) were used for the kneaded product residence time from the injection into the cylinder to the extrusion at the outlet of the die, and extrusion conditions (3) were used for the supply pressure of carbon dioxide gas.
In addition, the taper angle θ of the tapered outlet of the die attached to the extruder outlet via a head is 10 ° in Examples 1-4, Comparative Example 1-14 is 10 °, Comparative Example 15 is 2 °, and Comparative Example 16 is 30 °.゜.

  About the said Examples 1-4 and Comparative Examples 1-16, the outlet pressure (MPa) of the taper-shaped exit of a nozzle | cap | die, the foaming magnification (times) of a sheet-like foam, a cell diameter (micrometer), foaming by the method mentioned later. The state was evaluated. The evaluation results are shown in Table 1.

(Measurement of outlet pressure)
The taper-shaped outlet pressure of the base was measured using a resin pressure gauge installed in the vicinity of the base outlet. The appropriate value of the resin pressure is 6 MPa or more and 10 MPa or less.

(Measurement of expansion ratio)
The specific gravity after foaming and the specific gravity before foaming were measured, the foaming ratio was determined from (specific gravity before foaming / specific gravity after foaming), and the rate of increase in volume was measured. The volume increase rate is an appropriate value of 2 times or more, and more preferably 3 times or more.

(Measurement of cell diameter)
The cross section of the obtained foam was observed with an electron beam scanning microscope, and the average cell diameter of the cross section was determined.
An appropriate value is 200 μm or less, and a more preferable value is 100 μm or less.

(Foamed state)
The foamed state was judged from the foaming ratio and the cell diameter of the obtained foam.
“Good” for the foaming ratio and the preferred range of the cell diameter, “Slightly good” for the appropriate range, “Slightly bad” for those slightly out of the appropriate range, and “Bad” for those outside the appropriate range. It was.

  As is apparent from the results in Table 1, Examples 1 to 4 use ester-based thermoplastic elastomers with B / A of 0.1 or more, and the pressure of carbon dioxide gas (extrusion condition (3)) is 6 MPa or more and 10 MPa or less. The mixture is poured into the kneaded material and melted, and the temperature of the C4 of the extruder (extrusion condition (1) -1) is set to the elastomer melting temperature −5 ° C. or higher and the melting temperature + 40 ° C. or lower. The residence time in the extruder (extrusion condition (2)) is 3 to 6 minutes, and the temperature of the head and die attached to the tip of the extruder (extrusion condition (1) -2) is the melting temperature of the elastomer-25 Since extrusion molding was performed at a melting point of 15 ° C. or higher and a melting temperature of 15 ° C. or lower, the carbon dioxide gas was sufficiently dispersed and melted in the kneaded product, so that a foam having a small cell diameter could be obtained. Further, the pressure before the outlet of the die becomes a required high pressure, and the resin pressure can be drastically lowered when the resin is pushed out.

On the other hand, in Comparative Examples 1 to 6 and 9, since the pressure of the carbon dioxide gas was made smaller than 6 MPa (extrusion condition (3)), the amount of gas dissolved in the kneaded material was reduced, and the extrusion was not possible or the extrusion was low. A foam with an expansion ratio was obtained. In Comparative Example 7, since the pressure of carbon dioxide gas (extrusion condition (3)) was set higher than 10 MPa, the saturated dissolution amount of the gas into the kneaded product was exceeded, and bubbles were broken. In Comparative Example 8, since the resin residence time (extrusion condition (2)) was longer than 6 minutes and the pressure of carbon dioxide gas (extrusion condition (3)) was larger than 6 MPa, bubbles were broken in the same manner as in Comparative Example 7. In Comparative Examples 10 and 11, since the resin residence time (extrusion condition (2)) was shorter than 3 minutes and the pressure of carbon dioxide gas (extrusion condition (3)) was larger than 10 MPa, the carbon dioxide gas was not sufficiently dissolved. In Comparative Example 10, the foaming ratio was low, and Comparative Example 11 exceeded the saturated dissolution amount in the kneaded product, and bubbles were broken.
In Comparative Example 12, the temperature of C4 of the extruder (extrusion condition (1) -1) was set to 250 ° C. outside the range of the elastomer melting temperature −5 ° C. or more and the melting temperature + 40 ° C. or less. Became bad.
In Comparative Example 13, the temperature of the head and die attached to the tip of the extruder (extrusion condition (1) -2) was set to 230 ° C. outside the range of the elastomer melting temperature −25 ° C. to melting temperature + 15 ° C. The pressure was low, and the foamed state deteriorated.
In Comparative Example 14, since the residence time (extrusion condition (2)) in the extruder from when the kneaded material was supplied until it was extruded was 12 minutes outside the range of 3 minutes to 6 minutes, the resin deteriorated and did not melt. Bubbles with a large cell diameter of carbon dioxide were generated.
In Comparative Example 15, the taper angle θ of the die is 2 °, which is 5 ° or less, and in Comparative Example 16, the taper angle θ of the die is set to more than 20 ° and 30 °. Was not obtained.

Further, the melt temperature is 200 ° C., the melt viscosity A at 210 ° C. (melt temperature + 10 ° C.) is 2100 Pa · s, the melt viscosity B at 260 ° C. (melt temperature + 60 ° C.) is 1470 Pa · s, and the B / A is 0.7 Using TPEE-a, the temperature of the extruder where the carbon dioxide gas was injected and the temperature of the head and the base attached to the tip of the extruder were changed and extruded.
A SEM photograph of the extruded resin foam is shown in FIG.
As shown in FIG. 4, it was confirmed that the cell diameter was small and the foaming ratio was high when the temperature of the extruder at the carbon dioxide injection site and the temperature of the head / die attached to the tip of the extruder were in the above range. .

Furthermore, using TPEE-a having a B / A of 0.7 as the thermoplastic resin, the temperature of the extruder at the location where carbon dioxide gas is injected is 240 ° C., and the temperature of the head and die attached to the tip of the extruder is 180 °. The temperature was fixed at 0 ° C., and extrusion was performed by changing the screw rotation speed and the carbon dioxide flow rate.
FIG. 5 shows a SEM photograph of the extruded resin foam.
As shown in FIG. 5, it was confirmed that the cell diameter was small and the foaming ratio was high when the screw rotation speed and the carbon dioxide flow rate were in the above ranges.

  From the above results, by injecting carbon dioxide gas at a constant pressure into a thermoplastic resin whose melt viscosity is low in temperature dependence, keeping the extruder, head and die at a constant temperature, and setting a constant kneaded material residence time. It was confirmed that a resin foam having a small cell diameter and a high expansion ratio can be produced.

It is a diagram which shows the correlation with the temperature and melt viscosity of the thermoplastic elastomer used by this invention. It is the schematic of the extruder used for the manufacturing method of this invention. The nozzle | cap | die used for the manufacturing method of this invention is shown, (A) is sectional drawing, (B) is a front view. It is a figure which shows the foaming state of the foam by the temperature change of an extruder. It is a figure which shows the foaming state of the foam by a screw rotation speed and a carbon dioxide gas flow rate change. (A) (B) is sectional drawing which shows the exit shape of the nozzle | cap | die of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Extruder 10a Conveying space 10b Outlet 10c Carbon dioxide injection port 11 Hopper 12 Base 12a Land part 12b Outlet opening 12c Tapered outlet 20 High pressure gas supply apparatus 21 Head

Claims (6)

A kneaded product of an ester-based thermoplastic elastomer having a melt temperature B + B (B / A) of 0.1 to less than 1 with respect to a melt temperature + 10 ° C. melt viscosity A is put into an extruder and extruded. During the process, carbon dioxide gas of 6 MPa or more and 10 MPa or less is injected to dissolve the kneaded product,
The temperature of the carbon dioxide gas injection site of the extruder is set to −5 ° C. to + 40 ° C. of the melting temperature of the thermoplastic resin,
The residence time of the kneaded material in the extruder from the time when the thermoplastic resin kneaded material is introduced into the cylinder of the extruder to the time when it is extruded from the outlet is 3 minutes to 6 minutes,
The base attached to the tip of the extruder via a head is a tapered outlet having a diameter reduced toward the outlet opening, and the taper angle θ of the tapered outlet is 5 ° ≦ θ ≦ 20 ° with respect to the central axis of the outlet portion. And range
The temperature of the head and the base is set to a melting temperature of the thermoplastic resin of −25 ° C. or higher and a melting temperature of + 15 ° C. or lower,
The resin pressure is suddenly raised before the outlet opening of the die, and bubbles are generated by a sudden pressure drop when the gas dispersed and dissolved in the kneaded product is pushed out from the outlet. A method for producing a resin foam.   2. The method for producing a resin foam according to claim 1, wherein the resin pressure is increased by 240% to 330% before the outlet opening of the die with respect to the resin pressure at the time of plasticizing the kneaded material in the cylinder. The ester-based thermoplastic elastomer comprises a polyester based thermoplastic elastomer, chemical foaming agent method for producing a resin foam according to the foam and to that claim 1 or claim 2 in just extruded gas foaming was not added.   The method for producing a resin foam according to any one of claims 1 to 3, wherein bubbles generated by the extrusion gas foaming have an average of 200 µm or less and a foaming ratio of 2 or more.   The resin foam manufactured by the method of any one of Claim 1 thru | or 4.   A paper sheet multi-feed preventing member formed of the resin foam according to claim 5.