JP2656821B2 - Method for producing extruded foam having non-crosslinked polyolefin resin small-diameter cell structure and obtained foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a non-crosslinked foamable polyolefin-based resin which is melt-extruded and foamed in a non-crosslinked state to obtain a foam. The present invention relates to a method for producing an extruded foam having a small-diameter cell structure of a polyolefin resin having a cell diameter of not more than mm, and an extruded foam having a small-diameter cell structure of a polyolefin resin having a cell diameter of not more than 0.5 mm obtained by a non-crosslinking extrusion foaming method.

(Prior art)

A method for obtaining an extruded foam having a small-diameter cellular structure of a polyolefin resin has conventionally been disclosed in Japanese Patent Publication Nos.
It is limited to the method described in JP-A-29381. This method is essentially a chemical crosslinking agent, a crosslinking aid,
And the chemical foaming agent are mixed in advance and melt extruded at a temperature equal to or lower than the decomposition temperature of the chemical crosslinking agent or chemical foaming agent while maintaining the state of non-crosslinking and non-foaming. Mold into Then, the resin is first crosslinked by heating to the decomposition temperature of the chemical crosslinking agent, and then foamed at the decomposition temperature of the chemical foaming agent to form a foamed molded article. The advantage of this method is that, by crosslinking the resin, the foaming suitability of the resin is increased, and it is easy to suppress the formation of voids in the foam core where unevenness in temperature occurs and to suppress the generation of non-uniform bubbles. Therefore, a foam having a relatively large cross section having a cell structure with a small diameter and a uniform diameter distribution can be stably obtained. In other words, despite the inconvenience of the process becoming intermittent through stages, the large cross-section and small diameter of the polyolefin resin can be easily obtained due to the advantage of easily obtaining a high-quality foam that cannot be obtained by the non-crosslinking extrusion foaming technology. It is still used today as the only manufacturing method to obtain a foam having a cellular structure.

On the other hand, foams having a small-diameter cellular structure of a polyolefin resin are widely used for heat insulating materials, cushioning materials, floating materials, pad materials, and the like. However, recently, small items such as small tools, stationery, makeup tools, kitchen tools, etc.
There are many remarkable developments in display and sales products that put this in a storage case. The foam here is a fixing material of the storage target item (that is, a foam having a depression along the outer shape of the storage target item is
In which the storage item is fixed by inserting the storage item into the hollow of the storage case]. The foam as a fixing material inside the storage case is required to have sufficient elastic recovery properties while being flexible, and also to have a smooth surface appearance for making the stored product look good.

Heretofore, this requirement has been met by employing a foam having a uniform small cell diameter by the above-mentioned cross-linking foaming. Originally, crosslinked foams had the disadvantage of having a bad smell (it is said to be the smell of the residue of the crosslinking agent and the foaming agent). When the quality of the storage items in the case of "I don't want a bad smell" increased, as a result, the strong disadvantageous side of the smell was emphasized, and the polyolefin resin was foamed again in a non-crosslinked state,
The need to complete a foam with a small cell structure has arisen.

[Problems to be solved by the invention]

However, in extrusion foaming in which a polyolefin-based resin is foamed in a non-crosslinked state and a foam having a small diameter and a uniform cell structure is continuously obtained, for example, the cross-sectional area is less than 20 cm ² (thickness is less than 15 mm). Apart from experimental extrusion foaming, foams with a large cross-section area of at least 50 cm ² (thickness of 20 mm or more) and high foaming state (expansion ratio of 15 times or more) should be corrugated (irregularities due to waving). Phenomena), voids (cavities), large variations in cell diameter, and easy formation of foams with directional characteristic values. There has been a problem that a high-quality non-crosslinked polyolefin-based resin foam having a small-diameter cell structure having practicality such as being possible does not exist.

Thus, an object of the present invention is to provide a large cross-sectional area having a cross-sectional area of 50 cm ² or more (thickness of 20 mm or more) in a high foaming state [foaming ratio
Foam), which is not a corrugated phenomenon or a void phenomenon, but has a characteristic value with a uniform cell diameter and non-directionality. It is an object of the present invention to complete a method for producing an extruded foam, and thereby to provide an extruded foam having a high-quality and novel non-crosslinked polyolefin-based resin small-diameter cellular structure as described above.

[Means for solving the problem]

The main point in the production method of completing the novel extruded foam having a small-diameter cell structure of the present invention is as follows. First, a non-crosslinked foamable polyolefin resin is melt-extruded and foamed in a non-crosslinked state to obtain a foam. In the method for producing an extruded foam, the foamable polyolefin resin melt-extruded through a die into a low-temperature and low-pressure foaming region is in contact with a polyolefin resin as a base material and a foaming agent and thereafter until extruded. Between, at least 20 minutes to be placed in a closed system under high temperature and high pressure, the extrusion shear rate when melt extruding the foamable polyolefin resin into the low temperature and low pressure foaming region is 500 / The foaming of the foamed resin extruded as described above is in a state of natural foaming, and the “foaming angle” indicating the rate of expansion in the width direction of the extruded resin that expands due to the growth of bubbles in the resin. It should be less than 45 degrees.

As a result, a high-quality “extruded foam having a small-diameter cell structure of a non-crosslinked polyolefin resin having an average cell diameter of 0.5 mm or less” could be easily prepared.
The features of this extruded foam are: a) a non-crosslinked polyolefin resin; b) a large cross-sectional area of 50 cm ² or more (thickness of 20 mm or more); Pm is the average diameter measured in the extrusion direction of
m, when the average diameter measured in the thickness direction of the foam is Vmm and the average diameter measured in the width direction of the foam is Hmm, (P + H + V) ÷ 3 = 0.5 mm or less P: H: V = 1: 0.8 -1.2: An extruded foam having a small diameter cell structure of a non-crosslinked polyolefin resin having a cell diameter and cell shape of 0.8 to 1.2.

 Hereinafter, the contents of the present invention will be described in detail with reference to the drawings and the like.

FIG. 1 is a conceptual diagram showing a production process convenient for a method for producing an extruded foam having a small-diameter cellular structure of a non-crosslinked polyolefin resin of the present invention. In FIG. 1, a polyolefin-based resin supplied from a hopper 1 and melted by an extruder 2 is blown into a blowing agent (volatile foaming) which is metered and injected from a blowing agent supply port 4 drilled at the center rear of the extruder 2. Agent) supply,
The mixture is kneaded and transferred by the screw 3 to be a non-crosslinked foamable polyolefin resin containing a certain amount of a foaming agent. The subsequent kneading and temperature control tank 5 is where the above-mentioned foamable polyolefin-based resin is further kneaded and temperature controlled.
The side has a temperature gradient in which the temperature is high and the temperature is controlled so as to become the foaming temperature as it approaches the extrusion die 7 side. This kneading
The temperature is controlled by the action of a group of stationary rods 8 having a streamlined cross section, each of which is provided with a circulating device 6 capable of controlling the temperature in a closed system tank 5. That is, the resin is kneaded in a process in which the resin flow repeats distribution and integration between the standing rods 8, and the resin is adjusted to a desired temperature by contacting the surface of the rod 8 or the inner surface of the tank 5. You.

Thereafter, the expandable polyolefin-based resin is guided by a conduit 10, extruded in a molten state from an extrusion die 7 into a low-temperature and low-pressure foaming region (generally a region under normal temperature atmosphere) in a non-crosslinked state, foams, and is almost free foaming. Under the conditions, it forms into a foam. At this time, the growth of the bubbles is completed immediately after the extrusion die 7 and between the foaming end point X1 and the foam is solidified. The completed foam is carried out by the conveyor 11.

In the method for producing an extruded foam obtained by melt-extruding a foamable polyolefin-based resin and foaming it in a non-crosslinked state to obtain a foam, which is performed using the apparatus shown in FIG. `` The foamable polyolefin-based resin melt-extruded into a low-temperature and low-pressure foaming region via a die is in contact with the base material polyolefin-based resin and the foaming agent until it is extruded. The need to "place in a sealed system under high temperature and high pressure" is necessary to eliminate the void phenomenon and obtain a foam having a uniform cell size distribution.

Although this phenomenon is still unclear, the requirement is, in the case of the apparatus shown in FIG. 1 described above, "the foaming agent supply port 4 pierced behind the center of the extruder 2" and the "extrusion die 7". The emphasis is on the length of the journey, that is, how long the resin containing the foaming agent will remain in the sealed system under high temperature and pressure. The present inventors, at first thought that this phenomenon is in the mixing accuracy of the mixer, repeated experiments, but found that the thing of the standing time after mixing is much larger than the contribution rate of the mixing accuracy, It has come to be considered that "uniform dispersion of the foaming agent by dissolution in the resin" and "micro-uniformity of the resin temperature" are the main factors. Actually, a non-homogeneous bubble diameter distribution occurs and the "time to be placed"
When it is desired to extend the length, a sufficient homogenization effect can be obtained simply by extending the length of the conduit 10 whose temperature is controlled and maintained. The amount of time that can be left depends on the extrusion capacity and the type of foaming agent, but it has been set for 40 to 10 minutes.

Next, the constitutional requirements of the present invention, that is, the necessity of `` an extrusion shear rate of 500 / sec or more when the melt-extrusion of the foamable polyolefin resin into a low-temperature and low-pressure region '' is necessary, is that the diameter of the generated bubbles is small. It is to place a foamable resin system on the side of the conditions that are met.

When this process is captured, FIG. 2 shows the extrusion shear rate on the horizontal axis and the cell diameter on the vertical axis, and shows the "shear rate" and "the resulting cell diameter" of a certain foaming resin under specific foaming conditions. It is an experimental result figure which put together the relationship of "." The solid line shows the case of 30-fold foaming, and the broken line shows the case of 15-fold foaming.

As shown in the experimental results of FIG. 2, the value of the "extrusion shear rate" defined by the relationship between the area of the opening of the extrusion die and the amount of the foamable resin passing therethrough per unit time is as follows. It can be seen that the larger the size, the smaller the bubble diameter. The constitutional requirements of the present invention make use of this principle as it is, and “the extrusion shear rate is set to 500 / sec or more” is to facilitate uniformity of the cell diameter to 0.5 mm or less. Assuming continuous extrusion, an increase in the extrusion shear rate generally leads to an increase in the size of the extrusion apparatus, which is uneconomical.
Since the extrusion shear rate in ordinary extrusion foaming is about 250 / sec, but in the present application, it is "increased to 500 / sec or more", it is desirable to naturally keep the upper limit at about 2500 / sec.

And the constituent element of the invention of the manufacturing method of the present application, namely, "the foaming of the extruded foamable resin is in a state of natural foaming, and the rate of expansion in the width direction of the extruded resin which expands by the growth of bubbles in the resin is determined. Reduce the "foaming angle" shown to 45 degrees or less "
The importance of this is to obtain a large cross-section foam without corrugation.

FIG. 3 is a diagram showing the "foaming angle" in the present invention and the principle of occurrence of the corrugation phenomenon considered by the present inventors. The "foaming angle" referred to in the present invention in FIG. 3 will be described first in the case of normal foaming. The foamable polyolefin resin melt-extruded through a die 7 into a low-temperature and low-pressure foaming region is a resin within the resin. Are expanded by the growth of the bubbles, but the growth and expansion are stopped by the cooling and solidification that proceeds at the same time. This time point is the maximum width YY of the foam at the foaming end point X1. In this case, the foaming spreads greatly in the width direction at a relatively short distance between the die surface 7 'and the foaming end point X1. The ratio of this spread is determined by the angle Q1 (which is defined by the maximum foam width Y line and the straight line P1 when the end of the opening on the die surface and the maximum foam width Y at the foaming end point X1 are connected by a straight line P). Foaming angle). Similarly, in the present invention, when the foaming end point is set to the rear X2 and the distance from the die surface 7 'is increased,
The spreading ratio in the width direction becomes gentle, that is, the foaming angle becomes small as Q2.

Therefore, in FIG. 3, in the case of obtaining a foam having the same maximum width YY, when the foam angle is different from Q1 and Q2, the original flow velocity of the resin in the foam width direction is considered and modeled. When viewed, it can be shown as two sets of arrows, a solid line and a broken line. In other words, the decrease in the resin flow velocity at both ends in the width direction with respect to the center portion of the foam is larger in the case of Q1 which largely spreads in the width direction than in the case of Q2 which spreads gently. That is, the difference in the flow velocity of the resin should be large accordingly. In this case, if the foam has a single flow rate as a unitary one, it becomes a flow in a form such that the flow at the center pulls the resin at both ends, the foam grows twitching, and the foam becomes uneven, The so-called corrugation phenomenon occurs. Moreover, in order to correct this, the method of adjusting the resin flow that forcibly passes through a predetermined space or pulls the other by applying resistance to the local part has little corrugation prevention effect and gives distortion to bubble growth, There is a problem in that a foam having a directional bubble shape is formed.

On the other hand, according to the method of the present invention in which the “foaming angle” is reduced to Q2, the corrugation phenomenon does not occur because the flow rates of the resin at the central portion and at both end portions can be made relatively equal. Moreover, since the foaming by the method of the present invention is so-called "free foaming" in which no resistance or traction is applied to the bubble growth, there is an advantage that a foam having a non-directionally shaped bubble can be formed.

Adjustment of the foaming angle in the present invention is performed mainly by adjusting the relationship between the type of the foaming agent and the foaming temperature and the amount of the nucleating agent in addition to the length of the land of the die and the take-up speed. However, the knowledge of this place
Due to the fact that the extrusion shear rate is higher than the conventional level and the mixing accuracy of the employed mixers is not the same, the conventional experience cannot be directly employed.
Therefore, some preliminary experiments are required, but in this case, it is important to select a foaming agent with a relatively large value of the rate of escape from the resin, and to increase the amount of the large number of these "dissolution dispersion".
Disperse the resin up to the stage. And the foaming of this thing is extruded at a low foaming temperature in the presence of a large amount of nucleating agent,
Keep in mind that it is foamed. As an example of the foaming agent to be used, a volatile organic foaming agent having a boiling point below the melting point of the base resin is used. Specifically, for example, trichlorofluoromethane (F11), dichlorodifluoromethane (F12), dichlorofluoromethane (F21), chlorodifluoromethane (F22), trichlorotrifluoroethane (F113), 1,2 dichlorotetrafluoroethane (F
114), 1, chloropentafluoroethane (F115), 1, chloro1,1 difluoroethane (F142b), propane, butane, pentane and the like. These are used alone or in a mixed state. The addition amount is selected from the range of 5 to 45% by weight based on the amount of the resin, depending on the target density of the foam. In order to obtain a high foam having an expansion ratio of 15 times or more as referred to in the present invention, it is desirable to use an eye blowing agent having a wide range of 9.5 to 40% by weight.

Conventionally known nucleating agents, for example, fine powders of inorganic solids such as talc, clay and silica, sodium bicarbonate, sodium carbonate and carbonate or bicarbonate such as potassium bicarbonate can be used. On the other hand, it is selected from the range of 0.05 to 5% by weight in relation to the type of the nucleating agent used and the target foam.

 The foam obtained by the above-mentioned method of the present invention is a) a non-crosslinked polyolefin resin foam.

B) The cross-sectional area is 50cm ² or more (thickness is 20mm or more and large).

C) The average bubble diameter is equal to or less than 0.5 mm, and the shape of the bubble is small [P: H: V = 1:
0.8 to 1.2: 0.8 to 1.2].

D) An extruded foam having a small diameter cell structure.

There is a feature in saying. Such a foam of the present invention is a novel foam which has been craved for a long time and its completion has not been seen, and is a foam having utility at least as a substitute for a crosslinked polyolefin resin foam. For example, in the case of use as a fixing material for storage cases, non-crosslinking eliminates the “smell smell”, and the non-directional (close to true sphere) bubble shape matches the outer shape of the storage item. In addition to preventing "scratching" and "fluffing" of the cutting surface when drilling, there is an advantage that it exhibits beautifulness in combination with the uniform gloss of the surface of the small air bubbles and increases the value as a fixing material .

The polyolefin resin used in the present invention is, for example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ionomer, polybutene and the like. These may be used alone or in a mixture of two or more. Among them, it is most preferable to use an ethylene resin having a density range such as HD, LD, LL, and VL, which is generally referred to as polyethylene.

 The evaluation method according to the present invention is as follows.

◎ Method of measuring cell diameter (grit line method) From a predetermined location of the target foam, cut out the foam into a thin strip having a length of at least 30 mm in the direction of the cell to be measured. This is enlarged and projected to form a bubble photograph, and one inch (25.4m) is drawn on the photograph along the direction of the bubble diameter to be measured.
m) Draw a straight line (grid line) of the length, read the number (n) of bubbles in contact with this straight line, and calculate the bubble diameter by the following formula.

Cell diameter (mm) = 1.623 × (25.4 ÷ n) ◎ Cell diameter fluctuation The cell diameter fluctuation in the cross section perpendicular to the extrusion direction of the foam, from the center of the cross section of the foam in the width direction and from the width end. The cell diameter in the PVH direction is determined by the grit line method for a total of three points at each point inside 30 mm, and the cell diameter at the center: the cell diameter at the end = 1: 0.8 to 1.2 Will be ".

◎ Existence of voids Confirmation of the occurrence of large cavities inside the foam (some of the bubbles are connected together) created 50 arbitrary cross sections perpendicular to the longitudinal direction of the foam, and cavities in the cross section Judgment by the presence or absence of. At this time, the lower limit of the cavity size was set to be twice or more the average cell of the foam.

〔Example〕

Example 1 and Comparative Example 1 The practicality of the production method of the present invention is demonstrated using the production apparatus shown in FIG.

A mixture obtained by mixing 1 part by weight of talc (nucleating agent) with 100 parts by weight of low-density polyethylene [trade name; Suntech (manufactured by Asahi Kasei Corporation), density 0.921, MI 2.5]
Into the extruder 2, and heat and melt at about 200 ° C. while kneading and transferring with the screw 3.
4) is injected and kneaded at a ratio of 9.5 parts per 100 parts by weight of the resin to obtain a foamable resin composition. This composition is kneaded
It is further kneaded in the temperature control tank 5 and cooled to about 120 ° C.
It is cooled down to 108 ° C. in a conduit 10 and extruded and foamed from a die having slit-shaped orifices (H, W, L = 5,180, 10 mm) at room temperature in the atmosphere at a shear rate of 860 / sec. At this time, the foaming angle was adjusted to be equal to 35 degrees, the foaming was completed in a free state, and the obtained foam was transferred by the conveyor 11.

In this case, the point to be noticed is to adjust the length of the conduit 10 and set the "time from contact between the resin and the foaming agent to extruding" to 20, 30, 45, 60 minutes and 16 minutes. The obtained foams were given experiments No. 1.2.3.4 and No. 5 in order, and the state of each foam was observed. The results are shown in Table 1.

According to the results in Table 1, the production method of the present invention represented by Experiment No.
67kg / m ³ , bubble diameter of about 0.32mm, cross-sectional area of 318cm ² level, no voids, foam with small cell diameter variation and small cell shape distortion. It is confirmed that it can be done. On the other hand, in the conventional production method, that is, when the “time from contacting the resin and the foaming agent to extruding” is less than 20 minutes (Experiment No. 5, 16 minutes), voids were generated. It can be seen that only a foam having a large cell diameter variation and a large cell shape distortion can be obtained.

Example 2 and Comparative Example 2 In order to demonstrate the utility of the production method of the present invention, the extruding shear rate was changed to four levels of 500 / sec, 950 / sec, 1820 / sec, and 2450 / sec, and the obtained foam was obtained. The body was numbered Experiment No. 6.7.8.9 in sequence. Experiment No. 1 with a shear rate of 390 / sec for comparison
It was attached as 0. The experimental conditions in this case are:
The other components, "the time from contacting the resin and the foaming agent to the extrusion," are adjusted to 30 minutes, and the "foaming angle" is adjusted to be close to 35 degrees. 67kg body density
The method of Example 1 was repeated, with the condition that the adjustment was made to approximate the level of / m ³ , and the state of the obtained foam was observed. The results are shown in FIG.

According to the results in Table 2, the production method of the present invention represented by the experiment, No. 6.7.8.9, shows that both the obtained foams have a cell diameter of 0.
It is confirmed that a foam having a cross-sectional area of not more than 5 mm and a cross-sectional area of not less than 300 cm ² and having no voids, a small variation in cell diameter, and a small distortion in cell shape can be produced for the purpose of the present invention. On the other hand, the comparative manufacturing method,
The foam with less than 500 / sec (Experiment No.10, 390 / sec) is difficult to keep the bubble diameter level below 0.5mm, and the foam with large variation of bubble diameter and large distortion of bubble shape It is clear that

Example 3 and Comparative Example 3 In demonstrating the practicality of the production method of the present invention, an experiment was conducted with a view to the importance of making the “foaming angle” 45 degrees or less. That is, the land length of the orifice was adjusted in the range of 10 mm to 3 mm and the "foaming angle" was changed to three levels of 45, 35 and 31 degrees, and the conventional method was used for comparison with a foaming angle of 51 degrees. . As experimental conditions in this case, the other components, "the time from contact of the resin and the foaming agent to the extrusion," were 30 minutes, and the "shear rate" of the extrusion was 950. / Sec, and the method of Example 1 was repeated under the condition that the foam density was adjusted to a level of 67 kg / m ³ and the cell diameter was adjusted to a level of 0.32 mm. The obtained foams were given Experiment Nos. 11.12.13. And 14 (comparative products) in order,
Table 3 summarizes the observation results of the foaming state.

According to the results in Table 3, the method of the comparison (Experiment No. 14) has a remarkable occurrence of the "corrugation phenomenon" and cannot be formed into a foam having a target cross-sectional shape. On the other hand, in the case of the production method of the present invention represented by Experiment No. 11.12.13, the occurrence of the "corrugation phenomenon" was completely suppressed, and as a result, It is confirmed that a foam having a diameter of 0.32 mm and a cross-sectional area of 300 cm ² or more, and having no voids, a small variation in cell diameter, and a small distortion in cell shape can be produced for the purpose of the present application.

Example 4 Here, according to the production method of the present invention, it is demonstrated that the level of the density of the foam can be easily changed and adjusted and the practicability of the production can be demonstrated.

That is, the components of the foamable resin composition were measured in Experiment No. 15.
Modified as described in 16.17, the other main matter, "the time from contacting the resin with the foaming agent until extrusion" is
In 30 minutes, the extrusion "shear rate" was fixed at 1300 / sec, and the "foaming angle" was fixed at a level of 36 degrees, and the method of Example 1 was repeated. I put together on the table.

According to the results in Table 4, according to the production method of the present invention,
Foams with a density of at least 80 to 18 kg / m ³ (expansion ratio = 12 to 50) completely suppress the occurrence of the "corrugation phenomenon". In this state, the bubble diameter reaches a level of 0.30 mm, and the cross-sectional area is 300 c.
It is confirmed that a foam that meets the object of the present invention can be produced, which maintains the level of m ² or more, has no voids, and has small variation in cell diameter and small distortion in cell shape.

These three types of foams were cut together with the foam of Experiment No. 10 (comparative product) using a slitter equipped with a circular saw blade. The results are summarized in Table 5.

According to the results in Table 5, the foam of Experiment No. 15.16.17 (product of the present invention) having no voids and having a small variation in cell diameter and a small cell shape distortion has excellent cutting workability and has a good " It was a beautiful foam with a smooth surface without any collapse of bubbles, no swelling and no fluffing, and it was confirmed that the foam was highly aesthetic. In contrast, the foam of Experiment No. 10 (comparative product) had a “crushed” The “bubbled shape” was scattered, and “sasakare” and “fuzz” were conspicuous, and the aesthetic appearance of the surface layer was impaired.

〔The invention's effect〕

According to the present invention having the above-described structure, the "extruded foam having a large cross-sectional area of a small cell structure", which has not been completed by extrusion foaming of a conventional polyolefin resin in a non-crosslinked state, i.e. It is made of a non-crosslinked polyolefin resin foam. B) Its cross-sectional area is as large as 50 cm ² or more (thickness of 20 mm or more). C) The average cell diameter is equal to or less than 0.5 mm. Bubbles with small distortion [P: H: V = 1:
0.8-1.2: 0.8-1.2] d) Extruded foam having a small diameter cell structure.

Has a great effect that it can be manufactured easily and economically continuously for the first time.

Moreover, since this foam is in a non-crosslinked state, it has an “odor”
Since it is excellent in aesthetics and cutting workability by having small bubbles and small bubble shape distortion, it is extremely useful as a non-crosslinked polyolefin resin foam which has long been sought for, for example, as a fixing material inside a storage case. Things.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an extrusion foaming apparatus useful for the production method of the present invention, and FIG. 2.3 is an explanatory view of experimental results. [Symbol explanation] 1; hopper, 2; extruder, 3; screw, 4; foaming agent supply port, 5; kneading / temperature control tank, 6, 9; circulation device, 7; extrusion die,
7 '; die surface 8 as stationary rod, 10; conduit 11; conveyor, 12; foam, Q; foaming angle, X ₁ .X _2; foam end point

Claims (2)

(57) [Claims] 1. A method for producing an extruded foam in which a non-crosslinked foamable polyolefin-based resin is melt-extruded and foamed in a non-crosslinked state to obtain a foam, comprising: The foamable polyolefin-based resin to be placed in a closed system under high temperature and pressure for at least 20 minutes from the time when the base material polyolefin-based resin and the foaming agent are brought into contact and before being extruded. The extrusion shear rate when melt-extruding the foamable polyolefin-based resin into a low-temperature and low-pressure foaming region should be 500 / sec or more. The foaming of the foamable resin extruded is in a state of natural foaming. The `` foaming angle '', which indicates the rate of expansion in the width direction of the extruded resin that expands due to the growth of bubbles in the resin, is set to 45 degrees or less, and the average bubble diameter is 0.5 mm or less. There is nothing Method of manufacturing a small-diameter cell structure extruded foam bridge polyolefin resin 2. An extruded foam having a small-diameter cell structure, which is a polyolefin resin, comprising: (a) a cross-linked polyolefin resin having a cross-sectional area of 50 cm ² or more (thickness of 20 mm or more); (C) The bubble has an average diameter measured in the direction of extrusion of the foam.
When Pmm, the average diameter measured in the thickness direction of the foam is Vmm, and the average diameter measured in the width direction of the foam is Hmm, (P + H + V) ÷ 3 = 0.5 mm or less P: H: V = 1: 0.8 ~ 1.2: Extruded foam having a small diameter cell structure of non-crosslinked polyolefin resin characterized by having a cell diameter and cell shape of 0.8 to 1.2.