JPS58224727A - Manufacture of foamed object - Google Patents

Abstract

PURPOSE:To obtain the foamed object having the foaming ratio of more than three times, by supplying the permixed polyolefine pellet, chemical foaming agent powder and polyolefine powder dispersant to a molder, melting and mixing there, then making the foaming agent decompose and lowering a temperature, extruding it. CONSTITUTION:After premixing the foaming material composed mainly of a polyolefine pellet, chemical foaming agent powders {the use of two kinds having different thermal decomposition temperatures is preferable, e.g., a 4,4'-oxybis (benzene sulfonyl hydrazide) and an azodicarbonamide} and a polyolefine powder dispersant (the powder of the same polyolefine as the pellet) it is supplied to a molder and melted, mixed there, then its temperature is raised above the thermal decomposition temperature of the chemical foaming agent, then lowered and it is extruded from a die. The total amount of the foaming agent and the dispersant is preferably 1.1-10wt% of the pellet, the foaming agent is preferably more then 1.0wt% and the dispersant is preferably 0.1-1.0pt.wt. of the foaming agent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel manufacturing method for foaming polyolefin at a foaming ratio of 3 times or more using a chemical foaming agent. In particular, the present invention relates to a foam molding method for obtaining a highly foamed body, which has been impossible with conventional methods using chemical foaming agents (hereinafter simply referred to as chemical foaming method).

In the conventional method for producing polyolefin foam using the chemical foaming method, first, a chemical blowing agent (e.g., azo-dicarbonamide) is uniformly kneaded into polyolefin (e.g., polyethylene) using a mixer (e.g., an extruder for granulation). Then, pelletized non-foamed pellets are produced. Next, this pellet is heated with a foam manufacturing device (e.g. extruder),
After the blowing agent is thermally decomposed, it is extruded to obtain a foam.

However, with this conventional method, the foaming ratio increased only by about 2 times to 1, and it was not possible to obtain a high quality foamed product of 6 times or more. There are various possible reasons for this, but perhaps the biggest reason is that the foaming material and its processing conditions were inappropriately selected. For example, conventionally commercially available foaming polyolefins include those made by kneading low-density polyethylene with a chemical blowing agent [DFD 4960 (Western product name) manufactured by Union Carbide Co., Ltd., etc.]; It is thought that because only one type of each chemical blowing agent was used, it was difficult to balance the melt viscosity of the low density polyethylene and the thermal decomposition temperature of the chemical blowing agent, and the expansion ratio was not sufficiently increased.

Conventional methods still require a foaming material in which a blowing agent is uniformly kneaded into polyolefin, and as labor costs have soared in recent years, the cost of mixing has become comparable to the unit cost of raw materials. Regardless of whether they produced their own products or purchased them from other companies, they were expensive. We also adjust the formulation of foaming materials to suit various situations.
In particular, it often happens that it is desired to change the amount of blowing agent, but in this case it is not easy to manufacture kneaded pellets with a new formulation, and as mentioned above, it is expensive.

On the other hand, with the conventional chemical foaming method, it is not possible to obtain a foam with a foaming ratio of 6 times or more, but as a method to produce a highly foamed product with a foaming ratio of 5 times or more, there is a method using a physical foaming agent (hereinafter abbreviated as the physical foaming method). ) and polyolefin are crosslinked and then foamed (
Hereinafter, the cross-linking foaming method is well known, but each method has the following drawbacks.

Since the physical foaming method uses liquefied gases such as hydrocarbons and halogenated hydrocarbons as blowing agents, it is necessary to be careful about their flammability and explosiveness, and also to consider their effects on the human body. Mixing the foaming agent with the polyolefin still requires special equipment, such as a liquid injection pump system or a liquid injection extruder, and the physical foaming method cannot be used with general molding machines.

In the crosslinking and foaming method, the problem before foaming is that it is difficult to crosslink the polyolefin.

For example, electron beam irradiation and a peroxide catalyst are required, and if the degree of crosslinking varies, the degree of foaming will vary, so controlling the degree of foaming is not easy.

As mentioned above, it is not possible to obtain a high-quality, high-quality foam with a foaming ratio of 6 times or more using conventional chemical foaming methods.Although there are alternative methods for obtaining high-quality foams, such as the physical foaming method and the crosslinking foaming method, Both methods require special processes and equipment, which poses problems in terms of productivity and cost. Therefore, there has been a long-awaited development of a technology that can easily produce highly foamed products by improving the conventional chemical foaming method.

The present invention relates to a method for easily producing a highly foamed product of 6 times or more foaming, which could not be produced using conventional methods, by improving the problems of conventional chemical foaming methods.

In other words, foaming materials mainly consisting of polyolefin, chemical blowing agents, and dispersants are premixed in a tumbler or continuous mixer, then fed to a molding machine, melted and mixed in the molding machine, and then mixed with chemical blowing agents. This is a method for producing a foam with an expansion ratio of 6 times or more directly from a premixed composition for foaming, which is characterized by raising the temperature to a temperature higher than the thermal decomposition temperature, then lowering the temperature, and extruding it from a die of a molding machine. It also discloses important manufacturing conditions for producing high-quality, high-quality foams that can be put to practical use.

Characteristics The first object of the present invention is to easily produce a foam with a foaming ratio of 6 times or more, which was impossible with conventional chemical foaming methods. To that end, the characteristic means and effects of the present invention will be described below.

(1) In the present invention, a foaming material consisting mainly of polyolefin pellets, a chemical blowing agent, and a polyolefin dispersant powder is immediately supplied in a premixed state to a molding machine for producing a foam.

In the conventional chemical foaming method, as mentioned above, the foaming materials are generally kneaded in advance in a kneader or the like to produce pellets, and then fed to a molding machine for foam production. In order to obtain a high-quality foam, it was considered extremely important to uniformly knead and mix the blowing agent into the polyolefin in advance.

However, according to the study results of the present inventors, when producing a highly foamed product of 3 times or more, it is better to mix the foaming materials uniformly, but only at a premix level, and to directly mix the foaming materials into the foaming molding material. It was unexpectedly discovered that it is better to feed the foam to a machine and allow it to foam. For example, compared to the conventional method of extruding a foaming resin uniformly mixed with a chemical blowing agent at the extrusion rate, the degree of foaming is significantly more stable, the foaming state does not change even if the extrusion speed is changed, and the extrusion rate also increases. It was found to be stable. The reason for this may be that the method of the present invention (premixing) is less affected by shear in the extruder than in the case of kneading, but in any case, based on conventional common sense, is a completely unexpected fact. As a result, it is not only possible to produce a highly foamed body, but also the method for producing the foaming material is simplified, which dramatically improves productivity and reduces costs. In addition, in terms of material formulation, there are many advantages such as the ability to easily change the formulation to suit the situation depending on the finished state of the foam product, and the ability to quickly take measures against defects.

(2) When polyolefins used in the present invention are used in combination with polyolefins having different thermal properties such as at least melting points, a good highly foamed product can be obtained. For example, low density polyethylene (LDPE)
) High-density polyethylene (HDPE).

It is preferable to use polypropylene (PPr) or polystyrene in combination with polyethylene.

Conventional commercially available products include Union Carbide's DFD.
4960 uses a single piece of low-density polyethylene, and it was thought that a single piece of polyethylene was more preferable, especially in order to obtain a foam with a uniform cell diameter.

However, in order to produce a highly foamed product that could not be obtained conventionally, as in the present invention, it is preferable to use different materials, such as those with different melting points, bath melt viscosity, die swell properties, etc. The results were unexpected.

With conventional foaming technology, HDPK is preferred over LDPK.

PPr had a higher foaming ability. However, it was completely unexpected that by blending this resin, which is difficult to achieve high foaming, with LDPK, high foaming could be easily achieved.

(3) Conventionally, commercially available chemical blowing agents have been used, but in this case as well, optimal results can be obtained by combining agents with different thermal properties such as thermal decomposition temperature.

Example Id 4.4'-oxy-bis-benzene-sulfonyl hydrazide (thermal decomposition temperature: about 150°C) and azo-dicarbonamide (thermal decomposition temperature: about 200°C) are used together, or the thermal decomposition reaction is Use a combination of exothermic types such as heavy duty and endothermic types (such as bicarbonate of soda).

Conventional commercially available products generally use a single chemical blowing agent, and now a single polyolefin, which is the base of the foam, is also used. Therefore, the optimal foam molding conditions (temperature) are limited mainly by two points: the melting point of the polyolefin and the thermal decomposition temperature of the chemical blowing agent, so it is usually necessary to take a very narrow range of conditions, and it is necessary to maintain a high quality foam. could not be manufactured.

On the other hand, in the present invention, since a chemical blowing agent, preferably a polyolefin, is also used, the range of foaming conditions can be widened, and as a result, highly foamed products can be easily produced.

(4) In the present invention, it has been found that it is essential to use a dispersant for a foaming agent as a foaming material.

In order to obtain a high foam with a foaming ratio of 3 times or more,
This is because it is necessary to use a large amount of chemical foaming agent, about twice as much as in the conventional chemical foaming method. Particularly in the case of supplying the foaming material directly to the foam molding machine after premixing as in the present invention, it is necessary to premix the chemical foaming agent and polyolefin as uniformly as possible to prevent uneven distribution. Furthermore, since the polyolefin used in the present invention is in the form of pellets and the chemical blowing agent is in the form of powder, especially when blending 2 parts or more to 100 parts by weight of the polyolefin, both can be simply tumbled.
It was found that it was difficult to carry out the premixing process because the pellets and powder separated after mixing, the fluidity of the mixture decreased, and bridging occurred in a part of the hopper of the molding machine. . In the present invention, by using a dispersant that acts as a link between the polyolefin pellets and the blowing agent powder, it is possible to obtain a highly foamable material without separation or bridging phenomenon after premixing. ,
This is an extremely important means for producing high-quality foams with stable quality over a long period of time. As the dispersant, it is particularly preferable to use a powder whose particle size is at least smaller than that of the polyolefin pellets, and it is particularly preferable to use a powder of the same type of polyolefin as the pellets. In addition to powder, the use of a wet dispersant such as an adhesive can also bring about good results, especially when a large amount of chemical blowing agent powder is used. Examples of preferred adhesives include polyisobutylene, polyethylene glycol, silicone oil, and the like.

Regarding these blending ratios, the total amount of chemical blowing agent powder and polyolefin powder as a dispersant is 1.1 to 1.
00% by weight, and chemical blowing agent powder is 1.0% by weight.
As mentioned above, it is preferable to mix powdered polyolefin in an amount of 0.1 part by weight or more, preferably in the range of 0.5 to 10 parts by weight, per 1 part by weight of the blowing agent powder.

As mentioned above, it is preferable to use chemical blowing agents with different thermal decomposition points in combination;
It is particularly preferable that the high temperature decomposable foaming agent is used in an amount of 0.05 to 1 part by weight per 1 part by weight of the low temperature decomposable foaming agent.

(5) As a premixing method for the foaming material of the present invention,
Batch type (tumbler, etc.) or continuous type (static mixer, etc.)
However, a dry mixing method (commonly known as a tri-blend method) is usually particularly preferable than a wet method.

In order to obtain a low-foam product using the conventional chemical foaming method, a chemical blowing agent is uniformly kneaded and dispersed into polyolefin to produce a compound, which is then fed to a foam molding machine and allowed to flow through the foam to produce high-quality foam. It was thought to be important in keeping the body warm. However, in producing a highly foamed product of 3 times or more as in the present invention, the unexpected result was obtained that the triblend method is preferable to the kneading method.

If you are going to use the kneading method, it should be at least up to the level of masterno (tsuchi).

Therefore, according to the present invention, a foaming material can be produced in a very short time and at low cost, which is extremely advantageous in terms of productivity and cost.

In addition, by considering the formulation of foaming materials that cannot be covered due to the performance of the foam molding machine, it is extremely easy to find the optimal formulation for each molding machine and to cover up the unique shortcomings of each molding machine. Ru. Of course, the most important amount of foaming agent in obtaining a highly foamed product is not consumed due to partial decomposition or volatilization during the kneading process, which is the case with conventional kneading methods. There is no variation between lots,
Another great advantage of the present invention is that an expensive blowing agent can be used 100% effectively.

(6) When supplying the foaming material of the present invention to a molding machine, particular care must be taken to prevent uneven distribution of the foaming agent. For this purpose, each foaming material must be continuously fed in a fixed amount and passed through a continuous mixer to form the foam. Most preferably, it is fed into the machine's hopper. The reason for this is that since the present invention uses a tri-blend foaming material, it is not preferable to handle it like when using a conventional kneading pellet, and for example, after batch-type premixing,
It has been found that methods such as air feeding into a hopper cause the problem of separation of the foaming material. Therefore, it is best to feed the foaming material of the present invention to a molding machine through a continuous mixer, but as a second best method, it is possible to mix the material in a batch manner using a tumbler or the like and then foam it in a batch manner. It is also possible to supply it to a molding machine. In any case, in producing a highly foamed product, it is extremely important to feed the premixed foaming material to the foam molding machine without causing compositional changes (unevenness). However, especially when air transport is required and separation of the mixture is a concern, it is highly preferable to use an adhesive or the like as a dispersant.

(Force) In order to produce a highly foamed product from a foaming material in the present invention, the conditions for a foam molding machine are as follows: First, the opening area of the extrusion port is made as small as possible to prevent foaming at least before exiting the extrusion port. It is generally important to extrude under conditions that produce a large die swell.Specifically, when extruding a composition that does not contain a foaming material or foaming agent, it is important to extrude under conditions that produce a large die swell. It is preferable to set extrusion conditions such that the diameter of the extrudate is larger than the diameter of the extrudate, and extrude the composition of the present invention containing the foaming material under the same conditions.

(8) In order to obtain a highly foamed product, an essential requirement for foam molding conditions is how effectively the gas generated during foaming can be used. In order to prevent the blowing agent gas from evaporating from the foam surface during foaming, one requirement of the present invention is to mold the surface at least during foaming. For example, molding is performed while continuously foaming in a cylindrical molding die provided near the extrusion port.

In the conventional chemical foaming method, the amount of blowing agent used is small, so the amount of gas generated during foaming is small, and the viscosity of polyolefin is also high. Therefore, the blowing agent gas efficiently contributes to foaming, so special There was no need for any means to prevent degassing.

However, in the present invention, since it is necessary to use a blowing agent in an amount more than double that of the conventional blowing agent, in addition to the effect of reducing the viscosity of the polyolefin due to the blowing agent itself, the viscosity of the polyolefin is significantly reduced due to the heat generated by thermal decomposition of the blowing agent. Although the generated blowing agent gas foams the polyolefin, it then passes through the polyolefin membrane and scatters into the atmosphere, causing the foam to shrivel and eventually become a low-foam product.

In order to prevent this, it is believed that the most effective way is to cut off the scattering path of the blowing agent gas from the polyolefin, and in the present invention, the surface side of the foam, which makes up the majority of the scattering path (surface), is suppressed by a molding die. It is something. Therefore, in producing a highly foamed product, it is desirable to pass the foam through a molding die while the foam still contains foaming gas and has built-in foaming power.

In the present invention, it has been found that the use of a molding die is indispensable and extremely effective in obtaining a highly foamed product of 6 times or more foaming, especially 4 times or more foaming.

One major feature is that conventional methods for producing highly foamed materials such as cross-linking foaming and physical foaming do not require molding dies at all.

It is easiest to simply use a cylindrical pipe (a pipe whose inner diameter is at least υ smaller than the maximum foamed outer diameter of the foam) as the molding die. However, the maximum foamed outer diameter of the foam is not always constant; for example, when the molding machine starts or finishes working,
Or it changes significantly when work is stopped. Therefore, a molding die with a variable inner diameter that can follow this change is most preferable. In the present invention, one preferable condition is to use a paper wrapper-type expandable sizing die to mold the foam so that a constant resistance is always applied to the surface of the foam.

(9) Setting the temperature conditions of the foam molding machine is also extremely important in achieving high foaming. That is, since the present invention is a chemical foaming method, it is natural to heat the blowing agent to a temperature higher than the thermal decomposition temperature, but if extrusion is continued at the temperature at which the blowing agent is thermally decomposed, a highly foamed product cannot be obtained. This is because the gas generated due to the high temperature is dispersed from within the foam, leaving behind a low foamed material with deflated cells.

One of the requirements of the present invention is to obtain a high-υ foam by extruding it through a die after being thermally decomposed, once cooled to a temperature lower than that of the blowing process, and the purpose of this is to obtain a high-υ foam by extruding it through a die. The purpose is to prevent gas from scattering and to prevent shrinkage after foaming due to the collapse of bubbles. Although the cooling temperature before extrusion depends on the operating conditions, it has been found that when extruding with a general extruder, cooling is preferably 5° C. or higher, preferably 60 to 50° C.

QO) From the viewpoint of effective use of the blowing agent gas, before the foaming agent is extruded from the die and foamed, the surface or inner surface of the foaming agent, preferably the surface and the inner surface, must have at least a gas barrier property better than that of the foam. It is preferable to apply a coating of.

As a result, most of the gas in the foam is used for foaming the polyolefin. One preferred method for producing these gas barrier coatings is to extrude the unfoamed polyolefin through the outlet of a separate extruder connected to the outlet for the foaming material. In addition, when extruding this foam onto a metal base, plastic pipe, etc., the stone and foam layer should be brought into close contact with each other before or during foaming to create a path for degassing at the interface between the two. It is extremely important not to let this happen. To prevent this, it is effective to provide an adhesive layer with the foam layer on the core material in advance. It is also preferred to simultaneously extrude the material that will become the adhesive layer and the foam layer using a trench foam extruder.

As a more special example, if the core material is made of a similar material to the foam layer, it is possible to extrude the core material and the foam layer simultaneously from the same extrusion port. Of course, as mentioned above, it is preferable to simultaneously provide a degassing prevention layer on the surface of the foam layer.

θυ The final important issue in obtaining a highly foamed product is how to prevent volumetric shrinkage due to cooling, etc. after the foam has been made highly foamed. In the present invention, since the expansion ratio is 6 times or more, the volume fraction of gas in the foam is about 70 times or more. In other words, within the foam, only 30 inches or less of polyolefin is floating in the gas. In the case of a conventional low-foamed material with double foaming or less, the gas content is 50% or more, and since the polyolefin is in a state of enveloping the gas, the main character is completely reversed. Therefore, in the present invention, the shrinkage of the polyolefin due to the decrease in inner diameter (reduced pressure) caused by the volume reduction of gas in the foam due to cooling after foaming is large.

In the present invention, one preferable condition is to rapidly cool and solidify only the surface layer until the maximum foaming degree is reached. This causes foaming (bubbles) in the inner layer, which is the unsolidified part.
The layer is prevented from shrinking in volume due to subsequent cooling. As a means for rapid cooling of the surface layer, it is advantageous to use the above-mentioned molding die, and it is preferable to cool the surface with a molding die maintained at a temperature below the softening or melting point of the polyolefin.

Another surface cooling method is to cool the surface of the foam with a coolant, such as water, at least until maximum foaming is reached.

Although the method is somewhat different from the surface cooling method described above, as a method of preventing shrinkage of the foam, it is also preferable to coat the surface of the foam with a material that is less likely to shrink in volume than the foam layer. For example, there is a method in which a non-foamed polyolefin is tightly coated on the surface of a foamed layer and then the polyolefin is rapidly cooled. Non-foamed polyolefin can be cooled faster than a highly foamed layer, and a hard skin layer is formed quickly by cooling, so even if the inner foam layer (bubbles) cools, the skin layer will reduce the volume. Can prevent shrinkage. Of course, depending on the purpose of the skin layer, it is also possible to use a polyolefin or low foam polyolefin material different from that of the foam layer.

6.26 Means and Features for Stabilizing the External Shape of a Highly Foamed Body The second object of the present invention is how to stabilize the external shape of a highly foamed body. It has been found that a highly foamed product with a foaming ratio of 6 times or more can be easily obtained by chemical foaming using the various means described above. However, although it is a highly foamed material, its shape, especially its external dimensions, is extremely unstable, and if you try to stabilize the external diameter, you will end up having to keep the foaming ratio to about twice that of conventional foaming. It has been found that foaming of 4 times or more generally results in products that cannot be put to practical use. Therefore, in carrying out the present invention, stabilization of this external shape becomes a major issue. The means and features are listed below.

(1) Use of molding dies In the previous section, we described the use of molding dies as a means of increasing the expansion ratio, but they are also extremely effective in stabilizing the external shape of foams.

That is, by passing the foam through a molding die during foaming, non-uniformity in the foaming speed of each surface layer of the foamed layer can be eliminated, and a foamed product that conforms to the inner diameter of the molding die can be obtained.

Therefore, by using a molding die with an inner shape similar to the finished outer shape of the foam, it becomes possible to perform foaming and molding of the foam at the same time.

This type of molding die is not used in conventional chemical foaming methods. The reason for this is that the foaming is low, about twice the foaming or less, so that the external shape does not deteriorate due to foaming.

Another reason is that a low-density foam of about twice the original size is quite hard when foamed, so it is not easy to mold it with a cross-shaped die.

On the other hand, in the present invention, the expansion ratio is as high as 6 times or more, and the polyolefin is suspended in the gas as described above.
Extremely resilient. Therefore, it is extremely easy to mold this by passing it through a molding die. However, when considering the use of molding dies from the perspective of stabilizing the external shape, an optimal usage method that is different from that for increasing the expansion ratio mentioned above can be considered.

First, if molding is the sole purpose, it is not necessarily necessary to pass the foam through a molding die while it is in the foamed state.

That is, it can be molded at any time under conditions such that the surface of the foam can be molded by a molding die. In an extreme example, after the foam layer is cooled and solidified, only the surface of the foam layer is heated and softened, and then the foam layer is passed through a molding die to be molded. On the other hand, it is also possible to heat the molding die itself to a temperature higher than the thermal softening point of the foam layer, and to mold the foam by passing the foam through the molding die.

In this case, the time point at which the molding is performed can be arbitrarily selected. However, the important point is always to maintain the shape formed by the forming die.
The best means for this is to cool and solidify the surface of the foam immediately after molding as quickly as possible, or to maintain the molding die itself at a temperature below the softening point of the foamed polyolefin.
It is extremely important to foam in the die and to cool and solidify the surface.

Furthermore, in order to perform stable molding over a long period of time, it is necessary to further devise a molding die. In particular, when a molding die is used while being fixed at a specific position, the foaming state of the foam extruded from the foam molding machine changes over time, and the maximum foaming position fluctuates. As a result, the degree of molding by the molding die changes, and the shape of the molded product also changes. If the molding die is overmolded, molding becomes impossible and the foam breaks in the molding die. When the molding does not break, even though the molding looks very clean on the outside (surface), when you look at the foaming state of the inner layer, you can see that the bubbles have been broken and become continuous. This is a drawback caused by frictional resistance during excessive shaping with the shaping die. On the other hand, if the molding die is insufficient, it will be similar to not using the molding die, and the result will be a product with an uneven shape that easily changes over time.

The best way to prevent the above fluctuations in the molding state is to create a mechanism that allows the molding die to be moved to any position, while at the same time detecting fluctuations in the foaming state using a non-contact outer diameter measuring device, etc. to ensure that the molding state is always optimal. The process is to move the molding die to the position. It is also highly preferable to provide a mechanism for constantly detecting the degree of molding by attaching a detector such as a pressure sensitive or frictional resistance sensing element to the inner surface of the molding die and moving the molding die to a position where optimum molding can be obtained.

In order to further increase the effectiveness of the use of molding dies, type K. I can't think of any ingenuity. In order to make the inside of the foam open-celled when it has been over-shaped first, it is better to reduce the frictional resistance in the forming die. To this end, it is effective to make the inner surface of the molding die a highly slippery material or apply a lubricant. Furthermore, it is extremely effective to impart lubricity to the terrain die by means such as ultrasonic vibration. In particular, the present invention is based on a chemical foaming method and does not use a liquid foaming agent as in the physical foaming method, so the frictional resistance at the molding die is greater than that in the physical foaming method. This may sometimes be the main factor determining whether or not the present invention is compatible.

In order to stabilize the outer diameter, it is also extremely important to be able to change the diameter of the molding die in accordance with fluctuations in the finished diameter, as described above in the section on increasing the expansion ratio. In particular, if changing the position of the forming die alone cannot cover the dimensional variation of the finished product, it is necessary to change the inner diameter (shape) of the forming die.

(2) Selection of polyolefin It has been found that the method of stabilizing the external shape using the molding die is extremely effective as a countermeasure regardless of the cause of the external change. However, fundamentally, it is necessary to eliminate the cause of external shape variation. When looking at foaming materials from this point of view, the following measures are effective.

First, as a means for increasing the expansion ratio, it is effective to use polyolefins having different thermal characteristics in combination in this case as well. That is, when different types of polyolefins are used together, the foaming temperature range can be wider than when a single polyolefin is used. For example, rather than using low density polyethylene alone,
It is better to use high-density polyethylene together with this, the foaming ratio is 3.
The temperature range for obtaining more than double the amount can be more than twice as wide. Within this temperature range, it is possible to extrude the foam under temperature conditions that provide the best external shape. In particular, among the factors that cause the external shape of highly foamed products to change, the viscosity of polyolefin is low during foaming, so it is often seen that the external shape is maintained and the product slumps. This tendency is particularly strong when manufacturing large-diameter, thick-walled, highly foamed products. In such cases, polyolefins with a low melting point and polyolefin with a high melting point are used together, or in some cases, polyolefins with a low viscosity and a high viscosity are used together. By sharing the purpose with the holding tank, a highly foamed product with less distortion in external shape can be obtained. For example, by using about 40% or more of high-density polyethylene in combination with low-density polyethylene, a highly foamed product that retains its shape easily and has dramatically improved mechanical strength can be obtained.

(3) Dispersant and blending method To stabilize the external shape of the foam, it is expected that polyolefin, blowing agent, and dispersant should be premixed and fed to the foam molding machine compared to the case of using conventional blowing agent-mixed materials. It has an outside effect. The reason for this is that with this method, a stable foam can be obtained even if the operating conditions of the foam molding machine change; for example, even if the screw rotation speed of the extruder is changed, the expansion ratio and cell diameter will not change. There aren't many.

Therefore, there is an advantage that a foam with a stable outer shape can be easily obtained even during irregular operations such as when foam molding is started, finished, or interrupted.

(4) Feeding method to the foam molding machine It goes without saying that the composition of the foaming material must not fluctuate in order to stabilize the external shape. In particular, in the present invention, a premix is directly supplied to the molding machine without using completely kneaded pellets, so special attention must be paid to variations in each compounding agent. In order to prevent the foaming agent from separating from the polyolefin, a dispersant such as powdered polyolefin is used in the present invention, but there are concerns about feeding this premix to a molding machine by means such as air transport. Therefore, the most reliable method is to perform premixing in one part of the molding machine.In particular, the safest method is to quantitatively feed each compounding agent and feed it directly to the molding machine while continuously premixing. And it is particularly suitable for mass production using a dedicated machine.

Another method is to pre-mix in batches using a drum tumbler, etc., and then supply this to Tao Bin, but in this case, for safety reasons, we recommend using 1 + 1' as much as possible It is safe to mix the ingredients again before supplying them to the container to prevent separation of the ingredients, or to mold products stored for a long period of time to obtain a product with a stable external shape.

(5) Cooling method and other factors that deteriorate the foamed shape cannot be ignored. For example, in the case of highly foamed polyethylene of 4 times or more, if the foam is introduced into a water tank and subjected to rapid water cooling in the same manner as conventional chemical foaming, the foam may collapse due to the drop in water pressure and the gas pressure inside the bubbles due to rapid water cooling. There was found. It is surprising that this phenomenon is less likely to occur in physical foaming methods that use liquid freon, etc., but it is more common in chemical foaming methods. The reason for this is probably that the gas inside the bubbles is hot and the internal pressure drops rapidly due to cooling. The most effective countermeasure in such a case is to cool the surface of the foam with a refrigerant under conditions where no external pressure is applied. For example, methods such as pouring a shower of water or blowing cooling gas may be considered.

Another factor that causes deformation of the external shape when cooling the water tank is that the high foam pipe can be submerged in the water tank. From this point of view, it is necessary to use highly foamed materials and to be creative in the cooling method.

In addition, as a method to make the cooling effect effective, it is effective to apply a skin layer such as non-foamed polyolefin on the surface of the foam layer and then cool it, as described in the oil expansion amplifier, which is also effective in maintaining a uniform outer diameter. be. In this case, the skin layer may be extruded from the same extrusion port at the same time as the foam is extruded, but it is preferable that the skin layer be coated after extruding the foam layer and at least before being introduced into the cooling bath. In the latter case, in order to uniformly cover the skin layer, it is extremely necessary to apply the skin layer after forming the foam layer with the aforementioned molding die.

3-2-4 Means and characteristics for coating on stone The means for preparing the external shape of a highly foamed material with an expansion ratio of 6 times or more and producing it in a stable state are as already mentioned.
This is just a means of manufacturing a core material, such as a copper tube (still hollow at t); more means are needed to tightly cover the outside with a core material, such as a copper tube.The reason is When foaming with a foam that is more than 3 times larger, it is necessary to rapidly expand in the vertical direction, and the side in contact with the core paulownia also expands greatly in the vertical direction as shown in Figure 1. Large voids are formed, and there is almost no protective effect in terms of mechanical strength of the core material of the foam 2. In the figure, 4 is a nipple and 5 is a die. If water enters this interface, for example, , the insulation effect of the foam almost disappears.In the case of electrical insulators, the electrical properties deteriorate.In this way, adhesion with the core material is always important.If the foam is expanded twice as much as conventional foam, it will expand during foaming. Since there are few
This void hardly occurred, and in the case of large and low temperatures, it was possible to solve the problem by preheating the core material.

However, in the present invention, which obtains a foam with a foam that is 6 times or more higher, the problem can be solved by preheating one piece of the core material, as in the past, and the more the core material is preheated, the lower the adhesion with the core material. Since the result was unexpected, I will explain the solution below.

(1) Coating with adhesive layer In the present invention, the best solution to this problem is to apply an adhesive increments with foaming control on the core material. However, it is most preferable to apply the adhesive between the core and the foam material before the foam material starts foaming as described above in the foaming ratio increasing means. In this case, the stronger the adhesion to the core material, the better, and the better, and the more desirable it is to be able to easily pull out the foam manually, and the means for controlling this is as follows: .

When applying adhesive layers in tandem □ Conditions such as the angle of the die to apply the adhesive layer, position temperature, etc., cooling conditions after application, temperature of the core material before application, presence or absence of mold release agent, temperature of the foamed material, adhesive layer When coating with the foam layer at the same time: Core, paulownia pre-M (・, temperature, presence or absence of mold release agent, temperature of adhesive layer/foam layer, distance between the die and nipple when extruding the foam layer, adhesive layer is separated in advance) Although it is possible to coat the core material during the process, from the viewpoint of stabilizing the adhesive force and productivity, it is best to cover the core material during extrusion of the foam layer.

After coating the adhesive layer on the ribs, the surface condition of the adhesive layer often changes physically (dirt, etc.) or chemically (deterioration, etc.) due to changes over time, resulting in a decrease or fluctuation in adhesive strength. be.

Regarding the position where the adhesive layer is applied, when uneven thickness of the foam layer is a problem, it is preferable to apply the adhesive layer 6 at the tip of the nipple 4 as shown in FIG.

In the figure, 1 is a core material, 5 is a die, and 6' is an adhesive. This is because, for example, if the core material is a plastic such as polyethylene, it will melt when it comes into contact with the nipple, so the inner diameter of the nipple must be considerably larger than the diameter of the core material, so that it can be extruded without becoming a nipple. For this reason, the position of the core material within the nipple is not determined, resulting in uneven thickness of the foam layer.

In order to prevent this, the tip of the nipple is coated with an adhesive, which maintains the center core of the nipple and allows extrusion of a foam layer with less uneven thickness. On the other hand, if the adhesive layer is coated at the entrance of the crosshead, it is possible to obtain favorable results in adhesion to the core material. For example, it is extremely easy to cover the foam layer by drawing it down. As shown in Figure 3, a method is used to evacuate the space between the wick and the foam layer with a vacuum pump to make them adhere, but if the adhesive is damaged at the inlet of the crosshead, it is extremely easy to evacuate with a vacuum pump. In addition, since the degree of vacuum can be increased, it is possible to tightly adhere the foam layer on the core material.

Note that the adhesive is supplied using an extruder or other method. A hot melt type adhesive is most suitable for this purpose, and an extruder or other hot melt aggregator is used.

In addition, in some cases, a special compound may be used in the adhesive layer to prevent mutual deterioration due to contact between the adhesive layer and foam layer and the core material, such as an agent that prevents deterioration due to contact with metal. It is valid.

(2) Material for foaming The selection of material for foaming is still important in order to improve the adhesion to the stone. As already mentioned, if the viscosity of the foaming material is inappropriate, it will sag during foaming as shown in Figure 4 (in the figure, 8 is a gap due to dripping), and as a result, only one side will have no core material. A foam collar cover that does not stick tightly can be obtained. In particular, this becomes a fatal problem when the stone has a narrow diameter and is covered with a thick foam layer. In order to prevent this, it is necessary to maintain the temperature and viscosity of the material so that it does not sag, and as a means to do so, it is possible to use polyolefins with different melting points and viscosities, or to use blowing agents with different thermal decomposition temperatures. Extremely effective.

In order to make a foam with a high color, a large amount of foaming agent must be used, and a large amount of gas will be generated.No matter how effectively the foam is used for foaming, the number of gases degassed from the surface will be large, and as a result, A large number of degassing holes are created in the surface layer. It was found that this number was more than twice as high as in the case of conventional double foaming. Therefore, if the material is cooled by immersing it in a water tank as in the past, a large amount of water will be absorbed through the degassing holes, resulting in a substantial reduction in the foaming ratio. In other words, the heat insulation performance and electrical insulation performance of the foam layer decrease.

Therefore, a method to solve this problem is described below.

+11 Cooling method The factor that most promotes water absorption is water seepage through the degassing holes when water is soaked into the foam and water tank for cooling. Schematically shown in Figure 5 1, gas escapes from the surface of the generated bubbles through the cell walls until the maximum foaming region is reached (degassing region A), but after that, as the foam cools, the gas escapes from the surface. The gas pressure inside the bubbles decreases and the bubbles tend to contract somewhat due to external pressure.In particular, since minute gas degassing holes 9 are formed in the surface layer, water is sucked into the bubbles by reducing the pressure inside the bubbles. (Water absorption area B).Especially when water pressure is applied in the water tank 10, it is often seen that a significantly large amount of water is sucked in through the deaeration hole in the case of a foam with a foam size of 6 times or more. The most promising method is to sprinkle water on the foam in the form of a shower or mist in order to cool the foam without applying water pressure. When it evaporates, it is cooled by a large amount of heat of evaporation, providing the same cooling effect as when immersed in water in an aquarium.

However, as long as water is used, it is unavoidable that moisture will diffuse and enter through the cell walls even if there are no deaeration holes as shown in (2) in FIG. Therefore, in order to avoid damaging properties that are affected by slight moisture infiltration, such as thermal conductivity and electrical properties, water cooling should be limited to at least the maximum foaming position, and after that, non-aqueous substances such as cooling gas should be used. Particularly favorable results are obtained when cooling is preferably performed entirely by cold air.

(2) It has already been mentioned that a protective layer is applied to the surface of the waterproof foam coating foam to improve mechanical strength, but in this case, a skin layer is applied before the foam layer is cooled with water and then passed through a cooling tank. is also extremely desirable in terms of preventing water absorption.

Note that a large amount of deaeration pores on the surface are generated when foaming is allowed to reach maximum foaming, and as mentioned above when stabilizing the 9L diameter, foaming on the surface of the foam layer must be suppressed using a molding die. is effective in preventing water absorption. Furthermore, in this case, molding while applying a water-repellent lubricant to the molding part will further reduce the formation of degassing pores, and even if degassing pores occur, the pores will be covered by the water-repellent. There is almost no need to worry about water absorption due to subsequent water cooling.

(3) Foaming material Since the present invention uses chemical foaming agents, it is a big problem that many of the decomposition residues are hygroscopic.
Depending on the use of the product, it is unavoidable that a method such as drying the foam after manufacturing is required. However, in order to make this drying process as easy as possible, or even omit it if possible, the selection of the foam material is also important.

For example, chemical blowing agents contain water as a thermal decomposition product,
The use of substances that produce hygroscopic substances should be minimized, and it is desirable to use gases such as nitrogen gas and carbon dioxide gas together. In addition, among polyolefins, polymers with extremely low hygroscopicity,
For example, it is preferable to use polyethylene, polypropylene, etc. with a high vigor. As for other compounding agents, the less hygroscopic the better.

However, both of these are important in cases where the moisture absorption of the foam reduces the effective magnification of the foam, such as in thermal and electrical insulation materials, such as cushioning materials, sound absorbing materials, and filler applications. There is no need to worry too much about moisture absorption when used for.

Finally, the most desirable embodiment of manufacturing a tubular foam according to the method of the present invention is explained with reference to FIG. 6. After coating the thin polyolefin layer, the extruder 11 is used to extrude and coat the foaming polyolefin, the extruder 12 is used to extrude and coat the skin layer polyolefin, and the sizing die 13 forms a uniform tubular highly foamed body 2. The body is
After proceeding to a cooling water tank 10 adjacent to a sizing die 16 and being cooled down by a water spray nozzle 14, moisture is removed by an air wiper 15, and the material is wound up by a winding machine 16.

The foam produced by this method can be used as an insulator for electric wires and cables, especially for coaxial cables, and as a heat insulating layer for insulated pipes used for solar systems, water supply cold pipes used for hot water or steam heating, etc. It can be applied to.

Example 1 Pellet-shaped low density polyethylene (MI-4, density 09
Departed on 2)? Azodicarbonamide powder (variable) and low-density polyethylene powder (variable) were mixed as packaging materials, and the outflow rate and particle size segregation of each mixture were measured.

The outflow rate was measured by placing a sample of material 5002 into the hopper shown in Figure 7 (in units of 2/min).

Particle size segregation was performed using the same hopper used to measure the flow rate.
After the sample was filled in the hopper, it was allowed to flow out, and during the outflow, the effluent was collected in four portions to measure the powder and pellet content.

From the results shown in Table 1, when the blending amount of powdered low density polyethylene is 0.1 parts by weight or more per 1 part by weight of the blowing agent, the outflow rate of the mixture becomes significantly faster and particle size segregation becomes less likely to occur. The reason why particle size segregation appeared in Experiment 10 was because the total powder content increased to more than 10%, which weakened the effect of the powdered low-density polyethylene.

It was common knowledge that powder has poor fluidity compared to pellets and causes hopper bridging5, but it was a completely unexpected fact that the fluidity was improved by using both together. It is also a surprising fact that grain history segregation becomes less likely to occur when a substance with a completely unusual shape is used in combination.

Example 2 As polyolefin pellets, low density polyethylene (M knee 4, density 0.92) and high density polyethylene (
Mnee 04, density 0.95) f was used in combination with azodicarbonamide powder as a blowing agent, and the outflow rate and particle size segregation of the mixture were measured.

Table 2 shows that when using several polyolefin pellets in combination, it is effective to use powdered polyolefin in combination with a large amount of polyolefin powder. As in Experiments 14 and 15, when the measures for different types of polyolefins are the same, the effect is observed with either polyolefin powder.

Example 6 B A foaming resin mixture using 4,4'-oxybisbenzenesulfonyl hydrazide powder as a foaming agent was injected onto an 18mm diameter copper pipe using a 65mm screw extruder.
Foam coated tubes were produced by coating to a thickness of 3 mm at an extrusion temperature of 0°C.

Table 3 shows the characteristics of the obtained prototype.

These examples show that a foam with good properties can be easily obtained by adding a powdered chemical blowing agent and a powdered polyolefin to polyolefin pellets.

The method of the present invention not only requires less kneading cost than the conventional method of kneading the blowing agent, but also has the effect of reducing the loss of the blowing agent when mixing resin for foaming, and is less expensive than the conventional method. The resin composition is K''A.

However, in this example, because Experiment 19 used a different type of polyethylene powder from the main polyethylene, experiment 20
In Experiment 22, a larger amount of powdered polyethylene was used than the powdered foaming agent, and in addition, in Experiment 22, the total amount of powdered foaming agent and powdered polyethylene exceeded 10 parts by mass per 100 parts of pelleted polyethylene, so the appearance of the foam and The bubble diameter shows a tendency to deteriorate to some extent.

Example 4 2.5% by weight of 4,4'-oxybisbenzenesulfonyl hydrazide and 0.2% by weight of azodicarbonamide were added to each resin as blowing agent powder, and the mixture was fed to a 65 fermentation extruder. A heat-insulating foam-covered tube was fabricated by coating a 18-diameter copper tube to a thickness of 3 mm. The characteristics of the obtained prototype are shown below.1. Low-density polyethylene pellets (M knee 5, density 0.920) were used as the resin, and various high-density polyethylene pellets and powdered polyethylene were blended with this resin. The properties of this foam are shown in Table 4.

Density 0950 or more +7) HDPK 10-50iit
By blending ftH, the compressive strength is improved without affecting the expansion, foaming ratio, cell diameter, appearance, etc., compared to the case where it is not blended. When 50% or more of HDPIIO is blended, the cell diameter of the I"6 foam tends to become coarser, and as a result, the compressive strength tends to decrease. Furthermore, when using HDPE alone, the compression strength increases, but this is due to the low foaming ratio.

In this way, it is extremely difficult to produce high-density polyethylene foam using chemical blowing agents, and it has previously been impossible to produce high-density polyethylene foam with unexpected ease by using low-density polyethylene in combination. It turned out that it was possible to do this.

Example 5 Low density bo! J ethylene pellets (M work = 20° density 0.
A foaming resin containing 100 parts by weight of the specified blowing agent and 05 parts by weight of powdered low-density polyethylene (92 f/'t) was applied to 6W onto 18 diameter copper pipes using a 65cm extruder.
A foam coated pipe was produced by coating to a thickness of I+I+.

Table 5 shows the characteristics of the obtained prototype.

Table 5 Note 1) Azodicarbonamide is blended with LDPEK kneading. 2) 4.4'-Oxybisbenzenesulfonylhydrazide is blended with powder directly into pelletized LDPK to form a tri-blend low-temperature decomposable foam. By blending 0.05 to 1 or coarse part of a high temperature decomposable blowing agent (azodicarbonamide) to 1 part of the agent (4,4'-oxypisbenzenesulfonyl hydrazihede), an appropriate size can be obtained. It is possible to easily obtain a foam that has many cells and has a good appearance.

Example 6 Polyolefin resin for foaming In the production equipment shown in Figure 6, the adhesive layer coating equipment was used at a linear speed of 5 m.
Ethylene ionomer (Surlyn A) was placed on an 18-throat copper vibrator running at /' min.

DuPont Co., Ltd., trade name] was coated to a thickness of 01"!l; mm.

Then, the resin for photofoaming was supplied to a 65-barrel extruder 1 and passed through an extrusion die 2 to cover it to a thickness of 3 mm. Immediately after that, inner diameter 1
After molding the foam using a sizing die with 4 holes and a length of 550 mm, it was cooled in a 10 m cooling water tank equipped with a shower set nozzle located 5 km away from the sizing die.

Table 6 shows the properties of the obtained tubular high foam coated pipe.

Table 6 WS: Weight of test piece ρ0; Density before foaming v days = Apparent volume of test piece By using an adhesive layer and a sizing die, a tubular shape with closed cells and good adhesion to the center pipe with a good appearance was created. A high foam coated pipe is obtained.

Example 7 Example 6, Experiment 41 Manufacture The results of a comparison of two cooling methods, namely, the shower set cooling method under Zhuji↓ and the water cooling method using filled water, are shown in Table 7.

Table 7 Note: Flatness - major axis - minor axis It can be seen that the shower set cooling method is superior, with less flattening of the foam and less hygroscopicity than the water cooling method.

Example 8 Under the conditions of Example 7 and Experimental Section 44, the amount of suction in the foam was large, so a low-density polyethylene skin layer with a coating thickness of 1 yen was newly coated on the outside of the foam layer using the extruder 11. The results are shown in Table 8.

Before cooling the foam layer with water, a skin layer can be applied to the foam layer to prevent water absorption by passing it through a cooling bath.

[Brief explanation of the drawing]

Figures 1 to 5 are cross-sectional views showing problems when covering a core material with a high foam material, or aspects of the present invention. It is a vertical cross-sectional view (a) and a cross-sectional view (1)) showing the state of the situation.
FIG. 6 is a diagram showing an example of the position where the adhesive layer is applied between the core material and the foam, and FIG. 6 is a diagram showing the position 2 where the adhesive is applied when vacuuming between the core material and the foam layer. FIG. 4 is a diagram showing the dripping phenomenon during foaming, and FIG. 5 is a schematic diagram showing water intrusion from the degassing holes in the foam layer. Figure 6 is a flow sheet showing one embodiment of the method of the present invention, and Figure 7 is a flow sheet of a hopper used to measure the flow rate and particle size segregation of the foaming material in order to see the effects of the method of the present invention. It is a figure showing a structure. Agents 1) Akira Agent Ryo Hagiwara - Procedural Amendment (Method) October 15, 1980 Kazuo Wakasugi, Commissioner of the Japan Patent Office 1, Matters ('l's Large and Small Showa 574 White, 5 Patent Application No. 107551, 21) !fl
fl 8? I; Process for producing foam 3 Relationship with the issue of the sound to be amended Patent applicant fi', l'li 5-15-4 Kitahama, Aki-ku, Osaka, agent ti; l'li Tora, Minato-ku, Tokyo) Gate-Chome 24-11 No. 6, Number of inventions increased by amendment None 7 Subject of amendment (1) Page a written in ballpoint pen in the specification Contents of amendment (1) Pages 46, 47, 49 of the specification Pages 52, 54, 55, 56, 57, and 58 will be corrected in the appendix. (No change in content) Example 2 As polyolefin pellets, low density polyethylene (M knee 4, density (192)) and high density polyethylene (M
The outflow rate and particle size segregation of the mixture were measured when azodicarbonamide powder was added as a blowing agent and azodicarbonamide powder was used as a blowing agent. Table 2 From Table 2, when polyolefin pellets were used in combination with several polyolefins, a foam covered pipe was produced by coating powdered polyolethane 18w+mφ copper pipe to a thickness of 3-3. Table 5 shows the characteristics of the obtained prototype. Table 5 Note 1) Azodicarbonamide is LDPI! ! 2) 4.4'-Oxybisbenzenesulfonyl hydrazimad is directly added to the powder form of pelleted LDPI.
0.005 to 1 part by weight of a high-temperature decomposable blowing agent (azodicarbonamide) is added to 1 part by weight of a triblend low-temperature decomposable blowing agent (44'-oxypisbenzenesulfonylhydrazine) in C. Therefore, it is possible to easily obtain a koto foam with bubbles of appropriate size and good appearance. Example 6 Polyolefin resin for foaming In the production equipment shown in Figure 6, the adhesive layer coating equipment was used at a linear speed of 5 m.
An ethylene-based ionomer (Surlyn A, manufactured by DuPont, trade name) was coated to a thickness of 15IIllI on a 18m+φ copper pipe running at a speed of 18m/min. Then, the foaming resin was supplied to a 65 mm extruder 1 and passed through an extrusion die 2 to coat the resin to a thickness of 5 μm. Immediately after that inner diameter 14
After molding the foam using a sizing die with a length of +m++ and a length of 350-, it was cooled in a cooling water tank with a diameter of 10 mm and a shower nozzle installed at a position 5 mm away from the sizing die. Table 6 shows the properties of the obtained tubular high foam coated pipe. Table 6 Wθ: Weight of test piece Po: O density before foaming v8: Apparent volume of test piece By using an adhesive layer and a sizing die, a good appearance with closed cells and good adhesion to the center pipe was obtained. A tubular high foam coated pipe is obtained. Example 7 Table 7 shows the results of a comparison between two cooling methods: the shower set cooling method and the water cooling method using full water under the production conditions of Example 6 and Experiment Na41. Table 7 (Note) Flatness - major axis - minor axis It can be seen that the shower set cooling system is superior to the water cooling system as it causes less flattening of the foam and has no hygroscopicity. Example 8 Under the conditions of Example 7 and Experiment 44, the amount of moisture absorbed by the foam was large, so a low density polyethylene skin layer with a coating thickness of 1 wI was newly applied to the outside of the foam layer using the extruder 11. The results are shown in Table 8. Table 8 Water absorption can be prevented by applying a skin layer to the foam layer and passing it through a cooling bath before cooling the foam layer with water. 4. Brief explanation of the drawing

Claims (1)

[Claims] (1) Foaming materials mainly consisting of polyolefin pellets, chemical blowing agent powder, and polyolefin powder dispersant are premixed and supplied to a molding machine, and after being melt-mixed in the molding machine, After the temperature rises above the thermal decomposition temperature of the chemical blowing agent,
A method for producing a foam having an expansion ratio of 3 times or more, characterized by cooling the temperature and extruding through a die. (2) The total amount of both chemical blowing agent powder and polyolefin dispersant powder is 1.1 to 10.
0% by weight, and the chemical blowing agent powder is 1.0% by weight or more, and the powdered polyolefin is blended in an amount of 0.1 parts by weight or more per 1 part by weight of the blowing agent powder, according to claim 1. A method for producing a foam. (3) A method for producing a foam according to claim 1, wherein the polyolefin pellets are made of polymers with different melting points. (4) The polyolefin pellets are a low-density polyethylene and a high-density polyethylene having a density of 0.950 or more. A method for producing a foam according to claim 3, wherein 10 to 50% by weight of the foam is blended. Method for producing foam. (6) Using a low temperature decomposable blowing agent as a chemical blowing agent at a concentration of 1.0
6. The method for producing a foam according to claim 5, wherein 0.05 to 1 part by weight of the high-temperature decomposable foaming agent is blended per 1 part by weight of the low-temperature decomposable foaming agent. (7) After being extruded from the molding machine, at least while the foam retains its thermoplasticity, preferably before reaching the maximum foam diameter, the surface is molded using a molding die with a similar shape to the desired finishing shape. , a method for producing a foam according to claim 1. (8) The foam according to claim 7, characterized in that an adhesive layer is provided between the core material and the foaming material at the same time or before the core material is coated with 6 times or more of the foam material. manufacturing method. (9) Apply a skin layer with a foaming degree of at least 3 times or more on the surface of the foam from before the foaming material starts foaming to at least after the foaming until the surface is cooled with water. The method for producing a foam according to claim 7, wherein the surface of the foam is coated. Q(e) The method for producing a foam according to claim 7, wherein the extruded foam is cooled with shower-like water.