JP3520909B2 - Polyolefin resin foam and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin resin foam and a method for producing the same. More specifically, the present invention relates to a polyolefin resin foam directly foam-molded using an extruder and a method for producing the same.

[0002]

2. Description of the Related Art Extrusion direct foam molding of polyolefin resin foams has been popular since ancient times. Among them, for example, a polyolefin resin alone can be listed. . However, resins such as polypropylene and linear low-density polyethylene are not always easy to foam by a conventional method, and a foam with a high magnification and a high closed cell ratio cannot be obtained freely. For example, when such a resin is extruded and foamed by a usual method, the expansion ratio is only about 2 to 3 times, and if it is expanded more than that, the closed cell rate becomes low, and the surface becomes uneven due to bubble burst, The appearance will be impaired. In addition, exceptionally, a method of foaming about 10 times or several tens of times is also known, but it is necessary to use a specific freon or a physical foaming agent having a solvent plasticizing effect and to have a high closed cell rate. Was hard to get. Further, since there is no sufficiently wide range of foam molding conditions, the production itself is difficult.

In view of such circumstances, as a method of foaming a resin such as polypropylene or linear low density polyethylene, Japanese Patent Laid-Open No. 57-24221 and Japanese Patent Publication No. 6-860 have been proposed.
No. 87, etc., a method of foaming while modifying a resin with an organic peroxide or the like in an extruder, or radiation such as JP-A No. 62-121704, JP-A No. 2-69533, etc. There is known a method of foaming using a resin modified in advance. Furthermore, JP-A-61-1
As disclosed in Japanese Patent No. 126701, there has been a proposal of extrusion foaming while slightly cross-linking with a cross-linking agent selected from azide-functional silane, vinyl-functional silane, organic peroxide, polyfunctional vinyl monomer, oxygen and the like.

However, in these methods, since the resin used is a special resin, the manufacturing cost is high and
It is necessary to perform foaming with a limited foaming agent and foam molding condition range (particularly temperature range), and the effect is not always satisfactory. In addition, the following new defects have also occurred.
The method using an organic peroxide has drawbacks such as odor of a peroxide decomposition product, difficulty in controlling the degree of modification, brittleness and strength reduction which are considered to be due to main chain scission. In particular, this drawback is remarkable in polypropylene. Further, the modification of the resin itself requires a new process to treat the polymer with an expensive apparatus, which is disadvantageous in that the cost is high.

Further, in the method using a vinyl functional silane or a polyfunctional vinyl monomer, these are usually grafted to the polymer by an organic peroxide, but they can be involved in the decomposition residue of the organic peroxide and the grafting. There is a problem that an odor is generated due to the residual low molecular weight substance which has not been present.
There is also a problem that the foam is colored. Furthermore, there is a problem that it is difficult to control the degree of modification. Therefore, when extrusion-foaming a resin that is generally difficult to foam, such as normal grade polypropylene, linear low-density polyethylene, high-density polyethylene, etc., the range of extrusion foaming conditions is wide and foam molding is easy, and high-foaming or independent foaming is possible. It has been desired to produce a foam at a low cost, in which the control of the bubble ratio is easy, the quality such as strength is not impaired, and the colored odor is not a problem. Further, it has been desired that the obtained foam has easy secondary moldability such as thermoforming.

[0006]

Thus, according to the present invention, a base resin comprising 60 to 97% by weight of a polyolefin resin and 3 to 40% by weight of a silane crosslinkable polyolefin resin, a crosslinking catalyst, a crosslinking agent and foaming. Provided is a method for producing a polyolefin-based resin foam, which comprises melt-kneading an agent with an agent while allowing a cross-linking reaction up to a gel fraction of 25% to proceed in the extruder for foaming. Further, according to the present invention, there is provided a polyolefin resin foam obtained by the above method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The polyolefin resin that can be used in the present invention is not particularly limited, and a known polyolefin resin can be arbitrarily selected and used. Here, the polyolefin resin is various polypropylene resin such as isotactic, atactic, syndiotactic, high density polyethylene resin,
A linear low-density polyethylene resin is preferable because it can solve the above problems more effectively. Furthermore,
In the case of a polypropylene resin, the above problems can be solved particularly effectively, and a good foam can be obtained.

In addition to the above, various polyethylenes such as low density and medium density and modified products thereof, polypropylene and modified products thereof, and the like can be mentioned. Furthermore, a random copolymer of polypropylene and ethylene, a block copolymer, and other modified products can also be used. Also, vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid,
It may be a copolymer with acrylic acid ester, methacrylic acid ester or the like.

Various olefin homopolymers other than polypropylene and polyethylene, and copolymers of two or more olefins such as copolymer elastomers can also be used. Further, a polyolefin resin whose branched structure, degree of polymerization distribution and the like are controlled by a recent single site catalyst can also be used. In addition, a resin other than a polyolefin resin such as a polystyrene resin may be contained in a mixed or copolymerized form as long as the effect of the present invention is not impaired.

Examples of the silane-crosslinkable polyolefin resin that can be used in the present invention include resins obtained by introducing a hydrolyzable silyl group into the side chain of a polyolefin polymer as a matrix. Examples thereof include low-density polyethylene-based, high-density polyethylene-based, ethylene vinyl acetate copolymer-based, polypropylene-based, and other silane-crosslinkable polyolefin-based resins. Crosslinking is performed by hydrolysis of the substituted silyl group. It should be noted that the polyolefin resin having the silyl group at the terminal may be included.

This silane crosslinkable polyolefin resin is a method of randomly copolymerizing a monomer of the polyolefin resin and an ethylenically unsaturated silane compound in a container,
Alternatively, it can be obtained by a method of graft-copolymerizing an ethylenically unsaturated silane compound using a peroxide in a melt of a polyolefin resin. Here, as the base polyolefin-based resin, any of the same resins as described above can be used. Further, the base polyolefin-based resin does not necessarily have to be the same type as the above-mentioned polyolefin-based resin as long as the mixing or dispersion of both resins is allowed. The degree of mixing or dispersion varies greatly depending on the type of extruder used, and an appropriate compatibilizer can also be used. Therefore, the combined resins cannot be unconditionally classified, but the same type of resin is preferable.

Examples of the unsaturated silane compound for introducing the silyl group include those represented by the following formula. RSiR ¹ _n Y _3-n (wherein R is an ethylenically unsaturated carbyl or hydrocarbyloxy group, R ¹ is an aliphatic saturated hydrocarbyl group,
Y represents a hydrolyzable organic group, and n represents an integer of 0 to 2.
When Y is 2 or more, each Y may be the same or different. )

Examples of R include vinyl, allyl, propenyl, butenyl, cyclohexenyl, γ-methacryloxypropyl and the like. Examples of Y include γ-methoxy, ethoxy, formyloxy, acetoxy, propoxy, alkyl or arylamino and the like.
Examples of R ¹ include methyl, ethyl, propyl, decyl, phenyl and the like.

Particularly preferred unsaturated silane compounds are represented by the following formula. CH ₂ ═CHSi (OA) ₃ (where A is a carbon number of 1 to 8, more preferably a carbon number of 1).
The most preferred unsaturated silane compounds, which are hydrocarbyl groups of ~ 4) are vinylmethoxysilane, vinylethoxysilane and vinyltriacetoxysilane.

The blending ratio of the polyolefin resin as the base resin and the silane crosslinkable olefin resin having a silyl group in its side chain is preferably 60 to 97% by weight and 3 to 40 parts by weight. When a compatibilizing agent such as a compatibilizing resin is used, the compatibilizing agent may be incorporated into the polyolefin resin to calculate the blending ratio. When the blending ratio of the silane crosslinkable olefin resin is less than 3% by weight, the effect of improving extrusion foamability cannot be exhibited. On the other hand, when it is more than 40% by weight, there are the following problems or drawbacks.

First, since a large amount of unreacted substances are present in the silane-crosslinkable polyolefin resin, a large proportion of the silane-crosslinkable polyolefin resin causes odor and yellow coloring of the foam. Further, moisture adsorbed from the air or the like during long-term storage causes silanol formation due to hydrolysis, further condensation polymerization, and the like, which causes a lack of stability in foam production. Such a defect is strongly exhibited in the case of the graft polymerization modified product.

Further, depending on the type of the base polyolefin resin, the base itself is deteriorated, and the base has a low molecular weight so that a product having a low MI value cannot be produced, resulting in a decrease in the strength or brittleness of the obtained foam. In addition, the disadvantage that strong coloring, odor, etc. occur is also more strongly manifested. These defects are more strongly manifested in the base polyolefin resin than in the polypropylene resin.

As the crosslinking catalyst that can be used in the present invention, any compound exhibiting the performance of a known silanol condensation catalyst can be used. For example, dimethyltin diacetate, dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, stannous acetate,
Stannous caprylate, lead naphthenate, zinc caprylate, zinc stearate, carboxylates such as cobalt naphthenate, titanium chelate compounds, alkyl titanates, organometallic compounds such as alkyl zirconates, ethylamine,
Examples thereof include organic bases such as dibutylamine, hexylamine and pyridine, organic acids such as acetic acid, oleic acid, phthalic acid and toluenesulfonic acid, and inorganic acids such as sulfuric acid and hydrochloric acid. Of these, carboxylates are particularly preferred. The crosslinking catalyst is preferably used in a proportion of 0.001 to 3 parts by weight with respect to 100 parts by weight of the base resin.

The cross-linking agents usable in the present invention include the following. It is generally said that the silylated olefin-based resin is water-crosslinked. To be precise, however, it is said that moisture causes the alkoxy groups to hydrolyze to form silanol groups, and the silanol groups condense with each other to crosslink. Therefore, although water may be accurately distinguished as a crosslinking aid, here, it is referred to as a crosslinking agent for convenience. In addition,
The proportion of alkoxy groups in the resin is small and the required water content is small. Since a part of water may be regenerated by condensation, even a small amount of water may progress to crosslinking. In addition, it is preferable to consider the influence of moisture that is taken in unintentionally such as being attached to the resin or adsorbing from the air.

The water may be water itself, or may be supplied as a substance that retains water of crystallization, adsorbed water or the like and releases water under the conditions of heat, pressure, etc. in the extruder. Also, a substance that releases water by the reaction may be used. These substances that release water are referred to as water-generating substances in this specification. Examples of substances having releasable water of crystallization include hydrates of aluminum hydroxide, magnesium hydroxide, various phosphates and the like.

Examples of the substance capable of having adsorbed water include zeolite, colloidal silica, cyclodextrin, water-absorbing gel and other organic and inorganic fine particles. Examples of the substance that releases water by a chemical reaction include hydrogen peroxide solution, crystalline hydrogen peroxide, and a mixture of hydrogen peroxide and bleaching powder.

The water content is preferably 0.03 to 3 parts by weight with respect to 100 parts by weight of the base resin. Furthermore, in the present invention, polyhydric alcohols can also be used as a crosslinking agent. Moisture is generally used to crosslink the silylated olefin resin, but the inventors of the present invention can unexpectedly use polyhydric alcohols,
And found to be effective.

As the polyhydric alcohol, polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, pentaerythritol, and sorbitol, their condensation polymers, vinyl alcohol polymers and copolymers, and two or more hydroxy groups are left. Further, organic acid esters of polyhydric alcohols (for example, monoglycerides such as palmitic acid, citeanic acid, lauric acid, and sorbitanic acid) and many other polyhydric alcohols can be used. Among these, monoglycerides such as palmitic acid, cithenic acid, and lauric acid can be particularly preferably used.

The mechanism of action of these polyhydric alcohols on crosslinking is not clear, and it is not clear whether water is essential. However, it is effective for the method of the present invention even if the raw material dried at a realistic level is used and no water is particularly supplied. The polyhydric alcohol is preferably used in a proportion of 0.03 to 5 parts by weight with respect to 100 parts by weight of the base resin.

Blowing agents which can be used in the present invention are
Any material can be used as long as it exhibits a foaming action when extruded into a low pressure region by kneading and extrusion. One group of such blowing agents are easily volatile liquids and the other group are compressed gases, which together are referred to as physical blowing agents. Specific examples of the former include propane, butane, pentane, methyl chloride, trichloromonofluoromethane, dichlorodifluoromethane, and 1,2-dichlorotetrachloromethane, and specific examples of the latter include carbon dioxide and nitrogen. .
These two groups are widely used in extrusion foaming, from low to high foaming.

Further, as another type of foaming agent, there is a so-called chemical foaming agent such as a foaming agent which decomposes to generate a gas at a specific temperature or higher and a foaming agent which generates a gas by a chemical reaction. Specifically, a foaming agent that decomposes at a specific temperature or higher to generate gas, such as azodicarbonamide, dinitrosopentamethylenediamine, P, P'-oxybisbenzenesulfonyl hydrazide, N, N'-dinitrosoterephthalamide. , A foaming agent that generates gas by a chemical reaction such as a combination of sodium hydrogen carbonate and citric acid.

In the present invention, the former physical foaming agent is more preferable. Further, in the present invention, an additive such as a foam nucleating agent may be added. Examples of the foaming nucleating agent include chemical foaming nucleating agents such as talc, silica, fluororesin powder, azodicarbonamide, and sodium bicarbonate, and any other commonly used one can be used. In addition to these, a method of using sodium bicarbonate and citric acid in combination as a foam nucleating agent is well known, and this foam nucleating agent can be preferably used. In addition to the above, a bubble regulator, an ultraviolet absorber, an antioxidant, a colorant, a flame retardant, etc. may be added.

The method for producing the polyolefin resin foam of the present invention will be described below. First, in the present invention, the polyolefin resin foam is produced by extrusion foaming with an extruder. As an extruder that can be used in the present invention, what kind of apparatus can be used as long as it can supply a base resin, a cross-linking catalyst, a cross-linking agent, a foaming agent, etc., knead them, and extrude them into a low pressure region through a mold and simultaneously foam Things can also be used. As a specific extruder, a single-screw extruder, a twin-screw extruder, a multi-screw extruder, or a special one such as a rotary type or a disc type can be used. These may be used alone or in any combination. In addition to extruders, various kneading equipment, gear pumps,
Devices such as resin temperature control can also be arbitrarily combined.

In the present invention, an olefin resin and a silane-crosslinkable olefin resin are used as the base resin, but these base resins may be supplied from a single supply port of the extruder or a plurality of supply ports. You may. A crosslinking catalyst other than the base resin, a crosslinking agent, a foaming agent, etc. may be supplied from the same supply port as the base resin, or may be supplied by appropriately providing another supply port. Of the foaming agents, the volatile physical foaming agent is generally of a type in which an injection port is usually provided at a specific position after the base resin has been melted and press-fitted.

The crosslinking agent (moisture, water-generating substance, polyhydric alcoholic crosslinking agent) and the crosslinking catalyst can be supplied to an appropriate position at once in a total amount of all species. Furthermore, it is also possible to supply to an appropriate position by dividing into a plurality of times. Furthermore, when a plurality of types of crosslinking agents and crosslinking catalysts are used, they can be supplied to appropriate positions separately for each type. If crosslinking proceeds before mixing the base resin, there is a problem that the base resin cannot be sufficiently mixed thereafter, but it is preferable to supply the base resin at an appropriate position after melt-kneading. When the residence time is short, such as when the extruder is short or the amount of extrusion per unit time is large, or when the amount of silane-crosslinkable polyolefin-based resin used is small, or when a slow-reactive silane-crosslinkable polyolefin-based resin is used Alternatively, when the amount of the cross-linking agent or the cross-linking catalyst used is small, the cross-linking agent, the cross-linking catalyst, or both may be added in advance before mixing the base resin.
To supply to an appropriate position, adjust the amount of supply of crosslinking-related components (crosslinking agent, crosslinking catalyst, etc.) while monitoring the load of the extruder, the melt viscometer installed at the tip of the extruder and / or the mold pressure. , Can be performed while controlling the reaction in the extruder. This monitor enables more stable production.

Further, the method of supplying the crosslinking agent will be specifically described. Since it is difficult to adjust the amount of water, a large amount of water is usually used. The reaction can be controlled by selecting, for example, a substance containing water of crystallization that releases water over a period of time at a certain temperature or higher. Examples of such substances include aluminum hydroxide crystal hydrate. This aluminum hydroxide crystal hydrate usually requires heating at 200 ° C. for about 10 minutes, although it depends on the particle size. As a reaction control method other than the above, there is also a method by adjusting the amount of the crosslinking catalyst. This method is particularly realistic.

Many polyhydric alcohols as a cross-linking agent have the property of melting at low temperatures, and if the polyhydric alcohols are to be stably supplied and the amount of the polyhydric alcohols to be supplied is to be adjusted, a separate injection port is required. Is preferably provided. Furthermore, for example, the extruder is relatively small, the extrusion amount per unit time is relatively large and the crosslinking reaction in the extruder is insufficient, or it is sufficient to use a relatively small amount of silylated olefin polymer. In the case where the reaction is to be proceeded to, it may be desirable to preliminarily use the silanol formation by hydrolysis of the alkoxy group to a certain extent as a pretreatment. Examples of the method include a method of treating the silane crosslinkable olefin resin under humidification and heating for a certain period of time without supplying a crosslinking catalyst. The fixed time under humidification and heating means, for example, 40 ° C. or higher and 10 minutes or longer. More preferably, it means 40 to 170 ° C. and 1 to 3 months.

The inventors of the present invention have shown that this silanolization reaction is slower and more rate-determining than the condensation reaction in the next step, and that the reaction is not promoted by a crosslinking catalyst other than acid or alkali.
It has also been discovered that such pretreatment is possible and effective even if there is a reaction site that proceeds to a certain degree of condensation crosslinking. In addition, since the absolute amount of silanol groups may be small, the degree of silanolation is difficult to quantify and is not general. Therefore, when it is necessary to use a base resin having a degree of silanolation or a degree of cross-linking, it is possible to cover by the in-line control as described above.

Here, there is a difference between the degree of cross-linking that does not prevent extrusion in the extruder and the ability of the extruder,
In addition, it is difficult to grasp the degree of cross-linking in the extruder, which cannot be generally stated, but immediately after extrusion, that is, for 1 hour after extrusion (at room temperature,
Starting the gel fraction measurement of the extrudate within 65% relative humidity) is approximately within 25% gel fraction. It should be noted that there is no problem that cross-linking proceeds further under natural or forced conditions after extrusion. First, the foam immediately after extrusion is cut into about 5 mm square, and about 0.8 g is precisely weighed and placed in a flat bottom flask. Put 80 ml of xylene in the flask, 5
After boiling and refluxing for a while, the insoluble residue is filtered off with a wire mesh of 80 mesh in a hot state, and dried by heating together with the wire mesh. The weight ratio of the obtained insoluble residue (including the one adhered to the wire net) to the original foam was measured, and this value was called the gel fraction.

According to the method for producing a polyolefin resin foam of the present invention, it is possible to obtain a foam having a high expansion ratio of 3 times or more (particularly 3 to 100 times), which has been difficult to form by extrusion foaming. It is possible to easily form the base resin without any special treatment. Furthermore, a foam having a high closed cell rate (for example, 50% or more) and a beautiful cell structure can be obtained.

[0036]

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. Example 1 As the extrusion apparatus, a so-called tandem type apparatus in which a uniaxial extruder having a barrel diameter of 50 mm and L / D = 35 was connected to a uniaxial extruder having a barrel diameter of 65 mm and L / D = 30 was used.

The die has a diameter of 60 mm and a gap of 0.45 m.
A circular mold having a diameter of m was attached horizontally, and a cylindrical molding plug having an outer diameter of 170 mm was horizontally provided at a distance of about 150 mm from the die outlet. The cylindrical foam extruded from the extruder having this structure was cut open and taken off to obtain a foam sheet. Extrusion rate is 23k / h
It was set to g. Further, the resin temperature at the time of discharging the mold was set as low as possible so that smooth extrusion could be performed. The foaming agent and other liquid substances were press-injected with a pump from an injection port immediately after the first metering zone in the middle of the extruder. In the extruder, the total residence time of the material was about 23 minutes and the residence time after the inlet was about 17 minutes.

As the polyolefin resin, FY4 (MI value 5) manufactured by Nippon Polychem Co., which is homopolypropylene, was used. Silane-crosslinkable polyolefin resin is silylated polypropylene, Mitsubishi Chemical's Linklon XPK8
01H (MI value 5) was used, and dry blended with the above homopolypropylene and supplied to the extruder. As the nucleating agent, a combination of baking soda and citric acid was subjected to a coating treatment for suppressing the reaction, that is, Hydrocerol HK70 manufactured by Boehringer Ingelheim Co. was used, and dry blended with the above base resin and supplied to the extruder. did. As the foaming agent, liquid butane, which is a physical foaming agent, was used and supplied from an injection port.

Dibutyltin dilaurate (manufactured by Tokyo Fine Chemical Co., Ltd.) was used as a polymerization catalyst, and a suspension of this and water as a crosslinking agent was supplied from the middle of the extruder. The amount of each (part by weight) and the characteristics of the resulting foam (foaming ratio,
Table 1 shows the thickness, gel% immediately after extrusion, closed cell rate, appearance, and thermoformability). The gel fraction was measured by cutting a sample sheet into square pieces of about 5 mm, carefully measuring about 0.8 g, and placing the mixture in a flat-bottomed flask. Further, 80 ml of xylene was added and the mixture was boiled under reflux for 5 hours. Filter with mesh wire mesh,
The weight ratio of the insoluble residue obtained by drying to the original sample was defined as the gel fraction. The drying was carried out together with the wire mesh, and the amount of the wire mesh attached was included in the gel.

Further, Table 1 shows the values measured immediately after extrusion foaming (room temperature, within 1 hour). When this foam was treated in an air layer at a temperature of 80 ° C. and a relative humidity of 80% for 3 hours, the gel fraction became 9.2%, and further crosslinking proceeded. From this result, it was found that the gel fraction does not always indicate the degree of crosslinking in the extruder, but the gel fraction can be controlled by adjusting the addition method and amount of the crosslinking catalyst. The closed cell ratio is a value obtained by dividing the volume measured by an air pycnometer by the apparent volume, as a percentage. Evaluation of thermoformability is 70m outside diameter
The appearance of a thermoform molded by a single-wafer vacuum forming machine into a cup shape having a size of m and a height of 75 mm was visually evaluated. In the appearance and thermoformability, ⊚ means a very good state, and ∘ means a good state.

Example 2 The same material as that of the apparatus of Example 1 was used, but the composition ratio of the material was as shown in Table 1, and extrusion foaming was performed. However, the polymerization catalyst dibutyltin dilaurate was previously added to FY4 manufactured by Nippon Polychem Co., which is a homopolypropylene so as to be 1% by weight, and this was used as a masterbatch, to which the base resin having the composition ratio of Example 1 was added. It was dry blended and fed to the extruder. The polyolefin resin in Table 1 means the total amount of homopolypropylene in the masterbatch and homopolypropylene in the base resin. As a result, Example 1
Although not so much, a foam having an improvement effect as compared with Comparative Example 1 was obtained.

Example 3 Using the apparatus of Example 1, a homopolypropylene resin EA9 (MI made by Nippon Polychem Co., Ltd. was used as a polyolefin resin.
Value of 0.5), using Kihara Talc manufactured by Kihara Kasei Co., Ltd. as a nucleating agent instead of hydrocerol, and using Rikenal S manufactured by Riken Vitamin Co., whose main component is glycerin monostearate instead of water as a cross-linking agent. The same composition as in Example 1 was used except that the melted -100 was press-fitted with a pump in the middle of the extruder.
Extrusion foaming was performed as follows. As a result, it was found that the improvement effect was recognized as compared with Comparative Example 2 below.

Example 4 Using the apparatus of Example 1, water was used as a cross-linking agent and aluminum hydroxide trihydrate (B-308 manufactured by Alcoa Co.) was used, and the composition ratio of the polyolefin resin and the silane cross-linkable polyolefin resin was used. The same material as in Example 3 was used except that the composition was changed, and this was dry-blended with the base resin and supplied to the extruder, and the cross-linking catalyst was press-fitted into the injection port.
Extrusion foaming was performed as follows. As a result, a foam having a sufficient improvement effect was obtained as compared with Comparative Example 2.

Comparative Example 1 Using the apparatus of Example 1, 100% of the same polyolefin resin as in Example 1 was used so that the average MI of the base resin did not change, and the other compositions in Table 2 were used. Was extruded and foamed. The results are shown in Table 2. In the table, x means defective state in appearance and thermoformability. When Example 1 and Comparative Example 1 were compared, Example 1 yielded a finer foam with higher magnification, and the improvement effect of the present invention was remarkable.

Comparative Example 2 Using the apparatus of Example 1, the same polyolefin resin as in Example 4 was used in the same manner as in Example 4, except that the average MI of the base resin was the same as in Example 4, except that the same MI was used. As a homopolypropylene having the same MI value as the silane crosslinkable polyolefin used in the example, 30% by weight of FY4 manufactured by Nippon Polychem Co., Ltd.
The mixture was used, and extrusion foaming was performed with the composition ratios thereof as shown in Table 2.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

According to the present invention, in the case of extrusion-foaming a resin that is generally difficult to foam, such as normal grade polypropylene, linear low-density polyethylene, and high-density polyethylene, the range of extrusion foaming conditions is wide and foam molding is easy. Further, it is easy to control foaming at a high magnification and the closed cell ratio, and it is possible to produce a foam at a low cost without damaging the quality such as strength and causing no problem of colored odor. Furthermore, it is possible to obtain a foam having easy secondary moldability such as thermoforming.

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Claims (8)

(57) [Claims] 1. Polyolefin resin 60 to 97% by weight
While melting and kneading a base resin consisting of 3 to 40% by weight of silane crosslinkable polyolefin resin, a crosslinking catalyst, a crosslinking agent and a foaming agent in the extruder, a gel fraction of 25% in the extruder.
A method for producing a polyolefin-based resin foam, which comprises advancing the crosslinking reaction in step 1 to extrude and foam. 2. The production method according to claim 1, wherein the crosslinking agent comprises a polyhydric alcohol, water, a water-generating substance or a mixture thereof. 3. The production according to claim 1, wherein the required amount of the crosslinking agent, the crosslinking catalyst, or both is added at once in the middle of the extruder or dividedly added in the middle of the extruder. Method. 4. A silane-crosslinkable polyolefin resin,
The manufacturing method according to any one of claims 1 to 3, which is placed in an extruder after being brought into contact with water as a crosslinking agent at 40 ° C or more for 10 minutes or more in advance. 5. The method according to claim 1, wherein the polyolefin resin is a polypropylene resin, a high density polyethylene resin or a linear low density polyethylene resin. 6. The method according to claim 5, wherein the polyolefin resin is a polypropylene resin. 7. A polyolefin resin foam, the production method according to any one of claims 1 to 6 having three or more times the expansion ratio. 8. A polyolefin-based resin foam obtained by the method according to any one of claims 1 to 7 .