JPH10100182A - Polyolefin resin block-shaped foam and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thick polyolefin resin block-shaped foam having foams oriented vertically long in its thickness direction, and a method for producing the same. SOLUTION: A foamable resin mixture consisting of a foaming agent, a crosslinking agent and a polyolefin resin is supplied into a mold constituted of opposed operable molds and a piston to be hermitically sealed therein (1) and the resin mixture hermetically sealed in the mold is pressed and shaped by the piston and heated to the decomposition temp. of the foaming agent or more to generate gas (2). Subsequently, the molten resin is cooled within a range from softening temp. to an m.p. and the piston is set to a speed equal to or lower than the expansion speed of the resin to open the mold and resin foam is cooled and solidified to take out a molded product from the mold (3). In such a state that the slide part of the mold and the piston in the mold is held to temp. lower than the m.p. of the resin by 30 deg.C, the processes 2, 3 are performed and, further, the gel ratio in the resin foam is set to 0-50%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in rigidity in the thickness direction, shock absorption, etc., by orienting the cell structure vertically in the direction perpendicular to the surface of the foam (hereinafter referred to as the thickness direction). , Cushioning materials, packaging materials, various covers, heat insulating materials,
The present invention relates to a polyolefin resin block-like foam usable for building members and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a thick polyolefin resin block-shaped foam, a foaming agent and a cross-linking agent in a resin composition are decomposed in a pressurized closed mold, and then decompressed and expanded. The method of taking out a foam by taking it out is widely used industrially. The reason is that in a state where the resin composition is not expanded under pressure, the foaming agent in the resin composition, and the decomposition of the cross-linking agent are performed by heating, so that the rate of these decomposition does not greatly change in the thickness direction. Therefore, a block-shaped foam having a uniform thickness in the thickness direction can be obtained. As a method of obtaining a polyolefin resin block-like foam by such a method,
For example, there is a method as described in JP-A-7-88854.

[0003]

However, according to the above-mentioned method, the foam structure of the obtained foam is limited to a spherical shape, and a foam having a vertically long cell structure in the thickness direction cannot be obtained.
This is because the cavity in the method has a side surface inclined so as to diffuse toward the mold matching portion, and thus the expansion of the resin by opening the mold is performed three-dimensionally.

Further, in this method, the resin surface is taken out before foaming before cooling and solidifying, so that a glossy skin layer cannot be obtained.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a thick polyolefin resin block-like foam in which cells are oriented vertically in the thickness direction and a method for producing the same.

[0006]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found a method for preferably producing the above-mentioned polyolefin resin block-like foam, and have completed the present invention.

That is, the present invention provides: 1) a foamable polyolefin resin mixture comprising a foaming agent, a cross-linking agent and a polyolefin resin is supplied into a molding die constituted by a mold and a piston which can be opened to face each other and sealed; 2) a step of press-forming the foamable polyolefin resin mixture sealed in the mold with a piston, and then heating the foamable polyolefin resin mixture to a temperature higher than the decomposition temperature of the foaming agent to generate gas in the molten polyolefin resin; 3) foaming After the agent is decomposed, the temperature of the molten polyolefin resin is equal to or higher than the softening temperature of the polyolefin resin, and is cooled within a range equal to or lower than the melting point of the polyolefin resin. The foamable polyolefin resin is expanded two-dimensionally by releasing at a speed of Obtaining a body, 4) cooled and solidified the polyolefin resin foam,
Removing the molded product from the molding die, and the sliding portion between the die and the piston in the molding die is maintained at a temperature not higher than 30 ° C. lower than the melting point of the polyolefin resin. Steps 2) and 3) are performed, and the gel fraction in the polyolefin resin foam is reduced to 0.
And a method for producing a polyolefin resin block-shaped foam characterized by being in the range of from 50% to 50%, and further comprising a skin material and a polyolefin resin foam layer, or two or more polyolefin resin foam layers, and more than two layers of polyolefin resin. The present invention relates to a laminated foam, wherein an adhesive is not used on a laminated bonding surface of the laminated foam.

Hereinafter, the present invention will be described in detail.

The polyolefin resin used in the present invention includes, for example, high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene, ethylene-propylene random copolymer, ethylene-vinyl acetate copolymer, or propylene-α -Olefin copolymers and the like are preferable, and these can be used alone or in combination of two or more. The α-olefin is 1
-Butene, 1-pentene, 1-hexene, 4-methyl-
Examples thereof include 1-pentene and 1-octene.

[0010] These polyolefin resins may be a mixture of fillers, such as talc, calcium carbonate, silica, carbon black, metal powder, glass fiber, carbon fiber, magnesium hydroxide, trioxide. Antimony, zinc borate, bromine compounds,
Ceramic, zeolite and the like can be used.

The blowing agent to be mixed with the polyolefin resin is a chemical blowing agent capable of decomposing by heating to generate a gas, such as azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, 4,4'- Oxybis (benzenesulfonyl hydrazide), sodium hydrogen carbonate and the like are preferably used.

The crosslinking agent used in the present invention includes, for example, benzoyl peroxide, 2,5-dimethyl-
2,5-di-t-butylperoxyhexane, 2,5-
Dimethyl-2,5-di-t-butylperoxyhexine-3, dicumyl peroxide, t-butylhydroxyperoxide and the like. In this case, as a crosslinking aid for promoting crosslinking, for example, triallyl cyanurate, triallyl isocyanurate, trimethylolpropane trimethacrylate, 1,2-polybutadiene, divinylbenzene and the like can be used in combination.

In the present invention, the concentration of the gel formed in the polyolefin resin by the reaction between the crosslinking agent and the polyolefin resin (hereinafter abbreviated as gel fraction) is from 0 to 50%, more preferably from 0 to 50%. It is preferably in the range of 〜30%. When the gel fraction exceeds 50%, the high-concentration cross-linking structure introduced into the resin increases the viscosity and elongation stress of the resin at the time of foaming, thereby hindering the two-dimensional expansion of the resin. Will be done. The amount of the cross-linking agent mixed with the polyolefin resin in order to make the gel fraction within the above preferable range varies depending on the type of the cross-linking agent or the polyolefin resin, but is usually 0.05 to 0.5% by weight. preferable. Next, a method for producing a polyolefin resin block-like foam according to the present invention will be described.

FIGS. 1 to 4 schematically show a molding flow of a polyolefin resin block-like foam according to the present invention, and a method for producing a polyolefin resin block-like foam will be described with reference to these drawings.

First, as shown in FIG. 1, a foamable polyolefin resin mixture 1 comprising a foaming agent, a cross-linking agent and a polyolefin resin is constituted by a mold 2, a mold 3 and a piston 5 which can be opened to face each other. Supply into the mold and seal. The method for supplying the foamable polyolefin resin mixture is not particularly limited, but as a method preferably preferably used, for example, a foaming agent, a crosslinking agent and a polyolefin resin are extruded using a kneader such as a Banbury mixer or a roll. And a method in which a polyolefin resin mixture on a sheet-like or foamable lump obtained after melt-kneading is placed in a mold.

In order to further ensure the sealing performance in the process of FIG. 1, a ring-shaped seal is attached to one or both of the dies at a portion where the dies 2 and 3 are in contact with each other. It is effective to insert the material 4 and to install the ring-shaped sealing material 6 on the piston 5.

Subsequently, as shown in FIG. 2, the piston 5 is moved to form the foamable polyolefin resin mixture under pressure. In this case, the shapes of the surfaces of the mold 2 and the piston 5 that come into contact with the foamable polyolefin resin mixture are not particularly limited, and various shapes such as flat surfaces, uneven shapes, embossed patterns and the like are required according to the required shape of the molded product. You can choose. After the pressure shaping, the surface of the mold 2 and the piston 5 in contact with the foamable polyolefin resin mixture (hereinafter, abbreviated as a molding surface) is heated to a temperature equal to or higher than the decomposition temperature of the foaming agent, so that the molten polyolefin resin Generate gas. The crosslinking agent is selected to cause a crosslinking reaction under the temperature conditions in the step of FIG.

In the process shown in FIG. 2, the sliding portion between the mold 3 and the piston 5 is higher than the melting point of the polyolefin resin by three.
It must be kept below 0 ° C lower temperature. When the temperature is higher than the melting point of the polyolefin resin by more than 30 ° C. and higher than the melting point, the molten polyolefin resin enters the clearance between the mold 3 and the piston 5 (hereinafter referred to as “clearance”). As a result, burrs are generated and not only the yield of the molded product is deteriorated, but also it is difficult to take out the molded product from the molding die. As a method for controlling the temperature of these sliding parts, a method in which a pipe 7 is usually provided in the mold 3 and a cooling medium such as oil or water is passed is preferably used. Subsequently, the temperature of the molten polyolefin resin containing a foaming gas is equal to or higher than the softening temperature of the polyolefin resin, and
The polyolefin resin is cooled to the melting point or less, and then foaming is performed by opening the piston as shown in FIG. 3, and the opening is stopped before the surface of the piston 5 separates from the resin surface. In the process of FIG. 3, when the resin temperature during foaming is lower than the softening temperature of the polyolefin resin, the viscosity of the resin becomes too high, the growth of cells is inhibited, and a long and elongated cell structure can be obtained. Can not. If the melting point of the polyolefin resin is exceeded, the viscosity of the resin at the time of foaming will not be sufficient to withstand the pressure of the foaming gas, and the bubbles will be broken during the bubble growth process.

In the process shown in FIG. 3, the opening speed of the piston must be lower than the expansion speed of the expandable polyolefin resin. Creates a gap between
Since the foaming gas escapes from the resin surface to the outside of the resin, the foaming ratio is poor and the foam has an insufficient thickness. The opening speed of the piston 5 should be adjusted according to the content of the foaming agent, that is, the amount of gas generated in the resin, or the type of the polyolefin resin, but a speed of usually 5 mm / sec or less is preferably selected. .

Further, the sliding portion between the mold 3 and the piston 5 in the step of FIG. 3 is similar to the step of FIG.
It is necessary to keep the temperature below 30 ° C. lower than the melting point of the polyolefin resin. If the temperature is higher than 30 ° C. lower than the low temperature, the viscosity of the resin in contact with the clearance becomes insufficient. As a result, when the gas pressure in the resin is released by opening the piston, the gas in the resin becomes It breaks through the resin in the clearance and escapes to the outside of the resin.

Finally, after the foam obtained in the step shown in FIG. 3 is cooled and solidified, as shown in FIG. 4, the molds 2 and 3 are opened to form a mold from the inside of the mold. Product 8 is taken out.

When a block-shaped laminated foam is to be obtained as a molded product, a skin material and a foamable polyolefin resin mixture are supplied into a molding die in the step shown in FIG. The steps shown in FIGS. 2 to 4 may be sequentially performed in the same manner as in the case of obtaining a foam.

Examples of the skin material include metals such as aluminum, copper, and brass, fibers such as nonwoven fabric, cloth, and carbon fiber sheet, polyolefin resins, vinyl chloride resins, polyester resins, polyamide resins, and polystyrene resins. Thermoplastic resin, the thermoplastic resin elastomer, paper, natural rubber, natural leather, resin foam, and the like. These skin materials may be in the form of a film or a sheet. Further, the thermoplastic resin and the elastomer used for the skin material may include various fillers that can be mixed with the polyolefin resin.

The foamable polyolefin resin mixture supplied into the mold in the step shown in FIG. 1 is not limited to one kind. That is, a block-shaped laminated foam having two or more foam layers can be obtained by subjecting two or more foamable polyolefin resin mixtures to foam molding in the same manner according to the steps shown in FIGS.

The polyolefin resin block foam obtained by the present invention is obtained by covering a foam layer with a skin material in a sandwich form, including a single-layer foam and a two-layer foam in which a skin material and a foam layer are combined. A three-layer foam, or a laminated material having a skin material of two or more layers, and a laminated foam obtained by integrating the laminated body with a foam layer, or a laminated material obtained by integrating the skin material with two or more foam layers Laminated foam.

The polyolefin resin block-shaped laminated foam obtained by the present invention is characterized by integral foam molding, and is subjected to a secondary processing for bonding the laminated bonding surface of the laminated foam with an adhesive or the like. It can be obtained without.

(Function) The method for producing a polyolefin resin block foam according to the present invention is characterized in that the resin is two-dimensionally expanded by growing cells vertically in the thickness direction at the time of foaming. Yes, a mechanism for giving direction to the growth of bubbles will be described below.

In the foaming step, when the gas compressed in the resin is going to expand, the expansion direction is the direction in which the pressure is reduced. The resulting bubbles will be elongated.
On the other hand, when the pressure is released three-dimensionally as in the case of natural release, the direction in which the gas expands, that is, the direction in which the bubbles grow, also becomes three-dimensional. Therefore, in order to grow the bubbles vertically in the thickness direction, it is necessary to use a mold in which the side surfaces of the cavity are parallel to the thickness direction of the foam, instead of the conventional mold in which the side surfaces of the cavity are inclined. is there.

In the method of the present invention, the sliding surface between the mold and the piston is parallel to the thickness direction of the foam, and the piston is further moved in the direction in which the thickness of the foam increases along the sliding surface. It is open. However, only by these methods, it is not possible to obtain a foam in which cells are oriented vertically in the thickness direction. Because, when the foamed gas held in the resin under pressure is decompressed and expanded with the opening of the piston,
This is because the pressure in the clearance portion is significantly lower than the pressure of the foaming gas, so that the gas flows toward the clearance portion, as shown in FIG. 5, and the bubbles are not vertically oriented in the thickness direction. In the present invention, as described above, since the sliding portion between the mold and the piston is maintained at a temperature 30 ° C. lower than the melting point of the polyolefin resin,
The resin in contact with the clearance portion is in a softened or solidified state to form a gas seal layer, and gas flow to the clearance portion can be suppressed.

Further, the temperature control of the sliding portion is preferable in that the foaming gas generated in the resin by the decomposition of the foaming agent is kept in the resin under pressure until before the foaming step, and is effectively used during foaming. Is what you do. That is, since the surface layer of the resin in contact with the sliding surface before the foaming step does not reach the decomposition temperature of the foaming agent, an unfoamed layer maintained at a high viscosity is formed, and the foamed gas generated in the resin is formed by the unfoamed layer. Functions as a gas seal layer that effectively suppresses the flow to the clearance portion and escape to the outside of the resin.

Incidentally, it is more effective that the above-mentioned temperature control of the sliding surface is performed by a molding die using a combination of an upper and lower die and a piston, like the molding die in the present invention. For example, in the case of a molding die composed of a pair of concave and convex dies as shown in FIG. 6, the temperature of the sliding surface is controlled by providing a pipe through which the cooling medium passes at 9, or 10, or both positions. However, in this case, the temperature of the sliding surface is also transmitted to the periphery of the sliding surface, the temperature of the resin in contact with the periphery of the sliding surface decreases, and the undecomposed layer of the foaming agent or the gas seal is formed. The layer is formed as shown in FIG. As a result, the foam obtained is one in which the expansion of the ends is suppressed, and the portion obtained as a product is limited, so that the production method has low productivity. In order to suppress the heat conduction of these sliding surfaces, for example, as disclosed in JP-A-7-125031,
Although a method of interposing a heat insulating material between the member on the sliding surface and the other mold member is disclosed, the installation of the heat insulating material alone cannot be sufficient to suppress heat conduction.
On the other hand, in the mold according to the present invention, the mold 3 provided with the piping in FIG. 2 and the mold 2 are only in contact with each other by clamping, and a clearance is provided between the mold 3 and the piston 5. Therefore, the temperature of the sliding surface of the mold 3 is hardly transmitted to the periphery of the sliding surface. If a member having low heat conductivity is used for the mold 3, the piston 5 and the mold 2
Thermal effect on the substrate can be further reduced. However, when the periphery of the sliding surface of the uneven mold is made of a member having low heat conduction, the heat efficiency of the mold is reduced. Therefore, in a manufacturing method involving heating and cooling of the mold, This results in a lower molding cycle.

In order to grow the bubbles vertically in the thickness direction, it is essential to control the resin viscosity in the foaming step in addition to using the above-described molding die.
In other words, if the viscosity of the resin is too low in the foaming step, the bubbles will not be able to withstand the foaming gas pressure and will break during the bubble growth process. Further, if the viscosity of the resin and the elongation stress are too high, even if the direction in which the pressure is reduced is one direction, rapid expansion of the foaming gas in that direction is suppressed, and the thickness direction of the bubbles is reduced. Even if molding is performed using a molding tool devised for expansion into a foam, a wavy foam 12 as shown in FIG. 7 is obtained.

As a method for controlling the resin viscosity and elongation stress in the foaming step using a polyolefin resin, a method for adjusting the gel fraction is generally and widely employed. However, the resin viscosity and the elongation stress suitable for growing the cells vertically in the thickness direction cannot be obtained in the foaming step in the present invention only by adjusting the gel fraction. The present inventor added to the above gel fraction,
It has been found that by adjusting the resin viscosity in the foaming step, a resin viscosity and an elongation stress suitable for expanding the cells vertically in the thickness direction can be obtained. In other words, the resin temperature in the foaming step of the present invention is equal to or higher than the softening temperature of the polyolefin resin used for molding and is equal to or lower than the melting point, so that the resin viscosity and the tensile stress are significantly higher than those in the molten state. In addition, the breaking of bubbles during the bubble growth process can be suppressed. In addition, the resin viscosity and elongation stress described above are the resin viscosity and elongation stress in the conventional method of suppressing the expansion of the foaming gas as much as possible by introducing a cross-linking structure at a high concentration and fixing the growth of bubbles as fine spheres. In other words, the resin at the time of foaming in the present invention has an elongation property enough to grow cells elongated in the thickness direction.

The foam obtained by the production method of the present invention has a glossy skin layer.
Usually, such a skin layer is known to be obtained by melting or softening a polyolefin resin and then cooling and solidifying the polyolefin resin. However, in the present invention, as described above, the surface of the polyolefin resin in the mold during the foaming step is reduced. Since the temperature is maintained in the temperature range of the softening temperature or higher and the melting point or lower and the resin surface is cooled and solidified after the completion of foaming, a foam having the above gloss can be obtained.

As described above, since the production method of the present invention is a method suitable for growing bubbles vertically in the thickness direction, the resin can be expanded two-dimensionally. In addition, such a two-dimensional expansion of the resin effectively acts even when a block-shaped laminated foam is molded using a molding die, and the reason will be described below.

In order to obtain a block-shaped laminated foam in molding using a molding die, first, the skin material and the foamable resin mixture are compressed and integrated under heating. Operation is known to be easy. However, if the resin is three-dimensionally expanded at the time of foaming, the skin material does not expand in the direction perpendicular to the thickness direction, so the obtained molded product is partially formed by the skin material and the foam layer. They will be combined or wavy. Therefore, if a good block-shaped laminated foam is to be obtained using a molding die, the resin must be two-dimensionally expanded while maintaining the bonding surface between the skin material and the foam layer during compression. In this sense, the production method of the present invention can be said to be a method suitable for obtaining such a block-shaped laminated foam.

It is also possible to obtain a laminated foam having different foam layers by expanding the resin two-dimensionally during foaming. That is, by supplying two or more types of polyolefin resin mixtures into a mold and performing molding, a block-shaped laminated foam in which each polyolefin resin mixture is two-dimensionally expanded can be obtained. For example, if two or more kinds of polyolefin resin mixtures having different amounts of the foaming agent are used, foam layers having different expansion ratios are obtained. If two or more kinds of polyolefin resin mixtures having different amounts of the cross-linking agent are used, bubbles are generated. A foamed layer having a different shape can be obtained, and a laminated foam having a foamed layer having different physical properties can be obtained by using a mixture of two or more kinds of polyolefin resins using different resins.
Such a foam is obtained as a result of expanding the polyolefin resin mixture used to form each foam layer two-dimensionally, similarly to the case of obtaining a laminated foam using the skin material. When a layer which expands in a specific manner is included, the bonding surface is wavy or partially bonded, resulting in an insufficient laminated foam.

[0038]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples.

In the examples, the melt flow rate (hereinafter referred to as MF)
R is an abbreviation of JIS K 6758 (1981, 230 ° C.,
2.16 kg load), high density polyethylene, JIS K
6760 (1981, 190 ° C, load 2.16k
g), for the ethylene-vinyl acetate copolymer, JIS K
6730 (1981, 190 ° C, load 2.16 kg)
Depends on the conditions. In Table 1, the melting point was determined by the DSC method, and the softening temperature was determined by the ethylene-propylene random copolymer.
IS K 6758, high density polyethylene, JIS K
6760, ethylene-vinyl acetate copolymer
According to S K 6730. The gel fraction in Table 1 is
Cut foam 5mmg (referred to as W ₁₎ placed in a sample bottle, subjected to 12 hours extraction with 120 ° C. using an aluminum block bath xylene was added 50ml therein, on a wire mesh and filtered thereafter stainless screen The undissolved portion is dried at 105 ° C. for 5 hours, weighed (referred to as W ₂ ), and determined according to the following equation.

Gel fraction = (W ₂ / W ₁ ) × 100 Example 1 High-density polyethylene (manufactured by Tosoh Corporation, trade name Nipolon Hard 4010, MFR 5.5 g / 10 min) 100
Parts by weight, 5 parts by weight of azodicarbonamide as a foaming agent,
After preparing a mixture comprising 0.4 parts by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexine as a cross-linking agent, the mixture was melt-kneaded using a single screw extruder. And extruded as an unfoamed sheet. Next, the unfoamed sheet was placed in a molding die composed of an opposing upper die 3, lower die 2, and piston 5 schematically shown in FIG. A pipe was provided in the upper mold, and water was passed through the pipe as a cooling medium to maintain the sliding surface between the upper mold 3 and the piston 5 at 80 ° C. Subsequently, after sealing the unfoamed sheet by mold clamping, the unfoamed sheet is pressure-formed by the piston 5 at a pressure of 20 kgf / cm ² , and then the molding surface is heated to 200 ° C. to decompose the foaming agent. As a result, gas was generated in the molten resin. And after cooling the said molding surface to 130 degreeC, 0.1.
The resin was expanded by opening the piston at a speed of 8 mm / sec. Next, the opening of the piston was stopped, and after the foam was cooled and solidified, the molded article was taken out of the mold.

The foam obtained had a foam structure vertically elongated in the opening direction of the piston, that is, the thickness direction of the foam, and had a foaming ratio of 10 times and a glossy skin layer on the surface. Was.

Example 2 Ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation, trade name Ultracene 540, MFR 3.0 g / 10 min)
After preparing a mixture consisting of 100 parts by weight, 7 parts by weight of azodicarbonamide as a foaming agent, and 0.3 parts by weight of dicumyl peroxide as a crosslinking agent, the mixture is melt-kneaded using a single screw extruder and passed through a T-die. Extruded as an unfoamed sheet. Then, in Example 1, the sliding surface of the upper mold was maintained at 50 ° C., and after setting the molding surface to 95 ° C., the piston was opened at a speed of 1.2 mm / sec. Foaming was performed in the same manner as in Example 1.

The foam obtained had a foam structure in which the cell structure was elongated in the opening direction of the piston, that is, the thickness direction of the foam, and had a foaming ratio of 15 times and a glossy skin layer on the surface. Was.

Example 3 Ethylene-propylene random copolymer (manufactured by Chisso Petrochemical Co., Ltd., trade name: Chissopolypro XF1800, M
FR 1.9 g / 10 min) 100 parts by weight, azodicarbonamide 5 parts by weight as a foaming agent, 2,5-
0.08 parts by weight of dimethyl-2,5-di-t-butylperoxyhexane, and 0.1% of divinylbenzene as a crosslinking aid.
After adjusting the mixture consisting of 8 parts by weight, the mixture was melt-kneaded using a single screw extruder and extruded as an unfoamed sheet through a T-die. Then, foam molding was performed in the same manner as in Example 1 except that the piston was opened at a speed of 1.5 mm / sec after the molding surface was set to 135 ° C. in Example 1.

The foam obtained had a cell structure vertically elongated in the opening direction of the piston, that is, the thickness direction of the foam, and had a foaming ratio of 10 times and a glossy skin layer on the surface. Was.

Comparative Example 1 Molding was performed under the same conditions as in Example 1 except that the opening speed of the piston was set to 20 mm / sec and the opening was performed at a speed higher than the expansion speed of the resin. The obtained foam had a poor expansion ratio, and traces of outgassing were observed on the surface.

Comparative Example 2 Molding was performed under the same conditions as in Example 1 except that the piston was opened from the state where the molding surface was maintained at 150 ° C. The obtained foam had a poor expansion ratio and had a rough surface.

Comparative Example 3 Molding was performed under the same conditions as in Example 1 except that the piston was opened from the state where the molding surface was maintained at 115 ° C. The obtained foam had a poor degree of expansion of cells. .

Comparative Example 4 Molding was performed under the same conditions as in Example 1 except that the sliding surface was maintained at 120 ° C. The obtained foam had many burrs, and the cell structure was radially oriented from the center of the foam toward the periphery.

Comparative Example 5 In Example 1, the sliding surface was 12
Molding was carried out under the same conditions except that the temperature was maintained at 0 ° C. and the sliding surface was maintained at 80 ° C. in the foaming step. The obtained foam had many burrs and was poor in expansion ratio.

Comparative Example 6 In Example 1, the sliding surface was 80
C., and molding was performed under the same conditions except that the sliding surface was maintained at 120.degree. C. in the foaming step. The obtained foam had many burrs, and the cell structure was radially oriented from the center of the foam toward the periphery.

Comparative Example 7 In Example 2, the ethylene-vinyl acetate copolymer 10
0 parts by weight of dicumyl peroxide 1.0 as a crosslinking agent
Molding was carried out in the same manner as in Example 2 except that parts by weight were mixed. The obtained foam had a wavy shape.

Table 1 summarizes the results obtained in Examples 1 to 3 and Comparative Examples 1 to 6. The items in Table 1 will be described below.

(Bubble Shape) The obtained foam is cut at an arbitrary position from a direction parallel to the thickness direction, and the bubble diameter and the thickness in the thickness direction are determined for the bubbles observed at an area of 4 cm ^{2 of the} cut surface. The cell diameter in the direction perpendicular to the direction was measured, and the cell diameter ratio in the thickness direction was divided by the cell diameter ratio in the direction perpendicular to the thickness direction to obtain the cell diameter ratio. And it judged based on the following criteria based on the said bubble diameter ratio.

：: 80% or more bubbles having a bubble diameter ratio of 2 or more Δ: 50% or more and less than 80% of bubbles having a bubble diameter ratio of 2 or more ×: less than 50 bubbles having a bubble diameter ratio of 2 or more (surface property) ○: There is a glossy skin layer △: There is a rough surface ×: There is a trace of gas escape on the surface

[0056]

[Table 1]

Example 4 In Example 2, after a 0.1 mm aluminum sheet was placed as a skin material on the mold 2 side in the molding die shown in FIG. 1, an unfoamed sheet was placed on the piston 5 side. The molding was performed in the same manner as in Example 2 except that the skin material and the unfoamed sheet were sealed in a mold by tightening, and a block-shaped laminated foam in which the aluminum sheet and the foam layer were integrated was obtained. Obtained.

Example 5 In Example 2, a thermoplastic elastomer (trade name: DYNARON61, manufactured by Nippon Synthetic Rubber Co., Ltd.) was used as a skin material.
00P), the non-foamed sheet was covered in a sandwich shape and placed in a molding die, and then the skin material and the non-foamed sheet were sealed in the molding die by clamping, in the same manner as in Example 2. Molding was performed to obtain a block-shaped laminated foam in which the thermoplastic elastomer and the foamed layer were integrated.

Example 6 High-density polyethylene (manufactured by Tosoh Corporation, trade name Nipolon Hard 4010, MFR 5.5 g / 10 min) 100
Parts by weight, 2,5-dimethyl-2,5-di- as a crosslinking agent
After preparing a mixture consisting of 0.4 parts by weight of t-butyl peroxyhexine, and 2.5 parts by weight, 5 parts by weight, and 7 parts by weight of azodicarbonamide as a foaming agent,
The mixture was melt-kneaded using a single-screw extruder and extruded through a T-die as unfoamed sheets. Then, from the mold 4 side, each unfoamed sheet is formed in the order of an unfoamed sheet of 2.5 parts by weight of a foaming agent, an unfoamed sheet of 5 parts by weight of a foaming agent, and an unfoamed sheet of 7 parts by weight of a foaming agent. After setting in the mold, molding was performed in the same manner as in Example 1 except that the unfoamed sheet was sealed in the mold by closing the mold, and a block-like laminate including three types of foam layers having different expansion ratios was used. A foam was obtained.

[0060]

According to the present invention, there is provided a method for producing a block-shaped polyolefin resin foam having a cell structure vertically elongated in the thickness direction. ADVANTAGE OF THE INVENTION According to the manufacturing method in this invention, the foam which is thick and has excellent rigidity and shock absorption in the thickness direction can be obtained.

Further, in the production method of the present invention, in the foaming step, the pressure of the foaming gas is increased by the high viscosity
Since the cells are grown by relying on the pressure of the foaming gas rather than being suppressed by the high tensile stress characteristics, the foaming ratio is high and the foaming agent can be used effectively.

Furthermore, a laminated foam having a thick foam layer can be integrally molded, and it is not necessary to bond a skin material and a foaming agent or to heat and fuse them as in the related art, thereby improving production efficiency.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a step of sealing a foamable polyolefin resin mixture in a molding die in a production method according to the present invention.

FIG. 2 is a view schematically showing a step of press-forming a foamable polyolefin resin mixture in the production method of the present invention.

FIG. 3 is a view schematically showing a step of performing foaming by opening a piston in the manufacturing method according to the present invention.

FIG. 4 is a diagram schematically showing a step of taking out a molded product in the manufacturing method according to the present invention.

FIG. 5 is a view schematically showing gas flow in a resin during foaming.

FIG. 6 is a diagram schematically showing a foam formed by an uneven mold.

FIG. 7 is a schematic diagram of a three-dimensionally expanded foam.

[Explanation of symbols]

 1: foamable polyolefin resin mixture 2: lower mold 3: upper mold 4: sealing material 5: piston 6: sealing material 7: piping 8: molded product 9: piping 10: piping 11: gas seal layer 12: three-dimensional Expanded foam

Claims (6)

[Claims] 1. A step of supplying a foamable polyolefin resin mixture comprising a foaming agent, a cross-linking agent and a polyolefin resin into a molding tool constituted by a mold and a piston which are opposed to each other, and sealing the mold. ) A process in which the foamable polyolefin resin mixture sealed in the mold is pressed and shaped by a piston, and then heated to a temperature equal to or higher than the decomposition temperature of the foaming agent to generate gas in the molten polyolefin resin; 3) decomposition of the foaming agent After that, the temperature of the molten polyolefin resin is cooled within the range of not less than the softening temperature of the polyolefin resin and not more than the melting point of the polyolefin resin, and then the piston is cooled to a rate not more than the expansion rate of the expandable polyolefin resin. A two-dimensional expansion of the expandable polyolefin resin by releasing the foamable polyolefin resin to obtain a polyolefin resin foam. 4) After cooling and solidifying the polyolefin resin foam,
Removing the molded product from the molding die, and the sliding portion between the die and the piston in the molding die is maintained at a temperature not higher than 30 ° C. lower than the melting point of the polyolefin resin. Steps 2) and 3) are performed, and the gel fraction in the polyolefin resin foam is reduced to 0.
A method for producing a polyolefin resin block-shaped foam, which is in the range of 50% to 50%. 2. The process for producing a polyolefin resin block-like foam according to claim 1, wherein the cell structure of the polyolefin resin foam is vertically elongated in the thickness direction. 3. The method for producing a polyolefin resin block-like foam according to claim 1, wherein the polyolefin resin foam has a glossy skin layer. 4. The production of a polyolefin resin block foam according to claim 1, wherein the polyolefin resin foam is a block-shaped laminated foam comprising a skin material and a foam layer. Method. 5. A polyolefin resin foam comprising two or more foam layers obtained as a result of foaming a mixture of two or more polyolefin resins comprising a crosslinking agent, a foaming agent and a polyolefin resin by the above steps 1) to 4). The method for producing a polyolefin resin block-like foam according to any one of claims 1 to 4, wherein the polyolefin resin foam has a polyolefin resin foam. 6. A laminated foam of a skin material and a polyolefin resin foam layer, or two or more polyolefin resin foam layers or two or more polyolefin resin foam layers, wherein an adhesive is applied to the laminate bonding surface of the laminate foam. A polyolefin resin block-shaped foam characterized by not being used.