JPH07165964A - Production of foamed material - Google Patents

Abstract

PURPOSE:To obtain a foamed material having excellent softness, cushioning property and thermoformability and useful as a cushioning material for vehicle part, food container, etc., by forming a specific foamable resin composition to a sheet, crosslinking the sheet by the radiation of high energy rays and thermally foaming the crosslinked sheet. CONSTITUTION:This foamed material is produced by melting and kneading a resin composition composed of (A) a thermoplastic urethane resin, (B) triallyl isocyanate and (C) a heat-decomposable foaming agent such as azodicarbonamide, forming the composition to a sheet, crosslinking the sheet by the radiation of high energy rays and heating the crosslinked to effect the foaming of the sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foam, and more particularly to a method for producing a foam which is used for vehicle members, food containers, sundries and the like and has excellent cushioning properties and thermoformability.

[0002]

2. Description of the Related Art Conventionally, foams made of polyurethane, polyvinyl chloride, polyethylene, polypropylene and the like have been used as foams having excellent cushioning properties (flexibility). Further, foams made of polystyrene, polyethylene, polypropylene and the like have been used as foams having excellent thermoformability.

However, the polystyrene foam has a drawback that it is made of an amorphous resin and is relatively excellent in thermoformability, but it is inferior in flexibility, and the polyethylene and polypropylene resin foams are crystalline resins. Although the resin is crosslinked to give thermoformability, it still has the drawback of poor flexibility.

For example, a method for producing a sheet-shaped or film-shaped polyethylene foam as a polyethylene foam having excellent thermoformability such as vacuum molding has been disclosed (Japanese Patent Publication No. 41-6278). Further, a water-crosslinked polyolefin (foaming base material) comprising a composition of a crosslinked or non-crosslinked polyolefin and a water-crosslinked polyolefin and having excellent foamability.
Has been disclosed as a sea phase, and a method for producing a foamed body in which a non-crosslinking polyolefin that is difficult to foam is used as an island phase (Japanese Patent Publication No. Sho 62).
-209145).

Since the foams obtained by the above-mentioned production methods all use polyolefin as a base resin, they have a problem that they are excellent in thermoformability but lack flexibility and cannot obtain sufficient buffering properties.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above drawbacks, and an object thereof is to provide a method for producing a foam having excellent cushioning properties and thermoformability. .

[0007]

[Means for Solving the Problems]

The method for producing a foam of the present invention comprises a step of forming a resin composition into a sheet, a step of irradiating the sheet with a high energy ray to crosslink, and a step of foaming the sheet by heating after crosslinking. Is a manufacturing method.

The above resin composition comprises a thermoplastic urethane resin, triallyl isocyanate and a thermal decomposition type foaming agent. The thermoplastic urethane (hereinafter referred to as TPU) resin is a type that is generally used for thermoforming, and various types such as a polyester type, a polyether type, and a polycarbonate type can be used. Especially, hardness of TPU resin at room temperature (Shore A)
Is preferably 60 to 85.

Although the melt viscosity of the TPU resin varies depending on the manufacturing method and application of the foam, when it is low, the foaming gas is likely to escape during foaming and a high-magnification foam cannot be obtained. Since the foam of the above can no longer be obtained, the resin melt viscosity at 200 to 220 ° C. is 100 to
10,000 poise is preferable, more preferably 1,0
It is from 00 to 5,000 poise.

The above triallyl isocyanate (hereinafter referred to as TA
(IC) is used to increase the degree of cross-linking of the TPU resin, increase the closed cell ratio of the foam, and improve thermoformability. When the amount of TAIC added decreases, Since a foam having a high rate and excellent thermoformability cannot be obtained, 1 to 100 parts by weight of TPU resin is used.
10 parts by weight is preferred.

A crosslinking aid other than TAIC may be added to the resin composition. The cross-linking aid other than TAIC is a low molecular weight compound or a high molecular weight compound having one or more carbon-carbon unsaturated bonds in the molecule, and examples thereof include ethylene di (meth) acrylate, polyethylene glycol di (meth) acrylate and polypropylene. Glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, chlorohexyl (meth) acrylate, allyl (meth) acrylate, divinylbenzene, diallyl isocyanate, triallyl isocyanate, diallyl phthalate, vinyltoluene, vinylpyridine, diallyl itako Nate, triallyl phosphate and the like, and one or more of these are used.

In the above resin composition, if the amount of the crosslinking aid other than TAIC added is decreased, the decomposition reaction takes place preferentially over the crosslinking reaction to deteriorate the thermoformability, and if it is increased, unreacted crosslinking aid is added. Since it remains in the foam and emits an odor, T
It is preferably 5 parts by weight or less based on 100 parts by weight of the PU resin.

A thermal decomposition type is used as the foaming agent, and the decomposition temperature is preferably 160 to 200.degree. Examples of such a thermal decomposition type foaming agent include azodicarbonamide, p, p′-oxybisbenzenesulfonylhydrazine, azobisisobutyronitrile, p-toluenesulfonylhydrazide and the like. A foaming aid may be added to the foaming agent to control the decomposition temperature.

Further, the above resin composition includes an antioxidant;
A UV inhibitor; a conductive material for imparting antistatic properties; a flame retardant; a coloring agent such as a pigment or a dye may be added. Examples of the flame retardant include bromine-based, phosphorus-based, and inorganic-based flame retardants, and one or more of these are used.

Examples of the method for forming the resin composition into a sheet include an extrusion method, a pressing method, a calender method and the like.
The above-mentioned extrusion method is a method in which the TPU resin is dried by heating in advance, and then the thermal decomposition type foaming agent is mixed by a dry blending device such as a tumbler and melt-kneaded by an extruder having a kneading function to form a sheet.

In the pressing method, the TPU resin is dried by heating in advance, and then the thermal decomposition type foaming agent is mixed by a dry blending device such as a tumbler and melt-kneaded by a kneader or the like to obtain a bulk form. Then, the bulk material is pressed into a board shape (which is later formed into a sheet by slicing) or a sheet shape to form a sheet.

The above-mentioned calendering method is a method in which the TPU resin is dried by heating in advance, and then the thermal decomposition type foaming agent is mixed by a dry blending device such as a tumbler and melt-kneaded by a calender molding machine to form a sheet.

Irradiation with high energy rays is carried out in order to crosslink the sheet. Examples of high energy rays include electron rays and γ rays. When an electron beam is used, it is preferable to irradiate an electron beam having a voltage that completely penetrates the sheet from one side of the sheet, or to irradiate an electron beam having a voltage having a transmittance of not less than half the sheet thickness from both sides of the sheet.

When the irradiation dose of the above-mentioned high energy rays decreases, the viscosity of the obtained foam at the time of thermoforming decreases and the thermoformability decreases, and when the irradiation amount increases, the rate of decomposition reaction rather than crosslinking reaction of the resin composition Increase, and the thermoformability deteriorates.
10 Mrad is preferred.

As a method of foaming the sheet by heating, a horizontal foaming apparatus having a foam floating mechanism; a vertical suspension type vertical foaming apparatus; a salt bath foaming apparatus using a salt bath of nitrate; heating on a Teflon sheet A normal pressure foaming device such as a foaming device is used.

The cell diameter of the foam obtained by the production method of the present invention is related to the elongation of the sheet at the time of thermoforming (ratio of the drawing area of thermoforming) described later, and the one having a large sheet elongation at the time of thermoforming is If required, the bubble diameter is preferably large. For example, when the drawing area ratio in vacuum forming is 2 (double the initial area, and stretched by 200%), the bubble diameter is 0.1.
mm or more, and when the drawing area ratio in vacuum forming is 3, the bubble diameter is preferably 0.5 mm or more. However, if the bubble diameter becomes too large and it is made into a sheet,
Since the surface smoothness deteriorates, the bubble diameter is preferably 1 mm or less, and the bubble diameter of the sheet used for vacuum forming or other thermoforming methods is preferably 0.1 to 1 mm.

If the ratio of the closed cell ratio of the foam is small, the cell wall is easily expanded and ruptured during thermoforming, and the change in thickness is large in accordance with the change in elongation, and the thickness of the corner portion of the formed product is small. Since it becomes extremely thin, 30% or more is preferable. The ratio of the closed cell ratio is a value measured using an air comparison type hydrometer (air pycnometer).

The expansion ratio of the above foam depends on the application, use conditions,
Generally, it is 10 to 30 times for vehicles, 5 to 50 times for packaging / packing, depending on the necessity of thermoforming.
For miscellaneous goods, 5 to 30 times is preferable. Further, when the foam is subjected to thermoforming such that the drawing area ratio exceeds 2, the expansion ratio is preferably 10 to 20 times.

The foam preferably has a sheet shape.
In the case of a sheet, the thickness is preferably 0.5 to 10 mm,
More preferably, it is 1 to 5 mm. Further, another sheet may be laminated on the sheet-shaped foam.

Examples of the thermoforming method for the foam include a vacuum forming method, a press forming method, a pressure forming method, and a vacuum pressure forming method. Particularly, when the drawing area ratio becomes large, the vacuum forming method or the vacuum forming method is used. The pressure molding method is preferred. As the above-mentioned vacuum forming method, the most basic straight method (a method of heating and softening a foamed sheet to 140 to 170 ° C. on a female mold and applying vacuum to the inside of the mold to form the foamed sheet by suction), a drape method (male mold) The foamed sheet is heated and softened to 130 to 160 ° C to raise the male mold, and suction molding is further performed, and the air slip method (the foamed sheet is softened and heated to 140 to 170 ° C on the male mold, and once moved to the upper part. A method of raising the male mold after raising the air and further suction-molding).

In the press molding method, a foamed sheet is
It is a method of heating to ˜160 ° C. and compression molding in male and female molds. In addition, the above-mentioned pressure forming method is a straight method of vacuum forming method, and it is not vacuum suction but 140 to 17
This is a method of heating to 0 ° C. and pressing from the top with air pressure to a mold for molding. Further, the vacuum / pressure forming method is a method of heating a foamed sheet to 140 to 170 ° C. and forming it by using both vacuum and pressure.

[0028]

【Example】

(Example 1) TPU resin ("Pelecene 21" manufactured by Sumitomo Dow Co., Ltd.
03-70A ", Shore A [hardness]: 70) 100 parts by weight, azodicarbonamide as a foaming agent (" AZ-HM "manufactured by Otsuka Chemical Co., Ltd. (hereinafter ADCA)) 10 parts by weight, and TAIC (Shin-Nakamura) as a crosslinking aid. (Chemical Co., Ltd.) 3 parts by weight of the resin composition was charged into the hopper of a 30 mm twin-screw extruder in the same direction set at 170 ° C.
A mm thick sheet was extruded. On this sheet, voltage 5
After irradiating with an electron beam of 00 KV and 5 Mrad, it was placed on a Teflon sheet and heated in a hot air oven at 250 ° C. for 2 minutes to obtain a foam.

(Example 2) TPU resin ("Pelecene 2102-80A" manufactured by Sumitomo Dow, Shore A [hardness]: 8
0) A foam was obtained in the same manner as in Example 1 except that a resin composition consisting of 100 parts by weight, 8 parts by weight of ADCA and 2 parts by weight of TAIC was used.

(Example 3) TPU resin (Peresene 210)
3-80A) 100 parts by weight, ADCA 6 parts by weight, polypropylene glycol dimethacrylate (“NK ester 9PG” manufactured by Shin-Nakamura Chemical Co., Ltd.) 3 parts by weight as a cross-linking aid, and TAIC 0.5 parts by weight to a resin composition of 170 ° C. The sheet was put into the hopper of a set 30 mm twin-screw extruder in the same direction, and a 0.2 mm thick sheet was extruded from a T-die.
This sheet was irradiated with an electron beam having a voltage of 500 KV and 5 Mrad, and then foamed by a vertical foaming apparatus having a foaming zone temperature of 240 ° C. to obtain a foamed body.

(Example 4) TPU resin (Peresene 210)
2-80A) 100 parts by weight, ADCA 12 parts by weight, NK
A resin composition consisting of 3 parts by weight of ester 9PG and 0.3 parts by weight of TAIC was put into the hopper of a 50 mm different direction twin-screw extruder set at 180 ° C., and a 1 mm thick sheet was extruded from a T die. On this sheet, voltage 500KV,
After irradiating with 5 Mrad electron beam, the foaming zone temperature is 24
A foam was obtained by foaming with a vertical foaming apparatus at 0 ° C.

(Example 5) TPU resin (Peresene 210)
3-70A) 100 parts by weight, ADCA 15 parts by weight, NK
A resin composition consisting of 3 parts by weight of ester 9PG and 0.5 parts by weight of TAIC was put into a hopper of a 50 mm different-direction twin-screw extruder set at 170 ° C., and a sheet having a thickness of 1.5 mm was extruded from a T die. This sheet has a voltage of 500K
After irradiating with an electron beam of V and 5 Mrad, foaming was obtained by foaming with a horizontal foaming device having a foaming zone temperature of 250 ° C.

(Example 6) TPU resin (Peresene 210)
2-80A) 100 parts by weight, ADCA 15 parts by weight, NK
A resin composition consisting of 2 parts by weight of ester 9PG and 0.6 parts by weight of TAIC was put into a hopper of a 50 mm different direction twin-screw extruder set at 180 ° C., and a 1 mm thick sheet was extruded from a T die. On this sheet, voltage 500KV,
After irradiating with 5 Mrad electron beam, foaming zone temperature 25
A foam was obtained by foaming with a horizontal foaming apparatus at 0 ° C.

(Comparative Example 1) TPU resin (Peresene 210)
3-70A) 100 parts by weight and ADCA 10 parts by weight,
The sheet was put into the hopper of a 30 mm same-direction twin-screw extruder set at 170 ° C., and a sheet having a thickness of 0.2 mm was extruded from the T die. Place this sheet on a Teflon sheet and
A foam was obtained by heating for 2 minutes in a hot air oven at 0 ° C.

(Comparative Example 2) TPU resin (Peresene 210)
2-80A) 100 parts by weight and ADCA 7 parts by weight
The sheet was put into a hopper of a 30 mm same-direction twin-screw extruder set at 75 ° C., and a sheet having a thickness of 0.2 mm was extrusion-molded from a T die. After irradiating this sheet with an electron beam having a voltage of 500 KV and 5 Mrad, the sheet was placed on a Teflon sheet, and 250
A foam was obtained by heating for 2 minutes in a hot air oven at ℃.

Comparative Example 3 A foam was obtained in the same manner as in Example 3, except that TAIC was not used at all.

Performance Evaluation of Foams The foams obtained in the above Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1. (1) Moldability Sheet-like foam (size: 150 mm x 150 mm)
Was heated to a predetermined temperature on a box-shaped female mold to soften it, and this was vacuum-sucked into the female mold to perform vacuum forming so that the drawing area ratio was 3. The female mold has a bottom and side wall thickness of 20 m.
m, vertical 100 mm × horizontal 100 mm × depth 50 mm, the four corners of the bottom have R of 3 mmφ, and vacuum suction holes are provided at four locations on the bottom. The thickness of the corner portion of the obtained cup-shaped foamed product was measured, and the thickness ratio of the corner portion (original thickness of the sheet-shaped foam / thickness of the corner portion of the foamed product) was calculated. Good moldability.

(2) Buffering property The compressive stress (σ) at a compression speed of 10 mm / min per corner of the cup-shaped foamed product vacuum-formed in (1).
After obtaining the strain (ε) curve and the absorbed energy (e) for each value of σ, the buffer coefficient C is calculated by the formula C
= Calculated from σ / e. The smaller the minimum static stress (kg / cm ² ) of the buffer coefficient C, the better the buffer property.

[0039]

[Table 1]

[0040]

The method for producing a foam of the present invention is as described above, and the obtained foam has flexibility and excellent buffering property, and also has excellent thermoformability such as vacuum forming and pressure forming. It is suitable for use in deep-drawn parts of vehicles (for example, pad materials, seat covers) that could not be molded with conventional foams, cushioning materials for portable containers, packing materials and packaging materials for fruits and sweets, etc. is there.

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Claims (1)

[Claims] 1. A step of melting and kneading a resin composition comprising a thermoplastic urethane resin, triallyl isocyanate and a thermal decomposition type foaming agent to form a sheet, a step of irradiating the sheet with a high energy ray to crosslink, and a step after the crosslinking. A method for producing a foam, comprising a step of foaming a sheet by heating.