JPH10292060A - Foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foam which has a shape recovery time not greatly decreasing even when used at low temps., esp. at 0 deg.C or lower, and exhibits a delayed shape recovery by dispersing a specified amt. of a water-absorbent material in a resin. SOLUTION: In preparing a foam having delayed shape recovery properties by causing a closed-cell resin foam to shrink, 5-100 pts.wt. water-absorbent material comprising a water-absorbent polymer capable of absrobing or adsorbing water in an amt. of at least 5 times its own wt. and/or an inorg. porous material is dispersed in 100 pts.wt. resin for forming the closed-cell resin foam. An acrylic acid salt polymer, a starch-acrylic acid graft copolymer, etc., are listed as the water-absorbent polymer; and zeolite, silica gel, diatomaceous earth, etc., are the examples of the inorg. porous material. The resin for forming the foam pref. has a compression set of 20% or lower, and various resins such as olefinic. acrylic, and styrenic resins can be used as this resin. The foam is caused to shrink by such a method as physical compression.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foam having a delayed shape recovery property (hereinafter referred to as "shape recovery foam").
About.

[0002]

2. Description of the Related Art The inventors of the present invention have proposed that a raw material foam made of a closed-cell resin foam is initially formed in a state in which bubbles are shrunk within the elastic limit of the resin, and the bubbles are reduced by the elastic recovery force of the resin. We have already proposed a shape-recovery foam which gradually recovers to almost the original thickness of the raw material foam while being balanced with the internal and external pressures (Japanese Patent Application No. Hei 7-299654).
No.).

As described above, this shape-recovery foam is initially contracted and gradually recovers to almost the original thickness of the raw material foam. In this case, the filling can be easily performed, and the gap is densely filled by the shape recovery, so that the sealing property is also excellent. However, the conventional shape-recovery foam has a problem that the gas permeability is temperature-dependent, and even when the same shape-recovery foam is used, the recovery time varies depending on the ambient temperature.

That is, when the use atmosphere temperature is high such as in summer, a sufficient recovery speed can be obtained, but when the use atmosphere temperature is low such as in winter, the shape recovery speed becomes slow, and the actual construction site However, there is a problem that it takes too much time to obtain a desired sealing effect or the like, and lacks practicality. This tendency is remarkable especially when the use atmosphere temperature is 0 ° C. or lower.

[0005]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention has been made to provide a foam which does not greatly reduce the shape recovery time even in a low-temperature atmosphere, particularly an operating temperature atmosphere of 0 ° C. or lower. The purpose is.

[0006]

In order to achieve the above object, a foam according to the present invention comprises a foam having a delayed shape recovery property obtained by shrinking a raw foam made of a closed-cell resin foam. In the body, the water-absorbing substance was dispersed in the resin at a ratio of 5 to 100 parts by weight based on 100 parts by weight of the resin constituting the foam.

It is preferable to use a water-absorbing polymer and / or an inorganic porous material as the water-absorbing substance.

The water-absorbing polymer or the inorganic porous material used in the present invention is not particularly limited.
Those having the ability to absorb or adsorb water at least five times their own weight are preferred.

Specific examples of such water-absorbing polymers include acrylate polymers, starch-acrylic acid graft copolymers, vinyl alcohol-acrylate copolymers,
Examples thereof include a vinyl alcohol-based polymer and an ethylene oxide-based polymer. On the other hand, specific examples of the inorganic porous material include zeolite, activated carbon, alumina, silica gel, porous glass, activated clay, diatomaceous earth, and clay.

The amount of the water-absorbing substance is from 5 to 100 parts by weight, preferably from 10 to 70 parts by weight, per 100 parts by weight of the resin constituting the foam. That is, if the amount of the water-absorbing substance is less than 5 parts by weight, the temperature dependency of the obtained foam cannot be improved.
If the amount exceeds 100 parts by weight, the shape recovery rate becomes poor.

The method for shrinking the raw material foam is not particularly limited, and the following methods (1) to (4) can be mentioned.

[0012] greater than the gas permeability coefficient P _agent gas permeability coefficient P _{ai r} of air such as carbon dioxide gas and liquefied gas, it is those using a gas liquefied gas or ambient temperature at normal temperature as a blowing gas, in the bubble A method that utilizes the difference in gas permeability coefficient that causes natural contraction due to volume contraction due to gas replacement.

That is, when a gas that satisfies P _agent > P _air is used as a foaming agent, escapes from the inside of the closed cell (cell) to the outside (atmosphere) through the cell wall (cell membrane) (permeation).
The gas amount is larger than the gas amount entering the closed cell from the outside, and the closed cell internal pressure <the external pressure (atmospheric pressure). At this time, a force F ₁ compressed by the external pressure and an elastic force F _{2 of the} resin resisting the force are applied to the foam, and the foam shrinks until F ₁ and F ₂ are balanced. As the contraction progresses, the amount of gas escaping from the closed cells to the outside gradually decreases, and after a while, the amount of gas escaping from the inside of the closed cells to the outside and the amount of gas entering the closed cells from the outside reach equilibrium, and the contraction stops. After this, the shape recovery foam begins to expand.

A gas other than the above foaming gas is used as the foaming gas, and the compressive strain (preferably the strain in the elastic region of the resin) is applied to the closed-cell foam as a raw material for a predetermined time or more to compress the foam. Compression method. That is, when compressive strain is applied to the closed-cell foam as a raw material, the internal pressure of the closed cells constituting the foam increases, and immediately after the external force is removed, the foam returns to the original shape immediately. If the strain is held for more than an hour, the gas inside the bubble gradually escapes from the bubble wall due to the gas permeability of the resin, the internal pressure and the external pressure balance, and even if the external force is removed, instantaneous shape recovery does not occur, When the compression is released, the resin gradually recovers its original thickness while being balanced with the inner and outer pressures of the bubbles by the elastic recovery force of the resin.

[0015] A gas other than the foaming gas is used as a foaming gas. The gas is bubbled under reduced pressure, cooled and fixed in a state in which the gas pressure in the bubble is lower than the atmospheric pressure, and then taken out to the atmosphere. A method that utilizes deformation caused by a change in external air (environment) pressure at which a formed foam is compressed by atmospheric pressure.

A method of producing a foam using a foaming agent having a boiling point of not higher than a foaming molding temperature after liquefaction upon cooling, followed by foaming and cooling. That is, when the foam obtained by using a foaming agent having a boiling point equal to or lower than the foam molding temperature of the resin is cooled to the boiling point of the foaming agent,
The blowing agent in the closed cells is also cooled to change from gas to liquid.
At this time, due to the volume contraction of the foaming agent, the internal pressure of the closed cells becomes smaller than the external pressure (atmospheric pressure), and the foam shrinks.

In the above method, the compression method is not particularly limited. For example, the closed cell foam is passed between two endless belts arranged at a desired interval and compressed between the endless belts. And a method of compressing between two press plates to maintain a compressed state for a predetermined time.

The raw material foam, that is, the resin forming the shape-recovery foam is not particularly limited, but a resin having a compression set (according to JIS K 6767) of 20% or less, particularly 10% or less, is used for shape recovery. For example, olefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, polymethyl acrylate, polymethyl methacrylate, and ethylene- Acrylic resins such as ethyl acrylate copolymer, butadiene-styrene, acrylonitrile-styrene, styrene, styrene-butadiene-
Styrene resins such as styrene, styrene-isoprene-styrene, styrene-acrylic acid, acrylonitrile-
Polyvinyl chloride resins such as polyvinyl chloride and polyvinyl chloride-ethylene; vinyl fluoride resins such as polyvinyl fluoride and polyvinylidene fluoride; amide resins such as 6-nylon, 6.6-nylon and 12-nylon; polyethylene Saturated ester resins such as terephthalate and polybutylene terephthalate, polycarbonate, polyphenylene oxide, polyacetal, polyphenylene sulfide,
Examples include thermoplastic resins such as silicone resins, thermoplastic urethane resins, polyetheretherketone, polyetherimide, various elastomers, and crosslinked products thereof.

The closed cell ratio of the raw material foam is determined by the amount of recovery required by the shape recovery foam to be obtained, and is 5%.
If it is above, it can be used, but a particularly preferred range is 30% to 100%. The method for producing the raw material foam includes known methods including the method described in the Plastic Foam Handbook, and any foaming method using a pyrolytic foaming agent and a physical foaming agent may be used.

The raw material foam may contain a filler, a reinforcing fiber, a colorant, an ultraviolet absorber, an antioxidant, a flame retardant, and the like, if necessary. Examples of the filler include calcium carbonate, talc, magnesium oxide, zinc oxide, carbon black, titanium oxide, glass powder, and glass beads.

Examples of the reinforcing fibers include glass fibers and carbon fibers. Examples of the coloring agent include pigments such as titanium oxide. The antioxidant is not particularly limited as long as it is generally used,
For example, tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane, dilauryl thiodipropionate, 1,1,3-tris (2-methyl-4-hydroxy-5- t-butylphenyl) butane and the like.

Examples of the flame retardant include brominated flame retardants such as hexabromophenyl ether and decabromodiphenyl ether, phosphoric acid-containing flame retardants such as ammonium polyphosphate, trimethyl phosphate and triethyl phosphate, melamine derivatives, inorganic flame retardants and the like. One type or a mixture of two or more types may be mentioned.

The shape of the shape-recovered foam is not particularly limited, and examples thereof include a sheet, a rod, and a tube. The shape before shape recovery and the shape after shape recovery are non-similar. It doesn't matter.

Further, the shape recovery foam may be provided with an air passage extending from the surface to the inside closed cell. The ventilation path may be formed in the raw material foam before the contraction in advance, or may be formed later in the contracted shape recovery foam.

The shape of the ventilation path is not limited to a straight line, but is not particularly limited to a spiral shape or an arc shape. The cross-sectional shape of the air passage is not particularly limited, and examples thereof include a circle, a triangle, a square, a star, a line, and a wavy line.

Although the size of the ventilation path is not particularly limited,
The cross-sectional area is preferably 7 mm ² (when the cross section is circular, about 3 mm in diameter) or less, and more preferably the maximum (width) thereof is equal to or less than the average cell diameter of the closed cells. That is, if it is too large, the bubble structure may be broken, and the original shape may not be recovered. The interval between the centers of the air passages is not particularly limited. When the cross section of the air passage is smaller than the bubble diameter, it is set to twice or more the bubble diameter. Is preferably not less than the bubble diameter.

The depth of the ventilation path is determined by the required recovery time, and is not particularly limited. It is preferable that the depth of the ventilation path reaches three or more closed cells from the surface. further,
The ventilation path may be provided perpendicular to the surface of the raw material foam, or may be provided at a predetermined angle to the surface. Moreover, you may make it provide spirally toward the inside of a shape recovery foam.

The method of perforating the ventilation path is not particularly limited, but when a perforated ventilation path is provided, a needle (Kenyama),
A method using a drill, an electron beam, a laser beam, or the like can be used. When a groove-shaped ventilation path is provided, a cutter (knife) is used.
And the like.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 schematically shows a foam according to the present invention.

As shown in FIG. 1, the foam 1 has a shape recovery property in which a raw foam 2 made of a closed-cell resin foam shrinks and has a delayed shape recovery property. The water-absorbing substance 3 is dispersed and mixed. The foam 1 is configured as described above. When the use atmosphere temperature is 0 ° C. or lower, the water absorbed in the water-absorbing substance 3 freeze-expands.

Then, the freezing and expansion of the water destroys the cell walls 11 of the foam 1 and increases the number of gas passages.
Therefore, gas permeation is promoted, and the shape recovery time is shortened.

[0032]

Embodiments of the present invention will be described below in more detail.

Example 1 A resin composition having the following composition was mixed with a roll (140 ° C. × 5 minutes) and then pressed to obtain a sheet having a thickness of 3 mm.

[Resin Composition] Resin: 100 parts by weight of low density polyethylene (LF440HB, manufactured by Mitsubishi Chemical Corporation) Blowing agent: 17 parts by weight of azodicarbonamide (SO-L, manufactured by Otsuka Chemical Co., Ltd.) Foaming aid: 1 weight of zinc oxide Part Water-absorbing substance: 30 parts by weight of sodium acrylate polymer (NP-1010 manufactured by Sumitomo Chemical Co., Ltd.)

Next, an electron beam (800 kv × 5 Mra)
After irradiating d) to both sides of the sheet, the sheet was placed in an oven at 250 ° C. and foamed to obtain a closed cell resin foam as a raw material foam. The obtained raw material foam had an expansion ratio of 32 times, a closed cell ratio of 80%, and a thickness of 10 mm.

This raw foam was pressed with a press plate to a thickness of 0.5 mm, and the pressed state was maintained for 1 hour to obtain a shape-recovered foam. The thickness of the obtained shape recovery foam was 2 mm.

Example 2 A resin composition having the following composition was mixed with a roll (140 ° C. × 5 minutes) and then pressed to obtain a sheet having a thickness of 3 mm.

[Resin Composition] Resin: 100 parts by weight of low-density polyethylene (LF440HB, manufactured by Mitsubishi Chemical Corporation) Blowing agent: 17 parts by weight of azodicarbonamide (SO-L, manufactured by Otsuka Chemical Co., Ltd.) Foaming aid: 1 weight of zinc oxide Part Water-absorbing substance: Zeolite (Tosoh Corporation A5) 40 parts by weight

Next, an electron beam (800 kv × 5 Mra)
After irradiation of d) on both sides of the sheet, the sheet was placed in an oven at 250 ° C. and foamed to obtain a closed-cell resin foam. The obtained closed-cell resin foam has an expansion ratio of 31 times,
The closed cell ratio was 77% and the thickness was 10 mm.

A hole is formed in the closed cell resin foam with a needle of φ500 μm at a density of 8 holes / cm ² in the thickness direction to obtain a raw material foam.
, And the pressed state was maintained for 1 hour to obtain a shape-recovered foam. The thickness of the obtained shape-recovery foam is 2
mm.

Comparative Example 1 A resin composition having the following composition was mixed with a roll (140 ° C. × 5 minutes) and then pressed to obtain a sheet having a thickness of 3 mm.

[Resin Composition] Resin: 100 parts by weight of low-density polyethylene (LF440HB, manufactured by Mitsubishi Chemical Corporation) Blowing agent: 15 parts by weight of azodicarbonamide (SO-L, manufactured by Otsuka Chemical Co., Ltd.) Foaming aid: 1 weight of zinc oxide Department

Next, an electron beam (800 kv × 5 Mra)
After irradiation of d) on both sides of the sheet, the sheet was placed in an oven at 250 ° C. and foamed to obtain a closed-cell resin foam. The obtained closed-cell resin foam has an expansion ratio of 32 times,
The closed cell ratio was 82%, and the thickness was 10 mm.

Holes were drilled in the closed cell resin foam at a density of 8 holes / cm ² in the thickness direction with a needle of φ500 μm to obtain a raw material foam.
, And the pressed state was maintained for 1 hour to obtain a shape-recovered foam. The thickness of the obtained shape-recovery foam is 2
mm.

The recovery days when the shape-recovered foams obtained in Examples 1 and 2 and Comparative Example 1 were left at a constant temperature of 23 ° C. and −10 ° C. were measured, and the results are shown in Table 1.
It was shown to.

[0046]

[Table 1]

FIG. 2 is a diagram showing the shape recovery time at each use temperature of the shape recovery foam obtained in Example 1 and Comparative Example 1. As shown in Table 1 and FIG. 2, the foam of the present invention does not show a significant decrease in shape recovery even when it is used at an operating temperature below the freezing point. It can be clearly seen that the shape recovery sharply decreases.

[0048]

As described above, the foam according to the present invention is constructed as described above, so that the shape recovery property does not greatly decrease even at an operating temperature of 0 ° C. or less, and the workability as a sealing material is improved. It will be excellent.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a foam according to the present invention.

FIG. 2 is a graph showing the shape recovery time of each of the shape recovery foams obtained in Example 1 and Comparative Example 1 for each use temperature in comparison.

[Explanation of symbols]

 Reference Signs List 1 foam 2 raw material foam 3 water-absorbing substance

Claims (2)

[Claims] 1. A foam having a delayed shape recovery property obtained by shrinking a raw foam made of a closed cell resin foam, wherein a water-absorbing substance is at least 5 parts by weight based on 100 parts by weight of a resin constituting the foam. A foam which is dispersed in a resin in a proportion of 100 parts by weight or less. 2. The foam according to claim 1, wherein the water-absorbing substance is a water-absorbing polymer and / or an inorganic porous body.