JPH10265598A - Foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foam hardly deteriorating shape recovering properties even when allowed to stand in an intactly shrunk state in an atmosphere at high temperatures by shrinking a raw material foam in which the glass transition temperature of a resin in a closed-cell resin foam is a specific temperature or above. SOLUTION: This foam is obtained by shrinking a raw materials foam 2, composed of a closed-cell resin foam in which the glass transition temperature of the resin is >=30 deg.C, preferably >=50 deg.C and having preferably >=30 times, more preferably >=50 times expansion ratio and venting passages, communicating from the surface to the interior of the closed cells in the interior and previously bored at a prescribed pitch.

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 initially hold a bubble in a contracted state within the elastic limit of the resin, and gradually recover the original thickness while balancing the inner and outer pressures of the bubble by the elastic recovery force of the resin. A shape-recovery foam obtained by shrinking a raw material foam made of a closed-cell resin foam that recovers has already been proposed (see Japanese Patent Application No. 7-299654).

However, when the shape-recovered foam is left in a contracted state (a state before recovery) for a long time, the shape-recovery property is reduced (sometimes expressed as “relaxation”). This causes a problem that the original shape before shrinkage cannot be recovered. In particular, when left in a shrunk state in an atmosphere at a temperature higher than room temperature, the shape recoverability tends to be remarkably reduced in one to two days. For example, when a raw material foam having a thickness of 10 mm is shrunk to 2 mm and then left in an atmosphere at 40 ° C. for one day, the shape-recovery foam recovers only to an extent of less than 4 mm even if it is subsequently recovered.

The inventors of the present invention have found that the cause of the above problem is that when the shape-recovery foam is left in a contracted state,
It is speculated that the entanglement of the molecular chains is frayed (= disengaged) and the elasticity of the molecules required for recovery is reduced, and as a result of further intensive studies, the present invention was completed. Was.

[0005]

That is, the present invention provides:
In view of the above circumstances, it is an object of the present invention to provide a foam which is hardly deteriorated in shape recovery even when left in a contracted state for a long time in a high temperature atmosphere.

[0006]

In order to achieve the above object, a foam according to the first aspect of the present invention (hereinafter referred to as a "foam of the first aspect") is a closed-cell resin foam. In a foam having a delayed shape recovery property obtained by shrinking a raw foam made of a body, a resin having a glass transition temperature of 30 ° C. or more was used as a resin constituting the foam.

The foam according to the second aspect of the present invention (hereinafter referred to as “foam of the second aspect”) is the foam of the first aspect, wherein the raw material foam has an expansion ratio of 30 times or more. Was used.

The foam according to the third aspect of the present invention (hereinafter referred to as the “foam of the third aspect”) is the same as the foam of the first aspect or the second aspect, wherein the foam is from the surface to the inside of the closed cells inside. The communicating air passages were previously drilled at a predetermined pitch in the raw material foam.

In the foams according to the first to third aspects, the method for shrinking the raw material foam is not particularly limited, and the following methods are mentioned.

[0010] carbon dioxide gas and liquefied gas permeability coefficient P _agent such as a gas is greater than the gas permeability coefficient P _{ai r} of air, 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, the amount of (permeated) gas that escapes from the inside of the closed cell (cell) to the outside (atmosphere) through the cell membrane is independent of the outside. More than the amount of gas entering the bubbles,
The internal pressure of the closed cell <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 which uses a gas other than the foaming gas as the foaming gas, and applies compressive strain (preferably strain within the elastic region of the resin) 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 time, the gas inside the bubble gradually escapes from the bubble film 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.

[0013] 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 upon liquefaction upon cooling, followed by foaming and cooling. That is, when a 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 foaming agent in the closed cells is also cooled and changes 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 resin forming the raw material foam (shape recovery foam) is limited to those having a glass transition temperature (hereinafter referred to as “Tg”) of 30 ° C. or higher. C. or higher is more preferable. That is, under normal conditions of use of the shape-recovery foam, it is presumed that the movement of the molecules becomes too large and the fraying of the molecular chains is promoted during the storage in the contracted state, but the Tg is lower than 30 ° C. When a resin is used, the shape recovery property decreases when stored for a long period of time.

[0017] Resins satisfying such conditions include:
For example, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyethyl methacrylate, polyethylene terephthalate, nylon 6, nylon 66, polycarbonate, polyacetal, trifluoride resin, tetrafluoride resin, polyhydroxymethylene, polyacrylic acid, polymethacrylic acid , Polyacrylamide, polyvinyl alcohol, polyacrylonitrile, polyurethane, polyester, polysulfone, polyimide, polyarylonitrile butadiene styrene copolymer (ABS), styrene allylonitrile copolymer (SAN), acrylic acrylonitrile styrene copolymer (AAS) ) And the like.

The Tg is determined by a widely used technique (differential thermal analysis (DTA) or differential scanning calorimetry (D
SC) (calculated from a chart showing an endothermic or exothermic peak obtained by SC).

The expansion ratio of the raw material foam is preferably 30 times (more preferably 50 times) or more as in the foam of the second aspect. That is, when a foam having a foaming ratio of less than 30 is used as the raw material foam, when the raw material foam is contracted, the cell walls (posts) of the closed cells (cells) buckle, and the foam necessary for shape recovery is formed. It is presumed that the elastic force of the foam is lost, but the shape of the obtained shape-recovery foam may not be sufficiently recovered.

The closed cell rate of the raw material foam is determined by the recovery amount 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 coloring agent, an ultraviolet absorber, an antioxidant, a flame retardant, and the like, if necessary. Examples of the filler include calcium carbonate, talc, clay, magnesium oxide, zinc oxide, carbon black, silicon dioxide, titanium oxide, glass powder, glass beads and the like.

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; and inorganic flame retardants. One type or a mixture of two or more types may be mentioned. The shape of the shape-recovery foam is not particularly limited, and examples thereof include a sheet-like shape, a rod-like shape, and a tube-like shape, and the shape before shape recovery and the shape after shape recovery may be non-similar. Absent.

In shrinking the raw material foam,
As in the case of the foam according to the third aspect, an air passage may be provided in the raw material foam as required. That is, the shape recovery time of the obtained shape recovery foam can be controlled by adjusting the pitch and size of the ventilation path.

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 or less (when the cross section is circular, about 3 mm in diameter), 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 of the center of the air passage is not particularly limited, but when the cross section of the air passage is smaller than the bubble diameter,
When the cross section of the ventilation path is larger than the bubble diameter, the distance between the outer edges of the adjacent ventilation paths is preferably equal to or larger 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]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a method for producing a shape-recovery foam according to the present invention.

As shown in FIG. 1, the shape-recovery foam 1 is formed of a resin having a Tg of 30 ° C. or higher, and has an expansion ratio of 3
Strip-shaped raw material foam 2 wound into a roll of 0 times or more
Is continuously fed between the two press plates 31 of the compression device 3 to compress the raw material foam 2 between the press plates 31, 31 and to shrink the raw material foam 2 to a predetermined thickness.
It can be obtained by continuous winding by the winding device 4.

That is, as described above, since the resin constituting the raw material foam has a Tg of 30 ° C. or more, the shape-recovery foam 1 has a large molecular chain when the raw material foam 2 is shrunk. Even if distortion (deformation) occurs, it is difficult for the molecular chains to fray (= disconnect), and the molecules can be kept tightly entangled. Therefore, even when stored in a shrunk state for a long time in an atmosphere of room temperature or higher, the elasticity of the molecules required for shape recovery is not easily lost, and sufficient shape recovery properties can be maintained.

Further, since the foaming ratio of the raw material foam 2 is 30 times or more, buckling of the cell wall does not occur during shrinkage (the cell wall is broken and pressure can be absorbed), and the shape recovery rate can be further improved. The decrease can be reliably suppressed.

[0033]

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

Example 1 90-fold expanded polystyrene (T
g = 90 ° C.), and a hole serving as an air passage is formed in a raw material foam having a length of 100 mm × a width of 100 mm × a thickness of 20 mm with a needle of φ500 μm in a thickness direction at a hole interval of 5 mm (a hole density of 4 holes / cm ² ). After piercing, this raw material foam was compressed to 2.5 mm from above and below with a press plate and kept in a compressed state for 24 hours to obtain a shape-recovery foam.

(Example 2) 90-fold expanded polystyrene (T
g = 90 ° C.) instead of 50-fold foamed polyurethane (Tg
= 50 ° C) to obtain a shape-recovery foam in the same manner as in Example 1.

(Example 3) 90-fold expanded polystyrene (T
g = 90 ° C.), except that a 100-fold expanded styrene acrylonitrile copolymer (Tg = 100 ° C.) was used.
A shape-recovery foam was obtained in the same manner as in Example 1.

Example 4 90-fold expanded polystyrene (T
g = 90 ° C.) instead of 50 × foamed polymethyl methacrylate (Tg = 100 mm × width 100 mm × thickness 8 mm)
72 ° C.), and a shape-recovery foam was obtained in the same manner as in Example 1 except that the foam was compressed to 1.0 mm.

(Comparative Example 1) 90-fold expanded polystyrene (T
g = 90 ° C.) instead of 20-fold expanded polystyrene (Tg
= 90 ° C) to obtain a shape-recovered foam in the same manner as in Example 1.

(Comparative Example 2) 90-fold expanded polystyrene (T
g = 90 ° C.) instead of 40 × low-density polyethylene of 100 mm long × 100 mm wide × 10 mm thick (Tg = −45 ° C.)
And a shape-recovered foam was obtained in the same manner as in Example 1, except that the foam was recovered to 1.3 mm.

Comparative Example 3 90-fold expanded polystyrene (T
g = 90 ° C.) and a 30-fold low-density polypropylene (Tg = −10) having a length of 100 mm × a width of 100 mm × a thickness of 10 mm.
° C) and compressed to 1.3 mm,
A shape-recovery foam was obtained in the same manner as in Example 1.

The shape-recovered foams obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were kept in a contracted state at 40 ° C. for 5 days, and then left at normal temperature and pressure for 1 month. The thickness of the shape recovery foam was measured, and the results are shown in Table 1 together with the recovery rate and the thickness of the raw material foam.

[0042]

[Table 1]

[0043]

Since the foam according to the present invention is constituted as described above, even if it is left in a shrunk state in a high temperature atmosphere for a long period of time, the shape recovery is hardly reduced. In particular, when the expansion ratio of the raw material foam is set to 30 times or more, the shape recoverability is improved.

In addition, if a vent is formed in the raw material foam, the shape recovery time can be controlled.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a method for producing a foam according to the present invention.

[Explanation of symbols]

 1 Shape recovery foam 2 Raw material foam

Claims (3)

[Claims] In a foam having a delayed shape recovery property obtained by shrinking a raw foam made of a closed-cell resin foam, a resin constituting the foam has a glass transition temperature of 30 ° C.
A foam characterized by the above. 2. The foam according to claim 1, wherein the expansion ratio of the raw material foam is 30 times or more. 3. The foam according to claim 1, wherein an air passage communicating from the surface of the foam to the inside of the closed cells is formed in the raw foam at a predetermined pitch in advance.