JPH09193251A - Foam and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: It is an object of the present invention to provide a foam which has a delayed shape recovery property and whose shape recovery time can be controlled, and a manufacturing method thereof. A raw material foam having a closed cell ratio of 70 to 100% is provided with a ventilation passage at a desired portion, and the raw material foam is contracted within an elastic deformation region of a resin forming the raw material foam. I did it.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foam and a method for producing the same.

[0002]

2. Description of the Related Art Like a re-expandable plastic chip disclosed in Japanese Patent Laid-Open No. 62-13441, a raw material foam made of a closed-cell resin foam is once in a contracted state, and this raw material foam is used. The shape is gradually restored by the elastic recovery of the resin that constitutes the body and the permeation of air from the outside into the closed cells (cells) through the bubble film (cell film). Delayed shape recovery Foams having properties have already been proposed.

That is, as described above, the foam having the delayed shape recovery property is initially in a contracted state, and the shape gradually recovers to almost the original thickness of the raw material foam before the contraction. Therefore, when it is in a contracted state, it is not bulky and is excellent in transportability and workability. In addition, the shape is restored to have a sealing property and a heat insulating property, and is considered to be promising as a heat insulating material or a sealing material.

[0004]

However, since the foam having the delayed shape recovery property is in the shape of a chip, it is impossible to completely fill the gap, and the sealing property,
There is a problem that the airtightness is poor and the workability is poor. Therefore, the inventors of the present invention have already proposed a sheet-shaped foam having a delayed shape recovery property of a desired length (see Japanese Patent Application No. 7-159098).

That is, in the case of this sheet-shaped foam having a delayed shape recovery property, it can be cut into a required size and can be installed at a predetermined place, so that the sealing property and the airtightness are surely secured. It can be done and is excellent in workability. However, it was difficult to control the time required for the shape recovery of any foam.

In view of such circumstances, the present invention provides a foam which has a delayed shape recovery property and can control the shape recovery time freely, and a manufacturing method thereof. It is intended to be provided.

[0007]

In order to achieve such an object, the foam according to the present invention is a foam having a delayed shape recovery property, from the surface of the foam to desired closed cells inside. The ventilation passage is provided at a desired position. In the above structure, the foam having the delayed shape recovery property is as follows.

Gas permeation coefficient of carbon dioxide, liquefied gas, etc.
P_agentIs the gas permeability coefficient P of air_{ai r}Larger, room temperature
Gas or gas that liquefies at room temperature is used as foaming gas
Used for gas replacement in the bubbles or liquefaction.
Due to the volume shrinkage caused by the
The balance between the internal and external pressures of the bubbles is not
It gradually recovers to its original thickness. That is,
P_agent> P_airWhen a gas that becomes
In the case of a closed cell (cell) through the cell membrane,
The amount of gas that escapes (permeates) to the inside is more independent bubbles from the outside world
It becomes larger than the amount of gas entering the inside, and the internal pressure of the closed bubble is less than the external pressure.
(Atmospheric pressure). At this time, the foam is compressed by external pressure.
Force F₁And the elastic force F of the resin that resists it_TwoShy
, F₁And F _TwoThe foam shrinks until the balance is reached.
Escape from inside the closed bubbles to the outside as the contraction progresses
Gas gradually decreases, and after a while
Amount of gas that escapes from the outside to the outside world and gas that enters the closed bubbles from the outside world
The volume reaches equilibrium and contraction ceases. After this, the foam expands
To start.

When a gas other than the foaming gas is used as the foaming gas, the compressive strain in the elastic region is applied to the foam for a predetermined time or longer, and when the compression is released, the elastic recovery force of the resin causes the internal and external pressures of the bubbles. It has the property of gradually recovering to the original thickness while balancing.

That is, when a compressive strain in the elastic region is given to the foam, the internal pressure of the closed cells constituting the foam rises, and if the external force is removed immediately thereafter, the foam will instantly recover its original shape. , If the strain is maintained for a predetermined time or longer, the gas permeability of the resin causes the gas in the bubbles to gradually escape from the bubble film, and the internal pressure and the external pressure balance, and instantaneous shape recovery will occur even if the external force is removed. However, if the strain is in the elastic region of the resin, when the compression is released, the elastic recovery force of the resin balances the internal and external pressures of the bubbles and gradually recovers the original thickness.

A gas other than the bubbling gas was used as a bubbling gas, and the bubbling was performed under reduced pressure so that the gas pressure in the bubbling was kept below atmospheric pressure, and the gas was cooled and fixed and then taken out into the atmosphere. At this time, the foam is once compressed by atmospheric pressure and gradually recovers its original thickness while balancing the internal and external pressures of the bubbles by the elastic recovery force of the resin.

[0012] A foam produced by using a foaming agent which liquefies upon cooling and has a boiling point not higher than the molding temperature. That is,
When using a blowing agent whose boiling point is lower than the molding temperature of the resin,
When the foam is cooled to the boiling point of the blowing agent, the blowing agent in the closed cells is also cooled and changes from a gas to a 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 contracts. After that, the elastic recovery force of the resin balances the internal and external pressures of the bubbles to gradually restore the original thickness.

When the closed cell foam is compressed, the temperature at the time of compression depends on the softening point of the resin constituting the closed cell foam (the glass transition point for amorphous resin, and the glass transition point for crystalline resin). Is the melting point). That is, when compression is performed at a temperature equal to or higher than the softening point, there is a possibility that the shape recovery ability of the foam after removal of the weight may be lost. Further, the compression method is not particularly limited, but for example, a method of passing the closed-cell foam between two endless belts facing each other at a desired interval to compress between the endless belts or between two press plates. There is a method of compressing with and holding the compressed state for a predetermined time.

The closed cell ratio of the foam is determined by the amount of recovery required depending on the application and is not particularly limited.
It is preferable that the closed cell rate is as high as possible, and specifically, the closed cell rate is preferably 70% to 100%. That is, it is easy to produce a foam having a closed cell rate of 0% or 70 to 100%, but when producing a closed cell having a closed cell rate in the middle, it is impossible to control so that the distribution becomes uniform. In addition, in order to accurately control the number (area) of closed cells in contact with the atmosphere, it is preferable that the number of open cells formed during the production of the foam is small.

The cross-sectional shape of the raw material foam is not limited to a sheet shape or a flat plate shape, and is not particularly limited to a rod shape or an elliptical shape.

The resin constituting the foam is not particularly limited, but one having a compression set (according to JIS K 6767) of 20% or less, particularly 10% or less is preferable because of excellent shape recoverability. Examples of such a resin include the following thermoplastic resins or thermosetting resins.

[Thermoplastic resin] Olefinic resins such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-vinyl acetate copolymer, polymethyl acrylate,
Acrylic resins such as polymethylmethacrylate and ethylene-ethyl acrylate copolymers, styrene-based resins such as butadiene-styrene, acrylonitrile-styrene, styrene, styrene-butadiene-styrene, styrene-isoprene-styrene, styrene-acrylic acid, etc. Vinyl chloride resins such as acrylonitrile-polyvinyl chloride, polyvinyl chloride-ethylene, vinyl fluoride resins such as polyvinyl fluoride and polyvinylidene fluoride, amide resins such as 6-nylon, 6,6-nylon, 12-nylon Saturated polyethylene resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate,
Polyphenylene oxide, polyacetal, polyphenylene sulfide, silicone resin, thermoplastic urethane resin, polyether ether ketone, polyether imide, various elastomers and cross-linked products thereof.

[Thermosetting resin] Epoxy resin, phenolic resin, melamine resin, urethane resin, imide resin, urea resin, silicone resin, and cured product of unsaturated polyester resin. [Natural Resin] Natural Rubber, Cellulose, Starch, Protein, Sap such as Urushi, etc. These resins may be used alone or in combination of two or more kinds.

Among the above resins, olefin resins, styrene resins, amide resins, acrylic copolymers, soft polyurethanes, soft vinyl chloride resins, polyacetals, silicone resins, various elastomers are particularly excellent in shape recovery properties. Are particularly mentioned. Known foaming methods, including those described in the Plastic Foam Handbook, may be used, and any method may be used.

The liquefied gas used as the foaming agent in the present invention is not particularly limited, but for example, aliphatic hydrocarbons such as butane, pentane and hexane, aromatic hydrocarbons such as benzene, toluene and xylene, acetone, Ketone hydrocarbons such as methyl ethyl ketone, alcohol hydrocarbons such as methanol, ethanol, propanol, 1,
1-dichloro-1-fluoroethane, 2,2-dichloro-1,1,1-trifluoroethane, 1,1,1,2-
Examples thereof include halogenated hydrocarbons such as tetrafluoroethane and monochlorodifluoromethane, and water. Among these foaming agents, a foaming agent that foams at room temperature is preferable.

When the resin constituting the foam is polyethylene (foaming temperature 100 to 110 ° C.), methanol (boiling point 64.51 ° C.) and ethanol (boiling point 7) as the foaming agent.
8.32 ° C), acetone (boiling point 56.5 ° C), pentane (boiling point 36.07 ° C), hexane (boiling point 68.74).
C.), benzene (boiling point 80.1 ° C.), ethyl ether (boiling point 34.48 ° C.), water (boiling point 100 ° C.) are preferably used.

In producing the foam of the present invention, a foaming aid such as azodicarbonamide for controlling the foaming rate may be added together with the foaming agent.

The foam may be mixed with a filler, a reinforcing fiber, a colorant, an ultraviolet absorber, an antioxidant, a flame retardant, etc., 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 fiber include glass fiber and carbon fiber. 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 bromine flame retardants such as hexabromophenyl ether and decabromodiphenyl ether, phosphoric acid flame retardants such as ammonium polyphosphate, trimethyl phosphate and triethyl phosphate, melamine derivatives and inorganic flame retardants. Examples include one kind or a mixture of two or more kinds. 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 ventilation passage is not particularly limited, and examples thereof include a circle, a triangle, a quadrangle, a star, a line, and a wavy line. The size of the ventilation passage is not particularly limited, but the cross-sectional area is preferably 7 mm ² (about 3 mm in diameter when the cross-section is circular), and its maximum (width) is more preferably equal to or smaller 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 distance between the ventilation passages is not particularly limited, but when the cross-section of the ventilation passage is smaller than the bubble diameter, it should be at least twice the bubble diameter, and when the cross-section of the ventilation passage is larger than the bubble diameter, it should be separated from the adjacent ventilation passage. It is preferable that the distance is equal to or larger than the bubble diameter. The depth of the ventilation passage is determined by the recovery time and is not particularly limited, but it is preferable that three or more closed cells inside are reached from the front surface, and the back passage side of the foam may be penetrated. However, when used in a place where ventilation or water flow is disliked, it is better not to penetrate the back side.

Further, the ventilation passage may be provided perpendicularly to the surface of the foam, or may be provided at a predetermined angle with respect to the surface. Moreover, you may make it provide spirally toward the inside of a foam. The ventilation passage can be provided in the direction shown in FIG. 1 depending on the shape of the foam.

Incidentally, as shown in FIG. 1A, when the foam is in the form of a long sheet, one direction in the thickness direction of the foam,
As shown in FIG. 1B, when the foam is in the form of a long board, the foam is formed in at least one of the thickness direction and the width direction.
As shown in (c), when the foam is a long cylinder, the foam is radial, and as shown in FIG. 1D, when the foam is a block, at least in the thickness direction, the width direction, and the front-back direction. When the foam has a spherical shape in one direction as shown in FIG. 1 (e), it can be provided radially.

On the other hand, the method for producing a foam according to the present invention comprises a step of forming an air passage in a desired portion of the raw material foam,
The step of shrinking the raw material foam within the elastic deformation region of the resin forming the raw material foam is carried out. The method of forming the ventilation path is not particularly limited, but when a hole-shaped ventilation path is provided, a method using a needle (sword mountain), a drill, an electron beam, a laser beam, or the like may be used, and a groove-shaped ventilation path is provided. In this case, a method using a cutter (knife) or the like can be used.

Incidentally, if a spiral needle such as a corkscrew is screwed into the raw material foam, a spiral ventilation passage can be bored, and the foam is linearly distorted. By forming a hole, a non-straight air passage can be formed. In addition, any of the step of forming the ventilation path and the step of contracting the raw material foam may be performed first, or may be performed simultaneously in parallel.

However, when a gas having high gas permeability is used as the foaming agent, when the compressed state is maintained, when the ventilation path is not penetrated to the back side (especially in the case of a thin material), the ventilation path is formed. It is preferable to perform the step of performing the first step. In other words, when a gas having high gas permeability is used as the foaming agent, or when the compressed state is maintained, the gas must be removed from the bubbles during shrinkage. Can reduce the time required for shrinkage.

If the raw material foam is first shrunk if the ventilation passage is not penetrated to the back side, the thickness may be reduced and the needle or the like may penetrate.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. 2 and 3 schematically show the foam according to the present invention. As shown in FIG. 2, first of all, the foam 1 has holes 1 to be ventilation paths.
1 is the surface 1 of the raw material foam having a closed cell ratio of 70 to 100%
2 to the closed cells (cells) 13 inside are provided at a predetermined pitch, and as shown in FIG. 3, they are contracted in the elastic deformation region of the resin forming the raw material foam in the thickness direction.

That is, since the foam 1 is contracted within the elastic deformation region of the resin, when the biasing force in the compression direction is removed, the elastic recovery force of the resin gradually balances the internal and external pressures of the closed cells 13. Although the original thickness gradually recovers, not only the closed air bubbles 13 located on the surface portion but also the closed air bubbles 13 inside through the holes 11 come into direct contact with the outside air. The shape recovery time becomes shorter as compared with the case where no shape is provided. Moreover, the shape recovery time can be controlled by adjusting the size, depth and number of the holes 11.

[0036]

Next, embodiments of the present invention will be described in detail.

Example 1 100 parts by weight of low-density polyethylene (trade name G201 manufactured by Sumitomo Chemical Co., Ltd.) and azodicarbonamide as a foaming agent (decomposition peak temperature 200 ° C.)
20 parts by weight and 2 parts by weight of zinc stearate are φ65 mm
Into a single screw extruder (set at 135 ° C.), kneaded, extruded the kneaded material into a sheet having a thickness of 2.4 mm, and then irradiated both sides of the sheet with an electron beam of 750 kv × 5 Mrad to crosslink. The crosslinked product was heated and foamed at 240 ° C. to have a thickness of 8 mm, an expansion ratio of 41 times, and an average cell diameter of 720 μm.
m, a raw material foam having a closed cell ratio of 80% was obtained.

This raw material foam is 100 mm in length × 100 mm in width
After cutting to the size of the cut piece, a ventilation passage penetrating the front and back surfaces of the cut piece was formed with a hole having a hole diameter of 10 μm using a needle having a diameter of 500 μm.
mm (perforation density 1 hole / cm ² ). Next, this perforated raw material foam was compressed between press plates equipped with 1 mm spacers, and the compressed state was maintained for 12 hours to obtain a foam.

The foam obtained has a thickness of 1 mm and a length of 100 m.
The m and lateral dimensions were 100 mm and the shrinkage ratio was 12.5%.

(Example 2) A foam was obtained in the same manner as in Example 1 except that the ventilation passages were bored at a perforation interval of 5 mm (perforation density of 4 holes / cm ² ). (Example 3) Punching interval 2.5 mm (punching density 16 holes /
A foam was obtained in the same manner as in Example 1 except that the ventilation passage was formed in cm ² .

(Comparative Example 1) A foam was obtained in the same manner as in Example 1 except that the ventilation passage was not formed. Example 1 above
The foams obtained in Comparative Examples 1 to 3 and Comparative Example 1 were allowed to stand in the atmosphere, the number of days required until the shape recovery was stopped was measured, and the results are shown in Table 1 together with the shrinkage rate of the foam when stopped.

[0042]

[Table 1]

Example 4 100 parts by weight of low-density polyethylene (trade name LF440HB manufactured by Mitsubishi Chemical Co., Ltd.) and 1 part by weight of talc (MS manufactured by Nippon Talc Co.) as a nucleating agent were used in a uniaxial extruder (130 mm) having a diameter of 65 mm. (Setting at ℃) and kneading, and pentane as a foaming agent is added to the resin 10
After adding 10 parts by weight to 0 parts by weight of the kneaded product, the mixture was continuously extruded from an extrusion die having a thickness of 2 mm and a width of 100 mm set at 105 ° C. at 20 kg / hr to obtain a raw material foam. . The obtained raw material foam had a thickness of 8.1 mm and a width of 280.
mm, the average cell diameter was 750 μm, the closed cell ratio was 80%, and the expansion ratio was 30 times.

Immediately after foaming, the raw material foam was sandwiched between press plates from the thickness direction and cooled to room temperature to give a thickness of 1
mm (shrinkage 12.5%)
mm, width 100 mm, cut into a sheet, and the air passages that penetrate through the front and back surfaces of this cut piece are punched with a needle having a diameter of 500 μm at a perforation interval of 10 mm (perforation density of 1 hole / cm ² ) and foamed. Got the body

(Example 5) A foam was obtained in the same manner as in Example 4 except that the ventilation passages were formed with a hole spacing of 5 mm (hole density of 4 holes / cm ² ). (Example 6) Punching interval 2.5 mm (punching density 16 holes /
A foam was obtained in the same manner as in Example 4 except that the ventilation passage was formed in cm ² .

(Comparative Example 2) A foam was obtained in the same manner as in Example 4 except that the ventilation passage was not formed. Example 4 above
6 to 6 and the foams obtained in Comparative Example 2 were allowed to stand in the atmosphere, the number of days required until the shape recovery was stopped was measured, and the results are shown in Table 2 together with the shrinkage rate of the foam when the foam was stopped.

[0047]

[Table 2]

(Comparative Example 3) The amount of the foaming agent added was changed from 20 parts by weight to 15 parts by weight and extruded with a thickness of 2.8 mm to obtain a thickness of 8 mm, a foaming ratio of 31 times, and an average cell diameter of 70.
A thickness of 1 mm, a length of 100 mm and a width of 100 m were obtained in the same manner as in Comparative Example 1 except that a raw material foam having a size of 0 μm and a closed cell ratio of 80% was obtained.
A foam having m and a shrinkage rate of 12.5% was obtained.

When this foam was left at atmospheric pressure,
The shape recovery stopped after 80 days, and the shrinkage rate became 95%.

The above Examples 1 to 6 and Comparative Examples 1 to 1
In 3, the expansion ratio, the average cell diameter, and the closed cell rate were determined as follows. [Expansion ratio] A small piece of 35 mm in length × 35 mm in width is cut out from the obtained foam, and the small piece is submerged in a graduated cylinder filled with water, and its volume A is measured, and the volume is measured using an electronic balance. Measure the weight. Then, the weight of the obtained foam is divided by the volume A of the small piece of the foam, the density of the foam is calculated, and the expansion ratio = the density of the resin used / the foam density is determined.

[Average Cell Diameter] After taking an enlarged photograph of the cross section of the obtained foam, an average value of equivalent circular diameters was calculated from each cell area, and the average value was defined as the average cell diameter. [Independent bubble ratio] Using an air comparison type hydrometer 1000 (manufactured by Tokyo Science Co., Ltd.), the volume B is measured by the method of 1 to 1/2 to 1 atmosphere.
Measure (closed cell volume + resin volume). Then, the closed cell rate = (volume B-weight / resin density) / (volume A-weight / resin density) is calculated.

[0052]

EFFECTS OF THE INVENTION Since the foam according to the present invention is constructed as described above, it is not bulky and is excellent in transportability and workability, and the shape recovery time can be freely controlled. Further, the method for producing a foam according to the present invention can produce the foam with high productivity.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a direction in which a vent hole of a foam body according to the present invention is formed.

2A and 2B schematically show the state of the foam according to the present invention before contraction or after shape recovery. FIG. 2A is a plan view and FIG. 2B is a sectional view.

FIG. 3 is a cross-sectional view schematically showing a contracted state of the foam body of FIG.

[Explanation of symbols]

 1 Foam 11 Pore (Ventilation Path) 12 Surface 13 Closed Cell

Claims (2)

[Claims] 1. A foam having a delayed shape recovery property, wherein an air passage reaching from a surface of the foam to desired closed cells inside is provided at a desired position. 2. The method according to claim 1, further comprising a step of forming a ventilation passage in a desired portion of the raw material foam, and a step of shrinking the raw material foam within an elastic deformation region of a resin forming the raw material foam. The method for producing a foam according to 1.