JP2002363324A - Plastic sheet foamed in gradient manner and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foamed plastic that has excellent foaming properties, and maintains its mechanical strength when used as a foamed sheet in the field of packaging, civil engineering and construction, electronics and information, automobiles, etc., and to provide a method for manufacturing the plastic. SOLUTION: A gas that is gaseous at ordinary temperature and under normal pressure is dissolved into a plastic at a high temperature and under a high pressure. The plastic is exposed to a pressure that is lower than the pressure at the time when the gas has been dissolved into the plastic, and processed, during the exposure or thereafter, to form a sheet, wherein the two surfaces of the sheet are exposed, respectively, to atmospheres at temperatures that are different from each other, so that a plastic foamed in a gradient manner is manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to packaging, civil engineering, construction,
In fields where foamed plastic sheets are used, such as in electronics, information and automobiles, a method for producing a gradient foamed plastic sheet having desired foaming properties with high productivity without significantly lowering the original mechanical strength of the plastic sheet, and The present invention relates to the inclined foamed plastic sheet.

[0002]

2. Description of the Related Art Conventionally, foamed plastic sheets have been used in a wide range of fields, including packaging, civil engineering, electronics and information, and automobiles. The effects of foaming include reducing the amount of plastic used as a raw material, reducing the weight of the product, buffering, sound absorption, heat insulation / warming, lowering the dielectric constant, and the like.The bubble diameter required according to the purpose is large. They range from several hundred microns or more to small ones of about several tens of microns. A foamed sheet formed by a conventional physical foaming method or a chemical foaming method, which is composed of cells of several hundred microns or more, has a drawback that the original mechanical strength of plastic is significantly reduced by foaming. Means for covering the disadvantages include, for example, a method of increasing the thickness of the foam sheet itself and a method of bonding the foam sheet to a support. However, these means should be applied to applications where the thickness of the sheet is restricted. Is difficult, and there is a problem that productivity and quality are lowered.

[0003] In recent years, if the bubble diameter is reduced to a level of 100 microns or less, the amount of raw material used can be reduced without significantly lowering the original mechanical strength of the material. The production methods and devices for fine foamed plastics of several tens of microns level, so-called microcellular plastics, are being actively studied. However, microcellular plastics can be expected to be effective in reducing the usage fee of raw materials and reducing the weight of products, but in some fields, the desired foaming effect cannot be obtained because the bubble diameter is too small. There is a problem in that it is limited, and in reality, it is applied to only a small number of uses such as a reflector, a diaphragm of a speaker, and a vehicle.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems that the conventional uniform foamed sheet has difficulty in achieving both mechanical strength and foaming effect, or that the field of application is significantly limited. It is an object of the present invention to provide a method for producing an inclined foamed plastic sheet having a foaming property according to a demand by giving an inclined foamed state, and to provide the inclined foamed plastic sheet.

[0005]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned conventional problems, and as a result, have completed the present invention by the following means. That is, the present invention is an inclined foamed plastic sheet, characterized in that the average diameter of the air bubbles is inclinedly changed in the sheet thickness direction.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a general term for a general film, sheet and board is called a sheet. The inclined foamed plastic sheet of the present invention will be described with reference to FIG. The width direction of the sheet is the x direction, the longitudinal direction is the y direction, and the thickness direction is the z direction. In the xz cross section, when the average of the major axis and minor axis of each bubble is the diameter of a single bubble, the average value of the diameters of all the bubbles at least partially included in the unit area is the average diameter of the bubbles in the present invention. Determine. With the inclined foaming of the present invention, the average diameter of the bubbles changes in an inclined manner in the sheet thickness direction. It is defined as a foaming state of 90% or less and is distinguished from uniform foaming. Note that “near the surface” refers to a range from the sheet surface to a depth of 10% of the sheet thickness.

[0007] In the inclined foamed plastic sheet of the present invention, the average diameter of cells near at least one surface is 1
It is preferably less than 00 μm, more preferably less than 50 μm. A thickness of 100 μm or more is not preferable because the mechanical strength inherent in the plastic material is significantly reduced, as in the case of the conventional uniform foam sheet. In producing the inclined foamed plastic sheet of the present invention, at room temperature
The method of dissolving a gas in a gaseous state at normal pressure in a plastic at a high temperature and a high pressure and then exposing the plastic to a pressure lower than the pressure at the time of dissolving the gas is not particularly limited. Is dissolved in plastic in a molten state under high temperature and high pressure, mixed uniformly, and then extruded from a die. As an extruder,
Single-screw extruder, twin-screw extruder, and two single-screw extruders connected in series, usually any type of extruder of the type called tandem type may be used alone or They may be combined. The method of exposing both surfaces of the sheet to atmospheres having different temperatures is not particularly limited, but a thermostat, a roll whose temperature can be controlled, and a steel belt are preferable. These may be used alone or in combination. Preferably, as shown in FIG.
By means of temperature-controllable rolls arranged in series, for example, a method of exposing the sheet to different temperature atmospheres in the order of the upper surface, lower surface, and upper surface of the sheet, or as shown in FIG. After cooling the entire sheet, the sheet is pulled out of the thermostat, the lower surface of the sheet is applied to a roll controlled at a temperature higher than the refrigerant temperature, and then cooled again in the thermostat.

The gas used in the present invention is not particularly limited as long as it is an inert gas to plastics, and examples thereof include inorganic gas, chlorofluorocarbon gas, and organic gases such as low molecular weight hydrocarbons. And an inorganic gas is preferred.
The inorganic gas is not particularly limited as long as it is an inorganic substance that is a gas at normal temperature and normal pressure and can be dissolved in plastic, for example, carbon dioxide, nitrogen, argon, neon,
Helium, oxygen and the like are preferred, but carbon dioxide and nitrogen are more preferred because they have high solubility in plastics and are easy to handle. These may be used alone or in combination of two or more. When dissolving a gas in plastic, it is preferable to dissolve it in a supercritical state. The supercritical state means a state at or above a critical temperature and a critical pressure.
It is 7.3 MPa or more at ℃ or more. In the supercritical state, it has the property of being less viscous and more diffusive than the liquid state, and because it has a higher density than the gas state, a large amount of gas can be rapidly dissolved in plastic. preferable.

The plastic which is one of the constituent materials of the inclined foamed plastic sheet of the present invention is not particularly limited because it is properly used depending on the application. However, from the viewpoint of easy foaming control, polyurethane, polyethylene, polypropylene, polystyrene, and the like. Polyester, nylon, polyvinyl chloride, polyvinylidene chloride, polybutene, polyacetal, polyphenylene oxide, polyvinyl alcohol, polymethyl methacrylate, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyamideimide, polycarbonate,
Polyarylate, liquid crystal polymer, aromatic polysulfone resin, biodegradable polyester resin, polyamide resin, polyimide resin, fluorine resin, ethylene-propylene resin, ethylene-ethyl acrylate resin, epoxy resin, acrylic resin, norbornene resin, styrene Polymers (for example, vinyl polyisoprene-styrene copolymer, butadiene-styrene copolymer, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-
Styrene copolymer, etc.), natural rubber, synthetic rubber, or thermoplastic elastomer. These may be used alone, or may be mixed or copolymerized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments with reference to FIGS. 2 and 3. However, the present invention is not limited to the contents of the embodiments. (Sheet forming equipment) At the tip of a tandem-type extruder in which a first extruder having a barrel diameter of 50 mm and L / D = 32 and a second extruder having a barrel diameter of 65 mm and L / D = 36 are connected, a lip width of 20 is provided.
A T-die with 0 mm and a lip gap of 2 mm was attached.

(Example 1) Thermoplastic polyurethane manufactured by Bayer (trade name: DESMODERM KCWgra)
nute) at 80 ° C. for 4 hours and then put into an extruder hopper. First, the temperature of the first extruder, the second extruder, and the die is set to 200 ° C., and the sheet is extruded at a discharge speed of 20 kg / Hr. The internal pressure of the first extruder when the steady state was reached was 8.5 MPa. At the same time, carbon dioxide whose pressure was raised to 25 MPa was injected from a substantially central portion of the first extruder by a pump, and the temperature of the second extruder and the die were changed to 140 ° C. After the temperature and internal pressure of the extruder and the die were stabilized and the discharge state was stabilized, the sheets exiting the die were controlled at 5 ° C, 10 ° C, and 5 ° C, respectively.
After passing through this roll, the sheet was taken out by a take-up machine, and the sheet was sampled. The obtained sheet thickness was 2.3 mm. Break the sample sheet immersed in liquid nitrogen,
When the xz cross section was observed by SEM, it was observed that the bubble diameter was inclinedly changed in the sheet thickness direction.
35. Calculation of the average diameter of bubbles near one surface;
0 micron, average diameter of bubbles near the other surface is 150.
The average diameter of the bubbles near the surface on the side where the bubble diameter was small was about 23% of the average diameter near the surface on the side where the bubble diameter was large.

(Example 2) [0012] Until the sheet is extruded from the die, it is exactly the same as in Example 1, and the sheet exiting the dice is first passed through a thermostat in which cooling water of 10 ° C is circulated.
The distance between the water surface and the lip tip was adjusted to 3 mm. After the lower surface of the sheet pulled out of the constant temperature bath was applied to a roll controlled at 100 ° C., the sheet was again passed through the constant temperature bath to completely cool the sheet. The obtained sheet thickness was 2.4 mm.
The sample sheet immersed in liquid nitrogen is broken and its xz
When the cross section was observed by SEM, it was observed that the bubble diameter was inclinedly changed in the sheet thickness direction. The average diameter of the bubbles near one surface was calculated to be 12.3 microns, the average diameter of the bubbles near the other surface was 100.5 microns, and the average diameter of the bubbles near the surface with the smaller bubble diameter was: It was about 12% of the average diameter near the surface on the larger side.

[0013]

According to the present invention, it is possible to obtain an excellent inclined foamed plastic sheet which can achieve both the mechanical strength and the foaming property, which are the conventional problems, and does not limit the application field.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a sheet of the present invention.

FIG. 2 is an example of a step of exposing both surfaces of a sheet to atmospheres having different temperatures by using a roll alone, which is a preferred embodiment of the present invention.

FIG. 3 is an example of a step of exposing both surfaces of a sheet to atmospheres having different temperatures by combining a thermostat and a roll, which is a preferred embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 T-die 2 Sheet 3 Touch roll 4 Temperature control roll 5 Thermostat

Claims (6)

[Claims] 1. An inclined foamed plastic sheet characterized in that the average diameter of the air bubbles changes obliquely in the sheet thickness direction. 2. The inclined foamed plastic sheet according to claim 1, wherein the average diameter of the bubbles near at least one surface is less than 100 μm. 3. A gas which is in a gaseous state at normal temperature and normal pressure is
After dissolving in plastic under high pressure, after exposing the plastic to a pressure atmosphere lower than the pressure at the time of gas dissolution,
The method according to claim 1 or 2, wherein both surfaces of the sheet are exposed to atmospheres having different temperatures. 4. The method for producing an inclined foamed plastic sheet according to claim 3, wherein the high temperature and high pressure are in a supercritical state of the gas. 5. The method according to claim 3, wherein the gas is carbon dioxide, nitrogen or a mixed gas thereof. 6. The method for producing an inclined foamed plastic sheet according to claim 3, wherein the step of exposing to an atmosphere having a different temperature is a constant temperature bath, a roll, a steel belt, or a combination thereof. .