JP2001040131A - Thermoplastic resin foamed product and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide thermoplastic resin foamed products having fine cells at a high expansion ratio and excellent fabricability, and their production process. SOLUTION: Thermoplastic resin foamed products are composed of a crystalline thermoplastic resin which has one or more endothermic peaks in the endothermic curve measured by a differential scanning calorimeter(DSC) at a rate of raising temperature of 10 deg.C/min and a temperature width of >=15 deg.C which is represented by a length of segment DE when the highest peak point among the endothermic peaks is regarded as point A; the point at which a perpendicular line from point A to the temperature axis intersects the base line of the endothermic curve is regarded as point B; the point at which segment AB of said perpendicular line is interiorly divided at a ratio of 9:1 is regarded as point C; and the points at which lines passing therethrough and parallel to the temperature axis intersect the endothermic curve at the sides of the lowest temperature and the highest temperature, respectively, are regarded as point D and point E, respectively, and have an average cell diameter of not greater than 10 μm, and an expansion ratio of 2 to 40 times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic resin foam having fine cells at a high expansion ratio and excellent in secondary workability, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a supercritical foaming method for producing a resin foam having fine cells using a supercritical inert substance (such as carbon dioxide or nitrogen) has been developed (for example, a material and manufacturing process). (Mate
rials & Manufacturing Processes), 4 (2), 2
53-262 (1989) and US Pat. No. 5,160,674.
Issue). However, resin foams obtained according to the teachings of these documents, although having fine cells, are insufficient in lightness due to low expansion ratio and insufficient in secondary workability.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have developed a thermoplastic resin foam having fine bubbles, high expansion ratio, excellent lightness, and excellent secondary workability. As a result of intensive studies, it has been found that by using a crystalline thermoplastic resin whose endothermic curve measured using a differential scanning calorimeter (DSC) satisfies specific conditions, a resin foam satisfying the above requirements can be obtained. Heading, the present invention has been completed.

[0004]

That is, the present invention comprises a crystalline thermoplastic resin, which is measured at a rate of 10 ° C./min using a differential scanning calorimeter (DSC) of the crystalline thermoplastic resin. When the endothermic curve has one or more endothermic peaks, and the highest peak point among the one or more endothermic peaks is A, a perpendicular line from the point A to the temperature axis intersects the baseline of the endothermic curve. The point is B, and the perpendicular line segment AB is 9:
When a point that internally divides into 1 is C, a point where a straight line parallel to the temperature axis passing through C intersects the endothermic curve on the lowest temperature side is D, and a point that intersects on the highest temperature side is E, a line segment DE Is not less than 20 ° C. and the average cell diameter is 1
A crystalline resin foam characterized by having a foaming ratio of 0 μm or less and an expansion ratio of 2 times or more and 40 times or less. The resin foam having the above configuration has excellent lightness and excellent suitability for secondary processing such as vacuum forming. In addition, the present invention uses a differential scanning calorimeter (DSC) at 10 ° C./m
The endothermic curve measured at a temperature rise rate of in has one or more endothermic peaks, and the highest peak among the one or more endothermic peaks is A, and a perpendicular line from the point A to the temperature axis is an endothermic curve. A point that intersects the curve's base line is B, and a point that internally divides the perpendicular line segment AB at 9: 1 is C. A straight line parallel to the temperature axis passing through C intersects the endothermic curve at the lowest temperature side. When the point is D and the point that intersects on the hottest side is E, the line segment DE
Impregnating a crystalline thermoplastic resin having a temperature width represented by the length of not less than 20 ° C. with a fluid of the substance under a pressure equal to or higher than the critical pressure of the substance to be impregnated, and impregnating the substance with the fluid And releasing the crystalline thermoplastic resin from the pressurized state. According to the method having the above configuration, it is possible to produce a resin foam having high expansion ratio, fine cells, excellent lightness, and excellent secondary workability.

[0005]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a differential scanning calorimeter (D
SC), the endothermic curve measured at a heating rate of 10 ° C./min has one or more endothermic peaks, and the highest peak point among the one or more endothermic peaks is A, The point at which the perpendicular drawn to the temperature axis intersects the base line of the endothermic curve is B, and the point at which the line segment AB of the perpendicular is internally divided at 9: 1 is C. The straight line parallel to the temperature axis passing through C is the most. Assuming that a point that intersects the endothermic curve on the low temperature side is D and a point that intersects on the hottest side is E, the temperature width indicated by the length of the line segment DE is
A crystalline thermoplastic resin having a temperature of 0 ° C. or higher is used. The temperature width corresponding to the line segment DE is more preferably 25 ° C or more and 100 ° C or less, and still more preferably 30 ° C or more and 100 ° C or less. FIG. 1 shows an example (schematic diagram) of an endothermic curve by DSC of the crystalline thermoplastic resin. The crystalline thermoplastic resin used in the present invention is a differential scanning calorimeter (DSC).
If the endothermic curve measured using
The type is not particularly limited, and preferred examples thereof include:
Examples include polyolefin-based resins (polyethylene-based resins and polypropylene-based resins), polyamide-based resins, polyethylene terephthalate-based resins, syndiotactic polystyrene-based resins, and polyvinyl alcohol-based resins.
Among them, polyolefin resins are preferably used. As the crystalline thermoplastic resin, only one type may be used, or two or more types may be used in combination.

[0006] Polyethylene resins include low density polyethylene (LDPE) and high density polyethylene (HDP).
E), linear low-density polyethylene (LLDPE), ethylene / α-olefin copolymer, and the like.

As the polypropylene resin, a propylene homopolymer or a propylene monomer unit of 5
A propylene copolymer containing 0 mol% or more can be exemplified. As the propylene copolymer, a binary or ternary copolymer of propylene and ethylene and / or an α-olefin (excluding propylene) is preferable. Examples of the α-olefin include linear or branched α-olefins having 4 or more carbon atoms, such as 1-butene, 4-methylpentene-1, 1-octene and 1-hexene. From the viewpoint of polymerizability, a linear or branched α-olefin having 10 or less carbon atoms is preferable. From the viewpoint of the strength of the resin foam, a propylene homopolymer is preferable, and from the viewpoint of the flexibility and transparency of the resin foam, a propylene copolymer is preferable. When a propylene copolymer is used, the content of monomer units other than propylene in the copolymer is preferably 10% by weight or less for ethylene and 30% by weight or less for α-olefin. In addition, a mixture of a propylene homopolymer and a propylene / ethylene copolymer or a propylene / α-olefin copolymer is also preferable in that a resin foam having fine bubbles and excellent mechanical strength can be obtained. When such a mixture is used, a resin composition obtained by kneading a separately produced propylene homopolymer and a propylene copolymer with a kneader or the like may be used, or after performing propylene homopolymerization. Subsequently, a resin composition obtained by copolymerizing propylene with a copolymerizable monomer (ethylene or an α-olefin other than propylene) may be used. Of course, the latter resin composition may be mixed with a propylene homopolymer, a propylene / ethylene copolymer, a propylene / α-olefin copolymer, or the like.

Further, as the polypropylene-based resin, a polypropylene-based resin having a long-chain branch introduced by low-level electron beam crosslinking described in JP-A-62-121704 is also preferably used. Further, a polypropylene resin into which an ultrahigh molecular weight component is introduced is also preferably used. As a preferable example, in the first stage, a monomer having propylene as a main component is polymerized to have an intrinsic viscosity of 5 dl / g or more of a crystalline polypropylene polymer (I) is produced, and a monomer having propylene as a main component is polymerized in the second and subsequent steps to obtain a crystalline polypropylene polymer (II) having an intrinsic viscosity of less than 3 dl / g. Polymers obtained by continuous production are exemplified. In the polypropylene resin into which the ultrahigh molecular weight component is introduced, the content of the polymer (I) is 0.05% by weight from the viewpoint of melt viscosity.
Not more than 35% by weight, the intrinsic viscosity of the entire resin is 3 dl / g
And Mw / Mn of less than 10 are particularly preferred.

The melt flow rate (MFR) of the crystalline thermoplastic resin is preferably 0.1 g / 10 min or more from the viewpoint of processability during the production of the resin foam. From the viewpoint of the secondary workability, it is preferably 50 g / 10 minutes or less.

The resin foam of the present invention has an average cell diameter of 10
μm or less, preferably 0.01 to 1 μm, and the expansion ratio is 2 to 40 times, preferably 10 to 30 times. When the average cell diameter and / or the expansion ratio are out of the above ranges, the resin foam does not simultaneously have excellent lightness and mechanical strength.

In producing the resin foam of the present invention,
The crystalline thermoplastic resin is melt-kneaded in the presence of various additives, if desired, and then subjected to a foaming operation. For the melt-kneading, a single-screw or twin-screw extruder or a Banbury-type kneader can be used.

[0012] The resin foam of the present invention can be obtained by subjecting a crystalline thermoplastic resin whose endothermic curve measured by a differential scanning calorimeter (DSC) to satisfy the above conditions to a pressure higher than the critical pressure of a substance to be impregnated into the crystalline thermoplastic resin. A step of impregnating the substance with a fluid (hereinafter, impregnating step), and a step of releasing the crystalline thermoplastic resin impregnated with the substance from the pressurized state (hereinafter, pressure releasing step). Can be manufactured. By using the specific crystalline thermoplastic resin, it becomes possible to manufacture a resin foam having a high expansion ratio and having fine cells which could not be manufactured conventionally. In the following description, an embodiment in which the method of the present invention is mainly performed in a batch mode will be described. However, in the method of the present invention, for example, the impregnation step and the pressure release step are performed continuously using a single-screw or multi-screw extruder. It is also possible to apply a continuous method that is performed periodically.

In the impregnation step, the crystalline thermoplastic resin is impregnated with a fluid of the impregnating substance (ie, liquid or supercritical fluid) under a pressure equal to or higher than the critical pressure of the substance to be impregnated (impregnating substance). . As the substance preferably used, a gaseous substance at normal temperature and normal pressure, for example, an organic compound such as butane and pentane, or carbon dioxide,
Examples include inorganic compounds such as air, hydrogen, nitrogen, neon, and argon. The impregnated material may be a mixture of two or more. In terms of ease of handling, carbon dioxide, air,
Inert substances such as nitrogen, neon and argon are preferred. Particularly, carbon dioxide is preferably used from the viewpoint of economy and safety.

The amount of the impregnating substance impregnated into the crystalline thermoplastic resin is appropriately set according to the type of the impregnating substance, the expansion ratio of the target resin foam, the cell density, and the like. Usually, the amount is such that fine bubbles are formed at a sufficient expansion ratio. Although there is no particular upper limit for the amount of impregnation, it is usually an amount of saturated dissolution of the impregnated substance in the crystalline thermoplastic resin or an amount close thereto. The impregnation amount does not necessarily have to reach the saturation dissolution amount. For example, a preferred amount of impregnation when carbon dioxide is impregnated into a crystalline thermoplastic resin containing a polyolefin resin as a main component is in the range of 0.1 to 20 parts by weight, based on 100 parts by weight of the resin. Preferably it is in the range of 0.1 to 15 parts by weight.

The pressure (hereinafter referred to as impregnation pressure), temperature and time required for impregnation of the crystalline thermoplastic resin with the impregnated substance vary depending on the desired impregnation amount. For example, when the crystalline thermoplastic resin is impregnated with carbon dioxide having a critical pressure of about 7.5 MPa, the impregnating pressure may be at least this critical pressure, but is preferably at least 10 MPa. Although the upper limit of the impregnation pressure depends on the capacity of the apparatus and the like, it is usually 50.
It is on the order of MPa.

The temperature at which the impregnated substance is impregnated into the crystalline thermoplastic resin (hereinafter referred to as impregnation temperature) is a temperature at which the impregnated substance becomes a liquid or a supercritical fluid, and is not lower than the critical temperature of the impregnated substance. Is preferred. The upper limit of the impregnation temperature may be any temperature at which the crystalline thermoplastic resin used does not decompose, and is usually 300 ° C. or lower. When carbon dioxide having a critical temperature of about 31 ° C. is used, the impregnation temperature is preferably equal to or higher than the critical temperature, and in particular, is preferably 60 ° C. or higher from the viewpoint of the rate of penetration of carbon dioxide into the crystalline thermoplastic resin and productivity. It is preferably 230 ° C. or lower from the viewpoint of the amount of dissolution in the crystalline thermoplastic resin.

The time required to impregnate the crystalline thermoplastic resin with the impregnated substance (hereinafter referred to as impregnation time) depends on the rate of penetration of the impregnated substance into the crystalline thermoplastic resin, and depends on the impregnation pressure and the impregnation temperature. . When the impregnation operation is continued, the impregnation amount usually increases up to the saturation dissolution amount, but the impregnation time is usually set to the time until the impregnation amount of the impregnating substance reaches the saturation dissolution amount at most, and is usually up to several hours. . From the viewpoint of productivity, the shorter the impregnation time is, the more preferable it is. It is not always necessary to impregnate until the saturation amount is reached. For example, the impregnation time in the case of carbon dioxide in a supercritical state is usually about several minutes to about 5 hours, and is preferably about several minutes to about 3 hours from the viewpoint of the balance between productivity and impregnation amount.

In the method of the present invention, subsequent to the impregnation step, a step of releasing the crystalline thermoplastic impregnated with the impregnating substance from the pressurized state (pressure release step) is performed. In the pressure release step, foaming occurs inside the crystalline thermoplastic resin released from the pressurized state. After the pressure release step, the crystalline thermoplastic resin may be further heated. In the pressure release step, the release from the pressurized state is preferably performed in as short a time as possible. If this operation is performed slowly, a foam having a desired cell density may not be obtained.
Normally, the pressure is released instantaneously from the impregnation pressure to around normal pressure. Here, "to release the pressure momentarily" means to reduce the pressure from the impregnation pressure to near normal pressure in as short a time as possible. Depending on the capacity of the container used for impregnation of the impregnating substance, the thickness of the exhaust gas pipe, the pressure drop time from the impregnation pressure to around normal pressure is usually less than 10 seconds,
Preferably less than about 3 seconds.

The rapid release of the pressure in the pressure release step may be performed at a higher temperature than the impregnation step, at a lower temperature than the impregnation step, or at the same temperature as the impregnation step. Good. In order to achieve a finer cell diameter and a higher cell density, it is preferable to release the pressure in the impregnation step at a lower temperature than in the impregnation step.

For example, the impregnating step is performed at a temperature not lower than the critical temperature of the impregnating substance and not higher than the melting point of the crystalline thermoplastic resin.
For example, generating and growing cell nuclei by rapidly releasing pressure at a temperature equal to or higher than the melting point of the crystalline thermoplastic resin, and appropriately controlling the growth of cell nuclei by utilizing the temperature drop caused by the rapid release of pressure. By the above, a foam can be obtained.
Further, the crystalline thermoplastic resin in the impregnation step and its melting point or higher, in the pressure release step the crystalline thermoplastic resin is once lower than the temperature of the impregnation step, for example, cooled to a temperature below the melting point of the crystalline thermoplastic resin, Thereafter, the pressure can be suddenly released to generate cell nuclei, and the cell nuclei can be grown appropriately to obtain a foam. Further, in the impregnation step, the temperature may be lower than the melting point of the crystalline thermoplastic resin, and the pressure release step may be performed at that temperature. In order to obtain a finer cell diameter and a higher cell density, it is preferable to release the pressure at a lower temperature than in the impregnation step.

In order to suppress bubble breakage as much as possible, the temperature of the crystalline thermoplastic resin when the pressure is released is preferably equal to or lower than the melting point of the resin, and in order to achieve a fine bubble diameter and a high bubble density, Melting point of crystalline thermoplastic resin-100 ° C)
As described above, the range of not more than the melting point of the crystalline thermoplastic resin is preferable, and the range of not less than (the melting point of the crystalline thermoplastic resin−50 ° C.) and not more than the melting point of the crystalline thermoplastic resin is particularly preferable. The temperature at the time of releasing the pressure does not necessarily have to be constant, and usually, the temperature decreases with the release of the pressure. Although it is not always necessary to control the temperature drop, it is preferable to control the temperature drop from the viewpoint of controlling the bubble density.

In order to more appropriately control the bubble density, in the pressure release step, both the step of growing the bubble nuclei, which is performed subsequent to the step of generating the bubble nuclei, and the step of stopping the growth of the bubbles are performed. It is preferable to further control the temperature and time.

In the above-described bubble nucleus growth process, the temperature at which the bubble nuclei are grown is controlled in order to suppress bubble break as much as possible.
It is preferable to control the temperature within a range from the crystallization temperature of the crystalline thermoplastic resin to the melting point or less. The time for growing the bubble nuclei is appropriately set according to the desired bubble density, and is usually 20 seconds to 30 seconds.

In order to suppress bubble breakage due to excessive growth of bubbles, it is preferable to control not only the temperature of the bubble nucleus growth process but also the temperature of the bubble growth stop process. The temperature at which the growth of the bubbles is stopped is preferably equal to or lower than the crystallization temperature of the crystalline thermoplastic resin, and is preferably sufficiently cooled until the entire foam becomes equal to or lower than the crystallization temperature.

[0025]

According to the present invention, there is provided a thermoplastic resin foam having high expansion ratio, fine cells, excellent lightness, and excellent secondary workability. This resin foam has excellent mechanical strength, and can be suitably used for, for example, automotive materials, food trays or containers, building materials, cushioning materials, heat insulating materials, and the like.

[0026]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

Differential Scanning Calorimetry (DSC) Using a DSC-7 type manufactured by PerkinElmer, about 10 m
g of the sample at a rate of 10 ° C / min from 30 ° C to 20 ° C.
After the temperature was raised to 0 ° C., the temperature was maintained for one minute,
The crystal was cooled to 30 ° C. at a rate of ° C./min, maintained at that temperature for 1 minute, and heated again at a rate of 10 ° C./min to record an endothermic curve.

[0028] After cooling the average cell diameter foam in liquid nitrogen, were taken in cross section by cutting the foam with a razor under a scanning electron microscope. The magnification was adjusted so that about 50 bubbles could be seen in the field of view of the electron microscope. The maximum length of each cell in the visual field was measured from the photograph of the photographed cross section of the foam, and the average value was determined to obtain the average cell diameter (2r).

[0029]Average bubble density Using the electron microscope photograph used to measure the average bubble diameter
1cm cross section of foam ^TwoCalculate the number of bubbles per unit (n)
Then, it is raised to the power of 3/2 and the number of bubbles per unit volume (N)
Was calculated. The number of air bubbles (N) and the average air
From the bubble diameter (2r) per unit actual volume of the crystalline thermoplastic resin
Number of bubbles, that is, average bubble density (unit: individual bubbles / c
m^ThreeMaterial).

Secondary workability A foam sheet having a thickness of mm was formed into a container having a diameter of 15 cm and a height of 5 cm by vacuum forming, and the appearance of the obtained formed body was evaluated. The ratio of the area where appearance defects such as depressions and uneven thickness were recognized to the total surface area was determined. The higher the value of this ratio, the lower the secondary workability, and the lower the value, the better the secondary workability.

Example 1 Linear low density polyethylene (VL20 manufactured by Sumitomo Chemical Co., Ltd.)
0; MFR = 2 g / 10 min; melting point = 109 ° C.) to 160
After preheating at 3 ° C. for 3 minutes, the sheet was pressed for 1 minute, and cooled on a press plate kept at 30 ° C. for 5 minutes to prepare a sheet (thickness: 1.5 mm, length: 20 cm, width: 20 cm). FIG. 2 shows an endothermic curve of the used polyethylene by DSC. Next, the sheet was placed in a pressure-resistant container, which was provided with a pressure gauge and an exhaust pressure valve and was previously heated to a predetermined temperature, and was capped. Carbon dioxide is injected into the pressure vessel to make it supercritical, impregnation pressure: 20 MPa, impregnation temperature: 9
The sheet was impregnated at 0 ° C. for 2 hours. In addition,
The moment when the pressure gauge reached the predetermined impregnation pressure was defined as the impregnation start point, and the impregnation operation was continued while maintaining the impregnation pressure. After a lapse of a predetermined impregnation time, carbon dioxide was discharged from the pressure-resistant container via a discharge valve, and the pressure in the pressure-resistant container was released at a stretch until the pressure reached normal pressure (about 0.1 MPa). It took about 2 to 3 seconds to release the pressure. The temperature when the pressure was released was 90 ° C. After the inside of the pressure vessel became normal pressure, the obtained resin foam was taken out, and the average cell diameter and the average cell density were measured. Vacuum molding was performed using the obtained resin foam. Table 2 shows the results.

Comparative Example 1 A linear low-density polyethylene (FZ manufactured by Sumitomo Chemical Co., Ltd.) was used in place of the linear low-density polyethylene used in Example 1.
204-0; MFR = 2 g / 10 min; melting point = 124
C.), and a resin foam sheet was prepared in the same manner as in Example 1 except that the impregnation conditions were as shown in Table 1, and vacuum forming was further performed. FIG. 2 shows an endothermic curve of the used polyethylene by DSC. Table 2 shows the evaluation results.

[0033]

[Table 1]

[0034]

[Table 2]

[Brief description of the drawings]

FIG. 1 is an example (schematic diagram) of an endothermic curve by DSC of a crystalline thermoplastic resin.

FIG. 2 is an endothermic curve by DSC of the linear low-density polyethylene used in Example 1.

FIG. 3 is an endothermic curve by DSC of the linear low-density polyethylene used in Comparative Example 1.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4F074 AA17 AA18 AA20 AA24 AA32 AA42 AA50 AA66 BA32 BA33 BA37 BA39 CA34 CA35 CA39 DA02 DA03 4F212 AA08 AB02 AB16 AG01 AG20 UA17 UB01 UC05 UC06 UG02 UN11 UN1 4J003 A01 BB01

Claims (3)

[Purpose] [Claims] 1. A crystalline thermoplastic resin, wherein the crystalline thermoplastic resin has a temperature of 10 ° C. using a differential scanning calorimeter (DSC).
The endothermic curve measured at a heating rate of / min has one or more endothermic peaks, and the highest peak point among the one or more endothermic peaks is A, and a perpendicular line from the point A to the temperature axis is A point that intersects with the base line of the endothermic curve is B, and a point that internally divides the perpendicular line segment AB at 9: 1 is C. A straight line parallel to the temperature axis passing through C intersects the endothermic curve at the lowest temperature side. D is the point at which the highest temperature intersects, and E is the point where the highest temperature crosses, the temperature width indicated by the length of the line segment DE is 20 ° C. or more, the average cell diameter is 10 μm or less, and the expansion ratio is 2 or more. A thermoplastic resin foam having a size of 40 times or less. 2. Use of a differential scanning calorimeter (DSC) at 10 ° C.
The endothermic curve measured at a heating rate of / min has one or more endothermic peaks, and the highest peak point among the one or more endothermic peaks is A, and a perpendicular line from the point A to the temperature axis is A point that intersects with the base line of the endothermic curve is B, and a point that internally divides the perpendicular line segment AB at 9: 1 is C. A straight line parallel to the temperature axis passing through C intersects the endothermic curve at the lowest temperature side. Where D is the point of intersection and E is the point of intersection at the highest temperature, the critical temperature of the material to be impregnated into the crystalline thermoplastic resin having a temperature width indicated by the length of the line segment DE of 20 ° C. or more. A step of impregnating a fluid of the substance under a pressure equal to or higher than a pressure, and a step of releasing the crystalline thermoplastic resin impregnated with the substance from the pressurized state. Manufacturing method. 3. The method according to claim 2, wherein the step of releasing from the pressurized state is performed while the crystalline thermoplastic resin is at or below its melting point.