JPH0362832A - Foamed polyolefin resin and its production - Google Patents

Abstract

PURPOSE:To obtain the subject foamed material having improved formability, containing bubbles having a specific form and useful as a filler for interior trim of automobile, etc., by heating a crosslinked polyolefin resin sheet at a temperature above the softening point and stretching the sheet in lateral and longitudinal directions to effect the foaming of the resin. CONSTITUTION:A resin sheet is produced by adding azodicarbonamide, etc., as a foaming agent and divinylbenzene as a crosslinking agent to a polyethylene resin and a polypropylene resin, etc., and kneading the mixture with an extruder. The sheet is irradiated with electron ray to obtain a crosslinked polyolefin resin sheet 1. The sheet is foamed by heating at a temperature above the softening point with a hot air foaming oven 2 and the foamed material 5 is stretched in lateral direction and longitudinal direction with a stenter 3 and a chilled roll 4 to obtain the objective foamed material having a formability (H/L) satisfying the formula 1 (H is drawing depth in heat-forming; L is drawing diameter in heat-forming) and a bubble shape satisfying the formula II (LMD is bubble diameter of the foamed material in longitudinal direction; LZD is bubble diameter of the foamed material in the direction of thickness) and the formula III (LTD is bubble diameter in the lateral direction of the foamed material).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a foam and a method for producing the same, particularly a crosslinked polyolefin resin foam and a method for producing the same.

[Conventional technology]

This type of polyolefin resin foam is used, for example, as a filler for interior parts of automobiles. In use, a skin material such as a soft vinyl chloride sheet is attached to the surface of the foam using an adhesive or the like. The composite material thus obtained is set on an aggregate such as a polypropylene resin sheet that has been heated by an infrared heater or the like to a molten state, and is pressed in this state. As a result, an automobile interior molded product or the like having a desired shape is obtained.

Conventional polyolefin resin foams have a shape in which the cells have approximately equal lengths in the length direction, the width direction, and the thickness direction of the foam.

[Problem to be solved by the invention]

When pressing using the conventional polyolefin resin foam, the foam tends to be wavy or sag. For this reason, molded products using the conventional polyolefin resin foams are prone to wrinkles and the like, and differences in gloss due to uneven heating are likely to occur. That is, conventional polyolefin resin foams do not have sufficient heat moldability.

An object of the present invention is to provide a polyolefin resin foam having excellent heat moldability.

[Means to solve the problem]

The polyolefin resin foam according to the present invention is a crosslinked polyolefin resin foam, and has moldability (
H/L) and bubble shape satisfy the following formula.

H/L≧0. 6 4.0≧LMD/LZD≧1.4 4.0≧LTD/LZD≧1.4 However, H: Drawing depth during heat forming L: Drawing diameter Lo during heat forming: Length direction of foam Cell diameter LTゎ: Cell diameter in the width direction of the foam LZD: Cell diameter in the thickness direction of the foam. Note that the bubble shape is, for example, a shape formed by pulling the foam in the width direction and length direction. be.

Examples of the polyolefin resin include polypropylene resin and polyethylene resin. Preferably, a material consisting of 90 to 10% by weight of polypropylene resin and 10 to 90% by weight of polyethylene resin is used. These mixing ratios can be varied depending on the required properties of the foam.

Examples of the polypropylene resin include isotactic polypropylene, ethylene-propylene copolymer,
Examples include butene-propylene copolymer, ethylene-butene-propylene copolymer, and the like. The polypropylene copolymer resin may be either a random copolymer or a block copolymer, but it is preferable to use a random copolymer. When a random copolymer is used, it is desirable that the random coefficient is 0.9 or less.

If the random coefficient is greater than 0.9, it may be difficult to obtain a stable foam. Here, the random coefficient refers to, for example, the 720 cm-
Absorbance ratio of characteristic absorption at ' and 731 cm-' (A, □.

/A7. ) is the value indicated by The smaller the random coefficient, the more randomly ethylene is distributed in the copolymer. When the polypropylene resin is a random copolymer, the melt index is 0°5~
35, more preferably 0.5 to 15. Melt index is a value measured according to ASTM D 1238-62T at 230°C for 10 minutes.

For example, the polyethylene resin has a density of 0, 9
10-0. 940 g/cm' polyethylene resin, copolymers of vinyl acetate and ethylene, α-olefins containing vinyl acetate, copolymers of ethylene and monomer components such as acrylic acid and methacrylic acid, etc. .

The polyethylene resin preferably has a melt index of 0.5 to 40, more preferably 3 to 15. This melt index is ASTM D1238-
This is the value when measured at 190°C for 10 minutes using 62T. Polyolefin resins (for example, mixed resins of polypropylene resin and polyethylene resin) include
Homopolymers of α-olefins such as polybutylene or copolymers of α-olefins, thermoplastic resins such as chlorinated polyethylene, lubricants, antioxidants, ultraviolet absorbers, 3 colorants, antistatic agents, flame retardants, talc, calcium carbonate. Bulking agents, nucleating agents, and other inorganic substances may be added. Note that these additives are added within a range that does not impair the properties of the foam according to the present invention.

The foam according to the present invention can be obtained by foaming the polyolefin resin by a predetermined method. Note that the foaming ratio of the foam according to the present invention is usually 5 to 4.
0 times, preferably 10 to 30 times. The apparent density of the foam is 0.025 to 0.025. 200 g/cm3
It is preferably 0.033 to 0.100 g/cm3.

It is desirable that the moldability (H/L) of the foam according to the present invention is 0.6 or more. If the moldability is less than 0.6, the moldability required as a product may not be obtained.

The value of moldability (H/L) is a value measured as follows. Using a cylindrical mold that can change the depth H (cm) with respect to the diameter L (cm), one sample piece is
Vacuum forming is performed by heating to 20 to 200°C to create a molded product. Measure the maximum depth H of the mold when the obtained molded product does not tear, and use the following 2 to determine the molding processability (H/L
).

Molding Processability - H/L Next, the foam according to the present invention must have a cell shape that satisfies the following formula.

4.0≧L 14D/L zn≧1.44.0≧LT
D/L2Il≧1°4 In this bubble shape, it is more preferable that LMD/Lzn is within the range of 1.5 to 3°0 and LTD/LZD is within the range of 1.5 to 3.0. L) ID/LZD is 1°4
or when L rn/L zn is less than 1.4, the degree of deformation of the bubbles is too small and sufficient heat moldability cannot be obtained. On the other hand, LMD/LZD exceeds 4.0,
Alternatively, if LTD/LAD exceeds 4.0, the cells become excessively deformed, and as a result, sufficient heat moldability cannot be obtained.

The bubble shape ratio is a value measured as follows.

That is, 0.2 m from the skin surface of the foam thickness direction cross section.
Ratio of bubbles on the line of m (front and back) and on the center line L H
n / L z o, L T n / L z
10 pieces of n are continuously measured in each of the length and width directions of the foam.

That is, a total of 30 measurements are performed. By averaging these 30 measurements, the ratio L MD / L zn.

Obtain L-a-D/T-ZD.

＊＊＊＊＊＊＊ The foam manufacturing method according to the present invention is a method for manufacturing the above-mentioned polyolefin resin foam.

The first manufacturing method involves heating and foaming a crosslinked polyolefin resin sheet and pulling the foam obtained above the softening point in the width direction and length direction, thereby forming a foam having predetermined moldability and cell shape. It is characterized by gaining a body.

The second manufacturing method involves reheating a continuous body of crosslinked polyolefin resin foam at a temperature above its softening point and stretching it in the width and length directions to form a foam with predetermined moldability and cell shape. It is characterized by gaining a body.

Next, an example of the above-mentioned manufacturing method will be explained.

When using a mixed resin of a polypropylene resin and a polyethylene resin as the polyolefin resin, first, the polypropylene resin, the polyethylene resin, and a blowing agent are mixed at a desired mixing ratio. If necessary, the third
Mix together with additives such as inorganic substances. The mixing step is performed by a known method such as mixing using a Henschel mixer, mixing using a Panhari mixer, or mixing using a mixing roll.

Examples of the blowing agent include thermally decomposable blowing agents such as abdicarbonamide, dinitrosopentamethylenetetramine, and nitrofurazone.

Note that from the viewpoint of characteristics and price, it is desirable to use azodicarbonate.

The mixed resin to which a blowing agent has been added is molded into a desired shape (for example, a sheet shape) at a temperature below the decomposition temperature of the blowing agent. The obtained resin sheet is crosslinked using any method such as an ionizing radiation method or a chemical crosslinking method.

In the case of the ionizing radiation crosslinking method, α rays, β rays, T rays, X rays, electron beams, neutron rays, etc. can be used as high energy rays. For example, when using a high-energy electron beam irradiation machine, crosslinking is carried out by irradiating the electron beam at a dose of 1 to 20 Mr ad. In this case, a crosslinking aid such as divinylbenzene, diallyl phthalate, hydroquinone dimethacrylate, or trimethylolpropane triacrylate may be added to the mixed resin. The crosslinking aid is usually 0.0% for the mixed resin. 5-10% by weight
is added.

In the case of a chemical crosslinking method, a crosslinking method using an organic peroxide such as dicumyl peroxide or ditertiary butyl oxide is used. Alternatively, a silane crosslinking method may be used in which a vinyl silane such as vinyltrimethoxysilane is kneaded together with the organic iyJM compound to form a graft, and then crosslinked by a siloxane condensation reaction.

The crosslinked sheet thus obtained is heated in a hot air atmosphere or on a salt bath to rapidly decompose the foaming agent contained within the molded article, thereby causing foaming. At this time,
By stretching the foam in the width and length directions, a cell shape with a predetermined ratio LMD/LZo, Ltn/Lzn is achieved. For example, by deforming the bubble. When using a salt bath, the foam is deformed by pulling the foam immediately after foaming on the salt bath.

Furthermore, a configuration may be adopted in which the bubbles are not actively deformed in the foaming process, and the foam is stretched during annealing that is performed afterwards to remove distortion. In this case, the resin is softened by heating during annealing, and the bubbles are deformed by pulling the softened resin. In addition, in the step of deforming the bubbles described above, it is desirable that the temperature of the foam is 130° C. or higher.

As an example, an example of a foaming device that can deform bubbles when foaming in a hot air atmosphere will be described. The foaming apparatus shown in FIG. 1 mainly includes a foaming furnace 2 for heating and foaming a resin sheet 1, and a foaming furnace 2 provided below the foaming furnace 2 for widening the foam. It consists of a device 3 and a cooling roll 4 arranged below the width expanding device 3.

A pair of width expanding devices 3 are provided so as to face each other in the width direction of the foam 5 from the foaming furnace 2 . This width-expanding device 3 has a suction mechanism, which attracts both ends of the foam 5 to widen the width of the foam 5. By widening the width using the width expanding device 3, the cells of the foam 5 are deformed in the width direction. On the other hand, the cells of the foam are deformed in the longitudinal direction by both deformation due to the foam's own weight and deformation due to the feeding of the cooling roll 4.

The obtained polyolefin resin foam is used as, for example, a vehicle interior member by being molded into a desired shape with a skin material such as a vinyl chloride sheet laminated thereon. As a molding method, for example, an integral molding method, a hot stamping mold method, etc. are applied, and the foam is heated during molding by these methods. This heating deforms the cells of the foam in a rounded direction, thereby causing the foam to shrink slightly. Therefore, undulations and wrinkles are less likely to occur during heat molding, and heat moldability is improved.

〔Effect of the invention〕

Since the polyolefin resin foam according to the present invention has the cell shape as described above, heat moldability is improved. Moreover, according to the manufacturing method according to the present invention, it is possible to obtain such a foam.

〔Example〕

80 parts by weight of a polypropylene resin copolymerized with 5% by weight of ethylene in a random manner, 20M parts of a linear polyethylene resin having a density of 0.93Qg/cm3, and azodicarbonate as a blowing agent. A mixture consisting of 10 parts by weight of divinylbenzene and 45 parts by weight of divinylbenzene as a crosslinking agent was kneaded in a single screw extruder to a thickness of 2.5 parts by weight. A sheet of Omm was created. On this resin sheet,
After electron beam irradiation at a dose of 6 Mrad, heating and foaming was performed at 250°C in a hot air foaming furnace to obtain foams with different degrees of expansion in the length and width directions.

The width in the length direction was widened by changing the ratio of the sheet supply speed to the foam take-up speed, and the width in the width direction was widened by using a widening device installed at the exit of the foaming furnace.

Table 1 shows the results of examining the cell shape and heat moldability (160° C. shape) of these foams.

In Table 1, samples N003 and N014 are examples according to the present invention.

Table 1 However, Foam density: Measured according to JIs K-6767.

Heat moldability: The condition of the sample after heat molding was observed and the following results were obtained.

Condition: No waving or sagging Items with waving or sagging Indication: ○ ×, melt index 3.0) 50% by weight, polypropylene resin (intrinsic viscosity 200, isotactic degree 91)
．． A mixture consisting of 1.0 parts by weight of a mixture of 0%) and 50 parts by weight, 15 parts by weight of azodicarbonamide as a blowing agent, and 5 parts by weight of divinylbenzene as a crosslinking agent was foamed in the same manner as in Example 1. The relationship between the bubble shape and heat moldability was investigated. The results are shown in Table 2. In addition, in Table 2, sample No. 7 is an example according to the present invention.

Table 2 7 When the shape of the bubbles contained therein was photographed using an electron microscope, the results shown in FIGS. 2A to 4B were obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing an example of an apparatus for carrying out the method for producing a foam according to the present invention, FIG. 2A and FIG. 2B
The figure is a partial vertical cross-sectional view of a comparative example (sample No. 1), FIGS. 3A and 3B are partial vertical cross-sectional views of a comparative example (sample No. 2), and FIGS. No. 4) is a vertical cross-sectional partial view. DESCRIPTION OF SYMBOLS 1... Resin sheet, 2... Foaming furnace, 3... Widening device, 5... Roller, 6... Foaming body.

Claims (1)

[Scope of Claims] (1) A crosslinked polyolefin resin foam whose moldability (H/L) and cell shape satisfy the following formula. H/L≧0.6 4.0≧L_M_D/L_Z_D≧1.4 4.0≧L_T_D/L_Z_D≧1.4 However, H: Drawing depth during heat forming L: Drawing diameter during heat forming L_M_D: Cell diameter in the length direction of the foam L_T_D: Cell diameter in the width direction of the foam L_Z_D: Cell diameter in the thickness direction of the foam (2) The bubble shape is such that the foam is pulled in the width and length directions. The polyolefin resin foam according to claim 1, which has a shape formed by. (3) In the foam manufacturing method for manufacturing the foam according to claim (2), when heating and foaming the crosslinked polyolefin resin sheet, the foam obtained at a temperature equal to or higher than the softening point is heated in the width direction and length direction. A method for producing a foam, the method comprising: obtaining a foam having the moldability and cell shape as described above. (4) In the foam manufacturing method for manufacturing a foam according to claim (2), the continuous body of crosslinked polyolefin resin foam is reheated to a temperature higher than its softening point, and at the same time in the width direction and length direction. A method for producing a foam, the method comprising: obtaining a foam having the moldability and cell shape as described above.