JPH07119311B2 - POLYOLEFIN RESIN FOAM AND METHOD FOR HEAT FORMING THE SAME - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention makes good use of a foam and a method of thermoforming the same, and in particular, a crosslinked polyolefin resin foam used for thermoforming and characteristics of the foam. The present invention relates to a heat molding method.

[Conventional technology]

This type of polyolefin resin foam is used, for example, as a filler for automobile interior parts. 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 which is in a molten state by being heated by an infrared heater or the like, and is heat-molded by pressing in that state. As a result, an automobile interior molded product or the like having a desired shape can be obtained.

The conventional polyolefin-based resin foam has a shape in which the cells have lengths which are substantially equal in the length direction, width direction, and thickness direction of the foam.

[Problems to be Solved by the Invention]

When the conventional polyolefin resin foam is used for press working, the foam is likely to be wavy or drooping. For this reason, wrinkles and the like are likely to occur in a molded product using the conventional polyolefin resin foam, and a difference in gloss due to uneven heating is 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 excellent in heat moldability.

Another object of the present invention is to provide a method for hot-molding a polyolefin-based resin foam, which is highly resistant to waviness and wrinkles during thermoforming and has high thermoformability.

[Means for Solving the Problems]

The polyolefin resin foam according to the present invention is a crosslinked polyolefin resin foam, and has moldability (H / L) and cell shape satisfying the following formulas, and is used for heat molding.

H / L ≥ 0.6 4.0 ≥ L _MD / L _ZD ≥ 1.4 4.0 ≥ L _TD / L _ZD ≥ 1.4 However, H: drawing depth during hot forming L: drawing diameter during hot forming L _MD : foam length Cell diameter in the direction L _TD : Cell diameter in the width direction of the foam L _ZD : _Cell diameter in the thickness direction of the foam Note that the cell shape is formed, for example, by pulling the foam in the width direction and the length direction. The shape.

Examples of the polyolefin resin include polypropylene resin and polyethylene resin. Preferably, a polypropylene resin of 90 to 10% by weight and a polyethylene resin of 10 to 90% by weight are used. These mixing ratios can be variously changed according to the required characteristics of the foam.

Examples of the polypropylene resin include isotactic polypropylene, ethylene-propylene copolymer,
Examples thereof include butene-propylene copolymer and ethylene-butene-propylene copolymer. The polypropylene-based 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, the random coefficient is preferably 0.9 or less. If the random coefficient is larger than 0.9, it may be difficult to obtain a stable foam. Here, the random coefficient, in the IR spectrum of the copolymer measured at room temperature, for example, the absorbance ratio of the characteristic absorption at ₇₂₀ cm ^-1 and 731 cm ^-1 (A ₇₂₀ / A ₇₃₁ due to the copolymer component ethylene). ) 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 preferably 0.5 to 35, more preferably 0.5 to 15. The melt index is according to ASTM D1238-62T,
It is a value when measured at 230 ° C for 10 minutes.

As the polyethylene resin, for example, a density of 0.910 ~
0.940 g / cm ³ of polyethylene resin, copolymer of vinyl acetate and ethylene, copolymer of ethylene with a monomer component such as α-olefin containing vinyl acetate, acrylic acid, methacrylic acid, etc. . Also, as a polyethylene resin, the melt index is 0.5 to 40, and further 3
Those of -15 are desirable. This melt index is a value measured by ASTM D1238-62T at 190 ° C. for 10 minutes. Polyolefin resins (for example, mixed resins of polypropylene resin and polyethylene resin) include α-olefin homopolymers such as polybutylene or α-olefin copolymers, thermoplastic resins such as chlorinated polyethylene, lubricants, and antioxidants. Agent, UV absorber, colorant,
Antistatic agents, flame retardants, talc, fillers such as calcium carbonate, nucleating agents and other inorganic substances may be added. Note that these additives are added within a range that does not impair the characteristics 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.
The expansion ratio of the foam according to the present invention is usually 5 to 40.
Times, preferably 10 to 30 times. Moreover, the apparent density of the foam is 0.025 to 0.200 g / cm ^3, preferably 0.033 to 0.100 g / c.
m is ^3.

The molding processability (H / L) of the foam according to the present invention is preferably 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. Use a cylindrical mold that can change the depth H (cm) with respect to the diameter L (cm).
It is heated to vacuum and vacuum molded to create a molded product. The maximum depth H of the mold when the obtained molded product is not broken is measured, and the moldability (H / L) is calculated using the following formula.

Moldability = H / L Next, in the foam according to the present invention, it is necessary that the cell shape thereof satisfies the following formula.

4.0 ≥ L _MD / L _ZD ≥ 1.4 4.0 ≥ L _TD / L _ZD ≥ 1.4 Note that this bubble shape has L _MD / L _ZD within the range of 1.5 to 3.0, L
More preferably, _TD / L _ZD is in the range of 1.5 to 3.0.
When L _MD / L _ZD is less than 1.4 or L _TD / L _ZD is less than 1.4, the deformation degree of bubbles is too small to obtain sufficient heat formability. On the other hand, L _MD / L _ZD exceeds 4.0, or L _TD / L
_{When ZD} exceeds 4.0, the deformation of bubbles becomes excessive,
As a result, sufficient heat formability cannot be obtained.

The bubble shape ratio is a value measured as follows.
That is, the ratio of the bubbles on the 0.2 mm line (front and back) and the center line from the skin surface of the foam thickness direction section L _MD / L _ZD , L
Ten _TD / L _ZDs are measured continuously in the length and width directions of the foam. That is, a total of 30 measurements are performed. The ratios L _MD / L _ZD and L _TD / L _ZD are obtained by averaging the 30 measurement results.

The foam can be manufactured by the first or second manufacturing method described below.

The first manufacturing method is to foam a cross-linked polyolefin-based resin sheet having a predetermined molding processability and cell shape by pulling a foam obtained at a softening point or higher in a width direction and a length direction in heating and foaming the foamed sheet. Characterized by getting the body.

In the second production method, a continuous body of crosslinked polyolefin-based resin foam is reheated at a softening point or higher and is stretched in the width direction and the length direction to form a foam having a predetermined moldability and cell shape. Characterized by getting the body.

Next, an example of the above manufacturing method will be described.

When a mixed resin of polypropylene resin and polyethylene resin is used as the polyolefin resin, first, the polypropylene resin, the polyethylene resin, and the foaming agent are mixed in a desired mixing ratio. Third, if necessary
Mixing, including additives such as inorganic substances that are components. The mixing step is performed by a known method such as mixing with a Henschel mixer, mixing with a Banbury mixer, mixing with a mixing roll, or the like.

Examples of the foaming agent include thermally decomposable foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, and nitrofurazone. From the viewpoint of characteristics and price, it is desirable to use azodicarbonamide.

The mixed resin added with the foaming agent is molded into a desired shape (for example, a sheet shape) at a temperature not higher than the decomposition temperature of the foaming 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 ionizing radiation cross-linking method, as high energy rays, α rays, β rays, γ rays, X
Rays, electron rays, neutron rays, etc. can be used. For example, when using a high energy electron beam irradiator,
Crosslinking is carried out by irradiation with an electron beam at a dose of 20 Mrad.
In this case, mixed resins such as divinylbenzene, diallyl phthalate, hydroquinone dimethacrylate,
A crosslinking aid such as trimethylolpropane triacrylate may be added. Cross-linking aids are usually mixed resin
0.5-10% by weight is added.

In the case of the chemical crosslinking method, a crosslinking method using an organic peroxide such as dicumyl peroxide or ditertiarybutyl oxide is used. Further, it is also possible to use a silane cross-linking method in which vinyl silane such as vinyl trimethoxy silane is kneaded and grafted together with the organic peroxide and then cross-linked 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 in the molded article to foam it. At this time,
A bubble shape having a predetermined L _MD / L _ZD and L _TD / L _ZD is realized by pulling the foam in the width and length directions. For example, when foaming in a hot air atmosphere, the foam is deformed by pulling the foam in each direction at a temperature equal to or higher than the softening point immediately after foaming. When a salt bath is used, the bubbles are deformed by pulling the foam immediately after foaming on the salt bath. Furthermore, a configuration may be adopted in which bubbles are not positively deformed in the foaming step, and the foam is pulled during the annealing that is subsequently performed to take strain. In this case, since the resin is softened by the heating during the annealing, the bubbles are deformed by pulling the softened resin. 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 capable of deforming 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 / foaming a resin sheet 1, and a widening process for expanding a foam provided below the foaming furnace 2. The device 3 and the cooling roll 4 arranged below the widening device 3 are included.

A pair of widening devices 3 are provided so as to face each other in the width direction of the foam 5 from the foaming furnace 2. The widening device 3 has a suction mechanism, and by adsorbing both ends of the foam 5 by the suction mechanism, the foam 5 is widened. Due to the widening by the widening device 3, the foam of the foamed body 5 is deformed in the width direction. On the other hand, the deformation of the foam in the lengthwise direction of the bubbles is caused by both the deformation of the foam 5 due to its own weight and the deformation of the cooling roll 4 fed.

The thermoforming method of the present invention is characterized in that the polyolefin resin foam obtained above is thermoformed. This polyolefin-based resin foam is laminated and integrated into a composite body, for example, by sticking a skin material such as a vinyl chloride sheet and an adhesive, and set on an aggregate such as a polypropylene resin sheet. Then, it is pressed into a desired shape and used as, for example, an interior member for a vehicle. As the heat molding method, for example, an integral molding method, a hot stamping molding method or the like is applied. The heating during thermoforming deforms the foam cells in a rounding direction, which causes the foam to shrink slightly. For this reason, waviness and wrinkles are less likely to occur during heat molding, and heat moldability is improved.

〔The invention's effect〕

Since the polyolefin resin foam according to the present invention is set to have a cell shape represented by the above-mentioned formula, when this is used for heat molding, the heat moldability is improved by shrinking the cells in the rounding direction. Further, in the method for thermoforming a polyolefin resin foam according to the present invention, waviness and wrinkles are less likely to occur during thermoforming, and the thermoformability is high.

〔Example〕

Experimental Example 1 80 parts by weight of a polypropylene resin in which 5% by weight of ethylene was randomly copolymerized, 20 parts by weight of a linear polyethylene resin having a density of 0.930 g / cm ³ , and 10 parts by weight of azodicarbonamide as a foaming agent. And a mixture of 5 parts by weight of divinylbenzene as a cross-linking agent were kneaded with a single-screw extruder to prepare a sheet having a thickness of 2.0 mm. This resin sheet was irradiated with an electron beam at a dose of 6 Mrad, and then heat-foamed at 250 ° C. in a hot-air foaming furnace to obtain foams having different expansion degrees in the length and width directions. The width expansion in the length direction was performed by changing the ratio of the sheet feeding speed and the foam take-up speed, and the width expansion in the width direction was performed by using a width expansion device installed at the outlet of the foaming furnace.

Cell shape and thermoformability of those foams (160 ℃ molding)
Table 1 shows the results of investigation of the relationship. In Table 1, samples No. 3 and No. 4 are examples according to the present invention.

Experimental Example 2 50% by weight of polyethylene resin (density 0.924 g / cm ³ , melt index 3.0) and polypropylene resin (intrinsic viscosity 20
0, isotacticity 91.0%) 50% by weight and mixture 100
A mixture of 1 part by weight, 15 parts by weight of azodicarbonamide as a foaming agent, and 5 parts by weight of divinylbenzene as a cross-linking agent was foamed in the same manner as in Example 1, and the relationship between the cell shape and the heat moldability was investigated. It was The results are shown in Table 2. In Table 2, sample No. 7 is an example according to the present invention.

Microscopic Observation Regarding the above-mentioned samples No. 1, No. 2 and No. 4, the shapes of the bubbles contained therein were photographed with an electron microscope, and the results shown in FIGS. 2A to 4B were obtained.

[Brief description of drawings]

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

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area B29K 105: 04 B29L 7:00

Claims (3)

[Claims] 1. A cross-linked polyolefin resin foam, which has a molding processability (H / L) and a cell shape satisfying the following formula, and is used for heat molding. H / L ≥ 0.6 4.0 ≥ L _MD / L _ZD ≥ 1.4 4.0 ≥ L _TD / L _ZD ≥ 1.4 However, H: drawing depth during hot forming L: drawing diameter during hot forming L _MD : foam length Cell diameter in the direction L _TD : Cell diameter in the width direction of the foam L _ZD : _Cell diameter in the thickness direction of the foam 2. The polyolefin resin foam according to claim 1, wherein the cell shape is a shape formed by pulling the foam in a width direction and a length direction. 3. A method for thermoforming a polyolefin resin foam, which comprises thermoforming the polyolefin resin foam according to claim 1 or 2.