JPH02182427A - Method for heat-molding of polyolefinic sheet like foam - Google Patents

Abstract

PURPOSE:To enhance molding processability at the time of heat-molding by using a foaming uncompleted sheet like foam controlled in foaming reaction so as to set a ratio of the density at the time of the finish of the heat-molding of a foam and that at the time of the start of the heat-molding thereof, to a specific range. CONSTITUTION:When a polyolefinic sheet like foam consisting of a polyolefinic resin crosslinked by electron beam or containing a chemical crosslinking agent and a heat- decomposable foaming agent is molded under heating, a foaming uncompleted sheet like foam controlled in foaming reaction to a range of 0.70 < (d2/d1) <= 0.90 when the density at the time of the start of the heat-molding of a foam is set to d1 and the density at the time of the finish of the heat-molding thereof is set to d2 is prepared at first. In preparing this foam, a non-foamed sheet is molded at first. In this molding of the sheet, kneading molding is applied at temp. lower than the decomposition temp. of a foaming agent or chemical crosslinking agent. This molding is a necessary condition for forming a uniform sheet or foam. This foaming uncompleted sheet like foam is used to be subjected to heat-molding. At this time, a structure or cloth like fiber composed of polyvinyl chloride or an acrylic/butylstyrene copolymer may be simultaneously subjected to heat-molding.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for thermoforming polyolefin sheet-like foams, in particular, a method for thermoforming polyolefin resins crosslinked with electron beams or containing a chemical crosslinking agent and pyrolytic foaming. The present invention relates to a method of thermoforming a polyolefin sheet-like foam comprising a foaming agent.

[Conventional technology]

Foams made of polyolefin resins, such as polypropylene foams, do not get dirty or rot.

It has properties such as good formability, and is used in large quantities for cushioning agents, insulation materials, etc. For example, when used in an automobile, polypropylene foam is laminated with a polyvinyl chloride sheet or an acrylic butyl styrene sheet and then molded.

In the conventional heating molding method for polyolefin sheet foam, the unfoamed sheet is first heated to complete foaming.
A sheet-like foam is obtained. Next, the foamed product is heat-molded to obtain a molded product.

[Problems to be Solved by the Invention] When thermoforming a polyolefin sheet foam, if the foaming reaction is completed before the heat molding process as in the past, the surface of the foam will deteriorate due to the heating during the heat molding process. Roughness and gas dissipation from the foam tend to occur, and moldability tends to become unstable.

In other words, the conventional molding method has a problem in that the range of heat molding conditions is narrow.

An object of the present invention is to provide a thermoforming method with excellent moldability when thermoforming a polyolefin sheet-like foam.

[Means to solve the problem]

The method of thermoforming a polyolefin sheet foam according to the present invention is a method of thermoforming a polyolefin sheet foam made of a polyolefin resin crosslinked with electron beams or containing a chemical crosslinking agent and a pyrolyzable blowing agent. It is.

This thermoforming method includes the following steps.

■If the density at the start of heat molding of the foam is d1, and the density at the end of heat molding is d2, then 0.70<(dz/dl
) Prepare an unexpanded sheet-like foam whose foaming reaction is controlled within the range of 0.90.

■Using an unexpanded sheet-like foam, heat molding is performed to obtain a molded product.

Note that the step of performing heat molding may be a step of simultaneously heat molding the unexpanded sheet-like foam and the structure or cloth-like fiber made of polyvinyl chloride or acrylic butyl styrene.

＊＊＊＊＊＊＊ Polyolefin resins used in the present invention include, for example, polypropylene, polyethylene, and the like. Alternatively, a mixture thereof may be used.

As the polypropylene resin, for example, isotactic polypropylene resin is used. In addition, the melt flow rate (ASTM D 1238E) is 1 to 20 g.
It is preferable to have a fluidity of /10 minutes. Further, the polypropylene resin may be a copolymer. In this case,
A small amount copolymer of α-olefin containing ethylene with good randomness is preferred. Furthermore, other resins may be mixed to the extent that the properties of the polypropylene resin are not impaired. It is also possible to add a small amount of other thermoplastic resin to this polypropylene resin, and arbitrary additives such as flame retardants, fillers, stabilizers, antistatic agents, etc. can also be added.

The polyethylene resin preferably has a melt flow rate of 0.1 to 50 g/10 min (preferably 0.5 to 50 g/10 min).
20 g/l 0 min), density (ASTM D
1505) is 0.910 to 0.940 g/cm3 (preferably 0.915 to 0.935 g/cm') and has a melting point of 110 to 130°C (preferably 115 to 127°C).
), which is a copolymer of ethylene and an α-olefin having 4 to 20 carbon atoms (preferably 5 to 20 carbon atoms). More preferably, an ethylene copolymer having a molecular weight distribution (value of weight average molecular weight/number average molecular weight) of 6 or less is used.

α having 4 to 20 carbon atoms, which is a constituent component of ethylene copolymer
-Olefins include, for example, 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-1-butene, 4
-Methyl-1-pentene, 4,4-dimethyl-1-pentene, ■-octene, ■-decene, 1-dodecene, 1-
One or more compounds selected from tetradecene, 1-octadecene, etc. can be mentioned. Furthermore, these α
As long as olefin is a constituent component, a small amount of propylene component may be contained, but in that case, it is necessary to make the propylene component considerably smaller than the content of α-olefin. In order for the density of the entire polyethylene copolymer to be within the above range, it is sufficient that the ethylene content is approximately 88 to 97% by weight, although this varies depending on the type of α-olefin.

Note that the melting point of the polymer was measured using a differential scanning calorimeter (DSC).
) and after melting the sample at 200'C for 5 minutes,
This is the peak temperature when the endothermic curve is measured at a heating rate of 10"C/min after cooling to room temperature for crystallization at a rate of 25°C/min and keeping it at room temperature for 1 hour. There is one endothermic peak. It may be detected only one or more than one, but in the latter case, the highest peak temperature is taken as the melting point.
Molecular weight distribution (weight average molecular weight/number average molecular weight) was measured using a gel permeation chromatograph [measuring device: Model 150 (-LC) manufactured by Waters Associates (USA)].
/GPC, Column: Toyo Soda GMH-6 (10”~
107 people mixed gel),? Vehicle: 0-dichlorobenzene, measurement temperature: 135°C] to obtain a molecular weight distribution curve, and the weight average molecular weight and number average molecular weight were calculated using a universal calibration method using polystyrene as a standard. It is a value.

The electron beam crosslinking used in the present invention has an acceleration voltage of 5
This is carried out by irradiating ionizing radiation of 1 to 10 Mrad using an ionizing radiation irradiation device of about 00 to 1000 kV. Radiation includes, for example, X-rays, α-rays, β-rays,
Refers to ionizing radiation such as T-rays.

The chemical crosslinking agent used in the present invention has a decomposition point higher than the melting temperature of the polyolefin resin and lower than the decomposition temperature of the blowing agent used. The crosslinking agent preferably has a decomposition temperature of about 130° C. or higher, particularly preferably 150° C. or higher when the decomposition half-life is 1 minute. A specific example is methyl ethyl ketone peroxide (1
82°C), butyl peroxyisopropyl carbonate (153°C), dicumyl peroxide (171
'C), 2.5-dimethyl-235-di(L-butylperoxy)hexane (179°C), 2.5-dimethyl-
2,5-di(t-butylperoxy)hexyne-3(1
93°C), di-L-butylbaroxyphthalate (1
59°C). These organic peroxides are
It is used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight.

Note that crosslinking treatment using an electron beam and a chemical crosslinking agent may be used in combination.

The thermally decomposable blowing agent used in the present invention may be anything as long as it has a decomposition temperature higher than the melting temperature of the polyolefin resin used in the present invention. Preferred is abdicarbonamide, especially one whose main decomposition point is 196°.
C or higher is desirable. The decomposition point here refers to the melting point measuring device specified by the Japanese Industrial Standards (JIS K-8004), when a capillary tube is tightly filled with a sample of approximately 5 mm, and when the temperature reaches 190°C, the sample is measured. 2°C per minute up to 196°C.
This is the temperature at which the yellow color of the sample is completely decolored by increasing the temperature at a rate of 1°C per minute. In addition, hydrazodicarbonamide, azodicarboxylic acid barium salt, dinitrosopentethylenetetramine, nitroguanidine, p,p-oxybishenzenesulfonyl semi-hydrabazide, etc., which have a decomposition point equal to or higher than azodicarbonamide, are added. They can be used alone or in combination. These can also be used by mixing them with abdicarbonamide. In addition, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, barium azodicarboxylate, abbisisobutyronitrile, toluenesulfonyl hydrazide, etc. are used.

In the present invention, first, 0.70<(dZ/d,)≦0
．． An unexpanded sheet-like foam whose foaming reaction is controlled within a range of 90% is prepared.

To prepare this, it is first necessary to mold an unfoamed sheet. In forming this sheet, kneading and forming is performed at a temperature lower than the decomposition temperature of the blowing agent or chemical crosslinking agent. This is a requirement to create a uniform sheet and a uniform foam. If the foaming agent decomposes even partially during sheet forming, the generated gas is retained in the sheet, resulting in a sheet with fine cavities. See like this! - When heated and foamed, the cells in the foam become coarse and a good foam cannot be obtained. Further, if the chemical crosslinking agent decomposes during sheet molding, a crosslinking reaction of polyethylene occurs partially, and a gel component is generated in the sheet, making it impossible to obtain a homogeneous sheet or foam. Therefore, it is necessary to select a blowing agent and a chemical crosslinking agent whose decomposition temperature is higher than the kneading and molding temperature of the resin used. The degree of crosslinking suitable for the method of the invention is 10 to 80%, preferably 15 to 60% in terms of gel fraction.

If the degree of crosslinking is too small, the bubbles during foaming will not be retained and will tend to form large bubbles, making it difficult to increase the foaming ratio due to gas escaping to the outside of the system. On the other hand, if the degree of crosslinking is too high, the expansion of the foam will be hindered and the expansion ratio will be difficult to increase, the extensibility during heating will decrease, and the thermoformability will decrease. The gel fraction here is determined by heating the unfoamed sheet obtained as described above and measuring 0. 70 < (dz/d+)
Control the foaming reaction to a range of ≦0.90? IIIL: An unexpanded sheet-like foam is obtained. Next, the obtained unexpanded sheet-like foam is subjected to heat molding. In this case, the unexpanded sheet-like foam and the structure or cloth-like fibers made of polyvinyl chloride, acrylic butylstyrene, etc. can be simultaneously heat-molded.

Here, the reason why heat molding is performed using an unexpanded sheet-like foam is as follows. First, when thermoforming a polyolefin foam using a pyrolytic blowing agent, if the foaming reaction is completed before the heat molding process, the heating during the heat molding may cause surface roughness and damage to the foam. Gas dissipation is likely to occur, and moldability is likely to become unstable.

In other words, the range of heat forming conditions becomes narrower. On the other hand, when thermoforming is performed using a sheet-like foam whose foaming reaction has not yet been completed, as in the present invention, the foaming reaction can be actively utilized during thermoforming, resulting in surface roughness and Gas dissipation becomes less likely to occur. Therefore, the range of heat forming conditions can be widened. However, the foam density at the start of heat molding is 0°70< (dz /d+)≦
It needs to be in the range of 0.90. If this value is 0.7 or less, the dimensional change due to foaming during heat molding will be too large, making it difficult to bond with other materials, and the range of heat molding conditions will be narrowed. Moreover, if it exceeds 0.9, the foaming reaction during heat molding will not be effective. Furthermore, more preferably, 0.80<(dZ/d,)≦0.90.

The molded product obtained by the present invention is used for, for example, molded ceilings, instrument panels, door panels, seat hack pockets, wheel house covers, center pillar rear quarter trims, horn pads, etc. of automobiles.

〔Effect of the invention〕

According to the method of thermoforming a polyolefin sheet-like foam according to the present invention, an unexpanded sheet-like foam is prepared and heat-forming is performed using the foam, so that the surface of the obtained molded product is roughened. is less likely to occur, and moldability is improved.

〔Example〕

80 parts by weight of polypropylene resin randomly copolymerized with 5% by weight of ethylene and a density of 0.930 g/cm'
By a mixture consisting of 20 parts by weight of a linear polyethylene resin, 10 parts by weight of dicarbonamide as a blowing agent, and 5 parts by weight of divinyl bengaf as a crosslinking agent,
A sheet with a thickness of 2 mm was obtained. Next, 5Mr on that sheet
After performing ad electron beam irradiation, the temperature was 230° using a salt bath.
The sheet was heated and foamed at C. The obtained foam was heat-molded using a vacuum heat-molding machine at 160°C and 700 Torr.

In the above manufacturing method, various foams were manufactured with varying degrees of heat foaming, and console boxes were prototyped using a vacuum heat molding machine using the resulting foams.

The results are shown in Table 1.

As is clear from Table 1, when the density ratio (d2./d1) exceeds 0.90, cracks in some corners, a decrease in wall thickness due to uneven thickness, and surface roughness occur, resulting in unsatisfactory results. The desired results were not obtained. Also, the density ratio (at/a+) is 0
．． When it was 70 or less, good moldability could not be obtained. On the other hand, good results were obtained for samples with density ratios (ctz/a+) of 0.80 and 0.90.

Foam density: I S- Measured according to 67.

Surface condition t4: The surface condition of the sample after heat molding was observed and expressed as follows.

No change in display, roughness × Molding processability: The moldability of the sample after heat molding was observed and expressed as follows.

4 sex Nijo

Claims (2)

[Claims] (1) A method for thermoforming a polyolefin sheet foam made of a polyolefin resin crosslinked with electron beams or containing a chemical crosslinking agent and a pyrolyzable blowing agent, the method comprising: determining the density of the foam at the start of heat molding; d_1, and when the density at the end of heat molding is d_2, 0.70<(d_2/d
_1) Prepare an unexpanded sheet-like foam whose foaming reaction is controlled to a range of ≦0.90, and heat-form the unexpanded sheet-like foam to obtain a molded body. A method for thermoforming a polyolefin sheet-like foam, comprising: (2) The step of thermally forming the unfoamed sheet-like foam, a structure of polyvinyl chloride, a structure of acrylic butylstyrene, a cloth-like fiber of polyvinyl chloride, and a cloth-like structure of acrylic butylstyrene. The method for thermoforming a polyolefin sheet-like foam according to claim 1, which is a step of simultaneously thermoforming at least one selected from the group of fibers.