JPH06220238A - Production of crosslinked adhesive polypropylene form - Google Patents

Abstract

PURPOSE:To produce the subject foam improved in adhesion, flexibility, heat resistance, etc., by grafting a specified compound onto the surface of a molding containing a propylene/ethylene random copolymer, a linear low density PE and a blowing agent, and foaming the obtained molding. CONSTITUTION:100 pts.wt. in total of 10-90wt.% propylene/ethylene random copolymer of an ethylene content of 0.2-8.0wt.% and 90-10wt.% linear low-density PE is melt-kneaded with 1-30 pts.wt. blowing agent and 0.5-5.0 pts.wt. closslinking aid at 150-175 deg.C and extruded from a die to obtain a molding of a thickness of 0.5-3mm. A polar radical-polymerizable compound is applied to the surface of this molding, and the molding is irradiated with an ionizing radiation at a does of 0.1-50 Mrad to graft the compound onto its surface and to crosslink it, and foamed by heating at 200 deg.C for 0.5-5min.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a polypropylene-based crosslinked foam. More specifically, the present invention relates to a method for producing a polypropylene-based crosslinked foam having good adhesiveness, which is used as an interior material for automobiles, a cushioning material for sports goods and food packaging, a heat insulating material, a sound deadening material, and other exterior materials.

[0002]

2. Description of the Related Art Polypropylene foam is excellent in mechanical strength, flexibility, texture, heat resistance, chemical resistance and the like, and also has good secondary workability such as vacuum moldability and press moldability. It is widely used as interior materials for automobiles, heat insulation materials, cushioning materials for sports equipment and food packaging, and other sound deadening and exterior materials.

In general, these polypropylene foams are rarely used alone and in most cases,
It is a product after being bonded to other skin materials. When a sheet or film having the same basic resin composition as that of the foam is used as the skin material, it can be easily bonded by a heat fusion bonding method (heat sealing). On the other hand, when the basic resin composition of the skin material and the foam are different, an appropriate adhesive is selected and bonded / pasted, but the polypropylene foam itself is non-polar, whereas the Since many adhesives used for bonding have a chemically polar group, the adhesiveness with the polypropylene foam is not sufficient.

In order to improve the adhesion of plastics, it has been customary to pretreat the surface to which the adhesive is applied. As the surface treatment method, for example, (1)
A method of treating the surface with a solvent such as acetone or methyl ethyl ketone to remove plasticizers, fillers, stabilizers, release agents, etc. used as additives that hinder the adhesion and soften the surface. (2) Sandblast or buff Although a method of removing impurities on the surface by polishing or the like and making unevenness on the surface is implemented, it is not effective for a non-polar polypropylene foam.

As a surface treatment of nonpolar plastic,
(3) A method of oxidizing the polymer surface by a method such as corona discharge or plasma jet to generate polar groups, and
(4) There is a method of imparting polarity by grafting a vinyl monomer having a polar group. However, with the method of (3) using corona discharge, plasma jet, etc., the effect of imparting polarity to the material surface is temporary, the adhesive force decreases with time, and permanent adhesive force can be obtained. Can not. Also,
(4) A method for imparting polarity by grafting a vinyl monomer having a polar group onto the surface of a polymer is disclosed in JP-A-62-5
After subjecting the ultrahigh molecular weight polyolefin stretched product to plasma discharge treatment or electron beam irradiation treatment to 9637, a method of graft-polymerizing an unsaturated carboxylic acid or its derivative on the surface thereof, and olefin resin in JP-A-4-31445 A maleic acid, a monomer selected from maleic anhydride and maleimide, a foaming agent, and a foamed resin composition containing an organic peroxide, if desired, are molded into a sheet and heated to crosslink or foam, or to produce an electron. A method of irradiating with rays or radiation, crosslinking and then heat-foaming is disclosed. The former aims to improve the adhesiveness of plastic fibers used as a filler for fiber-reinforced composite materials.
It cannot be directly applied to foam-molded products. The latter is
Since the graft monomer is kneaded into the entire resin composition, the monomer components present inside do not contribute to the adhesiveness, and the graft monomer must be added in an extra amount.
Further, since sublimable maleic anhydride is used, there is a problem in working environment.

[0005]

[Means for Solving the Problems] The present inventors have diligently studied a method of incorporating a step of imparting a polar group to the surface in a normal production step of a polypropylene-based crosslinked foam,
As a result, in the step of cross-linking and foaming the polypropylene-based composition molded body by utilizing ionizing radiation, the method of the present invention has been reached in which only the surface of the molded body is cross-linked and at the same time a radically polymerizable reactive compound having polarity is grafted.

That is, the present invention has an ethylene content of 0.2-
8.0% by weight of propylene-ethylene random copolymer (a) 10 to 90% by weight, linear low density polyethylene (b) 90 to 10% by weight, and with respect to a total of 100 parts by weight of the above (a) and (b). A method for producing a polypropylene-based crosslinked foam, which comprises crosslinking 1 to 30 parts by weight of a foaming agent (c) by irradiation with ionizing radiation, and then foaming by heating, wherein the molded article is irradiated with the ionizing radiation. Is a method for producing a polypropylene-based crosslinked foam having improved adhesiveness, which comprises graft-polymerizing a polar radically reactive compound having a polarity on the surface thereof.

The present invention will be described in detail below. In the present invention, the raw material resin (a) for the polypropylene-based crosslinked foam is
The propylene-ethylene random copolymer as a component is a copolymer in which a repeating unit derived from propylene and a repeating unit derived from ethylene are randomly copolymerized. The propylene-ethylene random copolymer has an ethylene content of 0.2 to 8.0% by weight, preferably 5.0% by weight or less, particularly 0.3 to 4.0% by weight. When the ethylene content in the propylene-ethylene random copolymer is less than 0.2% by weight, the sheet moldability, the physical properties of the foam at room temperature, the cross-linking efficiency, etc. are insufficient.
If it exceeds 0% by weight, satisfactory mechanical properties cannot be obtained at high temperature of the foam.

In the present invention, the linear low density polyethylene (LLDPE) as the component (b) of the raw material resin for the polypropylene crosslinked foam is a linear copolymer of ethylene and an α-olefin having 4 to 8 carbon atoms. Is. Examples of the α-olefin include butene-1, 4-methylpentene-1, hexene-1, octene-1 and the like. In addition, the content of ethylene in the LLDPE is 90 mol% or more. Such LLDPE is usually 0.910 to 0.945.
It has a density of g / cm ³ and a melt index of 0.7 to 60 g / 10 min (MI: 190 ° C., 2.16 kg load), but preferably has a density of 0.915 to 0.935 g / cm ³ and an MI of 3 to 3. 20
Use g / 10 min.

The blending ratio of the propylene-ethylene random copolymer (a) and the linear low density polyethylene (b) is 10 to 90% by weight for (a) and 90 to 1 for (b).
It is 0% by weight, preferably (a) is 20 to 80% by weight, and (b) is 80 to 20% by weight. When the propylene-ethylene random copolymer (a) exceeds 90% by weight (the linear low density polyethylene (b) is less than 10% by weight), the cell nonuniformity is exhibited during foaming. Further, a propylene-ethylene random copolymer (a)
Is less than 10% by weight (the linear low-density polyethylene (b) exceeds 90% by weight), heat resistance and mechanical properties at high temperature deteriorate.

The foaming agent (c) used in the resin composition of the crosslinked foam of the present invention is a liquid or solid at room temperature and decomposes or vaporizes when heated above the melting point of the resin composition. Any compound can be used as long as it is a compound that does not substantially interfere with molding into a sheet or the like and the crosslinking reaction, but a compound having a decomposition temperature of 180 to 270 ° C. is particularly preferable. Specific examples of such a foaming agent include azodicarbonamide, azodicarboxylic acid metal salt,
Dinitrosopentamethylenetetramine, hydrazodicarbonamide, p-toluenesulfonyl semicarbazide,
Examples include s-trihydrazinotriazine and the like.

The blending amount of the foaming agent (c) is selected according to the type of the foaming agent and the expansion ratio, but it is usually the component (a) (propylene-ethylene random copolymer) and the component (b) (linear). Low density polyethylene) (resin component) 1
It is used in the range of 1 to 30 parts by weight based on 00 parts by weight.

In the present invention, in addition to the above-mentioned propylene-ethylene random copolymer (a), linear low density polyethylene (b) and foaming agent (c), a crosslinking reaction by ionizing radiation is carried out smoothly and efficiently. Therefore, it is preferable to add (d) a crosslinking aid. Specific examples of the crosslinking aid include trimethylolpropane trimethacrylate,
Trimethylolpropane triacrylate, bentaerythritol pentaacrylate, diallyl phthalate,
Examples include diallyl maleate and the like. The amount of the crosslinking aid added is 0.5 to 5.0 parts by weight, preferably 1.0 to 3.0 parts by weight, based on 100 parts by weight of the resin component.

In the present invention, in order to improve the characteristics of the polyolefin crosslinked foam, other compounding agents,
Specifically, a rubber substance, another resin, a pigment, various fillers, a flame retardant substance, an antioxidant and the like can be appropriately mixed.

In the present invention, in order to improve the surface adhesiveness of the polypropylene-based crosslinked foam, a radical polymerization reactive compound having a polarity is graft-polymerized on the surface of the crosslinked foam by utilizing an ionizing irradiation step for crosslinking. . As a specific method, (1) a method of crosslinking the molded body by ionizing radiation and grafting the polar compound on the surface after treating the molded body surface with a radical polymerization reactive compound having polarity,
(2) A method of irradiating the molded body with ionizing radiation to perform crosslinking and surface activation, and then treating the surface with a radical polymerization reaction compound having polarity, and grafting, and (3) radical polymerization having polarity. After kneading and blending the reactive compound with the resin component, aging, that is, heating to bleed the radical polymerization reactive compound on the surface, and then ionizing radiation is performed to carry out internal crosslinking and grafting on the surface to form a crosslinked foamed molded product surface. It is a method of grafting a radical polymerization-reactive compound having polarity to the.

Examples of the radical-polymerization-reactive compound (polar compound) having a polarity include unsaturated carboxylic acids or their derivatives. As the unsaturated carboxylic acid or its derivative, for example, acrylic acid, methacrylic acid,
Maleic acid, endo-bicyclo [2.2.1] -5-heptene-2,3-dicarboxylic acid (endic acid), fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, etc. Unsaturated mono- or dicarboxylic acids, or derivatives thereof, such as acid halides, amides, imides, anhydrides, esters and the like can be mentioned. Specific examples of the derivative include maleenyl chloride, maleimide, maleic anhydride, endic anhydride, methyl acrylate, methyl methacrylate, citraconic anhydride, monomethyl maleate, dimethyl maleate and the like. In the present invention, radical-polymerization-reactive oligomers, for example, urethane-based oligomers, ether-based oligomers, ester-based oligomers having a polymerizable functional group can also be used. As these radical-polymerization-reactive compounds (polar compounds), those having good compatibility with the adhesive used for bonding the polypropylene-based crosslinked foam and the skin material are preferable. Specific examples of a preferable combination include acrylic acid, methacrylic acid, and derivatives thereof for an acrylic adhesive and a urethane oligomer having a polymerizable functional group for a urethane adhesive (Shin Nakamura Chemical ( NK oligo U-122A) manufactured by K.K.

Next, a method for producing a polypropylene-based crosslinked foamed product comprising the above components will be described. First, the propylene-ethylene random copolymer (a), linear low density polyethylene (b), foaming agent (c).
A molded product is produced from each component of the crosslinking aid (d). Further, when an oligomeric compound is used as the polar radical-polymerizing reactive compound and bleeding on the surface, the compound is added at this stage. That is, (a),
The components (b), (c) and (d) and other optional compounding ingredients are kneaded by a Henschel mixer, an extruder or the like. The kneading order can be arbitrarily selected, but batch kneading is preferable. The melt-kneading temperature needs to be lower than the decomposition temperature of the foaming agent, and the preferable melt-kneading temperature is 150 to 17
It is 5 ° C. Next, the kneaded product of the resin composition of the present invention is extruded from a die such as an extruder to form a molded product such as a sheet. The thickness of the sheet is not particularly limited,
The thickness is preferably 0.5 to 3.0 mm, more preferably 1.0 to 2.0 mm. At this time, it is necessary to mold the sheet so that the foaming agent does not decompose and foaming does not occur.

As a method for graft-polymerizing a radical-polymerizable reactive compound (polar compound) having polarity on the cross-linking and surface of the molded body, there are a pre-irradiation method and a simultaneous irradiation method known from, for example, JP-A-62-277441. Etc. In the pre-irradiation method, the obtained molded product is irradiated with ionizing radiation and then a polar compound or a solution thereof (hereinafter, both are collectively referred to as a polar compound-containing liquid) is applied, or a polar compound-containing liquid is applied. It is performed by immersion treatment. The simultaneous irradiation method is performed by irradiating ionizing radiation immediately after treating (coating or spraying) the molded body with the liquid containing a polar compound. Further, when an oligomer is used as a polar compound, when kneading each component, the polar compound is also kneaded at the same time to obtain a molded product of a polar compound, and the concentration of the polar compound in the surface layer of the molded product is increased by aging treatment. After that, the polar compound can be grafted on the surface by irradiating with ionizing radiation.
By these methods, a foamable crosslinked molded article having a polar graft chain on the surface of the molded article and excellent in adhesiveness can be obtained.

The ionizing radiation applied to the molded product is α
Ionizing radiation such as rays, β rays (electron rays) and γ rays is used. The irradiation dose of the radiation is such that the gel fraction of the molded body after irradiation is 25 to
It may be set to 50% by weight, preferably 30 to 40% by weight. If the gel fraction is less than 25% by weight, the melt tension of the sheet in the foaming process will be insufficient.
If it exceeds 0% by weight, the mechanical properties of the obtained foam cannot be satisfied.

The irradiation dose varies depending on the type and amount of the crosslinking aid, the degree of crosslinking, the thickness of the molded article, etc.
-50 Mrad, preferably 0.5-30 Mrad. Also,
The acceleration voltage is, for example, 100 to 5000 kV, preferably 750 to 5000 kV for a molded product having a thickness of 1 mm. If it is less than 0.1 Mrad, crosslinking and graft polymerization of polar compounds are not sufficiently carried out, and if it is more than 50 Mrad, the resin composition is significantly deteriorated and the physical properties as a foam are deteriorated.

The cross-linked molded article thus obtained is foamed at a temperature higher than the melting point of the resin component, preferably 200 ° C.
Above, more preferably, it can be performed by heating to a temperature of 230 ~ 280 ℃. The heating time required for foaming is usually 0.5 to 5 minutes.

Next, each grafting process will be specifically described. Grafting by Pre-Irradiation Method A molded body having a desired thickness is prepared, and the molded body is irradiated with ionizing radiation with an accelerating voltage of 150 to 5000 kV, preferably about 200 to 1000 kV. By this irradiation, the molded body is crosslinked and unreacted radical reactive species are generated and remain.
Irradiation is usually performed in an air atmosphere, preferably with an oxygen concentration of 2.
It is performed in a nitrogen atmosphere of 0% by volume or less, and more preferably in an inert gas (nitrogen, argon, etc.) atmosphere. A suitable irradiation dose is about 0.5 to 50 Mrad. 0.
If it is less than 5 Mrad, the cross-linking of the molded product will be insufficient and 50 Mrad
If it exceeds, the molded product will be significantly deteriorated. Also,
After this irradiation, the adhesiveness can be further improved by a two-step irradiation method in which only the polymer surface layer is retreated with ionizing radiation having an acceleration voltage lower than the above radiation. After irradiation,
The molded body is treated with the polar compound-containing liquid to graft-polymerize the polar compound on the surface of the molded body. As a treatment method, the molded body may be floated or dipped on the polar compound-containing liquid. The treatment temperature may be room temperature or higher and the boiling point of the polar compound-containing liquid or lower, and the treatment time is preferably about 1 to 60 minutes.

When the polar compound is a liquid at room temperature and atmospheric pressure, a stock solution may be used as the solution used for the treatment, but a solution diluted to a desired concentration with an appropriate solvent is usually used. The solvent for dilution may be a general-purpose organic solvent, and preferably has no radical reactivity such as benzene or water. When water is used, it is preferable to add an emulsifier such as a surfactant or ferric ammonium sulfate sulfate, thereby suppressing the formation of a homopolymer of a polar compound and further promoting a grafting reaction with a substrate. It can be done efficiently. The concentration of the solution is preferably 5% by weight or more as the concentration of the polar compound. Next, the molded body that has been subjected to the graft treatment is thoroughly washed with a suitable detergent. As the cleaning agent, generally used organic solvents such as ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, dimethylformamide and pyrrolidone are used, and among these, dimethylformamide and pyrrolidone are preferable. After washing, the molded body is dried.

Grafting by Simultaneous Irradiation Method A molded article having a desired thickness is prepared, and the sheet is directly coated or sprayed with the polar compound-containing solution or floated on the solution as described in the pretreatment method. Or by dipping. Next, the molded body coated with the polar compound-containing liquid is irradiated with ionizing radiation, and the polar compound is graft-polymerized on the surface layer of the molded body simultaneously with the crosslinking of the molded body.
The irradiation of ionizing radiation is carried out under the same acceleration voltage, irradiation dose and atmosphere as in the pretreatment method, but in this case it is preferable to carry out irradiation at a low dose rate. When irradiation is performed at a high dose rate,
A homopolymer of a polar compound is produced, and the homopolymer is lost by washing after the grafting treatment, resulting in insufficient surface modification. Next, the grafted molded product is washed and dried in the same manner as in the case of the pre-irradiation described above.

Grafting by bleeding method At the time of kneading the above-mentioned respective components, a polar compound is also kneaded at the same time to prepare a molded body of the polar compound. The amount of the polar compound blended varies depending on the type of the polar compound used and cannot be generally specified, but it is 1 to 20 parts by weight, preferably 1 to 10 parts by weight per 100 parts by weight of the resin component. The polar compounds used are those that are difficult to volatilize and sublime, especially oligomers.
Those of the system are preferred. Kneading and molding are performed in the same manner as the above method. After molding, aging treatment is performed to bleed the polar compound in the molded body to the surface layer. The aging treatment can be performed by, for example, a method of leaving it at 40 to 80 ° C. for 5 to 48 hours. The molded product having the increased concentration of the polar compound in the surface layer by the aging treatment is irradiated with ionizing radiation, and the polar compound is graft-polymerized simultaneously with the crosslinking of the molded product. Next, the grafted molded product is washed and dried in the same manner as in the case of the pre-irradiation described above.

[0025]

The polypropylene-based crosslinked foam obtained by the production method of the present invention comprises a propylene-ethylene random copolymer (a), a linear low density polyethylene (b), a foaming agent (c), and a crosslinking aid. (D) is contained in the surface layer and a polar polymerizable reaction compound is graft-polymerized, so that the adhesive property becomes good when the adhesive layer is attached to another surface material. It is considered that this is because the polar group of the polymerization-reactive compound graft-polymerized and the polar group of the adhesive are firmly bonded to each other in the surface layer of the obtained crosslinked foam due to the affinity.

[0026]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples. The components used in Examples and Comparative Examples are as follows. (A) Propylene-ethylene random copolymer (RP
P): Contains 3.6% by weight of ethylene, MFR (230 ° C, 2.
16kg load) 9g / 10 minutes. (B) Linear low density polyethylene (LLDPE): MI
(190 ℃, 2.16kg load) 6g / 10min, density 0.915g / c
m ³ . (C) Foaming agent: azodicarbonamide. (D) Cross-linking aid: trimethylolpropane trimethacrylate (TMPT) and neopentyl glycol dimethacrylate (NPG).

Examples 1-3 Propylene-ethylene random copolymer (RPP) 70
Parts by weight, 30 parts by weight of linear low density polyethylene (LLDPE), 3 parts by weight of a crosslinking aid, 10 parts by weight of a foaming agent and 0.5 parts by weight of an antioxidant, and after mixing for 2 minutes at 500 rpm using a Henschel mixer, Supply to a single-screw extruder (with T-die, L / D ratio 28, 50 mmφ), extrusion temperature 16
It was extruded at 0 ° C to prepare a sheet having a thickness of 1.0 mm. This sheet is irradiated with an electron beam of 8 Mrad (750 kV) to obtain a degree of crosslinking (gel fraction: weight fraction of insoluble matter in refluxing xylene).
Was 30 to 40% by weight. Next, the raw sheet was immersed in an acrylic acid aqueous solution (60 ° C.) having the concentration shown in Table 1 for a predetermined time (Table 1). Incidentally, ammonium iron (II) sulfate (Morle's salt) was added as necessary. The raw sheet taken out from the reaction solution was washed with water and then dried. Then 2
It was put in an air oven at 70 ° C. for 2 minutes to decompose the foaming agent and foam it 20 times. For each crosslinked foamed sheet obtained in this manner, wetting index, measuring the adhesive strength,
In addition, the fracture state in the peeling test after adhesion was evaluated. The results are also shown in Table 1.

Example 4 The same operation as in Example 1 was performed except that the surface layer treatment (both sides) was carried out by irradiating the electron beam of 8 Mrad (750 kV) and then the electron beam of 5 Mrad (250 kV). Then, a crosslinked foamed product was obtained. The results are shown in Table 1.

Comparative Example 1 A crosslinked foamed sheet was obtained in the same manner as in Example 1, except that the surface treatment with the acrylic acid monomer was not carried out. With respect to each of the crosslinked foamed sheets thus obtained, the wetting index and the adhesive strength were measured, and the fracture state in the peeling test after the adhesion was evaluated. The results are shown in Table 1.

Comparative Example 2 A crosslinked foamed sheet was obtained in the same manner as in Example 4, except that the surface treatment with the acrylic acid monomer was not carried out. With respect to each of the crosslinked foamed sheets thus obtained, the wetting index and the adhesive strength were measured, and the fracture state in the peeling test after the adhesion was evaluated. The results are shown in Table 1.

[0031]

[Table 1]

Examples 5-8 Propylene-ethylene random copolymer (RPP) 70
Parts by weight, 30 parts by weight of linear low density polyethylene (LLDPE), 3 parts by weight of a crosslinking aid, 10 parts by weight of a foaming agent and 0.5 parts by weight of an antioxidant, and after mixing for 2 minutes at 500 rpm using a Henschel mixer, Supply to a single-screw extruder (with T-die, L / D ratio 28, 50 mmφ), extrusion temperature 16
It was extruded at 0 ° C to prepare a sheet having a thickness of 1.0 mm. This sheet was coated (sprayed) with an isopropanol solution of acrylic acid having the concentration shown in Table 2 on one surface of the sheet, and then irradiated with an electron beam of 8 Mrad (750 kV) to obtain a crosslinking degree (gel fraction: reflux). The insoluble matter weight fraction in xylene) was set to 30 to 40% by weight. After irradiation, the solvent and the like were evaporated and dried under warm air. Then, it was put in an air oven at 270 ° C. for 2 minutes to decompose the foaming agent and foam it 20 times. With respect to each of the crosslinked foamed sheets thus obtained, the wetting index and the adhesive strength were measured, and the fracture state in the peeling test after the adhesion was evaluated. The results are shown in Table 2 together.

[0033]

[Table 2]

Examples 9 to 11 Propylene-ethylene random copolymer (RPP) 70
Parts by weight, linear low density polyethylene (LLDPE) 30 parts by weight, crosslinking aid 3 parts by weight, foaming agent 10 parts by weight, antioxidant 0.5 parts by weight and urethane oligomer (manufactured by Shin-Nakamura Chemical Co., Ltd .; NK oligo U) -122A) was added in an amount shown in Table 3 and mixed using a Henschel mixer for 2 minutes at 500 rpm, and then a single-screw extruder (with T-die, L / D ratio 28, 50) was used.
mmφ) and extrude at an extrusion temperature of 160 ° C to obtain a thickness of 1.
A 0 mm sheet was prepared. After this sheet was left at 60 ° C. for 24 hours, it was irradiated with an electron beam of 8 Mrad (750 kV) to adjust the degree of crosslinking (gel fraction: weight fraction of insoluble matter in refluxing xylene) to 30 to 40 wt%. . Then, it was put in an air oven at 270 ° C. for 2 minutes to decompose the foaming agent and foam it 20 times. With respect to each of the crosslinked foamed sheets thus obtained, the wetting index and the adhesive strength were measured, and the fracture state in the peeling test after the adhesion was evaluated. The results are also shown in Table 3.

[0035]

[Table 3]

The methods for measuring the physical properties shown in Tables 1 to 3 are as follows. (1) Surface Wetting Index: A commercially available wetting reagent was applied, and the change in area after application was observed, and the numerical value of the reagent in which the area did not change for 2 minutes or more was taken as the wetting index of the sample. (2) Adhesive strength: A 25 mm wide strip-shaped sample was cut out from the one bonded to a PVC sheet in an overheated state using a urethane adhesive, and the PVC sheet and foam were gripped and pulled at room temperature. Tested and the maximum load is expressed per width of the bonded part. (3) Destruction state: A peeling test was carried out on the one laminated with a PVC sheet in an overheated state using a urethane-based adhesive, and evaluated according to the following criteria. Poor ... Peeled off at the adhesive interface due to poor adhesion to the foam layer, Material destruction ... Foam broken due to high adhesive strength.

As is clear from Tables 1 to 3, according to the present invention, the pre-irradiation method of treating the surface of the molded body with the radical-reactive compound having polarity after irradiation (Examples 1 to 1)
4), a simultaneous irradiation method of irradiating the surface of the molded body with a radically reactive compound having polarity (Examples 5 to 8), and kneading the radically reactive compound having polarity and aging after molding to bleed the surface. In any of the bleeding methods of post irradiation (Examples 9 to 11), the wetting index,
It can be seen that both the adhesive strength and the broken state are good, and the adhesiveness is excellent. Further, according to the two-step irradiation method in which only the polymer surface layer is re-treated with ionizing radiation having a low acceleration voltage (Example 4), the one-step irradiation method (Example 1)
It can be seen that the adhesiveness is further improved.

[0038]

According to the present invention, a polar compound can be grafted and modified only on the surface of a polypropylene-based crosslinked foam with good economy and workability, and the resulting crosslinked foam is a polypropylene-based crosslinked foam. Excellent adhesion without losing the advantages of the crosslinked foam. That is, the polypropylene-based cross-linked foam obtained by the method of the present invention comprises a propylene-ethylene random copolymer and a linear low-density polyethylene as a resin component, is excellent in flexibility, heat resistance, mechanical properties, and the like, and It is a cross-linked foam that has excellent adhesion on its surface, and it is used as interior materials for automobiles (door trim panels, instrument panels, ceiling boards, etc.), cushioning materials for sports equipment and food packaging, heat insulating materials, sound deadening materials, etc. It is preferably used as an exterior material.

Claims (1)

[Claims] 1. A propylene-ethylene random copolymer (a) having an ethylene content of 0.2 to 8.0% by weight, 10 to 90% by weight, and a linear low density polyethylene (b), 90 to 10% by weight.
And, for 100 parts by weight of the total of (a) and (b),
A method for producing a polypropylene-based crosslinked foam, which comprises cross-linking a molding containing 1 to 30 parts by weight of a foaming agent (c) by irradiation with ionizing radiation, and then heat-foaming the surface of the molding by irradiation with the ionizing radiation. A method for producing an adhesive polypropylene-based crosslinked foam, which comprises graft-polymerizing a radical-polymerization-reactive compound having a polarity.