JPH11228721A - Crosslinked polypropylene-based foamed resin composition and crosslinked foamed sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin composition for foaming and which is excellent in formability, mechanical strength, elongation, thermal stability, or the like, and to provide a foamed body therefrom. SOLUTION: A crosslinked polypropylene-based foamed resin composition comprises 1-10 pts.wt. of a bifunctional vinyl group-containing benzene compound (c) which has a content (M) of a benzene compound having a vinyl group located at a para position of 0.18-0.69, 0.5-5 pts.wt. of an alkyl group and monofunctional vinyl group-containing benzene compound (d) and 1-10 pts.wt. of a thermally decomposable chemical foaming agent per 100 pts.wt. as the sum of 50-90 wt.% of a polypropylene resin (a) having an MFR of 0.5-10 g/10 min. and 10-50 wt.% of a polyethylene-based resin (b) having an MFR of 1-30 g/10 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crosslinked polypropylene foamed resin composition and a crosslinked foamed sheet thereof.
More specifically, a cross-linked polypropylene type with excellent heat resistance, excellent workability to complex shapes, and excellent pressure resistance under high temperatures, can respond to a wide range of secondary processing methods, and can freely control flexibility etc. The present invention relates to a crosslinked polypropylene foamed resin composition suitable for continuously producing a foamed resin foam, and a crosslinked foamed sheet obtained by crosslinking and foaming the composition.

[0002]

2. Description of the Related Art A crosslinked foam using a polypropylene resin as a main component is bonded to a PVC sheet or a TPO sheet by various processing methods, utilizing its excellent moldability, cushioning property, heat insulation property and heat resistance. It is molded and used for interior materials such as car doors, instrument panels, console boxes, and seat back garnishes.

Conventionally, as one of the crosslinking methods in the production of a polyolefin resin foam, there is a method in which a foamable resin composition is formed into a sheet and crosslinked by irradiating with ionizing radiation. This method is very effective when using an ethylene-based resin that is susceptible to cross-linking by irradiating radiation. In addition, it is difficult to provide crosslinking suitable for foaming because the resin deteriorates. Therefore, when using a polypropylene resin,
JP-B-46-38716, JP-A-61-69844
No. 4, pp. 139, 148, pp. 1, pp. 1 to 3, pp. 1 to 3, the polypropylene resin is not deteriorated by irradiation with ionizing radiation via a polyfunctional monomer having a reactive vinyl group, an acryl group, and a methacryl group in a molecular structure. After crosslinking with irradiation energy of such a degree that only slight deterioration occurs, a foam is obtained by heating and foaming.

[0004]

However, conventional polyolefin resin foams cross-linked and foamed using a polyfunctional monomer may have various contents in the resin component depending on the type of the polyfunctional monomer and the mixing ratio of the resin. Since the compatibility with the resin is different, localization of the reactive monomer occurs as a result of poor dispersion, resulting in uneven crosslinking. This leads to irregularities in the stability and bubble diameter during foam production, leading to instability of general mechanical properties, and a reduction in required processing aptitude and heat resistance.

[0005] Recently, with the progress of processing methods, foams are required to have higher heat resistance and pressure resistance, and at the same time, flexibility, which is contrary to the above. For this, improvement of the resin composition itself is indispensable, but it is necessary to make the resin composition corresponding to each required physical property, and the number of product types will increase and the production efficiency will decrease. management,
There was a problem that quality control became extremely complicated. Heretofore, a technique has been employed in which a resin composition as close as possible is characterized by adjusting the degree of crosslinking.

The present inventors used a specific polyfunctional monomer, specifically, divinylbenzene in a limited resin composition ratio, and grasped the characteristics of each of the structural isomers of divinylbenzene. As a result of examining the correlation with the irradiation energy of ionizing radiation, it is possible to obtain a resin composition for a crosslinked polypropylene-based foam excellent in heat resistance, molding workability, and pressure resistance while maintaining a certain quality, and a foam thereof. And have led to the present invention.

[0007] That is, the object of the present invention is to provide a resin composition having the same resin composition without changing the amount of polyfunctional monomers and maintaining a constant quality by merely changing the irradiation energy of ionizing radiation while maintaining heat resistance, molding processability, and the like. An object of the present invention is to provide a resin composition for a crosslinked polypropylene foam having excellent pressure resistance and a foam sheet thereof.

[0008]

The crosslinked polypropylene foamable resin composition of the present invention has an MFR of 0.5 to 10 g / m2.
With respect to a total of 100 parts by weight of 50 to 90% by weight of the polypropylene resin (a) for 10 minutes and 10 to 50% by weight of the polyethylene resin (b) having an MFR of 1.0 to 30 g / 10 minutes, the following general formula: Chemical 2

[0009]

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Wherein the content (M) of the benzene compound having a vinyl group arranged at the p-position in the bifunctional vinyl group-containing benzene compound is 0.18 to 0.69 (c).
1 to 10 parts by weight, 0.5 to 5 parts by weight of an alkyl group-containing monofunctional vinyl group-containing benzene compound (d), and 1 to 10 parts by weight of a thermal decomposition type chemical blowing agent. is there.

The crosslinked polypropylene resin foam sheet according to the present invention is obtained by molding the above crosslinked polypropylene resin composition into a sheet, irradiating it with ionizing radiation, crosslinking, and then heating and foaming under normal pressure. Consisting of things.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The polypropylene resin used in the present invention is not particularly limited, but is preferably polymerized by a Ziegler catalyst, a metallocene catalyst, a heterogeneous catalyst by a gas phase method, a slurry method, a solution method, or the like. Propylene and ethylene or an α-olefin having 4 to 12 carbon atoms
~ 15% by weight, copolymerized with a melting point of 125-155
C., MFR of 0.5 to 10 g / 10 min. In this copolymer, one ethylene or a monomer of an α-olefin having 4 to 12 carbon atoms may be copolymerized with propylene, but one having as large a carbon number as possible in terms of mechanical strength and heat resistance is used. And terpolymerization is preferred.

Ethylene or 4 to 4 carbon atoms to be copolymerized
12 alpha olefins are 2 to 15% by weight, preferably 3 to
Although it is 8% by weight, if it is less than 2% by weight, the crystallinity of the resin is high, which is preferable in terms of heat resistance and mechanical strength. However, if the crystallinity is high, the resin becomes hard and the buffering property deteriorates, and the impact resistance at low temperatures is low. It is not preferable because the property is lowered. In addition, when irradiated with ionizing radiation and cross-linked, it is difficult to control the degree of cross-linking even when a large amount of reactive monomer is added.
It is not preferable because a degree of crosslinking of 40% or more required for improving the pressure resistance cannot be obtained. On the other hand, when it exceeds 15% by weight, it is preferable in terms of controlling crosslinking and flexibility, but it is not preferable because the melting point is lowered and heat resistance and pressure resistance at high temperatures are deteriorated.

The melting point is 125-155 ° C., preferably 13
The melting point is from 0 to 145 ° C, but if the melting point is less than 125 ° C, it is not preferable because the application is restricted from the viewpoint of heat resistance. However, it is not preferable because the heat generated by shearing in the extrusion step at the time of molding the sheet for foaming is increased and the decomposition of the foaming agent is easily caused.

The MFR is 0.5 to 10 g / 10 minutes, preferably 1 to 5 g / 10 minutes. MFR 0.5g / 10
When the heating time is less than 10 minutes, the foaming agent is decomposed due to the heat generated by shearing, and irregularity of air bubbles is easily generated.
If it exceeds 10 minutes, the melt viscosity becomes low, the decomposition of the foaming agent is suppressed, and the irregularity of the bubbles is eliminated. However, if a special cooling device is not used at the time of forming the sheet, a smooth sheet cannot be obtained or the foaming cannot be performed. Since the elongation of the body is reduced, the shape retention during heat molding is deteriorated, and a good molded product cannot be obtained.

The polyethylene resin used in the present invention is a copolymer of ethylene and an α-olefin having 4 to 12 carbon atoms using a Ziegler catalyst, a metallocene catalyst or the like to have a density of 0.890 to 0.940 g / cm ³ , MFRg is 1 to
30 g / 10 min. The type of α-olefin to be copolymerized with ethylene is not particularly limited as long as it is selected from among 4 to 12 carbon atoms, but is preferably 4 to 12 carbon atoms.
A copolymer of 8 is advantageous in terms of both price and physical properties. The density is from 0.890 to 0.940 g / cm ³ , preferably from 0.905 to 0.930 g / cm ³ ,
A density of less than 0.890 g / cm ³ is preferred in terms of flexibility, but lowers the melting point and deteriorates the heat resistance, and the resin becomes sticky, resulting in poor mixing of the foaming agent or the like in the raw material mixing step. It is not preferable because it causes blocking of the foam. If it exceeds 0.940 g / cm ³ , it is preferable in terms of mechanical strength, heat resistance and the like, but it is not preferable because the crystallinity becomes high and it becomes hard and the buffering property decreases. M
FRg is 1 to 30 g / 10 min, preferably 3 to 10 g / min.
10 minutes. If the MFRg is less than 1 g / 10 minutes, the melt viscosity of the resin becomes high, so that the foaming agent is decomposed due to heat generated by shearing at the time of sheet molding, and coarse bubbles are easily generated, which is not preferable. On the other hand, if it exceeds 30 g / 10 min, the melt viscosity becomes low and the decomposition of the foaming agent is suppressed, so that it is preferable in terms of the generation of coarse bubbles, but a smooth sheet can be obtained unless a special cooling device is used during sheet forming. It is not preferable because the shape retention during heat molding is deteriorated and a good molded product cannot be obtained because the elongation of the foam is reduced or the elongation of the foam decreases.

The following general formula 3 used in the present invention:

[0018]

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In the bifunctional vinyl group-containing benzene compound represented by the formula (1), the content (M) of the benzene compound in which the vinyl group is located at the p-position must be 0.18 to 0.69. When the content (M) is less than 0.18, the vinyl group involved in crosslinking is located at the p-position, and the amount of the benzene compound is small, so that a wide range of crosslinking degree cannot be set. Exceeds 0.69, which is preferable because the setting range of the degree of crosslinking is widened. On the other hand, the present benzene compound is liable to self-polymerize when heat or ultraviolet light is applied, so that a large amount of a polymerization inhibitor needs to be added. As a result, the ionizing radiation energy is undesirably increased.

In the present invention, it is necessary to add an alkyl group-containing monofunctional vinyl group-containing benzene compound (d). This is because the alkyl group is bonded to the benzene ring, and the resin component used in the present invention is not added. That the compatibility is improved,
Since the alkyl group-containing monofunctional vinyl group-containing benzene compound and the bifunctional vinyl group-containing benzene compound have good compatibility, as a result, the bifunctional vinyl group-containing benzene compound is uniformly dispersed in the resin component, and the degree of crosslinking is uniform. It is preferable since the property can be obtained.

The resin composition for a foam and the foam according to the present invention may contain 50 to 90% by weight, preferably 60 to 80% by weight of a polypropylene resin and 10 to 50% by weight of a polyethylene resin.
% By weight, preferably 20 to 40% by weight, and the content (M) of the benzene compound in which the bifunctional vinyl group is located at the p-position is 0.18 to 0.69, preferably 0.2 to 0. (C) of 1 to 10 parts by weight,
Preferably, 2 to 7 parts by weight, and 0.5 to 5 parts by weight, preferably 1.0 to 4 parts by weight of the alkyl group-containing monofunctional vinyl group-containing benzene compound (d) must be added.

The crosslinked foam obtained from the resin composition according to the present invention has excellent heat resistance, various moldability, elongation and flexibility, and is particularly suitable for molding at high temperatures or high pressure molding (stamping, injection). It is suitable.

In the present invention, if the content of the polypropylene resin is less than 50% by weight, it is preferable in terms of flexibility when it is formed into a foam, but it is not preferable because heat resistance is lowered.
Exceeding the weight percentage is preferable in terms of heat resistance, but is not preferable because it becomes hard and the buffering property deteriorates.

In the present invention, when the content of the polyethylene resin is less than 10% by weight, it is preferable in terms of heat resistance. However, it is not preferable because the resin becomes hard and the buffering property deteriorates, and the heat moldability deteriorates. Although it is preferable in terms of cushioning property and moldability, it is not preferable because heat resistance deteriorates.

When the amount of the benzene compound having a bifunctional vinyl group arranged at the p-position according to the present invention is less than 1 part by weight, the amount of vinyl groups involved in crosslinking becomes insufficient, and it becomes impossible to set a wide range of crosslinking degree. On the other hand, if it exceeds 10 parts by weight, it is preferable in terms of setting a wide degree of crosslinking, but since it is a liquid, the effect of a plasticizer in the extrusion step becomes excessive, and the molten state in the extruder becomes apparently low. It is not preferable because extrusion becomes difficult. Also,
It is considered that the number of crosslinking points is increased beyond the apparent degree of crosslinking, but the elongation is reduced, and consequently the moldability is reduced, which is not preferable. If the amount of the alkyl group-containing monofunctional vinyl group-containing benzene compound is less than 0.5 parts by weight, the compatibility between the benzene compound in which the bifunctional vinyl group is located at the p-position and the resin component is deteriorated, and the localization of the crosslinking agent is reduced. This results in loss of stability of cross-linking and irregularity of cell diameter, resulting in deterioration of moldability, which is not preferred. On the other hand, if it exceeds 5 parts by weight, the compatibility between the cross-linking component and the resin component becomes better, and Is preferred in terms of stability, but the concentration of the cross-linking component is lowered, and consequently, it is not preferable because it is necessary to increase the total amount.

As the thermal decomposition type chemical blowing agent used in the present invention, azodicarbonamide, azodicarboxylic ester compound, azodicarboxylate, tetrazole compound,
N, N'-dinitrosopentamethylenetetramine and the like are exemplified. These may be used alone or as a mixture, or may be used in combination with a zinc compound, an amine compound or the like to adjust foaming. it can. The addition amount is preferably in the range of 1 to 20 parts by weight.

In the present invention, antioxidants represented by hindered phenols, thios, etc., processing stabilizers, flame retardants, inorganic fillers, pigments, etc. are added according to the purpose to obtain desired quality. It can be.

In the present invention, after the resin composition of the present invention is melt-extruded and formed into a sheet, it is necessary to perform cross-linking at the stage of this sheet. Irradiation with an electron beam is industrially preferable, and the irradiation energy is 3 to 50 Mr.
Although ad is appropriate, it is desirable to crosslink with as little as 20 Mrad or less.

The foam of the present invention is produced by various foaming methods, specifically, a vertical (horizontal) hot air foaming method, a method exemplified by a foaming method in a chemical bath, and preferably a foaming method in a chemical bath. MD (longitudinal direction), TD (width direction) of foamed material by foaming method
This is desirable because a material having well-balanced properties in each direction can be obtained.

Next, one embodiment of a method for producing a crosslinked polyolefin foamed resin composition and a crosslinked foamed sheet according to the present invention will be described.

MFR obtained by random copolymerization of propylene with 4.2% by weight of ethylene has an MFR of 1.8 g / 10 min and a melting point of 13
MFR of 128 kg of 9 ° C. polypropylene resin powder and ethylene copolymerized with α-olefin having 6 carbon atoms is 8
g / 10 minutes, 32 kg of polyethylene resin powder having a melting point of 125 ° C., and “Irganox 1010” as a stabilizer
0.95 kg, azodicarbonamide 1 as blowing agent
7.7 kg, 4.8 kg of a benzene compound having a bifunctional vinyl group arranged at the p-position having a content (M) of 0.18 to 0.69, 0.5 kg of an alkyl group-containing monofunctional vinyl compound 0.5
kg, prepare a polypropylene resin, a polyethylene resin, a foaming agent, and a stabilizer into a Henschel mixer having an effective volume of 750 l, mix at a low speed of 200 to 400 rpm for about 3 minutes, and then rotate at a high speed of 800 to 1000 rpm. After mixing for 3 minutes, add the liquid vinyl compound,
The mixture is further mixed for 3 minutes to obtain a foaming resin composition.

The foaming resin composition is introduced into a vented extruder heated to a temperature at which the foaming agent is not decomposed, specifically, heated to 160 to 190 ° C., extruded from a T-die, and has a thickness of 1.75 mm and a width of 500 mm. It was formed into a sheet for crosslinking and foaming. The sheet is irradiated with a 15 Mrad electron beam and crosslinked, and then continuously introduced into a foaming apparatus on a chemical bath set at a temperature 20 to 50 ° C. higher than the decomposition temperature of the foaming agent, and heated and foamed to form a continuous sheet-like crosslink. Wound as a foam. The foam thus obtained has a thickness of 3.1 mm and a width of 13 mm.
50 mm, the degree of crosslinking was 55%, and the expansion ratio was 25 times.

As described above, in the present invention, the use of divinylbenzene as a crosslinking aid has been known, but the divinylbenzene has isomers and the mechanism involved in crosslinking of each structure is not known. Not, for example, P
If only the body is used, the crosslinkability is remarkably good, but the elongation of the foam is reduced, and it cannot be applied to various molding methods, or if only the m body is used, although the elongation of the foam is good, The disadvantage that a large amount of electron beam energy is required, or if these are mixed and used, such compounds are originally poorly compatible with polyolefin-based resins, so they are kneaded into the resin. However, there was a drawback that the cross-linking properties of the two could not be balanced and the cross-linking state became unstable. However, the use of an alkyl group-containing monofunctional vinyl compound compatible with both divinylbenzene and the polyolefin resin. It has been found that stabilization of crosslinkability can be obtained by the method. The crosslinked foam obtained from the resin composition according to the present invention has excellent heat resistance, various moldability, elongation, and flexibility, and is particularly suitable for molding under high temperature or high pressure molding (stamping, injection). It is.

[Evaluation Method and Evaluation Criteria] The evaluation method and evaluation criteria according to the present invention are as follows. (1) Degree of Crosslinking The foam is shredded and precisely weighed at 0.2 g. This was used as a solvent and extracted with xylene at a temperature of 100 ° C for 8 hours using a Soxhlet extractor. The insolubles were taken out, washed with pure water, further washed with acetone, and further dried with a vacuum dryer heated to 80 ° C. After heating for 1 hour to completely remove volatile components, the mixture is naturally cooled at room temperature. The weight (W ₁ ) g of this product is measured, and the degree of crosslinking is determined by the following equation. Degree of crosslinking = (W ₁ /0.2)×100(%)

(2) Formability Heat-formed with a vacuum forming machine equipped with a cup-shaped forming die having a depth (L) with respect to the diameter (D), and the L-shaped formed into a cup without breaking the foam. The / D ratio is defined as moldability. Normally, molds of up to 1.0 are arranged side by side in L / D 0.2 increments, and the depth to which the mold is torn is observed. Measure moldability.
L / D: Pass 0.5 or more

(3) Mechanical strength and elongation Measured according to JIS-K-6767. Mechanical strength is (expansion ratio × (−1.5) +45) or more.
Pass 50% or more.

(4) Heat Resistance A 15 × 15 cm piece is cut out from the foam sheet, and measurement marks are drawn at 10 cm intervals in the sheet longitudinal direction (MD) and the width direction (TD), and the thickness (T) is measured. Place this sample on a heat-resistant plate on which calcium carbonate was sprayed.
Place in a hot air oven heated to 0 ° C., heat for 2 hours, remove, and cool naturally to room temperature. The mark interval (MDx, TDx, Tx) of this sample is measured, the dimensional change rate is calculated by the following equation, and the heat resistance is evaluated based on the following criteria. MD: ((100−MDx) / 100) × 100 (%) TD: ((100−TDx) / 100) × 100 (%) T: (((T−Tx) / T) × 100 (%) Heat resistance : MD and TD are acceptable within ± 5%. T is acceptable within ± 7%.

(5) Melting point The largest peak in the melting endothermic spectrum measured with a scanning calorimeter (manufactured by PerkinElmer: DSCIII) is defined as the melting point.

(6) MFR The polypropylene resin was measured according to JIS-K-6758, and the polyethylene resin was measured according to JIS-K-6760.

(7) Density The polyethylene resin was measured according to JIS-K-6760.

[0041]

Next, the present invention will be described based on embodiments. Example 1 96 kg of polypropylene resin powder obtained by randomly copolymerizing ethylene with 3.6 wt% of propylene at a melting point of 142 ° C. and an MFR of 2.5 g / 10 min, and ethylene having 4 carbon atoms
MFR obtained by copolymerizing α-olefin of 5 g / 10 min, melting point of 125 ° C., 64 kg of polyethylene resin powder, 0.95 kg of “Irganox 1010” as a stabilizer,
As a blowing agent, 7.4 kg of azodicarbonamide, 3.2 kg of a benzene compound having a bifunctional vinyl group arranged at the p-position having a content (M) of 0.65, 3.2 kg containing 1 alkyl group
0.7 kg of a functional vinyl compound is prepared, and a polypropylene-based resin, a polyethylene-based resin, a foaming agent, and a stabilizer are charged into a Henschel mixer having an effective volume of 7501.
Mix at low speed of 00 rpm for about 3 minutes, then 800 ~
After high-speed rotation of 1000 rpm and mixing for 3 minutes, a liquid vinyl compound is added, and further mixed for 3 minutes to obtain a foaming resin composition.

The foaming resin composition was introduced into a vented extruder heated to a temperature at which the foaming agent did not decompose, specifically, heated to 160 to 190 ° C., extruded from a T-die, and had a thickness of 2.00 mm and a width of 640 mm. It was formed into a sheet for crosslinking and foaming. The sheet is irradiated with a 10 Mrad electron beam and crosslinked, then continuously introduced into a vertical hot air foaming apparatus set at a temperature 20 to 100 ° C. higher than the decomposition temperature of the foaming agent, and heated and foamed to form a continuous sheet-like crosslink. Wound as a foam.

The foam thus obtained had a thickness of 4.0 mm, a width of 1400 mm, a degree of crosslinking of 52% and an expansion ratio of 18 times.

The properties of this product are shown in Table 1.

[0045]

[Table 1]

As shown in the table, the resin composition according to the present invention was
Since it is a crosslinked foam, it is a polypropylene-based crosslinked foam excellent in moldability, elongation and heat resistance.

Example 2 and Comparative Example 1 A crosslinked foam was obtained using a component resin composition as shown in Table 2, and the properties of the obtained foam are shown in Table 3.

As described above, the crosslinked foam obtained from the resin composition according to the present invention shown in Example 2 has excellent heat resistance, various moldability, elongation and flexibility, and particularly high-pressure molding under high temperature. (Stamping, injection).

On the other hand, since the product shown in Comparative Example 1 was outside the scope of the present invention, it was an unsatisfactory crosslinked foam having insufficient elongation, moldability or heat resistance.

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

As described above, when the crosslinked polypropylene foamed resin composition of the present invention and the crosslinked foamed sheet thereof are used, the same irradiation with ionizing radiation as before can be performed without increasing the amount of polyfunctional monomers and the like. In terms of quantity, moldability,
A foaming resin composition and a foam sheet excellent in mechanical strength, elongation, heat resistance, and the like can be obtained.

Claims (2)

[Claims] 1. An MFR having a MFR of 0.5 to 10 g / 10 min and 50 to 90% by weight of a polypropylene resin (a).
Is a polyethylene resin (b) having a content of 1 to 30 g / 10 min.
For a total of 100 parts by weight of 10 to 50% by weight, the following general formula 1 In the bifunctional vinyl group-containing benzene compound represented by the formula (c) in which the content (M) of the benzene compound in which the vinyl group is located at the p-position is 0.18 to 0.69, 1 to 1
A crosslinked polypropylene foamed resin characterized by containing 0 parts by weight, 0.5 to 5 parts by weight of an alkyl group-containing monofunctional vinyl group-containing benzene compound (d), and 1 to 10 parts by weight of a thermal decomposition type chemical blowing agent. Composition. 2. A crosslinked polypropylene resin formed by molding the crosslinked polypropylene foamed resin composition according to claim 1 into a sheet, irradiating it with ionizing radiation or irradiating ultraviolet rays, and then heat-foaming under normal pressure. Foam sheet.