JPH0645717B2 - Continuous sheet-shaped electron beam crosslinked foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a foam, and more particularly to a continuous sheet-like foam obtained by electron beam crosslinking.

BACKGROUND ART Electron beam crosslinked foams are used as shock-absorbing materials and heat-resistant insulation materials for automobile interiors.

In JP-A-63-265935, the following crosslinked foam is disclosed:
The olefin resin is a linear ultra-low density polyethylene copolymerized with ethylene and an α-olefin having 4 or more carbon atoms.
According to the publication, the olefin resin may be a polymer of an olefin monomer such as polypropylene, or a mixture of an ethylene-ethyl acrylate copolymer. The linear ultra-low density polyethylene may be a mixture of butene-1, hexene-1, octene-
By copolymerizing ethylene with an α-olefin having 4 or more carbon atoms, such as 1,4-methylpentene-1, an appropriate number of short chain branches are introduced into a linear backbone polymer, thereby reducing the density.

Furthermore, the publication discloses the following examples.
Ethylene-propylene random copolymer 35 having a density of 0.89 g/cm ³ , MI of 7.0 g/10 min, and a melting point of 145°C
parts by weight, density 0.957 g/cm ³ , MI 6.5 g/
30 parts by weight of 10 minute high density polyethylene and a density of 0.9
Linear very low density polyethylene (4-methylpentene-1 copolymer) 35 g/cm ³ , MI 0.0 g/10 min
parts by weight, 15 parts by weight of a blowing agent (azodicarbonamide), and 3.0 parts by weight of trimethylolpropane trimethacrylate
The mixture was extruded into a 1.5 mm thick sheet, irradiated with 2.0 Mrad electron beams from both sides using an electron beam irradiator to crosslink the sheet, and then heated and foamed by passing the sheet through a hot air oven at 250°C to obtain a foamed sheet with a thickness of approximately 4 mm.

The conventional crosslinked foams have excellent flexibility but are inferior in toughness and dimensional stability.
Simply implementing the technology disclosed in JP-A-63-265935 would not provide sufficient toughness and dimensional stability because the resin selection and compounding ratio would be inappropriate.

Although it is not a resin using three components like the conventional example, it has a melting point of 117°C to 123°C and a density of 0.89
Resin compositions using copolymers of ethylene having a viscosity of 0 to 0.910 g/cm ³ and an α-olefin having 4 to 8 carbon atoms are disclosed in JP-A-56-155232 and JP-A-58-
This is shown in US Pat. No. 6,157,839.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous sheet-like electron beam crosslinked foam having excellent toughness and dimensional stability.

Another object of the present invention is to provide a continuous sheet-like electron beam cross-linked foam which is excellent in flexibility, toughness and dimensional stability.

A further object of the present invention is to provide a continuous sheet-like electron beam crosslinked foam which has improved toughness at high temperatures and which has improved moldability when used in a composite material.

A further object of the present invention is to provide a continuous sheet of an electron beam crosslinked foam which has excellent dimensional stability and is suitable as a cushioning material for automobile interiors.

Yet another object of the present invention is to provide a thermoplastic elastomer having high toughness at high temperatures,
The present invention provides a continuous sheet-like electron beam cross-linked foam suitable as a molded heat-resistant insulation material.

The continuous sheet-like electron beam cross-linked foam according to one aspect of the present invention comprises 100 parts by weight of a polypropylene-based resin (A) containing propylene as a main component, 5 to 40 parts by weight of a copolymer (B) of ethylene and at least one member selected from the group consisting of acrylic acid, ethyl acrylate, maleic anhydride and vinyl acetate, and 1 part by weight of a copolymer (C) of ethylene and an α-olefin having 4 to ⁸ carbon atoms, the copolymer having a melting point of 117 to 123°C and a density of 0.890 to 0.910 g/cm3.
The foam has a gel fraction of 20 to 60% and an expansion ratio of 5 to 40 times.

This foam has a toughness of 50 kg at 150°C.
/cm ² ·% or more, and the rate of dimensional change when heated to 120° C. is preferably 5% or less.

Detailed Description of the Invention The present inventors have found that a foam having excellent flexibility, toughness, dimensional stability and moldability can be realized by optimizing the compounding ratio of the three resins (A), (B) and (C) and subjecting them to electron beam crosslinking followed by foaming to obtain a foam.

The polypropylene-based resin (A) used in the present invention, which is mainly composed of propylene, may be, for example, a propylene homopolymer or a copolymer of propylene with at least one of ethylene and butene, which may be random, block, or random block copolymerized. In this case, the copolymerization amount is 2 to 35% by weight, preferably 3 to 30% by weight. More preferably, it is a random copolymer containing 4 to 15% by weight of ethylene.

The copolymer (B) of ethylene with at least one member selected from the group consisting of acrylic acid, ethyl acrylate, maleic anhydride and vinyl acetate preferably contains 5 to 10 copolymer components.
More preferably, the copolymer (B) contains 8 to 18% by weight of ethyl acrylate or 8 to 18% by weight of ethyl acrylate and maleic anhydride in total, such as ethylene ethyl acrylate (EEA), or ethylene-ethyl acrylate-maleic anhydride terpolymer (EEA).
A-MAH).

The copolymer (C) of ethylene and an α-olefin having 4 to 8 carbon atoms has a melting point of 117 to 123°C and a density of 0.89 to 1.00.
Preferably, the copolymer (C) is an α-olefin having 4 to ⁶ carbon atoms.
The melting point is 117-123°C and the density is 0.895-
The ethylene and α-olefin copolymer (C) is the copolymer of ethylene and α ^- olefin (C) described in the above-mentioned JP-A-58-157
The copolymer (C) used in the present invention is an ethylene-α-olefin copolymer described in the above-mentioned JP-A-639-839. The density and melting point of this copolymer correlate with each other, and the melting point increases as the density increases. However, by changing the catalyst, polymerization method, etc., it is possible to change the physical properties such as melting point, strength, elongation, and flexibility, even if the density of the resin is the same.
This is different from the linear ultra-low density polyethylene described in JP 265935, more specifically Ultzex (manufactured by Mitsui Petrochemicals) and Excellen (manufactured by Sumitomo Chemicals). For example, when the density is in the range of 0.890 to 0.910 g/ ^cm3 , the melting point of the polyethylene used in JP 63-265935 is 4 to 7°C lower. This low melting point causes a fatal drawback in terms of dimensional stability when the polyethylene is made into a foam. Therefore, in the present invention, flexibility and a temperature stability of 120°C are the only two factors that are important.
In order to simultaneously satisfy the thermal dimensional change rate, a material with a low density and a high melting point is selected.

In the present invention, the mixing ratio of the resin components (A), (B) and (C) is 5 to 40 parts by weight (preferably 5 to 25 parts by weight) of component (B) and 10 to 80 parts by weight (preferably 2 to 80 parts by weight) of component (C) per 100 parts by weight of component (A).
If the amount of component (B) exceeds 40 parts by weight, the dimensional stability (at 120°C) of the crosslinked foam may be deteriorated.
If the amount of component (B) is less than 5 parts by weight, flexibility, heat resistance, toughness, and moldability cannot be simultaneously satisfied. In particular, toughness at high temperatures is insufficient.
If the amount of component (C) is less than 5 parts by weight, only the properties of the crosslinked foam obtained by mixing component (A) and component (C) can be substantially obtained. If the amount of component (A) is too much, the foam obtained will have satisfactory low-temperature impact resistance and dimensional stability, but will lack flexibility. On the other hand, if the amount of component (C) is too much, the foam obtained will have excellent flexibility but poor heat resistance.
If the amount is less than 80 parts by weight, the flexibility of the resulting foam will be impaired, whereas if the amount of component (C) is more than 80 parts by weight, the flexibility will be satisfactory, but the dimensional stability will be impaired.

Gel fraction and expansion ratio In the foam of the present invention, the gel fraction is 20 to 60
%, and the expansion ratio must be 5 to 40 times.

If the gel fraction is less than 20%, the dimensional stability will be deteriorated due to the lack of gel, the foaming gas will escape during production, the desired density will not be obtained, the surface will become rough, and furthermore, the toughness at high temperatures will be insufficient, which is undesirable.
If the temperature exceeds 120°C, the shape memory property becomes significant, resulting in a dimensional stability (dimensional change rate when heated to 120°C) exceeding 5%, which is not preferable. In addition, in this case, flexibility also deteriorates.

The expansion ratio must be 5 to 40 times.
An expansion ratio of less than 40 times is preferable in terms of toughness and moldability, but is not preferable because the foam becomes hard and the flexibility deteriorates. On the other hand, an expansion ratio of more than 40 times is preferable in terms of flexibility, but is not preferable because the foam becomes too soft and the cushioning properties deteriorate.

The foam of the present invention preferably has a toughness of at least 50 kg/ ^cm² ·% at 150° C. If the toughness is less than 50 kg/ ^cm² ·%, when the foam is laminated with various skin materials (e.g., vinyl chloride sheets) and subjected to hot molding, the foam will not have enough toughness at high temperatures to withstand the elongation stress and elongation of the skin material at high temperatures, and the foam will be destroyed, which is undesirable.

Crosslinked foams obtained from conventional known resin compositions have a problem in that only very limited skin materials can be used for thermoforming due to their low elongation stress. The foam of the present invention has a toughness of 50 kg/ ^cm²- % or more, making it an excellent cushioning material. In other words, the foam's improved toughness at high temperatures reduces thickness variations in molded products, improving thermoformability. Its moldability (L/D) can be expanded to 1.2.

Dimensional Stability The dimensional stability (rate of dimensional change when heated to 120°C) of the foam of the present invention is preferably 5% or less.
%, it is not preferable because the desired processed product cannot be obtained due to shrinkage in a method which requires a heating step.

Compression Hardness/Stress Furthermore, the 25% compression hardness of the foam of the present invention at room temperature is preferably 0.1 to 1.0 kg/ ^cm² .
If the compression hardness exceeds 1.0 kg/cm ² , the foam will be too stiff and the feel will be poor, which is not preferred.
If the density is less than 1 kg/ ^cm² , the foam will be too flexible and will have a low stickiness (when pressed, the foam will feel as if it is reaching the opposite side).Furthermore, the foam will lose its stiffness during production and processing, which is undesirable as it will be difficult to handle.

In the foam of the present invention, the stress at 5% elongation at room temperature is 10
It is preferable that the range is 100K to 100Kg/ ^cm2 .
If the density exceeds ¹⁰ kg/cm², the cushioning effect will decrease and the stiffness will increase, which is not preferable. If the density is less than 10 kg/ ^cm² , the flexibility will be good, but the stiffness will decrease, which is not preferable.

The 25% compression hardness at room temperature and the stress at 5% elongation can be used as a scale for expressing softness to the touch. When foams falling within the above ranges are laminated with various skin materials and subjected to processing such as molding, and then evaluated as products, they exhibit softness to the touch that is clearly different from that of conventional foams.

The foam according to the present invention is in the form of a continuous sheet. It is preferable to produce the product by rolling it into a roll with a length of at least 10 m. This allows for continuous production in various processes and reduces processing losses.

Manufacturing Method One embodiment of the method for manufacturing the foam according to the present invention will be described.

The resin component (A) crushed to a 32 mesh pass,
(B) and (C) are prepared so that the blending ratio falls within the range of the present invention, and these are charged into a high-speed mixer (e.g., a Henschel mixer or super mixer). Furthermore, a known decomposition-type chemical foaming agent (e.g., azodicarbonamide, dinitrosopentamethylenetetramine, etc.) is added in an amount of 2 to 20 parts by weight per 100 parts by weight of the resin component composition. At this time, various additives are also added at the same time. Then,
The first stage of dispersion and mixing is carried out.
The mixture is then put into an extruder heated to 100°C, where it is melted, dispersed, and mixed. A continuous sheet with a thickness of 0.5 to 6 mm is obtained. At this time, it is important to prevent the foaming agent from decomposing as much as possible.

This sheet must be crosslinked to a degree that prevents the decomposition gas of the foaming agent from escaping during foaming. Only known ionizing radiation irradiation methods are used as the crosslinking method. A known peroxide compound may be added in advance. Depending on the purpose, polyfunctional monomers, dimers, and trimers such as divinylbenzene, trimethylolpropane triacrylate, and pentaerythritol triacrylate may be added as crosslinking aids in this crosslinking method. Furthermore, inorganic fillers such as calcium carbonate, talc, glass balloons, and glass fibers, antistatic agents, flame retardants, and colorants may be added within a range that does not impair the purpose.

The obtained continuous cross-linked foamable sheet is continuously introduced into a hot air atmosphere set at a temperature 10 to 100°C higher than the decomposition temperature of the foaming agent or onto a chemical solution such as a silicone oil bath, to rapidly decompose the foaming agent and obtain a cross-linked foam on a continuous sheet.

At least one side of the resulting foam can be subjected to a corona discharge treatment to increase the surface wetting tension to 37 dyne/cm or more, thereby improving adhesion to various coating agents. Furthermore, by providing an adhesive or pressure-sensitive adhesive layer by coating or the like, various skin materials, films, sheets, other foams, metal foils, paper, nonwoven fabrics made of natural or synthetic fibers, or synthetic leather can be laminated, and the resulting laminates can be molded by various methods.

Parameter Describes how to measure various parameters.

(a) Melting point (°C) The melting point is the peak temperature on the maximum side of the endothermic peak in a DSC (differential scanning calorimetry) measurement.

(b) Density (g/cm ³ ) The density is measured in accordance with JIS K6767.

(c) Gel fraction (%) The foam was shredded, 0.2 g of which was refined and immersed in tetralin heated to 135°C for 2 hours to elute the dissolved components.
Next, the insoluble matter was removed and tetralin was removed with acetone.
Then, remove the acetone with warm water at 40°C.
After drying for 1 hour in a vacuum oven heated to 00°C,
The weight of the insoluble matter (w1) (g) was measured. Gel fraction (%)
is calculated by the following formula: The number of test pieces is 10.

Gel fraction (%) = (w1/0.2) x 100 (d) Expansion ratio A foam piece of 10 x 10 cm square was cut out from the sheet foam.
The thickness t (cm) is measured, and the weight w2 (g) is precisely measured. Then, the expansion ratio is calculated using the following formula.
The number of samples was 10.

Foaming ratio = 1/[w2/(10 x 10 x t)] (e) Toughness at 150°C (Kg/ ^cm2 ·%) A 1 x 10 cm foam is cut out from the sheet foam and the thickness t (cm) is measured. Next, the foam is set in a Tensilon type tensile tester with a heating box heated to 150°C with a chuck distance of 5 cm. At this time, the chuck area is protected with paper or the like to prevent the foam from being cut at the chuck. Five minutes after setting in the heating box, the foam is tensile tested at a speed of 200 mm/s.
At this time, record the tensile breaking stress S1 (Kg) and breaking elongation S2 (cm) on the recording paper. Then, read S1 and S2 from the recording paper.

The toughness (kg/ ^cm2 ·%) at 150°C is calculated using the following formula: Five test pieces were used.

Breaking strength (kg/ ^cm2 ) = S1/(1 x t)... Breaking elongation (%) = S2/5 x 100... Toughness at 150°C (kg/ ^cm2 ·%) = × However, S1: 0.3 kg/ ^cm2 or more, S2: 100% or more.

(f) Dimensional change rate (%) when heated to 120°C (heat resistance) A square sample of 10 x 10 cm is cut out from the foam sheet, and the thickness t (mm) of the center part is measured.
The sample is placed in a hot air dryer heated to 0°C and heated for 1 hour. It is then left to cool at room temperature for 2 hours, after which the dimensions are measured. The dimensional change rate (%) when heated to 120°C is calculated using the following formula:

Dimensional change rate when heated to 120°C (%) _MD = (10 - X _MD ) / 10 x 100 Same as above (%) _TD = (10 - X _TD ) / 10 x 100 Where TD is the length direction and MD is the width direction.

(g) 25% compression hardness at room temperature (kg/cm ² ) Measured in accordance with JIS K-6767.

(h) 5% elongation stress at room temperature (Kg/cm ² ) A sample of 1 x 10 cm is cut out from the sheet foam and the thickness t (cm) is measured. The sample is set in a Tensilon type tensile tester with a chuck distance of 5 cm, and the sample is stretched for 20 mm.
The specimen is pulled at a rate of 1/min. The change in stress and elongation at this time are recorded on a recording paper, and the stress S1 (kg) is calculated when the specimen is elongated by 5%. The stress at 5% elongation at room temperature is calculated using the following formula:

5% elongation stress at room temperature (Kg/ ^cm2 ) = S1/(1 x t) (i) Moldability (L/D) Using a cylindrical mold with a depth (L)/diameter (D) set at 0.05 intervals, the foam or laminate is vacuum molded in a vacuum molding machine while heating to 160-180°C. The maximum ratio at which the foam can be molded without breaking is read off.

Moldability (L/D) = L/D Tables 1A and 1B show the resin structures, blending ratios, crosslinking methods, and properties of the resulting foams according to the examples of the present invention. In each table, "random" means random copolymer, "block" means block copolymer, and "homo" means single polymer. EPC means propylene-ethylene copolymer, BPC means propylene-butene copolymer, and E
EA is ethylene-ethyl acrylate, EVA is ethylene-vinyl acetate copolymer, EEA·MAH is ethylene-
It is an ethyl acrylate-maleic anhydride terpolymer. The Et-Bt in ethylene-α-olefin copolymer means that butene is copolymerized as the α-olefin with ethylene. Low-density polyethylene is high-pressure low-density polyethylene, and high-density polyethylene is low-pressure high-density polyethylene. Linear ultra-low-density polyethylene is,
This low-density polyethylene has a density of 0.910 g/cm ³ or less and is obtained by high-pressure ionic polymerization and medium- to low-pressure solution polymerization.

Next, examples of the present invention and comparative examples will be described.

In the examples of the present invention, a total of 150 kg of the resin components, foaming agents, and additives shown in the table were prepared and mixed in a 500 Henschel mixer. This mixed material was fed into an extruder with a cylinder temperature set at 170-180°C, melt-mixed, and molded into a continuous sheet 1.5 mm thick and 500 mm wide. This continuous sheet was introduced into an electron beam irradiation device and crosslinked by irradiating it with 2-10 Mrad electron beams. This expandable crosslinked sheet was then heated to 210-240°C.
The mixture was continuously introduced onto a silicone oil heated to °C to cause foaming, and then dried with hot air to obtain a continuous sheet-like crosslinked foam.
The foams according to the examples of the present invention were prepared by using resin components, compounding ratios, crosslinking methods, and
The optimized degree of crosslinking resulted in excellent flexibility, toughness, dimensional stability, and moldability. In particular, the flexibility parameters of 25% compression hardness and stress at 5% elongation were both excellent, resulting in a flexible foam with an excellent feel. Furthermore, this foam also possessed high-temperature toughness, which could not be achieved with foams made from conventional resin components.

On the other hand, for the comparative examples, the resin configurations, blending ratios, crosslinking methods, and properties of the obtained foams are shown in Tables 2A and 2B. For the comparative examples, crosslinking was carried out by the electron beam crosslinking method or the peroxide compound crosslinking method similar to the examples of the present invention, and foaming was carried out in the same manner as in the examples to obtain foams.

Comparative Examples 1 to 3 used ethylene-α-olefin copolymers. As shown in the table, the resin components, compounding ratios, and crosslinking methods were outside the ranges of the present invention, and therefore at least one of flexibility, toughness, and dimensional stability was inferior. In particular, toughness at high temperatures and dimensional change rate at 120°C were significantly inferior. Comparative Examples 4 to 7 used linear ultra-low density polyethylene (Excellent). As shown in the table, the resin components, compounding ratios, and crosslinking methods were outside the ranges of the present invention, and therefore at least one of flexibility, toughness, and dimensional stability was inferior. Similar to Comparative Examples 1 to 3, Comparative Examples 4 to 7 were clearly inferior to the Examples of the present invention in terms of toughness at high temperatures and dimensional change rate at 120°C. In the table, * indicates a difference.
The points marked with are unsatisfactory.

As described above, the foams of the present invention have good flexibility, particularly softness to the touch, and significantly improved toughness, particularly toughness at high temperatures, which dramatically improves the molding processability when used in various composite materials. Furthermore, since they also satisfy dimensional stability, they can be suitably used as cushioning materials for automobile interiors, such as doors, ceilings, and instrument panels. Furthermore, based on the above properties, these foams can be used in the following ways:
It can also be used as a base material for heat-resistant adhesive tape, a base material for packing, and a heat-resistant insulating material for molding various valves, pipes, etc.

Claims (12)

[Claims] [Claim 1] A composition comprising 100 parts by weight of a polypropylene-based resin (A) containing propylene as a main component, 5 to 40 parts by weight of a copolymer (B) consisting of ethylene and at least one member selected from the group consisting of acrylic acid, ethyl acrylate, maleic anhydride, and vinyl acetate, and 1 part by weight of a copolymer (C) of ethylene and an α-olefin having 4 to 8 carbon atoms, the copolymer having a melting point of 117 to 123°C and a density of 0.890 to 0.910 g/cm³ ^.
0 to 80 parts by weight, and a gel fraction of 20 to 60%,
A continuous sheet-like electron beam crosslinked foam having an expansion ratio of 5 to 40 times. Claim 2: Toughness at 150°C of 50 kg/ ^cm² ·%
2. The continuous sheet-like electron beam cross-linked foam according to claim 1, wherein the dimensional change rate upon heating at 120°C is 5% or less. Claim 3: 25% compression hardness at room temperature is 0.1 to 1.0 kg
/cm ² , and the stress at 5% elongation at room temperature is 10 to 100 kg/cm ²
3. The continuous sheet-like electron beam cross-linked foam according to claim 2, wherein [Claim 4] A continuous sheet-like electron beam cross-linked foam described in claim 3, which consists of 100 parts by weight of the polypropylene-based resin (A), 5 to 25 parts by weight of the copolymer (B), and 20 to 50 parts by weight of the copolymer (C). [Claim 5] A continuous sheet-like electron beam crosslinked foam described in claim ⁴ , wherein the copolymer (C) has an α-olefin carbon number of 4 to 6, a melting point of 117 to 123°C, and a density of 0.895 to 0.905 g/cm3. 6. The copolymer (B) contains 5 to 10 copolymer components.
6. The continuous crosslinked foam sheet according to claim 5, wherein the content is 30% by weight. 7. The copolymer (B) contains 8 to 10 copolymer components.
7. The continuous sheet-like electron beam cross-linked foam according to claim 6, wherein the content is 25% by weight. 8. The copolymer (B) is an ethylene ethyl acrylate copolymerized with 8 to 18% ethyl acrylate, a copolymer of ethyl acrylate and maleic anhydride in a total amount of 8%.
8. The continuous electron beam crosslinked foam sheet according to claim 7, wherein the terpolymer is at least one selected from the group consisting of ethylene ethyl acrylate copolymerized to 18% or less, and ethylene-ethyl acrylate-maleic anhydride terpolymer. 9. The polypropylene-based resin (A) is a propylene homopolymer or a copolymer of propylene with at least one member selected from the group consisting of ethylene and butene,
9. The continuous sheet-like electron beam crosslinked foam according to claim 8, which is randomly, block or random block copolymerized. 10. The continuous sheet-like electron beam cross-linked foam according to claim 9, wherein the polypropylene resin (A) has a copolymerization amount of 2 to 35% by weight. 11. A continuous sheet-like electron beam cross-linked foam according to claim 10, wherein the polypropylene resin (A) has a copolymerization amount of 3 to 30% by weight. 12. A continuous sheet-like electron beam cross-linked foam according to claim 11, wherein said polypropylene resin (A) is a random copolymer of 4 to 15% by weight of ethylene.