JPH0625275B2 - High-performance crosslinked polyethylene resin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides two essential ethylene / propylene random copolymers (A) and low density polyethylenes (B).
The present invention relates to a high-performance crosslinked ethylene-based foam excellent in vacuum moldability, which is composed of a blended polymer containing components.

[Prior Art] Conventionally, a foam having a vacuum formability is disclosed in JP-A-57-20.
It is known from the publication 2326.

This foam is composed of a blended polymer containing low-density polyethylene, which has relatively good cross-linking properties, and linear polyethylene or medium-density polyethylene, which has low cross-linking properties, as essential components. Since there is a large difference in cross-linking, uneven cross-linking is likely to occur, and as a result, large foaming is likely to occur when producing a long sheet-like foam, and there is a drawback that bubbles and shake phenomena are likely to occur during vacuum forming. .

[Problems to be Solved by the Invention] An object of the present invention is to provide a high-performance crosslinked polyethylene-based resin foam which does not have the above-mentioned drawbacks at the time of vacuum molding and has less cross-linking unevenness, air bubbles and blurring.

[Means for Solving Problems] The object of the present invention is as follows: A: As a copolymerization component, a propylene component is contained in an amount of 15 to 30% by weight, and a melting point (Tm) of 100 to 118 ° C.
And an ethylene-propylene random copolymer having a crystallization temperature (Tmc) of 85 to 100 ° C and B: a melting point (Tm) of less than 115 ° C and 0.935 g /
cm ³ made of a blend polymer of a low density polyethylene as an essential component having the following density, the formula _{[R = I 30/2 ·} I 20] 13 C-NMR relative intensity by spectrum represented by (R) is 20 300, the gel fraction is 15 to 45%, and the molding reduction ratio (K) is within the range of K ≧ 2d + 0.40 (where d is the apparent density: g / cm ³ ). Can be achieved.

The foam of the present invention is composed of a blended polymer containing ethylene / propylene random copolymer (A) and low density polyethylene (B) as essential components. It is desirable that these essential components (A) and (B) account for at least 90% by weight based on the total amount of the polymer blend constituting the foam.

The ethylene / propylene random copolymer (A) that constitutes the foam of the present invention has a propylene copolymerization rate of 1
In the range of 5 to 30% by weight, Tm of 100 to 118 ° C, preferably 105 to 115 ° C and 85 to 100.
It is characterized in having a Tc of 87 ° C, preferably 87 to 97 ° C.

Here, Tm and Tmc are values detected by a differential scanning calorimeter (DSC), respectively.

That is, having Tm and Tmc in the above range means that the copolymer still has crystallinity, which is clearly different from amorphous ethylene-propylene elastomers such as EPR, EPT, and EPDM. It is shown to be a different polymer.

In the above-mentioned copolymer of the present invention, when the content of propylene is less than 15%, the crystallinity of the polymer becomes large and the melting point (Tm) becomes high, which is advantageous in terms of heat resistance. Low density polyethylene (B), one of the essential ingredients
Is not preferable because the effect of improving the vacuum formability when blended is insufficient. On the other hand, if the propylene content exceeds 30% by weight, the polymer becomes completely amorphous and the heat resistance is lowered, so that the surface roughness of the foamed body occurs during molding, which is not preferable.

In addition, it is important that the copolymer (A) of the present invention has a melting point (Tm) and a crystallization temperature (Tmc) within the above range, and when the melting point is outside the range of the above formula, For example, when Tm is less than 100 ° C., the heat resistance of the foam deteriorates,
The foam is likely to have surface roughness, and the Tm is 118.
When the temperature exceeds ℃, the elongation is lowered and the vacuum moldability is deteriorated, which is not preferable, and when the crystallization temperature (Tmc) is out of the above range, for example, when the Tmc is less than 85 ° C., the foam has a shape when used at high temperature. When the stability decreases and exceeds 100 ° C., the processability when molding a foam sheet becomes poor, making it difficult to produce products with stable quality and performance, and variations in foam characteristics. It is not preferable because it becomes large.

The low-density polyethylene (B) constituting the bund polymer of the present invention is a polymer obtained by radical polymerization under high pressure which is conventionally used as a cross-linking type foam raw material, and has a melting point (Tm) of less than 115 ° C. and 0. .935 g
/ Cm ³ is a polyethylene having a density of ³ or less.

In the present invention, a blended polymer containing the above-mentioned two kinds of polymers (A) and (B) as essential components is used. Preferably, the third component is linear polyethylene (hereinafter referred to as C component), Especially its melting point (Tm) is 11
It is preferable to further blend linear polyethylene in the range of 5 to 135 ° C.

Examples of such linear polyethylene include, for example, 0.1 to 50 g / 10 min. Having a melt flow rate (ASTM-D-1238) of 0.915 and a density of 0.915.
-0.945 g / cm < ³ >, Tm in the range of 115-127 [deg.] C. linear low and medium density polyethylene,
That is, a polymer obtained from an α-olefin having 4 to 20 carbon atoms can be mentioned.

Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc., and at least one of these or two or more or a small amount thereof. It can be obtained by polymerizing propylene by the medium- and low-pressure method polymerization in such a proportion that a predetermined density can be obtained.

In addition to these, the highly crystalline density obtained by the above-mentioned medium / low pressure method polymerization is 0.940 to 0.970 and the melting point is 12
Polyethylene within the range of 5-135 ° C can be used.

The blending ratio of the linear polyethylene (C) is preferably in the range of (B) / (C) = 10 to 90 parts by weight with respect to the low density polyethylene (B).

And, the foam of the present invention made of a blend polymer containing the above-mentioned two components (A) and (B) as essential components is 20 to 20.
¹³ C-N in the range of 300, preferably 25-200
Area intensity ratio (R) by MR spectrum and 15-4
5%, preferably 20-40%, more preferably 25
Satisfies the gel fraction of ˜35% and the following formula: K ≧ 2d + 0.40 Preferably, K ≧ 2d + 0.45 (where d is the apparent density of the foam: g / cm ³ ) Molding draw ratio (K ) Has.

That is, in the foam of the present invention, the above ¹³ C-NM
If the area intensity ratio (R) according to the R spectrum is less than 20, stretch back occurs in the cooling process during vacuum forming, and molding shrinkage increases, which is not preferable.
When R is more than 300, the moldability is not so different from that of low-density polyethylene itself, and the object of the present invention cannot be sufficiently achieved.

In addition, the foam of the present invention having an area intensity ratio (R) according to the ¹³ C-NMR spectrum within the above range is unlikely to cause the cross-linking unevenness generally found in foams composed of polymer blends, and has a fine cell structure. And has an extremely close relationship in obtaining a foam that satisfies the molding draw ratio (K) specified in the present invention.

Further, the foam according to the present invention has a gel fraction of 15 to 45.
%, Preferably 20-40%, more preferably 25-
If the range of 35% is good and the gel fraction is lower than 15%, the draw-forming ratio satisfies the range specified in the present invention, but the heat resistance becomes insufficient, and the surface area of the foamed body during molding becomes insufficient. Is likely to occur, which is not preferable. Also, when the gel fraction exceeds 45%, there is no problem of surface unevenness,
The elongation of the foam decreases, the moldability deteriorates, and the molding reduction ratio (K) defined in the present invention is not satisfied.

Hereinafter, one embodiment of the method for producing a highly foamed / high performance crosslinked polyethylene resin foam according to the present invention will be described.

100 parts by weight of a blend polymer composed of the ethylene / propylene random copolymer (A) having the above copolymerization composition and the low density polyethylene (B) was added to a known thermal decomposition type foaming agent such as azodicarbonamide or dinitrosopenta. Methylenetetramine and the like and, if necessary, a cross-linking agent that generates a radical by heating are mixed, and the mixture is molded while being kept at a temperature at which the foaming agent and the cross-linking agent are not decomposed, for example, a sheet. This molded sheet material is crosslinked so that the gel fraction is 15 to 45% by applying any known method such as an ionizing radiation crosslinking method or a chemical crosslinking method.

More specifically, in the case of the ionizing radiation crosslinking method, a high energy electron beam irradiator such as α, β, γ, X-ray, electron beam, neutron beam, etc. is usually used as the high energy beam. The sheet is crosslinked by irradiating the sheet with an electron beam having a dose of ˜50 Mrad. In this case, 0.1 to 10 parts by weight of various known crosslinking aids such as divinylbenzene, relative to 100 parts by weight of the blended polymer of the present invention,
Electron beam cross-linking may be carried out by adding diallyl phthalate, trimethylol propane triacrylate or the like. Instead of this irradiation with radiation, an ultraviolet sensitizer such as benzophenone may be added and irradiated with ultraviolet rays to crosslink.

In the case of the chemical crosslinking method, dicumyl peroxide,
A cross-linking method using an organic peroxide such as ditertiary butyl peroxide, and a silane cross-linking method in which vinyl silane such as vinyl trimethoxysilane is kneaded and grafted with these cross-linking agents and then cross-linked by a siloxane condensation reaction. Can be applied.

The cross-linked molded article thus obtained is heated in a hot air atmosphere or on a salt bath to rapidly decompose the foaming agent contained in the molded article, thereby being converted into a foam.

Further, within a range that does not impair the object of the present invention, a small amount of various polymers such as polyethylene, polypropylene, polybutylene, and chlorinated polyethylene in the ethylene resin composition used in the production of the foam of the present invention in an amount of 10% by weight as an upper limit. It can be added and mixed, and, if necessary, also imparts a lubricant, an antioxidant, an ultraviolet absorber, a colorant, an antistatic agent, a flame retardant, and other performances within a range that does not impair the object of the present invention. Various inorganic substances and the like can be added for desired purposes.

Further, the high-performance crosslinked polyethylene resin foam according to the present invention may be coated with an adhesive by corona discharge treatment, coating or the like on at least one surface thereof, and may be laminated to improve its processability. , A plastic film or sheet, another foam sheet or a metal foil may be attached to each other, or a composite structure may be imparted by extrusion laminating, that is, various processing techniques can be applied.

[Effects of the Invention] The high-performance crosslinked polyethylene resin foam of the present invention thus obtained has excellent vacuum formability from low expansion ratio to high expansion ratio, and utilizes this property. Thus, various molding applications, for example, a polyvinyl chloride sheet, a fabric sheet and the like are integrally molded in a laminated state, so that various automobile interior members and other products can be obtained. Of course, by utilizing its cushioning property, heat resistance, heat insulating property, etc., various packings, adhesive tape bases, mat substrates, heat insulating materials, cushioning materials, etc.
Furthermore, it can be used and developed in many other applications such as clothing, building materials, and medical applications.

Below, the effects of the present invention will be described more specifically based on examples.

In the present invention, the melting point (Tm), crystallization temperature (Tm
mc), area intensity ratio (R) by ¹³ C-NMR spectrum, and molding drawing ratio (K) are values measured by the following methods.

(1) Tm and Tmc Using a DSC-2 type differential scanning calorimeter (DSC) manufactured by Perkin Elmer Co., the melting endothermic peak temperature after once melting and recrystallization was taken as the melting point (Tm). Also, Tmc
Was once melted and then taken as Tmc by the exothermic peak temperature due to recrystallization during cooling.

⁽²⁾ 13 C-NMR relative intensity by spectrum in ^(R) 13 C-NMR integration curve of the spectrum, 29 to
The area intensity between 31 ppm is I _30, and 19.5 to 2
When the integrated intensity between 0.5ppm was _{I 20,} defined by _{R = I 30/2 · I} 20. The measuring method of ¹³ C-NMR spectrum is as follows.

First, using a 10 mmφ NMR sample tube, ortho-dichlorobenzene (1.4 cc) and deuterated benzene (0.2 cc)
After adjusting the solid content concentration of the sample to 20% by weight in the mixed solvent of, the JNM-FX100 device [manufactured by JEOL Ltd.] was used, the frequency was 25.00 MHz, and the mode was the pulse FT method. ¹³ C-NMR at 120 ° C
Was measured.

(3) Molding draw ratio (K) When using a vacuum molding machine and heating in a vertical cup-shaped mold having a diameter D and a depth H under optimum heating conditions to perform straight molding, the foamed body does not break and is cup-shaped. The drawing ratio (K) was defined as the limit H / D for elongation. In addition,
The D of the cup was fixed at 50 mm.

(4) The gel fraction chopped foam was about 0.2g taken (the _{W 1)} is accurately weighed. The precisely weighed foam was placed in 135 ° C tetralin for 3 times.
The insoluble portion subjected to the time immersion treatment is taken out, washed with methanol, air-dried and vacuum-dried, and then precisely weighed (denoted as W ₂ ).

The gel fraction is calculated from the values of W ₁ and W ₂ according to the following formula.

Gel fraction (%) = 100. (W ₂ / W ₁ ) (5) Apparent density of foam (d) Foam was cut into 10 cm × 10 cm squares, and the weight and thickness were measured. It is shown by the weight per unit volume (g / cm ³ ) divided by the volume.

(6) Surface Arrangement A phenomenon in which bubbles in the surface layer of the foam are broken by heating during vacuum forming, and the surface of the foam is distorted. The judgment was made by applying the oil-based magic ink to the foam and wiping with a cloth, and the state in which the ink remained in spots was judged according to the following judgment criteria.

◯: No spots to very few spots are recognized (pass) X: Clearly lots of spots (7) Stretch back Stroke back After the vacuum molding, the shrinkage is large and the corner part is not well-shaped. , There is no problem is indicated by a circle.

Examples 1 to 5 and Comparative Examples 1 to 4 Ethylene and propylene were polymerized with a catalyst system containing an organometallic compound and a titanium compound to prepare ethylene / propylene random copolymers having different propylene contents.

These ethylene / propylene random copolymers have a density of 0.921, a melting point of 108 ° C. and a melt flow rate of 4.
Low density polyethylene of 8 g / 10 min was blended at the blending ratio shown in Table 1, and 5 parts of azodicarbonamide as a blowing agent was added to 100 parts by weight of the blended polymer.
After adding 15 parts by weight and mixing with a Henschel mixer,
Melt extrusion was performed to obtain a molded sheet.

The amount of azodicarbonamide added was 12 parts by weight in Example 2 and Comparative Example 3, and 15 parts by weight in all other Examples and Comparative Examples. However, only in Comparative Example 4, 3 parts by weight of divinylbenzene was added as a crosslinking aid.

These formed sheets were irradiated with an electron beam irradiation device (IR-2 manufactured by Nisshin High Voltage Co., Ltd.) at a dose of 5 Mrad,
Crosslinked These crosslinked sheets are put on a salt bath for 225
It was foamed by heating to 230 ° C. An evaluation test was performed on the obtained foam sheet. The results are shown in Table 1.

From the table, all of the foam sheets satisfying the requirements of the present invention of Examples 1 to 5 showed excellent vacuum formability, but did not satisfy the requirement of R specified in the present invention of Comparative Examples 1 and 2. The sheet had poor vacuum formability, and Comparative Example 1 had a large stretchback property after forming. Further, the ethylene / propylene random copolymer of Comparative Example 3 in which the propylene content does not satisfy the requirements of the present invention has both a low melting point and a low crystallization temperature, and therefore not only has poor vacuum moldability, The surface and stretch back properties were also great.

Similarly, in Comparative Example 4 in which the gel fraction was too high, the vacuum formability was poor.

Examples 6 to 10 and Comparative Examples 5 to 8 Ethylene and propylene were polymerized with a catalyst system containing an organometallic compound and a titanium compound to prepare ethylene / propylene random copolymers having different propylene contents.

These ethylene / propylene propylene copolymers have a density of 0.921, a melting point of 108 ° C. and a melt flow rate of 4.8.
g / 10 min of low density polyethylene and linear polyethylene were blended, and 5 to 15 parts by weight of azodicarbonamide as a foaming agent was added to 100 parts by weight of the blended polymer and mixed with a Henschel mixer. Then, melt extrusion was performed to obtain a molded sheet.

The linear polyethylene used in Example 9 had a density of 0.963, a melting point of 132 ° C., and a melt flow rate of 8 g.
/ 10 min high density polyethylene was used, in other examples and comparative examples, density 0.925, melting point 124 ° C.,
A linear low density polyethylene having a melt flow rate of 8 g / 10 min was used.

Further, in Example 8 and Comparative Example 7, divinylbenzene was added as a crosslinking aid in an amount of 2% by weight and 5% by weight, respectively.
In the other examples and comparative examples, no crosslinking aid was added.

These formed sheets were irradiated with an electron beam irradiation device (IR-2 manufactured by Nisshin High Voltage Co., Ltd.) at a dose of 5 Mrad,
Crosslinked These crosslinked sheets are put on a salt bath for 225
It was foamed by heating to 230 ° C. An evaluation test was performed on the obtained foam sheet. The results are shown in Table 2.

From Table 2, the foam sheets according to the present invention of Examples 6 to 10 were highly advanced foams having excellent vacuum forming properties without surface dislocation and stretch back.

On the other hand, the foam sheets of Comparative Examples 5 to 7 did not satisfy the gel fraction specified in the present invention and had poor moldability.
In Comparative Example 5, stretch back occurred, and Comparative Example 8
In addition, both the melting point and the crystallinity were low, so that the heat resistance was insufficient, and in addition, surface defects and stretch back occurred.

Claims (2)

[Claims] 1. A: A propylene component is contained as a copolymerization component in an amount of 15 to 30% by weight, and has a melting point (Tm) of 100 to 118 ° C. and a crystallization temperature (Tm of 85 to 100 ° C.).
ethylene / propylene random copolymer with c) and B: melting point (Tm) below 115 ° C. and 0.935 g /
becomes the blended polymer to low density polyethylene as an essential component having a density of cm ³ or less from a blend polymer containing, as essential components, the area by ¹³ C-NMR spectra of the formula _{[R = I 30/2 ·} I 20] The strength ratio (R) is 20 to 300, the gel fraction is 15 to 45%, the molding drawing ratio (K) is K ≧ 2d + 0.40 (where d is the apparent density: g / cm ³ ), which is high. Performance cross-linked polyethylene resin foam. 2. A high-performance crosslinked polyethylene resin foam according to claim 1, wherein the blended polymer contains linear polyethylene having a melting point (Tm) of 115 to 135 ° C.