JPS6234929A - Crosslinked polyethylene resin foam having excellent formability - Google Patents

Abstract

PURPOSE:To obtain a crosslinked foam containing a specific polyethylene copolymer, a low-density polyethylene and a straight-chain polyethylene, having excellent vacuum-formability and formable by vacuum-forming without causing the surface-roughening. CONSTITUTION:The objective foamed material is composed of a blended polymer containing (A) a polyethylene copolymer containing one or more compounds selected from monobasic or dibasic aliphatic unsaturated carboxylic acid and its derivative as a copolymerized component, (B) a low-density polyethylene and (C) a straight-chain polyethylene as essential components. The blending ratio of (B+C)/A is 12-19 (by weight), the gel fraction is 15-45% and the draw ratio (K) satisfies the formula K>=2d+0.40 (d is apparent density g/cm<3>).

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to a polyethylene copolymer (A>, The present invention relates to a crosslinked polyethylene foam having excellent vacuum formability and made of a blend polymer containing three components: low density polyethylene (B) and linear polyethylene (C).

“Prior Art” Conventionally, foams with vacuum formability were developed in Japanese Patent Application Laid-Open No. 57-20
This publication is known from Japanese Patent No. 2326, and this publication proposes a foam made of a blend polymer whose essential components are low-density polyethylene, which has relatively good cross-linking properties, and linear polyethylene or medium-density polyethylene, which has low cross-linking properties. However, this foam is difficult to uniformly disperse when forming a sheet from the blend polymer due to the difference in melt viscosity between the two components that make up the blend polymer. There is a problem in that unevenness is likely to occur, and large bubbles are generated in the production of a long sheet-like foam, resulting in bubble bursting or surface unevenness during vacuum forming.

[Problems to be Solved by the Invention] An object of the present invention is to provide a crosslinked polyethylene resin foam that has excellent vacuum formability without the occurrence of surface roughness during vacuum forming.

[Means for Solving the Problems] The object of the present invention is to provide a copolymerization component containing at least one compound selected from the group consisting of monovalent or divalent aliphatic unsaturated carboxylic acids and derivatives thereof. A polyethylene copolymer (A>, consisting of a blend polymer containing low density polyethylene (B) and linear polyethylene (C) as essential components, the blend ratio ((B + C) / A)
is within the range of 2 to 19 in terms of weight ratio, the gel fraction is 15 to 45%, and the drawing ratio (K>) shown by the following formula is ≧2d+0.40 ( where d is the apparent density (Ω/cm 3 ).

In the present invention, polyethylene copolymers (A>, low density polyethylene (B) and linear polyethylene (C)
It is desirable that the blended polymer containing the above as an essential component accounts for at least 90% by weight based on the total pH of the polymers constituting the foam.

Polyethylene copolymer (A) is a copolymer containing at least one monovalent or divalent aliphatic unsaturated carboxylic acid and its derivative as a copolymerization component (an example of A> is an ethylene/alkyl acrylate copolymer). ethylene/acrylic acid copolymer (FAA), ethylene/methyl methacrylate copolymer (EMMA), ethylene/methyl methacrylate/maleic anhydride terpolymer (EMM)
A・MAH> can be mentioned.

The ethylene/alkyl acrylate copolymer preferably has a copolymerization ratio of 10 to 25% by weight and a melting point (Tm) of 86 to 102°C. The alkyl group in the ethylene/alkyl acrylate copolymer is not particularly limited, but from the viewpoint of sheet formability of the blend polymer, those having 1 to 10 carbon atoms are preferred, and among them, an ethyl group is most preferred.

The method for producing this ethylene/alkyl acrylate copolymer is not particularly limited, but includes, for example, a polymerization method with a high conversion rate of the polymer, i.e., supplying ethylene and alkyl acrylate from one end and supplying the product from the other end. Examples include a method of continuous production by changing the concentration of the monomer, the concentration of the polymerization catalyst, etc. in the tubular reactor from which it is taken out.

Here, if the copolymerization ratio of the copolymer components is less than 10%, the crystallinity of the polymer increases and the melting point (Tm) increases, which is advantageous in terms of heat resistance, but it is also Blending component polyethylene (B) and (C>) is not preferable because the effect of improving vacuum formability is not sufficient, and if it exceeds 25% by weight, the quality of the polymer increases and the heat resistance deteriorates. This is not preferable because the surface roughness of the foam is likely to occur during molding.

Furthermore, ethylene/acrylic acid copolymer (EAA), ethylene/methyl methacrylate copolymer (EMMA)
In the case of ethylene/methyl methacrylate/maleic anhydride terpolymer (EMMA/MAH), the copolymerization ratio of the copolymer components is within the range of 2 to 10% by weight, and the melting point (Tm) is 86. ~102°C is preferred. In other words, in these copolymers, the sheet formability of the blend polymer and the vacuum formability of the foam itself, which are the objects of the present invention, are not achieved until the copolymerization ratio of the copolymer components satisfies the above range T. This has an excellent effect on preventing surface roughness during molding.

In addition, the melting point (
When Tm) does not satisfy the above range, for example l'
If -m is less than 86°C, stickiness tends to occur during sheet molding.

Here, Tm is a value detected by a differential scanning calorimeter (DSC).

Furthermore, the low-density polyethylene (B> constituting the blend polymer of the present invention is a polymer obtained by radical polymerization under high pressure, which is conventionally used as a raw material for cross-linked foams, and is less than 115°C). It is a polyethylene having a melting point (Tm) of and a density of 0.9350/cm3 or less.

Furthermore, the linear polyethylene (C) constituting the blend polymer of the present invention has a melting point (Tm) of 115 to
Those within the range of 135°C, especially 0°1 to 50g/10
It has a melt flow rate (according to AsTM-D-1238, hereinafter referred to as MFR) of 0.915~
0.945CJ/cm3,"'[11 is 115-127
°Ck linear low-density to medium-density polyethylene, specifically α-olefins having 4 to 20 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, A polyethylene copolymer obtained by copolymerizing at least one copolymer component such as 1-octene or a small amount of propylene by medium/low pressure polymerization, or a high crystallinity obtained by the above medium/low pressure polymerization with a density of 0.9
Polyethylene having l'-m of 40 to 0.970 and 125 to 135°C can be exemplified.

And these essential components (A>, (B) and (C)
The blend ratio (B 10/A > is 2 to 19 by weight)
, preferably within the range of 3 to 9.

If the value of ((B+C)/Δ) is less than 2, adhesion tends to occur when molding sheets etc., making it difficult to set casting conditions, and when it exceeds 19, the resulting foam This is not preferred because the moldability becomes insufficient.

In addition, the blend ratio (B/C) of low density polyethylene (B) and linear polyethylene (C) is 1, extrusion processability,
Considering the balance of heat resistance, vacuum formability, etc., the monomer ratio is 90/10 to 10/901, preferably 80/20.
A range of ~20/80 is preferable.

The foam of the present invention, which is made of a blend polymer containing the three components (Δ), (B), and (C) as essential components, has a gel content of 15 to 45%, preferably 20 to 40%. rate and forming drawing ratio (K) within the range shown by the following formula
It is necessary to have

K≧2d+0.40゜Preferably, K≧2d+0.45 (where d is the weight of the foam) density Q/Cm3) In other words, in the case of a foam with a gel fraction lower than 15%, the heat resistance is low. , surface roughness is likely to occur during molding, and 45
%, the elongation of the foam decreases, the moldability deteriorates, and it becomes impossible to obtain a foam that satisfies the drawing ratio specified in the present invention.

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

A polyethylene copolymer having the above copolymer composition (A
), low-density polyethylene (B) and linear polyethylene (C) are blended at the above blend ratio ((B10>/A), and a known thermally decomposable blowing agent such as azodicarbonamide, dicarbonate, etc. Nitrosopentamethylenetetramine and the like and, if necessary, a crosslinking agent that generates radicals upon heating are mixed, and the mixture is held at a temperature at which the foaming agent and crosslinking agent do not decompose, and molded, for example, into a sheet shape.

This formed sheet material is cross-linked by applying any known method such as ionizing radiation cross-linking method or chemical cross-linking method so that the gel fraction becomes 15 to 45%, preferably 20 to 40%. do.

More specifically, in the case of the ionizing radiation crosslinking method, α, β, γ, X-rays, electron beams, neutron beams, etc. are used as high-energy rays, and a high-energy electron beam irradiation machine is usually used. Crosslinking is achieved by irradiating the sheet with an electron beam at a dose of ~50 Mrad. In this case, 0.1 to 10 parts by weight of various known crosslinking aids such as divinylbenzene, diallyl phthalate, trimethylolpropane triacrylate, etc. may be added to the blend polymer of the present invention for electron beam crosslinking. good. Instead of this radiation irradiation, it is also possible to add an ultraviolet sensitizer such as benzophenone and crosslink by irradiating ultraviolet rays.

In addition, in the case of 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 a vinyl silane such as vinyltrimethoxysilane is kneaded with these cross-linking agents to form a graft, and then cross-linked by a siloxane condensation reaction are used as appropriate. Can be applied.

The thus obtained crosslinked molded article is heated in a hot air atmosphere or on a salt bath to rapidly decompose the foaming agent contained within the molded article, thereby converting it into a foam.

In addition, the polyethylene copolymer (A) used for producing the foam of the present invention, within a range that does not impair the purpose of the present invention,
Low density polyethylene (B) and linear polyethylene (
A small amount of various polymers such as polypropylene, ethylene propylene copolymer, polybutylene and other α-olefin homopolymers or copolymers, chlorinated polyethylene, etc. can be added to the blend with C) in a small amount up to 10 mm%. , If necessary, lubricants, antioxidants, ultraviolet absorbers, colorants, antistatic agents, FL refueling agents, and various other inorganic substances that impart other properties may be added as desired, within a range that does not impair the purpose of the present invention. It can be added for the purpose of

Further, the cross-linked polyethylene resin foam of the present invention is coated with an adhesive on at least one surface thereof by a solar discharge treatment, dicing, etc., and then laminated to improve its workability. In other words, various processing techniques can be applied, such as laminating plastic films, sheets, foam sheets, or metal foils, or creating a composite structure using extrusion lamination.

"Effects of the Invention" The crosslinked polyethylene resin foam of the present invention thus obtained has excellent vacuum formability, ranging from low expansion ratios to high expansion ratios, and by taking advantage of this property, By integrally molding polyvinyl chloride sheets, fabric sheets, etc. in a laminated state, it is possible to make a variety of automobile interior parts and other products.Of course, the cushioning properties, heat resistance, and insulation properties By taking advantage of its properties, it can be used and developed in many applications such as various packing materials, adhesive tape bases, mat substrates, insulation materials, cushioning materials, and other applications such as clothing, building materials, and medical applications.

The effects of the present invention will be explained in more detail below based on Examples.

In addition, in the present invention, melting point (Tm), forming drawing ratio (K
), gel fraction, and surface roughness are values measured by the following method.

(1) Melting point (Tm> DSC-2 differential scanning calorimeter manufactured by PerkinElmer Co., Ltd. (
Using DSC), the endothermic peak temperature of melting -Fl after melting and recrystallization was determined as the melting point (Tm>).

(2) Forming drawing ratio (K) Using a vacuum forming machine, the ζ foam does not break when it is heated in the optimal heating strip 1 in a vertical cup-shaped mold with a diameter and depth H, and is straight-molded. , the limit H/D at which the material can be stretched into a cup shape was defined as the forming drawing ratio (K). Note that the D of the cup is 50 mm.

(3) Gel fraction About 0.2 g of the shredded foam is collected and accurately weighed (determined as Wl). Precisely weighed foam was placed in Tetralin at 135°C for 3 hours.
After the immersion treatment for a period of time, the insoluble portion is taken out, washed with methanol, air-dried, vacuum-dried, and accurately weighed (referred to as W2). W
The gel fraction is calculated from the values of l and W2 according to the following formula.

Gel fraction - 100x (W2/W1) (4) Apparent density (d) Cut the foam into a 10cm x 10cm square, measure the weight and thickness, and divide this weight by the volume to find the weight per unit volume ( g/cm3).

(5) Surface area: Due to the heating during vacuum forming, the air bubbles on the surface layer of the foam are ruptured.
This refers to the phenomenon in which the surface of a foam becomes uneven. Judgment was made based on the following criteria: when oil-based marker ink was applied to the foam and wiped off with a cloth, the ink remained in spots.

○: No spots to very few spots observed (passed).

×: Many obvious spots are observed.

Examples 1 to 9, Comparative Examples 1 to 5 Polyethylene copolymers (A> include copolymer components edyl acrylate (FA), acrylic acid (AA), methyl methacrylate/maleic anhydride (MMA-MA)
Ethylene-edyl acrylate copolymer (EEA), ethylene-acrylic acid copolymer (EAA), ethylene-methylmeth)7 acrylate-maleic anhydride ternary containing H) in the range of 5 to 30% by weight Copolymer (FM
MA-MAH), low density polyethylene, etc.
Density is 0.92IQ/cm3, l'-m is 108°C,
Low-density polyethylene with an MFR of 4.8 CI/10 minutes is used, and the density is 0.9 as a roughly linear polyethylene.
25a/cm3, Tm is 124℃, MFR is 8CI/1
0 minute linear low density polyethylene was used.

These three components (A), (B), and (C) were blended at the blend ratio shown in Table 1.

5 to 15 parts by weight of azodicarbonamide as a blowing agent was added to 100 parts by weight of these blended polymers, mixed in a Henschel mixer, and then melt-extruded to obtain a molded sheet.

Further, only in the case of Examples 1 and 9, 3 parts by weight of divinylbenzene was added as a crosslinking aid.

These formed sheets were irradiated with a dose of 5 Mrad using an electron beam irradiation device (IR-2 manufactured by Nissin High Voltage Co., Ltd.).
Foaming was effected by heating to 0'G.

An evaluation test was conducted on the obtained foam sheet. The results are shown in Table 1.

From the table, it can be seen that the foams of Examples 1 to 9 that satisfied the essential point 1'1 of the present invention exhibited excellent vacuum formability without causing surface roughness. On the other hand, the blend ratio (K) of Comparative Example 1
The foam that did not satisfy the requirements of and the foam that did not satisfy the gel fraction of Comparative Example 2 lacked vacuum formability.

In addition, the foaming of Comparative Examples 3 to 5 obtained from a blend polymer containing a polyethylene copolymer (A) that does not satisfy the copolymerization amount of the copolymer component ethyl acrylate (EA)-16= and acrylic acid (AA) The body had poor vacuum formability and surface scratches occurred.

Claims (1)

[Claims] (1) A polyethylene copolymer (A) containing at least one compound selected from the group consisting of monovalent or divalent aliphatic unsaturated carboxylic acids and derivatives thereof as a copolymerization component, low density polyethylene ( B) and linear polyethylene (C) as essential components, the blend ratio {(B+C)/A} is 2 in weight ratio.
A crosslinked polyethylene resin foam having excellent moldability, having a gel fraction of 15 to 45% and a drawing ratio (K) expressed by the following formula. K≧2d+0.40 (in the above formula, d is the apparent density (g/cm^3))