JPH0257578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sheet-shaped crosslinked polyethylene foam with improved toughness and moldability. In recent years, polyethylene foams have been used in large quantities for cushioning and insulation materials, and their properties include being stain-resistant and rot-resistant, having good shapeability, being available in a wide variety of sizes, and being inexpensive and beautiful. However, as the uses have expanded, the required properties have also diversified, and there has recently been an increase in the number of fields that require higher quality foams, and the development of particularly strong and moldable foams has been awaited. The present inventors have developed a sheet-shaped crosslinked polyethylene foam that maintains the excellent physical properties of conventional polyethylene foam, has improved toughness and moldability, and can be applied to application fields that require advanced properties. The present invention was arrived at as a result of intensive studies aimed at developing the following. That is, the present invention is a foam made essentially of polyethylene with a gel fraction of 20 to 50%, obtained by an over-bath foaming method, with a coefficient γ indicating toughness of 5.5 or more and moldability. It is characterized by a sheet-shaped radiation-crosslinked polyethylene foam having a coefficient R of 0.55 or more. The cross-linked polyethylene foam of the present invention is a completely new cross-linked foam material that has various properties that are significantly superior to conventional polyethylene foams, and is an excellent foam material that has almost no limitations in the field of application. . For example, in the field of insulating steel sheets for building materials, with conventional polyethylene foam, the foam often breaks at the sharp edge during sharp bending, and the skin layer often cannot withstand the straining of press rolls and breaks. In addition, in the field of insulation materials for coolers for light electrical appliances, there is a demand for toughness and improved peel strength due to problems with skin peeling. Furthermore, in the field of insulation and waterproofing for building materials, it is used by laminating it with roofing materials, but its toughness during typhoons and strong winds,
There is a demand for improved skin peel strength, and conventional polyethylene foam products are no longer able to meet these demands. Automotive applications require even higher characteristics, such as a drawing ratio (drawing depth/diameter) of 0.7 or higher, which is impossible with conventional polyethylene foams, and especially in the seat back pocket field, existing polyethylene foams cannot meet these requirements. It's a situation. If the foam of the present invention is used, it will be possible to fully meet all kinds of uses without causing the above-mentioned processing troubles. The coefficient γ indicating the toughness of the foam of the present invention is defined by the following equation. γ=x+y+5z≧5.5…(1) where x: Tensile strength in the longitudinal direction of the foam (Kg/cm ² ) y: Tear strength of 〃 (Kg/cm) z: Skin peel strength of 〃 (Kg/cm 2 ) /cm) ρ: Apparent density (g/cm ³ ) The x and y values used here are measured by the following method. Both are Japanese Industrial Standards JIS K-6767 for foams.
The values (X ₀ , Y ₀ ) measured in are converted using the following formula. x=X ₀ +195(ρ−0.025)−241(ρ−0.025) ² y=Y ₀ +92(ρ−0.025)−185(ρ−0.025) ² The z value is the value converted from the Z ₀ value and is calculated by the following formula. represent z = Z ₀ + 13.6 (ρ - 0.025) Here, the Z ₀ value represents the skin peel strength. A test piece with a length of 100 mm and a width of 25 mm is prepared from the foam, and on the measurement surface of the test piece, A completely adhesive material that does not stretch during the measurement (for example, PVC sheet or gum tape) is pasted together, and using an autograph, peeling is performed at 180 degrees at a tensile speed of 50 mm/min, and the strength is expressed in kg per 1 cm. do. It is preferable that these x, y, and z values satisfy equation (1) as well as the following equation (2). x≧2.3, y≧1.3, z≧0.3 (2) Furthermore, the coefficient R indicating the moldability of the foam of the present invention must satisfy the following formula. R=H/L≧0.55 where, H: Depth of drawing when forming the foam (cm) L: Diameter of drawing when forming the foam (cm) If the coefficient R=H/L is less than 0.55, it is high grade. It is difficult to obtain molded products with high precision, and deep drawing may cause the foam to break or become thin and uneven. H/L is defined by the following measurement method. The foam is heated from above and below with a far-infrared heater until the surface temperature of the foam reaches 150-160℃ (internal temperature 100-120℃).
℃), vacuum forming is performed using a cylindrical female mold, and the ratio of the depth H to the diameter L of the foam molded product is expressed. During heating, it is necessary to eliminate distortion of the foam and make it flat before molding. Further, in the foam of the present invention, it is desirable that the coefficients S _n and S _t indicating the tensile elongation satisfy the following formula. S _n ≧2000ρ＋190 S _t ≧2000ρ＋150 where, S _n : Tensile elongation in the length direction of the foam (%) S _t : Tensile elongation in the width direction of the foam (%) In general, toughness refers to strength. It is well known that the larger the , and the greater the elongation, the better the energy absorption and conformability of the material during processing, but there are almost no conventional commercially available foams that satisfy this relationship. It is clearly seen that the foam of the present invention is excellent. To measure S _n and S _t, follow the Japanese Industrial Standard JIS K-
You can use 6767. Here, with toughness coefficient γ≧5.5, S _n <2000ρ±190, S _t
When <2000ρ+150, the foam generally exhibits a formability H/L<0.55, leading to fracturing of the foam during molding, particularly during deep drawing. Even if H/L≧0.55 is satisfied, it cannot be put to practical use in deep drawing due to insufficient thickness uniformity. The polyethylene foam of the present invention having such excellent physical properties can be produced by using the following polyethylene (hereinafter referred to as polyethylene A) as at least a part of the raw material. That is, polyethylene A has a melt flow rate (ASTM D1238E) of 0.1 to 50 g/10 min,
Preferably 0.5-20g/10min, density (ASTM
D1505) is 0.910 to 0.940g/cm ³ , preferably 0.915
~0.935g/cm ³ and a melting point of 110-130°C, preferably 115-127°C, consisting mainly of ethylene and α having 4-20 carbon atoms, preferably 5-20 carbon atoms.
- It is a copolymer with olefin. Further, it is more preferable that this polyethylene A has a molecular weight distribution (value of weight average molecular weight/number average molecular weight) of 6 or less. Even if an ethylene propylene copolymer or so-called high-pressure polyethylene is used instead of polyethylene A, a crosslinked polyethylene foam with improved moldability and toughness cannot be obtained. In addition, polyethylene A has a high melt viscosity when the melt flow rate is less than 0.1 g/10 min.
When molding with a blowing agent added, it is difficult to mold, and if the melt flow rate exceeds 50g/10min, the melt viscosity is low, and when molded with a blowing agent added, the shape of the molded product becomes unstable. Undesirable. If the density is less than 0.910 g/cm ³ , the surface of the resulting foam will become sticky, and if it exceeds 0.940 g/cm ³ , the flexibility of the foam will be impaired and the tensile elongation will be reduced. Undesirable. If the melting point is less than 110℃, the heat resistance of the foam will be insufficient, and if it exceeds 130℃, it is necessary to add a blowing agent and raise the molding temperature, so there is a risk of foaming before crosslinking. I don't like it because there is. Further, if a foam having a molecular weight distribution (value of weight average molecular weight/number average molecular weight) of 6 or less is used, a foam having a high tensile elongation can be obtained. Examples of α-olefins having 4 to 20 carbon atoms, which are constituents of polyethylene A used in the present invention, include 1-butene, 1-pentene, 1-hexene,
3,3-dimethyl-1-butene, 4-methyl-1
-pentene, 4,4-dimethyl-1-pentene,
1-octene, 1-decene, 1-dodecene, 1-
One or more types selected from tetradecene, 1-octadecene, etc. can be mentioned. In addition, as long as these α-olefins are used as constituent components, a small amount of propylene component may be contained, but in that case, the content needs to be considerably smaller than the content of α-olefins. In order for the density of the entire polyethylene A to be within the above range, it is sufficient that the ethylene content is approximately 88 to 97% by weight, although this varies depending on the type of α-olefin. The polyethylene A having the above properties used in the present invention is:
It is obtained by polymerizing ethylene and α-olefin in a ratio that provides the required density by a so-called medium-low pressure method using a transition metal catalyst. In this case, a molecular weight regulator such as hydrogen may be used to obtain a desired melt flow rate. Polymerization can be carried out by various methods such as slurry polymerization, gas phase polymerization, and high temperature solution polymerization. The melting point of the polymer was measured using a differential scanning calorimeter (DSC).
After melting the sample at 200℃ for 5 minutes using
Cool to room temperature at a rate of min to crystallize, and cool to room temperature for 1
This is the peak temperature when the endothermic curve was measured at a heating rate of 10°C/min after the temperature was maintained for 1 minute. The polyethylene A used in the present invention may have only one endothermic peak or may have a plurality of endothermic peaks, but in the latter case, the highest peak temperature is taken as the melting point. In addition, the molecular weight distribution (weight average molecular weight/number average molecular weight) can be measured using a gel permeation chromatograph (measuring device: Waters Associates (USA)).
Model 150C-LC/GPC, Column: Toyo Soda
Co., Ltd., GMH-6 (10 ³ - 10 ⁷ Å mix gel), solvent, 0-dichlorobenzene, measurement temperature: 135°C}
was used to obtain a molecular weight distribution curve, and the weight average molecular weight (hereinafter abbreviated as _w ) and number average molecular weight (hereinafter abbreviated as _o ) were determined by the universal calibration method using polystyrene as a standard. The polyethylene A used in the present invention may be used in combination with one or two of other polyolefins such as high-pressure low density polyethylene, high density polyethylene, and polypropylene, as long as the purpose of the present invention is not impaired. To give an example, the polyethylene to be mixed has a melt flow rate of 0.1 to 50g/10min,
Preferably 0.5-20g/10min, density 0.935g/
Preferred are low density polyethylenes of less than cm ³ , preferably from 0.910 to 0.930 g/cm ³ , and whose viscosities at the melting temperature are approximately similar. In addition,
The mixing amount is 90 parts by weight or less, preferably 80 parts by weight or less. Naturally, it is also possible to add other thermoplastic resins to the polyethylene A of the present invention,
Further, optional additives such as flame retardants, fillers, stabilizers, antistatic agents, etc. can also be added. The foam manufacturing method of the present invention will be explained. First, a raw material containing at least a portion of polyethylene A, a blowing agent and, if necessary, a crosslinking accelerator and other additives are uniformly mixed in a mixer, and the mixture is fed to an extruder so that the blowing agent does not decompose. The mixture is melt-kneaded and molded into any shape, preferably a sheet, under the following conditions. Next, the molded article is irradiated with ionizing radiation to crosslink it until a desired gel fraction is reached. Next, the foamable molded product is foamed by a bath foaming method and cooled. Here, the above-bath foaming method refers to a heating medium bath heated to a temperature higher than the decomposition temperature of the blowing agent, such as molten metal, molten inorganic salt, silicone oil, polyethylene glycol, etc. This is a method in which the foam is foamed while the foam is being foamed. In this bath foaming method, the lower surface of the sheet to be foamed is directly heated by a heating medium, but the upper surface may be auxiliary heated by an infrared heater, hot air, or the like. As the crosslinking accelerator, the following polyfunctional compounds are particularly suitable. Divinylbenzene, diallylbenzene, divinylnaphthalene, divinibiphenyl, divinylcarbazole, divinylpyridine and their nuclear substituted compounds and close analogs, polyacrylates and polymethacrylates of aromatic polyhydric alcohols such as ethylene glycol dimethacrylate and hydroquinone dimethacrylate, Polyvinyl esters of aliphatic and aromatic polycarboxylic acids such as divinyl phthalate, diallyl phthalate, diallyl maleate, bisacryloyloxyethyl terephthalate, polyallyl esters, polyacryloyloxyalkyl esters, polymethacryloyloxyalkyl esters, diethylene glycol divinyl ether, Polyvinyl ethers of aliphatic and aromatic polyhydric alcohols such as hydroquinone divinyl ether, bisphenol A diallyl ether-polyallyl ethers, triallyl cyanurate, triallyl phosphate, trisacryloxyethyl phosphate and polybutadiene. Polymers having saturated bonds are also applicable. The amount added is preferably 0.1 to 10 parts by weight. The blowing agent used in the above may be any decomposition type blowing agent as long as it has a decomposition temperature higher than the melting temperature of the raw material polyethylene, but is preferably azodicarbonamide, especially its decomposition point is 196 Temperatures above ℃ are desirable. The decomposition point here refers to the Japanese Industrial Standards (JIS K-
8004), fill the capillary tube tightly with the sample by approximately 5 mm, and when the temperature reaches 190℃, insert the capillary tube filled with the sample,
Increase temperature to 196℃ at a rate of 2℃ per minute, then 1℃ per minute
This is the temperature at which the yellow color of the sample is completely decolored by increasing the temperature at a rate of ℃. In addition, hydrazodicarbonamide, azodicarboxylic acid barium salt, dinitrosopentamethylenetetramine, nitroguanidine, P,P'-oxybisbenzenesulfonyl semicarbazide, etc., which have a decomposition point equivalent to or at a high temperature as azodicarbonamide, may be used singly or in combination.
In particular, it can also be used by mixing with azodicarbonamide. Further, the degree of crosslinking that gives a preferable crosslinked foam is
The gel fraction is 20-50%. If the degree of crosslinking is too low, the bubbles during foaming will not be retained and will tend to aggregate.
It tends to form large bubbles, and it is difficult to increase the foaming ratio due to the escape of gas to the outside of the system. If the degree of crosslinking is too high, the expansion of the foam will be hindered, the expansion ratio will be difficult to increase, the extensibility during heating will decrease, and the thermoformability will decrease. The gel fraction here refers to 0.2g of sample.
This is the weight percent of the insoluble portion when immersed in 50 ml of tetralin at 135°C for 3 hours. As mentioned above, the present invention has a gel fraction of 20 to 50.
% of polyethylene A, with γ of
Since the sheet-like radiation-crosslinked polyethylene foam obtained by the bath foaming method had an R of 5.5 or more and an R of 0.55 or more, excellent effects were obtained in that both toughness and moldability were improved. moreover,
When using foam, a wide variety of products with high toughness and moldability were prepared, but with the foam of the present invention, which has both excellent toughness and moldability, only a small number of products need to be prepared. We were also able to obtain the excellent effects of saving labor in preparation work and reducing errors caused by incorrectly applying varieties. An embodiment of the present invention will be described below. Example 1, Comparative Example 1 Polyethylene A [density = 0.920 g/cm ³ , melt flow rate = 9.0 g/10 min, melting point = 120°C (hereinafter abbreviated as density P, melt flow rate as MI, and melting point as MP) )] 15 parts by weight of the blowing agent azodicarboxylic acid amide and 2 parts by weight of the crosslinking accelerator divinylbenzene were added to 100 parts by weight, and the two were mixed,
The mixture was kneaded using a single-screw extruder to produce a sheet with a thickness of 3.0 mm. This foam sheet was irradiated with radiation at a dose of 6 Mrad using an electron beam accelerator. This irradiated sheet was floated on the surface of the molten metal at 230°C and heated and foamed from the top with hot air at 260°C to obtain a normal foam. The physical properties of this foam were measured and are shown in Table 1 as Example 1. As a comparison sample, P=0.925g/cm ³ , MI=4.0
g/10min, MP=100℃ using high pressure low density polyethylene resin Mirason #16 (manufactured by Mitsui Polychemicals) to make a foam under the same conditions and measure its physical properties. Table 1 shows Comparative Example 1. Indicated. As shown in Table 1, the obtained foam had extremely excellent toughness, high tensile elongation, and good formability, and could be used in the fields of building materials and heat-insulating steel plates. Example 2 Polyethylene A [P=0.924g/cm ³ , MI=3.0
g/10min, MP=122°C] 50 parts by weight and 50 parts by weight of high-pressure low density polyethylene resin Mirason #16 (Mitsui Polychemical Co., Ltd.) were mixed, and 18 parts by weight of the blowing agent azodicarboxylic acid amide was added and mixed. The mixture was then kneaded using a single-screw extruder to produce a sheet with a thickness of 4.0 mm.
This foam sheet was irradiated with 6 Mrad radiation using an electron beam accelerator. This irradiated sheet was foamed by the same method as in Example 1,
A good foam was obtained. The physical properties were measured and shown in Table 1 as Example 2. The obtained foam was very strong and had extremely good workability when it was laminated with a PVC sheet and bent.

[Table] Example 3 The foams obtained in Example 1 and Comparative Example 1 were sliced in half in the thickness direction to vacuum form a sink cover. This sink cover is
It is 40cm tall, 30cm wide, and 15cm deep. In the conventional general-purpose product (Comparative Example 1) using the foam, the wall thickness was significantly reduced due to breakage at the corners and uneven thickness at the rising parts. However, in the case of using the foam obtained in Example 1, no tearing was observed, and a good molded product with relatively little thickness deviation was obtained.

Claims (1)

[Scope of Claims] 1. A foam made essentially of polyethylene with a gel fraction of 20 to 50%, obtained by an over-bath foaming method, with a coefficient γ indicating toughness of 5.5 or more, and moldability. 1. A sheet-shaped radiation-crosslinked polyethylene foam having a coefficient R of 0.55 or more. However, γ=x+y+5z R=H/L x: Tensile strength in the longitudinal direction of the foam (Kg/cm ² ) y: Tear strength in the longitudinal direction of 〃 (Kg/cm) z: Skin peel strength of 〃 ( Kg/cm) H: Depth of drawing during molding (cm) L: Diameter of drawing (cm)