JPH05287104A - Electric beam-crosslinked polyethylene foam - Google Patents

Abstract

PURPOSE:To provide electron beam-crosslinked polyethylene foam having high toughness, heat resistance and reduced thickness irregularity. CONSTITUTION:The electron beam-crosslinked polyethylene foam comprises (A) a low-density polyethylene of lower than 115 deg.C melting point (Tm) and less than 0.930 g/cm<3> density and (B) a high-density polyethylene of over 120 deg.C melting point and more than 0.950 g/cm<3> density, as essential components, at a weight ratio of 1 to 9 A/B and a gel fraction of 8 to 45%.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a low density polyethylene (A) and a high density polyethylene (B) as essential components.
It relates to an electron beam crosslinked polyethylene foam comprising a blended polymer containing components. More specifically, the present invention relates to an electron beam crosslinked polyethylene foam having improved rigidity and heat resistance, which is suitable for industrial materials such as bath mats and other household items, packing, heat insulating materials, pipe covers, etc.

[0002]

2. Description of the Related Art Generally, low density polyethylene foams are
It has excellent heat insulation and cushioning properties, but on the other hand, if the mechanical properties, especially the apparent density is less than 0.07 g / cm ^3, it becomes a so-called inflexible (stiff) foam and various processing problems. However, there is a problem in that it is not possible to cope with the recent increase in processing speed.

On the other hand, the heat resistance of the low-density polyethylene type is at most 80 ° C., and its use at ambient temperature higher than that is limited, and the surface of the foam is coated with a solvent type adhesive or a water emulsion type adhesive. However, there was a problem that the temperature for removing the solvent and water after the heating could not be increased, and thus the productivity could not be improved. Four

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron beam crosslinked polyethylene foam which has no defects in the above-mentioned processing steps, has excellent rigidity and heat resistance, and has a small thickness unevenness.

[0005]

The above-mentioned object of the present invention is to provide a low-density polyethylene (A) having a melting point (Tm) of less than 115 ° C. and a density of less than 0.930 g / cm ³ and a melting point (Tm) of 120 ° C.
As described above, it is made of a blend polymer containing a high density polyethylene (B) having a density of 0.950 g / cm ³ or more as an essential component, and the blend ratio (A / B) is within a range of 1 to 9 by weight, and This can be achieved by an electron beam crosslinked polyethylene-based foam having a gel fraction of 8 to 45%.

The foam of the present invention is composed of a blend polymer containing low density polyethylene (A) and high 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 blended polymers constituting the foam.

The low density polyethylene (A) constituting the foam of the present invention has a Tm of less than 115 ° C. and a density of 0.930 g / c.
It must have a property of less than m ³ , which can be polymerized by conventional high pressure processes. Here, Tm is a value detected by a differential scanning calorimeter (DSC). The low density polyethylene (A) may be an ethylene / propylene random copolymer containing a range of less than 10% by weight of propylene.

The high density polyethylene (B) constituting the foam of the present invention has a Tm of 120 ° C. or higher and a density of 0.950 g /
It must have properties of cm ³ or higher, which can be polymerized by the so-called low pressure method.

The blend polymer of the low-density polyethylene (A) and the high-density polyethylene (B) constituting the foam of the present invention has a blend ratio (A / B) of 1-9 by weight, preferably 1.5-5. It is characterized in that it is within the range of 0.8.
When the blend ratio (A / B) is less than 1, the resulting foam has good rigidity and heat resistance, but it becomes difficult to knead the blended polymer in the extruder, and the die (die) of the extruder is used.
It is difficult to obtain a sheet having a uniform thickness and a smooth surface condition when molding the blended polymer through the above procedure, and the thickness unevenness of the resulting foam becomes large, which is not preferable.

On the other hand, if the blend ratio (A / B) exceeds 9, it is not preferable because the resulting foam has low rigidity and low heat resistance.

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 (C), especially its melting point ( It is preferable to further blend a linear polyethylene having a Tm) in the range of 115 to 135 ° C.

As a specific example of such a linear polyethylene, a melt flow rate (ASTM-D-min) composed of α-olefin having 4 to 20 carbon atoms and ethylene and containing 0.1 to 50 g / 10 min. 1238) and has a density of 0.9
15-0.940 g / cm ³ , Tm 115-135 ° C
There are linear low- to medium-density polyethylenes, wherein α-olefin having 4 to 20 carbon atoms as the copolymerization component is, for example, 1-butene, 1-pentene, 1-hexene, 4-methyl-1. -Pentene, 1-octene and the like can be exemplified.

The blending ratio of the linear polyethylene (C) with the low density polyethylene (A) is (A) / (C) = 10/90 to 90/10 parts by weight, more preferably Is preferably 40/60 to 85/25 parts by weight.

Further, the foam according to the present invention preferably has a gel fraction in the range of 8 to 45%, preferably 12 to 40%. If the gel fraction is lower than 8%, the high temperature for producing the foam will be obtained. It is difficult to obtain a foam having a desired apparent density because the sheet shape retention property under the sheet becomes poor, or foaming gas escapes, and even if a foam is obtained,
Uneven thickness is not preferable. Also, the gel fraction is 45
%, When the foam is produced, the seam at high temperature
Although the shape retention property is not a problem, the bubble diameter of the obtained foam is not uniform, and it is difficult to obtain a foam having a uniform thickness, which is not preferable.

An embodiment of the method for producing the electron beam crosslinked polyethylene foam according to the present invention will be described below.

100 parts of a blend polymer composed of the above-mentioned low density polyethylene (A) and high density polyethylene (B) is added to a known thermal decomposition type foaming agent such as azodicarbonamide, dinitrosopentamethylenetetramine and, if necessary, A cross-linking agent that generates radicals by heating is mixed, the temperature is maintained at a temperature at which the foaming agent and the cross-linking agent are not decomposed, and the sheet is molded into a sheet. When forming this sheet,
If the roll temperature when the sheet is drawn into a roll is set to be lower than the Tm of the high density polyethylene (B) used by 25 to 45 ° C., a sheet having a more uniform thickness can be obtained. This molded sheet-like material is cross-linked by the ionizing radiation cross-linking method so as to be 8 to 45%.

The cross-linked molded article thus obtained is heated in a hot air atmosphere or in a salt bath to rapidly decompose the foaming agent contained in the molded article and convert it into a foam. It is more preferable to heat and decompose the above because the rigidity and heat resistance of the obtained foam will be improved.

Within a range that does not impair the object of the present invention, a small amount of various polymers such as polypropylene, polybutylene, chlorinated polyethylene and the like can be added to the ethylene resin composition used in the production of the foam of the present invention in an amount of 10 parts by weight. Lubricants, antioxidants, ultraviolet absorbers, colorants, antistatic agents, flame retardants, and other various additives can be added and mixed, as required, in the same manner as long as the object of the present invention is not impaired. Can be added within a range capable of achieving the desired purpose.

Further, the polyethylene foam according to the present invention is laminated on at least one surface thereof with an adhesive by corona discharge treatment, coating, etc.
Its processability can be improved, and plastic films, sheets, foam sheets of other foam sheets, metal foils, etc. can be stuck together, or a composite structure can be added by extrusion laminating, etc. That is, various processing techniques can be applied.

The effects of the present invention will be described more specifically below with reference to examples. The measuring method of various parameters in the present invention will be described.

(1) Tm Using a DSC-2 type differential scanning calorimeter (DSC) manufactured by Perkin-Elmer Co., the melting endothermic peak temperature after melting and recrystallization is once determined as the melting point (Tm). ).

(2) Gel Fraction (%) 0.2 g of the cut foam is precisely weighed and immersed in tetralin heated to 135 ° C. for 3 hours to dissolve the dissolved content.
Next, insoluble matter is taken out, tetralin is removed with acetone, and acetone is further removed with warm water at 40 ° C. Then, after drying for 1 hour in a vacuum dryer heated to 100 ° C., the weight W1 (g) of the insoluble matter is measured. The gel fraction (%) is calculated by the following formula.

Gel fraction (%) = (W1 / 0.2) × 100 (3) Apparent density of foam The foam was cut into a 10 cm × 10 cm square, the weight and thickness were measured, and this weight was calculated as the volume. It was divided by and shown in terms of weight per unit volume (g / cm ³ ).

(4) Rigidity (waist) After cutting out the foam to a length of 125 mm and a width of 25 mm, it is placed on a plate-shaped stand up to a length of 25 mm, and the bending angle is 30 ° at the other end. Apply the load so that The load at this time is shown by the bending load (g). It can be said that the larger the value of the bending load (g), the greater the rigidity, and the smaller the value, the smaller the rigidity.

(5) Heat resistance (percentage of dimensional change) After marking the width of the foam with a width of 10 cm (L1) in each of the length direction and the width direction, the foam was taken out by heating in a constant temperature dryer at 110 ° C. for 24 hours. After that, it was left at room temperature for 1 hour, and then the length between the markings was measured (L2) to calculate the dimensional change rate (%).

Dimensional change rate = (L1−L2) × 100 / L
1 The value in the MD direction (the length direction of the foam roll) of this dimensional change rate (the negative symbol indicates shrinkage) is -8%, and the value in the TD direction (the width direction of the foam roll) is-. When the shrinkage is larger than 5%, the effect of the present invention cannot be substantially obtained.

(6) Thickness unevenness (%) The foam was sampled in a 100 cm × 100 cm square,
Measure the thickness at intervals of 10 cm in the length and width directions,
(Maximum thickness-Minimum thickness) x 100 / Average thickness was calculated, and the thickness unevenness (%) was calculated according to the following criteria.

◯: Thickness unevenness (%) is less than 15% Δ: Thickness unevenness (%) is 15% or more and less than 20% ×: Thickness unevenness (%) is 20% or more

[0029]

【Example】

Examples 1 to 6 and Comparative Examples 1 to 4 15 parts by weight of azodicarbonamide as a foaming agent was added to 100 parts by weight of the polyethylene blend component,
After uniformly mixing with a Henschel mixer, melt extrusion was carried out to obtain a continuous molding sheet having a thickness of 2.0 mm.

These continuous molding sheets were used in an electron beam irradiation device (IR-2 manufactured by Nisshin High Voltage Co., Ltd.) so that various gel fractions having different gel fractions could be obtained at 3 to 18 M.
Electron beams were irradiated in the range of rad to crosslink.

Next, the foamable crosslinked sheet was heated at 225 ° C.
A continuous sheet-like foam was obtained by continuously guiding and foaming on a salt bath heated to a constant temperature.

These foams have a thickness of 3.3 mm-4.
7 mm, apparent density 0.029-0.045 g / cm
^It was obtained in the range of ³ . The results are shown in Table 1.

[Table 1] In the examples of the present invention, since the blending ratio of the polyethylene component and the gel fraction were optimized, the thickness unevenness, rigidity (bending angle), and heat resistance were all excellent.

On the other hand, in the comparative example of the present invention, since either the blending ratio of the polyethylene component or the gel fraction does not satisfy the constitution of the present invention, the obtained foam has uneven thickness,
The rigidity (bending angle) and heat resistance were clearly inferior.

[0034]

The polyethylene foam of the present invention thus obtained has excellent rigidity and heat resistance ranging from low apparent density to high apparent density. It can be used and deployed in many applications such as packing, adhesive tape base, pipe cover, mat base material, and other applications such as clothing and building materials.

Claims (2)

[Claims] 1. A melting point (Tm) of less than 115 ° C. and a density of 0.9.
It is composed of a low-density polyethylene (A) of less than 30 g / cm ^{3 and} a high-density polyethylene (B) having a melting point (Tm) of 120 ° C. or more and a density of 0.950 g / cm ³ or more as essential components. The ratio (A / B) is in the range of 1 to 9 by weight, and the gel fraction is 8 to 45.
% Electron beam crosslinked polyethylene foam. 2. The blended polymer has a melting point (Tm) of 115-115.
The electron beam crosslinked polyethylene-based foam according to claim 1, comprising a linear polyethylene (C) having a temperature of 135 ° C.