JPS60166441A - Expansion molded shape and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve stiffness and heat resistance by forming a discontinuous phase consisting of a granular crosslinked high melting-point polyethylene group resin foam uniformly dispersed in a continuous phase composed of a crosslinked low melting-point polyethylene group resin foam. CONSTITUTION:Low melting-point polyethylene and high melting-point polyethylene are mixed, and formed to a pellet shape. The pellets are crosslinked by using a crosslinking agent. The crosslinked pellets are charged into an autoclave together with a blowing agent and water, and heated. The heated material is expanded by opening a discharge point in the bottom of the autoclave and discharging contents into atmospheric air, thus obtaining pre-expanded grains. The grains are left as they are at the normal temperature and normal pressure, and put into a pressure tank, the pressure of the tank is elevated and the grains are changed into ones having inner pressure, a molding die is filled with the grains, which are heated by steam, molded and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foamed molded product made of a crosslinked low melting point polyethylene thread U1 resin and a crosslinked high melting point polyethylene resin, and a method for producing the same.

High-magnification foam molded products made of various thermoplastic synthetic resins are
Its excellent lightness, heat insulation, and cushioning properties are achieved through raw materials.
It is widely used in insulation materials, cushioning materials, floating newspapers, bedding, building materials, packaging materials, etc. Among these, those made of cross-linked low-density polyethylene have the advantage of unique flexibility and good thermal bonding properties, but their rigidity is insufficient compared to other general-purpose foam moldings, so it is difficult to use is extremely limited. As a means of solving this problem, using high-density polyethylene, which has high rigidity, is not practical because crosslinking and foaming of high-density polyethylene is difficult. In addition, foam molding has been attempted by mixing low-density polyethylene and high-rigidity high-density polyethylene in a molten state, but the cells in the foam molded product tend to become continuous, and as a result, the resulting molded product is inferior in terms of physical properties. I can't get it. In addition, special public service 1975-3
Publication No. 9572 describes a method in which composite resin particles having a polystyrene-based 14 resin as a core and coated with polyethylene are foamed after crosslinking treatment and then molded, but the particles are mixed into the product in a dispersed state. Because the spherical foamed polystyrene is large and the adhesion between the foamed polyethylene portion and the foamed polystyrene portion is poor, the effect of improving physical properties is not as great as expected, especially in the case of a thin sheet-like molded product.

The present invention has succeeded in improving polyethylene resin foam molded products by a method free from the above-mentioned drawbacks, and consists of two inventions. The second invention is a foam molded product having a composite structure, which has a continuous phase consisting of polyethylene foam and a discontinuous phase consisting of granular crosslinked high melting point polyethylene resin foam uniformly dispersed in the continuous phase. A melting point polyethylene resin and a particulate high melting point polyethylene resin 91 were mixed at a temperature higher than the melting point of the former and lower than the melting point of the latter, and then formed into particles. 1
1*+E+ particles are crosslinked under conditions in which both (h1 fats) are crosslinked, and then foamed using a foaming agent to form pre-expanded particles, which are then molded. This is an invention of method j for manufacturing a foam molded product according to the invention.

In addition, in the present invention, the terms "high melting point" and "low melting point" are used in a relative sense, and two types of polyethylene + J (if the fat has a melting point difference of 10'C or more,
The resin with the higher melting point is called high melting point polyethylene resin, and Ikega is called low melting point polyethylene resin.

The foam molded product according to the present invention has a surface made of a cross-linked high melting point polyethylene resin foam, so it exhibits the flexibility and good thermal adhesion characteristic of the foam, but the foamed molded product as a whole has a continuous foamed polyethylene phase and strong lubricant properties. By kneading the bonded granular cross-linked high melting point polyethylene resin foam, it is possible to create a molded product made of only a single polyethylene resin foam or a cross-linked foamed product made by simply mixing polyethylenes with different melting points. It has high rigidity and excellent heat resistance.

The foam molded product according to the first invention can be produced by various methods, but the method according to the second invention is the easiest to implement and the one that is most likely to yield a product of excellent quality. This manufacturing method will be elaborated below.

As the raw material low-melting polyethylene resin, low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, or modified products thereof by graft copolymerization can be used, but particularly preferred ones are: Low density polyethylene and linear low density polyethylene. These may be used in combination of two or more types.

In addition, the high melting point polyethylene resin has a melting point of 10°C or more than the melting point of the low melting point polyethylene 11 resin used,
Preferably, the temperature higher than 15° C. is selected from among medium density polyethylene, linear low density polyethylene, high density polyethylene, and graft modified products of Inx resins thereof.

Although the particle size of the low melting point polyethylene T31 fat is arbitrary,
It is necessary to use the high melting point polyethylene type +34 resin in the form of sufficiently fine particles. If even a small portion of coarse particles are used, an unnatural area made of high-melting point polyethylene resin foam will be formed in the product, and especially in the case of thin sheet-shaped molded books, the surface properties and the physical properties of the safe will be affected. have an unfavorable effect on Therefore, the particle size of the high melting point polyethylene 471 resin is about 7 (10/J or less, preferably about 51) U/J or less, particularly preferably about 3
f, l Use fine particles of 0 to 30 JJ.

A series of low melting point polyethylene resins (fats and high melting point polyethylene resins are mixed at a temperature 1 degree higher than the melting point of the latter), but the preferred mixing ratio of the two is , 10 to 100 parts by weight (particularly preferably 20 to 70 parts by weight) of the high melting point polyethylene resin per 100 parts by weight of the low melting point polyethylene resin. An appropriate mixing means is to mix the raw material 4 between rolls heated to a predetermined temperature.
There is a method of kneading through a 34-fat mixture, a method of mixing using a mixer, a method of mixing with a twin screw extrusion (a method of mixing with a screw, etc.).If the temperature conditions are appropriate, mixing with a low melting point A mixture in which the high melting point polyethylene resin is uniformly dispersed in the form of particles in the polyethylene resin is obtained, but if the resin temperature during mixing is higher than the melting point of the high melting point polyethylene 111 resin, the high melting point polyethylene resin also dissolves. Care must be taken to ensure that the temperature is not too high, as this will melt and lose the particulate form, making it impossible to produce the foam molded product according to the first invention.

The obtained mixture is cooled and then shredded by an appropriate method to form particles with a particle size of 2 to 30111111.

The crosslinking treatment and the foam molding treatment of the particles of the resin mixture having a 9μ diameter can be carried out in the same manner as in the case of producing a usual crosslinked polyethylene resin foam molded product by so-called bead foam molding. A typical method is to first heat mixed resin particles in the presence of a crosslinking agent such as nocumyl peroxide to crosslink them to a desired degree of crosslinking. The degree of crosslinking is determined by the degree of modification required for both polyethylene 1'J resins, and is not particularly limited in the present invention, but it is important that both 1'J resins are appropriately crosslinked. is necessary. Excessive crosslinking may lead to poor molding due to a decrease in foamability, and may require a large amount of the main blowing agent. It is particularly desirable to keep the degree of crosslinking of the high melting point polyethylene resin portion to a level lower than that of the low melting point polyethylene resin portion. As is well known,
High melting point polyethylene? Since AI resin is a resin that is less crosslinkable than low-melting point polyethylene-based 134 resin, it is easy to carry out selective crosslinking treatment such as ``double''.

The method of foaming the cross-linked +jl fat particles is also arbitrary;
The most advantageous method is the method according to the invention of Japanese Patent Publication No. 56-134.4, in which resin particles are made to absorb a volatile solvent-based blowing agent, and then heated together with a dispersion medium under pressure in a closed container, and then released from the inside of the container. This is also a method of foaming by discharging into a low-pressure atmosphere. A suitable expansion ratio is usually 3 to 80 times, particularly preferably 5 to 60 times.

The pre-expanded particles obtained after the foaming process are made from a crosslinked low melting point polyethylene resin foam containing a large number of foamed crosslinked high melting point polyethylene resin foam particles based on the mixed state of the raw material resins such as "double series". It is what it is. If necessary, the expanded particles are stored and aged in a pressurized atmosphere such as nitrogen or air according to a conventional method until molding.

The step of molding the pre-expanded particles in a mold can also be carried out in exactly the same manner as the molding of ordinary pre-expanded polyolefin particles in a mold.

That is, no special mold, type of heating medium, temperature, etc. are required.

There may be various foaming states in the foam molded product of the present invention produced as described above, but the preferred state in relation to the purpose of the present invention is the average of the crosslinked low-melting point polyethylene resin foam portion. Bubble diameter I)1 is 30 to 1000/
J, (especially preferably 100 to 700 tt), the expansion ratio E1 is 5 to 50 times, and the average cell diameter D2 of the crosslinked high melting point polyethylene resin foam part is 5O-2000u
(especially preferably 1.51)-1000/no), foaming ratio E2 or 10-80 times tear, D2/I), crab o,
1-15 (particularly preferably 0.3-8) TeE2/E,
Power 0. S − ] 0 (particularly preferably 1 to 16). According to the production method of the present invention, the values of D2/D and E2/E can be easily achieved by changing the combination of raw resins and the degree of crosslinking treatment.

The manufacturing method of the present invention can uniformly introduce the crosslinked high melting point polyethylene TJJ resin foam into the crosslinked low melting point polyethylene +11 resin foamed wood in the form of fine particles. By adjusting the foaming conditions, the average cell diameter of the crosslinked high melting point polyethylene resin foamed wood portion can be made larger than that of the crosslinked low melting point polyethylene resin foamed portion. This improves the physical properties of the polyethylene resin foam molding, which brings about extremely favorable results. In other words, regarding the influence of the size of the bubbles in a synthetic resin foam molded product on the properties of the molded product, (
The larger the diameter of the bubbles, the better the pressure A11i hardness and compressive elasticity recovery, but if the diameter is too large, the surface will be hard and the surface will be noticeably uneven.

It becomes easy to break, and its physical properties such as strength and elasticity deteriorate.

It is known from experience that the cross-linked high melting point polyethylene resin foam forms large cells inside the foam molding, which improves the rigidity of the molded product without deteriorating its surface properties. 1-Crosslinked high melting point polyethylene system 13
This will make the effect of introducing the single-fat foam book even more pronounced.

The present invention will be explained below with reference to Examples 3 and Comparative Examples.

The main test methods for foaming property values shown in this specification are as follows.

Melting point: By differential calorimetry (sample weight 6~) (,1+
ng+heating rate 1 +)'(: /n+i++).

Gel fraction: Calculated from the amount of residue after treatment in boiling xylene for 8 hours and the amount of each component in the residue (based on an infrared spectrum calibration curve).

Expansion magnification 2 The cut surface of the foamed molded product was dyed with a disperse dye, and the area S1 of the low melting point polyethylene portion and the area S of the high melting point polyethylene portion in the entire field of view were determined to determine the difference in dyeing concentration when observed under a microscope. . At the same time, the average and average cell diameters of the eight components were also determined.

Low-temperature fusion property ○: Welds firmly and maintains the molded shape at the molding temperature of cross-linked low-melting point polyethylene △: Welds at the molding temperature of cross-linked low-melting point polyethylene, but the strength is insufficient ×: Molding temperature of cross-linked low-melting point polyethylene In-mold formability O: Shrinkage rate in the length direction is 1% according to the mold τ method.
molded within.

Δ: The above shrinkage rate is more than 4% and less than 6%.

×: 2 shrinkage rate or more than 6%.

Heat resistance: No\STM C21] According to method 1, temperature 81
After leaving it for 48 hours at a J'C1 load of 100 H7cm2, ↑1j is determined based on the magnitude of the strain 11 (%) in consideration of the expansion ratio E, using the following J rule.

○: 'I+/ E≦(J, 5 △: (1, 5< b/ E≦1.()X: II/
> 1:.

Flexibility: According to NDS ZO5U3, thickness% 10 +1
1 m, width 2 t) 111111, length 20 (l m
m test piece along a cylinder with a diameter of 3 (ln+m) and
゛Check for bending and cracks.

○: No cracks occur △: Cracks are seen in some parts X: @L<scraped ) Hardness: According to JISK6767.

Appearance ○: Smooth and uniform coating surface △: Uneven coating surface ×: Defects such as cracks on the surface Examples and Comparative Examples Density fJ, ! ]23g7cm3, melt index 2.5B710 minutes, melting point 105°C low melting point polyethylene and density 0,9561i7'cm3, melt index 0.2g710 minutes, melting point 135'C high melting point polyethylene After mixing with a roll, it is formed into a pellet shape with a diameter of 5+nl.The obtained pellet is mixed with dicumyl peroxide (for tat fat 0) as a crosslinking agent.
．． Cross-linking treatment was carried out for 3 hours using a 5-year-old polymer. The crosslinked resin particles were then charged into an autoclave together with a blowing agent (dichloronoralolomethane) and water, heated, and at 148°C the outlet at the bottom of the autoclay 7 was opened to release the contents into the atmosphere. By foaming, pre-expanded particles having an expansion ratio of about 18 times are obtained.

After leaving the expanded particles at room temperature and pressure for 18 hours, they were placed in a pressurized tank and the pressure was increased to 1.7 Kg/c+112 at a pressure increase rate of 0.05 Kg/c+n2/Ilr to obtain particles with internal pressure. This is 300 mm x 300 +
nmX 5t) +am filling mold and
, 1 KB/cm2 of steam and then dried at 60°C for 2 hours.

In the above manufacturing method, as high melting point polyethylene 0) average particle size 601J (maximum 90μ, minimum 40μ) ■ average particle size 2 (1 (J / J (large 250μ, minimum 160μ))
■ Average particle size, 1.5 +-+ horns (maximum 6007z
, a minimum of 300 zd, and by variously changing the resin mixing ratio, 11 types of foam molded products were manufactured (Examples 1 to 11).

In addition, as a comparative example, an example (comparative example 1) in which only the above-mentioned low melting point polyethylene is used, the melting point polyethylene is heated at a temperature higher than the melting point of the low melting point polyethylene and lower than the melting point of the high melting point polyethylene. The high melting point polyethylene of Example 4.6 was foamed without any treatment (Comparative Example 2).

Example of crosslinking and foaming only melting point polyethylene (Comparative example: 3
), 1-Note 1((Mix melting point polyethylene and high melting point IJ ethylene of Example 1 above at 2(1(1'C)
It is extruded in the molten state and molded into granules. After jjL, crosslinking treatment, foaming and molding are carried out in the same manner as in 1.
75 parts by weight of the pre-expanded particles of Comparative Example 1 and 25 parts by weight of the pre-expanded particles of ratio I++13 were mixed to form a 1M shape (+1 (Lhi 11 Example 5)). .

Claims (2)

[Claims] (1) It has a continuous phase made of a foam of crosslinked low melting point polyethylene and F-131 resin, and a discontinuous phase made of granular crosslinked high melting point polyethylene resin foam uniformly dispersed in the continuous phase. Composite structure foam molding. (2) A low melting point polyethylene resin and a particulate high melting point polyethylene resin are mixed at a temperature higher than the melting point of the former and lower than the melting point of the latter, and then formed into particles, and the resulting mixed resin particles are Crosslinked resin strip 19: A continuous phase consisting of a crosslinked low melting point polyethylene resin foam, which is characterized by being crosslinked at the bottom, then foamed using a blowing agent to form pre-expanded particles, and then molded. A method for producing a foam molded product having a composite structure, which has a discontinuous phase made of granular crosslinked high-melting point polyethylene resin foam uniformly dispersed in a continuous phase.