JPS59230036A - Foamed polyolefin resin and its production - Google Patents

Abstract

PURPOSE:To provide the titled foamed article having high elasticity, suitable as a packaging material, and containing a number of uniform and fine cells even in the absence of a nucleation agent, by impregnating a styrene monomer in a crosslinked polyolefin resin, polymerizing the monomer, impregnating a foaming agent, and foaming the product. CONSTITUTION:A polyolefin resin crosslinked to a crosslinking degree of preferably 15-80% is impregnated with preferably 13-75% of a styrene monomer. After polymerizing the monomer, the obtained polymer resin is impregnated with a foaming agent (preferably a halogenated hydrocarbon having low boiling point), and foamed to obtain the objective foamed article containing >=200 cells, preferably cells of the number defined by the formula [d is density of the foamed article (g/cc) and 0.02<=d<=0.08] per 1mm.<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyolefin resin foam and a method for producing the same. More specifically, the present invention relates to a polyolefin resin foam obtained by foaming a styrene-impregnated polymerized polyolein resin obtained by impregnating and polymerizing a styrene monomer into a final olefin resin, and a method for producing the same.

Styrene-impregnated polymerized polyolefin resin foam has superior strength compared to polyolefin resin foam, and has good dimensional accuracy when processed into molded products, and the molded products can be used as packaging materials. Unfortunately, it has the advantage of good buffering performance. However, due to the rigidity of the styrene component, the soft feel and elasticity, which are the characteristics of HoIJ Ole7in resin foam, deteriorate, and when the molded product is sliced, the texture of the sliced surface becomes rough and it feels rough to the touch. This makes it unsuitable for packaging items that are susceptible to impact, such as cameras, watches, and printers, and items whose surfaces are easily scratched, such as high-end accessories.

It is presumed that such defects can be improved by uniformly refining the cells of the foam, and a method for refining the cells of such a styrene-impregnated polymerized polyolefin resin foam is described in Japanese Patent Publication No. 51-46138, etc. Regarding styrene-impregnated polymerized cross-linked polyolefin resin foam using specific polyethylene with low
No. 10150 proposes a styrene-impregnated polymerized uncrosslinked polyolefin resin foam.

However, the foam obtained by the above method has a density of 60 to 1 mm in 1 mm.
Contains 150 cells, the cell diameter is not yet sufficiently refined, the cell diameter fluctuates widely, large cells are mixed in, so the rough texture cannot be resolved, and the softness and elasticity are insufficient. It is. Further, since the above-mentioned specific polyethylene and uncrosslinked polyolein resin having a low softening temperature have poor heat resistance, the styrene-impregnated polymerized polyolefin resin foam coated with such resin also has poor heat resistance.

As a method for solving the above problems and making it possible to use 7 +) olefins with arbitrary softening humidity and to further refine 7I, Japanese Patent Publication No. 461-68/1983 describes impregnating polyolefin resins with styrene monomers. A method of crosslinking such polyoleain yarn resin after polymerization is disclosed. However, in this method, any styrene monomer is impregnated into the molecular gaps in the amorphous region of the polyoleaine resin and polymerized, so the styrene polymer component in the resulting styrene-impregnated, polymerized and crosslinked polyoleaine resin is small. It was found that the cells exist as large particles, and as a result, the cells formed by foaming are small and large.

In view of the above-mentioned circumstances, the present inventors have conducted extensive research with the aim of developing a styrene-impregnated polymerized polyolein resin foam that contains uniformly finely divided cells and has excellent strength, molded product dimensional accuracy, and cushioning performance. As a result, we found that by using a pre-crosslinked polyole-7-ene resin, impregnating the resin with a styrene monomer and polymerizing it, the amorphous region of the polyole-7-yne resin Since the molecular gap is divided into a large number of minute gaps by crosslinking, only a small amount of the impregnated styrene monomer enters the minute gaps, and as a result, in the styrene-impregnated polymerized crosslinked polyolefin resin obtained by this method. It was discovered that the styrenic polymer component exists as a large number of finely dispersed particles, and that the foam contains a large number of uniform fine cells even without the addition of a nucleating agent, leading to the completion of the present invention.

That is, the present invention relates to a polyolefin resin foam that is characterized by having a polyolein resin as a base material impregnated with a styrene monomer and containing 200 or more cells in 1 mm2, and a method for producing the same. An appropriate method for producing such a foam is to impregnate a styrene monomer into a pre-crosslinked polyolefin resin, polymerize it, and then impregnate the resulting styrene-impregnated, polymerized and crosslinked polyolein resin with a foaming agent to cause foaming. However, it is more preferable to add 15 parts of a styrene monomer to 100 parts of a pre-crosslinked polyolefin resin with a degree of crosslinking of 15 to 80% (the same applies below).
It is preferable that the styrene-impregnated polymerized crosslinked polyolefin resin obtained by impregnating and polymerizing up to 600 parts is impregnated with a foaming agent and foamed. Note that the shape of the foam of the present invention is not limited, and may be particles. The degree of crosslinking of the above-mentioned polyolefin resin is measured as the insoluble content after a sample is placed in a 200-mesh wire gauze and extracted by immersion in boiling xylene for 24 hours.

Examples of pre-crosslinked polyolefin resins used in the present invention include ethylene, propylene, butene-1, pentene-1,6-methylbutene-1,4-methylbutene-
Homopolymers or copolymers of monoolefins such as 1,4-methylhexene-1, ethylene-vinyl acetate copolymers, ethylene-vinyl chloride copolymers, ethylene-methyl methacrylate copolymers, etc. A copolymer of a monoolefin and another polymerizable vinyl monomer or a mixture thereof having an arbitrary density, M modulus, and softening point is mixed with dicumyl peroxide, 2
It is preferable to use an organic peroxide such as 15-t-butyl perbenzoate or benzoyl peroxide, or one that is crosslinked by irradiation with radiation such as alpha rays or beta rays, and has a degree of crosslinking of 15 to 80%.

If the degree of crosslinking is less than 15%, the impregnation of the styrene monomer will be uneven, causing open cells and cavities, and the dispersion of styrene polymer particles will be poor, making it difficult to form uniform, fine cells. Become. Furthermore, as the degree of crosslinking decreases, the heat resistance of the styrene-impregnated polymer resin deteriorates, and the heat resistance of the foam also deteriorates. On the other hand, when the degree of crosslinking exceeds 80%, there is no problem in obtaining fine cells, but a variety of crosslinking agents are required, and when foamed particles are heated and fused to form a foamed molded product, there is no problem in obtaining fine cells. Both are unfavorable because they may make fusion difficult.

Styrene thread monopolymers that are impregnated into a pre-crosslinked polyolein resin and polymerized (impregnated polymerization) include, for example, nuclear-substituted styrenes such as 1-styrene, α-methylstyrene, p-methylstyrene, and the like. As a method of dispersing the resin, a cross-linked polyolein resin is dispersed in an aqueous dispersion system using an inorganic dispersant such as calcium phosphate, magnesium pita phosphate, or calcium carbonate, and a polymerization catalyst such as benzoyl peroxide is dissolved therein. A method in which a styrene monomer is added all at once or gradually to carry out impregnation polymerization, and a method in which only the styrenic monomer is added to the system all at once or gradually to impregnate the crosslinked polyolefin resin with the styrenic monomer. Examples include a method in which a polymerization catalyst is subsequently added and polymerized.

The amount of the styrene monomer to be impregnated and polymerized is preferably 15 to 600 parts per 100 parts of the pre-crosslinked polyolefin resin, in other words, it is preferably contained in the obtained styrene impregnated polymerized crosslinked polyolein resin in an amount of 13 to 75%. If the amount of impregnated polymerized styrene monomer is less than 15 parts, the cell diameter will not be sufficiently small, and if it exceeds 300 parts, the cell diameter will become large and it will not be possible to obtain a foam with a smooth texture. Undesirable.

The thus obtained styrene-impregnated polymerized crosslinked polyolefin resin particles with a particle size o of 25 to 1Q mm are dispersed as they are or in water according to a conventional method, and then impregnated with a low boiling point organic blowing agent under pressure to produce expandable particles. do.

Examples of the above-mentioned low-boiling point organic blowing agents include aliphatic hydrocarbons such as butane, butane, pentane, and hexane, cyclic aliphatic hydrocarbons such as cyclotetrapane, cyclobutane, cyclopentane, and cyclohexane, and methyl Examples include halogenated hydrocarbons such as fulleride, ethyl chloride, tri-Opfluoro-methane, di-11-tetrafluoroethane, and tetra-Sifu/I/Oda ethane, but aliphatic hydrocarbons or cycloaliphatic When using hydrocarbons as a blowing agent, it is not possible to change the cells into uniform and fine cells unless the expandable particles are cured after impregnation with the blowing agent. It is preferable to use

The expandable particles impregnated with a foaming agent are foamed by a known method such as Method 1, in which the particles are foamed by heating with steam, and a method in which the impregnated state under pressure is released all at once to atmospheric pressure and foamed.

The polyolein resin foam of the present invention thus obtained contains 200 or more cells in 1 mm.

As used herein, the number of cells contained in 1 mm2 refers to the area of the center of 10 foamed particles whose cell diameter is considered to be the average [cells observed in mm2] when at least 100 foamed particles are cut. This is the average value calculated. The number of cells was calculated at the center of the foamed particles.If the foamed particles were used as they were, there would be no large difference in cell density between the center and the periphery, except for the skin area around the outermost cell layer 2.6 of the foamed particles. However, if a molded body is made by filling a mold with foamed particles, inappropriate molding conditions may disturb the state of the cells in the periphery. The number of cells was calculated in the section.

In order to eliminate the rough feel of the sliced surface of the foam and improve its surface properties, it is better to uniformly refine the cells until 1m+n2 contains 200 or more cells, but it is also desirable to give it an even smoother and softer feel. In order to contain 200 or more cells in 1 mm and relate to the foaming ratio: Number of cells ≧ 200 x (50a) (where d represents the foam density (q/aQ),
02≦d≦0.08) is preferably included in 1 mm2.

Foam density d (g/co) In the submersion method, the capacity of the foam tends to decrease, making it difficult to stably obtain particles with uniform fine cells. The body becomes stiff and the soft feel cannot be changed, both of which are undesirable.

When such a polyolefin resin foam is further foam-molded and used as a molded product, it has good cushioning performance, can withstand repeated compression, and has excellent chemical resistance, etc., like a styrene-impregnated polymerized polyolefin foam obtained by a known method. It maintains its characteristics and has a beautiful, smooth, and soft surface when sliced. Furthermore, since the cell diameter is uniform and fine, cell shrinkage and buckling will not occur.Also, it is a highly foamed material, rich in elasticity, and exhibits properties that are resistant to compression and bending.

As described above, the foam of the present invention is highly useful as a packaging material for items that are susceptible to impact or whose surfaces are easily damaged.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

Examples 1 to 4 Ethylene-vinyl acetate copolymer (beer acetate content 15%)
(wt%, same below), M work 1.5, Vicat softening point 6
7°0, density 0.93 (910Q)) crosslinked with dicumyl peroxide with a degree of crosslinking of 77% and styrene monomer 1009 in which 0.19 dicumyl peroxide was dissolved were placed in 11 reactors. Then, 2.09% of calcium phosphate and 90% of sodium dodecylbenzenesulfonate as an emulsifier were added, and 5009 pure water was added and stirred and dispersed, and the temperature was raised to 513-oo.
Styrene monomer was impregnated into the crosslinked ethylene-vinyl acetate copolymer by holding at C for 4 hours to obtain styrene-impregnated polymer particles having an average particle size of about 1.2 mm.

The obtained styrene-impregnated polymer particles were cut and immersed in Tetrahyde 07 run for 24 hours to extract almost the entire amount of styrene.
Figure 1 is a sketch diagram of OO times). As shown in Figure 1, the styrene polymer was dispersed as many very small particles.

These styrene-impregnated polymer particles were impregnated with dichlorodifluoromethane in a saturated dichlorodifluoromethane atmosphere at 50°C to form expandable particles, and then expanded to 9/cm2G to 0.4 using a known pressurized patch type pre-expansion number. Under the water vapor pressure of
The mixture was foamed by heating for 4 seconds, 16 seconds, 8 seconds, and 10 seconds, respectively, to obtain expanded particles having four densities as shown in Table 1. Measure the number of cells of the foamed particles obtained,
The results are shown in Table 1.

The cells of the obtained expanded particles were all uniform and fine, and the sliced surface did not have a rough texture and was soft and beautiful.

Table 1 However, the number of calculated cells is the value determined by the formula: Number of calculated cells=200X(50d)T (in the formula, d represents the foam density).

Comparative Examples 1-2 The same ethylene-vinyl acetate copolymer 100. as used in Examples 1-4. and 100 g of styrene monomer in which 2 g of dicumyl peroxide and 0.5 g of benzoyl peroxide are dissolved. was added to 11 reactors, and then 1 g of magnesium birophosphate and 0.4 g of sodium dodecylbenzenesulfonate as an emulsifier were added. 8oo after adding pure water and stirring and dispersing.

The temperature was raised to 80°C and held at 80°C for 4 hours to impregnate and polymerize styrene monomer. Then, the temperature was raised to 140'O and held for 6 hours to perform crosslinking, resulting in an average particle size of about 1.2 mm.
Styrene-impregnated polymer particles were obtained.

The cut surfaces of the obtained styrene-impregnated polymer particles are shown in Examples 1 to 4.
Figure 2 is a sketch of a photograph (10,000x magnification) taken using an electron microscope in the same manner as above.

Comparing with Figure 1, it can be seen that the styrene polymer particles have non-uniform particle sizes, with many large particles and a small number.

Next, in the same manner as in Examples 1 to 4, dichlorodifluoromethane was impregnated, and the two types shown in Table 2 were foamed by heating for 4 seconds and 7 seconds, respectively, under a Ti water vapor pressure of 0-5 7 cm''G. The foamed particles were changed and the number of cells was measured.The results are shown in Table 2.The cells of the expanded particles were all large and visible, non-uniform, and few in number.The sliced surface of the cells had a hard and rough texture. Was.

Table 2 Examples 5 to 7 and Comparative Example 3 Low density polyethylene (M engineering 1.5, Picat softening point 95
140.°0, density 0.924 (g/Go)) crosslinked with dicumyl peroxide in four different amounts as shown in Table 3. and 0.3 g of benzoyl peroxide dissolved in styrene monomer 60. and were dispersed in 11 reactors in the same manner as in Examples 1 to 4 and impregnated with styrene monomer at 90°0 for 2 hours, and then heated to 130°0 and held for 4 hours to form styrene. The monomers were polymerized to obtain styrene-impregnated polymer particles each having an average particle size of about 2.7 mm.

The thus obtained styrene-impregnated polymer particles had 60 qO,
Expandable particles were impregnated with dichlorodifluoromethane in a saturated dichlorodifluoromethane atmosphere, and heated for 12 seconds each under a water vapor pressure of 1.2 k,/am2G using a known pressurized batch prefoamer. Four types of expanded particles were obtained. The degree of crosslinking, foamed particle density, and cell number of the obtained expanded particles were measured, and the results are shown in Table 6.

Table 6 As is clear from Table 6, as the degree of crosslinking decreases, the cells open up, the expanded particles contract, and the fluctuation range of the cells increases, so the lower limit of the degree of crosslinking is about 15%. I understand that.

Example 8 Low density polyethylene (M work 15, Vicat softening point 95°
To 100 parts of 50% crosslinked particles having a density of 0-921 (9/ca), 0.10.15 parts of styrene #mer in which 0.5% benzoyl peroxide was dissolved was added as shown in Table 4. After impregnating 20.30 parts, styrene-impregnated polymer particles having an average particle size of about 2 mm were obtained by polymerizing in the same manner as in Examples 5-i.

The particles were then impregnated with dichlorodifluoromethane in the same manner as in Examples 5 to 7, and 1 to 2 kg were each impregnated with 10 n''G under a steam pressure of 10 n''G using a pressurized batch prefoaming machine.
Adjust the heating time in the range of ~15 seconds to achieve a density of 0.039~
Five types of foamed particles of 0.0'BB910o were obtained.

The number of cells in the obtained foamed particles was examined after curing the particles for 24 hours.
Fill a mold that can be closed but cannot be sealed, with a pressure of 1 mm.
A molded body was produced by heating with water vapor of -Okg/am2G for 20 seconds. The molded product was dried at 70°CJ for 5 hours, then sliced with a knife and the sliced surface was examined. The results are shown in Table 4.

Table 4 When the amount of styrene impregnated was 15 parts or more, there was almost no variation in cell diameter between particles or within particles, and the appearance of the sliced surface was that the cells were uniform and beautiful, and the surface texture was very good.

Examples 9 to 11 and Comparative Example 4 Ethylene-vinyl acetate copolymer (vinyl acetate content 10%)
, Mll, 5, Vicat softening point 76°a1 density 0.95
(9/cc)) cross-linked with dicumyl peroxide with a degree of cross-linking of 52.4% '1 kg is 40! 1. Put into a reactor and add 50g of magnesium pyrophosphate and 10g of sodium dodecylbenzenesulfonate. ．． 2r: rt pure water was added and dispersed. Add 1.8 kg, 6 kg, 5.4 kg of styrene monomer to the mixture, respectively.
7 and 2 kg were added and heated at 80°0 for 3 hours to impregnate the styrene monomer, respectively. Then 5
0.2 kg of styrene monomer in which r4% benzoyl peroxide was dissolved, 0.4 to 9.0.6 kg,
After adding 0.8 kg each over 1 hour while maintaining the pressure at 800 G, the temperature was raised to 110° O and held for 5 hours to polymerize, thereby obtaining styrene-impregnated crosslinked polyethylene particles each having an average particle size of about 2 mm. 6 to the obtained particles
Expandable particles were obtained by impregnating dichlorofluorocarbon methane under a saturated dichlorofluorogastric methane atmosphere at 0°0.

These expandable particles are placed in a pressurized batch foaming machine.
The particles were heated for 17 seconds under water vapor pressure of 1 and 2 kg/am2 () to obtain four types of particles with densities of 0.024 (g/cc). The number of cells was investigated and the results are shown in Table 5.

Table 5 As the amount of styrene impregnated increases, the cell diameter increases, and its upper limit was approximately 50 [3 parts].

Examples 12-16 Ethylene-vinyl acetate co-rBB4 (vinyl acetate content 5%
, M work 2, Picatto softening point 83, density o, 92 (g/
Co)) Particles with a degree of crosslinking of 64.7% crosslinked with dicumyl peroxide (10 to 9) and 10 kg of styrene monomer were placed in an 80 polymerization machine to form 409 calcium phosphate and 8.
9 of sodium dodecylbenzenesulfonate was added, and 40
! After adding and dispersing pure water, the temperature was raised to 140°O and held for 5 hours to impregnate the crosslinked particles with styrene monomer and polymerize the styrene monomer with the remaining dicumyl peroxide to determine the particle size. Styrene-impregnated crosslinked polyethylene particles of 0.25-10B were obtained. The particles were impregnated with a blowing agent shown in Table 6 under a saturated gas atmosphere at 6,000 kg/ar using a pressurized patch foaming machine.
Five types of expanded particles were prepared by heating for 8 seconds under a water vapor pressure of n2G. The density and cell number of the expanded particles thus obtained were examined, and the results are shown in Table 6.

Table 6 When n-butane or 1so-butane is used as a blowing agent, the cells will become open cells and will not foam unless the foam is impregnated with the blowing agent and then cured. Ta.

Di1. A molded article was prepared by placing the foamed particles using fluoromethane as a foaming agent into a mold that could be closed but not sealed. The density of the obtained compact is 0.0268 (ri/c
o), the molded product was soft to the touch, highly elastic, had excellent surface properties, and had a smooth sliced surface.

Figure 3 is a micrograph of the sliced surface of the compact (16x magnification)
Figure 4 is a commercially available foamed molded product (trade name: Bioflex, manufactured by Tanezu Kaseihin Kogyo ■) made by impregnating polyethylene-vinyl acetate copolymer with styrene monomer and crosslinking it using a known method. It is a sketch of a micrograph (15 times magnification) of a sliced surface of.

It is clear that in the molded body obtained from the foam of the invention shown in FIG. 3, the cells are much more uniform and fine-grained than those of the molded body shown in FIG.

[Brief explanation of drawings]

Figure 1 shows the styrene impregnated polymer obtained in the example of the present invention.
Figure 2 is a sketch of an electron micrograph (10,000x) of the cross-sectional structure of the particles, Figure 2 is a sketch of an electron microscope photograph (10,000x) of the cross-sectional structure of styrene-impregnated polymer particles obtained by the conventional method, and Figure 6 is a sketch of the cross-sectional structure of the particles. Micrograph (15x magnification) of a cross-sectional structure of a molded body made from a foam obtained in an example of the invention
and FIG. 4 are sketches of micrographs (15x magnification) of the cross-sectional structure of a commercially available foam molded product obtained by a conventional method. Figure 2

Claims (1)

[Scope of Claims] 1. A polyolefin resin foam characterized by having a base material of a polyolein resin obtained by impregnating and polymerizing a styrene monomer and containing 200 or more cells in 1 mm2. 2 1 mm Formula: %Formula %) (In the formula, d represents the foam density (97ca), and 0.
02≦d≦0.08). 02≦d≦0.08. 6. The foam according to claim 1, wherein the polyolein resin obtained by impregnating and polymerizing a styrene monomer is a polyolefin resin obtained by impregnating and polymerizing a styrene monomer into a pre-crosslinked polyoleain resin. 4. The foam according to claim 1, wherein the polyolefin resin is a crosslinked polyolein resin. 5 The degree of crosslinking of the crosslinked polyolein resin is 15 to 80%
The foam according to claim 4, which is 6 The amount of styrene monomer impregnated and polymerized is crosslinking $
15 to 60 parts per 100 parts by weight of +3 year old reflex resin
The foam according to claim 4 or 5, which contains 0 parts by weight. 7. A polyolefin resin foam characterized by impregnating a styrene monomer into a pre-crosslinked polyolefin resin and polymerizing it, then impregnating the obtained styrene-impregnated polymerized crosslinked polyolein resin with a foaming agent and foaming it. manufacturing method. 8 The degree of crosslinking of the pre-crosslinked polyolefin resin is 15
80%. 9. The manufacturing method according to claim 7 or 8, wherein the amount of the styrene monomer to be impregnated and polymerized is 15 to 300 parts by weight based on 100 parts by weight of the crosslinked polyolefin resin. 10. The manufacturing method according to claim 7, 8 or 9, wherein the blowing agent is a halogenated hydrocarbon with a low boiling point.