JPS6254816B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to produce a high-magnification foam having excellent heat resistance and made of a vinyl acetate-ethylene copolymer containing a large amount of inorganic material.

In general, adding large amounts of inorganic substances to polymers improves physical properties such as heat resistance and sound absorption, and mechanical properties such as tensile strength and rigidity, as well as greatly reducing material costs. This is extremely important. It also has great social significance from the standpoint of resource conservation by saving oil resources.
Therefore, various materials have been developed in which inexpensive fillers such as calcium carbonate are added to general-purpose polymers such as polyethylene and polypropylene, and these materials are mainly used in the field of injection molded products.

On the other hand, with the aim of obtaining foams with excellent heat resistance, various studies have been made to increase the foaming rate of polymers highly filled with inorganic substances, but it has been extremely difficult to achieve this. The reason for this is that in polymers containing a large amount of inorganic substances, the foaming gas escapes so much during foaming that the foaming ratio cannot be increased. For example, Japanese Patent Publication No. 51-37300 proposes a method in which a foaming agent and a crosslinking agent are added to a composition consisting of a polyethylene resin and aluminum hydroxide, and the composition is heated and foamed. In this method, 40 parts by weight of high-pressure polyethylene and aluminum hydroxide are placed in a sealed mold.
60 parts by weight of the composition plus 0.25 parts by weight of crosslinking agent and blowing agent
A foam with a maximum expansion ratio of 17.5 times (density 0.134 g/cm ³ ) was obtained by adding 3.5 parts by weight of the foam and opening the mold all at once after heating. However, foams of this level cannot be said to have sufficient density or expansion ratio, and are also inferior in heat resistance.

Furthermore, a small amount of inorganic substances such as calcium carbonate and a blowing agent are added to the ethylene-vinyl acetate copolymer,
A foam obtained by heating and foaming this foam is used for footwear such as sandals, but even in this foam, the expansion ratio is extremely low, at most about 5 to 6 times.

In view of the current situation, the present inventors extensively studied the types of polymers and inorganic substances, and found that inorganic substances should be used only when selecting and using a vinyl acetate-ethylene copolymer with an extremely high vinyl acetate content. The present invention was achieved by discovering that even if it is contained in a large amount, it can foam at a high ratio and maintain a closed cell structure. That is, the present invention has a vinyl acetate content of 50 to
A blowing agent and a crosslinking agent are added to a composition prepared by adding 50 to 300 parts by weight of an inorganic substance to 100 parts by weight of a 90 wt% vinyl acetate-ethylene copolymer, and this is heated to crosslink and foam, or the composition is Add foaming agent,
This is characterized by crosslinking with radiation and then heating and foaming to obtain a foam with a high magnification.

In the method of the present invention, only a special vinyl acetate-ethylene copolymer with a high vinyl acetate content can produce a particularly excellent foam with a high expansion ratio. Although it is not possible to explain this in detail, the above-mentioned copolymer and It is assumed that this is because, in addition to the interfacial interaction with the inorganic material surface preventing destruction at the interface during the foaming process, a viscoelastic state suitable for foaming is created.

The characteristics of the foam produced by the method of the present invention are that it foams at a high ratio despite containing an extremely large amount of inorganic substances, has a closed cell structure, and has excellent heat resistance. It can also be used satisfactorily. In other words, the heat resistance of a foam is expressed by its heating dimensional change rate, but for the polyethylene foam mentioned above, its crystal melting point (115
When the temperature rises above 130°C, the foam deforms to the extent that it no longer retains its original shape, whereas the foam produced by the method of the present invention
Even at temperatures of 150 to 200°C, the dimensional shrinkage is only a few percent.

Therefore, the vinyl acetate content of the vinyl acetate-ethylene copolymer in the present invention is limited to 50 to 90 wt%. Its molecular weight can be used in a wide range of melt index at 190°C from 0.01 to 300. Also, the density of the above copolymer is
It is usually greater than 1.01 g/cm ³ and smaller than 1.10 g/cm ³ . This copolymer may also contain other polymers as an auxiliary. For example, a crystalline vinyl acetate-ethylene copolymer with a vinyl acetate content of 40% or less, polyethylene, ethylene-propylene copolymer, polyvinyl chloride or its copolymer, etc., in a content of less than 50wt%, preferably 30wt%. They may be mixed in proportion.

Furthermore, the vinyl acetate-ethylene copolymer in the present invention must be crosslinked by irradiation with radiation or crosslinked with a chemical crosslinking agent, and the degree of crosslinking is 30% or more in terms of gel fraction. It is.
The degree of crosslinking is measured according to the method specified for polyethylene, which is extracted in hot toluene at 90°C for 10 hours, washed with acetone, air-dried, thoroughly vacuum-dried, and then weighed. do. Since inorganic substances and organic substances that cannot be extracted in the above manner remain in the weighed sample, the degree of crosslinking of the vinyl acetate-ethylene copolymer was determined by correcting this point.

In addition, in the present invention, the content of inorganic substances is 50 to 300.
Parts by weight were preferably limited to 80 to 200 parts by weight, but
If the amount is less than 50 parts by weight, the effect of incorporating a large amount of inorganic material cannot be achieved. or
If it exceeds 300 parts by weight, it will not be possible to obtain a product with a sufficiently high expansion ratio.

Examples of inorganic substances include carbonates such as calcium carbonate and magnesium carbonate; silicates such as kaolin, calcined clay, hard clay, talc, bentonite, loastone, mica, zeolite, wollastonite, attapulgite, and feldspar; diatomaceous earth and silica powder. , silicic acids such as finely divided silicic acid; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide; sulfates such as barium sulfate and calcium sulfate; metal oxides such as aluminum oxide, magnesium oxide, tin oxide, iron oxide, etc. substances; various phosphates such as aluminum phosphate, potassium metaphosphate, and sodium metaphosphate; residues such as mineral slag and slag. These are usually contained in fine powder form,
Its average particle size is 0.01~20μ preferably 0.05~10μ
However, they may also be used in the form of fibers, such as rock wool, glass wool, etson guide, dawsonite, potassium titanate, etc.

In addition, inorganic substances may be used not only singly but also in combination depending on the purpose and use. In particular, when it is desired to obtain a flame-retardant foam, hydrated metals such as aluminum hydroxide and basic magnesium carbonate may be used. Preferably, oxides are used. This hydrated metal oxide and vinyl acetate
Compositions with ethylene copolymers exhibit excellent flame retardancy; for example, 100, 150, or 230 phr of aluminum hydroxide powder is added to a vinyl acetate-ethylene copolymer containing 68% vinyl acetate. It can be seen that the index is 33, 45, and 75, respectively, indicating extremely high flame retardancy.

In addition, if the effect as a bulking agent is desired, an inexpensive filler such as calcium carbonate is used.

Examples of blowing agents include azodicarbonamide, sodium bicarbonate, sodium bicarbonate, dinitrosopentamethylenetetramine, and PP'-oxybisbenzenesulfonyl hydrazide; examples of crosslinking agents include dicumyl peroxide, 2,
5-dimethyl-2,5-di-(tert-butylperoxy)hexane, 1,3-bis(tert-butylperoxyisopropyl)benzene, etc. are used.

Various other additives such as antioxidants, colorants, carbon black, crosslinking aids, lubricants, flame retardants, etc. may also be used.

The production method of the present invention involves, for example, mixing a vinyl acetate-ethylene copolymer, an inorganic substance, a blowing agent, a crosslinking agent, and an antioxidant using a Banbury mixer, kneader, or two-roll mill, pelletizing the mixture, and then using an extruder to form a sheet. It may be molded into a sheet, molded using a calendar, or continuously kneaded into a sheet using a twin-screw extruder. This sheet is crosslinked under pressure using a hot press, and then heated and foamed in an air constant temperature bath. Alternatively, the sheet may be introduced into a heating device such as a hot air oven or a molten salt bath, and heated as it is for crosslinking and foaming.

Also, vinyl acetate-ethylene copolymer, inorganic substances,
It is also possible to irradiate and crosslink a molded sheet made of a foaming agent, a crosslinking aid, and an antiaging agent with electron beams, gamma rays, etc., and then heat it to form a foam. Furthermore, a vinyl acetate-ethylene copolymer, an inorganic substance, a blowing agent, a crosslinking agent, and an antioxidant are mixed, and the kneaded mixture is filled into a closed mold and heated under pressure to form a thick block foam. It can also be made into a body or a irregularly shaped foam.

Next, examples of the present invention will be described.

Examples (1) Commercially available vinyl acetate-ethylene copolymer (product of Nippon Reichhold Co., Ltd., Everthrene 450-
P, vinyl acetate content 60wt%, melt index 30-50, density 1.05g/ ^cm3 ) and 100 parts by weight of finely ground calcium carbonate powder (product of Nitto Funka Co., Ltd.,
NS#1000, density 2.7g/cm ³ , average particle size 0.4μ) 150
Parts by weight, 20 parts by weight of azodicarbonamide (VAC #1L, manufactured by Eiwa Kasei Co., Ltd.) and 3 parts by weight of dicumyl peroxide (Percyl-D, manufactured by NOF Corporation) were mixed into a small Banbury. The mixture was kneaded in a mixer at 120°C for 5 minutes.
A portion of this was formed into a sheet with a thickness of 3 mm using a hot press, and then held at 160° C. for 10 minutes using a hot press to decompose dicumyl peroxide and crosslink it. After taking out this foam sheet and cooling it,
When heated for 15 minutes in a hot air constant temperature bath set at 200°C, it foamed significantly and a foamed product with a density of 0.06 g/cm ³ was obtained. When this foam was observed using a scanning electron microscope, the cells were extremely fine and had a closed cell structure. A small piece of this foam was pressed into a bubble-free sheet using a hot press, and its density was measured to be 1.47 g/cm ³ . Therefore, the foam was expanded 24.5 times. In addition, after extracting in hot toluene at 70°C for 10 hours, the extracted residue is taken out, air-dried and vacuum-dried, weighed, and completely burned to calculate and correct the content of inorganic substances. The gel fraction was determined to be 76%.

Furthermore, when the heating dimensional change rate of this foam was measured using the method according to JIS6767, it was found that at 180℃
% shrinkage and exhibited extremely good heat resistance.

Example (2) Aluminum hydroxide (Showa Denko K.K. product, Hygilite H-42M, density
2.42g/cm ³ , average particle size 1μ) was added, and a foaming agent and a crosslinking agent were added in the same manner as in Example (1). When molded and foamed, the density was 0.04.
A foam with a foaming ratio of ³⁸ times was obtained.

Further, when the heating dimensional change rate of this foam was measured in the same manner as in Example (1), it shrank by 3% at 160°C. Furthermore, slice this foam into 4mm thick pieces.
Cut into a size of 22mm x 22mm, and the thickness of the same shape is 0.4
Heat laminated to mm galvanized iron plate, JIS A1321−
When a combustion test was conducted using the method shown in 1975, the product passed grade 1 flame retardancy.

As detailed above, according to the method of the present invention, it was possible to obtain a foam having fine closed cells, high foaming, high elasticity, and excellent heat resistance. Therefore, it is extremely useful as a low-cost, resource-saving foam as a filler for joints, heat insulating materials, cushion materials, and clothing materials.

Claims (1)

[Claims] 1 100 parts by weight of vinyl acetate-ethylene copolymer with a vinyl acetate content of 50 to 90 wt% and 50 to 300 parts of an inorganic substance
A blowing agent and a crosslinking agent are added to a composition to which parts by weight have been added, and this is heated to cause crosslinking and foaming, or a blowing agent is added to the composition, and this is crosslinked with radiation, and then heated and foamed. A method for producing a vinyl acetate-ethylene copolymer foam, characterized by: