JPS6071215A - Manufacture of foamed product molded in cross-linking polyolefine - Google Patents

Abstract

PURPOSE:To obtain a cross-linking polyolefin foamed product having excellent molding and processing properties and extremely low density by extruding foamed polyolefine resin into a non-foamed strand, processing it into foamed pieces through cross-linking, foaming and cutting steps and subjecting them to heating and compression forming. CONSTITUTION:A foamed polyolefine resin product containing a chemical foaming agent is extruded into the form of substantially non-foamed strands. Next, after cross-linking and foaming processes, foamed strands thus obtained are sliced into pieces of foamed polyolefine product. These pieces of foamed product 1 are charged into gas-permeable heating dies 2 and then hot blast is introduced into said heating dies to the afore-mentioned pieces of foamed product. After melting their surface, said pieces of foamed product are overcharged into dies for compression molding 9 while the pieces retain thermal melting and adhesive property, and then are compressed at a compression rate of more than 1/2. After this step, they are cooled. Thus it is made possible to obtain a low-density foamed product with high molding and working properties.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cross-linked polyolefin foam molded article, and more particularly to a method for molding a cross-linked polyolefin foam having an extremely low density that can be molded into various shapes. .

Crosslinked polyolefin foams are widely used in various applications such as cushioning materials and heat insulating materials due to their excellent physical properties.

According to the conventional method, a crosslinked polyolefin foam that has been foamed and molded into a block or sheet shape is subjected to secondary processing by cutting, cutting, etc. into a molded product of desired size and shape, and then used for the various purposes mentioned above. It was served to However, with this method, there is a problem in that it is not possible to obtain a product with a complicated shape, and a large amount of processing waste is generated.

Recently, various polyolefin bead molding methods using volatile solvent-based blowing agents have been proposed as methods for manufacturing polyolefin foam molded articles, but none of these methods It is also difficult to impregnate the center of the polyolefin particles with a solvent-based blowing agent.

Even if it were possible to impregnate the center.

There is a risk of ignition because the beads cannot be stored due to escape of the volatile solvent-based blowing agent and because some volatile solvent-based blowing agent remains in the pre-expanded beads or molded product. There are various drawbacks, such as storage problems.

On the other hand, due to the waste pollution and resource saving aspects of plastic foams, the above-mentioned polyolefin foam scraps, that is, scraps generated during the manufacturing and processing processes of the foams, can be used to produce molded products. Attempts are being made to manufacture However, when utilizing such foam waste.

First, in terms of materials, there is a limit to the supply of materials, and it is generally difficult to randomly mix and use foam scraps with various degrees of crosslinking and expansion ratios. There is a problem with the need to collect and manage foam debris. In addition, in K, when molding a molded product from one foam scrap, it is necessary to first cut the foam scrap to produce small pieces of foam, but it is not always possible to cut the foam scrap into small pieces of a fixed size. It is extremely difficult. As a result, when such small pieces of foam are molded by heating and compression, the pattern of the product based on the grain boundaries of each small piece of foam is not constant, and the degree of filling is not stable, resulting in a homogeneous molded product. There is a problem that it is difficult to understand.

In addition to these problems in manufacturing and quality of foam pieces, various methods have been proposed for molding them, but they have the following problems.

For example, recently, it has been reported that microscopic polyolefin foam particles are filled into a mold with a large number of heated steam permeation holes, heated by introducing heated steam into the mold, and the foam particles are fused and molded. A method is proposed. However, according to this method, the part of the mold located in the heated steam permeation hole produces a patch that looks like a whisker, and it takes extra effort to remove it after the product is released from the mold. There is a problem in that the removal marks remain on the product surface and spoil the product appearance. Also,
Pressure molding at a high compression rate produces better mechanical properties of the product, but in this method, when foam particles are filled into a mold at a high compression rate, heating by heated steam is not uniform. Therefore, there is a drawback that intergranular fusion is insufficient and cracking or peeling between grains occurs when bending stress is applied.

Furthermore, when heated steam is used as a heat medium...
When the foam particles are heated and melted, steam penetrates into the particles and condenses, causing shrinkage of the particles and making it impossible to obtain the desired molding.

As an improvement to the above method, polyolefins are used.

It is conceivable to fill the foam particles into a pressurized mold and to heat the pressurized mold externally. However, according to this method,
The heating is not uniformly transmitted to the particles inside the mold, that is, it is difficult to uniformly melt the particles to the surface inside the mold, and this is especially true for molded products that have a certain thickness. However, it also suffers from the problems of intergranular cracking and peeling mentioned above. Conversely, if the internal particles are heated sufficiently, the particles close to the mold wall will melt and shrink.

The present invention has been made in view of the above circumstances, and is intended to solve all the problems in manufacturing and quality of small pieces of polyolefin foam, as well as in the molding process.

That is, 1. The method for producing a molded article of crosslinked polyolefin foam according to the present invention includes producing polyolefin foam pieces by extruding a foamable polyolefin resin composition containing a chemical blowing agent into substantially unfoamed strands. After shaping and then crosslinking and foaming, the resulting foamed metrand is shredded, making it possible to produce homogeneous polyolefin foam pieces of a certain size in a series of steps, and in this way. The production of a molded article from the polyolefin foam pieces produced in the above manner is carried out by filling the foam pieces shredded as described above into a heating mold with air permeability, and introducing hot air into the heating mold. After the foam pieces are heated to melt their surfaces, they are overfilled into a compression mold while the foam pieces remain heat-sealable.

This is done by compressing to a compression ratio of μ or more and then cooling, resulting in a good product appearance and stable filling degree.

In addition, crosslinked polyolefin foam moldings of desired shapes with excellent chemical and mechanical properties can be easily and efficiently molded without causing intergranular cracks or scratches under bending stress. This made it possible.

To explain the present invention in detail, a foamable resin composition obtained by kneading a mixture of a polyolefin resin, a chemical blowing agent, or an organic peroxide, and further a foaming aid as needed. The article is first extruded into a substantially unfoamed strand. That practice is a roll.

It is preferable to use a common mixing machine such as a kneader at a temperature of 70 to 130°C depending on the type of resin.

Further, a normal extruder can be used for extrusion molding, but if possible, an extrusion mode having a rapid compression type screw is preferable.

Furthermore, if the polyolefin resin is in powder form and can be easily and uniformly mixed with other additives, the mixture can be directly fed to an extruder, kneaded in the extruder, and then extruded. May be molded. Usually, the extrusion temperature is 80-140'08 degrees, which is the set temperature of the extruder.

The shape of the extruded strand may have any arbitrary cross-sectional shape, such as circular, elliptical, or polygonal.

In the present invention, the substantially unfoamed strand thus obtained by extrusion molding is then crosslinked and foamed according to a known method. By the way.

The term "substantially non-foamed strand" includes not only strands that are not foamed at all but also strands with a foaming ratio of 2 times or less. This is because the foaming ratio of this level is due to the initial decomposition of the foaming agent and is far from the concept of one foaming.

Various crosslinking and foaming methods have been known in the past, but any of these methods can be used in the present invention and is not limited to the 1% method. For example, if the foamable polyolefin resin composition does not contain a crosslinking agent, the extruded strand is irradiated with an electron beam to uniformly crosslink it, and then heated to decompose the chemical blowing agent and foam. method can be adopted. in this case.

It is preferable that the steps of extrusion molding of the strand, electron beam irradiation (crosslinking), and heating (foaming) be performed continuously from the viewpoint of productivity etc. When the foamable polyolefin resin composition contains a crosslinking agent can be crosslinked and foamed by heating the extruded strand.

When focusing on crosslinking of a foamable resin composition.

■ A method of crosslinking at the same time as foaming (depending on the heating temperature during foaming), ■ A method of crosslinking or pre-crosslinking according to the extrusion-like heating temperature when extruding into strands, ■ A two-step heating process after extrusion molding. There is a method 1 in which the extruded strand is crosslinked or precrosslinked by preheating the extruded strand before heating and foaming. When crosslinking is performed during extrusion molding into strands (method ① above).

If the crosslinking progresses too much, the resin composition will solidify in the extruder, and extrusion molding may not be carried out well. Therefore, the gel fraction is usually set to 140% or less, preferably 30%. It is desirable to suppress the crosslinking to a level below, and when crosslinking is performed beyond this level, it is desirable to use the above-mentioned method 02 in combination.

In addition, when crosslinking the strands by preheating before foaming (method ① above), by heating the strands for several minutes or more at a temperature below the decomposition temperature of the foaming agent, for example, 120 to 140°C. can be done. moreover,
When crosslinking is carried out at the same time as heating during foaming (in method
Selection of types and combinations of crosslinking agents.

Furthermore, it is necessary to accurately control the amounts added. It is preferable that the gel fraction has increased to at least 1□% or more before the strands start foaming.

By any of the methods described above, the extruded strand is heated to a temperature equal to or higher than the decomposition temperature of the chemical foaming agent to foam it.

In this case, it is desirable to heat and foam the extruded strand by passing the continuously extruded strand through a heating zone. (It is desirable to carry out the electron beam irradiation step and the preheating step continuously.) However, there is no problem even if there is an unlucky heating and foaming. However, from the viewpoint of productivity and operability, a continuous process is preferable. Heating of the extruded strands can be accomplished by any heating means, such as an infrared heater, a heating bath using hot air, steam, a salt bath (e.g., one consisting of 50% potassium nitrate, 7 g of sodium nitrate, and 7 g of sodium chloride). Can be adopted.The heating temperature depends on the type of chemical blowing agent.

Although it varies depending on whether a foaming aid is added or not, from the viewpoint of ease of controlling the amount of foaming agent decomposed and the shape of the cells in the foamed strands and their appearance, the temperature is between 150 and 200°C.
A range of is preferred.

Next, the strand foamed as described above is cut into small pieces using a cutter or the like. The size of the foam pieces is 1
Approximately 5 to 50 m is appropriate depending on the diameter of the foamed strand. If the size of the small pieces is too small, shrinkage will be large in the next heating step, while if the size is 50 mg or more, voids are likely to occur between the particles during compression molding.

Next, as shown in FIG. 1, the foam pieces 1 obtained as described above are filled into a heating mold 2 having air permeability, and a heater 3 and a blower 4 are connected to the mold 2. Then, the air heated by the heater 3 is introduced into the heating mold 2 by the blower 4, and heated for a predetermined period of time until only the surface of the foam piece is melted. The heating time varies slightly depending on the type of resin and the size of the foam pieces, so it is best to set the optimal heating time (hot air temperature) for each in advance.
Since only the surface of the foam piece is heated and melted,
It is preferable to carry out the process at high temperature for a short time. If heated too much, the inside of the foam pieces will melt and the foam pieces will shrink during heating, but a slight amount of shrinkage will not impede compression molding. Further, in the case of a foam having a high expansion ratio, the small pieces of the foam may fuse together in this heating step, but this does not cause any trouble.

It is better to use a heating mold 2 that has a sealed side wall and has breathable support plates 5 removably provided on the upper and lower surfaces of the foam small piece storage section. This is advantageous in that it can be used as a guide cylinder for the press plate 8 (or upper die) of the compression press in the next compression molding process.

As the support plate 5, a wire mesh or a metal plate with a large number of small holes is preferably used, but other breathable support plates may be used.

As a heating method, it is preferable to introduce hot air from the bottom of the heating mold 2 and let it come out from the top. By this method, a stirring effect is exerted as well as a heating effect on the foam pieces, and uniform heating can be performed. Further, since there is no need to use a stirrer or the like, there is no problem that a small piece of foam whose one surface is heated and melted is fused to the stirrer.

Next, the foam pieces whose surfaces have been heated and melted in this way are overfilled into a compression mold while retaining their heat-adhesive properties, and
Subjected to compression molding. In this case, the foam pieces may be filled into the compression mold by any means, but preferably as shown in FIG. 2. That is, the heating mold 2 that has completed the heating process is moved onto the compression molding mold 9 with the foam pieces stored therein, and the upper and lower breathable support plates 5 are slid aside and the foam pieces 9 are pulled out. The small piece is dropped into the cavity of the compression molding mold 9, and the press cylinder 6
Compression molding is performed using a press plate 8 (or an upper mold) fixed to a rod 7 of. By carrying out this process in a short time, the foam pieces 2 are thermally fused into layers and the desired molding is achieved.

Note that in the above compression molding process, the compression ratio of one foam piece should be at least 50%. If this compression ratio is smaller than W, there is a problem that the intergranular fusion of the foam pieces is insufficient, and cracking or peeling between the particles occurs when bending stress is applied to the obtained product. This is remarkable in the case of highly cross-linked polyolefin foams with a gel fraction of 60 to 95 inches or polyolefin foams mainly composed of polyolefin foams, and in the case of such foams, the above-mentioned compressibility difference The numbers are even critical. For example, to set the compression ratio to 1.

The foam pieces may be overfilled to a volume of 300 times the volume of the compression mold when compressed.

Since the foam pieces compressed in this way have a recirculating force, the top cover is first fixed to the compression mold 9 with pins (not shown), then taken out of the compression press and showered with cold water. After continuing cooling until the heat-sealed portion of the foam piece solidifies, the product is taken out. Cooling can also be achieved by providing coolant channels in or on the wall of the compression mold.

In this way, a compression molded product with poor intergranular fusion can be obtained. In this case, a molded product of any shape can be obtained depending on the cavity shape of the compression mold.

Although the method of the present invention is particularly suitable for polyolefin foams with a high degree of crosslinking, it is not inapplicable to polyolefin foams with a low degree of crosslinking. A wide range of magnification materials can be used. Furthermore, even if materials with the same magnification are used, molded products with any magnification can be obtained depending on the compression ratio.

Polyolefin resins used in the method of the present invention include polyethylene produced by high, medium, and low pressure methods, poly-1,2-butadiene, ethylene-propylene copolymer, ethylene-butene copolymer, and ethylene-acetic acid. Vinyl copolymers, copolymers of ethylene and methyl, ethyl, globy, and butyl acrylates or methacrylates, or chlorinated products or mixtures thereof, or polypropylene having an atactic or isotactic structure with these. There are also mixtures with

The crosslinking agent as used in the present invention is one having a decomposition temperature at least higher than the flow initiation temperature of the polyolefin in the polyolefin.

Organic peroxides that are radical generators that are decomposed by heating to generate free radicals and create cross-links between or within the molecules 1 For example, dicumyl peroxide, 1,1-ditertiary-butyl peroxide −
3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-ditertiary-butylperoxyhexane, 2,5-dimethyl-2,5-ditertiary-butylperoxyhexane, α,α-ditertiary Examples include butylperoxydiinglobylbenzene, tertiary-butylperoxyketone, and tertiary-butylperoxybenzoate, but the most suitable organic peroxide must be selected depending on the type of polyolefin used.

The blowing agent that can be used in the present invention is a chemical blowing agent having a decomposition temperature higher than the melting temperature of the polyolefin, such as azo dicarbonamide of an azo compound, barium azodicarboxylate, etc.; Nitrosopentamethylenetetramine, trinitrosotrimethyltriamine, etc.; hydrazide compounds such as p, p'-oxybisbenzenesulfonyl hydrazide, and other irises sulfonyl semicarbazide compounds;

PF-oxybisbenzenesulfonyl semicarbazine:
-, toluenesulfonyl semicarbazide, etc. The amount of the foaming agent added may be selected depending on the foaming ratio.

In the present invention, a foaming aid can be added depending on the type of foaming agent. Examples of foaming aids include compounds that produce urea, metal oxides such as zinc oxide and lead oxide, compounds whose main components are salicylic acid and stearic acid, ie, higher fatty acids or metal compounds of higher fatty acids.

In addition, in the present invention, for the purpose of improving the physical properties of the composition used or reducing the price, compounding agents (fillers) that do not have a significant adverse effect on crosslinking, such as carbon black, zinc oxide, titanium oxide, calcium oxide, Metal oxides such as magnesium oxide and silicon oxide, and magnesium carbonate.

Carbonates such as calcium carbonate, fibrous materials such as pulp, various dyes, pigments, fluorescent substances, and other rubber compounding agents for room use may be added as necessary.

As described above, the method of the present invention involves producing small pieces of foam by crosslinking, foaming, and cutting extruded strands, and subjecting the pieces to heating and compression molding. As a result, when the foam pieces are heated and compression molded, a molded article having a stable filling degree and a constant pattern appearance can be obtained. In addition, the method of the present invention uses heat fusion instead of a binder to bond the small pieces of foam together, so the process is simple.The heating process and compression molding process are separated, and the Since the compression molding process is carried out at a high compression rate, each small piece of foam can be heated evenly and in a short time, and it can produce molded products that are uniform and have excellent mechanical properties without cracking or peeling between grains due to bending stress. obtained in a short time.

Furthermore, among polyolefin foams, those using an organic blowing agent as a blowing agent generate a bad odor due to by-products of the organic blowing agent, but in the method of the present invention, the foam is treated with hot air in the heating step.

The foul-smelling dregs in the cells of the foam pieces are pushed out 1
Since the process is forcibly deodorized, the resulting molded product has the advantage of being odorless. In addition, due to hot air heating, the penetration of steam into the foam pieces in the case of heating with conventional heated steam,
There is also no problem of shrinkage of the foam pieces due to condensation.

The uses of the molded product obtained by the method of the present invention include:
Can be used as insulation material, joint material, etc.

Hereinafter, the method of the present invention will be specifically explained with reference to Examples.

100 parts by weight of low-density polyethylene (manufactured by Mitsubishi Yuka Co., Ltd., trade name Yucalon LK-30i).

20 parts by weight of azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name Vinifol ACΦ508), 1 part by weight of zinc oxide
parts by weight, and 1 part by weight of dicumyl peroxide were added and thoroughly kneaded with a roll. The roll surface temperature during this kneading was maintained at 100°C.

The obtained mixed wire material was extruded into a strand shape having a diameter of 2 to 4 m using an extruder heated to a die temperature of IIQ'Q. The gel fraction of the polyethylene in the obtained strand was Oq6, and there was no foaming at all.

The resulting unfoamed strand was then continuously heated at 170
When heated by immersing it in a salt bath heated to .degree. C., it foamed to a foaming ratio of 30 times about 10 minutes after the start of heating. This foam strand had a diameter of approximately 15W.

The foamed strand thus obtained was cut to a length of about 15 mK to form a 300 x 300 x 3 piece as shown in Figure 6.
00 m size heating mold (upper and lower support plates are wire mesh) K
Injected to a height of 200 ms, and then ls by a blower.
The heated mold was heated for 3 minutes by blowing hot air from the bottom of the heating mold upward. Then, 3 as shown in Figure 2.
Move the heated mold onto a compression mold of 00 x 300 x 50 tw, remove the upper and lower support plates, and place the heated foam material (4.0 OS of the volume of the compression mold).
The product was dropped into a T-compression molding mold, immediately compression-molded using a compression press to the above-mentioned mold volume, and cooled by showering with cold water.

After cooling, the product is removed from the compression mold.

The apparent density is 0. It was a plate-shaped molded product with a rating of 'l 4 f/cr& and excellent inter-grain fusion.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an example of the heating step of the method of the present invention, and FIG. 2 is a schematic explanatory diagram showing an example of the compression molding process of the present invention. f is a foam piece; 2 is a heating mold; 3 is a heater; 4 is a blower; 15 is a permeable support plate; 9 is a compression mold. Applicant Sanwa Kako Co., Ltd. Agent Patent Attorney Masaaki Yonehara Patent Attorney Tadashi Hamamoto

Claims (1)

[Claims] A foamable polyolefin resin composition containing a chemical blowing agent is extruded into a substantially non-foamed strand, and then crosslinked and foamed according to a conventional method. The cut pieces of polyolefin foam are filled into an air-permeable heating mold, and hot air is introduced into the heating mold to heat the foam pieces and melt their surfaces. 1. A method for producing a crosslinked polyolefin foam molded product, which comprises overfilling a compression mold while maintaining fusion properties, compressing to a compression ratio of A or more, and then cooling.