JPH02240145A - Preparation of polyolefin resin foam - Google Patents

Abstract

PURPOSE:To obtain a polyolefin resin foam with uniform and fine closed cells and a smooth and beautiful surface by mixing a polyolefin resin and a copolymer resin prepd. by graft-polymeizing a polyorganosiloxane onto a polyolefin resin and extrusion-molding the product together with a foaming agent. CONSTITUTION:A resin compsn. wherein the loading of silicone is 0.1-5 pts.wt. based on the whole resin is prepd. by mixing a polyolefin resin (A) and a copolymer resin (B) prepd. by graft-polymerizing a polyorganosiloxane onto a polyolefin resin. Then, this resin compsn. is fed in an extruder and an easily volatile foaming agent is additionally mixed and melted therein together. The mixture is extruded from the apex of the extruder to form a foam. As the polyolefin resin as the component B, polyethylene, ethylene-vinyl acetate copolymer resin, etc., are especially pref. As the polyolefin resin as the component A, low-density polyethylene and polypropylene are especially pref. IF necessary, an inorg. fine powder and other additives can be compounded in said resin compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing a polyolefin resin foam such as polyethylene or polypropylene, particularly a polyolefin resin foam having uniform fine closed cells and a smooth and beautiful surface.

(Prior art) Polyolefin resin foams have been used in a variety of fields in recent years, but fine cells are generally preferred, and uniform fine cells are particularly preferred for cushioning materials, insulation materials, decorative materials, etc. There is a strong demand for foams having the following properties. The reasons for this are: first, as a cushioning material, the finer the bubbles, the more flexible and cushioning properties; as a heat insulating material, the finer the bubbles, the lower the thermal conductivity and superior insulation performance; As for the material, the finer the cells, the more beautiful the appearance of the surface and cut surface.

As a method for continuously obtaining a polyolefin resin foam having uniform and fine cells, the polyolefin resin is mixed with peroxide or irradiated with an electron beam to cause a crosslinking reaction in the polyolefin resin, and then foamed. There is a cross-linking foaming method that allows Although this method does yield a foam having fine cells, it has the drawbacks of a complicated foaming process and high equipment costs.

Separately, as a method for obtaining everything from thin sheets to thick plates using a simple process, polyolefin resin and a foaming agent are melt-mixed in an extruder to form a fluid gel, and then heated in a low pressure region. There is a so-called extrusion foaming method that involves extrusion and foaming. However, although this method can efficiently obtain a foam, it has the disadvantage that the cells are larger in size than those obtained by crosslinking and foaming. Furthermore, the foam density used as heavy packaging material is 0.05g/cn? In relatively low-magnification materials such as polyolefin foams mentioned above, the amount of blowing agent is reduced, so the disadvantage is that the amount of friction heat generated in the extruder is large, which tends to cause poor foaming and a decrease in the closed cell ratio. It had

In order to solve this problem, using a polyolefin resin with a higher melt index has the effect of preventing frictional heat, but it also causes roughening of the cells in the produced foam and lacks the strength of the foam, which is a fatal drawback as a heavy packaging material. Polyolefins with a high melt index cannot be used because this will result in .

In addition, in order to solve the above problems, a method of uniformly making the bubbles finer by using silicone oil or modified polysiloxane oil in polyolefin resin was disclosed in JP-A-62-89.
No. 738, JP-A-62-8974 No. 1, JP-A-62-
No. 285930 and the like. However, when these silicone oils or modified siloxane oils are used, they tend to have an effect that prevents crosstalk between the olefin resin and the blowing agent (lower aliphatic hydrocarbon or halogenated hydrocarbon), especially in the extrusion foaming method. The drawback was that stable continuous production was difficult.

In addition, when the manufactured foam is used as a packaging material, silicone oil or modified polysiloxane oil, etc. that bleed onto the surface of the foam migrates to the packaged product, causing cloudiness and significantly losing its value, which is fatal as a packaging material. This brings about problems such as defects, decreased thermal adhesion, and decreased surface printability.

(Problems to be Solved by the Invention) In view of the current situation, the present inventors have developed a foam with a high closed cell ratio that has uniformly fine cells, and which is suitable for packaging when used as a packaging material. As a result of intensive study on a method for stable and continuous production of polyolefin foam that does not cause problems such as cloudiness in the products to be manufactured, we formulated a copolymer obtained by graft polymerizing polyorganosiloshikin to polyolefin resin and polyolefin resin. After adding inorganic fine powder and feeding it to an extruder, mixing and blending a blowing agent with it,
By extruding from the tip of the extruder, we have completed the present invention that satisfies the above-mentioned characteristics.

(Means for Solving the Problems) According to the present invention, a polyolefin resin and a copolymer resin obtained by graft polymerizing polyorganosiloxane to the polyolefin resin are mixed, and the silicone content in the total resin is 0.1. A resin composition of ~5 parts by weight, preferably 0.2 to 2 parts by weight is prepared, 0.1 to 2 parts by weight of inorganic fine powder is added, the resin composition is fed to an extruder, and foamed. An object of the present invention is to provide a method for producing a polyolefin resin foam, which comprises mixing and blending easily volatile hydrocarbons or halogenated hydrocarbons as agents, and then extruding the foam from the tip of an extruder to obtain a foam.

In the present invention, a polyolefin copolymer resin obtained by graft polymerization of polyorganosiloxane is mixed with a polyolefin resin, an inorganic powder is added thereto, the mixture is fed to an extruder, and a blowing agent is mixed and blended with the mixture. By adopting the method of obtaining a foam by extrusion, a polyolefin foam having uniform, fine closed cells and a smooth and beautiful surface can be industrially advantageously produced.

Next, the present invention will be explained in more detail.

The polyolefin copolymer resin obtained by graft polymerization of polyorganosiloxane used in the present invention has the general formula R, -SiO(R, Sin) n-SiR, (however,
R is a group selected from an alkyl group, a phenyl group, and hydrogen, all R's may be the same group, or some R's may be different groups, and n is 1 to 10,000. is an integer. ) is graft-polymerized onto a polyolefin resin by reactive modification or ionizing radiation. Graft polymerization may be carried out at any ratio, but preferably, a ratio of 30 to 70% by weight in terms of silicone content is efficiently and generally used.

The polyolefin resin to be graft-polymerized with polyorganosiloxane may be a homopolymer of ethylene, brobylene, butene, etc., a copolymer thereof, or a copolymer of these olefin resins with other vinyl monomers. It means a polymer or a mixture of these polymers. In particular, polyethylene, ethylene-vinyl acetate copolymer resin, etc. are preferably used.

Furthermore, the polyolefin copolymer resin obtained by graft polymerizing the polyorganosiloxane needs to be stable at the processing temperature during production.

In the present invention, in particular, when a copolymer obtained by graft polymerizing polyorganosiloxane to polyethylene is used, a polyethylene and polypropylene foam having uniform, fine closed cells, and a beautiful foam with a smooth surface can be obtained. The reason for this is not necessarily clear, but for example, the polyorganosiloxane graft polyolefin copolymer has a surfactant effect, which increases the flexibility of the foamed membrane produced during foaming and reduces its surface tension. It is thought that this is due to the early stabilization of the bubble membrane, which prevents the bubble membrane from being destroyed and suppresses the growth of bubbles due to bubble fusion, thereby making the bubbles smaller. Furthermore, it has been graft-polymerized with polyorganosiloxane. Even when extrusion foaming is performed using easily volatile hydrocarbons or halogenated hydrocarbons as the foaming agent, there is no defective kneading of the resin and the foaming agent, there is no extrusion shift, etc., and it is possible to perform extrusion foaming successfully. It is also believed that when the produced foam is used as a packaging material, it is possible to obtain a foam having uniform fine cells that does not have any adverse effects such as cloudiness due to migration of the polysiloxane into the packaged product.

In the present invention, the copolymer resin obtained by graft polymerizing polyorganosiloxane to a polyolefin resin is mixed with a polyolefin resin, and the silicone content in the total resin is 0.1.
A suitable amount is 5 parts by weight, preferably 0.2 to 2 parts by weight. If it is less than 0.1 ffiX, the copolymer obtained by graft polymerizing polyorganosiloxane to polyolefin resin has frictional heat suppressing effect, melt fracture prevention effect, bubble uniformity and fineness effect, and surface smoothing and beautifying effect. This is because it was fully demonstrated. Also, 5
If it exceeds 1 part by weight, the excess slip effect will cause significant cross-contamination between the resin and the foaming agent, which will easily cause extrusion fluctuations and open cell formation of the foam, which will significantly reduce its productivity and quality, which is undesirable.

The polyolefin resin used in the present invention refers to a homopolymer of ethylene, propylene, butene, etc., a copolymer thereof, or a copolymer mainly composed of these olefin resins with other vinyl monomers. or 2 of these polymers
It means a mixture of more than one species. Especially low density polyethylene,
Polypropylene is preferably used.

Easily volatile blowing agents used in the present invention include, for example, propane, butane, pentane, methyl chloride, methylene chloride,
Trichloromonofluoromethane, dichlorodifluoromethane, monochrome trifluoromethane, dichloromonofluoromethane, monochrome difluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane. Refers to easily volatile hydrocarbons or halogenated hydrocarbons such as monochrome pentafluoroethane, monochlorotetrafluoroethane, tetrafluoroethane, chlorodifluoroethane, etc., and these may be used alone or in combination of two or more as necessary. The above blowing agent can be used as
It is usually added in an amount of J to 30 parts by weight per 100 parts by weight of resin, but especially in polyolefin foams used as heavy packaging materials with a blowing agent amount of 15 parts by weight or less, friction in the extruder is Due to the increase in heat printing, the closed cell ratio of the produced foam tends to decrease and the cells become non-uniform.The mixed resin of the present invention, which is a copolymer obtained by graft polymerizing polyolefin resin with polyorganosiloxane, has a tendency to reduce the frictional heat described above. It is thought that it exhibits a very effective effect due to its prevention effect, bubble equalization effect, etc.

In addition, fine inorganic powders such as talc, calcium carbonate, silica, calcium stearate, etc. are used as cell nucleating agents for foams.
A small amount of organic fine powder such as zinc stearate or higher fatty acid ester of polyhydric alcohol as a dimensional stabilizer may be added.

Furthermore, the composition of the present invention may contain an ultraviolet absorber, an antioxidant, an antistatic agent, a coloring agent, etc. depending on the purpose.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

In addition, the property evaluation of the foam in Table 1 means the following.

Apparent density: Method according to JIS K-6767.

Average cell diameter: ^STM D-3576 #Closed cell ratio: ASTM D-2856 II Cell uniformity: Visually observed with a magnifying glass ◎: Very good O: Good Beauty was evaluated: ◎: Very good ○: Good △: Average X: Bad Example 1 Density 0.921 g/ant, Melt index 0.3
A polyolefin resin (trade name: SP-300, manufactured by Dow Corning, hereinafter referred to as polyolefin resin (trade name: SP-300, manufactured by Dow Corning Co., Ltd.), which is obtained by graft polymerizing 100 parts by weight of low-density polyethylene (hereinafter abbreviated as LDPE) and a reactive polyorganosiloxane with a silicone content of 40% to a polyethylene resin. (referred to as organosiloxane graft polymer) was mixed with 0.3 part by weight of finely powdered talc and fed at a rate of about 8 kg per hour to two extruders each having a diameter of 40 m/m connected together. As a blowing agent, dichlorotetrafluoroethane was press-mixed into the resin from near the tip of the first extruder at a ratio of 10 parts by weight per 10 parts by weight of the resin. A rod die having a resin discharge opening with a diameter of 4 ml/I1 was used as the guide. The resin composition supplied to the first extruder was heated and melt-mixed to a maximum of 200°C, and then the resin temperature was adjusted to about 110°C in the second extruder, and the resin composition was supplied to a die that was also set at 110°C. .

The resin discharged from the nozzle foams and has a diameter of about 15l1/
The rod-shaped foam of Il1 had uniform fine bubbles and had a smooth and beautiful appearance.

The properties of the obtained foams are shown in Table 1 along with their blending ratios. The obtained foam had good cushioning properties.

Examples 2 to 3 The mixing ratio of LDPE and polyorganosiloxane graft polymer in Example 1 The same equipment as in Example 1 was used except that the mixing ratio of blowing agent and resin was changed as shown in Table 1.
It was done by method. However, in Example 3, the polyorganosiloxane graft polymer mixture was found to have a remarkable effect of preventing friction heat, and was able to be stably and continuously manufactured even when the output rate was increased by about 20% from the extruder. This is one of the merits worth mentioning. Further, the obtained foam had uniform fine cells and had an excellent appearance as in Example 1.

Example 4 Density 0.910 instead of LDPE in Example 1,
Polypropylene (hereinafter abbreviated as PP) with a melt index of 0.5 was used, the blowing agent was replaced with butane, and resin + o
The procedure was carried out using the same apparatus and method as in Example 1, except that 5 parts by weight was used for the omm part, the resin temperature was adjusted to 160°C in the second extruder, and the die temperature was set at 160°C. The obtained foam had an excellent appearance and fine bubbles.

Comparative Example 1 In order to clarify the effect of the polyorganosiloxane graft polymer, a test was carried out using the same equipment and method as in Example 1, except that no polyorganosiloxane graft polymer was added. The resin temperature could not be adjusted sufficiently in the extruder No. 2 (this is thought to be due to too much heat generation due to frictional heat), and the resin temperature reached 115° C., making it impossible to obtain a foam that could be measured and evaluated.

Comparative Example 2 In order to clarify the effect of the polyorganosiloxane graft polymer, silicone oil (kinematic viscosity:
The same apparatus and method as in Example 1 were used except that 1 part by weight of 400 cs) was used. The obtained foam had non-uniform cells, was coarse, had a low closed cell ratio, and had a poor appearance.

Comparative Example 3 In order to clarify the effect of the polyorganosiloxane graft polymer, a test was carried out using the same equipment and method as in Example 4, except that no polyorganosiloxane graft polymer was added. The closed cell ratio was low and the appearance was poor.

Furthermore, the properties of the foams obtained in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 to clarify the effects of the present invention.

There are blank spaces below the table (Effects) The method for producing a polyolefin resin foam having uniform microcells according to the present invention has the above-described structure, and includes a polyorganosiloxane copolymer obtained by graft polymerization with a polyolefin resin, especially a polyolefin resin. By adopting a method in which a polyorganosiloxane copolymer graft-polymerized with polyethylene is prepared, supplied to an extruder, mixed with a foaming agent, and then extruded and foamed, the previously known method described above is achieved. It has the following advantages compared to other manufacturing methods, and can be said to be an industrially extremely advantageous manufacturing method.

(1) Stable and continuous production of foam with uniform microcells without causing cross-contact between the resin and foaming agent, and without clouding the packaged product when the produced foam is used as a packaging material. can do.

(2) Density 0.05g/cn? In the production of the polyolefin foam described above, a uniform fine-cell foam having a high closed cell ratio (80% or more) can be obtained without causing a decrease in the closed cell ratio of the manufactured foam due to frictional heat during extrusion. It will be done.

(3) Density 0.05g/cn! In the above continuous production of polyethylene foam, I1l during extrusion! The stable extrusion rate can be improved by about 20% due to the reduction in the actual heat.

Applicant: Sekisui Plastics Co., Ltd.

Claims (1)

[Claims] 1. (A) polyolefin resin and (B) a copolymer resin obtained by graft-polymerizing polyolefin resin with polyorganosiloxane, and the silicone content in the total resin is 0.
．． A resin composition of 1 to 5 parts by weight is prepared, the resin composition is fed to an extruder, and an easily volatile foaming agent is mixed and blended with the resin composition, and then extruded from the tip of the extruder to form a foam. A method for producing a polyolefin resin foam, the method comprising: obtaining a polyolefin resin foam;