JPH0553175B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an ethylene resin open-cell foam composition that has an ethylene resin as a main component and is capable of producing an open-cell foam in a continuous process without post-processing. . (Prior art) Foams made of ethylene resin are currently used in large quantities as insulation materials, packaging materials, cushion materials, etc., but most of them are closed-cell foams that have poor water absorption, breathability, etc. It cannot be used for the required purpose. There is also a conventional method of manufacturing a closed-cell foam using ethylene resin, and then foaming it by heating and expanding it to produce a foam with open cells.
Foams produced by this method "sag" and have no elasticity, making it difficult to break the bubbles uniformly, and the cell diameter becomes coarse.As a result, the foam has a rough texture, poor hand feel, and has a low commercial value. It was low. To solve this problem, Special Publication No. 56-121739,
Japanese Patent Publication No. 60-49657 describes a method of forming closed cells using ethylene resin and then bursting the cells under pressure. The thickness of the resulting foam becomes thin, and even though the cells are made continuous, the cell membranes overlap, resulting in insufficient absorbency and breathability.The product is only in the form of a single plate, making it difficult to use. The problem was that it caused various problems. Furthermore, Special Publication No. 54-63172, Special Publication No. 55-
Publication No. 42100 describes methods for producing open-cell foams made of cross-linked open-cell ethylene resins, but the open-cell foams obtained by these methods all have poor mechanical properties, texture, etc. There was a problem. It is also known that a surfactant is added as a foam stabilizer to make the cells uniform in the foam.
Most surfactants are difficult to mix into ethylene resins or tend to bleed over time, resulting in a problem of lowering the commercial value of foams. (Problems to be Solved by the Invention) As mentioned above, conventional open-cell foams made of ethylene resin tend to "sag";
Either the foam has no elasticity and is difficult to break uniformly, and the cell diameter is coarse, or the process is two-step, and the resulting foam is thin, and even if the cells are continuous, the cell membranes overlap. It had poor absorbency and breathability. The present invention has been made to overcome these conventional drawbacks, and is intended to improve compressive properties, water absorption, weather resistance, and feel in a simple, single step, without the need for a separate step for foam breaking. An object of the present invention is to provide a composition that can produce a continuous ethylene resin foam. (Means for Solving the Problems) That is, the composition for a crosslinked ethylene resin open-cell foam of the present invention contains (a) 100 parts by weight of an ethylene resin (b) a decomposition start temperature (T _DS ) of 120 to 160 A blowing agent whose decomposition completion temperature (T _DP ) is 150 to 210 degrees Celsius and T _DS = melting point of the ethylene resin + 20 to 70 degrees Celsius 1 to 20 parts by weight (c) 1 minute half-life temperature (T _{1 /2} ) Organic peroxide crosslinking agent with a temperature of 140 to 190°C 0.3 to 5 parts by weight (d) α-olefin modified surfactant
It is characterized by consisting of 0.1 to 10 parts by weight and (e) 0.1 to 30 parts by weight of process oil. The ethylene resin (a) used in the present invention is a homopolymer or copolymer containing ethylene as a main component, such as high-pressure polyethylene, low-pressure low-density polyethylene, linear low-density polyethylene (LLDPE). , ethylene-vinyl ester copolymer,
Examples include ethylene-alkyl acrylate copolymers, ethylene-propylene copolymers, ethylene-α-olefin copolymers, and mixtures thereof. In addition, as the blowing agent (b) used in the present invention,
Examples include azobisisobutyronitrile, azodicarbonamide, P-toluenesulfonylhydrazide, dinitropentamethylenetetramine, 4,4'-oxybisbenzenesulfonylhydrazide, and among these, azodicarbonamide is particularly suitable. The blending amount of these blowing agents is
The range of 1 to 20 parts by weight per 100 parts by weight is appropriate, but the amount to be used is appropriately determined within this range based on the desired expansion ratio and the gas generation amount of the blowing agent used. Further, the blowing agent used in the present invention has a decomposition start temperature (T _DS ) of 120 to 160°C and a decomposition completion temperature (T _DP ) of 150 to 210°C. If the decomposition start temperature (T _DS ) is lower than 120°C, the cells will become coarse, whereas if it is higher than 160°C, crosslinking will tend to occur first, resulting in a closed-cell foam. Since it is often difficult to satisfy the above decomposition temperature conditions with a single product, decomposition accelerators such as urea compounds, zinc oxide, zinc compounds, lead compounds, etc.
It is desirable to add ~10 parts by weight to adjust the decomposition start temperature (T _DS ) and completion temperature (T _DP ) of the blowing agent, respectively. Furthermore, if necessary, it is also possible to use two or three types in combination, and this is rather preferable. The decomposition start temperature (T _DS ) and decomposition completion temperature (T _DP ) are measured using a differential thermal balance at a heating rate of 10°C/min, and are measured at each point on the differential thermal analysis curve (DTA) shown in the figure. means. The blowing agent or the combination of the blowing agent and the decomposition accelerator is adjusted to have the following relationship depending on the ethylene resin used. Decomposition start temperature (T _DS ) = (melting point of the ethylene resin used) + 20 to 70°C If the decomposition start temperature (T _DS ) is lower than the melting point of the ethylene resin used + 20°C, the viscosity of the resin will not be able to follow the foaming. However, if the melting point of the ethylene resin exceeds +70°C, the resin will flow and bubbles will not be generated properly. The organic peroxide crosslinking agent (c) used in the present invention has a 1-minute half-life temperature (T _1/2 ) of 140°C to
A temperature range of 190℃ is used. If the one-minute half-life temperature (T _1/2 ) is lower than 140°C, crosslinking will occur first and the foam will become closed cells, and if it is higher than 190°C, the degree of crosslinking will be insufficient and the foam will become coarse cells. Although coarse bubbles can be prevented by adding a larger amount of organic peroxide, it is uneconomical to add such a large amount of organic peroxide. Examples of the organic peroxide crosslinking agent used in the present invention include the following. Note that the numbers in parentheses are the 1-minute half-life temperature. 1,1-bis(t-butylperoxy)cyclohexane (154), t-butylperoxymaleic acid (167), t-butylperoxylaurate (165), t-butylperoxy-3,5,5 -Trimethylhexane (165), cyclohexane peroxide (174), t-butylperoxyallyl carbonate (172), t-butylperoxyisopropyl carbonate (158), 2,5-dimethyl-
2,5-di(benzoylperoxy)hexane (162), 2,2-bis(t-butylperoxy)
Octane (159), t-butylperoxyacetate (160), 2,2-bis(t-butylperoxy)butane (160.5), t-butylperoxybenzoate (170), n-butyl-4,4- screw (t
-butyl peroxyverate (166), di-t-
Butyl diperoxyisophthalate (168), methyl ethyl ketone peroxide (171), dicumyl peroxide (171), 2,5-dimethyl-2,
5-di(t-butylperoxy)hexane (179), α,α'-bis(t-butylperoxy-
m-isopropyl)benzene (179), t-butylcumyl peroxide (176), di-t-butyl peroxide (186) These organic peroxide crosslinking agents are used in amounts of 0.3 to 100 parts by weight of ethylene resin. It is necessary to mix within the range of 5 parts by weight. If it exceeds 5 parts by weight, no improvement in crosslinking efficiency can be expected, and if it is less than 0.3 parts by weight, a sufficient degree of crosslinking cannot be obtained. In addition, the organic peroxide crosslinking agent used in the present invention is
The foaming agent is selected so that the difference between the decomposition completion temperature (T _DP ) and the one-minute half-life temperature (T _1/2 ) (T _DP - T _1/2 ) is close to 0°C, or the foaming agent decomposition accelerator is selected. It is preferable to select As described above, in the present invention, the decomposition start temperature (T _DS ), the decomposition completion temperature (T _DP ) of the blowing agent, and the 1-minute half-life temperature (T _1/2 ) of the crosslinking organic peroxide are balanced, and The bubbles generated by adding surfactant and process oil are kept fine and broken. The α-olefin-modified surfactant (d) used in the present invention is suitably one modified with an α-olefin having 4 to 16 carbon atoms, such as α-olefin-modified silicone. . These α-olefin-modified surfactants have good compatibility with ethylene-based resins and can be smoothly kneaded into ethylene-based resins, so that the effect as a foam stabilizer can be stably obtained. These α-olefin-modified surfactants need to be blended in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the ethylene resin. If the amount is less than 0.1 part by weight, the effect will not be sufficiently obtained, and if it exceeds 10 parts by weight, the effect will not increase any further and it will be uneconomical, and problems such as bleeding will occur more easily. Furthermore, the process oil (e) used in the present invention includes naphthenic oils used for rubber, adhesives, etc., but especially the aniline point is 100°C.
Below, the viscosity at 40℃ is 150cSt or less, and the PS value is
Stable effects can be obtained when using naphthenic oil of 7.5 to 8.5. The blending amount of these process oils needs to be in the range of 0.1 to 30 parts by weight per 100 parts by weight of the ethylene resin. The optimal blending amount varies depending on the type of ethylene resin used, but if it is less than 0.1 part by weight, the surfactant effect and plasticizer effect will not be sufficient.
If the amount exceeds 30 parts by weight, bleeding will occur. Furthermore, the composition of the present invention may optionally contain antioxidants, pigments, ultraviolet stabilizers, inorganic fillers, flame retardants,
Other additives or other resins can be blended. The composition of the present invention is foamed by heating at a temperature higher than the temperature necessary for foaming and crosslinking, specifically between 150 and 250°C. This heating is preferably carried out rapidly up to the foaming start temperature, and then slowly heated after the foaming start temperature. Any heating method can be used, such as hot air, infrared heaters, and high frequency heating. In the foam composition of the present invention, the cell structure is fixed by cooling after foaming. The cooling temperature at this time is preferably 50°C or less. Note that, if necessary, in order to promote crosslinking, after completion of foaming, it is possible to heat and ripen at a temperature and time that does not destroy the cell structure, and then cool it. When the foam composition of the present invention is foamed,
It can be foamed by a one-step heating method, and does not require a step of breaking the foam by applying pressure. For this reason, not only a batch-type manufacturing method but also an endless-type manufacturing method is possible. Further, the composition before foaming can take various forms such as pellet powder, film, and sheet form. Therefore, pellet-like, powder-like, film-like,
Open-cell foams can be obtained from the composition of the invention in sheet form. Furthermore, online foam molding in which these are made continuous is also possible. For example, a thin foam sheet can be produced by forming the composition of the present invention into a thin film and passing it through a heating furnace, and a thick sheet can be produced by passing pellets spread in a single layer through a heating furnace. can. Furthermore, it is also possible to improve productivity compared to the conventional method of once producing a bulk foam and slicing it.
Of course, if an extruder, kneader, or other mixing method is used in the step of obtaining these compositions, the temperature must be such that the crosslinking agent and foaming agent are not substantially decomposed. The foam obtained in this way is pure white, has excellent breathability, water absorption, and weather resistance, and is more flexible than closed cell foam, and has a superior texture and feel, and can be used for cushions, pillows, mats, winter clothing, etc. carpet lining,
Suitable as a ball, toy, supporter or cushioning material, heat insulating material, sound absorbing material or material. (Example) Next, an example will be described. Example 1 Melt index 15.0, vinyl acetate content 14%
Ethylene vinyl acetate copolymer (melting point 89℃) 100
Parts by weight, 8 parts by weight of azodicarbonamide, 1.5 parts by weight of dicumyl peroxide (1 minute half-life temperature 171°C), 3 parts by weight of urea, 2 parts by weight of zinc oxide, α-olefin modified silicone as α-olefin modified surfactant 2 parts by weight and 10 parts by weight of process oil were kneaded for 5 minutes on a mixing roll with a surface temperature of 100°C. Note that the decomposition start temperature (T _DS ) of azodicarbonamide in this kneaded material is 140°C, and the decomposition completion temperature (T _DP ) is 160°C. Next, this kneaded product was molded into a 1 mm thick sheet using a press molding machine at 100°C. This sheet was placed on a Teflon sheet and heated in a hot air oven at 180°C for about 4 minutes, resulting in uniform foaming. This foam was cooled at room temperature for 10 minutes to obtain a pure white open-cell foam that was soft to the touch. The properties of this foam are shown in Table 1.

[Table] Example 2 The sheet molded by the molding machine in Example 1 was placed on a Teflon sheet, placed in a cooking microwave oven (manufactured by Matsushita Electric Industrial Co., Ltd.) preheated to 180°C, and heated with high frequency, and the sheet was uniformly heated in 2 minutes. It foamed. When this was taken out and allowed to cool at room temperature, a foam similar to the foam obtained in Example 1 was obtained. Example 3 100 parts by weight of low density polyethylene (melting point 114°C) with a melt index of 20 and a density of 0.916 g/cm ³ , 8 parts by weight of azodicarbonamide, α,α′-bis(t-
Butylperoxy-m-isopropyl)benzene (1 minute half-life temperature 176°C) 2.0 parts by weight, urea 3 parts by weight,
2 parts by weight of zinc oxide, 2 parts by weight of α-olefin modified silicone as an α-olefin modified surfactant, and 5 parts by weight of process oil at a surface temperature of 110
The mixture was kneaded for 5 minutes using a mixing roll at ℃. The decomposition start temperature (T _DS ) of azodicarbonamide in this kneaded material is 140℃, and the decomposition completion temperature (T _DP ) is 160℃.
It is ℃. Next, this kneaded material was heated to 1.0 in a press molding machine at 115℃.
It was made into a sheet with a thickness of mm. When this sheet was placed on a Teflon sheet and heated in a hot air oven at 180°C, it foamed uniformly in 5 minutes. When this was taken out and cooled at room temperature for 10 minutes, a pure white foam having open cells was obtained. The properties of this foam are shown in Table 2.

[Table] Comparative Example 1 100 parts by weight of the ethylene vinyl acetate copolymer used in Example 1, 8 parts by weight of azodicarbonamide,
1.5 parts by weight of dicumyl peroxide, 2 parts by weight of α-olefin modified silicone as an α-olefin modified surfactant, and 10 parts by weight of process oil were kneaded using a mixing roll with a surface temperature of 100°C. Note that the decomposition start temperature (T _DS ) of azodicarbonamide in this kneaded material is 198°C, and the decomposition completion temperature (T _DP ) is 214°C. Next, add this kneaded material to 100%
It was molded into a sheet with a thickness of 1 mm using a press molding machine at ℃. Place this sheet on a Teflon sheet at 180°C.
It was placed in a hot air oven at ℃ and heated for 10 minutes, but no foaming was observed. On the other hand, when a similar press sheet was heated in a hot air oven at 230°C, it foamed uniformly but three-dimensionally, resulting in a closed-cell foam. Comparative Example 2 The press sheets obtained in Examples 1 and 2 were heated to 250°C.
When the foam was heated for 2 minutes in a hot-air oven, the foam contracted significantly during cooling and became a foam with coarse bubbles. Comparative Example 3 A foam was produced in the same manner as in Comparative Example 1 using low-density polyethylene (melting point 114°C) with a melt index of 20 and a density of 0.916 instead of the ethylene-vinyl acetate copolymer of Comparative Example 1. It became a foam. Comparative Example 4 A composition obtained by removing the α-olefin-modified surfactant and process oil from the composition of Example 1 was foamed in the same manner as in Example 1. The internal cells became coarse, non-uniform open cell foam. Comparative Example 5 A composition obtained by removing the process oil from the composition of Example 1 was prepared in the same manner as in Example 1 and foamed to obtain a white foam in about 4 minutes. The apparent specific gravity of this foam was 0.07 g/cm ³ and the open cell ratio was 93%, which was close to a satisfactory open cell foam. However, as shown in Table 3, the foam of Example 1 In comparison, it was inferior in feel, open cell ratio, and flexibility.

[Table] (Effects of the Invention) As is clear from the above examples, the foam composition of the present invention can be used in a single step, that is, without using a separate step for foam breaking. Open-cell foams can be produced that have extremely fine and uniform foam structures and have excellent compression properties, water absorption, weather resistance, and feel.

[Brief explanation of the drawing]

The drawing is a differential thermal analysis curve (DTA) shown to explain the decomposition start temperature (T _DS ) and decomposition completion temperature (T _DP ) of the blowing agent.

Claims (1)

[Claims] 1 (a) 100 parts by weight of ethylene resin (b) Decomposition start temperature (T _DS ) is 120 to 160°C, decomposition completion temperature (T _DP ) is 150 to 210°C, and T _DS = A blowing agent that satisfies the melting point of the ethylene resin +20 to 70°C (c) 1 to 20 parts by weight (c) An organic peroxide crosslinking agent with a 1-minute half-life temperature (T _1/2 ) of 140 to 190°C 0.3 to 5 parts by weight (d) α-olefin modified surfactant
1. A composition for open-cell ethylene resin foam, comprising 0.1 to 10 parts by weight and (e) 0.1 to 30 parts by weight of process oil. 2. The composition for an ethylene resin open-cell foam according to claim 1, wherein the ethylene resin is polyethylene. 3 Claims 1 or 2 in which a blowing agent and a decomposition accelerator for the blowing agent are used together.
The composition for an ethylene-based resin open-cell foam as described in 2. 4. The composition for an ethylene resin open-cell foam according to any one of claims 1 to 3, wherein the blowing agent is azodicarbonamide. 5 α-olefin modified surfactant has 4 carbon atoms
The composition for an open-cell ethylene resin foam according to any one of claims 1 to 4, which is modified with an α-olefin of 1 to 16. 6 The process oil has an aniline point of 100℃ or less,
Viscosity at 40℃ is 150cSt or less, SP value is 7.5 to 8.5
The composition for open-cell ethylene resin foam according to any one of claims 1 to 5, which is a naphthenic oil.