JP2014105329A - Sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin-based resin crosslinked foamed sealing material which is highly softened by improving an expansion ratio to the utmost limit, and is flexible and excellent in sealing properties by holding a closed-cell structure.SOLUTION: A sealing material is formed from a crosslinked foamed body which is obtained from a resin composition that contains a polyolefin-based resin as a main component, and has 50% compressive hardness of 50 kPa or less and a closed-cell rate of 70% or more.

Description

  The present invention relates to a polyolefin-based resin-crosslinked foamed sealing material that is flexible and excellent in sealing properties by increasing the expansion ratio to the limit while maintaining the closed cell structure.

  Sealing materials using foams are variously used for automobiles, civil engineering, housing, and home appliances. These sealing materials are mainly used for water stop and airtight purposes. As the sealing material, a foam having an open cell structure such as EPDM or polyurethane is generally used, and flexibility is imparted by flexibility of a rubber material and suppression of repulsion due to gas escape in open cells. Since these foams are excellent in flexibility, they can easily follow the gaps in the mold and can be easily attached to complex shapes. I couldn't do it.

  In order to solve this problem, Patent Document 1 discloses that the foam has a closed cell layer on both surfaces of the EPDM and has an open cell layer in the center in the thickness direction, thereby providing excellent flexibility. Sealing materials having high water-stopping properties have been proposed. However, in such a sealing material, there is a concern that the production stability is inferior because the flexibility and water stoppage change greatly due to the variation of the thickness of the closed cell layer and the thickness of the open cell layer.

  Further, Patent Document 2 discloses that a dimer acid polyol is used as a polyurethane raw material to improve water repellency, and further, by improving the water stopping property by miniaturization of the cell, it has an open cell structure and a low density, but has a high water stopping property. Sealing materials with water performance have been proposed. However, since polyurethane is inferior in weather resistance and hydrolysis resistance, there has been a problem that the surface of the sealing material is deteriorated and the mechanical strength is lowered due to long-term use.

JP 2005-350571 A JP 2009-173806 A

  In view of the background of the prior art, the present invention is intended to provide a polyolefin-based resin-crosslinked foamed sealing material that is flexible and excellent in sealing properties by increasing the expansion ratio to the limit while maintaining the closed cell structure. is there.

The present invention employs the following means in order to solve such problems. That is, the polyolefin resin cross-linked foam sealant of the present invention is as follows.
(1) A sealing material comprising a cross-linked foam obtained from a resin composition containing a polyolefin resin as a main component, having a 50% compression hardness of 50 kPa or less and a closed cell ratio of 70% or more.
(2) The sealing material according to (1), wherein the crosslinked foam has an 80% compression set of 20% or less.
(3) The resin composition contains 15 parts by mass or more and 35 parts by mass or less of azodicarbonamide with respect to 100 parts by mass of the polyolefin resin.
The sealing material according to (1) or (2), wherein the azodicarbonamide satisfies the following conditions (A) and (B).

(A): Decomposition temperature is 197 to 207 ° C
(B): Generated gas velocity at 190 ° C. is 20 to 50 ml / min
(4) The sealing material according to any one of (1) to (3), wherein the polyolefin resin contains an ethylene-vinyl acetate copolymer.

  ADVANTAGE OF THE INVENTION According to this invention, the polyolefin-type resin bridge | crosslinking foaming sealing material which is flexible and excellent in the sealing performance can be provided by raising foaming magnification to the maximum, maintaining a closed cell structure.

  The present invention will be specifically described below.

  The sealing material of this invention will not be specifically limited if it is a sealing material use. Among sealing material applications, preferably, sealing materials for buried piping joints such as rainwater and drainage, sealing materials for wall spaces in unit baths, sealing materials for commercial air conditioner parts, etc. Is used for applications that require.

  These sealing materials are desired to exhibit stable sealing performance even at low density as well as the original sealing performance. If the foam has a low density, that is, a high expansion ratio, the cost of the sealing material can be reduced, and it is also effective for reducing the weight of the sealing structure.

  The resin composition used for producing the cross-linked foam which is the sealing material of the present invention contains a polyolefin resin and azodicarbonamide, and the content thereof is 15 parts by mass or more with respect to 100 parts by mass of the polyolefin resin. The range is preferably 35 parts by mass or less. More preferably, it is the range of 20 to 30 mass parts. If the content of azodicarbonamide is 15 parts by mass or less, the amount of generated gas is small, so that it is difficult to achieve a high expansion ratio and flexibility is lowered. On the other hand, if it is 35 parts by mass or more, a high expansion ratio can be achieved. However, some of the bubbles are connected to each other and the closed cell ratio is lowered, resulting in deterioration of the water-stopping property.

  Moreover, it is preferable that the decomposition temperature of the azodicarbonamide in the resin composition used for producing the crosslinked foamed material is in a range of 197 to 207 ° C. More preferably, the decomposition temperature is 200 to 205 ° C. When the decomposition temperature of azodicarbonamide is lower than 197 ° C., foaming is started in a state where the resin viscosity is high, and it is difficult to achieve a high expansion ratio and flexibility is lowered. On the other hand, when the temperature is higher than 207 ° C., it is possible to increase the expansion ratio.

  Further, the azodicarbonamide in the resin composition used for producing the crosslinked foamed material preferably has a generated gas velocity at 190 ° C. of 20 to 50 ml / min, more preferably a generated gas velocity at 190 ° C. of 30 to 45 ml / min. min. If the generated gas velocity at 190 ° C. is less than 20 ml / min, it is not preferable because it is difficult to increase the expansion ratio and the flexibility is lowered. Further, when the generated gas velocity at 190 ° C. exceeds 50 ml / min, the generated gas is suddenly generated, so that part of the bubble film is broken and closed, and the closed cell rate is lowered and the water stoppage is deteriorated. Absent.

  The cross-linked foam, which is the sealing material of the present invention, preferably has a 50% compression hardness of 50 kPa or less. If it is higher than 50 kPa, when there is a part with different compressibility depending on the shape of the mold when used as a sealing material, the part cannot be sealed and water or air may be passed through, which is not preferable. More preferably, it is 40 kPa or less. The lower limit of the 50% compression hardness of the sealing material is not particularly limited, but is preferably 15 kPa or more. When the pressure is lower than 15 kPa, when such a sealing material is rolled up, the foam is crushed by tension, and thickness unevenness in the longitudinal direction tends to occur, which is not preferable.

  The crosslinked foam which is the sealing material of the present invention preferably has an 80% compression set of 20% or less. If it is larger than 20%, the settling becomes large, so that the long-term sealing performance may be lowered, which is not preferable.

The polyolefin resin in the resin composition used for producing the cross-linked foam which is the sealing material of the present invention is not particularly limited, and examples thereof include low density polyethylene, high density polyethylene, linear low density polyethylene, and ultra low density. Polyethylene resin typified by polyethylene and the like (the definition of density here is as follows. Ultra-low density: less than 0.910 g / cm ³ , low density: 0.910 g / cm ³ or more and 0.940 g / cm ³ or less , density: 0.940 g / cm ³ or more 0.965 g / cm ³ or less) or ethylene copolymer. the may be any of these mixtures. Examples of the ethylene copolymer include ethylene and an α-olefin having 4 or more carbon atoms (for example, ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-heptene, An ethylene-α-olefin copolymer, an ethylene-vinyl acetate copolymer, and the like obtained by polymerizing octene). The polyolefin resin is more preferably a low density polyethylene, a linear low density polyethylene, an ultra low density polyethylene, an ethylene-α-olefin copolymer, or an ethylene-vinyl acetate copolymer. More preferred are low density polyethylene, linear low density polyethylene, and ethylene-vinyl acetate copolymer. These polyolefin resins may be either one kind or a mixture of two or more kinds. Most preferably, the polyolefin-based resin in the resin composition used for producing the crosslinked foam which is the sealing material of the present invention contains an ethylene-vinyl acetate copolymer. When the polyolefin resin in the resin composition contains an ethylene-vinyl acetate copolymer, the content of the ethylene-vinyl acetate copolymer in 100 mass% of the polyolefin resin is 70 mass% or more and 100 mass% or less. It is preferable that In this combination, 50% compression hardness and 80% compression set are reduced, so that the sealing material is excellent in flexibility and long-term sealability.

  Various additives such as a foaming agent decomposition accelerator, a cell nucleus modifier, an antioxidant, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and an inorganic filler, as long as the characteristics of the present invention are not impaired. Can be contained in the polyolefin resin composition which is a raw material of the sealing material of the present invention.

  It is important that the cross-linked foam, which is the sealing material of the present invention, be obtained from a resin composition containing a polyolefin resin as a main component. Here, the main component means the largest component in mass in the sealing material. More preferably, the polyolefin resin is 50 parts by mass or more and 99.5 parts by mass or less based on 100 parts by mass of all components of the sealing material. Additives other than the polyolefin-based resin described above are 0 parts by mass or more and 50 parts by mass or less in 100 parts by mass of all components of the sealing material.

  The closed cell ratio of the cross-linked foam which is the sealing material of the present invention is not particularly limited, but 70% or more is preferably used. More preferably, it is 80% or more. The larger the closed cell ratio, the better. There is no upper limit. If the closed cell rate is less than 70%, the water-stopping property is deteriorated, which is not preferable.

  In the present invention, for example, a polyolefin resin cross-linking sealant is produced by molding a polyolefin resin composition containing a polyethylene resin, azodicarbonamide and various additives into a predetermined shape, followed by crosslinking and foaming.

  Specifically, the following manufacturing method is mentioned, for example. A predetermined amount of the polyolefin-based resin composition is uniformly melt kneaded at a temperature lower than the decomposition temperature of azodicarbonamide using a kneading apparatus such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer, a mixing roll, or the like. This is formed into a sheet shape.

  Next, the resulting sheet is irradiated with ionizing radiation to crosslink the resin constituting the foamable sheet. As the ionizing radiation, electron beam, X-ray, β-ray, γ-ray and the like are used. In addition, although the crosslinking degree of the sealing material of this invention is not specifically limited, 10 to 40% is used suitably. More preferably, it is 15 to 35%. If the degree of cross-linking is less than 10%, the holding power of the generated gas becomes weak at the time of foaming. is there. On the other hand, if it exceeds 40%, the cross-linking becomes dense, which is preferable in terms of foamability and surface smoothness. However, the cross-linking becomes too dense and the retention force of the generated gas becomes excessive, resulting in partial destruction of bubbles. In some cases, the water stoppage may deteriorate. The degree of crosslinking shown here is measured by the following procedure. The sealing material is cut into about 0.5 mm square, and about 100 mg is weighed in units of 0.1 mg. After immersing in 200 ml of tetralin at 130 ° C. for 3 hours, it is naturally filtered through a 100 mesh stainless steel wire mesh, and the insoluble matter on the wire mesh is dried in a hot air oven at 120 ° C. for 1 hour. Next, the mixture is cooled in a desiccator containing silica gel for 10 minutes, the mass of this insoluble matter is accurately weighed, and the degree of crosslinking is calculated as a percentage according to the following formula.

Degree of crosslinking (%) = {mass of insoluble matter (mg) / weight of weighed polyolefin resin foam (mg)} × 100
The resin-crosslinked foamable sheet is heated to a temperature higher than the decomposition temperature of azodicarbonamide and higher than the melting point of the resin, for example, 190 ° C. to 290 ° C. by hot air, infrared rays, metal bath, oil bath, salt bath, etc. The resin is foamed by heating and decomposing gas of the foaming agent, and thus a sealing material is obtained.

  The sealing material obtained in the present invention is suitably used as a sealing material for automobiles, civil engineering, housing, and home appliances. The necessary properties as a sealing material are water-tightness and airtightness, as well as flexibility to follow the shape of the seam. Until now, many open-cell foams having excellent followability have been used. However, unless high compression is performed, water-stopping and airtightness cannot be exhibited. However, the sealing material obtained by the present invention is flexible and follows by using azodicarbonamide whose decomposition temperature and generated gas velocity are controlled, and by increasing the expansion ratio to the limit while maintaining the closed cell structure. It is characterized by having good water tightness and airtightness peculiar to closed cells, and it is economically advantageous because it exhibits sealing properties while being low in compression and low density.

The physical properties were evaluated by the following methods.

(1) Thickness: Measured according to ISO 1923 (1981) “Measurement method for foamed plastic and rubber alignment”.

(2) Density The density was measured in accordance with JIS K6767 (1999) “Foamed plastic-polyethylene test method”. The average value of 3 points obtained by removing the upper and lower limit values from the values obtained by the measurement of 5 samples was defined as the density.

(3) 50% compression hardness
Measured according to JIS K6767 (1999) “Foamed plastics-polyethylene test method”. Specifically, the foams are stacked so that the total thickness is 25 mm or more, and the drag when the foams are compressed by 50% of the total thickness is measured. As the measuring device, here, Tensilon universal testing machine UCT-500 manufactured by Orientec Co., Ltd. is used.

(4) 80% compression set Measured according to JIS K6767 (1999) “Foamed plastics-polyethylene test method”. Specifically, foams having a length of 50 mm and a width of 50 mm are stacked so that the total thickness is 25 mm or more, the thickness is measured accurately, sandwiched between predetermined test devices, and the thickness of the test piece. The sample is compressed and fixed by 80% of that and left in a standard state for 22 hours. Then, after removing a test piece and leaving it to stand in the place of a standard state for 24 hours, the thickness of the same location as before is measured, and it calculates according to the following formula | equation.

C = (t0−t1) / t0 × 100
Where C: 80% compression set (%)
t0: initial thickness (mm) of the test piece
t1: Thickness (mm) after the test of the test piece.

(5) Closed cell ratio Measured according to JIS K7138 (2006) "Rigid foamed plastic-Determination of open cell ratio and closed cell ratio". Calculation was performed according to the following formula.
Apparent closed cell ratio = 100−ω _r
ω _r = ((V _g −V _i ) / V _g ) × 100
ω _r : Apparent open cell ratio V _g : Geometric volume V _i : Non-ventilated volume (6) A test piece punched into a U shape having a water blocking width of 10 mm and a length of 30 cm was prepared. The shape was maintained and sandwiched between two acrylic resin plates, and the gap between the two acrylic resin plates was sandwiched so that the compression rate of the test piece was 50%, 70%, and 90%. Next, the U-shaped opening was stood up, and water having a height of 10 cm was placed inside the U-shape, which was controlled at room temperature, and the presence or absence of water leakage after 30 minutes was confirmed.
Evaluation criteria ○: Compressible to the specified compression rate and no leakage after 30 minutes ×: Leakage within 30 minutes, or compression to the specified compression rate even when force is applied (7) Decomposition The decomposition temperature of the temperature azodicarbonamide was a sample by observation using a melting point measuring instrument B-540 manufactured by BUCHI, with the temperature rising program of the apparatus set to a starting temperature of 170 ° C., a heating rate of 5 ° C./min, and an end temperature of 215 ° C. The temperature was measured when swelled and expanded. The sample used was a foaming agent stored for 24 hours in a room with a room temperature of 25 ° C. and a humidity of 50%.

(8) Generated gas amount The generated gas amount of azodicarbonamide was measured by the following procedure. Place 0.50 g of sample in a test tube and add about 10 ml of liquid paraffin (first grade reagent). The test tube is heated in a silicon oil bath heated to 190 ° C., and the generated gas is collected by a gas burette. The water surface of the gas burette and the water surface of the spirit level are combined, the memory of the water surface position of the gas burette is read, and the generated gas amount (actual value) V1 is measured. Gas generated after 1 minute of heating and after 20 minutes is calculated as the amount of generated gas by the following equation.
V2 = V1 × ((P1−P2) /101.32) × (273 / (273 + 35)) × 1 / S
V1: Generated gas volume (ml / 0.5g)
V2: Generated gas amount in the standard state (ml / g)
P1: Atmospheric pressure (kPa)
P2: Vapor pressure of water at a water temperature of 35 ° C (kPa)
S: Sample amount (g)
(9) Generated gas velocity (8) In the measurement of the generated gas amount, the generated gas amount and time after heating for 1 min are plotted on a graph, and this graph is used to calculate the generated gas velocity by the following equation.
_{R = ((V 90 -V 10} ) / (T 90 -T 10)) × S
R: generated gas velocity (ml / min)
V ₉₀ : 90% of the amount of generated gas (ml / g)
V ₁₀ : 10% of the amount of generated gas (ml / g)
T ₉₀ : Time when the amount of generated gas is 90% (min)
T ₁₀ : Time when the amount of generated gas is 10% (min)
S: Sample amount (g)

Example 1
100 parts by mass of low density polyethylene (MFR: 6.7 to 9.3 g / 10 min, melting point: 118 ° C., density: 0.922 to 0.926 g / cm ³ ) as polyolefin resin, 30 parts by mass of azodicarbonamide (Decomposition temperature 200 ° C., generated gas rate 40 ml / min), 0.1 parts by weight of phenolic antioxidant as a heat stabilizer are mixed in a Henschel mixer, put into a 60φ extruder, and the temperature in the cylinder is 150 ° C. In a state where the temperature is adjusted so as to become, after melting and kneading, a sheet having a thickness of 4 mm is once wound up.
This polyolefin resin foamed sheet was irradiated with ionizing radiation using an electron beam irradiator and then foamed on a salt salt bath (salt bath temperature 230 ° C.). As a result, foam having the characteristics shown in Table 2 was obtained. Got the body.
Examples 2-5
In Examples 2 to 5, as the polyolefin resin, in addition to the low density polyethylene of Example 1, linear low density polyethylene (MFR: 6.7 to 9.3 g / 10 min, melting point: 123 ° C., density: 0.923) ˜0.927 g / cm ³ ) and ethylene-vinyl acetate copolymer (MFR: 1.5 g / 10 min, melting point: 90 ° C., density: 0.936 g / cm ³ , vinyl acetate content: 15%), A foam was prepared in the same manner as in Example 1 except that mixing was performed as described in 1. As a result, a foam having the characteristics shown in Table 2 was obtained.
Comparative Examples 1-4
In Comparative Examples 1 to 4, polyolefin resin, heat stabilizer, ionizing radiation and the like are the same as in Example 1. However, in the foaming agent, azodicarbonamide having a decomposition temperature different from that in Example 1 and a generated gas velocity is used. A foam was prepared by the same method as in Example 1 with mixing. As a result, a foam having the characteristics shown in Table 2 was obtained.
Comparative Example 5
In Comparative Example 5, polyolefin resin, heat stabilizer, ionizing radiation and the like are the same as in Example 1. However, in the foaming agent, 10 parts by mass of azodicarbonamide is added as compared with Example 1, and the others. Produced a foam by the same method as in Example 1. As a result, a foam having the characteristics shown in Table 2 was obtained.

  About an Example and a comparative example, the raw material composition and the foam (sealing material) physical property were shown in Table 1, Table 2, respectively.

  The sealing material of the present invention requires flexibility, water tightness, and airtightness such as sealing material for buried pipe joints such as rainwater and drainage, sealing material for wall gaps of unit baths, sealing material for commercial air conditioner parts, etc. May be used for certain applications.

Claims (4)

  A sealing material comprising a crosslinked foam obtained from a resin composition containing a polyolefin resin as a main component and having a 50% compression hardness of 50 kPa or less and a closed cell ratio of 70% or more.   The sealing material according to claim 1, wherein the crosslinked foam has an 80% compression set of 20% or less. The resin composition contains 15 parts by mass or more and 35 parts by mass or less of azodicarbonamide with respect to 100 parts by mass of the polyolefin resin.
The sealing material according to claim 1 or 2, wherein the azodicarbonamide satisfies the following conditions (A) and (B).
(A): Decomposition temperature is 197 to 207 ° C
(B): Generated gas velocity at 190 ° C. is 20 to 50 ml / min   The sealing material according to claim 1, wherein the polyolefin-based resin contains an ethylene-vinyl acetate copolymer.