JPH0248562A - Azodicarbonamide for blowing agent and modification thereof - Google Patents

Abstract

PURPOSE:To obtain a blowing agent providing crosslinked polyolefin foam having uniform and fine closed cells by dissolving azodicarbonamide crystal in an organic solvent and abruptly precipitating the crystal in a short time by using a non-solvent such as water. CONSTITUTION:Widely useful azodicarbonamide(ADCA) crystal is dissolved in an organic solvent such as DMF, maintained at 2-25 deg.C, poured into 1.5-3.5 times as much as water to precipitate the ADCA precipitate. In the operation, precipitation of crystal is completed within one hour to give ADCA for blowing agent of thermal decomposition type capable of producing polyolefin foam having uniform and fine closed cells and high expansion ratio. ADCA obtained by this method has 2.5-3.5 of relative intensity ratio I2/I1 where intensity strength I1 is at 3875cm<-1> and intensity strength I2 is at 3620cm<-1> in infrared spectrum of diffuse reflection Fourier transformation and 6-25mu average particle diameter.

Description

Detailed Description of the Invention (Industrial Application Field) In recent years, polyolefin resins have been blended with azodicarbonamide (hereinafter referred to as ADCA), which is a thermally decomposable blowing agent, and after being molded, they are subjected to heating, infrared lamp irradiation and , high frequency (UHF)
A widely used method is to thermally decompose the polyolefin in a heating foaming furnace using a foam, etc., to obtain a high-strength crosslinked polyolefin foam.

In addition, the high-density crosslinked polyolefin foam produced by this method has heat insulation, cushioning, elasticity, soundproofing, and
In order to exhibit excellent foaming properties such as improved electrical insulation, it is used as insulation materials, cushioning materials, packaging materials,
Widely used in soundproofing materials, electrical insulation materials, structural materials, household goods, etc.

The present invention utilizes the pyrolytic blowing agent ADC, which is the most widely used in the field of producing high-strength crosslinked polyolefin foams.
This invention relates to AD CA crystal, which is a pyrolytic blowing agent that enables the production of crosslinked polyolefin foam having a uniform and fine closed cell structure using A.

(Prior art) Conventional AD CA uses hydrazodicarbonamide (hereinafter referred to as H
It is manufactured by a method of oxidizing DCA) using various oxidizing agents described below, a method of electrolytic oxidation, etc.

Oxidizing agents include peroxides such as hydrogen peroxide, chlorine gas,
Chlorine compounds such as hypochlorite 1 noda, perchloric acid, bromides such as bromine, etc. are generally used.

In addition, in the field of producing cross-linked polyolefin foams with high expansion ratios, there has been a strong desire for the development of ADCA, a pyrolytic blowing agent that can produce cross-linked polyolefin foams with a uniform and fine closed cell structure. It's here.

Conventionally, foaming agent AD was able to satisfy these demands.
As a proposal for the conditions that CA should have,
956, the average particle size is 10 to 30 μ and 5
The use of ADCA in which the microcrystalline solid forms parallel intergrowth in JP-A No. 4B-34393, or the use of ADCA in which microcrystalline solids form parallel intergrowth in JP-A No. 51-114469, in thermogravimetric analysis. Therefore, it has been proposed to use ADCA whose 1% weight loss point is below 180°C and whose total decomposition is above 185°C. Then, as a cell refinement technology for foams, a method such as adding a crosslinking aid was proposed in JP-A-154-25972, and as a method for modifying the blowing agent ADCA, JP-A-5
9-188035, the value of the intensity ratio II/12 of the diffraction line intensity ■2 at the X-ray diffraction angle 2θ = 15.8° and the diffraction line intensity 1+ at the X-ray diffraction angle 2θ = 28.9° is 1. 7 to 4.
The use of AD CA within the range of 0 and a method of heat-treating the blowing agent ADCA produced by a known method in water or a solvent have been proposed, but Wako Pure Chemical Industries, Ltd.! !
Reagent ADCA and ADCA(1)X registered in ASTM (American Society for Testing and Materials) Rin quasi-X-ray diffraction data
Line Diffraction Day'1F (JCPDS, 1978; Card No. 28-11535 and 30-1531
) etc., which are manufactured by conventionally known methods, are within the scope of this claim, and are further refined? Even poor AD CA that cannot form fi falls within this range.

Therefore, the above-mentioned proposals are sufficient to clarify whether it is necessary to use ADCA having the following characteristics when producing a high-density crosslinked polyolefin foam having a uniform and fine closed cell structure. Since it has not been carefully examined, it is not necessarily satisfactory.

(Object of the Invention) The various physical properties of a high-magnification crosslinked polyolefin foam are greatly influenced by the cell structure of the foam, and the foam having a uniform and finer closed cell structure exhibits better foaming characteristics.

For these reasons, in the field of manufacturing high-strength crosslinked polyolefin foams, there has been a strong desire to develop a blowing agent AD CA that can form a uniform and fine closed cell structure.

The present invention provides a thermally decomposable blowing agent ADCA crystal that can satisfy the above-mentioned demands when producing a high-magnification crosslinked polyolefin foam in which it is extremely difficult to form a uniform and fine closed-cell structure. conditions and a stable supply of this blowing agent ADCA.

(Structure of the Invention) As a result of intensive research in order to achieve the above-mentioned request, the present inventors have discovered that ADCA is capable of producing a high-magnification crosslinked polyolefin foam having a uniform and fine closed cell structure.
In the case of crystals, 3875c in the diffuse reflection Fourier transform infrared spectroscopy spectrum (hereinafter abbreviated as DRIFT spectrum)
It has been found that the relative intensity ratio I2/11 between the absorption intensity I2 at 3620 cm-' and the absorption intensity I2 at 3620 cm-' falls within the range of 2.5 to 3.6. In this way, we discovered extremely specific absorption bands on the DRIFT spectra of various ADCA crystals, leading to the present invention.

In the present invention, we have clarified the conditions that the blowing agent ADCA must meet in order to form a uniform and fine closed cell structure in a high-strength crosslinked polyolefin foam, and we have also made use of this new foaming technology theory. In addition, we are planning to modify the blowing agent AD CA.

AD CA crystals manufactured by a conventionally known method and having an average particle size within the range of 6 to 25μ as determined by air permeation type powder specific surface area measurement have an average particle diameter of 38μ in the DRI FT spectrum.
The value of the relative intensity ratio 12/II between the absorption intensity 11 at 75 cm-' and the absorption intensity I2 at 3620 cm-' falls within the range of 0.5 to 3.5.

In addition, as a result of determining the degree of cell refinement of AD CA manufactured by various methods based on Table 2, the degree of cell refinement and the value of the above-mentioned relative strength ratio 1a/I+ are as shown in Fig. 1. It has become clear that as the relative intensity ratio increases, the degree of bubble refinement also increases.

For these reasons, ADCA crystals with a relative strength in the range of 2.5 to 3.5, particularly preferably 2.8 to 3.
It has been found that when a high-magnification crosslinked polyolefin foam is produced using ADCA crystals falling within the range of 5, it is possible to form a uniform and fine closed-cell structure.

In the present invention, as described above, the value of the relative intensity ratio I2/II observed from the DRI FT spectrum is 2.6 to 3.
It is believed that the ADCA crystal that falls within the range of 5 and contains more defects between the bc planes (hydrogen bond forming planes) in the crystal lattice, the more excellent the ADCA of the present invention will exhibit its functions. It was made clear.

In addition, those having the above-mentioned relative intensity ratio of less than 2.5 are classified as A of the present invention.
The excellent functions exhibited by DCA cannot be obtained. Therefore, even if a high-density crosslinked polyolefin foam is produced using such ADCA, uniform and fine closed cells are not formed.

Next, the above-mentioned pyrolytic blowing agent ADCA having a relative strength in the range of 2.5 to 3.5 can be manufactured by a conventionally known method, but the manufacturing yield is low and the cost is high. Therefore, it is not an industrially practical manufacturing method.

DRIFT of the pyrolytic blowing agent AD CA crystal of the present invention
The characteristic absorption bands on the spectrum will be explained in more detail with reference to FIG. 2. FIG. 2 is an example of DRIFT spectra of various types of ADCA crystals manufactured by a known method, and the relative intensity ratio 12/II is 0.5.
shows a value of 3.3.

In addition, the ADCA samples subjected to DRI FT spectrum analysis showed that when a high-magnification crosslinked polyolefin foam was manufactured,
Various types of A exhibiting various foaming characteristics such as the state of the cells in the foam being fine or coarse.
DCA crystal was used.

In addition, the DRIFT spectra of these AD CA samples were obtained using 0.055 g of potassium bromide and 0.05 g of various ADCA samples in a stainless steel sample dish with a diameter of 5 mm and a depth of 2 mm.
．． 0029 g and an attachment for diffuse reflection spectrum measurement (manufactured by Harrick: DRA-PMN
) into the sample holder in the Fourier transform infrared spectrophotometer (NicoIeti!FTIR-
6000 type (using MCT detector). The horizontal axis of FIG. 2 represents the wave number (unit: cm-'), and the vertical axis represents the reflected absorbance [unit: f (Ro6)]. Also 3875cm
-+ absorption intensity is 1 in Figure 2 and 3620c
The absorption intensity of m-' is indicated by 12 in FIG. The relative intensity ratio referred to in the present invention is calculated as I2/II.

In addition, the average particle diameter of ADCA in the present invention is measured using an air permeation type powder specific surface area measuring device [Shimadzu Corporation! l 5S-
1001 was used.

The special AD CA that is the object of the present invention can be manufactured, for example, by the following method.

Among the conventionally known methods for producing AD CA, industrially,
Although it is possible to produce it extremely efficiently, the above-mentioned relative intensity ratio 12/II is 0.5 (Fig. 2, a), which is outside the range indicated by the ADCA of the present invention, and the bubble TI! A solution of a general-purpose AD CA crystal with a fineness degree of about 1.5 dissolved in an organic solvent such as dimethylformamide (hereinafter abbreviated as DMF) at room temperature acts as a non-solvent for ADCA like water. In addition, there is a method in which DMF is poured into a solvent that acts as a good solvent to precipitate ADCA crystals, and a method in which the above-mentioned DMF solution is kept at room temperature and water is dropped into this AD CA solution to precipitate AD CA crystals. , upon recrystallization, A
By controlling the precipitation rate of DCA crystals, ADCA crystals having the characteristics of the present invention can be produced.

Next, a method for modifying ADCA having the features of the present invention described above will be described in detail.

First, a solution prepared by dissolving the above-mentioned general-purpose ADCA crystal in DMF was heated to 2"C to 25°C.
For liquid 1. f5 into 3.5 times the volume of water to precipitate ADCA crystals, or if the above-mentioned inferior ADCA crystals were dissolved in DMF and kept at 25 °C with stirring. Drop twice the amount of water into the ADCA solution at a rate of about 7 ml/min,
When ADC crystals are precipitated, etc., ADC is removed from an organic solvent.
When precipitating the A crystal, by rapidly precipitating the crystal so that the crystal precipitation is completed within one hour, ADCA having the excellent functions exhibited by the ADCA of the present invention can be produced.

During the recrystallization of the ADCA crystals mentioned above, the solvent used to dissolve the ADCA crystals is not limited to DMF, but dimethyl sulfoxide (hereinafter abbreviated as DMSO), which can dissolve the ADCA crystals. Alternatively, it is also possible to use an organic solvent such as N-methyl-2-pyrrolidone.

In addition, during the recrystallization of the ADCA crystals mentioned above, the solvent used as a non-solvent is not limited to water, but can also be used as a solvent that does not dissolve the ADCA crystals and is used to dissolve the ADCA crystals, such as DMF. Dissolved in methanol (hereinafter referred to as M e OH
It is also possible to use ethanol (hereinafter abbreviated as EtOH) or the like. However, from economic and pollution standpoints, the use of water is practical.

Regarding the amount of non-solvent used, 1. About 3.5 times the amount from f5, preferably 2
．． 5 to 3.5 times the amount.

Further, the temperature of the solution when mixing the ADCA solution and the non-solvent is in the range of 2''C to 25C, preferably in the range of 2C to 15C.

In the case of A.DCA crystals produced by the above two types of recrystallization methods, the relative intensity ratio on the DRIFT spectrum!
The value of 2/II is between 2.9 and 3.4, which is within the relative intensity ratio (12/I+) of the special ADCA of the present invention.
That is, within the range of 2.5 to 3.5, particularly preferably 2.8
It is possible to produce an ADCA having the characteristics of the present invention.

Although the special ADCA of the present invention can be manufactured by the method described above, it is not necessarily limited to the method described above.

The resin with which a foam can be produced by blending the ADCA of the present invention as a blowing agent is not particularly limited to polyolefin resins.10 For example, polyolefin resins,
Although it can be used for polyamide-based, polyester-based, rubber-based, and polyvinyl-based resins, it is particularly preferably used for polyolefin-based resins.

In addition, when producing a foam by ADCA of the present invention, plasticizers, stabilizers, cell regulators, crosslinking agents, crosslinking aids, lubricants, fillers, ultraviolet absorbers, antistatic agents, surfactants, and foaming aids. There is no problem in using it in combination with various additives such as.

The physical properties of the ADCA of the present invention, such as average particle size, decomposition temperature, and amount of gas generated, are no different from those of conventionally known ADCA, so there are no restrictions when using it as a blowing agent. The foam manufacturing method to which the ADCA of the invention is applied is applied to a method of manufacturing a foam by, for example, kneading and molding using an extrusion molding machine and then thermally decomposing the foam agent ADCA under normal pressure in a heating foaming furnace. 0 When the AD CA of the present invention is used as a blowing agent and a high-magnification crosslinked polyolefin foam is produced by the method described above, a foam having a uniform and fine closed cell structure with excellent heat insulation and cushioning properties can be obtained. Since the ADCA of the present invention can be easily formed, the significance of the ADCA of the present invention is extremely large.

The present invention will be further explained below using Reference Examples, Examples, and Comparative Examples.

(Reference example) Reference example (1) To 250 ml of 20% sulfuric acid, 1 part of hydrazodicarbonamide
18 g and 0.9 g of sodium bromide were added, and 125 g of 30% hydrogen peroxide solution was added dropwise over 3 hours at 55"C under stirring and suspension.
The temperature was kept at the same temperature for a minute and stirring was continued to complete the reaction. The produced yellow crystals of AD CA are separated by filtration, washed with water, and dried.
t, 3g (yield 96.0%.

Purity: 9B, 8%) was obtained. The average particle diameter of this ADCA crystal was 6.8 μ, the value of the relative intensity ratio 12/II on the DRIFT spectrum was 0.5, and the decomposition temperature was 208”C.

Further, FIG. 2, a shows a DRIFT spectrum diagram of this ADCA.

Reference example (2) 118g of hydrazodicarbonamide in 500ml of water
(1 mol) and 1.55 g (1.5 mol %) of sodium bromide were added, and chlorine gas was introduced while stirring while maintaining the reaction temperature at 25°C. The chlorine gas was fed at a rate of log/hour for 7.5 hours. The amount fed was 73.2 g.

The produced yellow crystals of ADCA were filtered, washed with water, and dried to give 113.3 g (yield: 97.7%, purity: 99.0%).
) was obtained. The average particle diameter of this ADcA is 8.3μ, and D
The value of relative intensity 12/II on the RIFT spectrum was 0.65, and the decomposition temperature was 207.5°C.

Moreover, FIG. 5 shows a DRI FT spectrum diagram of this ADCA.

(Example) Example (1) 20 g of the ADCA raw material produced in Reference Example (1) was
It was completely dissolved in 3000 ml of DMF at 9C and then cooled to 2'''C.

, m(7)AD CA+7)DMF? A liquid, 2″″C
Add it to 9000 ml of distilled water (3.0 times the amount of DMF solution) cooled to
Crystals were precipitated. After this, the precipitated yellow crystals of ADC
A was filtered off, washed with water, and dried to obtain 17.4 g of AD CA crystals. (Yield: 87.0%, Purity: 98.8%>
DMF can then be recycled by removing water from the collected waste liquid. AD manufactured by this method
The average particle diameter of the CA crystal is 8.9μ, and the value of the relative intensity ratio I2/I11 on the DREFT spectrum is 3.
18 and the decomposition temperature was 207.5°C. Further, FIG. 3 shows a DRIFT spectrum diagram of this ADCA, and Table 1 lists each analytical value.

Example (2) 17.5 of the A-D CA raw material produced in Reference Example (1)
completely dissolved in 350 ml of DMSo at 25”C, followed by 350 ml of distilled water maintained at 25°C.
1 (1.0 times the volume of the DMSO solution) and thoroughly mixed to precipitate ADCA crystals.

Thereafter, the precipitated yellow crystals of ADCA were separated by filtration, washed with water, and dried to obtain 15.8 g (7) ADCA crystals. (yield:
(90.3%, purity: 98.6%) DMSO can also be recycled by removing water from the collected waste liquid. The average particle diameter of the ADCA crystal produced by this method is 6.5μ, the value of the relative intensity ratio 12/II on the DRIFT spectrum is 2.8, and the decomposition temperature is 20
It was 7.0@C. Also, Figure 4 shows the DRI of this ADCA.
An FT spectrum diagram is shown, and each analytical value is listed in Table 1.

Example (3) Using the ADCA raw material obtained in Reference Example (2) and using the same recrystallization conditions as in Example (1), ADCA of the present invention was obtained as shown in Table 2. Also, this AD CA is shown in Figure 6.
A DRI FT spectrum diagram of the sample is shown, and each analytical value is listed in Table 1.

Example (4) The AD CA raw material obtained in Reference Example (2) was used, and the recrystallization conditions were the same as in Example (2>).
I got an A. Further, FIG. 7 shows a DRI FT spectrum diagram of this ADCA, and Table 1 lists each analytical value.

(Comparative example) Comparative example (1) In reference example (1), ADC manufactured by a known method
A raw material (relative intensity ratio 1 on DPIFT spectrum)
The value of 2/II was 0.5 (average particle diameter was 6.8 μ), and a high-magnification crosslinked polyethylene foam was produced according to the following method. That is, 100 parts by weight of low-density polyethylene with a melt index of 1.0, 0.8 parts by weight of dicumyl peroxide as a crosslinking agent, and ADCA16 as the blowing agent obtained in Reference Example 1.
Add parts by weight and knead uniformly with a kneading roll heated from 110°C to 115°C, then 150mm x 150mm x
Put into 2mm mold, 120”C, 46kg/C
120°C 1125k after 4 minute leap press down m z
Press under g/cm2 for 3 minutes to 150 mm x 1
A 50 mm x 2 mm foamable polyethylene sheet was prepared. 50 mm from the center of this object
A sheet measuring 50 mm x 2 mm square was cut and used as a foaming sample. This sample was placed in a hot air circulation drying oven and heated at 220°C for 5 minutes to obtain a high-strength crosslinked polyethylene foam. The cell structure of the obtained foam had a large cell diameter and was non-uniform.

The density of the foam was 0.031 g/m I (30 times foaming).

Cut the center of this foam and measure the diameter of the largest bubble within 1 cm2. (mm) and the diameter of the smallest bubble was damn (mm), and the value of d m@x-d sin (In m) was thoroughly determined to examine the uniformity of the bubbles. Regarding the degree of bubble refinement, as mentioned above, within 1 cm of the center of the foam,
The number of bubbles existing on a 10 mm straight line was determined, and the degree of bubble refinement was determined according to the standards in Table 2. As a result, the degree of bubble refinement was 1. It showed an extremely low value of 5. These results are listed in Table 1.

Comparative Example (2) Using the AD CA obtained in Example (1), Comparative Example (1)
A high-magnification cross-linked polyethylene foam was produced using the same method as above, and the state of the cells formed in the foam was confirmed. As a result, it was found that a uniform and fine closed-cell structure was formed inside the foam. confirmed. The results of these measurements are listed in Table 1.

Comparative Example (3) Using the AD CA obtained in Example (2), Comparative Example (1)
A high-magnification cross-linked polyethylene foam was produced using the same method as above, and the state of the cells formed in the foam was confirmed. As a result, it was found that a uniform and fine closed-cell structure was formed inside the foam. confirmed. The results of these measurements are listed in Table 1.

Comparative Example (4) In Reference Example (2), ADC manufactured by a known method
Raw material A (the value of I2/It for the relative intensity t on the DRIFT spectrum is 0.65; the average particle diameter is 8.3 μ
), a high-magnification crosslinked polyethylene foam was produced in the same manner as in Comparative Example (1). The cell structure inside the obtained foam had a large cell diameter and was non-uniform. The results are listed in Table 1.

Comparative Example (5) Using the ADCA obtained in Example (3), a high-magnification crosslinked polyethylene foam was produced in the same manner as Comparative Example (1), and the state of the cells formed in the foam was confirmed. As a result, it was confirmed that a uniform and fine closed cell structure was formed inside the foam. The results of these measurements are listed in Table 1.

Comparative Example (6) Using the ADCA obtained in Example (4), a high-magnification crosslinked polyethylene foam was produced in the same manner as Comparative Example (1), and the state of the cells formed in the foam was confirmed. As a result, it was confirmed that a uniform and fine closed cell structure was formed inside the foam. The results of these measurements are listed in Table 1.

Comparative Examples (7), (8) Relative intensity ratio on DRIFT spectrum 12/II
Among the blowing agent AD CAs with a value smaller than 2.5, there are two types of AD CA grades marketed by two companies (relative intensity ratio 12/I on the DRIFT spectrum).
I is listed in Table 1), a high-magnification crosslinked polyethylene foam was produced in the same manner as in Comparative Example (1).

No uniform and fine closed cells were formed inside the resulting foam.

The results of these experiments are listed in Table 1.

[Brief explanation of the drawing]

Figure 1: Relationship between the degree of bubble refinement and relative strength 12/It of the blowing agent AD CA Figure 2: DRIFT spectra of various ADCA crystals Degree of bubble refinement a: 1.5 (ADCA of Reference Example 1) ) b: 3.0 (commercially available ADCA) c: 4.0 (commercially available ADCA) d: 15.0 (commercially available ADCA) Figure 3: DRIFT of ADCA manufactured in Example 1
Spectrum diagram Figure 4: DRIFT of ADCA manufactured in Example 2
Spectrum diagram Figure 5: DRIFT of ADCA manufactured in Reference Example 2
Spectrum diagram Figure 6: DRIFT of ADCA manufactured in Example 3
Spectrum diagram Figure 7: DRIFT of ADCA manufactured in Example 4
Spectral diagram Figure 2 Wave number (CI+ Figure 1 2.0 3.0 4.0 Bubble machine conversion degree 5.0 Figure 3 Wave number (cm-') Figure 6 Wave number (c + n Figure 6 Figure 7 Wave number (cm”)

Claims (1)

[Claims] 1. Diffuse reflection-Fourier transform infrared spectra; 3.
Absorption intensity I_1 of 875cm^-^1 and 3620cm
Relative intensity ratio I_2/I_ with absorption intensity I_2 of ^-^1
Azodicarbonamide, a thermally decomposable blowing agent, characterized in that the value of 1 is in the range of 2.5 to 3.5, and the average particle diameter is in the range of 6 to 25μ. 2. Azodicarbonamide, a thermally decomposable blowing agent which completes crystal precipitation within one hour when azodicarbonamide crystals are dissolved in an organic solvent and then precipitated using a non-solvent, and has the characteristics described in item 1. Modification method to amide.