JP3510364B2 - Crosslinked polyolefin resin foam sheet and heat insulating pipe cover for copper pipe using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin crosslinked foam sheet having excellent dimensional stability and a heat insulating pipe cover for copper pipes using the same.

[0002]

2. Description of the Related Art For heat insulation of pipes for construction or home electric appliances, an inorganic material such as glass fiber, rock wool or various plastic foams processed into a tape shape, a cylindrical shape, etc. It is used as a pipe cover). Among these materials, plastic foams are widely used because of their excellent properties such as lightness, heat insulation and impact absorption. In particular, polyolefin resin cross-linked foam is superior to other plastic foams in heat resistance, water resistance, chemical resistance, mechanical strength, etc. Due to its excellent properties, it is considered to be the most suitable material for the above heat insulating applications.

[0003]

By the way, in recent years, due to high efficiency, noise reduction, and reduction in size and weight of air conditioning equipment, it is inevitable that various air conditioning refrigerant pipes become hot, and further high heat resistance is required. Is required. However, the conventional polyolefin resin crosslinked foam has a
There are problems such as discoloration or lack of dimensional stability when exposed to temperatures above ℃. In particular, the shrinkage in the thickness direction causes a significant decrease in heat insulation performance, which has been a serious problem for the function of the heat insulation pipe cover of the pipe. Therefore, JIS
Even with an insulating pipe cover that clears the thickness shrinkage ratio of 120 ° C as specified in A 9515, the thickness shrinkage ratio becomes large when used in an environment of 120 ° C or higher, and the insulating performance of the insulating pipe cover is unsatisfactory. It's getting enough.

Among the polyolefin resin cross-linked foams, electron beam cross-linked polypropylene foam is relatively excellent in dimensional stability, but only a thin product can be produced due to the problem of electron beam transmission ability, and desired heat insulation is obtained. In order to do so, a two-layer structure in which the above polypropylene foam was laminated on a polyethylene foam having a high expansion ratio was inevitable. As a result, there have been problems that the manufacturing process becomes complicated and that delamination occurs due to the difference in heat shrinkage between polyethylene foam and polypropylene foam, which causes a problem in practical use. Further, since polypropylene foam is inferior in flexibility, there are problems that it becomes brittle and that elastic recovery after compression is poor.

The present invention uses a polyolefin resin crosslinked foam sheet which maintains dimensional stability even when exposed to a temperature of 120 ° C. or more without deteriorating processability and flexibility and has no discoloration, and the same. It is intended to provide a heat insulating pipe cover for a copper pipe.

[0006]

That is, according to the present invention, a low density polyethylene resin having a melt flow rate of 0.3 to 3.5 g / 10 min, 60 to 95% by weight, and a density of 0.94.
Peroxide to 100 parts by weight of a polyolefin resin composed of 5 to 0.975 g / cm ³ , a melting point of 120 to 135 ° C., and a high density polyethylene resin of 5 to 40% by weight of a melt flow rate of 10 to 30 g / 10. A polyolefin resin crosslinked foam sheet obtained by crosslinking and foaming a resin composition containing 0.1 to 5 parts by weight of a decomposable antioxidant and 0.1 to 5 parts by weight of a copper damage inhibitor, the foam sheet comprising: Of at least one side having a gel fraction of 65% or more, and a polyolefin resin crosslinked foam sheet, and a foam sheet having a gel fraction of 65% or more are molded into a cylindrical shape so that the surface is an inner surface. Provided is a heat-insulating pipe cover for a copper pipe which is processed.

The low density polyethylene resin (hereinafter referred to as LDPE) used in the present invention is made of ethylene as a raw material,
It is preferably radical-polymerized by a known method such as an autoclave method or a tubular method and has a melt flow rate (hereinafter referred to as MFR) of 0.3 to 3.5 g / 10 minutes. If the MFR is less than 0.3 g / 10 minutes, the resin will generate excessive heat in the process of kneading the compound in the extruder, causing troubles during cross-linking and foaming.
If it exceeds 3.5 g / 10 minutes, the torque during extrusion becomes too low, which leads to a decrease in the extrusion amount and a decrease in productivity.
A foam with a high expansion ratio cannot be obtained.

The high-density polyethylene (hereinafter referred to as HDPE) used in the present invention contains ethylene as a main component,
It is ion-polymerized by a known method such as a slurry method, a solution method or a gas phase method using a Ziegler catalyst, chromium oxide or the like as an initiator, and its density is 0.945 to 0.975 g /
cm ^3, a melting point is preferably 120 to 135 ° C.. When the density is 0.945 g / cm ³ or less, the dimensional stability of the foam is not sufficient. If the melting point is less than 120 ° C, the dimensional stability that is the object of the present invention becomes insufficient, and if it exceeds 135 ° C, the heat of the resin becomes excessive in the step of kneading the compound in the extruder, which causes troubles during cross-linking and foaming. Cause of. Further, the MFR is preferably 10 to 30 g / 10 minutes. If the MFR is 10 g / 10 min or less, the heat of the resin becomes excessive in the step of kneading the compound in the extruder,
It causes trouble during cross-linking and foaming, and also 30g / 1
If the time is 0 minutes or more, the torque during extrusion becomes too low, resulting in a decrease in extrusion amount and not only a marked decrease in productivity, but also a foam having a high expansion ratio cannot be obtained.

It is essential that the polyolefin resin crosslinked foam sheet of the present invention contains LDPE and HDPE. The mixing ratio of LDPE is preferably 60 to 95% by weight, and HDPE is preferably 5 to 40% by weight. If the blending ratio of HDPE exceeds 40% by weight, shearing heat will increase and the resin temperature will rise excessively, which will cause troubles during cross-linking and foaming, which not only deteriorates the workability of the pipe cover but also improves the heat insulating property. Inferior foam sheet. If the blending ratio of LDPE exceeds 95% by weight, the foam sheet excellent in dimensional stability, which is the object of the present invention, cannot be obtained.

The peroxide decomposition type antioxidant used in the present invention has a function of decomposing the peroxide generated during the oxidative deterioration of the polyolefin resin and stopping the subsequent auto-oxidation cycle. What you have, for example, 2,
2-methylenebis (4,6-di-t-butylphenyl)
Octyl phosphite, cyclic neopentane tetrayl bis (octadecyl phosphite), distearyl pentaerythritol diphosphite, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-
4-hydroxyphenol) propionate] and other phosphite-based antioxidants, pentaerythritol-tetrakis- (β-lauryl-thiopropionate), bis [2-methyl-4- {3-n-alkylthiopropionyloxy} Thioethers such as -5-t-butylphenyl] sulfide, dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate Examples include system antioxidants and the like. When an antioxidant other than a peroxide decomposition type antioxidant is used as the antioxidant, for example, a peroxy radical scavenging antioxidant represented by a phenolic antioxidant is used, the radicals generated during crosslinking are trapped. As a result, the cross-linking efficiency is lowered and the foam sheet is inferior in dimensional stability.

The antioxidant is preferably added in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the polyolefin resin. If the amount is less than 0.1 parts by weight, the desired antioxidant effect cannot be obtained, the crosslinking becomes insufficient, and the foam sheet has poor dimensional stability. If it exceeds 5 parts by weight, not only does it no longer contribute to the improvement of the antioxidant effect, but also the surface of the foam sheet is roughened and the appearance is significantly impaired.

The copper damage inhibitor used in the present invention has the effect of reducing the oxidative deterioration promoting action of the metal on the resin. For example, 2,2'-oxaminobis-
[Ethyl 3- (3,5-di-t-butyl 4-hydroxyphenyl) propionate], 3- (N-salicyloyl) amino 1,2,4 triazole, decamethylene dicarboxylic acid acid disalicyloyl hydrazide, NN '-Bis [3- (3,5-di-t-butyl-4
-Hydroxyphenyl) propionyl] hydrazine, isophthalic acid bis (2-phenoxypropionylhydrazide) and the like.

The amount of the copper damage inhibitor added is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the polyolefin resin. This is because if it is less than 0.1 parts by weight, the dimensional stability is poor, and if it exceeds 5 parts by weight, it not only contributes to the improvement of dimensional stability, but also the surface of the foam sheet is roughened and the appearance is remarkably impaired. . In the present invention, since the peroxide decomposition type antioxidant and the copper damage inhibitor are used in combination, the dimensional stability of the foam sheet can be maintained even in the state of contacting with copper at 120 ° C. or higher. , No discoloration occurs.

The gel fraction on at least one side of the foam sheet is preferably 65% or more. The gel fraction does not need to be uniform in the thickness direction, and the gel fraction in the thickness direction of about 1 mm on the surface exposed to a temperature of 120 ° C. or higher is 6
It may be 5% or more. When the gel fraction is less than 65%, the dimensional stability becomes poor and discoloration may occur when used at a temperature of 120 ° C. or higher. Since the foam sheet of the present invention contains HDPE that is difficult to crosslink,
The gel fraction of the foam sheet obtained during ordinary cross-linking foaming tends to be lower than that in the case where HDPE is not mixed. Therefore, when the gel fraction on at least one side of the foam sheet does not reach 65%, the gel fraction is reduced to 65% by irradiating the foam sheet with an electron beam or the like.
It is necessary to adjust to more than%.

The foam sheet of the present invention comprises LDPE and HD.
Use of PE blends, peroxide decomposition type antioxidants,
When the gel fraction on at least one side of the foam sheet is 65% or more together with the copper anti-corrosion agent, there is no risk of discoloration and a high degree of dimensional stability can be maintained.

One embodiment of the method for producing a crosslinked foamed polyolefin resin sheet of the present invention and the method for producing a heat insulating pipe cover for copper pipes using this foam will be described below.

A resin composition containing the above-mentioned polyolefin resin, a peroxide decomposition type antioxidant, and a copper damage inhibitor in a predetermined ratio, a known thermal decomposition type foaming agent (eg, azodicarbonamide), and a known crosslinking agent. After being melt-kneaded with an agent (for example, dicumyl peroxide), it is molded into a sheet by means such as extrusion molding at a temperature at which the foaming agent and the cross-linking agent are not decomposed. The sheet thus obtained is put into a hot air oven maintained at, for example, 230 ° C. to be crosslinked and foamed at the same time, and then electron beam irradiation is performed so that the gel fraction on the surface of the foamed sheet becomes 65% or more, The foam sheet of the present invention is obtained. Crosslinking finally results in a gel fraction of 6 on the surface of the foam sheet.
It may be 5% or more, and may be performed only with the chemical crosslinking agent, or may be performed by only irradiating the sheet extruded without using the chemical crosslinking agent with the electron beam.

The obtained foam sheet is cut in the longitudinal direction to obtain a belt-shaped sheet having a predetermined width. The band-shaped sheet is rolled in the width direction so that the surface irradiated with the electron beam becomes the inner surface, and the end faces abutted against each other are welded and molded into a pipe shape to obtain the heat-insulating pipe cover of the present invention.

In the heat insulating pipe cover of the present invention, a resin film may be laminated on the outer peripheral surface of the heat insulating pipe cover in order to protect the surface or improve the workability of the heat insulating pipe cover to the piping, and a slit is formed in the longitudinal direction. You can also

[0020]

The present invention will be described in more detail based on the following examples. In addition, the test evaluation was performed as follows (1)-(6) about each characteristic of an Example and a comparative example. However, when the characteristics of (1) and (2) are defective,
The characteristics of (5) and (6) were not evaluated.

Test Evaluation Method (1) Extrudability When the resin composition shown in Table 1 was molded into a sheet using an extruder at a temperature not higher than the thermal decomposition temperature of the foaming agent and the crosslinking agent used, the extrusion amount, By observing the internal pressure of the extruder and the appearance of the sheet and making a comprehensive judgment, good ones are good, bad ones are bad.
And (2) Foaming processability When the extruded sheet is placed in a hot air oven maintained at 230 ° C. for cross-linking and foaming, the foaming state of the sheet in the hot air oven, the appearance of the foamed sheet, and the density are comprehensively judged. The good ones were marked with ◯, and the bad ones were marked with x. (3) Density of Foamed Sheet The density of the foamed sheet was measured according to the method described in JIS k 6767 “Polyethylene foam test method”. (4) Measurement of gel fraction The surface of the produced foam sheet irradiated with an electron beam was cut into a sample having a thickness of 1 mm, and the sample was dipped in a xylene solvent heated to 120 ° C. for 24 hours, then dried and dipped. The gel fraction was calculated from the mass of the sample before and after by the following formula. Gel fraction (%) = (mass of sample after immersion drying) / (mass of sample before immersion) × 100 (5) Dimensional stability of heat insulating pipe cover JIS A 9515 “Polyethylene foam heat insulating material”
According to the test method of. The heat-insulating pipe cover made from the foam sheet is set in a copper pipe, and heated steam adjusted to 140 ° C. is continuously passed through the copper pipe, and after 168 hours have passed, the heat-insulating pipe cover is removed and allowed to cool, The thickness shrinkage (%) was measured. (6) Presence or absence of discoloration of heat insulating pipe cover After the test of (5), presence or absence of discoloration of the heat insulating pipe cover was observed.

Example 1 100 parts by weight of a polyolefin resin consisting of 70% by weight of LDPE * 1 and 30% by weight of HDPE * 2, 0.1 part by weight of a phosphite-based antioxidant * 4, and a copper damage inhibitor * 6
A resin composition consisting of 0.1 parts by weight was melt-mixed with a compound in which 0.8 parts by weight of dicumyl peroxide as a crosslinking agent and 28 parts by weight of azodicarbonamide (decomposition temperature 180 ° C.) as a foaming agent were blended, L / D = 28
Was extruded using a φ40 mm extruder to produce a sheet having a thickness of 2 mm. This sheet was placed in a hot air oven at 230 ° C. to crosslink and foam. Test evaluation was performed on the properties (1) to (3) of the obtained foam sheet. Subsequently, an acceleration voltage of 400 k was applied to one side of the obtained foam sheet.
Irradiating with electron beam of eV and irradiation dose of 100 kGy, (4)
Was tested. Then, a slit is formed in the longitudinal direction of the foam sheet to form a strip-shaped sheet having a predetermined width, and the strip-shaped sheet is rolled in the width direction so that the surface irradiated with the electron beam is the inner surface, and the abutted end surfaces are welded together to form a pipe. To form a heat-insulating pipe cover having a diameter of 20 mm. Test evaluation was performed on the properties (5) and (6) of the obtained heat insulating pipe cover.

Examples 2 and 3 In Example 2, LDPE 65% by weight, HDPE * 2 35
A foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that the weight percentage was changed. Further, in Example 3, a foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that LDPE was 80% by weight and HDPE * 2 was 20% by weight.

Example 4 A foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that HDPE * 3 was used as the high density polyethylene.

Example 5 A foam sheet was produced with the same resin composition and the same molding conditions as in Example 1 except that a thioether type antioxidant * 5 was used as the antioxidant.

Comparative Example 1 A foam sheet was produced with the same resin composition and the same molding conditions as in Example 1 except that HDPE was not blended and LDPE was 100% by weight.

Comparative Example 2 A foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that LDPE was 55% by weight and HDPE * 2 was 45% by weight.

Comparative Example 3 A foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that no antioxidant was added.

Comparative Example 4 A foam sheet was produced under the same resin composition and the same molding conditions as in Example 1 except that the copper damage inhibitor was not added.

Comparative Example 5 A foam sheet was produced with the same resin composition and the same molding conditions as in Example 1 except that the foam sheet was not irradiated with an electron beam.

Comparative Example 6 Foaming under the same resin composition and the same molding conditions as in Example 1 except that LDPE was 100% by weight, no antioxidant and no copper damage inhibitor were added, and no electron beam was irradiated. A body sheet was produced. Table 1 shows the test evaluation results of the characteristics of Examples 1 to 5 and Comparative Examples 1 to 6.

[0032]

[Table 1]

As is clear from Table 1, Examples 1 to 5
Had a thickness shrinkage of 7% or less, had no discoloration, and had excellent properties as a pipe cover.

On the other hand, in Comparative Example 1, since HDPE was not mixed, the wall thickness of the pipe cover was greatly shrunk,
In addition, the contact surface of the foam sheet with the copper tube was discolored. In Comparative Example 2, since the blending ratio of LDPE and HDPE was unsuitable, the resin temperature was excessively increased during extrusion processing, and the obtained sheet hardly foamed. In Comparative Example 3,
Since no antioxidant was added, the wall thickness of the pipe cover was greatly shrunk, and the contact surface of the foam sheet with the copper pipe was discolored. In Comparative Example 4, since the copper damage inhibitor was not mixed, the wall thickness of the pipe cover was greatly shrunk, and the contact surface of the foam sheet with the copper pipe was discolored. In Comparative Example 5, since the electron beam irradiation was not performed, the gel fraction on the surface of the foam sheet in contact with the copper tube was 65% or less, the pipe cover had a significantly large wall thickness shrinkage, and the copper tube of the foam sheet was The contact surface of the was discolored. In Comparative Example 6, HDPE, an antioxidant,
Since no copper damage inhibitor is added and the gel fraction of the surface in contact with the copper pipe is 65% or less, the shrinkage of the wall thickness of the pipe cover is significantly large, and the contact surface of the foam sheet with the copper pipe Was markedly blackened and had holes in some parts, and did not remain in its original form.

[0035]

EFFECT OF THE INVENTION The polyolefin resin crosslinked foam sheet of the present invention is rich in flexibility and almost never shrinks in sheet thickness even when heated to a temperature not lower than the melting point of constituent resin components, for example, 120 ° C. or higher. It has excellent dimensional stability and does not cause discoloration. Utilizing these characteristics, it can be used as a heat insulating material in application fields such as building materials or home electric appliances such as air conditioners.
In particular, a heat-insulated pipe cover formed by molding is useful in the above-mentioned application fields.

Claims (2)

(57) [Claims] 1. A melt flow rate of 0.3 to 3.5 g /
Low density polyethylene resin 60 to 95% by weight for 10 minutes, density 0.945 to 0.975 g / cm ³ , melting point 120 to 1
0.1 to 5 parts by weight of a peroxide decomposition type antioxidant with respect to 100 parts by weight of a polyolefin resin composed of 5 to 40% by weight of a high-density polyethylene resin having a melt flow rate of 10 to 30 g / 10 minutes at 35 ° C. And copper damage inhibitor 0.1
A polyolefin resin crosslinked foam sheet obtained by crosslinking and foaming a resin composition containing 5 parts by weight, wherein the gel fraction on at least one side of the foam sheet is 65% or more. Crosslinked foam sheet. 2. A heat-insulating pipe cover for a copper pipe, which is formed by cylindrically processing the polyolefin resin crosslinked foam sheet according to claim 1 so that a surface having a gel fraction of 65% or more is an inner surface.