JP2000191880A - Gasket for refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a non-halogenated resin coping with environmental problems by using a resin composition obtained by mixing polypropylene, a hydrogenated block copolymer, a thermoplastic copolymer and a softner of a paraffin-based process oil, each mixing ratio being in a specific range. SOLUTION: 15-21 wt.% of polypropylene having MFR of 0.5-10, 25-41 wt.% of a hydrogenated block copolymer having a number average molecular weight of 100,000-200,000, the polymer block thereof comprising an aromatic vinyl compound and a conjugated diene compound as major components, the content of the aromatic vinyl compound being 5-50 wt.% and hydrogenation degree of the diene component being not less than 70%, 12-22 wt.% of a thermoplastic elastomer having xylene-insoluble content of 30-50 wt.% which is a dynamically or statically vulcanized mixture of ethylene-α.olefin(-conjugated diene) copolymer and an olefin-based resin and 26-38 wt.% of a softner having viscosity at 40 deg.C of 200-500 cSt and an aniline point of 130-160 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refrigerator gasket which uses a resin which is unlikely to become a harmful substance such as halogen and which is environmentally friendly.

[0002]

2. Description of the Related Art In general, refrigerator gaskets are made of soft vinyl chloride, but foodstuffs are usually stored in refrigerators, and vinyl chloride resin, which is a problem with environmental hormones, has become an environmental problem. Further, when the refrigerator is disposed of, there is a problem that dioxin and the like cannot be easily incinerated because halogen is contained in vinyl chloride. In order to solve these problems, a study was conducted using a resin that does not use vinyl chloride.However, due to problems such as abrasion, insufficient heat welding at corners, and stickiness on the surface, the use of non-halogen resins was In many cases, the replacement of refrigerator gaskets made of vinyl chloride resin, which has been pointed out due to environmental issues, cannot be promoted.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a refrigerator molded from a halogen-free resin, such as environmental hormones and dioxins, having the same characteristics as conventional refrigerator gaskets molded from vinyl chloride resin. To provide a gasket.

[0004]

The present invention relates to (a) a melt flow (hereinafter abbreviated as MFR: ASTM-D-1238).
L condition, 230 ° C. Hereinafter, the same condition) is 0.5 to 10 g /
(B) at least one or more polymer blocks A mainly composed of a vinyl aromatic compound and at least one or more polymer blocks B mainly composed of a conjugated diene compound; And the content of the vinyl aromatic compound is in the range of 5 to 50% by weight, 70% or more of the conjugated diene compound is hydrogenated, and the number average molecular weight is 100,000 to 2%.
25 to 41% by weight of 100,000 hydrogenated block copolymer (c) A blend of a dynamically or statically vulcanized ethylene-α-olefin copolymer rubber and a polyolefin resin, or a dynamic or static blend Statically vulcanized ethylene
xylene-insoluble matter in a blend of α-olefin-non-conjugated diene copolymer rubber and polyolefin resin (elution condition; immersion at 120 ° C x 20 hours, filtration through 100 mesh, and 100 mesh residue as a whole before treatment) To obtain a gel percentage (hereinafter referred to as a gel fraction) of 30 to 50%.
12 to 22% by weight of a thermoplastic elastomer having a viscosity (40 ° C.) of 300 to 500 centist.
This is a refrigerator gasket using a resin containing 26 to 38% by weight of a paraffinic process oil softener having an aniline point of 130 to 160 ° C.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The polypropylene in the resin composition is
Good appearance and heat resistance are imparted to the resulting composition. The type of polypropylene is not particularly limited, and may be homopolypropylene, random polypropylene, or block polypropylene. Among them, homopolypropylene is preferable in terms of heat resistance. The polypropylene is M
When the FR is 0.5 to 10 g / 10 min and the MFR is less than 0.5 g / 10 min, the flowability of the whole composition is lowered and the moldability is deteriorated. If it exceeds 10 g / 10 min, the hydrogenated block copolymer is poorly dispersed, resulting in uneven appearance of the product and unstable physical properties, which is not preferable. Preferably, it is 0.5 to 10 g / 10 min. If the addition amount is less than 15% by weight, the flowability of the entire resin composition is reduced, moldability is deteriorated, and flexibility is impaired at 21% by weight. If necessary, a polypropylene containing a nucleating agent, an antistatic agent and a weathering stabilizer may be used as long as the above properties are not impaired.

The hydrogenated block copolymer in the resin composition comprises at least one polymer block A mainly composed of a vinyl aromatic compound and at least one polymer block B mainly composed of a conjugated diene compound. Having the above, and
The content of the vinyl aromatic compound is in the range of 5 to 50% by weight, and 70% or more of the conjugated diene compound portion is obtained by hydrogenation. As the vinyl aromatic compound in the hydrogenated block copolymer, styrene, α-
Methylstyrene, o, m and p-methylstyrene,
Examples thereof include 1,3-dimethylstyrene, vinylnaphthalene, and vinylanthracene. Incidentally, the polymer A is a polymer composed of a homopolymer or a mixture thereof. The conjugated diene compounds include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3 butadiene, 1,3-butadiene,
Examples thereof include pentadiene and 1,3-hexadiene, and the polymer block B is a homopolymer or a mixture of these. The content of the vinyl aromatic compound in the hydrogenated block copolymer is 5 to 50% by weight. If the content of the vinyl aromatic compound is out of this range, the rigidity of the whole composition becomes high, and the flexibility cannot be maintained.

The number average molecular weight of the hydrogenated block copolymer (M
n) is at least 100,000, preferably 130,00
0 to 200,000, with a molecular weight distribution Mw /
Mn is 10 or less (Mw: weight average molecular weight), preferably 5 or less, more preferably 2 or less. When the number average molecular weight is less than 100,000, sufficient oil resistance cannot be provided. In addition, the number average molecular weight is 200,000
If it exceeds, the fluidity is extremely reduced and molding cannot be performed. Further, the hydrogenated block polymer has 70% of the conjugated diene portion.
The above is the result of hydrogenation. If the hydrogenation ratio of the conjugated diene portion is less than 70%, the weather resistance is extremely poor and the use is greatly restricted, which is not preferable. The structure of the hydrogenated block copolymer may be linear or branched. Further, the hydrogenated block copolymer used in the present invention may be a further modified one, that is, one having a polar group such as a hydroxyl group, a carboxyl group, or an epoxy group at the molecular terminal or in the molecular chain. . In addition, the hydrogenated block copolymer used here has a low number-average molecular weight and thus poor fluidity. Therefore, if it exceeds 41% by weight, the fluidity becomes extremely poor, and if it is less than 25% by weight, oil resistance is impaired. Preferably it is 27 to 33% by weight.

The blend of the dynamically or statically vulcanized ethylene-α-olefin copolymer rubber and the polyolefin resin used in the present invention or the dynamically or statically vulcanized ethylene- A thermoplastic elastomer having a xylene-insoluble content of 30 to 50% in a blend of an α-olefin-non-conjugated diene copolymer rubber and a polyolefin resin greatly contributes to improvement in heat welding characteristics and moldability, and appearance. Also, there is a feature very similar to the surface state of the halogen resin. As the α-olefin in the copolymer rubber, one having 3 to 15 carbon atoms is suitable. As the non-conjugated diene, dicyclopentadiene, 1,4-hexadiene, ethylidene norbornene, methylene norbornene and the like can be used. In the present invention, polypropylene is suitable as the α-olefin from the viewpoint of availability and improvement of heat resistance. Therefore, the so-called E
PDM is preferred. The ethylene / α-olefin ratio of the copolymer rubber is preferably from 50/50 to 90/10 by weight, more preferably from 60/40 to 80/20.

As the vulcanizing agent, ordinary vulcanizing agents for rubber can be used, and in particular, in addition to sulfur, alkyl phenol
Organic peroxides such as formaldehyde resin and dicumyl peroxide are particularly preferably used. In addition to the vulcanizing agent, a vulcanizing aid, an antioxidant and the like may be used in combination. The addition amount of the alkylphenol-formaldehyde resin is preferably in the range of 0.5 to 15 parts by weight based on 100 parts by weight of the copolymer rubber in view of the balance between strength and processability. In the case of an organic peroxide, 0.05 wt.
The range of 1 part by weight to 1 part by weight is preferable in view of strength and workability. It is indispensable to contain 5 parts by weight or more of the polyolefin resin with respect to 100 parts by weight of the copolymer rubber in order to maintain processability. While dynamically blending and kneading the blend of the copolymer rubber and the polyolefin resin, a vulcanizing agent is added and vulcanized to obtain the component (c).

The gel fraction of the above component (c) (elution conditions;
After immersion in xylene at 120 ° C. for 20 hours, the mixture is filtered with 100 mesh, and the 100 mesh residue is divided by the total weight before treatment to obtain a percentage. ) Is preferably 30% by weight to 50% by weight. When the gel fraction is less than 30% by weight, the heat-welding property of the corner portion is insufficient, and when it exceeds 50% by weight, the abrasion is rapidly reduced and a problem occurs. The amount of the component (c) is
It can be selected in the range of 12 to 22% by weight. Preferably, it is 16 to 20% by weight. If the content is less than 12% by weight, the heat-sealing property is insufficient, and the adhesiveness of the surface by the oil used as the softener cannot be suppressed, and the adhesiveness on the appearance surface of the molded product is undesirably increased. On the other hand, if it exceeds 22% by weight, there is a drawback that the strength is extremely reduced and the abrasion is reduced.

The softening agent in the resin composition has characteristics of softening the composition and imparting fluidity. As a kind of the softening agent, a paraffinic oil having a viscosity (40 ° C.) of 300 to 500 centistokes and an aniline point of 130 to 160 ° C. in terms of bleed is used from the viewpoint of compatibility. There is a need to. The amount of addition should be 26 to 38% by weight from the viewpoint of fluidity, softening effect, bleed, and surface tackiness. Preferably, it is 30 to 34% by weight.

[0012] If necessary, an inorganic filler, a nucleating agent,
Outer lubricant, inner lubricant, light stabilizer, ultraviolet absorber, antioxidant,
You may add a coloring agent and a surface modifier. As a method for producing the composition of the present invention, all general methods used for producing ordinary resin compositions and rubber compositions can be employed. Basically, it is a mechanical melt kneading method, in which a single-screw extruder, a twin-screw extruder, a Banbury mixer, various kinds of kneaders, Brabenders, rolls and the like are used. At this time, the temperature for melt-kneading can be suitably selected from 180 to 300 ° C. Since the composition obtained here is thermoplastic, it can be molded using a commonly used thermoplastic resin molding machine.

A resin gasket can be formed by molding the obtained resin with an extruder usually used for vinyl chloride. Cut the molded product obtained by extrusion molding into a fixed size, insert a magnet in the bag on the surface that comes in contact with the refrigerator iron plate, insert a little foam in the corner part to keep the shape, and heat weld the corner parts together. Obtain a refrigerator gasket.

[0014]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Each component blended in Examples and Comparative Examples,
It is as follows. <Component a (1)> Polypropylene (MFR =
<1g / 10min) <Component a (2)> JPO polypropylene (MFR =
15g / 10min) <Component b (1)> Polystyrene- manufactured by Asahi Kasei Corporation
Hydrogenated block copolymer having a structure of hydrogenated butadiene-polystyrene (styrene content: 30%, hydrogenation rate: 70% or more, number average molecular weight 120,000) <Component b (2)> Asahi Kasei Corporation ) Made of polystyrene
Hydrogenated block copolymer having a hydrogenated butadiene-polystyrene structure (styrene content: 30%, hydrogenation rate: 70% or more, number average molecular weight: 60,000) <Component b (3)> Kuraray polystyrene Hydrogenated block copolymer having a hydrogenated isoprene-polystyrene structure (styrene content: 30%, hydrogenation rate:
<70% or more, number average molecular weight 170,000) <Component b (4)> Hydrogenated block copolymer having a polystyrene-hydrogenated isoprene-polystyrene structure manufactured by Kuraray (styrene content: 30%, hydrogenation rate:
70% or more, number average molecular weight 80,000) <Component c (1)> Ethylene-propylene copolymer manufactured by Nippon Synthetic Rubber Co., Ltd. (gel fraction 0%) <Component c (2)> manufactured by Sumitomo Chemical Co., Ltd. Olefin-based thermoplastic resin (gel fraction 42%) <Component d (1)> Idemitsu Kosan's paraffin-based process oil (viscosity (40 ° C) = 382)
(Centisto-kus aniline point = 144 ° C.) <Component d (2)> Idemitsu Kosan's paraffin-based process oil (viscosity (40 ° C.) = 96 centist-kus aniline point = 128 ° C.) <Component d (3)> Idemitsu Kosan's naphthenic Process oil (viscosity (40 ° C) = 238 centistokes-Kusaniline point = 90 ° C)

The above components (a) to (d) are replaced with Banbury.
Kneading with a mixer at a kneading temperature of 220 ° C.
Into a thin sheet. It was pulverized by a pulverizer to form a square pellet to obtain a thermoplastic resin. Φ5
It is molded using a 0 mm extruder, and cuts, inserts a magnet, inserts a foam, and heat-welds a corner to obtain a refrigerator gasket. Then, a predetermined test piece was cut out and the following items were evaluated.

(1) Tensile strength: JIS K6301 (tensile speed: 200 mm / min) Evaluation symbol and criteria 1 ○: 10 Mpa or more ×: less than 10 Mpa (2) Formability and appearance: Extrudability with a 50 mm extruder and its surface The appearance of the properties was evaluated visually and by touch. Evaluation symbol and criterion 2 ○: There is no stickiness in the surface state, and there is no defect due to large foreign matter and the like, and it can be molded as soft PVC. X: The surface condition is sticky, has a large foreign matter defect, or cannot be molded as well as soft PVC. (3) Flexibility: Hardness: JIS K6301 (JIS A
(Value after 5 seconds) Evaluation symbol and criterion 3 ○: less than 80 ×: 80 or more

(4) Heat-welding property at the corners
After treating at 0 ° C. for about 1 to 2 minutes, the welding strength was determined by percentage in comparison with the welding strength of a conventional vinyl chloride resin in a 90 ° C. peel test. Evaluation symbol and criterion 4 ：: PVC welding strength ratio of 60% or more ×: PVC welding strength ratio of less than 60% (5) Oil resistance: immersed in soybean oil and left at 40 ° C. for 48 hours. Subsequent evaluation of the weight change rate and evaluation criteria 5: Less than 10% weight change ×: More than 10% weight change (6) Bleed characteristics: Accelerated weathering test (sunshine weather, black panel temperature 63) ℃, with rain x 300hr
The surface condition of the test piece after s) was observed. Evaluation symbol and judgment criteria 6 ○: No bleed ×: With bleed (7) Opening / closing test in refrigerator: A gasket is attached to the refrigerator, and open / close test is performed 200,000 times at a rate of 10,000 times / day. Evaluation symbol and judgment standard 7 ：: No abnormality in 200,000 open / close tests. ×: Defects such as tears are confirmed. These results are shown in Tables 1 to 3.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

According to the present invention, the secondary processing such as heat welding is good, and the surface of the molded product is matte, flexible, less sticky, and has a wide molding processing width balanced in strength, oil resistance and the like. By using a non-halogen thermoplastic resin having a good appearance, a refrigerator gasket which has the same characteristics as a refrigerator gasket formed of vinyl chloride and is compatible with environmental issues can be obtained.

Claims (1)

[Claims] (1) Melt flow is from 0.5 to 10 g /
(B) at least one or more polymer blocks A mainly composed of a vinyl aromatic compound and at least one or more polymer blocks B mainly composed of a conjugated diene compound; And the content of the vinyl aromatic compound is in the range of 5 to 50% by weight, 70% or more of the conjugated diene compound is hydrogenated, and the number average molecular weight is 100,000 to 2%.
25 to 41% by weight of 100,000 hydrogenated block copolymer (c) A blend of a dynamically or statically vulcanized ethylene-α-olefin copolymer rubber and a polyolefin resin, or a dynamic or static blend Statically vulcanized ethylene
α-olefin-non-conjugated diene copolymer rubber and polyolefin resin blend with 30 xylene insolubles
12 to 22% thermoplastic elastomer
% By weight (d) Viscosity (40 ° C.) of 300 to 500 centi-
A refrigerator gasket using a resin containing 26 to 38% by weight of a paraffinic process oil softener having an aniline point of 130 to 160 ° C.