JPH0873746A - Organopolysiloxane composition for heating element and production of heating element - Google Patents

Abstract

PURPOSE: To obtain a heating element which sufficiently retains the initial PTC characteristics even after repeated heat cycles over a long term and has a practically useful temp. self-control function. CONSTITUTION: An organopolysiloxane compsn. for a heating element is prepd. by compounding as the essential ingredients 100 pts.wt. organopolysiloxane having at least two alkenyl groups at the molecular ends and a viscosity at 25 deg.C of 10,000cSt or higher, 0.1-30 pts.wt. organohydrogenpolysiloxane having at least three hydrogen atoms directly bonded to silicon atoms in the molecule, a catalytic amt. of a cure catalyst, 0.1-30 pts.wt. adhesive component, 45-400 pts.wt. carbon particles having a BET specific surface area of 10m<2> /g or lower, and 10-30 pts.wt. carbon black having a BET specific surface area of 20m<2> /g or higher.

Description

Detailed Description of the Invention

[0001]

The present invention has a positive temperature coefficient,
The present invention relates to an organopolysiloxane composition that provides a heating element that retains this property even after repeated long-term heat cycles, and a method for producing a heating element using the composition.

[0002]

2. Description of the Related Art A conductive polymer obtained by blending an organic resin or a rubber-like material with carbon powder is suddenly heated when its electric resistance reaches a certain temperature range. It has already been known that the positive temperature coefficient is increased (hereinafter referred to as PTC characteristic), and that it has a self-temperature control function useful as a heating element (Japanese Patent Publication No. 33707/1975). 3-28
No. 0381).

The above Japanese Patent Publication No. 50-33707 discloses that
A composition in which a spherical polymer powder of 0.008 to 200 μm is mixed with a crystalline polymer is disclosed and disclosed in JP-A-3-280381.
Japanese Patent Publication discloses a self-regulating surface heating element obtained by filling spherical carbon or carbon fiber in rubber or elastomer resin.

[0004] Similarly, an attempt to make a heating element by filling carbon with an organopolysiloxane as a medium is also known. For example, JP-A-63-207081 discloses that
Disclosed is a sheet heating element in which a silicone rubber composition is filled with carbon having a powder, fiber or whisker-like morphology and cured at a temperature of room temperature or higher. Furthermore, Japanese Patent Laid-Open No. 1-1
Japanese Patent Publication No. 08276 discloses a conductive heat-generating coating material containing carbon particles, which are spherical particles having a particle diameter of 500 μm or less, and a synthetic resin as main components.

The object of these inventions is to generate heat by passing an electric current through a conductive heating element and to provide a switch function by the high coefficient of thermal expansion of organopolysiloxane to control the temperature. (PTC characteristic).

However, these conventional heating elements are
There is a problem in that the initial PTC characteristics are not maintained when the temperature is repeatedly raised and lowered for a long period of time, and the performance deteriorates, which is not practical.

The present invention has been made in view of the above circumstances, and it is an organopolysiloxane that provides a heating element having a self-temperature control function that sufficiently retains the initial PTC characteristics even during repeated heat cycles over a long period of time and is practically usable. It is an object to provide a composition and a method for producing a heating element using the composition.

[0008]

Means and Actions for Solving the Problems The present inventors have
As a result of intensive studies to achieve the above object, (A) an organopolysiloxane having at least two alkenyl groups at the molecular chain terminals and having a viscosity at 25 ° C. of 10,000 cs or more: 100 parts by weight, (B) one molecule Organohydrogenpolysiloxane having hydrogen atoms directly bonded to at least 3 silicon atoms: 0.1 to 30 parts by weight, (C) Platinum-based catalyst: catalytic amount (D) Adhesive component: 0.1 to 30 parts by weight Parts (E) carbon particles having a BET specific surface area of 10 m ² / g or less: 45 to 400 parts by weight, (F) carbon black having a BET specific surface area of 20 m ² / g or more: 10 to 30 parts by weight as essential components It was found that the above-mentioned organopolysiloxane composition is effective.

That is, an organopolysiloxane having a large coefficient of thermal expansion is used as a main component in order to develop a critical PTC characteristic, and the molecular weight between the cross-linking points of the organopolysiloxane is increased so that this large heat is generated in repeated heat cycles. To follow the displacement due to expansion,
At the same time, in order to maintain the initial positional relationship with the carbon powder which is the filler, an adhesive component is blended for the purpose of strengthening the bond between the filler and the silicone resin, and fine carbon powder is used in combination with large carbon particles. By doing so, it is necessary to use a large amount of compounding in order to obtain a certain conductivity only with carbon particles having a relatively large particle size, and as a result, the strength as a heating element decreases and it cannot be put to practical use. In addition to being able to prevent it, the addition of fine carbon powder can also contribute to the improvement of heat resistance. With these, the initial PTC characteristics can be sufficiently maintained even in repeated heat cycles for a long time, and a self-temperature control function that can withstand practical use can be obtained. It has been found that an organopolysiloxane composition is obtained which gives a heating element having.

Further, in this organopolysiloxane composition, the curing temperature is an important factor for exerting the critical PTC characteristics, and the curing temperature is 100 ° C.
It has been found that when it exceeds the above range, good PTC characteristics are not expressed, and the present invention has been completed.

Therefore, the present invention provides the organopolysiloxane composition for a heating element and the organopolysiloxane composition for a heating element, which are characterized in that the components (A) to (F) are essential components. Provided is a method for producing a heating element, which is characterized in that, after being shaped into a shape, the shaped body is heated at a temperature of 100 ° C. or lower and cured.

The present invention will be described in more detail below. The organopolysiloxane composition for a heating element of the present invention comprises the organopolysiloxane (A) as described above.
(B) Organohydrogenpolysiloxane, (C)
The platinum-based catalyst, (D) adhesive component, (E) carbon particles and (F) carbon black are essential components.

Here, the organopolysiloxane of the component (A) is the main component of the composition of the present invention, and it withstands the high temperature when used as a heating element and has a role of self-controlling heat generation by its large thermal expansion coefficient. It is the ingredient responsible for. Therefore, the viscosity at 25 ° C. having at least two alkenyl groups at the end of the molecular chain needs to be 10,000 cs or more, and thereby the heating element obtained by curing is made to have sufficient stretchability, and the organopolysiloxane itself has In addition to having the characteristic that the molded body does not break due to thermal expansion, it can be put to practical use in the PTC characteristic. In this case, the upper limit of the preferable viscosity range is 1
It is 000000 cs, and when the viscosity becomes higher than this, P
TC characteristics are good, but the physical strength is weak and
Even if the viscosity of the composition itself becomes too high and the composition is diluted with a solvent, it may cause trouble in the heating element manufacturing work, which is not preferable. More preferable viscosity range is 10,000 to 5
It is 00000cs.

The organopolysiloxane as the component (A) has the following general composition formula. _Ra SiO _{(4-a) / 2}

R is an alkyl group such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, hexyl group, cyclohexyl group, octyl group, vinyl group, allyl group,
Propenyl group, isopropenyl group, butenyl group, alkenyl group such as hexenyl group, phenyl group, tolyl group, aryl group such as xylyl group, aralkyl group such as benzyl group, phenylethyl group and a part of hydrogen atom of these groups Or a chloromethyl group in which all are substituted with halogen atoms,
A chloropropyl group, a 3,3,3-trifluoropropyl group, etc., preferably having 1 to 10 carbon atoms, particularly 1 to 1 carbon atoms.
8 represents an unsubstituted or substituted monovalent hydrocarbon group, and a is 1.
The number of 8 ≦ a ≦ 2.205 is shown.

As such an organopolysiloxane, more specifically, those represented by the following formula (1) can be used.

[0017]

Embedded image

In the above formula, R ² is R in the above general composition formula.
Shows the same unsubstituted or substituted monovalent hydrocarbon group, preferably having 1 to 10 carbon atoms, particularly 1 to 8 carbon atoms, specifically, an alkyl group such as a methyl group, an aryl group such as a phenyl group, It is a group selected from halogen-substituted alkyl groups such as trifluoropropyl group. R ¹ is a group selected from aliphatic unsaturated groups having 2 to 8 carbon atoms represented by alkenyl groups such as vinyl group, allyl group and butenyl group similar to the alkenyl group in R above, and n is 500 or more. Represents a positive number.

The component (B), an organohydrogenpolysiloxane, is a compound that acts as a cross-linking agent for curing the composition of the present invention. Therefore, it is necessary to have at least three hydrogen atoms directly bonded to silicon atoms in one molecule. There is. The molecular structure is not particularly limited, and various types such as conventionally produced linear, cyclic and branched structures can be used.

The organohydrogenpolysiloxane as the component (B) has the following general composition formula. R ³ _b H _c SiO _{(4-bc) / 2}

R ³ is the same as R in the preferred general compositional formula of the component (A), preferably an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms. And it is particularly preferred that it does not contain an aliphatic unsaturated bond. Also, b and c are each 0.002
≦ c ≦ 1.0, 1.8 <b <2.2, 1.8 <b + c ≦
It is a number that satisfies 3.0, and the viscosity of the organohydrogenpolysiloxane of the component (B) is 1 to 25 at 25 ° C.
It is preferably in the range of 1000 cs.

The blending amount of the component (B) is the same as the component 1 of the component (A).
0.1 to 30 parts, preferably 0.5 to 1 with respect to 00 parts
It is in the range of 0 part, and is 0.5 to 5 with respect to one aliphatic unsaturated group such as an alkenyl group contained in the composition of the present invention, particularly in the component (A) and / or the component (D). The amount is 0 equivalent, preferably 0.8 to 3.0 equivalents. 0.5
If the amount is less than the equivalent, the crosslink density becomes too low, which may adversely affect the heat resistance of the cured heating element.
If it is more than 0 equivalents, there may be a problem of foaming due to a dehydrogenation reaction, and again, heat resistance may be adversely affected.

As the platinum-based catalyst of the component (C), platinum,
Compounds used in ordinary addition-curable silicone compositions such as chloroplatinic acid, alcohol modified products of chloroplatinic acid, complexes of chloroplatinic acid with olefins, aldehydes, vinyl siloxanes, etc. can be used, and the compounding amount thereof is Although it is a catalytic amount, specifically, it is preferable that the amount of platinum metal be in the range of 1 to 2000 ppm with respect to the entire composition.

The adhesive component of the component (D) is the carbon particles of the component (E), which will be described later, which is a filler when the composition of the present invention is cured, carbon black of the component (F) and the component (A),
When the resin component of component (B) is fixed to prevent the movement due to expansion and contraction in the case of a heating element, the sheet heating element is formed when the sheet heating element is molded into the shape of the sheet heating element and integrated with the support. It is a component that also has a role of adhering to the surface of the support. As this adhesive component, epoxy group-containing trialkoxysilane, (meth) acroyl group-containing trialkoxysilane,
At least one aliphatic unsaturated group-containing trialkoxysilane, triazine group-containing trialkoxysilane, and SiH group
Examples thereof include organopolysiloxane compounds each having an alkoxy silyl group and / or an epoxy group, and specifically, a compound having the following structure and a methoxy group in each of the following structural formulas, an ethoxy group, a propoxy group, and a butoxy group. And the like substituted with other alkoxy groups.

[0025]

Embedded image

[0026]

[Chemical 3]

The blending amount of the component (D) is the same as that of the above component (A) 1.
0.1 to 30 parts with respect to 00 parts, preferably 0.5 to 10 parts
Parts, more preferably 0.5 to 5 parts, and if the amount of the component (D) is less than 0.1 parts, the above effect is not exhibited, and if it is more than 30 parts, the strength of the cured heating element is high. It has the disadvantage of decreasing.

The following carbon particles of component (E) are components for exhibiting good PTC characteristics when the composition is cured, and therefore the BET specific surface area (nitrogen adsorption method) is
It should be 10 m ² / g or less, preferably in the range of 0.05 to ⁵ m ² / g, and if it exceeds this range, PTC characteristics will not occur and electric conduction will always occur. The morphology of the carbon particles is preferably spherical. The average particle size is 1
It is preferably ˜100 μm. Examples of such carbon particles include Glass Bon P manufactured by Owada Carbon Co., Ltd.,
Carbides such as ICB, PC, MC, and MSB manufactured by Nippon Carbon Co., Ltd., glassy carbon manufactured by Ube Industries, mesocarbon manufactured by Osaka Gas Co., Ltd., and graphitized materials can be used.

The blending amount of the component (E) is the same as the component 1 of the component (A).
45-400 parts, preferably 50-35 with respect to 00 parts
It must be within the range of 0 copy. When the compounding amount is less than 45 parts, the expression of PTC properties is insufficient, while when it exceeds 400 parts, good PTC properties cannot be obtained.

The carbon black as the component (F) is a component added for the purpose of maintaining the strength as a heat-generating molded body and further for reducing the resistance value as a heat-generating body, and therefore has a BET specific surface area of the above ( It is necessary to be larger than the carbon particles of the component E), specifically, 20 m ² / g or more,
It should preferably be in the range of 25 to 1000 m ² / g. If the specific surface area is smaller than this, the same effect as that of the carbon powder of the component (E) cannot be obtained, and the reinforcing effect cannot be obtained, and the decrease in resistance value is also small, so that the object of the present invention cannot be achieved. The average particle size of this carbon black is preferably 0.01 to 0.1 μm.

Examples of such carbon black include acetylene black manufactured by Denki Kagaku, Ketjen black manufactured by Lion.

The blending amount of the component (E) is the same as the component 1 of the component (A).
The amount should be 10 to 30 parts, preferably 10 to 25 parts, relative to 00 parts. If the blending amount is less than 10 parts, the reinforcing effect and the decrease in resistance value are not sufficient, and if the blending amount exceeds 30 parts, continuity is maintained and PTC characteristics are not exhibited.

In the composition of the present invention, in addition to the above essential components,
Vinyl group-containing organopolysiloxanes such as vinylcyclotetrasiloxane, triallyl isocyanurate, alkyl maleates, acetylene alcohols and their silanes and siloxane modified products as addition reaction control agents for the purpose of adjusting the pot life in actual work. Compounds selected from the group consisting of, hydroperoxide, tetramethylethylenediamine, benzotriazole and mixtures thereof may be used.

Further, the composition of the present invention may optionally further contain other components known in this type of composition, for example, reinforcing fillers such as fumed silica and wet silica, and semi-reinforcement such as quartz powder and alumina. It is also possible to add a functional filler, a colorant, a heat resistance imparting agent and the like.

The composition of the present invention can be obtained by uniformly mixing the above-mentioned components, and in this case, the order of compounding is not particularly limited.

The organopolysiloxane composition thus obtained can be molded into a shape of a heating element by a known method, and a sheet heating element is particularly preferable. The planar heating element may have a structure as shown in FIG. 1, for example. That is, in the planar heating element structure 1 of FIG. 1, cured products of the composition of the present invention, which are formed into rectangular film shapes as the heating elements 2 and 2, are arranged on the left and right, and between the heating elements 2 and 2 and on the outer side. The electrodes 3 are respectively arranged in
Further, the heating element 2, 2 and the electrode 3 covered with an insulator 4 are integrated with the sheet base material 5.

Here, when a cured product of the composition of the present invention is obtained, a solution in which the composition of the present invention is dissolved in a solvent such as toluene is applied to a substrate to form a film, and then heated. To cure. The curing temperature in this case is 100
It is necessary to set the temperature in the range of 40 ° C or lower, preferably 40 to 100 ° C, and if it exceeds 100 ° C, the required PTC characteristics cannot be obtained as shown in Fig. 4.

[0038]

EFFECTS OF THE INVENTION The organopolysiloxane composition for a heating element of the present invention provides a heating element having a self-temperature control function that sufficiently retains the initial PTC characteristics even in a repeated heat cycle for a long period of time and is practically usable. Is.

Further, according to the method for producing a heating element of the present invention, a heating element having excellent PTC characteristics can be reliably produced using the above composition.

[0040]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. In the following examples, all parts are parts by weight. [Examples] 20 parts of acetylene black (average particle size: 0.05 μm) having a specific surface area of 32 m ² / g, to 100 parts of dimethylpolysiloxane having a viscosity of 30,000 cs at room temperature and having a terminal blocked with a vinyldimethylsilyl group, a specific surface area Is 0.
14 m ² / g spherical carbon particles (average particle size 6 μm) 100
Part, 0.2 part of propyl alcohol reaction solution of chloroplatinic acid containing 1% as platinum atom, 1,2,3,4-tetravinyl-1 ′, 2 ′, 3 ′, 4′-tetramethylcyclotetrasiloxane 0.1 parts and 1 part of the adhesive component represented by the following formula (A) are mixed with a universal stirrer until uniform, and further, a hydrogen polysiloxane having a viscosity at room temperature of about 10 cs represented by (B) 0 .7 parts was added. This composition was dissolved in 150 parts of toluene, uniformly applied on a PET film, and heated at 75 ° C. to cure the composition, whereby the planar heating element structure shown in FIG. 1 was produced.

[0041]

[Chemical 4]

A heat cycle was repeated in which the sheet heating element was energized for 1 hour and stopped for 3 hours. FIG. 2 shows data comparing the electric resistance values of the heating element with respect to the temperature for one cycle and after 100 cycles. According to FIG. 2, the PTC characteristics of the produced sheet heating element showed almost no change even after 100 cycles.

[Comparative Example 1] A specific surface area of 0.14 m was obtained with 100 parts of dimethylpolysiloxane having a terminal end blocked with hydroxydimethylsilyl group and having a viscosity of 20000 cs at room temperature.
After adding 100 parts of ² / g spherical carbon particles, 6 parts of methyltris (butanooxime) silane and 150 parts of toluene,
The mixture was mixed with a universal stirrer until uniform, and 0.1 part of an organotin compound was added as a curing catalyst. PE for this composition
It was applied evenly on a T film and cured at 25 ° C. for 24 hours to produce the sheet heating element shown in FIG. The heat cycle was repeated for this planar heating element in the same manner as in the example. FIG. 3 shows data comparing the electric resistance values with respect to the temperature of the heating element after one cycle and after 100 cycles. According to FIG. 3, the PTC characteristics of the 1-cycle and the 100-cycle are significantly different, and it is recognized that the heat cycle stability of the PTC characteristics is poor.

[Comparative Example 2] A composition exactly the same as that of the example was heated at 120 ° C for 1 hour to be cured to prepare the sheet heating element shown in Fig. 1. The initial PTC characteristics of this sheet heating element are shown in FIG. From FIG. 4, it can be seen that the PTC characteristics of the one cured at 120 ° C. are poor.

[Brief description of drawings]

FIG. 1 shows a planar heating element structure using a composition of the present invention, (a) is a plan view and (b) is a sectional view.

FIG. 2 is a graph showing heat cycle stability of PTC characteristics of heating elements manufactured in Examples.

FIG. 3 is a graph showing heat cycle stability of PTC characteristics of a heating element manufactured in Comparative Example 1.

FIG. 4 is a graph comparing the initial PTC characteristics of the heating element manufactured in Comparative Example 2 with that of Example.

[Short description of reference numeral] 1 planar heating element structure 2 heating element 3 electrode 4 insulator 5 sheet base material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location B29K 83:00 (72) Inventor Yoshiteru Nakagawa 370 Koizumicho, Yamatokoriyama City, Nara Prefecture (72) Inventor Hironao Fujiki 1-10, Hitomi, Matsuida-cho, Usui-gun, Gunma Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Inventor Kaoru 1-10 Hitomi, Matsuida-cho, Usui-gun, Gunma Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Technology Laboratory

Claims (2)

[Claims] 1. An organopolysiloxane (A) having at least two alkenyl groups at a molecular chain terminal and having a viscosity at 25 ° C. of 10,000 cs or more: 100 parts by weight, (B) at least three silicon atoms in one molecule. Organohydrogenpolysiloxane having a hydrogen atom directly bonded to: 0.1 to 30 parts by weight, (C) platinum-based catalyst: catalytic amount (D) adhesive component: 0.1 to 30 parts by weight (E) BET specific surface area A heating element characterized in that carbon particles having an amount of 10 m ² / g or less: 45 to 400 parts by weight, (F) carbon black having a BET specific surface area of 20 m ² / g or more: 10 to 30 parts by weight are essential components. Organopolysiloxane composition for use. 2. A heating element characterized by molding the organopolysiloxane composition for a heating element according to claim 1 into a predetermined shape, and then heating the molded article at a temperature of 100 ° C. or lower to cure it. Production method.