JPS61125102A - Thermistor material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an improved thermistor material used in heating devices such as electric carpets and electric blankets, and more particularly to a heat-sensitive polyamide composition. (Background Art) Electrical For example, a structure as shown in FIG. 1 is used as a structure of a heat-sensitive sheet heating element such as a large-area heating device such as a carpet or an electric blanket.

In the figure, l is the thermistor material, 2 is the temperature sensing electrode, and 3 is the thermistor material.
is a heating line, and 4 is an insulating film. However, this thermistor material has a negative resistance characteristic, and the temperature of the heat-sensitive sheet heating element is controlled by changing the resistance of the thermistor material l between the electrodes 2 and 3.

Temperature detection devices such as electric carpets, electric blankets, and other large-area heating devices include those using polyvinyl chloride materials, which are conventionally known as polymer thermistor materials, and those using polyamide materials.

However, the former has a large amount of plasticizer added to give it flexibility, so it is difficult to use due to the heat resistant properties of the plasticizer.
Must be used below 000. Additionally, quaternary ammonium halide and the like are added to increase the thermistor characteristics (B constant), but there is a limit to increasing the thermistor characteristics (B constant). This is a serious drawback as a thermistor material for large-area heating devices such as electric carpets. In other words, thermistor characteristics (B constant) are used to detect localized high temperature areas caused by local insulation.
It is necessary that the thermistor characteristics (B constant) be large enough, and if the thermistor characteristics (B constant) are not sufficiently large, the thermistor material must have a characteristic value that does not change over time depending on its local temperature (no bleed-out of plasticizer). That's why.

For this reason, polyamide materials are widely used because they have particularly excellent mechanical properties and heat resistance, and are easy to design in length-mister characteristics (B constant). However, polyamide resin has greater hygroscopicity than polyvinyl chloride, and its impedance characteristics change significantly due to moisture absorption.When applied to electric carpets, the problem arises that it becomes lukewarm when absorbing moisture and becomes too hot when dry. As such, it could not necessarily be said to be optimal.

In order to improve this drawback, the present inventor focused on the fact that polyamide resin is plasticized due to moisture absorption, and
Nylon 12, which already has low hygroscopicity among polyamide resins, is pre-plasticized by kneading a commercially available plasticizer and ion conductive additives to reduce the extent to which plasticization progresses due to moisture absorption. proposed a method to reduce impedance fluctuations due to moisture absorption.

This behavior occurs because the increase in the thermistor constant due to the addition of an ion-conducting material occurs at a temperature above the glass transition point of nylon 12, but this glass transition point is significantly lowered due to moisture absorption of nylon. This can be explained by the fact that by lowering the glass transition point by K, the fluctuations in the glass transition point due to moisture absorption are reduced, thereby reducing changes in the temperature at which ionic conductivity occurs.

However, commercially available plasticizers for polyamide have low heat resistance.
When applied to electric carpets, the plasticizer bleeds out over time, the glass transition temperature rises, and the impedance drying characteristics change in the direction of increasing impedance. If the plasticizer bleeds out, it becomes impossible to control the temperature, which is not only dangerous, but conversely, when the plasticizer bleeds out, the hygroscopicity increases, and the impedance characteristics decrease due to moisture absorption. This indicates that the phenomenon is on the rise.

Therefore, the present invention examines plasticizers for various structures.
The results showed that a thermistor material without plasticizer bleed-out at high temperatures was obtained.

(Object of the invention) The present invention relates to the improvement of thermistor materials used in heat-sensitive bodies such as electric carpets, by reducing changes in impedance temperature characteristics due to moisture absorption of polyamide resin,
Another object of the present invention is to provide a thermistor material that eliminates plasticizer bleed-out at high temperatures and is stable for a long time.

(Disclosure of invention) Examples of the present invention will be described below.

The first P shows the degree of weight loss of 5% obtained by differential thermal balance analysis (i'! It is something that

Table 2 shows 71 press sheets with a thickness of 0.5 mm made by kneading the plasticizer of the present invention, the conventional example, the plasticizer of the comparative example, and potassium iodide as an ion conductive additive into nylon 12. The value △T which captures the impedance fluctuation around 50°C when drying at 80°C and 40°C x 90% moisture absorption as a temperature change, the glass transition point temperature of the dried sample piece by a viscoelasticity tester, and 120'O This figure shows the weight loss due to plasticizer bleed-out when left in an atmosphere.

As can be seen from Table K1, the heat resistance as a plasticizer tends to improve as the molecular weight is higher than that of conventional plasticizers, but when comparing Comparative Examples 1 and 4, it is found that not only the molecular weight but also the side of the ester moiety It can be seen that as the number of chains increases, the heat resistance decreases even if the molecular weight is large. Further, as can be seen from Table 2, the lower the Tg, the smaller the ΔT, which indicates the effectiveness of plasticizing.

Furthermore, there is a tendency that the larger the molecular weight, the less the weight loss (please do!7), but there is also a tendency for weight loss to be greater for those with side chains in the ester moiety.

Furthermore, plasticizers without OH groups have little plasticizing effect △T
It is also not effective in this respect. On the other hand, esters with no side chains and VcOH groups at both ends are also insufficient in terms of ΔT.For this reason, as plasticizers for highly polar nylon 12, esters with no polarity (comparative Example 3) and esters that are too polar (Comparative Example 2) are Chiron 12
It can be inferred that sufficient plasticizing effect and heat resistance cannot be obtained due to poor compatibility with the polymer.

Therefore, it can be said that esters having no side chain having an OH group as in the present invention are effective. In the present invention, the plasticizer is limited to a paraoxybenzoic acid ester monomer having 18 or more carbon atoms and no side chain because, as mentioned above, the heat resistance of the plasticizer itself will deteriorate unless the molecular weight is larger than a certain level. This is because the temperature of the resin kneaded into nylon 12 is usually about 200 to 210°C, and esters having fewer than 18 carbon atoms are insufficient.

The reason why it does not have a side chain is because, as mentioned above, those with a side chain are inferior in heat resistance.

Furthermore, the reason why it is made into a monomer is that it is usually possible to make it into a polymer by condensation polymerization or the like in order to obtain a high molecular weight ester, but if the polarity of the OH group is too strong, the compatibility with nylon 12 will be poor. The reason why the amount to be kneaded is set to 10 to 35% by weight is that if it is less than that, the plasticizing effect will be low, and if it is more than that, bleed-out of the plasticizer will increase.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce fluctuations in thermistor characteristics due to dry moisture absorption, and to obtain a thermistor material with almost no change in characteristics due to plasticizer bleed-out at high temperatures.

Table 2 shows that according to the present invention, the weight loss is not zero even for samples to which a plasticizer is added, but when this type of thermistor material is actually used, for example, when it is used in a heat-sensitive sheet heating element, the thermistor material is insulated. This type of thermistor is used with polyethylene, polyester film, etc. pasted on both sides to prevent plasticizer from bleeding, and this type of thermistor is used in electric blankets, electric carpets, etc. Therefore, there is almost no possibility that the temperature will reach 120'O, making it a very effective material.

[Brief explanation of the drawing]

FIG. 1 shows an example of a heat-sensitive sheet heating element. l...Thermistor material, 2...Temperature detection electrode, 3.
...Heating line, 4...Insulating film Figure 1 Procedural amendment (voluntary) February 28, 1985 Gakudono Shiga, Commissioner of the Indian Office 1, Indication of the case 1982 Patent Application No. 247286 2, Invention Name thermistor material 3, relationship with the case of the person making the amendment Patent applicant name Matsushita Suiko Co., Ltd. 4, "Detailed explanation of the invention" column 6 in the attorney's specification, contents of the amendment K1 table Todo comparison (-'

Claims (1)

[Claims] A thermistor material obtained by kneading a polyamide resin with 10% to 35% by weight of a plasticizer consisting of a paraoxybenzoic acid ester monomer having 18 or more carbon atoms and no side chain, and an ion conductive additive.