JPH0217886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical insulating board having a novel structure, and an object thereof is to provide an electrical insulating board that has excellent electrical properties, dimensional stability, and heat resistance even when water or moisture is absorbed. Our goal is to provide the following. The term "electrical insulating board" as used in the present invention refers to a laminate used as a substrate or support plate for various electronic components and devices, and in particular, a resistance component using a laminate with a resistance paste applied to the surface of the laminate. Including an insulating substrate for manufacturing. Generally, boards with a thickness of 0.5 mm are often used for these insulating boards, and according to JIS-K-6912, the allowable thickness range for this type of board is 0.5 ± 0.08 mm, i.e.
It is specified as 0.42 to 0.58 mm. Conventionally, these insulating boards were made of phenolic resin, paper,
Alternatively, it is manufactured by using epoxy resin and paper as materials, for example, by impregnating the paper base material with resin varnish to make a prepreg, stacking many sheets of this prepreg, and hot-pressing molding. As an example of a conventional electrical insulating board manufactured in this manner, FIG. 1 shows a cross section of a 0.5 mm thick insulating board made of a paper base material and a phenol resin. Three or more paper substrates impregnated with phenolic resin are laminated, and the paper fibers are entangled between each substrate. On the other hand, electrical laminates inevitably lose their electrical properties, heat resistance, or dimensional stability due to moisture absorption, which is undesirable from a practical standpoint. Moisture mainly permeates into the inside of the insulating board from the surface layer, but since paper is generally hydrophilic, the presence of the paper base layer facilitates the permeation of moisture into the insulating board. Therefore, a conventional insulating board as shown in Fig. 1, that is, one with a structure in which there is no continuous resin layer on the surface of the insulating board and also without a continuous resin layer between the paper base materials inside the insulating board, is called an insulating board. Each paper base material is intertwined inside,
Moisture permeates easily in the vertical direction of the insulating plate, resulting in a large amount of moisture absorption, leading to a significant decrease in electrical insulation properties, especially the volume resistivity and insulation resistance specified in JIS-C-6481, and further heating. Sometimes blistering occurs and heat resistance is impaired. In view of the current situation, the present inventors have conducted research and have already published in JP-A-55-103786, a thermosetting resin layer is formed between each base material to substantially cut off contact between each base material layer, and We have proposed an electrical insulating laminate with a continuous resin layer formed on the surface, but as a result of further research, we have found that kraft paper, linter paper,
Alternatively, a paper mainly composed of cellulose fibers such as cotton paper is used, and the paper base material is pre-impregnated with a compound containing a methylol group, such as a dehydration condensation type resin, as a pre-impregnation treatment agent, and then a curable resin or the like is pre-impregnated. It has been found that an insulating plate with extremely good electrical properties and heat resistance can be obtained when the insulating plate is laminated and cured by impregnating it with an unsaturated polyester resin or an epoxy resin. Furthermore, the present invention was completed by discovering that the number of paper base materials constituting the electrical insulating board having a thickness of around 0.5 mm according to the present invention is most preferably two. The present invention uses a paper base material mainly composed of cellulose fibers that has been pre-impregnated with a compound containing a methylol group or a pre-impregnation treatment agent containing the compound as a main component, which does not contain a solvent component and reacts during curing. An electrical insulating board having a thickness in the range of 0.42 to 0.58 mm, which is obtained by impregnating a curable resin that is liquid at room temperature without substantially generating by-products, laminating two sheets of the impregnated base material, and curing the same. , the impregnated base material is laminated so that the high fiber density sides or low fiber density sides of the paper base materials face each other, and a layer of the curable resin cured as a substantially continuous layer is present between them. The present invention relates to an electrical insulating board with characteristics. The electrical insulating board of the present invention has excellent electrical properties and heat resistance, especially when it absorbs moisture. Further, when there is a layer of a curable resin, such as an unsaturated polyester resin or an epoxy resin, impregnated into the base material as a substantially continuous layer on the surface of the electrical insulating board, or in addition, the pre-impregnation When the treatment agent is a mixture or condensation product of a compound containing a methylol group and a higher fat derivative containing at least one group capable of condensing with a methylol group in the molecule, the electrical The properties, heat resistance, punching workability, and slitting workability are more favorable. In the present invention, examples of the methylol group-containing compound include N-methylol acrylamide and other various compounds, but dehydration condensation resins such as phenol resins, melamine resins, and urea resins, among which methylol melamine and/or methylol guanamine are particularly preferred. These are initial condensates of formaldehyde and guanamines such as melamine or formoguanamine, acetoguanamine, propioguanamine, benzoguanamine, and adiposiguanamine, or etherification of some or all of their methylol groups with lower alcohols such as methanol or butanol. refers to things that have become Furthermore, with these as main components, thermoplastic resins, various vegetable oils, modified products thereof, etc. may be appropriately mixed, for example, for the purpose of improving mechanical properties. Furthermore, better results can be obtained by mixing or condensing the following higher aliphatic derivatives in addition to the compound having a methylol group. Higher aliphatic derivatives include, for example, saturated fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid; Saturated fatty acids and esters of the above fatty acids with polyhydric alcohols such as ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, sorbitol, aliphatic amides that are derivatives of the above fatty acids, and caprylic alcohol and lauryl alcohol , saturated or unsaturated higher alcohols such as myristyl alcohol, cetyl alcohol, stearyl alcohol, oleyl alcohol, linoleyl alcohol, ethers of higher alcohols and polyhydric alcohols, and aliphatic amines that are derivatives of higher alcohols. be able to. Oxyfatty acids such as ricinoleic acid and derivatives thereof can also be used in combination for the purpose of improving punching processability and slitting processability. In short, punching is achieved by having in the molecule both a group that can condense with the methylol group of the amino resin, such as a hydroxyl group, a carboxyl group, an amino group, an amide group, and a long-chain alkyl group that acts to weaken the cohesive force of the amino resin. This is a necessary condition as a modifier for processability or slitter processability. The number of higher aliphatic derivatives that meet these conditions is extremely large, but according to the results of studies conducted by the present inventors, when the number of carbon atoms is 8 or more, the effect as a modifier is When using oleic acid, oleyl alcohol, and their derivatives, such as oleic acid monoglyceride, oleic acid diglyceride, oleic acid amide, and oleylamine, which have 18 carbon atoms and one unsaturated group, the performance of the resulting laminate becomes unbalanced. It was also revealed that the film was easily removed and was a preferred embodiment of the present invention. The amount of such modifier used depends on the unsaturated polyester resin or epoxy resin used for the laminate.
The optimum amount varies, but is usually in the range of 3 to 40 parts per 100 parts of the compound having a methylol group. Regarding the method of using the treatment agent, either a compound having a methylol group or the compound and the above-mentioned modifier are mixed in the form of a solution or suspension, or the two are used by condensing them in advance. It may also depend on The methylol group-containing compounds of the present invention generally have a suitable affinity for both cellulose fibers and unsaturated polyester resins or epoxy resins, helping to form excellent composites, which in turn Forms an excellent electrical insulation board. To obtain a pre-impregnated paper base material, for example, prepare a solution of the above-mentioned methylol group-containing compound in water or alcohol as a solvent, and immerse it in this solution.
This can be achieved by drying. The final amount of the methylol group-containing compound treatment agent applied to the paper base is usually about 5 to 30%, preferably about 10 to 20%, based on the weight of the paper. By using a paper base material that has been subjected to such a pre-impregnation treatment, the bending strength is improved. Undesirable whitening that often occurs due to peeling of unsaturated polyester resins or epoxy resins from cellulose fibers during punching is improved. In particular, the deterioration of heat resistance and electrical insulation properties is slight when exposed to a humid environment. The curable resin used in the present invention is one that is cured by heat, light, radiation, etc. Among these, the most commonly used unsaturated polyester resins and epoxy resins are generally well-known ones. Generally applicable. However, it is preferable to select a more appropriate grade depending on the use of the insulating plate. For example, the bending strength and bending elastic modulus of the board at room temperature or when heated are also important properties of the insulating board of the present invention, which is mainly 0.5 mm thick, and in order to improve these mechanical properties, It is preferable to select a harder resin. In addition, in the present invention, the curable resin or the like may be an unsaturated polyester resin or an epoxy resin, which is liquid at room temperature and can be easily impregnated into a pre-impregnated paper base material without diluting with a solvent. Particularly preferred. This is because the paper base material used in the present invention has been pretreated with a pre-impregnating treatment agent whose main component is, for example, a dehydration condensation type resin, so that these treatment agents do not adhere to the surface of the cellulose fibers. , coating the surface. When this paper base material is impregnated with a resin diluted with a solvent, that is, a resin varnish, an undesirable phenomenon occurs in which the dehydration condensation resin present on the surface of the cellulose fibers dissolves depending on the type of solvent used. This is because it may exhibit the following. In the present invention, the number of paper base materials used is preferably two. Generally, in paper mainly composed of cellulose fibers, the density of fibers on the front and back sides of the paper inevitably varies during the paper making process. This difference in density between the fibers on the front and back sides of the paper manifests as a curling phenomenon, for example, when moisture is absorbed. This curl phenomenon does not change even if impregnated with the pre-impregnated treatment agent of the present invention. In addition, an insulating plate obtained by impregnating one of the treated base materials with, for example, an unsaturated polyester resin or an epoxy resin according to the present invention and curing the same, that is, one base material layer and the cured resin. Even in the case of an insulating plate made of unsaturated polyester resin or epoxy resin and having a thickness equal to or less than that of the present invention, the curling phenomenon does not change in the same way. In the case of an insulating plate having such a structure, the shrinkage due to curing shrinkage of the resin is relatively small on the side surfaces with high fiber density because they are supported by the fibers, whereas the shrinkage on the side surfaces with low fiber density is relatively large. Therefore, the shrinkage strain is released as warpage by occurring during the curing process or by, for example, heat treatment. In a thin substrate having a thickness of around 0.5 mm, the phenomenon of warpage due to the anisotropy in the through-layer direction of the substrate becomes particularly noticeable. In view of the above points, the present inventors solved this problem by stacking two pre-impregnated paper base materials so that the sides with high fiber density or the sides with low fiber density face each other. . Of course, the anisotropy in the through-layer direction of the substrate can be offset by using an even number of paper substrates of 4 or more. When it is made, the following defects occur. That is, according to the research conducted by the present inventors, the tensile strength and tear strength of the impregnated paper base material according to the present invention often decrease to about 1/2 that of the untreated base material, and the insulating It is easily damaged during handling during plate manufacturing. For example, when the bulk density is 0.4 to 0.6 g/cm ² , the thickness of the base material is preferably about 200 μm or more from this point of view. Therefore 0.5mm
(500 μm), it is realistic that the number of paper base materials is two. It will be shown next that in the present invention, it is further preferable that a substantially continuous layer of a curable resin, such as an unsaturated polyester resin or an epoxy resin, is formed not only between the base materials but also on the surface of the insulating plate. It will be done. The structural concept of the present invention is shown in the second section as a cross-sectional view of an insulating plate.
As shown in the figure. FIG. 3 shows that on one side of the insulating plate of the present invention,
2 shows a resistor with some kind of printing, for example a resistor paste 4; In FIG. 3, the continuous layer 2 of resin formed on the back side largely restricts the ingress of moisture into the insulating plate. Even a small amount of moisture that has entered is blocked by the resin layer 3 existing between the first layer base material and the second layer base material. Therefore, there is almost no water intrusion into the inside of the insulating board, and dimensional changes, warping, and heat resistance deterioration due to moisture absorption and water absorption are significantly improved, and deterioration of the resistance paste due to moisture is reduced. I can do it. The curable resin used in the present invention does not contain a solvent component that is essentially unnecessary for curing, and is mainly composed of a type of thermosetting resin in which the entire resin component becomes a component of the thermoset product. It is preferable to use a resin that does not substantially generate reaction by-products such as condensed water or carbon dioxide gas during curing. For example, they are radical polymerization type or addition reaction type resins such as unsaturated polyester resins, epoxy acrylate resins (so-called vinyl ester resins), diallyl phthalate resins, and epoxy resin liquids. A curing agent, a curing catalyst, a curing aid, etc. are appropriately added to these curable resins. Furthermore, fillers such as charcoal, talc, glass powder, mica, clay, and calcium silicate are often added for the purpose of improving electrical and mechanical properties. In addition, for unsaturated polyester resins, polyfunctional hydrocarbon monomers such as divinylbenzene are used, and for epoxy resins, for example, monofunctional epoxy resins are used to impart flexibility. A modifier may be included as appropriate, such as by adding a modifier. The thickness of the continuous resin layer constructed according to the present invention is generally preferably 1 to 100 microns. This thickness is preferably equal to or less than the thickness of the base material used, and
If it is unnecessarily thick, it may break during cutting or impair punching workability, for example. To check the thickness of this resin layer,
The cross section can be cut with a sharp knife, or a specimen surrounded by a special resin can be cut and polished, and then accurately observed using an optical microscope with a magnification of 10 to 100 times. One of the preferred methods for manufacturing the electrical insulating board according to the present invention is the following method. Using epoxy resins and unsaturated polyester resins that are liquid at room temperature in an uncured state,
A method such as impregnating an excessive amount of these resin liquids into a base material that has been previously treated with a treatment agent, or, if the amount of resin impregnated is small, further applying the resin liquid onto the base material when the base materials are stacked on top of each other. After that, each impregnated base material is laminated continuously or discontinuously by passing it through slits having an interval calculated in advance from the thickness of the base material or the thickness of the resin layer between the base materials, etc. ,
This can be achieved by heat curing. During lamination and curing, a cover sheet such as metal foil, cellophane, or plastic sheet may be used as appropriate to improve surface properties or protect the resin which is affected by oxygen in the atmosphere during curing. This kind of uncured resin, which is liquid at room temperature, does not contain volatile components such as solvents, so it does not require drying, and in addition, the thickness of the resin layer between each base material is easy to control and is suitable for the present invention. Furthermore, in order to control the impregnation into the base material and the thickness of the resin layer between the base materials, the viscosity of the uncured resin liquid is also a factor;
Particularly suitable in the present invention is an unsaturated polyester resin which is liquid at room temperature and allows easy preparation of a resin liquid in the range of 0.05 to 35 poise. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example A melamine resin consisting of 12 parts by weight of commercially available trimethylolmelamine (S-305 manufactured by Nippon Carbide), 1.6 parts by weight of oleic acid monoglyceride, 0.2 parts by weight of a surfactant (Emulgen 905 manufactured by Kao Soap) and 100 parts by weight of water was used. Prepare an aqueous solution (pre-impregnation treatment agent) containing the main component, soak commercially available kraft paper (ZB-S manufactured by Sanyo Kokusaku Pulp) in this solution, squeeze to contain the same weight of the aqueous solution as the paper, and heat at 100°C It was dried for 10 minutes to obtain a paper base material that had been previously impregnated.
On the other hand, an unsaturated polyester resin solution prepared by adding 1 part by weight of Perbutyl O (manufactured by NOF Corporation) as a curing catalyst to an unsaturated polyester resin (Polymer 6304 manufactured by Takeda Pharmaceutical Co., Ltd.) that is liquid at room temperature was applied to the pre-impregnated paper base. impregnate the material, and apply it to the front and back of the two paper base materials.
Further, the unsaturated polyester resin liquid was applied, the two were stacked together and cured without pressure to obtain a 0.54 mm insulating plate having the structure shown in FIG. 2. The thickness of the continuous resin layer on the surface was about 2 to 3 μm, and the thickness of the continuous resin layer between the base materials was about 10 μm. Comparative Example 1 In the example, two sheets of the paper substrates impregnated with an unsaturated polyester resin liquid were overlapped, and after removing the excess resin liquid by applying pressure, they were cured, and between the paper substrates and on the surface layer, An insulating plate was obtained in which almost no resin layer was present. Comparative Example 2 In Example 2, an insulating board having the structure shown in FIG. 2 was obtained using a paper base material that had been impregnated with an unsaturated polyester resin solution without being impregnated with a pre-impregnating agent. Comparative Example 3 A commercially available product having the structure shown in FIG. 1 and manufactured from a phenolic resin and a paper base material was used. As shown in Table 1, the insulating board according to the present invention is
It has significantly better characteristics than conventional products. 【table】

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view of a conventional product. FIG. 2 is an explanatory cross-sectional view of the electrical insulating plate of the present invention. FIG. 3 is an explanatory cross-sectional view of an application example of the electrical insulating plate of the present invention. 1... Paper base material of the present invention which has been pre-impregnated with the pre-impregnation treatment agent for the present invention and further impregnated and cured with a thermosetting resin, 2... Continuous surface resin layer, 3...
... Resin continuous layer between substrates, 4 ... Baked resistance paste, 5 ... Resistor protective coating, 6 ... Conventional impregnated paper base material.

Claims (1)

[Scope of Claims] 1. A paper base material mainly composed of cellulose fibers that has been pre-impregnated with a compound containing a methylol group or a pre-impregnation treatment agent containing the compound as a main component, which does not contain a solvent component and is cured. An electrical insulating board with a thickness in the range of 0.42 to 0.58 mm obtained by impregnating a liquid curable resin at room temperature, which does not substantially generate reaction by-products, and laminating and curing two sheets of the impregnated base material. The impregnated base material is laminated so that the high fiber density sides or the low fiber density sides of the paper base materials face each other, and there is a layer of the curable resin cured as a substantially continuous layer between them. An electrical insulating board characterized by: 2. The electrical insulating board according to claim 1, wherein the same resin layer as the resin layer existing between the impregnated base materials is also present on the surface of the electrical insulating board. 3. A pre-impregnation treatment agent containing a methylol group-containing compound as a main component is a mixture or condensation of the methylol group-containing compound and a higher aliphatic derivative containing at least one group capable of condensation with a methylol group in the molecule. Claim 1 which is a product
The electrical insulating board according to item 1 or 2. 4. The electrical insulating board according to claim 1, 2, or 3, wherein the curable resin layer existing as a substantially continuous layer has a thickness in the range of 1 to 100 μm. 5 Claim 1 in which the curable resin is an unsaturated polyester resin or an epoxy resin
The electrical insulating board according to item 2, item 3, or item 4.