JP7480802B2 - Glass fiber and its manufacturing method, as well as glass cloth, prepreg for circuit boards, and printed wiring board - Google Patents

Description

The present invention relates to glass fibers with excellent dielectric tangents and their manufacturing method, as well as glass cloth, substrate prepregs, and printed wiring boards that use the glass fibers.

Currently, with the high performance and high-speed communication of information terminals such as smartphones, the printed wiring boards used are becoming increasingly dense and extremely thin, as well as becoming lower in dielectric constant and dielectric loss tangent. As an insulating material for these printed wiring boards, laminates are widely used in which prepregs obtained by impregnating glass cloth with thermosetting resins such as epoxy resins (hereinafter referred to as "matrix resins") are laminated and heated and pressurized to harden. It is known that the transmission loss of signals in a board is improved as the dielectric constant (ε) and dielectric loss tangent (tanδ) of the material are smaller, as shown by the Edward A. Wolff formula: transmission loss ∝√ε×tanδ, and it is known that the dielectric loss tangent contributes more to the transmission loss, particularly from the above formula. For this reason, a low dielectric loss tangent is required for glass cloth, and glass cloths with improved dielectric properties such as D glass, NE glass, L glass, and Q glass have been proposed (Patent Documents 1 to 4). However, in order to achieve sufficient transmission speed performance in future applications such as 5G communications, there is still a need to improve on these low dielectric glass cloths, which have excellent low dielectric constants and low dielectric tangents.

Normally, glass cloth is coated with a sizing agent when spinning or warping the glass fiber bundles to prevent fuzzing or thread breakage caused by mechanical wear during winding or weaving. However, in the final process of glass cloth production, a silane treatment is performed to improve adhesion with the matrix resin used in the laminate. If the sizing agent remains on the glass cloth, the adhesion between the silane coupling agent and the glass cloth will deteriorate. For this reason, the sizing agent is usually completely removed by a thermal decomposition treatment, known as a heat cleaning treatment, before the silane treatment.

If sizing agent remains on the glass cloth after heat cleaning, the silane coupling agent treatment on the glass cloth will be insufficient, resulting in poor adhesion with the resin and deterioration of the dielectric properties due to the remaining sizing agent. Therefore, although heat cleaning processing is important, no study has been conducted on the effect of the heat cleaning process on the dielectric tangent of the glass cloth.

Japanese Patent Application Laid-Open No. 5-170483 JP 2009-263569 A JP 2009-19150 A JP 2006-282401 A

The present invention was made in consideration of the above problems, and aims to provide heat-cleaned glass fibers that have the inherent low dielectric tangent of glass.

Existing heat cleaning processes use gas furnaces, which use the combustion of city gas as a heat source, resulting in large amounts of carbon dioxide and water. Glass cloth is more than 50% _SiO2 , and the Si-OH groups on the surface of glass are highly active. It is believed that moisture is absorbed through hydrogen bonds, particularly in high-temperature atmospheres, and Si-OH groups are generated by cleaving Si-O-Si bonds ( _SiO2 + _H2O → Si-OH).

The present inventors have found that the dielectric tangent of glass fiber is reduced by reducing the number of Si-OH groups, and that there is a correlation between the Si-OH groups and the dielectric tangent. It is considered that when the proportion of SiO ₂ in the glass composition is 55% by mass or more, the dielectric tangent increases due to the cleavage of Si-O-Si bonds by moisture in the heat cleaning process. It has been found that this tendency is particularly prominent in glass fibers with a proportion of SiO ₂ of 95% by mass or more. The present inventors have found this situation and, as a result of repeated intensive studies, have found that by using a heating furnace having a heat generating mechanism that does not generate moisture in the heat cleaning process, it is possible to provide glass fibers having the dielectric tangent inherent to glass having a low dielectric tangent by removing the sizing agent while suppressing the deterioration of the dielectric tangent. The silane-treated glass fibers obtained by silane-treating this are also silane-treated glass fibers having a low dielectric tangent.

Therefore, the present invention provides the following inventions.
1. A glass fiber having a _SiO2 composition of 55% by mass or more, in which the sizing agent has been heat-cleaned, a dielectric tangent at 10 GHz of 0.0016 or less, and a residual carbon content derived from the sizing agent of 0.1% by mass or less.
2. The glass fiber according to 1, wherein the glass fiber has a dielectric loss tangent of 0.0020 or less at 40 GHz.
3. The glass fiber according to 1, wherein the glass fiber is Q glass having an _SiO2 composition of 95 mass % or more.
4. The glass fiber according to 1, wherein the Si—OH content of the glass fiber is 10,000 ppm or less.
5. Silane-treated glass fiber obtained by treating the glass fiber according to 1 with silane.
6. The silane-treated glass fiber according to 5, having a volatile content of 0.5 mass% or less.
7. The silane-treated glass fiber according to 6, wherein the amount of the silane coupling agent attached to the glass fiber is 0.02 to 0.5% by mass.
8. The silane-treated glass fiber according to 5, wherein the dielectric loss tangent at 10 GHz after the silane treatment is at most twice that before the silane treatment.
9. The silane-treated glass fiber according to 5, wherein the dielectric loss tangent at 40 GHz after the silane treatment is not more than twice that before the silane treatment.
10. A prepreg for printed circuit boards containing the glass fiber according to any one of 1 to 9.
11. A printed wiring board using the glass fiber according to any one of 1 to 9.
12. A method for producing the glass fiber according to any one of 1 to 9, comprising a step of heat cleaning the sizing-treated glass fiber having an _SiO2 composition of 55 mass% or more with a gas heated to 300 to 600°C, in which the amount of water generated per unit heat value (1,000 kcal) is 0.12 L or less.
13. The method according to 12, wherein the change ratio of the dielectric tangent at 10 GHz before and after the heat cleaning step is 0.7 to 1.3.
14. The method according to 12, wherein the change ratio of the dielectric tangent at 40 GHz before and after the heat cleaning step is 0.7 to 1.3.

The present invention makes it possible to obtain glass fibers by heat cleaning a sizing agent with a low dielectric tangent, which has the remarkable effect of suppressing transmission loss in substrates used in high-speed communications such as 5G, which will become more common in the future.

The present invention will be described in detail below.
The glass fiber of the present invention is a glass fiber in which the sizing agent has been heat-cleaned, the _SiO2 composition amount is 55 mass% or more, the dielectric tangent at 10 GHz is 0.0016 or less, and the residual carbon content derived from the sizing agent is 0.1 mass% or less. Note that the glass fiber also includes glass cloth such as filament, strand, chopped strand, yarn, plain weave cloth, satin weave cloth, flat cloth, and nonwoven fabric.

The glass fiber of the present invention is obtained by coating glass with a sizing agent and then removing the sizing agent by heat cleaning. The glass before coating with a sizing agent and the glass fiber after heat cleaning have _SiO2 of 55 mass% or more, preferably 95 mass% or more of Q glass, and more preferably 99.9 mass% or more of Q glass.

The dielectric loss tangent at 10 GHz in the heat-cleaned glass fiber of the present invention, or the dielectric loss tangent at 10 GHz before the silane treatment described below, is 0.0016 or less, preferably 0.0010 or less, and more preferably 0.0008 or less. The dielectric loss tangent at 40 GHz is preferably 0.0020 or less, more preferably 0.0018 or less, and even more preferably 0.0015 or less. The method for measuring the dielectric loss tangent is based on the description of the examples described below.

In the heat-cleaned glass fiber of the present invention, the carbon content of the residual carbon derived from the sizing agent, that is, the carbon content before the silane treatment described below, is 0.1% by mass or less, preferably 0.06% by mass or less, more preferably 0.03% by mass or less, and may be 0% by mass. The method for measuring the amount of residual carbon derived from the sizing agent is based on the description of the examples described below using a carbon analyzer. Methods for reducing the residual carbon content derived from the sizing agent to 0.1% include removing the sizing agent by washing with water and removing it by heat cleaning, but from the viewpoint of suppressing the generation of fluff and removing the sizing agent uniformly, the method using heat cleaning is preferred.

The Si-OH content in the heat-cleaned glass fiber of the present invention is preferably 10,000 ppm (by mass) or less, more preferably 8,500 ppm or less, even more preferably 7,500 ppm or less, and may be 0 ppm. The method for measuring the Si-OH content in the glass fiber is based on the description in the examples described below.

[Method of manufacturing glass fibers]
The method for producing the glass filament is not particularly limited, but includes a method of heating and drawing an ingot of a specified glass composition, and a method of melting the ingot to obtain molten glass and then forming the glass into a filament shape using a bushing. In particular, when the proportion of _SiO2 is 95 mass% or more, the melting temperature becomes high and drawing using a bushing becomes difficult, so heating and drawing using an oxyhydrogen burner is preferred.

Glass strands can be formed by applying a bundling agent to the surface of the drawn glass filaments and bundling them. The bundling agent is made mainly from starch, and softeners and lubricants can be added to impart functionality. The bundling agent composition is generally called a sizing agent. Sizing can be performed using known methods. There are no particular restrictions on the type of sizing agent or the method of sizing, and a method that is less likely to cause fluff or thread breakage is appropriately selected. Sizing reduces fluff and thread breakage. Examples of processing methods include immersion, roller or belt applicators, and spraying. Glass yarn is obtained by twisting the obtained glass strands. The twisting frequency is preferably 0.1 to 5.0 times per 25 mm.

Glass cloth is obtained by weaving glass yarn. The glass cloth is not particularly limited, but one having a basis weight of 10 to 100 g/ ^m3 is preferably used. The weaving method is not particularly limited, but examples thereof include weaving methods using an air jet loom, a water jet loom, a rapier loom, a shuttle loom, etc. When weaving is performed using an air jet loom, etc., PVA (polyvinyl alcohol) or starch can be attached as a secondary sizing agent to further obtain lubricity.

[Heat cleaning method for glass fiber]
A manufacturing method for obtaining the above-mentioned heat-cleaned glass fiber includes a process for heat-cleaning the sizing-treated glass fiber with a gas heated to 300 to 600° C., in which the amount of water generated per unit heat value (1,000 kcal) is 0.12 L or less.

The amount of water generated per unit calorific value (1,000 kcal) is 0.12 L or less, and the specific method of heat cleaning using gas heated to 300 to 600 °C is not particularly limited. The amount of water generated per unit calorific value (1,000 kcal) is 0.12 L or less, and preferably less than 0.10 L. The temperature is preferably 300 to 600 °C, and more preferably 400 to 600 °C. If the temperature is within this range, there is no need to heat for a long time, and the sizing agent can be sufficiently removed. If the temperature exceeds 600 °C, there is a risk of affecting the strength. In other words, by adjusting the temperature, it is possible to obtain glass fibers that have the inherent low dielectric tangent of glass and have excellent strength. The time for heat cleaning varies depending on the heating temperature, and is preferably 5 to 100 hours, more preferably 12 to 72 hours, and even more preferably 30 to 72 hours. In addition, if there is a shortage of oxygen in the heating furnace and the sizing agent carbonizes and turns black, oxygen may be taken in by opening and closing a damper, etc. as necessary.

As long as the device has such a heat generating mechanism, the amount of water generated per unit heat value (1,000 kcal) is 0.12 L or less, and is not particularly limited, so long as it has such a heat generating mechanism, and examples of such devices include electric furnaces, muffle furnaces, laser heating, and other devices that include heating furnaces with heat generating mechanisms that are capable of the above. In particular, since electric furnaces do not involve combustion, the amount of water in the gas can be 0.12 L or less, less than 0.1 L, less than 0.10 L, or 0 L. For example, when using a gas furnace that uses city gas as the combustion source, the amount of water generated per unit heat value (1,000 kcal) is 0.16 L.

The change ratio of the dielectric tangent at 10 GHz and 40 GHz before and after the heat cleaning process is preferably 0.7 to 1.3, and more preferably 0.9 to 1.1. The change ratio of the dielectric tangent at 10 GHz and 40 GHz is based on the description of the examples described later.

The tensile strength of the glass fiber after the heat cleaning process and before the silane treatment is preferably 0.05 GPa or more, more preferably 0.1 GPa or more, as measured by the tensile strength measurement method of JIS R 3420. There is no particular upper limit, but it can be 0.5 GPa or less.

[Silane-treated glass fiber]
The glass fiber subjected to the heat cleaning treatment of the present invention can be a silane-treated glass fiber. The silane treatment liquid is not particularly limited, but from the viewpoint of productivity and environmental burden, an aqueous solution in which a silane coupling agent is dispersed at 0.05 to 1 mass % is preferable. The pH can be adjusted according to the type of silane coupling agent to be dispersed. The method of adjusting the pH is not particularly limited, but adjustment with acetic acid or ammonia is preferable according to the silane coupling agent used.

Silane coupling agents include trimethylmethoxysilane, trimethylethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, trimethoxysilane, triethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenylmethylvinylethoxysilane, naphthyltrimethoxysilane, naphthyltriethoxysilane, 1,4-bis(methoxydimethylsilyl)benzene, tetramethoxysilane, tetramethyl ... p-ethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 1,6-bis(trimethoxysilyl)hexane, vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, Cyclohexyl)ethylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2 -aminoethyl-3-aminopropyltrimethoxysilane and its hydrochloride, N-(vinylbenzyl)-2-aminoethyl-3-aminopropylmethyldimethoxysilane and its hydrochloride, 3-isocyanatepropyltriethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, bis(trisethoxysilylpropyl)tetrasulfide and other alkoxysilane compounds may be used alone or in combination of two or more. Among these, 3-aminopropyltrimethoxysilane, N-(2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, etc. are preferred. The silane coupling agent is not limited to these, and one type may be used alone or two or more types may be used in combination.

The method of applying the silane treatment liquid is not particularly limited, but examples include a method of permeating glass fibers into the silane treatment liquid and treatment by roll coating. The method of drying the silane treatment liquid is not particularly limited, but examples include hot air drying, infrared rays, and drying by hot rolls. The drying temperature is appropriately selected from, for example, 80 to 180°C, and 90 to 150°C is preferable in terms of evaporating more water and reacting the silane coupling agent with the Si-OH group on the surface of the glass fiber. In this range, the silane coupling agent is dispersed on the surface of the glass fiber, and the silane coupling agent and the Si-OH group on the surface of the glass fiber react favorably. If the temperature is less than 80°C, not only will the water in the silane treatment liquid not evaporate, but the silane coupling agent will not react with the Si-OH group on the surface of the glass fiber, and in addition to worsening the dielectric tangent, water and alcohol will be generated as outgassing when the printed wiring board is made, causing swelling and adversely affecting reliability. The alcohol referred to here is derived from the silane coupling agent and is mainly methanol or ethanol. If the temperature exceeds 180°C, not only will the silane coupling agent react rapidly with the Si-OH groups on the surface of the glass fiber, preventing uniform silane treatment of the glass fiber, but the hydrocarbons in the silane coupling agent will be rapidly oxidized, which may adversely affect the dielectric tangent.

The drying time can be appropriately changed depending on the concentration of the silane treatment solution, but is preferably 30 seconds to 30 minutes, more preferably 1 to 10 minutes. Within such a range, the moisture in the silane treatment solution is removed, and the silane coupling agent and the Si-OH group on the glass fiber surface react favorably.

The volatile content of water or alcohol in the silane-treated glass fiber is preferably 0.5 mass% or less, more preferably 0.3 mass% or less, even more preferably 0.2 mass% or less, and particularly preferably 0.1 mass%. In order to obtain such a volatile content, the drying process after the silane treatment may be adjusted. The method for measuring the volatile content is the method described in the Examples. In particular, the inherent dielectric tangent of glass having a proportion of SiO ₂ of 95 mass% or more depends on the amount of Si-OH contained in the glass, but is on the order of 1.0×10 ⁻⁴ at 10 GHz, and there are some with a smaller amount of Si-OH than synthetic quartz, etc., on the order of 1.0×10 ⁻⁵ . In addition, it was found that the dielectric tangent of glass fibers with a high proportion of SiO ₂ is significantly affected by the amount of Si-OH groups, and that unless treatment is performed with an appropriate amount of silane coupling agent in the subsequent silane treatment, not only will the Si-OH groups, SiOMe groups, and SiOEt groups themselves due to an excessive amount of coupling agent have a negative effect on the dielectric tangent, but the water and alcohol from which these functional groups are generated will have a significant effect on the dielectric tangent and reliability of the glass fiber. That is, the inventors have found that by controlling the amount of volatile water and alcohol generated when drying glass fibers after silane treatment to 0.5 mass % or less relative to the glass fibers, it is possible to provide silane-treated glass fibers while maintaining the dielectric tangent inherent to glass.

The amount of silane coupling agent attached after silane treatment is preferably 0.01 to 0.5% by mass relative to the glass fiber, and more preferably 0.02 to 0.4% by mass. Within this range, the adhesion to the resin when made into a printed wiring board is better and the reliability is improved. If more than 0.5% by mass is attached, the silane coupling agent becomes excessive relative to the Si-OH on the glass fiber surface, which not only deteriorates the dielectric tangent but also causes the glass cloth to lose flexibility. In addition, excessive amounts of silane coupling agent also contain unreacted silane, which is not preferable because it generates alcohol as an outgas. The amount of silane coupling agent attached can be measured by the loss on ignition as described in JIS R3420.

The dielectric loss tangent (10 GHz, 40 GHz) of the silane-treated glass fiber obtained as described above is preferably 2 times or less, more preferably 1.5 times or less, and even more preferably 1.3 times or less, compared to before silane treatment. In particular, Q glass fiber of 95% by mass or more obtained by heat cleaning in a device having a heating mechanism that generates 0.12 L or less of water per unit heat output (1,000 kcal) has a very low dielectric loss tangent and is easily affected by silane treatment. If the dielectric loss tangent is within the above range, silane treatment can be performed without deteriorating the dielectric loss tangent of the glass fiber, which has the original dielectric loss tangent of glass.

[Prepreg for printed circuit boards]
Since the glass fiber of the present invention has a low dielectric tangent, the use of the glass fiber makes it possible to obtain a prepreg for a printed circuit board having improved dielectric properties. The method for producing the prepreg is not particularly limited, and a method for producing a general glass cloth-containing substrate, film, prepreg, etc. can be applied.

[Printed board]
Since the glass fiber of the present invention has a low dielectric tangent, by using the glass fiber, a printed circuit board with improved dielectric properties can be obtained. The printed circuit board can be suitably used for electronic components having a circuit that transmits an electric signal of 10 GHz or more. The method for manufacturing the printed circuit board is not particularly limited, and a general method for manufacturing a printed circuit board can be applied.

The present invention will be specifically explained below with examples and comparative examples, but the present invention is not limited to the following examples.

[Example 1]
[Step 1-1]
A glass fiber sizing agent was prepared, consisting of 3.0% by mass of starch, 0.5% by mass of beef tallow, 0.1% by mass of emulsifier, and the remainder water. A glass ingot containing 60% by mass of _SiO2 was heated and stretched to produce glass fibers consisting of quartz glass filaments with a diameter of 5.3 μm. The glass fiber sizing agent was applied with an applicator, and the fibers were bundled with a bundler and wound up to produce a glass strand with 200 glass filaments. The wound glass strand was twisted at 24 T/m to produce a glass yarn.

An aqueous solution of 1.5% by mass of PVA (polyvinyl alcohol) and 1.5% by mass of starch was applied to the obtained glass yarn as a secondary sizing agent, and then an air jet loom was used to produce a glass cloth conforming to IPC standard 1078. The glass cloth with a sizing agent and a _SiO2 content of 60% by mass was subjected to a heat cleaning treatment at 400°C for 72 hours using an electric furnace FO-610 manufactured by Yamato Scientific Co., Ltd., in which the amount of water generated per unit heat value (1,000 kcal) is less than 0.1 L, essentially 0 L, to obtain a heat-cleaned glass fiber.

[Step 1-2]
The heat-cleaned glass fiber obtained in step 1-1 was impregnated with an aqueous silane treatment solution containing 0.2% by mass of KBM-503 (manufactured by Shin-Etsu Chemical Co., Ltd., product name: 3-methacryloxypropyltrimethoxysilane) so that the amount of KBM-503 attached was 0.1% by mass. The glass cloth obtained after heat cleaning was then impregnated with the aqueous silane treatment solution, and dried at 110°C for 10 minutes in a constant temperature incubator DKN602 manufactured by Yamato Co., Ltd., to obtain a silane-treated glass fiber.

[Example 2]
[Step 2-1]
A glass cloth was woven in the same manner as in step 1-1 using a quartz glass ingot having a _SiO2 content of 99.9% by mass or more as a raw material, and the glass cloth was subjected to a heat cleaning treatment by heating at 400°C for 72 hours using an electric furnace FO-610 manufactured by Yamato Scientific Co., Ltd., to obtain a heat-cleaned glass cloth.

[Step 2-2]
The heat-cleaned glass fiber obtained in step-1 was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Example 3-2]
The heat-cleaned glass fiber obtained in step 3-1 was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Example 4]
[Step 4-1]
A heat-cleaning treated glass fiber was obtained in the same manner as in step 2-1, except that the heat-cleaning treatment was performed at 300° C. for 72 hours.

[Step 4-2]
The heat-cleaned glass fiber obtained in Example 4-1 was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Example 5]
[Step 5-1]
A heat-cleaning treated glass fiber was obtained in the same manner as in step 2-1, except that the heat-cleaning treatment was performed at 450° C. for 72 hours.

[Example 5-2]
The heat-cleaned glass fiber obtained in step 5-1 was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Example 6]
[Step 6-1]
A heat-cleaning treated glass fiber was obtained in the same manner as in step 2-1, except that the heat-cleaning treatment was performed at 600° C. for 72 hours.

[Example 6-2]
The heat-cleaned glass fiber obtained in step 6-1 was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Example 7]
The heat-cleaned glass cloth obtained in step 2-1 was impregnated with an aqueous silane treatment solution containing 0.2% by mass of KBM-503 so that the amount of KBM-503 attached was 0.1% by mass, and the obtained heat-cleaned glass cloth was dried at 110° C. for 30 seconds in a constant temperature incubator DKN602 manufactured by Yamato Co., Ltd., to obtain a silane-treated glass fiber.

[Example 8]
The heat-cleaned glass cloth obtained in step 2-1 was impregnated with an aqueous silane treatment solution containing 0.05% by mass of KBM-503 so that the amount of KBM-503 attached was 0.02% by mass, and the resulting heat-cleaned glass cloth was dried at 110°C for 10 minutes in a constant temperature incubator DKN602 manufactured by Yamato Co., Ltd., to obtain a silane-treated glass fiber.

[Example 9]
The heat-cleaned glass cloth obtained in step 2-1 was impregnated with an aqueous silane treatment solution containing 1% by mass of KBM-503 so that the amount of KBM-503 attached was 0.4% by mass, and the obtained heat-cleaned glass cloth was dried at 110°C for 10 minutes in a constant temperature incubator DKN602 manufactured by Yamato Co., Ltd., to obtain a silane-treated glass fiber.

[Comparative Example 1]
A glass fiber sizing agent consisting of 3.0% by mass of starch, 0.5% by mass of beef tallow, 0.1% by mass of emulsifier, and the remainder water was prepared, and a glass ingot with a _SiO2 content of 53% by mass was heated and stretched to produce glass fibers consisting of quartz glass filaments with a diameter of 5.3 μm. The glass fiber sizing agent was applied with an applicator, and then the fibers were bundled with a bundler and wound up to produce a glass strand with 200 glass filaments. The wound glass strand was twisted at 24 T/m to produce a glass yarn. An aqueous solution consisting of 1.5% by mass of PVA and 1.5% by mass of starch was applied to the obtained glass yarn as a secondary bundling agent, and then an IPC standard 1078 glass cloth was produced using an air jet loom. The glass cloth having a sizing agent attached thereto and a SiO content of ₅₃ % by mass was subjected to a heat cleaning treatment by heating at 400°C for 72 hours using an electric furnace FO-610 manufactured by Yamato Scientific Co., Ltd., in which the amount of water generated per unit heat value (1,000 kcal) is less than 0.1 L, essentially 0 L, to obtain a heat-cleaned glass fiber.

[Comparative Example 2]
A heat-cleaning treated glass fiber was obtained in the same manner as in step 2-1, except that the heat-cleaning treatment was performed at 200° C. for 72 hours.
The heat-cleaned glass fiber obtained above was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Comparative Example 3]
A glass cloth was woven in the same manner as in step 2-1 using a quartz glass ingot raw material containing 99.9% or more by mass of _SiO2 . The heating furnace was changed to a heating furnace (7 ^m3 fiber superior kiln, gas furnace manufactured by Mino Ceramics Co., Ltd.) that generates 12 L or more of water per unit heat value (1,000 kcal), and the glass cloth was subjected to a heat cleaning treatment at 400°C for 72 hours to obtain a heat-cleaned glass fiber.
The heat-cleaned glass fiber obtained above was treated in the same manner as in step 1-2 to obtain a silane-treated glass fiber.

[Cleaning cloth (corresponding to Reference Example 1)]
The glass cloth having the sizing agent attached thereto before heat cleaning used in Example 1 was washed with alkaline electrolytic water S-2665 manufactured by Suzuki Oil Industries Co., Ltd. at 60°C for 2 hours, and after removing the attached sizing agent, the glass cloth was dried at 100°C for 30 minutes to obtain a sizing-cleaned glass cloth.

[Cleaning cloth (corresponding to Reference Example 2)]
The glass cloth having the sizing agent attached thereto before heat cleaning used in Example 2 was washed with alkaline electrolytic water S-2665 manufactured by Suzuki Oil Industries Co., Ltd. at 60°C for 2 hours, and after removing the attached sizing agent, the glass cloth was dried at 100°C for 30 minutes to obtain a sizing-cleaned glass cloth.

The removal of sizing agents using alkaline electrolyzed water in Reference Examples 1 and 2 above does not result in cleavage of Si-O-Si bonds due to heating, so the dielectric tangent of the glass cloth before heat cleaning can be measured, and the amount of change in the dielectric tangent due to heat cleaning in this invention can be evaluated.

The glass cloth obtained above before and after the heat cleaning treatment, the glass cloth before and after the silane treatment, and the cleaning cloth were evaluated using the following methods. The results are shown in the table below.

1. Measurement of dielectric tangent The dielectric tangent of the glass cloth was measured using a dielectric constant measurement SPDR (split post dielectric resonator) with a dielectric resonator frequency of 10 GHz (manufactured by Keysight Technologies, Inc.). The thickness of the glass cloth was measured using the theoretical film thickness, which is expressed as follows: Theoretical film thickness t (m) = basis weight (g/ ^m2 ) / specific gravity (g/ ^cm3 )
Calculated from.

2. Dielectric loss tangent ratio The change in dielectric loss tangent before and after removal of the sizing agent was calculated based on the following formula.
Dielectric loss tangent ratio = dielectric loss tangent of the examples and comparative examples / (dielectric loss tangent of cleaning cloths with the same _SiO2 content)

3. Measurement of the amount of carbon remaining from the sizing agent 100 mg of glass fiber after heat cleaning was weighed out into a porcelain crucible that had been baked empty at 1,000°C for 2 hours, and 1.0 g of tungsten and 1.5 g of tin-coated copper were added as combustion improvers. The amount of carbon remaining was measured from the amount of gas when the material was burned at 2.2 kW using a carbon and sulfur analyzer CS774 manufactured by LECO. The result of this measurement method is referred to as the "amount of carbon remaining from the sizing agent."

4. Measurement of silanol group (Si-OH) content The silanol content of Q glass fiber is a value measured and calculated by the following method.
The dielectric loss tangent of plate-shaped Q glass having a known silanol content was measured in the same manner as for the glass cloth, and the following relational expression between the silanol content and the dielectric loss tangent was obtained.
Dielectric tangent (10 GHz) = 9.04 x 10 ^-8 x silanol content (ppm) + 5.26 x 10 ^-5
The amount of silanol was calculated from the dielectric loss tangent of the glass cloth using the obtained relational expression. When the amount of residual carbon was more than 0.1 mass%, the amount of silanol was calculated from the dielectric loss tangent after reducing the amount of residual carbon to 0.1 mass% or less using alkaline electrolyzed water.

5. Method for measuring volatile content of silane-treated glass cloth The silane-treated glass cloth was dried at 150° C. for 1 hour, and the change in mass was measured.
Volatile content (%)=((silane-treated glass cloth before heating−silane-treated glass cloth after heating)/silane-treated glass cloth before heating)×100

6. Amount of silane coupling agent attached: This was measured according to the ignition loss method described in JIS R3420.

7. Tensile strength The glass cloth before and after the silane treatment was measured using an autograph AGS-X manufactured by Shimadzu Corporation in accordance with the tensile strength measurement method of JIS R 3420. The results are reported as strength (GPa) = (strength (N/25 mm)/25)/theoretical film thickness (μm).

8. Reliability Evaluation 100 parts by mass of SLK-3000 (product name: manufactured by Shin-Etsu Chemical Co., Ltd.) and 2 parts by mass of dicumyl peroxide (product name: Percumyl D, manufactured by NOF Corp.) were added to toluene as a solvent and premixed with a stirrer to prepare a resin varnish.
The silane-treated glass cloth obtained in the Examples and Comparative Examples was impregnated with the prepared resin varnish and dried at 110°C for 10 minutes to prepare a prepreg. At that time, the adhesion amount was adjusted to 55 mass%. Then, three prepared prepregs were laminated and cured by step curing at 150°C for 1 hour and then at 180°C for 2 hours using a vacuum pressure reduction press. The obtained board was boiled in ion-exchanged water for 1 hour, and then immersed in a solder bath at 260°C for 30 seconds. Those that did not blister were judged as "◯", and those that blistered were judged as "×".

As shown in Table 1, in the heat cleaning method of the present invention, the heat-cleaned glass cloth with a _SiO2 content of 55% by mass or more has a dielectric loss tangent of 0.0016 or less at 10 GHz and 0.0020 or less at 40 GHz, which is 0.7 to 1.3 times that of the cleaning cloth. On the other hand, even in the glass cloth with a _SiO2 content of 55% by mass or more, the dielectric loss tangent ratios of Comparative Examples 2 and 3 are 4.6 and 2.4 at 10 GHz, respectively, which are insufficient as a substrate material for high-speed communication. In Comparative Example 2, the sizing agent was oxidized without burning, so the dielectric loss tangent was significantly deteriorated.

In addition, by subjecting the heat-cleaned glass cloth obtained in Example 2 to a silane treatment, it was possible to obtain a silane-treated glass cloth that was reliable when used as a substrate without deteriorating the dielectric tangent of the resulting silane-treated glass cloth.

Claims (7)

The silane-treated glass fiber is obtained by silane-treating a glass fiber having a _SiO2 composition amount of 55 mass% or more, the silane-treated glass fiber having a volatile content of 0.2 mass% or less, an adhesion amount of a silane coupling agent of 0.02 to 0.1 mass%, and a dielectric loss tangent at 10 GHz of 0.0017 or less. The silane-treated glass fiber according to claim 1, wherein the dielectric tangent of the silane-treated glass fiber at 40 GHz is 0.0021 or less. 2. The silane-treated glass fiber according to claim 1, wherein the glass fiber is Q-glass having an _SiO2 composition of 95 mass % or more. The silane-treated glass fiber according to claim 1, having a tensile strength of 0.07 to 0.24 GPa. The silane-treated glass fiber according to claim 1, having a volatile content of 0.02 to 0.05 mass%. A prepreg for printed circuit boards containing the glass fiber according to any one of claims 1 to 5. A printed wiring board using the glass fiber according to any one of claims 1 to 5.