JP2024048028A - Glass cloth, prepreg, and printed wiring board - Google Patents

Abstract

[Problem] To provide a low dielectric glass cloth with little slack and uniform properties in thickness, air permeability, and resin impregnation, as well as a prepreg and a printed wiring board using said glass cloth. [Solution] A glass cloth having a thickness of 5 μm to 100 μm and configured with glass threads consisting of a plurality of glass filaments as warp and weft threads, the glass cloth has a length in the width direction of 1000 mm or more, and the difference X in the warp width between the end portions in the width direction and the center portion in the width direction of the glass cloth is equal to or less than the standard deviation α of the warp width. [Selected Figure] None

Description

The present invention relates to glass cloth, prepregs, and printed wiring boards.

With the recent development of the information and communications society, data communications and/or signal processing have become large-volume and high-speed, and the dielectric constant of printed wiring boards used in communication devices or measuring instruments, such as high-end servers or high-end routers/switches, supercomputers, and base stations, has been significantly reduced. For this reason, many low-dielectric glass cloths have been proposed for use in the glass cloths that make up printed wiring boards.

For example, the low dielectric glass cloth disclosed in Patent Document 1 achieves a low dielectric constant by blending a large amount of boron oxide (B ₂ O ₃ ) in the glass composition compared to the E-glass cloth that has been commonly used in the past, while at the same time adjusting the blending amounts of other components such as silicon dioxide (SiO ₂ ).

As a method for improving the variation in the performance and quality of low dielectric glass cloth in the width direction, Patent Document 2 discloses a glass cloth with improved end slackness, and Patent Document 3 discloses a glass cloth with improved board warpage.

JP 2010-508226 A International Publication No. 2021/124913 JP 2017-132651 A

The inventors' investigations revealed that low-dielectric glass cloth made from such low-dielectric glass yarns has a large variation in performance and quality compared to the E-glass cloth that has been used conventionally.

Low dielectric glass cloth tends to have more slack than conventional E-glass cloth. Particularly, large slack occurs at the widthwise ends and the center. This is presumably because low dielectric glass cloth has a low elastic modulus and a weak texture. In addition, the inventors of the present invention observed the low dielectric glass cloth in detail and found that the thickness distribution differs in the width direction, and the thickness at the widthwise ends tends to be about 10% thicker than the thickness at the center. Furthermore, it was found that the properties such as air permeability and resin impregnation also differ in the width direction, especially at the widthwise ends. Such variations in the performance and quality of glass cloth also affect the properties and quality of prepregs and laminates for printed wiring boards obtained using it (resin content, heat resistance, copper foil peel strength, dimensional stability, etc.).

The glass cloth disclosed in Patent Document 2 discloses that the difference in the slope of the stress-strain curve in the direction parallel to the warp yarns is kept to 10% or less between the ends and the center in the width direction, thereby improving the slackness of the glass cloth at its ends. However, the glass cloth disclosed in Patent Document 2 still has room for improvement in terms of the slackness of the low dielectric glass cloth.

The glass cloth disclosed in Patent Document 3 is a low dielectric glass cloth in which the difference in the widthwise amount of elongation in the stress-strain curve in the warp direction is kept to 10% or less, thereby improving the warping of the board. However, the amount of elongation in the weft direction also plays a large role in the warping of the board, and since glass cloth usually has the property that the weft elongates more than the warp, it is not possible to improve the warp warping by simply controlling the amount of elongation in the warp, and there is still room for improvement in the sagging of the glass cloth.

The present invention was made in consideration of the above problems, and aims to provide a low-dielectric glass cloth that has little sagging and is uniform in thickness, air permeability, and resin impregnation properties, as well as a prepreg and a printed wiring board that use the glass cloth.

As a result of intensive research into solving the above problems, the inventors discovered that the above problems could be solved by setting the difference in warp width between the ends and the center of the glass cloth within a specified range relative to the variation in warp width, and thus completed the present invention.

That is, the present invention is as follows.
[Item 1]
A glass cloth having a thickness of 5 μm to 100 μm, the glass cloth being configured with glass yarns consisting of a plurality of glass filaments as warp yarns and weft yarns,
A glass cloth having a width direction length of 1000 mm or more, and a difference X in warp width between an end portion in the width direction and a center portion in the width direction of the glass cloth is equal to or less than a standard deviation α of the warp width.
[Item 2]
2. The glass cloth according to item 1, wherein the warp width difference X is 0.7 times or less the standard deviation α of the warp width.
[Item 3]
3. The glass cloth according to item 1 or 2, wherein the warp width difference X is 0.5 times or less the standard deviation α of the warp width.
[Item 4]
4. The glass cloth according to any one of items 1 to 3, wherein the standard deviation α of the warp width is 0.08 times or less the average value β of the warp width.
[Item 5]
5. The glass cloth according to any one of items 1 to 4, wherein the standard deviation α of the warp width is 0.04 times or less the average value β of the warp width.
[Item 6]
6. The glass cloth according to any one of items 1 to 5, wherein the standard deviation α of the warp width is 0.03 times or less the average value β of the warp width.
[Item 7]
Item 7. The glass cloth according to any one of items 1 to 6, wherein the TEX of the glass yarn is 1.0 or more and 25 or less.
[Item 8]
8. The glass cloth according to any one of items 1 to 7, which is composed of glass yarns having an elastic modulus of 50 GPa or more and 70 GPa or less.
[Item 9]
Item 9. The glass cloth according to any one of items 1 to 8, which is composed of glass yarns having an elastic modulus of 50 GPa or more and 63 GPa or less.
[Item 10]
Item 10. The glass cloth according to any one of items 1 to 9, wherein the sum of the boron content and the phosphorus content in the glass cloth is 5 mass% or more and 20 mass% or less.
[Item 11]
Item 11. The glass cloth according to any one of items 1 to 10, wherein the sum of the boron content and the phosphorus content in the glass cloth is 6.5 mass% or more and 20 mass% or less.
[Item 12]
Item 12. A prepreg comprising the glass cloth according to any one of items 1 to 11 and a matrix resin composition impregnated into the glass cloth.
[Item 13]
Item 12. A printed wiring board comprising the glass cloth according to any one of items 1 to 11 and a cured product of a matrix resin composition impregnated into the glass cloth.

The present invention makes it possible to provide a low dielectric glass cloth that has little sagging and is uniform in properties such as thickness, air permeability, and resin impregnation.

The following describes in detail an embodiment of the present invention (hereinafter referred to as the "present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the gist of the present invention.

〔Glass cloth〕
The glass cloth of this embodiment is a glass cloth having a thickness of 5 μm to 100 μm, which is constituted of glass yarns consisting of a plurality of glass filaments as warp yarns and weft yarns, the length of the glass cloth in the width direction is 1000 mm or more, and the difference in warp width between the end portions in the width direction and the center portion in the width direction is equal to or less than the standard deviation of the warp width.

The term "widthwise end" as used herein refers to a region extending from 100 mm to 250 mm from the widthwise end of a glass cloth having a widthwise length of 1000 mm or more, and the term "widthwise center" refers to a region extending from the widthwise center of a glass cloth having a widthwise length of 1000 mm or more to 75 mm on both ends.
The difference in warp width between the end portion and the center portion in the width direction, and the standard deviation of the warp width are measured as described in the examples below.

Compared to E-glass cloth, low dielectric glass cloth is more likely to develop slack at both ends and in the center in the width direction. In addition, the thickness tends to be about 10% thicker near both ends in the width direction. Furthermore, properties such as air permeability and resin impregnation also tend to differ in the width direction, particularly at the ends in the width direction. In order to solve the above problems with low dielectric glass cloth, the inventors first investigated the causes of the above problems, and found that the woven structure of the glass cloth at both ends in the width direction is significantly different from the woven structure in the center in the width direction.

That is, in the case of glass cloth with a width of 1000 mm or more, the warp threads are arranged horizontally in a line in the width direction in a range of 150 mm from the end to the center in the width direction (the area from 100 mm from the end to 250 mm from the end in the width direction), and there is almost no wavy structure and they are almost straight. On the other hand, in the range of 100 mm from the end to the center and in the center, the warp threads are arranged alternately up and down the horizontal, and have a wavy structure. Because of the formation of such a woven structure, it was found that when the glass cloth is transported in the horizontal direction, the warp threads stretch due to the action of gravity in the range from the end to about 100 mm toward the center and in the center, and the glass cloth sags downward and slackens (in the range from 100 mm from the end to 150 mm toward the center, the warp threads are taut and do not slacken due to the action of gravity). In other words, it was found that the cause of the slackness of the low dielectric glass cloth is due to the uneven woven structure in the width direction. They also discovered that by correcting the distortion in the width direction of the woven structure described above, it is possible to improve the slack in the low dielectric glass cloth.

It was also found that the thickness of the low dielectric glass cloth was increased in the range of 150 mm from the end to the center, because the warp yarns were aligned almost horizontally in a line and the weft yarns formed large undulations along the line. As described above, it was found that the thickness of the low dielectric glass cloth could be made uniform in the width direction by correcting the distortion in the width direction of the woven structure. Furthermore, it was found that the air permeability, resin impregnation, and the difference in the stretch amount and the slope in the warp direction in the stress-strain curve in the width direction could be improved by correcting the distortion in the width direction of the woven structure.
Furthermore, since the warp and weft yarns are densely packed, the thickness of the glass cloth is also reduced.

As described above, in the glass cloth of this embodiment, the warp width difference X between the widthwise end portion and the widthwise center portion is equal to or less than the standard deviation α of the warp width. More preferably, the warp width difference X is equal to or less than 0.7 times the warp width standard deviation α, and even more preferably, the warp width difference X is equal to or less than 0.5 times the warp width standard deviation α. When the warp width difference X between the widthwise end portion and the widthwise center portion is equal to or less than the warp width standard deviation α, the woven structure becomes uniform in the width direction, and the differences in the slackness, thickness, resin impregnation property, and air permeability of the glass cloth in the width direction are reduced and improved.
The smaller the difference X in the warp width between the widthwise end portion and the widthwise center portion, the better, and it is most preferable that the warp widths are substantially the same. Even if the widthwise end portion is wider than the widthwise center portion, the difference X in the warp width between the widthwise end portion and the widthwise center portion is preferably −0.3α (minus 0.3 times the standard deviation), since the differences in the slackness, thickness, resin impregnation, and air permeability of the glass cloth in the widthwise direction are improved if the difference X is up to 0.3 times the standard deviation of the warp width.

The present inventors have discovered that the distortion of the woven structure occurs during the flattening and opening processes, when the filaments of the glass yarn bundle are scattered and the yarn bundle is expanded, thereby reforming the woven structure, due to the following mechanism of action.
The flattening and opening processes are carried out by processes using high-pressure water sprays, processes using a vibro washer, or processes using high-frequency vibrations using liquid as a medium. These processes are carried out while applying tension in the warp direction of the glass cloth and transporting it horizontally, and at this time, a force that causes the glass cloth to sag downward due to its own weight acts on the glass cloth. Furthermore, since these processes are carried out using water, the weight of the glass cloth containing water increases, and the force that causes it to sag downward becomes greater. In this way, the glass cloth is subjected to a combination of support by the transport rolls, tension in the warp direction, and a downward force due to its own weight. As a result, the warp tension acts locally and strongly in the range from 100 mm from the end to 300 mm from the end. As a result, the warp does not widen in the range from 100 mm from the end to 300 mm from the end, and the warp remains taut. On the other hand, the warp widens in the range 100 mm inside the end and in the center, and warp undulations are also formed in the process of forming the woven structure. In this way, it has been found that a strain across the width of the woven structure is created.

Based on the above-mentioned knowledge of the mechanism by which the width-wise distortion of the woven structure is formed, the width-wise distribution of the pressure of the high-pressure water spray, the processing force of the size water washing and high-pressure water, and the tension applied in the MD were adjusted during the size washing and high-pressure water spray opening process of the glass cloth (grey fabric), and the silane coupling agent treatment followed by the high-pressure water spray opening process, so that the warp yarn expansion in the range from 100 mm from the end in the width direction to 300 mm from the end is equivalent to the other ranges, as follows:

- In the warping and weaving stage, the warp tension is set so that the tension of the warp threads in the range from 100 mm from the end to 300 mm from the end is weaker than in other ranges, and a green fabric is created and flattened and opened.
- A method of weakening the processing force in the range of 100 mm from the end and in the center, and strengthening the processing force in the range of 300 mm from the end than the point 100 mm from the end,
A method of reducing the tension during flattening and opening, thereby reducing the difference in tension between the tension acting on the warp yarns in the range from 100 mm from the end to 300 mm from the end and the tension in other ranges during flattening and opening.
- A method of reducing the processing power of flattening and opening to minimize changes in the cross-sectional structure of the yarn bundle and changes in the fabric structure.
It has been found that the use of these alone or in suitable combination improves the distortion in the width direction of the woven structure.

In the glass cloth of this embodiment, it is preferable that the standard deviation α of the warp width is 0.08 times or less than the average warp width value β.

When the standard deviation α of the warp width is 0.08 times or less than the average warp width β, the woven structure is more likely to be uniform in the width direction, and the difference in the slackness, thickness, resin impregnation, and air permeability of the glass cloth between the ends and the center in the width direction is reduced, which is preferable.

The standard deviation α of the warp width is preferably 0.04 times or less the average value β of the warp width, and more preferably 0.03 times or less the average value β of the warp width.
The average warp width is measured as described in the Examples below.

The smaller the standard deviation of the warp width, the easier it is to make the fabric structure uniform in the width direction, so it is preferable. Although not particularly limited, it is preferably 0 or more.
In order to keep the standard deviation of the warp width within the above range, it is effective to use glass yarns with small variations in twist number, filament diameter, TEX, etc., for the warp, to make the tension and processing force in the warp weaving process and the flattening process uniform in the width direction, and to reduce the fluctuation of the tension and processing force. Also, as mentioned above, it is effective to reduce the yarn width difference between the end and center in the width direction.

The glass cloth of this embodiment has a thickness of 5 μm or more and 100 μm or less. If the thickness of the glass cloth of this embodiment is 100 μm or less, it is possible to increase the density and multi-layer of the printed wiring board. The above thickness is preferably thin from the viewpoint of thinning and increasing the density of the printed wiring board, but from the viewpoint of maintaining practical strength, the lower limit of the thickness is 5 μm. The thickness of the glass cloth of this embodiment is preferably 6 μm or more, more preferably 8 μm or more. In addition, the thickness of the glass cloth of this embodiment is preferably 98 μm or less, more preferably 96 μm or less.
The thickness of the glass cloth of this embodiment can be measured by the method described in the Examples.

The elastic modulus of the glass yarn constituting the glass cloth of the present embodiment is preferably 50 GPa or more, more preferably 51 GPa or more, and further preferably 52 GPa or more.
If the elastic modulus is 50 GPa or more, the rigidity of the glass yarn is improved, structural changes during flattening and opening during glass cloth processing are controlled, and a uniform woven structure in the width direction tends to be easily achieved.
On the other hand, the elastic modulus of the glass yarn is preferably 70 GPa or less, more preferably 65 GPa or less, and even more preferably 63 GPa or less. If the elastic modulus is 70 GPa or less, the glass yarn has a moderate flexibility, so that the woven structure is easily changed under the influence of tension and processing force during the warping and weaving process, flattening process, and fiber opening process during glass cloth processing, and therefore, it tends to be easy to make a woven structure uniform in the width direction. In addition, if the elastic modulus is 70 GPa or less, the glass yarn and glass cloth are soft, so that in the conventional glass cloth, the woven structure tends to be distorted in the width direction, and it is useful to make a woven structure uniform in the width direction by this embodiment.
The elastic modulus of the glass yarn can be measured by the method described in the Examples.

The dielectric constant of the glass cloth of this embodiment is preferably 5.0 or less, more preferably 4.7 or less, further preferably 4.5 or less, and particularly preferably 4.0 or less, at a frequency of 1 GHz. In this embodiment, the dielectric constant refers to the dielectric constant at a frequency of 1 GHz, unless otherwise specified.
The weave structure of the glass cloth of the present embodiment is not particularly limited, and examples thereof include plain weave, sash weave, satin weave, twill weave, etc. Among these, the plain weave structure is more preferable.

The glass yarn constituting the glass cloth of the present embodiment is obtained by bundling a plurality of filaments and twisting them as necessary. In this case, the glass yarn is classified as a multi-glass filament, and the filament (glass filament) contained in the glass yarn is classified as a mono-glass filament.
The weft density of the warp and weft yarns constituting the glass cloth of the present embodiment is preferably 30 to 120 yarns/25 mm, more preferably 40 to 110 yarns/25 mm, and further preferably 50 to 100 yarns/25 mm.
The average diameter of the monoglass filaments constituting the warp and weft is preferably 2.5 to 9 μm, more preferably 3.0 to 8 μm, and further preferably 3.5 to 7.5 μm, and can be appropriately selected depending on the desired thickness of the glass cloth.
The average number of monoglass filaments constituting the warp and weft is preferably 20 to 250, more preferably 30 to 230, and further preferably 33 to 220.

The preferred range of the ignition loss value of the glass cloth of this embodiment is 0.25% by mass to 1.5% by mass, more preferably 0.3% by mass to 1.4% by mass, and even more preferably 0.35% by mass to 1.3% by mass.

The composition of the glass cloth of this embodiment will be described below. The composition of the glass cloth is synonymous with the composition of the glass yarn that constitutes the glass cloth. The elements that constitute the glass cloth include at least one selected from the group consisting of silicon (Si), boron (B), aluminum (Al), calcium (Ca), magnesium (Mg), phosphorus (P), sodium (Na), potassium (K), titanium (Ti), zinc (Zn), iron (Fe), and fluorine (F).

The silicon (Si) content of the glass yarn is preferably 40 to 60 mass%, more preferably 45 to 55 mass%, even more preferably 47.0 to 53.5 mass%, and even more preferably 48.0 to 52.0 mass%, calculated as _SiO2 . Si is a component that forms the skeletal structure of the glass yarn.
For this reason, when the Si content is 40 mass% or more in terms of _SiO2 , the strength of the glass yarn is further improved, and breakage of the glass cloth tends to be further suppressed in downstream processes such as a process for producing a glass cloth and a process for producing a prepreg using the glass cloth.
In addition, when the Si content is 40 mass% or more in terms of _SiO2 , the dielectric constant of the glass cloth of the present embodiment tends to be lower. On the other hand, when the Si content is 60 mass% or less in terms of _SiO2 , the viscosity at the time of melting is lowered in the manufacturing process of the glass filaments, and glass fibers having a more homogeneous glass composition tend to be obtained.
Therefore, the obtained glass filament is less likely to have a portion that is easily devitrified or a portion where bubbles are difficult to escape, and therefore the glass filament is less likely to have a portion with locally weak strength. As a result, the glass cloth made of the glass yarn obtained by using this is less likely to break. The Si content can be adjusted according to the amount of raw material used to produce the glass filament.

The _boron (B) content of the glass yarn, calculated as _B2O3 , is preferably 15 to 40 mass%, more preferably 17 to 30 mass%, or preferably 20 to 40 mass%, even more preferably 18 to 28 mass%, still more preferably 19 to 26 mass%, even more preferably 20 to 25 mass%, and most preferably 20.5 to 24.5 mass%.

When the B content is 15% _by mass or more in terms of _B2O3 , the dielectric constant tends to be further decreased. Also, when the B content is 15% by _mass or more in terms of _B2O3 , the brittleness resistance of the glass cloth of the present embodiment is improved and appropriate flexibility or pliability is imparted to the glass cloth, so that fluffing tends to be less likely to occur when the glass yarn comes into contact with loom components such as a yarn guide and a reed.

On the other hand, in order to maintain the strength of the glass yarn, the B content is preferably 40 mass% or less in terms of B ₂ O _3. By setting the B content to 40 mass% or less, the moisture absorption resistance is improved, and the stability of the glass yarn surface characteristics described below is easily maintained appropriately.

In particular, it is preferable that the Si content in the glass yarn is within the above range in terms of _SiO2 and the _B content is within the above range in terms of _B2O3 , since the above effects related to Si and B are easily achieved synergistically.

The B content can be adjusted by the amount (charge amount) of the raw materials used in producing the glass filaments. If the production conditions, amount used, or content may change during the production of the glass filaments, the charge amount of the raw materials can be adjusted in advance in anticipation of this.

The aluminum (Al) content of the glass filament is preferably 11 to 18 mass%, more preferably 11 to 17.5 mass%, and even more preferably 12 to 17.0 mass%, calculated as Al ₂ O _3. When the Al content is within the above range, calculated as Al ₂ O ₃ , the electrical properties and strength tend to be further improved. The Al content can be adjusted by the amount (charge amount) of the raw material used to prepare the glass filament.

The calcium (Ca) content of the glass filaments is preferably 5.0 to 10 mass%, more preferably 5.0 to 9.0 mass%, and even more preferably 5.0 to 8.5 mass%, calculated as CaO. When the Ca content is 5.0 mass% or more calculated as CaO, the viscosity at the time of melting tends to be lower during the glass filament manufacturing process, and glass fibers with a more homogeneous glass composition tend to be obtained. Furthermore, when the Ca content is 10 mass% or less calculated as CaO, the dielectric constant tends to be improved. The Ca content can be adjusted by the amount (charge amount) of the raw materials used to manufacture the glass filaments.

The phosphorus (P) content of the glass yarn is preferably 8.0 mass% or less, more preferably 7.0 mass% or less, and even more preferably 6.0 mass% or less, calculated as _{P2O5 .} The P content may be more than 0 mass% calculated as _P2O5 . When the P content is more than 0 mass% calculated as _P2O5 , the dielectric properties of the glass cloth tend to be better. In addition, when the P content is _8.0 mass% _or less calculated as _P2O5 , the heat resistance of the glass cloth tends to be improved. The P content can be adjusted by the amount (charge amount) of the raw material used to prepare _the glass filament.

The sum of the boron content and the phosphorus content in the glass cloth is preferably 5% by mass or more and 20% by mass or less from the viewpoint of easily reducing the dielectric constant and the dielectric loss tangent of the glass cloth and from the viewpoint of easily forming a woven structure uniform in the width direction. The larger the sum of the boron content and the phosphorus content in the glass cloth, the smaller the dielectric constant and the dielectric loss tangent of the glass cloth tend to be. By making the sum of the boron content and the phosphorus content 5% by mass or more, the dielectric constant and the dielectric loss tangent are significantly reduced compared to a laminate obtained using a general E-glass cloth, and therefore the applicability to large capacity and high speed data communication and signal processing is improved.
In the glass cloth, the sum of the boron content and the phosphorus content is preferably 6.5 mass % or more and 20 mass % or less from the viewpoint of making it easier to reduce the dielectric constant and the dielectric tangent of the glass cloth and to make it easier to have a uniform woven structure in the width direction.
The larger the sum of the boron content and phosphorus content in the glass cloth, the smaller the dielectric constant and dielectric loss tangent of the glass cloth tend to be. When the sum of the boron content and phosphorus content is 6.5 mass% or more, the dielectric constant and dielectric loss tangent are significantly reduced compared to laminates obtained using general E-glass cloth, improving applicability to large capacity and high speed data communication and signal processing.
For example, while the dielectric constant of E-glass is about 7, when the sum of the boron content and the phosphorus content is 7.4 mass%, the dielectric constant is about 4.8, and when the sum of the boron content and the phosphorus content is 9.2 mass%, the dielectric constant is about 4.4, so the dielectric constant tends to be smaller.

When the sum of the contents of boron and phosphorus is 5% by mass or more, the glass cloth of the present embodiment has appropriate flexibility, and therefore tends to have a uniform woven structure in the width direction since the woven structure is easily changed by the influence of tension and processing force during the warping and weaving steps, flattening and opening processes in the glass cloth processing.
In addition, when the sum of the contents of boron and phosphorus is 6.5% by mass or more, the glass cloth of the present embodiment has appropriate flexibility, and therefore tends to have a uniform woven structure in the width direction since the woven structure is easily changed by the influence of tension and processing force during the warping and weaving steps, flattening and opening processes in the glass cloth processing.

By keeping the sum of the boron content and phosphorus content at 20% by mass or less, the moisture absorption resistance and/or heat resistance of the glass cloth of this embodiment can be maintained at the same level as that of E-glass, in which the sum of the boron content and phosphorus content is about 2% by mass.

The sum of the boron content and phosphorus content in the glass cloth can be adjusted by the amount of glass raw material containing boron and phosphorus added in the process of producing the glass yarn. In addition, since the boron and phosphorus contents in the glass change during the process of melting the glass raw material in the process of producing the glass yarn, the amount of addition may be appropriately adjusted by taking into account the amount of change.
The above contents can be measured by ICP atomic emission spectrometry. Specifically, the Si content and the B content can be obtained by fusing a weighed amount of glass cloth with sodium carbonate, dissolving it in dilute nitric acid to a predetermined volume, and measuring the obtained sample by ICP atomic emission spectrometry.
The Fe content can be obtained by dissolving a weighed amount of glass cloth by an alkali dissolution method to a predetermined volume, and measuring the obtained sample by ICP emission spectrometry.
Furthermore, the Al content, Ca content, P content and Mg content can be obtained by subjecting weighed glass cloth to thermal decomposition with perchloric acid, sulfuric acid, nitric acid and hydrogen fluoride, dissolving it in dilute nitric acid to a predetermined volume, and measuring the obtained sample by ICP atomic emission spectrometry.
As the ICP optical emission spectrometer, PS3520VDD II manufactured by Hitachi High-Tech Science Corporation can be used.

Here, the content of the above elements constituting the glass cloth of the present embodiment described in this specification is the weight of the element itself unless there is a description in terms of oxide, and is the weight of the above element when converted into an oxide if there is a description in terms of oxide.
Furthermore, if necessary, even if the contents of the above elements are described in terms of weight when converted into oxides, they can also be converted into the weight of the element itself, rather than into oxides.

From the viewpoint of making it easier to adjust the thickness of the glass cloth of the present embodiment to 5 μm to 100 μm, the TEX of the glass yarn is preferably 1.0 or more and 25 or less, more preferably 1.5 or more and 23 or less, and even more preferably 2.0 or more and 21 or less.
The glass cloth of the present embodiment may be surface-treated with a surface treatment agent. The surface treatment agent is not particularly limited, but may be, for example, a silane coupling agent, and may be used in combination with water, an organic solvent, an acid, a dye, a pigment, a surfactant, or the like, as necessary.

The silane coupling agent is not particularly limited, but examples thereof include compounds represented by formula (1).
X(R) _{3- nSiYn} ... (1)
(In formula (1), X is an organic functional group having at least one of an amino group and an unsaturated double bond group, each Y is independently an alkoxy group, n is an integer of 1 to 3, and each R is independently a group selected from the group consisting of a methyl group, an ethyl group, and a phenyl group.)
X is preferably an organic functional group having at least three or more of amino groups and unsaturated double bond groups, and more preferably an organic functional group having at least four or more of amino groups and unsaturated double bond groups.
The alkoxy group may be in any form, but from the viewpoint of stabilizing the treatment of the glass cloth of this embodiment, an alkoxy group having 5 or less carbon atoms is preferred.
Specific examples of the silane coupling agent include N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropylmethyldimethoxysilane and its hydrochloride, N-β-(N-di(vinylbenzyl)aminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-di(vinylbenzyl)aminoethyl)-N-γ-(N-vinylbenzyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N- Examples of the alkylsilane include known simple substances such as β-(N-benzylaminoethyl)-γ-aminopropyltrimethoxysilane and its hydrochloride, N-β-(N-benzylaminoethyl)-γ-aminopropyltriethoxysilane and its hydrochloride, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, aminopropyltrimethoxysilane, vinyltrimethoxysilane, methacryloxypropyltrimethoxysilane, and acryloxypropyltrimethoxysilane, and mixtures thereof.
The molecular weight of the silane coupling agent is preferably 100 to 600, more preferably 150 to 500, and even more preferably 200 to 450. Among these, it is preferable to use two or more types of silane coupling agents having different molecular weights. By treating the surface of the glass yarn with two or more types of silane coupling agents having different molecular weights, the density of the surface treatment agent on the surface of the glass cloth tends to be increased, and the reactivity with the matrix resin tends to be further improved.

<Method of manufacturing glass cloth>
The manufacturing method of the glass cloth of the present embodiment is not particularly limited, but may be a method in which glass yarns are used as warp and weft yarns, woven by a conventional method, and then post-processed by treating the green glass cloth with a silane coupling agent. The weaving structure of the glass cloth is not particularly limited, but may be, for example, a plain weave, a sash weave, a satin weave, or a twill weave. Furthermore, a mixed weave structure using different types of glass yarns may be used. Among these, a plain weave structure is preferred.

The method for manufacturing the glass cloth in this embodiment is not particularly limited, but a suitable example is a method having a coating process in which a treatment liquid having a silane coupling agent concentration of 0.1 to 3.0 wt % is applied to the glass cloth to almost completely cover the surface of the glass filaments with the silane coupling agent, a fixing process in which the silane coupling agent is fixed to the surface of the glass filaments by heating and drying, and a fiber-opening process in which the glass threads of the glass cloth are opened.

As a solvent for dissolving or dispersing the silane coupling agent, either water or an organic solvent can be used, but from the viewpoint of safety and global environmental protection, it is preferable to use water as the main solvent. As a method for obtaining a treatment liquid in which water is the main solvent, either a method in which the silane coupling agent is directly poured into water, or a method in which the silane coupling agent is dissolved in a water-soluble organic solvent to obtain an organic solvent solution, and then the organic solvent solution is poured into water, is preferable. In order to improve the water dispersibility and stability of the silane coupling agent in the treatment liquid, it is also possible to use a surfactant in combination.

Methods for applying the silane coupling agent treatment solution to the glass cloth include (a) a method in which the silane coupling agent treatment solution is collected in a bath and the glass cloth is immersed and passed through the solution (hereinafter referred to as the "immersion method"); and (b) a method in which the silane coupling agent treatment solution is directly applied to the glass cloth using a roll coater, die coater, gravure coater, or the like. When applying the solution using the immersion method (a) above, it is preferable to immerse the glass cloth in the treatment solution for 0.5 seconds or more and 1 minute or less. In addition, methods for heating and drying the solvent after applying the treatment solution to the glass cloth include known methods such as hot air and electromagnetic waves.

The heating and drying temperature is preferably 90°C or higher, more preferably 100°C or higher, so that the reaction between the silane coupling agent and the glass is sufficiently carried out. In addition, the heating and drying temperature is preferably 300°C or lower, more preferably 200°C or lower, to prevent deterioration of the organic functional groups of the silane coupling agent.

The method of opening the fibers in the opening process is not particularly limited, but examples include opening the glass cloth with spray water (high pressure water opening), a vibro washer, ultrasonic water, a mangle, etc. In order to keep the total area of the basket holes within a certain range, it is preferable to perform the opening process with spray water.

When using spray water to open the fibers, the water pressure may be set as appropriate, and it is preferable to keep the water pressure constant in order to adjust the total area of the basket holes in the glass cloth. Here, keeping the water pressure constant means reducing the difference between the spray water pressure set for opening the fibers and the maximum and minimum values of the actual water pressure. A heating and drying process may also be performed before or after the opening process.

<Prepreg>
The present embodiment also relates to a prepreg which is a composite of the above-mentioned glass cloth and a matrix resin composition. The matrix resin composition is impregnated into the glass cloth.
The prepreg can be produced by a conventional method, for example, by impregnating a glass cloth with a varnish prepared by diluting a matrix resin composition with an organic solvent, and then volatilizing the organic solvent in a drying furnace to produce a matrix resin composition-impregnated prepreg.

Either thermosetting resin or thermoplastic resin can be used as the resin that constitutes the matrix resin composition. Examples of thermosetting resins include, but are not limited to, a) epoxy resins that are cured by reacting a compound having an epoxy group with a compound having at least one of an amino group, a phenol group, an acid anhydride group, a hydrazide group, an isocyanate group, a cyanate group, and a hydroxyl group that reacts with the epoxy group without a catalyst or by adding a catalyst having a reaction catalytic ability such as an imidazole compound, a tertiary amine compound, a urea compound, or a phosphorus compound; b) radical polymerization type curing resins that are cured by using a thermal decomposition type catalyst or a photodecomposition type catalyst as a reaction initiator to cure a compound having at least one of a vinyl group, an allyl group, a methacryl group, and an acrylic group; c) maleimide triazine resins that are cured by reacting a compound having a cyanate group with a compound having a maleimide group; d) thermosetting polyimide resins that are cured by reacting a maleimide compound with an amine compound; e) benzoxazine resins that are crosslinked and cured by thermal polymerization of a compound having a benzoxazine ring.

Thermoplastic resins are not particularly limited, but examples include polyphenylene ether, modified polyphenylene ether, polyphenylene sulfide, polysulfone, polyether sulfone, polyarylate, aromatic polyamide, polyether ether ketone, thermoplastic polyimide, insoluble polyimide, polyamide imide, fluororesin, etc. Thermosetting resins and thermoplastic resins may also be used in combination.

The resin constituting the matrix resin composition in the prepreg composed of glass cloth and a matrix resin composition, which is one of the present embodiments, is preferably a polyphenylene ether resin. More preferably, it is a polyphenylene ether resin having 1.5 to 5 functional groups containing carbon-carbon double bonds, such as vinyl groups, allyl groups, methacrylic groups, and acrylic groups, at the main chain terminal per molecule. Also, it is preferably a polyphenylene ether resin having a number average molecular weight of 500 to 8,000. The matrix resin is preferably a polyphenylene ether resin, since it has excellent dielectric properties.

In addition, since the resin constituting the matrix resin composition has the above-mentioned functional groups and number average molecular weight, it is assumed that the resin composition easily penetrates into the glass cloth during the prepreg production process and press molding process, and many adhesion points with the glass cloth are secured, resulting in excellent dielectric properties. However, even in a system in which the number of direct adhesion points between the resin matrix layers formed above and below the glass cloth is reduced due to the high in-plane uniformity and low air permeability of the glass as in this embodiment, the strong adhesion at the interface between the glass cloth and the resin composition is expressed, improving heat resistance and insulation reliability.

<Printed wiring board>
This embodiment also relates to a printed wiring board having the above-mentioned glass cloth and a cured product of the matrix resin composition impregnated into the glass cloth.
The printed wiring board of the present embodiment is manufactured using the prepreg. That is, the printed wiring board of the present embodiment is a printed wiring board formed by molding the prepreg of the present embodiment. By manufacturing a printed wiring board using the prepreg of the present embodiment, it is possible to provide a high-quality printed wiring board in which the difference in signal propagation speed between a plurality of transmission lines is reduced.

The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples.

[Elastic modulus]
The elastic modulus of the glass filament was measured by the pulse-echo overlap method using a glass bulk obtained by melting and cooling the glass filament as a test piece.

[Evaluation: average value of warp width over the entire width, standard deviation of warp width]
The camera was scanned in the MD direction and the direction perpendicular to the MD direction of the glass cloth to obtain images of the warp yarns over the entire width of the glass cloth, and the yarn width of each warp yarn was measured. The average value and standard deviation of the warp widths over the entire width of the glass cloth were calculated.

[Evaluation: warp width at the end and center]
The camera was scanned in a direction perpendicular to the MD direction of the glass cloth to obtain images of the warp yarns over the entire width of the glass cloth, and the yarn width of each warp yarn was measured.
The average warp width was calculated within a range of 250 mm from each end of the glass cloth in the width direction, starting from a point 100 mm from each end, and the narrower width was taken as the warp width at the end. The average warp width was calculated within a range of 75 mm to the left and right of the center in the width direction, and taken as the warp width at the center.

[Evaluation: average thickness]
The thickness was measured at three measurement points in the width direction of the glass cloth so that the distance between both ends in the width direction and each measurement point was equal, in accordance with JIS R 3420. The thicknesses measured at the three measurement points were averaged and rounded off to the nearest whole number to obtain the average thickness (μm).

[Evaluation: Thickness at the ends and center]
The thickness of the glass cloth was measured in accordance with JIS R 3420, with the measurement points being 100 mm inside from both ends in the width direction of the glass cloth. Of the two thicknesses measured, the larger value was taken as the thickness (μm) at the end.

The thickness was measured in accordance with JIS R3420, with the center of the glass cloth in the width direction as the measurement point. The thickness obtained was taken as the thickness (mm) at the center.

[Evaluation: Air permeability at the ends and center]
The air permeability was measured in accordance with JIS R 3420, with the measurement points being 100 mm inside from both ends in the width direction of the glass cloth. Of the two air permeabilities obtained, the larger value was taken as the air permeability (cm ³ /cm ² /s) at the end.

In addition, the air permeability was measured in accordance with JIS R 3420, with the center of the glass cloth in the width direction as the measurement point. The obtained air permeability was defined as the air permeability (cm ³ /cm ² /s) at the center.

[Evaluation: Evaluation of resin impregnation of glass cloth]
Test pieces for impregnation measurement were taken from 100 mm inside from both ends in the width direction of the glass cloth, and also from the center in the width direction of the glass cloth.

A varnish for impregnation evaluation with a viscosity of 230±5 mPa·s was prepared by dissolving a bisphenol A type epoxy resin in benzyl alcohol in an environment of 23±2° C. Next, a glass cloth test piece was immersed in the varnish for impregnation evaluation, and the state of the varnish for impregnation evaluation impregnating the glass cloth was observed with an optical microscope while irradiating light from the side.
The number of voids (parts not impregnated with the varnish for evaluating impregnation properties) was counted after a predetermined time from the immersion of the glass cloth test piece in the varnish for evaluating impregnation properties. At this time, the visual field of the glass cloth observed with an optical microscope was about 6.5 mm in the warp direction and about 9 mm in the weft direction.

For both ends in the width direction, the value with the greater number of voids was used as the remaining number of voids (pieces) at the end.

For the glass cloths of Example 1 and Comparative Example 1, the number of voids was counted after 2 minutes.
For the glass cloths of Examples 2, 2B, 2C, 2D, 2E, and 2F and Comparative Example 2, the number of voids after 3 minutes was counted.
For the glass cloths of Examples 3 and 4, Comparative Examples 3 and 4, and Reference Example 1, the number of voids was counted after 5 minutes.
For the glass cloths of Examples 5 and 6 and Comparative Examples 5 and 6, the number of voids after 8 minutes was counted.

[Evaluation: Amount of slack during cross transport]
The glass cloth was unwound from a rolled glass cloth wound around a core under a tension of 150 N, and when the glass cloth had been conveyed for 2 m, it was bent by 90° by a guide roll. The fluttering of the glass cloth between the unwound and guide rolls was measured using a displacement meter (a laser applisensor manufactured by Keyence Corporation). Displacement meter was installed at two points 100 mm inside from both ends in the width direction of the glass cloth and at the center in the width direction, and the difference between the maximum position and the minimum position in the vertical direction of the glass cloth measured by the displacement meter was taken as the fluttering magnitude of the glass cloth (unit: mm).

[Evaluation: Difference in the amount of elongation in the warp direction in the stress-strain curve (%) when a load of 50 N/inch is applied, and difference in the slope of the stress-strain curve in the width direction (%)]
The amount of elongation and the slope when tension was applied to the glass cloth in the warp direction were measured by applying the method described in JIS R3420, Glass Testing - General Testing Method, Section 7.4 Tensile Strength. In the JIS-specified method, a test piece with a width of about 30 mm and a length of about 250 mm was taken from the warp direction of the fabric, the yarns at both ends of the test piece were loosened to a width of about 25 mm, and the test piece was attached to the gripping parts with a gripping distance of about 150 mm, and pulled at a pulling speed of about 200 mm/min to determine the load at break. In this embodiment, the tensile test was performed under the same conditions as the JIS-specified method, except that the pulling speed was set to about 5 mm/min to improve the measurement accuracy.
Test pieces for measuring the stress-strain curve were taken from the range of 50 mm to 200 mm inside from both ends in the width direction of the glass cloth. In addition, a test piece for measuring the stress-strain curve was taken from the center in the width direction of the glass cloth.
The amount of displacement (mm) when a load of 50 N was applied per 25 mm width of the glass cloth was obtained, and the ratio of the amount of elongation at the end and the center in the width direction was calculated. For both ends in the width direction, the larger amount of elongation was taken as the amount of elongation (mm) at the end.
The slope was calculated from the elongation (mm) when a load of 50 N was applied per 25 mm width of the glass cloth (elongation (mm)/50 N), and the ratio of the slope of the end portion to the central portion in the width direction was calculated. For both ends in the width direction, the larger slope was regarded as the slope of the end portion.

<Comparative Example 1>
Low dielectric glass yarn LCBC1700 (elastic modulus 61 GPa, TEX 2.92) manufactured by AGY was used for both the warp and weft yarns, and a glass cloth (grey) with a warp pick density of 74 threads/25 mm and a weft pick density of 74 threads/25 mm was woven using an air jet loom.
The obtained greige fabric was washed with starch and subjected to a fiber-opening treatment using a high-pressure water spray. Next, the fabric was heated at 400°C for 24 hours to remove the starch, and then the glass cloth was immersed in a treatment solution using a silane coupling agent as a surface treatment agent, squeezed, and dried at 120°C for 1 minute. Further, a fiber-opening treatment using a high-pressure water spray was performed to obtain a glass cloth having a width of 1,300 mm.

Example 1
A glass cloth having a width of 1,300 mm was produced in the same manner as in Comparative Example 1, except that the tension during warping and the pressure of the high-pressure water spray during fiber-spreading were adjusted in the width direction so that the warp width in the range from 100 mm from the end to 300 mm from the end in the width direction was equivalent to that in the other ranges, and the line tension during size washing and fiber-spreading processing by high-pressure water spray was adjusted to a lower value.

The tension during warping was set at 0.8 times the tension in the range from 100 mm from the end in the width direction to 300 mm from the end. The pressure of the high-pressure water spray was set at 1.2 times the pressure in the range from 100 mm from the end in the width direction to 300 mm from the end. The line tension during size washing and fiber opening processing with high-pressure water spray was set at 0.5 times that of Comparative Example 1.

<Comparative Example 2>
Low dielectric glass yarn LCD1020 (elastic modulus 61 GPa, TEX 4.86) manufactured by AGY was used for both the warp and weft yarns, and a glass cloth (grey) with a warp pick density of 69 threads/25 mm and a weft pick density of 69 threads/25 mm was woven using an air jet loom.
The obtained greige fabric was washed with starch and subjected to a fiber-opening treatment using a high-pressure water spray. Next, the fabric was heated at 400°C for 24 hours to remove the starch, and then the glass cloth was immersed in a treatment solution using a silane coupling agent as a surface treatment agent, squeezed, and dried at 120°C for 1 minute. Further, a fiber-opening treatment using a high-pressure water spray was performed to obtain a glass cloth having a width of 1,300 mm.

Example 2
A glass cloth having a width of 1,300 mm was produced in the same manner as in Comparative Example 2, except that the tension during warping and the pressure of the high-pressure water spray during fiber-spreading were adjusted in the width direction so that the warp width in the range from 100 mm from the end to 300 mm from the end in the width direction was equivalent to that in the other ranges, and the line tension during size washing and fiber-spreading processing by high-pressure water spray was adjusted to a lower value.

The tension during warping was set at 0.8 times the tension in the range from 100 mm from the end in the width direction to 300 mm from the end. The pressure of the high-pressure water spray was set at 1.2 times the pressure in the range from 100 mm from the end in the width direction to 300 mm from the end. The line tension during size washing and fiber opening processing with high-pressure water spray was set at 0.5 times that of Comparative Example 2.

Example 2B
The tension in the range from 100 mm from the end to 300 mm from the end in the width direction was set to 0.9 times the tension in other ranges.
The pressure of the high-pressure water spray was set at 1.2 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 2.

Example 2C
The tension in the range from 100 mm from the end to 300 mm from the end in the width direction was set to 0.8 times the tension in other ranges.
The pressure of the high-pressure water spray was set at 1.1 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 2.

Example 2D
The tension in the range from 100 mm from the end to 300 mm from the end in the width direction was set to 0.9 times the tension in other ranges.
The pressure of the high-pressure water spray was set at 1.1 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 2.

Example 2E
The tension in the range from 100 mm from the end to 300 mm from the end in the width direction was set to 0.9 times the tension in other ranges.
The pressure of the high-pressure water spray was set at 1.1 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.8 times that of Comparative Example 2.

Example 2F
A glass cloth having a width of 1250 mm was produced in the same manner as in Example 2, except that after the fiber-opening process was carried out using a high-pressure water spray, both ends including the selvedge tassels were cut off and the width was processed to 1250 mm.

<Comparative Example 3>
Low dielectric glass yarn LCD510 (elastic modulus 61 GPa, TEX 9.73) manufactured by AGY was used for both the warp and weft yarns, and a glass cloth (grey) with a warp pick density of 52.5 threads/25 mm and a weft pick density of 52.5 threads/25 mm was woven using an air jet loom.
The obtained greige fabric was washed with starch and subjected to a fiber-opening treatment using a high-pressure water spray. Next, the fabric was heated at 400°C for 24 hours to remove the starch, and then the glass cloth was immersed in a treatment solution using a silane coupling agent as a surface treatment agent, squeezed, and dried at 120°C for 1 minute. Further, a fiber-opening treatment using a high-pressure water spray was performed to obtain a glass cloth having a width of 1,300 mm.

Example 3
A glass cloth having a width of 1,300 mm was produced in the same manner as in Comparative Example 3, except that the tension during warping and the pressure of the high-pressure water spray during fiber-spreading were adjusted in the width direction so that the warp width in the range from 100 mm inside the end to 300 mm inside the end in the width direction was equivalent to that in the other range, and the line tension during size washing and fiber-spreading processing by high-pressure water spray was adjusted to a low value.

The tension during warping was set at 0.8 times the tension in the range from 100 mm from the end to 300 mm from the end in the width direction.
The pressure of the high-pressure water spray was set at 1.2 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 3.

<Comparative Example 4>
A glass cloth having a width of 1,300 mm was obtained in the same manner as in Comparative Example 3, except that low dielectric glass yarn LCD520 (elastic modulus 56 GPa, TEX 9.47) manufactured by AGY was used for both the warp and weft.

Example 4
A glass cloth having a width of 1,300 mm was obtained in the same manner as in Example 3, except that low dielectric glass yarn LCD520 (elastic modulus 56 GPa, TEX 9.47) manufactured by AGY was used for both the warp and weft.

<Comparative Example 5>
Low dielectric glass yarn LCDE340 (elastic modulus 61 GPa, TEX 14.59) manufactured by AGY was used for both the warp and weft yarns, and a glass cloth (grey) with a warp pick density of 59 threads/25 mm and a weft pick density of 61 threads/25 mm was woven using an air jet loom.
The obtained greige fabric was washed with starch and subjected to a fiber-opening treatment using a high-pressure water spray. Next, the fabric was heated at 400°C for 24 hours to remove the starch, and then the glass cloth was immersed in a treatment solution using a silane coupling agent as a surface treatment agent, squeezed, and dried at 120°C for 1 minute. Further, a fiber-opening treatment using a high-pressure water spray was performed to obtain a glass cloth having a width of 1,300 mm.

Example 5
A glass cloth having a width of 1,300 mm was produced in the same manner as in Comparative Example 5, except that the tension during warping and the pressure of the high-pressure water spray during fiber-spreading were adjusted in the width direction so that the warp width in the range from 100 mm from the end to 300 mm from the end in the width direction was equivalent to that in the other ranges, and the line tension during size washing and fiber-spreading processing by high-pressure water spray was adjusted to a low value.

The tension during warping was set at 0.8 times the tension in the range from 100 mm from the end to 300 mm from the end in the width direction.
The pressure of the high-pressure water spray was set at 1.2 times that of the other range in the range from 100 mm from the end in the width direction to 300 mm from the end.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 5.

<Comparative Example 6>
Low dielectric glass yarn LCE255 (elastic modulus 61 GPa, TEX 19.45) manufactured by AGY was used for both the warp and weft threads, and a glass cloth (grey) with a warp thread pick density of 60 threads/25 mm and a weft thread pick density of 57 threads/25 mm was woven using an air jet loom.
The obtained greige fabric was washed with starch and subjected to a fiber-opening treatment using a high-pressure water spray. Next, the fabric was heated at 400°C for 24 hours to remove the starch, and then the glass cloth was immersed in a treatment solution using a silane coupling agent as a surface treatment agent, squeezed, and dried at 120°C for 1 minute. Further, a fiber-opening treatment using a high-pressure water spray was performed to obtain a glass cloth having a width of 1,300 mm.

Example 6
A glass cloth having a width of 1,300 mm was produced in the same manner as in Comparative Example 6, except that the tension during warping and the pressure of the high-pressure water spray during fiber-spreading were adjusted in the width direction so that the warp width in the range from 100 mm from the end to 300 mm from the end in the width direction was equivalent to that in the other ranges, and the line tension during size washing and fiber-spreading processing by high-pressure water spray was adjusted to a low value.

The tension during warping was set at 0.8 times the tension in the range from 100 mm from the end to 300 mm from the end in the width direction.
The pressure of the high-pressure water spray was set at 1.2 times that of the other range in a range 100 mm from the end in the width direction and 300 mm inward from the center.
The line tension during size washing and fiber opening processing by high-pressure water spray was set to 0.5 times that of Comparative Example 6.

<Reference Example 1>
A glass cloth having a width of 1,300 mm was obtained in the same manner as in Comparative Example 3, except that E glass yarn D450 (elastic modulus 74 GPa, TEX 11.05) was used for both the warp and weft.

The low dielectric glass cloth of the Example had less flapping than the glass cloth of the Comparative Example.The glass cloth of the Example had the same thickness, air permeability, resin impregnation, and elongation and slope of the stress-strain curve at the ends and center in the width direction as the glass cloth of the Comparative Example.
The conventional E-glass cloth having a high elastic modulus shown in the reference example was produced in the same manner as in Comparative Example 3. Compared with the glass cloths of Comparative Examples 3 and 4, the flapping was smaller, and the thickness, air permeability, resin impregnation property, and elongation amount and slope in the stress-strain curve were also equivalent between the ends and the center in the width direction.
The large slack and fluttering are problems specific to low dielectric glass cloth having a low elastic modulus, but it has become clear that this embodiment can solve these problems.

Claims (13)

A glass cloth having a thickness of 5 μm to 100 μm, the glass cloth being configured with glass yarns consisting of a plurality of glass filaments as warp yarns and weft yarns,
A glass cloth having a width direction length of 1000 mm or more, and a difference X in warp width between an end portion in the width direction and a center portion in the width direction of the glass cloth is equal to or less than a standard deviation α of the warp width. The glass cloth according to claim 1, wherein the warp width difference X is 0.7 times or less the standard deviation α of the warp width. The glass cloth according to claim 1 or 2, wherein the warp width difference X is 0.5 times or less the standard deviation α of the warp width. The glass cloth according to claim 1 or 2, wherein the standard deviation α of the warp width is 0.08 times or less the average value β of the warp width. The glass cloth according to claim 1 or 2, wherein the standard deviation α of the warp width is 0.04 times or less the average value β of the warp width. The glass cloth according to claim 1 or 2, wherein the standard deviation α of the warp width is 0.03 times or less the average value β of the warp width. The glass cloth according to claim 1 or 2, wherein the TEX of the glass yarn is 1.0 or more and 25 or less. The glass cloth according to claim 1 or 2, which is made of glass yarns having an elastic modulus of 50 GPa or more and 70 GPa or less. The glass cloth according to claim 1 or 2, which is made of glass yarn having an elastic modulus of 50 GPa or more and 63 GPa or less. The glass cloth according to claim 1 or 2, wherein the sum of the boron content and the phosphorus content in the glass cloth is 5% by mass or more and 20% by mass or less. The glass cloth according to claim 1 or 2, wherein the sum of the boron content and the phosphorus content in the glass cloth is 6.5% by mass or more and 20% by mass or less. A prepreg comprising the glass cloth according to claim 1 or 2 and a matrix resin composition impregnated into the glass cloth. A printed wiring board comprising the glass cloth according to claim 1 or 2 and a cured product of the matrix resin composition impregnated into the glass cloth.