JP7626402B2 - Glass Cloth - Google Patents

Description

The present invention relates to glass cloth.

In recent years, with the miniaturization of electronic devices, printed wiring boards are required to be lighter, and the materials used are also required to be light in mass. Prepregs, which are glass cloth impregnated with resin, are used to manufacture printed wiring boards, but with the weight reduction of the above-mentioned electronic devices, the prepregs are also required to be light in mass. Similarly, the glass cloth contained in the prepregs is also required to be light in mass.

As a low-mass glass cloth, for example, a glass cloth satisfying the following (i) to (iv) is known (see, for example, Patent Document 1).
(i) The degree of opening shown in the following formula (1) is 70 to 90% for the warp yarn and 95 to 120% for the weft yarn.
Openness (%) = {(25 x 1000) / WD-I} / (D x N) x 100 (1)
WD: Warp or weft density (threads/25mm)
I: Gap distance between adjacent warp or weft yarns (μm)
D: average filament diameter of warp or weft (μm)
N: Average number of filaments in the warp or weft
(ii) Either the gap between adjacent warp yarns or the gap between adjacent weft yarns is 100 μm or less.
(iii) A thickness measured in accordance with JIS R 3420:2013 7.10.1 is 14 μm or less.
(iv) A cloth weight measured in accordance with JIS R 3420:2103 7.2 is ^not more than 11 g/m2.

According to the glass cloth in Patent Document 1, when the thickness is reduced to 14 μm or less, for example, when a thin prepreg having a thickness of 20 μm or less and a substrate using the prepreg are made, the occurrence of pinholes can be suppressed.

Also, as a low-mass glass cloth, there is provided a glass cloth which is composed of warp threads and weft threads formed by bundling 14 to 55 glass filaments having a diameter in the range of 3.0 to 4.2 μm, the weaving density of the warp threads and weft threads being in the range of 86 to 140 threads/25 mm, the thickness being in the range of 7.5 to 12.0 μm, and the mass being in the range of 6.0 to 10.0 g per ^m2 , the average number of steps, expressed as the value obtained by dividing the thickness of the glass cloth by the average value of the diameter of the glass filaments of the warp threads and the diameter of the glass filaments of the weft threads (thickness of the glass cloth/{(diameter of the glass filaments of the warp threads+diameter of the glass filaments of the weft threads)/2}), is in the range of 2.00 or more and less than 3.00, and the opening degree of the warp threads (width of the warp threads/(diameter of the glass filaments constituting the warp threads×diameter of the glass filaments constituting the warp threads) is in the range of 2.00 or more and less than 3.00, There is known a glass cloth in which the average degree of opening, which is expressed as the geometric mean ((warp opening degree×weft opening degree)/2) of the degree of opening of the weft (weft width/(diameter of glass filaments constituting the weft×number of glass filaments constituting the weft)), is in the range of 1.000 to 1.300, and the width ratio, which is expressed as the ratio of the warp width to the weft width (warp width/weft width), is in the range of 0.720 to 0.960 (see, for example, Patent Document 2).

According to the glass cloth of Patent Document 2, even if the average number of rows is less than 3.00, it is possible to suppress the occurrence of pinholes in a prepreg using the glass cloth, and since the glass cloth has little fuzz, it is possible to maintain the excellent appearance quality of the prepreg.

JP 2017-43873 A JP 2018-21274 A

From the viewpoint of insulation reliability, low-mass prepregs are often used with a low mass ratio of glass cloth, for example, with the mass ratio of glass cloth to the total mass of the prepreg being about 10 to 40 mass%. However, the inventors have found through their investigation that when the glass cloths of Patent Documents 1 and 2 described above have a low mass ratio of glass cloth when made into prepregs and are impregnated with a resin solution and cured, the resulting prepregs may develop wrinkles (vertical wrinkles) running in the machine direction during production.

Therefore, the main objective of the present invention is to solve the above problems and provide a glass cloth that can remarkably effectively suppress the occurrence of pinholes and the above-mentioned vertical wrinkles, even when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg.

The inventors have studied the cause of the above problem and found that when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low and cured, the tension in the weft direction (width direction of the glass cloth) of the glass cloth is significantly lower than the tension in the warp direction (length direction of the glass cloth). In the glass cloth of Patent Document 1, the weft tends to move slightly in the width direction of the glass cloth due to the curing shrinkage when the resin impregnated in the glass cloth is cured, and as a result, the vertical wrinkles are likely to occur. Specifically, in the glass cloth of Patent Document 1, the following factors (i) to (iii) and the like combine to cause the weft to move slightly in the width direction of the glass cloth, and as a result, the vertical wrinkles are likely to occur.
(i) The spacing between the gaps between adjacent warp threads is larger than the spacing between the gaps between adjacent weft threads, so that the weft threads are not adequately gripped by the warp threads.
(ii) The glass cloth is originally thin, and the warp and weft threads are thin and flexible.
(iii) When a low-mass glass cloth is impregnated with a resin solution and cured so that the mass ratio of the glass cloth is low, the weft yarns are more likely to move in the width direction of the glass cloth due to curing shrinkage, compared to when the glass cloth is impregnated with a resin solution and cured so that the mass ratio of the glass cloth is relatively high.

The inventor also considered that the glass cloth of Patent Document 2 was subjected to an excessive fiber opening process, and that, in particular, each filament constituting the weft thread would bend, which would cause vertical wrinkles to occur easily. In other words, when each filament constituting the weft thread bends, each filament will be present in the glass cloth in a loose state. The loose filaments are in a state in which they are likely to move in the width direction of the glass cloth, and if a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low and then cured, the weft thread will move slightly in the width direction of the glass cloth due to the loose filaments during curing and shrinkage, and vertical wrinkles will occur easily as a result.

On the other hand, taking the above-mentioned mechanism of action into consideration, it was thought that both the suppression of pinholes and the suppression of vertical wrinkles could be achieved by increasing the warp and weft densities of the glass cloth or by increasing the number of filaments in the warp and weft. However, the inventors have found that increasing the warp and weft densities of the glass cloth or increasing the number of filaments in the warp and weft increases the mass of the glass cloth and the mass of the prepreg. They have also found that if the mass ratio of the glass cloth in the prepreg is too high, the glass cloth is exposed from the prepreg surface, and the exposed glass cloth comes into direct contact with the signal layer, thereby impairing the insulation reliability.

Furthermore, the inventors have discovered that as the glass cloth becomes thinner, if the warp and weft densities of the glass cloth are increased, the number of filaments in the warp and weft threads is increased, or excessive fiber-opening processing is performed, the gap space surrounded by adjacent warp and weft threads becomes extremely small, which can result in internal distortion of the glass cloth and vertical wrinkles becoming more likely to occur.

The inventors have conducted intensive research to solve the above problems and have found that by satisfying the following conditions: (1) in the glass cloth, the design value Iwd of the gap between adjacent warp threads and the design value Ifd of the gap between adjacent weft threads are set to 95 μm or less; (2) in order to sufficiently hold the warp threads and the weft threads together while keeping the glass cloth mass at or below a specific mass, the ratio (Iw/If) of the actual gap value (Iw) between adjacent warp threads and the actual gap value (If) between adjacent weft threads is set to 1.23 to 1.45; and (3) the area ratio of basket holes (openings) formed by adjacent warp threads and adjacent weft threads is set to 12.0% to 20.0%. The present invention has been completed based on such findings and through further research.

項２． 前記隣接する経糸間の隙間設計値Ｉｗｄが７０μｍ以上９５μｍ以下、及び前記隣接する緯糸間の隙間設計値Ｉｆｄが７０μｍ以上９５μｍ以下であり、且つ
ガラスクロスのバスケットホール面積割合が１２．０％以上１８．０％以下である、項１に記載のガラスクロス。
項３． 項１又は２に記載のガラスクロスを含むプリプレグ。
項４． プリプレグの質量に対するガラスクロスの質量の割合（ガラスクロスの質量／プリプレグの質量）が１０～４０質量％である、項３に記載のプリプレグ。
項５． 質量が１０ｇ／ｍ²以下、下記式（１）に示す隣接する経糸間の隙間設計値Ｉｗｄが９５μｍ以下、且つ下記式（２）に示す隣接する緯糸間の隙間設計値Ｉｆｄが９５μｍ以下であるガラスクロスに対して開繊処理を行う工程を含み、
前記開繊処理が、隣接する経糸間の隙間実測値（Ｉｗ）と隣接する緯糸間の隙間実測値（Ｉｆ）との比（Ｉｗ／Ｉｆ）が１．２３以上１．４５以下、且つ下記式（３）に示すバスケットホール面積割合が１２％以上２０％以下となるように行われる、
ガラスクロスの製造方法。

That is, the present invention provides the following aspects.
Item 1. A glass cloth having a mass of 10.0 g/m2 or ^less ,
The gap design value Iwd between adjacent warp yarns shown in the following formula (1) is 95 μm or less, and the gap design value Ifd between adjacent weft yarns shown in the following formula (2) is 95 μm or less,
A glass cloth having a ratio (Iw/If) of an actual gap value (Iw) between adjacent warp yarns to an actual gap value (If) between adjacent weft yarns of 1.23 or more and 1.45 or less, and a basket hole area ratio represented by the following formula (3) of 12.0% or more and 20.0% or less.

Item 2. The glass cloth according to item 1, wherein the design gap value Iwd between adjacent warp yarns is 70 μm or more and 95 μm or less, and the design gap value Ifd between adjacent weft yarns is 70 μm or more and 95 μm or less, and the basket hole area ratio of the glass cloth is 12.0% or more and 18.0% or less.
Item 3. A prepreg comprising the glass cloth according to item 1 or 2.
Item 4. The prepreg according to item 3, wherein the ratio of the mass of the glass cloth to the mass of the prepreg (mass of glass cloth/mass of prepreg) is 10 to 40 mass%.
Item 5. A method for manufacturing a glass cloth having a mass of 10 g/m2 or ^less , a design value Iwd of a gap between adjacent warp yarns as shown in the following formula (1) of 95 μm or less, and a design value Ifd of a gap between adjacent weft yarns as shown in the following formula (2) of 95 μm or less, comprising a step of performing a fiber-spreading process on the glass cloth,
The fiber-spreading process is performed so that a ratio (Iw/If) of an actual gap value (Iw) between adjacent warp yarns to an actual gap value (If) between adjacent weft yarns is 1.23 or more and 1.45 or less, and a basket hole area ratio represented by the following formula (3) is 12% or more and 20% or less.
A method for manufacturing glass cloth.

According to the glass cloth of the present invention, the glass cloth has a mass of 10.0 g/m2 or ^less , the designed gap value Iwd between adjacent warp yarns is 95 μm or less, the designed gap value Ifd between adjacent weft yarns is 95 μm, the ratio (Iw/If) of the actual gap value (Iw) between adjacent warp yarns to the actual gap value (If) between adjacent weft yarns is 1.23 to 1.45, and the basket hole area ratio is 12.0% to 20.0%, so that when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, it becomes possible to remarkably effectively suppress the occurrence of pinholes and the above-mentioned vertical wrinkles.

1. A glass cloth having a glass cloth mass of 10 g/m2 or ^less , characterized in that the design gap value Iwd between adjacent warp yarns shown in formula (1) is 95 μm or less, the design gap value Ifd between adjacent weft yarns shown in formula (2) is 95 μm or less, the ratio (Iw/If) of the actual gap value (Iw) between adjacent warp yarns to the actual gap value (If) between adjacent weft yarns is 1.23 to 1.45, and the basket hole area ratio shown in formula (3) is 12.0% to 20.0%. The glass cloth of the present invention will be described in detail below.

The glass cloth of the present invention may have a mass of 10.0 g/m ² or less, preferably 9.5 g/m ² or less. The lower limit of the above mass range is not particularly limited, but is, for example, 5.0 g/m ² or more, preferably 6.0 g/m ² or more, more preferably 7.0 g/m ² or more, even more preferably 8.0 g/m ² or more, and particularly preferably 8.5 g/m ² or more. Specific examples of the mass of the glass cloth of the present invention include 5.0 g/m ² or more and 10 g/m ² or less, preferably 6.0 g/m ² or more and 10 g/m ² or less, more preferably 7.0 g/m ² or more and 9.5 g/m ² or less, and even more preferably 8.5 g/m ² or more and 9.5 g/m ² or less. In the present invention, the mass is a value measured and calculated in accordance with the provisions of "7.2 Mass of cloth and mat (mass)" in the Japanese Industrial Standard JIS R 3420 2013 (general test method for glass fibers).

In the glass cloth of the present invention, the design value Iwd of the gap between adjacent warps as shown in the following formula (1) is 95 μm or less, and the design value Ifd of the gap between adjacent wefts as shown in the following formula (2) is 95 μm or less. The lower limit values of the design value Iwd of the gap between the warps and the design value Ifd of the gap between the wefts are not particularly limited, but from the viewpoint of making it easier to achieve both the suppression of pinhole generation and the suppression of vertical wrinkle generation, it is preferably 60 μm or more, more preferably 70 μm or more, and even more preferably 75 μm or more. Specific examples of the design value Iwd of the gap between the warps in the glass cloth of the present invention include 60 μm or more and 95 μm or less, preferably 70 μm or more and 95 μm or less, and more preferably 75 μm or more and 95 μm or less. Specific examples of the design value Ifd of the gap between the wefts in the glass cloth of the present invention include 60 μm or more and 95 μm or less, preferably 70 μm or more and 95 μm or less, and more preferably 75 μm or more and 95 μm or less. In particular, by having both the designed gap value Iwd and the designed gap value Ifd be 75 μm or more, it becomes easier to preferably obtain the range of the ratio (Iw/If) of the actual measured gap value (Iw) between adjacent warp yarns to the actual measured gap value (If) between adjacent weft yarns and the range of the basket hole area ratio, which will be described later.

The above-mentioned warp gap design value Iwd and weft gap design value Ifd are first assumed to be arranged in a line without gaps in the glass thread width direction in the warp and weft (glass thread) consisting of multiple filaments. In this assumption, the width (μm) of the virtual glass thread can be calculated by the average filament diameter x the average number of filaments (i.e., Dw x Nw for warp threads, Df x Nf for weft threads). Next, since the weave density (warp thread density is Ww, weft thread density is Wf) is the number of glass threads per 25 mm (25,000 μm) as described below, the sum of the width of the glass thread and the gap between adjacent glass threads can be calculated by dividing 25,000 μm by the weave density (25,000/Ww for warp threads, 25,000/Wf for weft threads). Then, by subtracting the virtual glass thread width from the sum of the width of the glass thread and the width of adjacent glass threads, the virtual gap spacing between adjacent warp threads and the virtual gap spacing between adjacent weft threads can be calculated, and these are set as the gap design value Iwd between adjacent warp threads and the gap design value Ifd between adjacent weft threads, respectively.

The glass cloth given as a specific example in Patent Document 2 is designed so that the warp gap design value Iwd and the weft gap design value Ifd exceed 100 μm, and is manufactured by a method of reducing the gap by excessive fiber opening. Therefore, the inventors thought that the glass cloth in the example of Patent Document 2 has each filament present in the glass cloth in a loose state, which causes each filament constituting the weft in particular to bend, and as a result, vertical wrinkles are likely to occur. The inventors then discovered that by setting the warp gap design value Iwd and the weft gap design value Ifd within the above specific range, the occurrence of pinholes and the occurrence of vertical wrinkles can be suppressed significantly more effectively.

In the glass cloth of the present invention, the warp density Ww and weft density Wf (threads/25 mm) of the glass cloth are not particularly limited, but from the viewpoint of making it easier to achieve both the suppression of pinhole generation and the suppression of vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, 90 threads/25 mm or more and 160 threads/25 mm or less are preferable, 95 threads/25 mm or more and 150 threads/25 mm or less are more preferable, and 100 threads/25 mm or more and 125 threads/25 mm or less are even more preferable. In the present invention, the warp density and weft density are values measured and calculated in accordance with the provisions of "7.9 Density (weaving density)" of the Japanese Industrial Standard JIS R 3420 2013 (General test method for glass fibers).

In the glass cloth of the present invention, the average filament diameter Dw of the filaments constituting the warp threads (glass threads) and the average filament diameter Df of the filaments constituting the weft threads (glass threads) are not particularly limited, but from the viewpoint of making it easier to simultaneously suppress the occurrence of pinholes and the occurrence of vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, a diameter of 2.5 μm or more and 4.0 μm or less is preferable, and a diameter of 3.0 μm or more and 3.7 μm or less is more preferable.

In the glass cloth of the present invention, the average number Nw of filaments constituting the warp threads (glass threads) constituting the glass cloth and the average number Nf of filaments constituting the weft threads (glass threads) constituting the glass cloth are preferably 25 to 50, more preferably 30 to 40, and even more preferably 34 to 40, from the viewpoint of making it easier to simultaneously suppress the occurrence of pinholes and the occurrence of vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg.

In the present invention, the average filament diameters (Dw and Df) and the average number of filaments (Nw and Nf) are measured and calculated as follows.

That is, two pieces of glass cloth were prepared by cutting them into 30 cm squares, one for observing the warp threads and the other for observing the weft threads, and each was embedded in epoxy resin (product name 3091, manufactured by Marumoto Struers K.K.), hardened, and polished to the extent that the warp and weft threads could be observed. Using a scanning electron microscope (SEM), the filament diameter was observed and measured at a magnification of 1000x, and the number of filaments was observed and measured at a magnification of 500x.
(1) Average filament diameter of glass yarn (μm)
Thirty warp and weft threads are randomly selected, and the diameters of all filaments (largest part) of the 30 glass threads are measured and the average value is calculated to obtain the average filament diameter of the warp and weft threads.
(2) Average number of filaments (pieces)
Twenty threads are randomly selected for each of the warp and weft yarns, and the total number of filaments in the 20 glass threads is measured and the average value is calculated to obtain the average filament diameter of the warp and weft yarns.

In the glass cloth of the present invention, the count (tex) of the warp and weft yarns is not particularly limited, but from the viewpoint of making it easier to achieve both the suppression of pinholes and the suppression of vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to make a prepreg, the count is preferably 0.5 tex to 1.2 tex, more preferably 0.6 tex to 1.1 tex, and even more preferably 0.9 tex to 1.1 tex. In the present invention, the count of the warp and weft yarns is a value measured and calculated in accordance with the specification in "7.1 Count" of the Japanese Industrial Standard JIS R 3420 2013 (General Test Method for Glass Fibers).

In the glass cloth of the present invention, the glass material constituting the warp and weft is not particularly limited, and known glass materials can be used. Specific examples of glass materials include alkali-free glass (E glass), acid-resistant alkali-containing glass (C glass), high-strength, high-elasticity glass (S glass, T glass, UT glass (manufactured by Unitika Glass Fiber Co., Ltd.), etc.), alkali-resistant glass (AR glass), low-dielectric glass (NE glass, L glass, LU glass (manufactured by Unitika Glass Fiber Co., Ltd.), etc.). Among these glass materials, alkali-free glass (E glass), which is highly versatile, is preferable. The glass fibers constituting the glass cloth may be made of one type of glass material, or may be a combination of two or more types of glass fibers made of different glass materials.

In the glass cloth of the present invention, the ratio (Iw/If) of the measured gap between adjacent warp threads (Iw) to the measured gap between adjacent weft threads (If) is 1.23 or more and 1.45 or less. By making the ratio (Iw/If) 1.45 or less, the weft threads are sufficiently gripped by the warp threads, and when a low-mass glass cloth is impregnated with a resin solution and hardened so that the mass ratio of the glass cloth is low, the weft threads are prevented from moving slightly in the width direction of the glass cloth, and the occurrence of vertical wrinkles due to this can be sufficiently prevented. In addition, by making the ratio 1.23 or more, it is possible to sufficiently suppress the occurrence of pinholes when a low-mass glass cloth is impregnated with a resin solution and hardened so that the mass ratio of the glass cloth is low. When a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, from the viewpoint of making it easier to achieve both the suppression of pinhole generation and the suppression of vertical wrinkles, the ratio (Iw/If) is preferably 1.25 to 1.45, more preferably 1.30 to 1.40, and even more preferably 1.34 to 1.44.

In the present invention, the measured gap value Iw between adjacent warp threads and the measured gap value If between adjacent weft threads are measured and calculated as follows. That is, first, the glass cloth is cut to a size that allows 100 consecutive gaps to be observed for both the warp and weft threads from three randomly selected locations, and samples are prepared. Next, the sample is observed and measured for the gap interval at a magnification of 150 times using a microscope. Specifically, 100 consecutive gaps on the same straight line in the warp and weft directions of the cloth are observed from the normal direction of the glass cloth plane. This is performed for the three randomly selected locations, and the gap intervals are measured for a total of 300 locations for both the warp and weft threads, and the average value of the gap intervals at these 300 locations is taken as the measured gap value.

In the glass cloth of the present invention, the measured gap Iw between adjacent warp threads is not particularly limited as long as the above ratio (Iw/If) is satisfied, but may be, for example, 70 μm or more and 120 μm or less. When a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, in order to further suppress the occurrence of pinholes and the occurrence of vertical wrinkles, the measured gap Iw between adjacent warp threads is more preferably 80 μm or more and 110 μm or less, and even more preferably 90 μm or more and 110 μm or less.

In the glass cloth of the present invention, the measured gap If between adjacent weft yarns is not particularly limited as long as the above ratio (Iw/If) is satisfied, but may be, for example, 60 μm or more and 100 μm or less. When a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, in order to further suppress the occurrence of pinholes and the occurrence of vertical wrinkles, the measured gap If between adjacent weft yarns is more preferably 60 μm or more and 80 μm or less, and even more preferably 62 μm or more and 80 μm or less.

In the glass cloth of the present invention, the ratio (Iw/Iwd) of the measured gap (Iw) between adjacent warp threads to the designed gap Iwd (μm) between adjacent warp threads is, for example, 1.00 or more and 1.30 or less. When a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, from the viewpoint of further achieving both suppression of pinhole generation and suppression of vertical wrinkle generation, the ratio (Iw/Iwd) is preferably 1.10 or more and 1.18 or less.

In the glass cloth of the present invention, the ratio (If/Ifd) of the measured gap value (If) between adjacent weft yarns to the designed gap value Ifd (μm) between adjacent weft yarns is, for example, 0.70 or more and 1.00 or less. When a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, from the viewpoint of further achieving both suppression of pinhole generation and suppression of vertical wrinkle generation, the ratio (If/Ifd) is preferably 0.80 or more and 1.00 or less.

The glass cloth of the present invention has a basket hole area ratio of 12.0% or more and 20.0% or less, as shown in the following formula (3). By making the basket hole area ratio 12% or more, the glass cloth of the present invention is less likely to have internal distortion, and is less likely to have vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg. In addition, by making the basket hole area 20.0% or less, the glass cloth of the present invention is more likely to suppress the occurrence of pinholes when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg. From the viewpoint of further achieving both the suppression of pinhole occurrence and the suppression of vertical wrinkle occurrence when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, the basket hole area ratio is preferably 12.0% or more and 18.0% or less, and more preferably 12.0% or more and 17.0% or less.

In the glass cloth of the present invention, the basket hole area is not particularly limited as long as it satisfies the basket hole area ratio described above, but from the viewpoint of further achieving both suppression of pinhole generation and suppression of vertical wrinkle generation when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, the basket hole area is, for example, 3000 to 12000 μm ² , more preferably 5000 to 9000 μm ² , and even more preferably 5500 to 8500 μm ^2. The basket hole area is calculated by multiplying the measured gap value Iw (μm) between adjacent warp yarns and the measured gap value If (μm) between adjacent weft yarns described above.

In the glass cloth of the present invention, the basket hole area design value is not particularly limited, but from the viewpoint of further achieving both suppression of pinhole generation and suppression of vertical wrinkle generation when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, for example, 3000 to 12000 μm ² is mentioned, 5000 to 9000 μm ² is more preferable, and 5500 to 9000 μm ² is even more preferable. In the present invention, the basket hole area design value is a value calculated by multiplying the above-mentioned gap design value Iwd (μm) between adjacent warps and the gap design value Ifd (μm) between adjacent wefts.

In the glass cloth of the present invention, the ratio of the basket hole area to the above-mentioned basket hole area design value (basket hole area/basket hole area design value) is not particularly limited, but from the viewpoint of further achieving both the suppression of pinhole occurrence and the suppression of the above-mentioned vertical wrinkle occurrence when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg, the ratio is 0.8 to 1.2, and 0.9 to 1.1 is more preferable.

The thickness of the glass cloth of the present invention is not particularly limited, but may be, for example, 12 μm or less, and preferably 11 μm or less. The lower limit may be, for example, 6 μm or more, preferably 7 μm or more, and more preferably 8 μm or more. Specific examples of the thickness of the glass cloth of the present invention include 6 μm or more and 12 μm or less, preferably 7 μm or more and 11 μm or less, and more preferably 8 μm or more and 11 μm or less.

The weave of the glass cloth is not particularly limited, but examples thereof include plain weave, satin weave, twill weave, diagonal weave, and rib weave. Of these, plain weave is preferred. The glass cloth of the present invention is preferably made into a glass cloth roll product. The length of the glass cloth roll product is, for example, 100 m or more, preferably 100 m or more and 3000 m or less.

The method for producing the glass cloth of the present invention is not particularly limited, as long as it is possible to obtain a glass cloth that satisfies the above-mentioned characteristics. Below, a preferred example of the method for producing the glass cloth of the present invention is described.

A preferred example of the method for producing a glass cloth of the present invention is a method for producing a glass cloth having a mass of 10 g/m2 or ^less , in which a fiber-opening process is performed so that a designed gap value Iwd between adjacent warp yarns shown in the following formula (1) is 95 μm or less, and a designed gap value Ifd between adjacent weft yarns shown in the following formula (2) is 95 μm or less, while a ratio (Iw/If) of an actual measured gap value (Iw) between adjacent warp yarns and an actual measured gap value (If) between adjacent weft yarns is 1.23 to 1.45, and a basket hole area ratio shown in the following formula (3) is 12% to 20%.

As described above, the weave density of the warp and weft threads constituting the glass cloth, and the average diameter and number of the filaments constituting the warp and weft threads are adjusted to set the design gap between adjacent warp threads and the design gap between adjacent weft threads, and a fiber-opening process is performed so that the ratio (Iw/If) of the actual gap between adjacent warp threads (Iw) to the actual gap between adjacent weft threads (If) is 1.23 to 1.45, and the basket hole area ratio is 12% to 20%, thereby achieving both the suppression of pinholes and the suppression of vertical wrinkles when a low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg.

That is, a suitable example of the method for producing a glass cloth of the present invention includes a step of performing a fiber-opening process on a glass cloth having a mass of 10 g/m2 ^or less, a designed gap value Iwd between adjacent warp yarns of 95 μm or less, and a designed gap value Ifd between adjacent weft yarns of 95 μm or less, wherein the fiber-opening process is performed such that the ratio (Iw/If) of the actual gap value (Iw) between adjacent warp yarns to the actual gap value (If) between adjacent weft yarns is 1.23 to 1.45, and the basket hole area ratio is 12% to 20%.

A glass cloth having a mass of 10 g/m2 or ^less , a design gap value Iwd between adjacent warp yarns of 95 μm or less, and a design gap value Ifd between adjacent weft yarns of 95 μm or less can be obtained by adjusting the weaving density of the warp yarns and weft yarns used, and the average diameter and number of filaments constituting the warp yarns and weft yarns, and weaving the warp yarns and weft yarns. Any conventionally known method may be used as a method for weaving a glass cloth, and examples of the method include a method in which the warp yarns are subjected to a warping process and a sizing process, and then the weft yarns are driven in using a jet loom (e.g., an air jet loom, a water jet loom, etc.), a Sulzer loom, a Rapier loom, etc.

The woven glass cloth is subjected to a fiber-opening process so that the ratio (Iw/If) is 1.23 to 1.45 and the basket hole area ratio is 12% to 20%. Examples of the method of fiber-opening include water flow processing that applies water flow pressure; processing that applies high-frequency vibration using water (e.g., degassed water, ion-exchanged water, deionized water, electrolytic cation water, electrolytic anion water, etc.) as a medium; and pressure processing using rolls. In addition, a known method can be used to adjust the degree of opening of the warp and weft threads. Specifically, a method of applying and adjusting tension in the warp direction (length direction of the glass cloth) and weft direction (width direction of the glass cloth) of the glass cloth while performing the fiber-opening process can be used. To apply tension to the glass cloth, for example, a pinch expander, a curved rubber roller, a rotating roller, a Mirabeau roller, or a tenter may be used.

From the viewpoint of ensuring that the glass cloth after the fiber-opening process satisfies the above-mentioned range of ratio (Iw/If) of 1.23 or more and 1.45 or less, and basket hole area ratio of 12% or more and 20% or less, one method of fiber-opening is to carry out water flow processing with the water flow pressure set to 0.9 to 1.6 MPa while adjusting the tension in the warp direction to 18 to 22 N/m and the tension in the weft direction to 5 to 10 N/m.

If substances (such as bundling agents) that impair the adhesion or impregnation of resin when made into prepreg are attached to the glass cloth before or after the fiber-spreading process, it is preferable to remove the substances, for example, by heat cleaning treatment. Furthermore, it is preferable that the glass cloth that has been heat-cleaned is surface-treated with a conventionally known silane coupling agent. Such surface treatment means may be conventionally known means, such as a method of impregnating the glass cloth with a silane coupling agent, a method of applying the agent, or a method of spraying the agent. The above-mentioned heat cleaning treatment and surface treatment may be performed before or after the fiber-spreading process.

2. Prepreg The prepreg of the present invention is characterized by including the glass cloth of the present invention described above. Specifically, the prepreg of the present invention is characterized by including the glass cloth and a matrix resin composition impregnated into the glass cloth.

The mass ratio of the glass cloth in the prepreg of the present invention is not particularly limited. The glass cloth has the above-mentioned characteristics even though it has a low mass of 10.0 g/m ² or less, and therefore even if the mass ratio of the glass cloth in the prepreg is reduced to 40 mass% or less, the occurrence of pinholes and the occurrence of vertical wrinkles in the prepreg can be effectively suppressed. In view of such characteristics, a suitable example of the prepreg of the present invention is one in which the mass ratio of the glass cloth is low. Specifically, the ratio (mass of glass cloth/mass of prepreg) of the mass of the glass cloth (g/m ² ) to the mass of the prepreg (total mass of the glass cloth and the matrix resin composition) (g/m ² ) is preferably 10 to 40 mass%, more preferably 20 to 30 mass%, even more preferably 22 to 30 mass%, and particularly preferably 22 to 25 mass%.

The matrix resin composition includes a thermosetting resin. The thermosetting resin is not particularly limited as long as it is a resin that is cured by heat, but examples thereof include phenolic resin, epoxy resin, non-halogen epoxy resin, cyanate resin, maleimide resin, bismaleimide resin, modified bismaleimide resin, isocyanate resin, benzocyclobutene resin, vinyl resin, bismaleimide triazine resin, phenolic resin, thermosetting polyphenylene ether resin, etc. The thermosetting resin may be used alone or in combination of two or more types.

The matrix resin composition may also contain a curing agent or curing accelerator as needed. The curing agent and curing accelerator may be selected appropriately depending on the type of thermosetting resin used.

Furthermore, it is preferable that the matrix resin composition contains an inorganic filler other than the glass cloth. Examples of inorganic fillers include silicas such as natural silica, fused silica, amorphous silica, and hollow silica; boehmite; molybdenum compounds such as molybdenum oxide and zinc molybdate; glass fillers such as alumina, talc, calcined talc, mica, glass short fibers, and spherical glass (glass fillers using E glass, T glass, UT glass (manufactured by Unitika Glass Fiber Co., Ltd.), S glass, D glass, NE glass, L glass, and LU glass (manufactured by Unitika Glass Fiber Co., Ltd.) as glass materials). These inorganic fillers may be used alone or in combination of two or more.

The average particle diameter (D50) of the inorganic filler is not particularly limited, but from the viewpoint of providing excellent properties when used for thin multilayer printed wiring board applications and further improving dispersibility, it is preferably 10 nm to 5.0 μm, more preferably 100 nm to 2.0 μm, and even more preferably 100 nm to 1.0 μm. Here, the average particle diameter (D50) means the median diameter, which is the diameter at which the larger and smaller sides are equal when the particle size distribution of the measured powder is divided into two. More specifically, the average particle diameter (D50) is the value (median diameter) when the particle size distribution of the powder dispersed in methyl ethyl ketone is measured using a laser diffraction scattering type particle size distribution measuring device, and the volume accumulation from the smallest particles reaches 50% of the total volume.

From the viewpoint of improving moisture resistance, it is preferable that the inorganic filler is surface-treated with a surface treatment agent such as a silane coupling agent. The type of the surface treatment agent is not particularly limited, but examples include aminosilane coupling agents, vinylsilane coupling agents, epoxysilane coupling agents, styrylsilane coupling agents, methacrylsilane coupling agents, and silicone oligomer coupling agents. Among these, aminosilane coupling agents are preferred. The aminosilane coupling agent is a silane having one or two amino groups and one silicon atom, preferably a silane having one amino group and one silicon atom. Commercially available products of silica surface-treated with aminosilane coupling agents include "SC-2050KNK" (average particle size 0.5 μm, manufactured by Admatechs Co., Ltd.).

In the matrix resin composition, the mass ratio of the inorganic filler to the thermosetting resin is not particularly limited, but for example, it is preferable that the inorganic filler is 10 to 400 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of the thermosetting resin in terms of solid content.

The prepreg of the present invention can be manufactured by a known method. Specifically, the method for manufacturing the prepreg of the present invention includes a method in which the glass cloth is impregnated with a resin solution (varnish) containing a matrix resin composition, and then, if necessary, dried to volatilize the volatile components, and the thermosetting resin is cured to a B-stage state (semi-cured state).

The resin solution (varnish) used in the production of the prepreg of the present invention may consist only of the matrix resin composition (non-volatile component), but may also contain a dilution solvent (volatile component). The concentration of the non-volatile component in the resin solution (varnish) may be, for example, 50 to 100% by mass.

There are no particular limitations on the uses of the prepreg of the present invention, but it is suitable as a constituent material for printed wiring boards.

The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

(1) Production of Glass Cloth and Prepreg (Example 1)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.3 μm, an average number of filaments of 35, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 125/25 mm and a weft density of 125/25 mm and a width of 130 cm. Next, the spinning sizing agent and weaving sizing agent attached to the obtained glass cloth were removed by heating at 400° C. for 30 hours. After that, the glass cloth was immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 85 μm, a designed gap value Ifd between adjacent weft yarns of 85 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.23, and a basket hole area ratio of 19.6%.

Next, two types of varnishes for obtaining prepregs were prepared.
<Composition of Varnish A>
Epoxy resin (jER5045B80 manufactured by Mitsubishi Chemical Corporation) 100 parts by mass Hardener (jER Cure DICY7 manufactured by Mitsubishi Chemical Corporation) 2.7 parts by mass (dicyandiamide)
Curing accelerator (2-ethyl-4-methylimidazole, manufactured by Mitsubishi Chemical Corporation) 0.2 parts by weight Dilution solvent (dimethylformamide, manufactured by Kishida Chemical Co., Ltd.) 20 parts by weight Inorganic filler ("SC-2050KNK", average particle size 0.5 μm, spherical silica surface-treated with a silane coupling agent, manufactured by Admatechs Co., Ltd.) 25 parts by weight

<Composition of Varnish B>
Modified bismaleimide resin (HR3070, manufactured by Printec Co., Ltd.) 60 parts by weight Curing accelerator (2-ethyl-4-methylimidazole, manufactured by Mitsubishi Chemical Corporation) 0.3 parts by weight Dilution solvent (methyl ethyl ketone, manufactured by Kishida Chemical Co., Ltd.) 40 parts by weight Inorganic filler ("SC-2050KNK", average particle size 0.5 μm, spherical silica surface-treated with a silane coupling agent, manufactured by Admatechs Co., Ltd.) 25 parts by weight

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time, which indicates the degree of cure of the resin, was about 110 seconds, and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

Example 2
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.1 μm, an average number of filaments of 34, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 135/25 mm and a weft density of 135/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.5 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 80 μm, a designed gap value Ifd between adjacent weft yarns of 80 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.29, and a basket hole area ratio of 18.4%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is, to obtain a prepreg roll product B.

Example 3
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 115/25 mm and a weft density of 115/25 mm and a width of 130 cm. Next, the spinning sizing agent and weaving sizing agent attached to the obtained glass cloth were removed by heating at 400° C. for 30 hours. After that, the glass cloth was immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 88 μm, a designed gap value Ifd between adjacent weft yarns of 88 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.34, and a basket hole area ratio of 16.4%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

Example 4
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 105/25 mm and a weft density of 105/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 94 μm, a designed gap value Ifd between adjacent weft yarns of 94 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.38, and a basket hole area ratio of 14.9%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

Example 5
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven with an air jet loom to obtain a plain weave glass cloth roll having a warp density of 110/25 mm and a weft density of 110/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.2 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 83 μm, a designed gap value Ifd between adjacent weft yarns of 83 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.40, and a basket hole area ratio of 12.5%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

Example 6
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a width of 130 cm and a warp density of 120/25 mm and a weft density of 122/25 mm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 79 μm, a designed gap value Ifd between adjacent weft yarns of 75 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.44, and a basket hole area ratio of 13.8%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

(Example 7)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a width of 130 cm and a warp density of 105/25 mm and a weft density of 110/25 mm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 94 μm, a designed gap value Ifd between adjacent weft yarns of 83 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.44, and a basket hole area ratio of 15.0%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, a glass cloth roll product obtained separately was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 1, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

(Comparative Example 1)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 105/25 mm and a weft density of 105/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 50 N/m in the warp direction (length direction) and a tension of 20 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and then subjected to a water flow processing at a pressure of 1.2 MPa to open the glass cloth, thereby obtaining a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 94 μm, a designed gap value Ifd between adjacent weft yarns of 94 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.02, and a basket hole area ratio of 19.1%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 2)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.1 μm, an average number of filaments of 32, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 148/25 mm and a weft density of 148/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) JNC Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 70 μm, a designed gap value Ifd between adjacent weft yarns of 70 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.13, and a basket hole area ratio of 19.4%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 3)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a width of 130 cm and a warp density of 100/25 mm and a weft density of 100/25 mm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a water flow processing at a pressure of 1.5 MPa while applying a tension of 20 N/m in the weft direction (width direction) while holding both ends of the glass cloth in the weft direction with a tenter, and a glass cloth roll product was obtained by subjecting the glass cloth to a fiber-opening process. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 106 μm, a designed gap value Ifd between adjacent weft yarns of 106 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.22, and a basket hole area ratio of 18.3%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time, which indicates the degree of cure of the resin, was about 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 4)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 125/25 mm and a weft density of 125/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 20 N/m was also applied in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 56 μm, a designed gap value Ifd between adjacent weft yarns of 56 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.25, and a basket hole area ratio of 9.8%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 5)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 110/25 mm and a weft density of 110/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.0 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 98 μm, a designed gap value Ifd between adjacent weft yarns of 98 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.29, and a basket hole area ratio of 18.9%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 6)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 38, and a twist number of 0.5Z. The glass yarn was woven with an air jet loom to obtain a plain weave glass cloth roll having a warp density of 105/25 mm and a weft density of 110/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 0.8 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 101 μm, a designed gap value Ifd between adjacent weft yarns of 90 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.33, and a basket hole area ratio of 21.7%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 7)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 115/25 mm and a weft density of 115/25 mm and a width of 130 cm. Next, the spinning sizing agent and weaving sizing agent attached to the obtained glass cloth were removed by heating at 400° C. for 30 hours. After that, the glass cloth was immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 0.5 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 88 μm, a designed gap value Ifd between adjacent weft yarns of 88 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.34, and a basket hole area ratio of 21.5%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 8)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 105/25 mm and a weft density of 105/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a water flow processing at a pressure of 0.5 MPa while applying a tension of 10 N/m to the weft direction (width direction) of the glass cloth and a tension of 20 N/m to the warp direction (length direction) of the glass cloth while holding both ends of the weft direction of the glass cloth with a tenter, and a glass cloth roll product was obtained. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 94 μm, a designed gap value Ifd between adjacent weft yarns of 94 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.35, and a basket hole area ratio of 21.5%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 9)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 130/25 mm and a weft density of 130/25 mm and a width of 130 cm. Next, the spinning sizing agent and weaving sizing agent attached to the obtained glass cloth were removed by heating at 400° C. for 30 hours. After that, the glass cloth was immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 50 N/m in the warp direction (length direction) and a tension of 25 N/m in the weft direction (width direction) while both ends of the glass cloth in the weft direction were held by tenters, and the glass cloth was subjected to a fiber-opening treatment by water flow processing at a pressure of 1.5 MPa to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 63 μm, a designed gap value Ifd between adjacent weft yarns of 63 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.50, and a basket hole area ratio of 8.6%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 10)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 125/25 mm and a weft density of 125/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a tension of 20 N/m in the warp direction (length direction) and a tension of 10 N/m in the weft direction (width direction) while both ends of the glass cloth were held by tenters, and then subjected to a water flow processing at a pressure of 1.0 MPa to open the glass cloth, thereby obtaining a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 70 μm, a designed gap value Ifd between adjacent weft yarns of 70 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.53, and a basket hole area ratio of 13.3%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 11)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven with an air jet loom to obtain a plain weave glass cloth roll having a warp density of 110/25 mm and a weft density of 110/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a water flow processing at a pressure of 0.5 MPa while applying a tension of 10 N/m to the weft direction (width direction) of the glass cloth and a tension of 20 N/m to the warp direction (length direction) of the glass cloth while holding both ends of the weft direction of the glass cloth with a tenter, and a glass cloth roll product was obtained. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 83 μm, a designed gap value Ifd between adjacent weft yarns of 83 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.58, and a basket hole area ratio of 16.8%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the amount of varnish A applied to the glass cloth coated with varnish A was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the glass cloth was passed through a dryer so that the gel time was about 110 seconds and then wound up as it was, to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the amount of varnish B applied to the glass cloth coated with varnish B was adjusted using a gap roll so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the glass cloth was passed through a dryer so that the gel time was around 110 seconds and then wound up as it was, to obtain a prepreg roll product B.

(Comparative Example 12)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 40, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 105/25 mm and a weft density of 105/25 mm and a width of 130 cm. The spinning bundling agent and weaving bundling agent attached to the obtained glass cloth were then removed by heating at 400° C. for 30 hours. The glass cloth was then immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a water flow processing at a pressure of 1.0 MPa under a tension of 50 N/m in the warp direction (length direction) and no tension in the weft direction (width direction) to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warps of 94 μm, a designed gap value Ifd between adjacent wefts of 94 μm, a ratio of the measured gap value (Iw) between adjacent warps and the measured gap value (If) between adjacent wefts of 1.64, and a basket hole area ratio of 17.6%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(Comparative Example 13)
The glass material for the warp and weft was E-glass, and the glass yarn had an average filament diameter of 3.6 μm, an average number of filaments of 36, and a twist number of 0.5Z. The glass yarn was woven by an air jet loom to obtain a plain weave glass cloth roll having a warp density of 115/25 mm and a weft density of 115/25 mm and a width of 130 cm. Next, the spinning sizing agent and weaving sizing agent attached to the obtained glass cloth were removed by heating at 400° C. for 30 hours. After that, the glass cloth was immersed in an aqueous solution containing 10 g/L of a silane coupling agent (S-350: N-vinylbenzyl-aminoethyl-γ-aminopropyltrimethoxysilane (hydrochloride) Chisso Corporation), squeezed with a padder roll, and then dried and cured at 120° C. for 1 minute. The glass cloth was subjected to a water flow processing at a pressure of 0.5 MPa to open the glass cloth, with the tension of the glass cloth in the warp direction (length direction) set to 50 N/m and no tension applied in the weft direction (width direction), to obtain a glass cloth roll product. The obtained glass cloth had a designed gap value Iwd between adjacent warp yarns of 88 μm, a designed gap value Ifd between adjacent weft yarns of 88 μm, a ratio of the actual gap value (Iw) between adjacent warp yarns and the actual gap value (If) between adjacent weft yarns of 1.70, and a basket hole area ratio of 17.1%.

Next, varnish A and varnish B were prepared as varnishes to obtain prepregs, as in Example 1.

The obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and thoroughly immersed in varnish A to apply varnish A to the glass cloth. Next, the glass cloth coated with varnish A was rolled using a gap roll to adjust the amount of varnish A applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was about 110 seconds. The glass cloth was then passed through a dryer and wound up as is to obtain a prepreg roll product A.

Separately, the obtained glass cloth roll product was continuously unwound in the longitudinal direction (warp direction) and this time thoroughly immersed in varnish B to apply varnish B to the glass cloth. Next, the glass cloth coated with varnish B was rolled using a gap roll to adjust the amount of varnish B applied so that the ratio of the mass (g/ ^m2 ) of the glass cloth to the mass (g/ ^m2 ) of the prepreg satisfied the conditions shown in Table 2, and the drying conditions were adjusted so that the gel time was around 110 seconds. The product was then passed through a dryer and wound up as is to obtain a prepreg roll product B.

(2) Measurement and Evaluation Methods The physical properties of the glass cloth and prepreg roll were measured and evaluated by the following methods.

1. Average filament diameters Dw and Df (μm), average number of filaments Nw and Nf (number)
The measurement was performed using a scanning electron microscope (SEM) (manufactured by JEOL Ltd., trade name JSM-6390A) according to the method described above.

2. Count (tex)
This was carried out in the manner described above.

3. Warp density Ww and weft density Wf (threads/25 mm)
This was carried out in the manner described above.

4. Measured gap value Iw between adjacent warp yarns and measured gap value If between adjacent weft yarns (μm)
This was carried out in the manner described above.

5. Mass (g/ ^m2 ) and thickness (μm) of glass cloth
The mass of the glass cloth was measured and calculated according to the specification of "7.2 Mass of cloth and mat (mass)" in the Japanese Industrial Standard JIS R 3420 2013 (General test method for glass fiber). The thickness of the glass cloth was measured and calculated according to the method A specified in "7.10.1 Thickness of cloth" in the Japanese Industrial Standard JIS R 3420 2013 (General test method for glass fiber).

6. Evaluation of Pinhole Occurrence For each of the obtained prepreg roll products A and B, three prepregs (one set) were cut into a 400 mm x 400 mm square shape from three arbitrary positions aligned in the width direction and parallel to the width direction. A total of 50 sets were taken, and a total of 150 prepregs were prepared. The number of pinholes was visually counted for each of the 150 prepregs, and prepregs with four or less pinholes per sheet were considered to be good products, and the good product rate (%) of the 150 sheets was calculated. Those with a good product rate of 90% or more were considered to be acceptable.

7. Evaluation of Vertical Wrinkles The prepreg roll products A and B obtained were each visually inspected at random over a length of 1000 m to observe the number of vertical wrinkles, and the number of vertical wrinkles per 100 m was calculated and evaluated according to the following criteria. Vertical wrinkles with a length of 10 cm or more were counted.
A: The number of vertical wrinkles was 0.0 per 100 m.
B: The number of vertical wrinkles was 0.1 to 1.0 per 100 m.
C: The number of vertical wrinkles was 1.1 to 5.0 per 100 m.
D: The number of vertical wrinkles was more than 5.1 per 100 m.

(3) Results The physical properties of the examples and comparative examples are shown in Tables 1 and 2.

The glass cloths of Examples 1 to 7 had a mass of 10 g/m2 ^or less, a design gap value Iwd between adjacent warps of 95 μm or less, a design gap value Ifd between adjacent wefts of 95 μm or less, a ratio (Iw/If) of the measured gap value (Iw) between adjacent warps to the measured gap value (If) between adjacent wefts of 1.23 to 1.45, and a basket hole area ratio of 12.0% to 20.0%. In the glass cloths of Examples 1 to 7, when a low-mass glass cloth was impregnated with a resin solution so that the mass ratio of the glass cloth was low to form a prepreg, the occurrence of pinholes and vertical wrinkles was significantly suppressed. In particular, the glass cloths of Examples 3 to 7, which had a basket hole area ratio of 12.0% to 18.0%, had a non-defective product rate of 99% or more in the pinhole occurrence evaluation, and the occurrence of pinholes in the prepreg was significantly suppressed.

On the other hand, the glass cloths of Comparative Examples 1 and 2 had a ratio (Iw/If) of less than 1.23, and therefore were unable to sufficiently suppress the occurrence of pinholes when the low-mass glass cloth was impregnated with a resin solution and cured so that the mass ratio of the glass cloth was low.

In the glass cloth of Comparative Example 3, the design gap value Iwd between adjacent warp threads and the design gap value Ifd between adjacent weft threads exceed 95 μm, the ratio (Iw/If) is less than 1.23, and the basket hole area ratio is 12.0% to 20.0%, so that each filament is present in the glass cloth in a loose state, which causes each filament constituting the weft thread in particular to bend, which makes vertical wrinkles more likely to occur. In addition, the glass cloth of Comparative Example 3 was not able to sufficiently suppress the occurrence of pinholes in the prepreg.

The glass cloth of Comparative Example 4 satisfies the design gap value Iwd between adjacent warps of 95 μm or less, the design gap value Ifd between adjacent wefts of 95 μm or less, and the ratio (Iw/If) of 1.23 to 1.45, but the basket hole area ratio is less than 12.0%, so that internal distortion is likely to occur in the glass cloth, and it is difficult to suppress the occurrence of vertical wrinkles when the low-mass glass cloth is impregnated with a resin solution so that the mass ratio of the glass cloth is low to form a prepreg. In addition, the mass of the glass cloth of Comparative Example 4 exceeds 10 g/ ^m2 .

The glass cloth of Comparative Example 5 has a design gap value Iwd between adjacent warp threads and a design gap value Ifd between adjacent weft threads that exceed 95 μm, and is subjected to a fiber-opening process so that the ratio (Iw/If) of the actual gap value (Iw) between adjacent warp threads and the actual gap value (If) between adjacent weft threads is 1.23 to 1.45, and the basket hole area ratio is 12.0% to 20.0%. As a result, each filament is present in the glass cloth in a loose state, and as a result, the filaments that make up the weft threads in particular are bent, which makes vertical wrinkles more likely to occur.

The glass cloth of Comparative Example 6 had a design gap value Iwd between adjacent warp threads of more than 95 μm, and because it was subjected to a fiber-opening process under relatively mild conditions, the basket hole area ratio exceeded 20.0%. Even if the ratio (Iw/If) was 1.23 or greater and 1.45 or less, it was difficult to prevent the occurrence of pinholes when the low-mass glass cloth was impregnated with a resin solution to make a prepreg with a low mass glass cloth having a low mass ratio.

The glass cloths of Comparative Examples 7 and 8 had a design gap value Iwd between adjacent warp threads of 95 μm or less, a design gap value Ifd between adjacent weft threads of 95 μm or less, and a ratio (Iw/If) of 1.23 to 1.45, but the basket hole area ratio exceeded 20.0%, making it difficult to prevent the occurrence of pinholes when the low-mass glass cloth was impregnated with a resin solution to reduce the mass ratio of the glass cloth to a low level to form a prepreg.

The glass cloth of Comparative Example 9 had a ratio (Iw/If) of more than 1.45 and a basket hole area ratio of less than 12.0%, so that the glass cloth was prone to internal distortion and it was difficult to prevent the occurrence of vertical wrinkles when the low-mass glass cloth was impregnated with a resin solution to reduce the mass ratio of the glass cloth to make a prepreg.

The glass cloths of Comparative Examples 10 to 13 satisfy the following requirements: the design gap value Iwd between adjacent warp threads is 95 μm or less, the design gap value Ifd between adjacent weft threads is 95 μm or less, and the basket hole area ratio is 12.0% or more and 20.0% or less. However, because the ratio (Iw/If) exceeded 1.45, the weft threads were not sufficiently gripped by the warp threads. When the low-mass glass cloth was impregnated with a resin solution and hardened so that the mass ratio of the glass cloth was low, it became difficult to prevent the weft threads from moving slightly in the width direction of the glass cloth. As a result, the occurrence of vertical wrinkles could not be sufficiently suppressed.

Claims (5)

A glass cloth having a mass of 10.0 g/m2 ^{or less} ,
The gap design value Iwd between adjacent warp yarns shown in the following formula (1) is 95 μm or less, and the gap design value Ifd between adjacent weft yarns shown in the following formula (2) is 95 μm or less,
A glass cloth having a ratio (Iw/If) of an actual gap value (Iw) between adjacent warp yarns to an actual gap value (If) between adjacent weft yarns of 1.23 or more and 1.45 or less, and a basket hole area ratio represented by the following formula (3) of 12.0% or more and 20.0% or less.

2. The glass cloth according to claim 1, wherein a designed gap value Iwd between adjacent warp yarns is 70 μm or more and 95 μm or less, and a designed gap value Ifd between adjacent weft yarns is 70 μm or more and 95 μm or less, and a basket hole area ratio of the glass cloth is 12.0% or more and 18.0% or less. A prepreg comprising the glass cloth according to claim 1 or 2. The prepreg according to claim 3, wherein the ratio of the mass of the glass cloth to the mass of the prepreg (mass of glass cloth/mass of prepreg) is 10 to 40 mass%. The method includes a step of performing a fiber-spreading process on a glass cloth having a mass of 10 g/m2 or ^less , a design gap value Iwd between adjacent warp yarns represented by the following formula (1) of 95 μm or less, and a design gap value Ifd between adjacent weft yarns represented by the following formula (2) of 95 μm or less,
The fiber-spreading process is performed so that a ratio (Iw/If) of an actual gap value (Iw) between adjacent warp yarns to an actual gap value (If) between adjacent weft yarns is 1.23 or more and 1.45 or less, and a basket hole area ratio represented by the following formula (3) is 12% or more and 20% or less.
A method for manufacturing glass cloth.