JP4195719B2 - Interleaving paper for glass substrate - Google Patents

Description

  The present invention relates to a glass substrate slip sheet, and more particularly to a slip sheet interposed between glass substrates when a plurality of glass substrates used for glass panels for various image display devices are stacked and packaged.

  Conventionally, glass substrates used for glass panels for various image display devices such as liquid crystal displays, plasma displays, and electroluminescence displays are packaged in a state where a plurality of glass substrates are overlapped with an interleaf. Packed, stored and stored, or transported to a user and processed into a desired size by the user.

When manufacturing glass panels for various image display devices, a method of taking a plurality of glass panels for display from a single glass substrate has been adopted. Substrates are becoming larger in size.
Since the glass substrate has a large size and a thickness of about 0.7 mm and is easily broken, the packaging and packing are strictly performed. Further, when packaging and packing this type of glass substrate, it is necessary to prevent contamination of the glass surface due to external dust and dirt adhering to the glass substrate. As a method of packaging and packaging glass substrates, a plurality of glass substrates are usually placed in parallel in a vertical arrangement with a certain interval between each glass substrate with interleaving interposed between the glass substrates, and packed in a packaging box. Packed. For example, Patent Document 1 discloses the use of a polypropylene sheet or a polyethylene sheet as a slip sheet. Patent Document 2 uses a foamed resin sheet having a cushioning property, and in particular, wraps a plurality of glass substrates in a manner to protrude from the upper edge and / or both left and right edges of the glass substrate. A packaging method is disclosed. Patent Document 3 discloses a resin sheet containing a water-soluble polymer in order to eliminate the problem of contamination of the glass plate surface due to a slip sheet containing sodium tetraborate or sodium tripolyphosphate, which has been used conventionally. Is used for slip sheets.

JP 2003-226354 A JP 2005-239242 A JP 2005-239184 A

  The glass substrate is packaged by stacking a plurality of glass substrates with a glass substrate placed vertically in a packaging box and interposing a paper between the glass substrates. As the interleaf interposed between the glass substrates, a foamed resin sheet (hereinafter sometimes referred to as a foamed sheet) is preferably used from the viewpoint of surface protection. At the time of this packaging, for example, as in Patent Document 2, a plurality of glass substrates are arranged in parallel in a packaging box, and a paper slip is placed between the glass substrates rather than the size of the glass substrates. In order to protect the upper and lower portions or the left and right portions of the glass substrate, it is preferable to arrange them so as to protrude to some extent. The glass substrates packaged and packed in this way are transferred to the processing production line in a state in which the glass substrates are placed vertically in the packing box or in parallel with the horizontal placement, and are interposed between the glass substrates in the processing production process. The slip-sheet is removed from the glass substrate surface by a suction operation.

  The foam sheet used for the interleaving paper interposed between the glass substrates is much thinner than the general packaging foam sheet. In addition, the foam sheet is increased with the increase in size of the glass substrate. A wide range is used. When the foam sheet interposed between the glass substrates as described above is removed from the glass substrate surface during processing and manufacturing operations, if the foam sheet is weak, the protruding portion may sag or wrinkle, and may be sucked. Eliminating work efficiency such as elimination is reduced.

Therefore, when removing the interleaving paper from the glass substrate surface, it is extremely thin, but the foam is strong and does not cause the protrusion of the periphery of the glass substrate to sag or wrinkle without deteriorating the surface protection and buffering properties. There is a need for slip sheets made of sheets.
In order to prevent the slipping of the interleaving paper interposed between the glass substrates and the generation of wrinkles in a state where the glass substrates are arranged in parallel vertically, the elastic modulus of the foamed sheet is mainly bent, so-called It is necessary to strengthen the stiffness of the foam sheet. In order to strengthen the stiffness of the foamed sheet, for example, it is conceivable to reduce the foaming ratio. However, the low foaming is restricted from the viewpoint of surface protection and buffering properties. Although it is conceivable to increase the thickness, since the foam sheet used for the slip sheet is extremely thin as described above, the sheet thickness is also limited.

  An object of the present invention is to provide a slip sheet interposed between glass substrates made of a foam sheet that is thin and lightweight and has a strong stiffness and excellent surface protection.

  In view of the above circumstances, in order to achieve the above-mentioned purpose, a glass substrate interleaf made of a foam sheet is subjected to various studies from various perspectives, with a focus on the base resin and the cell structure and surface state of the foam sheet. As a result, the present invention was achieved.

That is, the present invention
(1) It consists of a polyethylene resin extruded foam sheet having a thickness of 0.3 to 1.5 mm and an apparent density of 18 to 180 g / L. The foam sheet contains a polymer type antistatic agent in 100 parts by weight of the polyethylene resin. The base resin of the foamed sheet has a melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min. The sheet has a number of bubbles in the thickness direction of 4 to 10 / mm, a bubble flatness of 0.1 to 0.6, a surface centerline average roughness of 25 μm or less, and a surface after ultrasonic cleaning using ethanol. A glass substrate interleaving paper having a resistivity of 1 × 10 ⁸ to 1 × 10 ¹⁴ (Ω),

(2) The average thickness of 10 cm intervals calculated based on the thickness (A) [mm] of the foam sheet measured at 1 cm intervals in the width direction of the extruded foam sheet is calculated based on the thickness (A) of the foam sheet. The average thickness (B) [mm] of the entire width is within the range of (average thickness (B) × 0.8) to (average thickness (B) × 1.2), and the foamed sheet has a width. The glass according to (1) above, wherein the difference between the maximum value and the minimum value of the thickness (A) of the foamed sheet (A) of each part divided into 5 equal parts is 0.08 mm or less. Interleaving paper for substrates,

(3) The width of the extruded foam sheet is 1400 to 3200 mm, and the apparent density is 40 to 180 g / L, the glass substrate interleaf as described in (1) or (2) above,

Furthermore, (4) a polyethylene-based resin foam sheet continuous body for cutting into the glass substrate interleaf according to any one of (1) to (3) above,
Is the gist.

The interleaving paper for the glass substrate made of the foamed sheet of the present invention has a small sag and strong stiffness, and the interleaving paper interposed between the glass substrates in a state where the glass substrates are placed vertically or horizontally in parallel. When suction is removed by suction or the like, sagging and wrinkle generation at the periphery of the glass substrate of the slip sheet can be suppressed, and handling is easy and workability is improved.
In addition, the base resin composed of a polymer-type antistatic agent and a polyethylene-based resin forming an extruded foam sheet as a glass substrate interleaf of the present invention is excellent in permanent antistatic properties, and can be applied to a glass substrate. It is possible to suppress dust and dust adhesion, and to prevent the antistatic agent from moving and contaminating the glass substrate surface, making it easy to remove the slip-sheet from the glass substrate by suction operation, etc. Has an effect.

The foam sheet for slip sheets in the present invention is a polyethylene resin extruded foam sheet having a thickness of 0.3 to 1.5 mm and an apparent density of 18 to 180 g / L. If the thickness of the foam sheet is too thick, the load capacity is limited, and there is a risk of damage to the glass substrate when an unbalanced load or partial load is applied to the package. Therefore, the thickness may be an effective thickness as a slip sheet, and may be 0.3 mm or more and less than 1.0 mm, further 0.3 to 0.7 mm, particularly 0.3 mm to 0.5 mm. This is preferable from the viewpoint of the loading efficiency.

On the other hand, if the apparent density of the foamed sheet is too high, the surface protection is poor and the advantage of using the foamed sheet is reduced. On the other hand, if the apparent density of the foamed sheet is too low, it is not possible to obtain a foam sheet having the desired stiffness. From such a viewpoint, the apparent density is preferably 25 to 150 g / L, more preferably 40 to 120 g / L, and particularly preferably 40 to 90 g / L. In addition, the said foam sheet thickness is an average thickness (B) [mm] of the full width of the extrusion foam sheet mentioned later, and the apparent density of the said foam sheet is a value measured as follows. The basis weight (g / m ² ) of the foamed sheet was cut out from a test piece having a length of 25 mm × width 25 mm × foamed sheet, the weight (g) of the test piece was measured, the weight was multiplied by 1600, and the unit was converted. Next, the value obtained by dividing the basis weight (g / m ² ) of the obtained foamed sheet by the average thickness (B) [mm] of the entire width of the extruded foamed sheet to be described later is converted into a unit, and the appearance of the foamed sheet is obtained. The density (g / L).

  Further, the foam sheet is composed of a base resin having a melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min. It is made of a base resin having such melting characteristics, and is made of a specific cell structure or surface state. It becomes a sheet. The base resin is a mixed resin composed of a polymer type antistatic agent and a polyolefin resin, and the melt tension of the base resin and the physical properties of the melt mass flow rate generally constitute the base resin. The melt tension of the polyolefin resin and the physical properties of the melt mass flow rate can be adjusted as a guide. More specifically, using an extruder for obtaining a foamed sheet of a polymer type antistatic agent and a polyolefin resin having a melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min. The physical properties of the base resin can be adjusted based on the melt tension and the physical properties of the melt mass flow rate obtained by melt-kneading. However, the temperature conditions and pass time during extrusion are adjusted to be substantially the same as the conditions during extrusion foaming. According to this method, even when the polyolefin resin is a mixture of a plurality of polyolefin resins, the melt tension of the base resin and the physical properties of the melt mass flow rate can be adjusted.

The foamed sheet made of a base resin having a melt tension of more than 40 cN or a melt mass flow rate of less than 0.2 g / 10 minutes is a molten resin in an extruder or die when extrusion foaming to obtain a foamed sheet. The resulting foam sheet has a large number of wrinkles in the foam film, the stretched foam film is not formed, the foam sheet surface is uneven, and the centerline average roughness is large It is. In addition, fine tears may occur on the surface of the foam sheet. Therefore, the firmness of the foam sheet is also reduced, making it difficult to handle as a glass substrate interleaf. On the other hand, a foamed sheet made of a base resin having a melt tension of less than 3 cN or a melt mass flow rate of more than 10 g / 10 minutes is obtained by foaming obtained by low foamability of the melted resin during extrusion foaming. The sheet is inferior in appearance and lightness, has a small bubble flatness, and a large centerline average roughness. Therefore, the stiffness of the foam sheet is also reduced, making it difficult to handle as a glass substrate slip, and also adversely affecting the thickness accuracy in the sheet width direction, reducing the performance as a glass substrate slip. There is a risk of being.
From the above viewpoint, the melt tension of the base resin is preferably 3 to 25 cN, and more preferably 4 to 20 cN.

  The melt tension is measured by a capillograph 1D manufactured by Toyo Seiki Seisakusho. Specifically, a cylinder having a cylinder diameter of 9.55 mm and a length of 350 mm and an orifice having a nozzle diameter of 2.095 mm and a length of 8.0 mm are used. When the polyolefin resin is a polypropylene resin, the temperature is 230 ° C., and when the polyethylene resin is a polyethylene resin, the temperature is set to 190 ° C. The molten resin is extruded into a string from the orifice at a speed of 10 mm / min, and this string is hung on a tension detection pulley with a diameter of 45 mm. The pulling speed is increased from 0 m / min to 200 m / min in 4 minutes. While the take-up speed is increased at high speed, the string-like object is taken up by the take-up roller to obtain the maximum value of the tension immediately before the string-like object is broken. Here, the reason why the time until the take-up speed reaches 0 m / min to 200 m / min is set to 4 minutes is to suppress the thermal deterioration of the resin and increase the reproducibility of the obtained value. Using a different sample for the above operation, measuring a total of 10 times, removing the three values in order from the largest value of the maximum value obtained in 10 times, and the three values in order from the smallest value of the maximum value, The value obtained by arithmetically averaging the remaining four intermediate maximum values is taken as the melt tension (cN) in the method of the present invention.

However, when the melt tension is measured by the method described above and the string-like material is not cut even when the take-up speed reaches 200 m / min, the melt tension obtained by setting the take-up speed to a constant speed of 200 m / min. The value of (cN) is adopted. Specifically, in the same manner as in the above measurement, the molten resin is extruded into a string from the orifice, and this string is put on a tension detection pulley, and a constant speed increase is made so that the speed reaches 0 m / min to 200 m / min in 4 minutes. Rotate the take-up roller while increasing the take-up speed, and wait until the rotation speed reaches 200 m / min. When the rotational speed reaches 200 m / min, the data acquisition of the melt tension is started, and the data acquisition is finished after 30 seconds. The average value (Tave) of the tension maximum value (Tmax) and the tension minimum value (Tmin) obtained from the tension load curve obtained during this 30 seconds is taken as the melt tension in the method of the present invention. Here, the Tmax is a value obtained by dividing the total value of detected peak (peak) values in the tension load curve by the detected number, and the Tmin is detected in the tension load curve. It is a value obtained by dividing the total value of the dip (valley) values by the detected number.
Of course, when the molten resin is extruded from the orifice into a string shape in the above measurement, bubbles are prevented from entering the string as much as possible. Moreover, when preparing a sample from the base resin of the foam sheet, the foam sheet is heated in a vacuum oven and defoamed, and the heating temperature in the vacuum oven at that time is the same as that of the base resin. The temperature is 230 ° C. when the polyolefin resin is polypropylene resin, and 190 ° C. when the resin is polyethylene resin.

The melt mass flow rate of the base resin is preferably 0.3 to 8 g / 10 minutes, and more preferably 0.4 to 6 g / 10 minutes.
According to JIS K7210-1999, the melt mass flow rate employs condition code M when the polyolefin resin constituting the base resin is a polypropylene resin, and condition code D when it is a polyethylene resin. It is a value measured using a material resin as a sample. When preparing a sample from the base resin of the foamed sheet, the foamed sheet is heated in a vacuum oven and defoamed. In this case, the heating temperature in the vacuum oven is 230 ° C. when the polyolefin resin constituting the base resin is a polypropylene resin, and 190 ° C. when the polyolefin resin is a polyethylene resin.

The polyolefin resin constituting the substrate resin of the foam sheet for interleaf paper of the present invention is a resin having an olefin component unit of 50 mol% or more. Examples of the polyolefin resin include polyethylene resins and polypropylene resins . In the present invention, polyethylene resins are used. The polyolefin resin is preferably used because of its low surface hardness, excellent flexibility, and excellent surface protection of the package, and a polyethylene resin is particularly preferable.

  Examples of the polyethylene-based resin include resins having an ethylene component unit of 50 mol% or more, ethylene homopolymers such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, and ethylene-vinyl acetate copolymer. Polymer, ethylene-vinyl acetate copolymer and high density polyethylene resin mixture, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer Examples thereof include polymers, ethylene-based copolymers such as ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, and mixtures of two or more thereof.

Among these polyethylene resins, those having a main component of a polyethylene resin having a density of 935 g / L or less are preferable. Specifically, it is preferable to use low-density polyethylene, linear low-density polyethylene, or the like, and low-density polyethylene with good foamability is more preferable.
Incidentally, the phrase “the main component” means a polyethylene resin having a density of 935 g / L or less means that the content of the polyethylene resin is 50% by weight or more of the total weight of the foamed sheet. The lower limit of the density of the polyethylene resin is approximately 890 g / L.

  Examples of the polypropylene resin include a propylene polymer or a copolymer with another olefin copolymerizable with propylene. Examples of other olefins copolymerizable with propylene include ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1- Examples thereof include α-olefins having 2 to 10 carbon atoms such as heptene and 3-methyl-1-hexene. The copolymer may be a random copolymer or a block copolymer, and may be not only a binary copolymer but also a ternary copolymer. The other olefin copolymerizable with propylene in the copolymer is preferably contained in a proportion of 25% by weight or less, particularly 15% by weight or less, and the lower limit is 0.3% by weight. Preferably there is. These polypropylene resins can be used alone or in admixture of two or more.

Among the polypropylene resins constituting the base resin of the foamed sheet, a resin suitable for extrusion foaming is preferably a polypropylene resin having a higher melt tension than a general polypropylene resin. Specifically, for example, as described in JP-A-7-53797, (1) polypropylene having a branching index less than 1 and significant strain hardening elongation viscosity, (2) (a) Z average The molecular weight (Mz) is 1.0 × 10 ⁶ or more, or the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is 3.0 or more, (b) and A polypropylene-based resin containing polypropylene having an equilibrium compliance J ₀ of 1.2 × 10 ⁻³ Pa ⁻¹ or more or a shear strain recovery Sr / S per unit stress of 5 m ² / N or more is preferable. In the present invention, (3) a compound containing a radical polymerizable monomer such as styrene and a radical polymerization initiator or an additive is melted at a decomposition temperature of the radical polymerization initiator when the polypropylene resin melts. It may be a polypropylene resin modified by melt kneading, or (4) a modified polypropylene resin obtained by melt kneading a polypropylene resin, an isoprene monomer and a radical polymerization initiator.

  The melting point of the polyolefin resin is approximately 100 to 170 ° C. As a method for measuring the melting point of the polyolefin-based resin, 3 to 5 mg of a polyolefin-based resin constituting the foamed sheet was measured with a differential scanning calorimeter (heat flux differential scanning calorimetry) in a nitrogen gas atmosphere at a heating rate of 10 ° C. The temperature was raised from room temperature (15-30 ° C.) at 220 ° C./min to obtain the first DSC curve, and then immediately lowered to 40 ° C. at a temperature lowering rate of 10 ° C./min. A temperature at the top of the main melting peak (the peak with the largest area) appearing on the second DSC curve obtained when the temperature is raised to 220 ° C. in minutes. When there is another peak having a peak area of 80% or more with respect to the peak area of the peak having the largest area, the sum of the peak temperature of the peak and the peak temperature of the peak having the largest area is added. The average value is adopted as the melting point.

The foam sheet for interleaf of the present invention has a number of bubbles in the thickness direction of 4 to 10 / mm and a bubble flatness of 0.1 to 0.6.
When the number of bubbles in the thickness direction is less than 4 (pieces / mm), the surface protection performance of the foam sheet is insufficient. Further, when the number of bubbles in the thickness direction is reduced, the appearance of the foam sheet is deteriorated. From such a viewpoint, the number of bubbles in the thickness direction is preferably 5 (number / mm) or more. On the other hand, if an attempt is made to make the number of bubbles in the thickness direction exceed 10 (pieces / mm), the bubbles constituting the foam sheet are significantly broken, leading to a decrease in strength of the foam sheet. From such a viewpoint, the number of bubbles in the thickness direction of the foamed sheet is preferably 9 (pieces / mm) or less, and more preferably 7 (pieces / mm) or less.

  In addition, the bubble flatness is in the above range because the bubble shape is not spherical and the bubble diameter is larger in the width direction and / or length direction (extrusion direction) than in the thickness direction, and has a flat shape. Means that When the bubble flatness is too small, the surface protection performance of the foamed sheet is deteriorated and the strength of the stiffness is also lowered, so that it becomes difficult to handle as a glass substrate slip. When the bubble flatness is too large, it is difficult to sufficiently prevent thickness unevenness called a corrugate, and not only the appearance of the foam sheet is deteriorated, but also the thickness accuracy is lowered. From such a viewpoint, the bubble flatness is preferably 0.2 to 0.5, more preferably 0.2 to 0.4. The bubble flatness in the present invention may be at least the bubble flatness in the widthwise vertical section or the extrusion direction vertical section of the foamed sheet is within the above range, and the widthwise vertical section and the extrusion direction vertical section of the foamed sheet. It is preferable that the bubble flatness ratio is in the above range.

  In the present invention, the center line average roughness on the surface of the foamed sheet is 25 μm or less, preferably 20 μm or less. When the center line average roughness is within the above range, there is no wrinkle conspicuous in the bubble film, and good foam is formed, resulting in a foam sheet having excellent physical properties and appearance, and thus excellent surface protection. A strong foam sheet can be obtained. That the centerline average roughness of the surface of the foam sheet is within the above range means that the bubbles constituting the foam sheet have a tight cell wall without contracting.

  In the above foam sheet, the number of bubbles in the thickness direction, the bubble flatness, and the centerline average roughness of the surface are within the above ranges, respectively, and satisfying them at the same time, combined with the configuration of the specific base resin. Thus, it is excellent in surface protection and suitable for use as a slip sheet for a glass substrate that is thin but has strong stiffness.

  Furthermore, the interleaf sheet of the present invention has an average thickness of 10 cm intervals calculated based on the thickness (A) (mm) of the foam sheet measured at 1 cm intervals in the width direction of the extruded foam sheet. The average thickness (B) (mm) of the total width calculated based on A) is within the range of (average thickness (B) × 0.8) to (average thickness (B) × 1.2), And it is preferable that the difference between the maximum value and the minimum value of the thickness (A) of the foam sheet of each part obtained by dividing the foam sheet into 5 equal parts is 0.08 mm or less. There is no specific high-thickness portion in the foamed sheet, and the surface state is excellent.

The thickness of the foam sheet can be measured using an offline thickness measuring machine TOF-4R manufactured by Yamabun Electric Co., Ltd. First, the width of the foam sheet is measured at 1 cm intervals. Based on the thickness (A) of the foam sheet measured at 1 cm intervals, the average thickness at 10 cm intervals, the average thickness (B) of the entire width, and the maximum thickness of each portion obtained by dividing the foam sheet into 5 equal parts. Further, the measurement of the thickness of the foam sheet will be described in detail. The measurement of the average thickness at intervals of 10 cm is performed in the width direction of the 1 cm portion, the 2 cm portion, the 3 cm portion,... 10 cm portion from one end of the foam sheet. The average thickness of the first 10 cm intervals at a total of 10 locations, the second 10 cm at 10 locations in total, 11 cm, 12 cm, 13 cm, ... 20 cm from one end of the foam sheet The average thickness of the interval is obtained, and thereafter, the average thickness of the third, fourth,. Further, when the other end portion of the foam sheet is not a measurement position of the tenth foam sheet thickness (A) for obtaining the average thickness at the last 10 cm interval, that is, there is a measurement part that is less than 10 cm at the end. In this case, the portion is excluded from the average thickness measurement target at intervals of 10 cm. Moreover, let the average thickness (B) of a full width be all the arithmetic mean values of the foam sheet thickness (A) measured at a 1-cm space | interval from one edge part of a foam sheet to the other edge part in the width direction. Further, the difference between the maximum value and the minimum value of the thickness (A) of the foam sheet in each part obtained by dividing the foam sheet into 5 parts in the width direction is obtained by dividing the foam sheet into 5 parts in the width direction. In each part, out of the thickness (A) of the foam sheet obtained by the above method, the maximum value of the data corresponding to each part divided into the five parts is defined as the maximum thickness of each part, and a total of 5 parts is obtained. Focusing on the maximum value and the minimum value among the two maximum thicknesses, the value is obtained as a difference between these values (maximum value−minimum value). In addition, the foam sheet used for said measurement uses what adjusted the state for 24 hours or more on conditions of temperature 23 +/- 5 degreeC and relative humidity 50%.

In the present invention, the number of bubbles in the thickness direction is measured as follows.
In each cross section of the lengthwise vertical section and the widthwise vertical section of the foamed sheet, a microphotograph magnified 30 times was taken at 5 locations selected at random to obtain a total of 10 microphotographs, Draw a straight line in a direction that coincides with the thickness direction of the foam sheet at one randomly selected location on each photograph, and calculate the number of bubbles by counting the number of bubbles that intersect the straight line. By dividing by the length (mm) of the line segment from the front surface to the back surface of the straight foam sheet, the number of bubbles per unit length (number / mm) is obtained. An arithmetic average value of the number of bubbles per unit length (number / mm) obtained at a total of 10 positions of 10 photographs is defined as the number of bubbles in the thickness direction of the foam sheet.

In the present invention, the bubble flatness is measured as follows.
The bubble flatness in the vertical cross section in the width direction is determined by the ratio (T1 / W) between the average cell diameter T1 in the thickness direction and the average cell diameter W in the width direction in the vertical cross section when the cross section to be measured is the cross section in the width direction of the foam sheet. This is a calculated value. The average cell diameter T1 in the thickness direction and the average cell diameter W in the width direction are obtained as follows. The average cell diameter T1 in the thickness direction draws a line segment over the entire thickness of the foam sheet in the thickness direction near the center of the vertical section (width direction vertical section) perpendicular to the extrusion direction of the foam sheet. The number (number) of air bubbles intersecting with each other is measured, and the value obtained by dividing the length of the line segment by the number of air bubbles is adopted as the average cell diameter T1 (mm) in the thickness direction. For the average bubble diameter W in the width direction, a line segment having a length of 30 mm is drawn in the width direction near the center of the vertical cross section in the width direction, and the number of bubbles intersecting this line segment is measured. A value obtained by dividing the length by (number of bubbles (number) -1) is adopted as an average bubble diameter in the width direction: W (mm).

On the other hand, the bubble flatness ratio in the vertical cross section in the extrusion direction is the ratio of the average cell diameter T2 in the thickness direction to the average cell diameter L in the extrusion direction (T2 / L). ). The average cell diameter T2 in the thickness direction and the average cell diameter L in the extrusion direction are determined as follows. The average cell diameter T2 in the thickness direction is obtained by cutting the center part in the width direction of the foam sheet vertically along the extrusion direction, and the total thickness of the foam sheet in the thickness direction near the center part in the cross section of the test piece (vertical section in the extrusion direction). The number of bubbles intersecting this line segment is measured, and the value obtained by dividing the length of the line segment by the number of bubbles is adopted as the average bubble diameter T2 (mm) in the thickness direction. . The average cell diameter in the extrusion direction is determined by drawing a line segment having a length of 30 mm in the extrusion direction in the vicinity of the center of the vertical cross section in the extrusion direction, measuring the number of bubbles (pieces) intersecting the line segment, A value obtained by dividing the size by (number of bubbles (number) -1) is adopted as an average cell diameter in the extrusion direction: L (mm).

The method for adjusting the average cell diameter of the foam sheet can be adjusted by, for example, a method of reducing the average cell diameter by increasing the die pressure or the amount of the cell regulator, although it depends on the polyolefin resin used.
In addition, the method for adjusting the bubble flatness ratios T1 / W and T2 / L is adjusted, for example, as follows although it depends on the polyolefin resin used.
When it is desired to adjust the bubbles in the extrusion direction so as to be flat, it can be adjusted by a method such as decreasing the discharge amount or increasing the take-up speed. On the other hand, when it is desired to adjust the bubbles in the extruding direction so as to become longer in the thickness direction, it can be adjusted by a method such as increasing the discharge amount or decreasing the take-up speed. In addition, when it is desired to adjust the bubbles in the width direction to be flat, it can be adjusted by a method of extruding so that the foam sheet spreads in the width direction. When using an annular die, the discharge port diameter of the annular die and the cylinder It can be adjusted by a method of increasing the blow-up ratio (the diameter of the mandrel as the cylindrical cooling device / the discharge port diameter of the annular die) with the diameter of the mandrel as the cylindrical cooling device. On the other hand, when it is desired to adjust the bubbles in the width direction to be longer in the thickness direction, the foam sheet can be adjusted by a method of extrusion so that the foam sheet does not spread in the width direction. And a method for reducing the blow-up ratio between the diameter of the mandrel that is a cylindrical cooling device.

The centerline average roughness of the foam sheet surface in the present invention is measured under the following conditions in accordance with JIS B0601-1994.
Measuring instrument: Keyence Co., Ltd. high-precision shape measuring system KS-1100 (Laser measuring instrument: LT-9500, shape measuring software: KS-H1A)
The measurement conditions of KS-1100 are as follows.
Reference length: 8000 μm, measurement pitch: 2 μm, moving speed (stage driving speed): 1000 μm / second,
Stage feed: Continuous Also, the LT-9500 settings are as follows.
Scan / width: OFF, average count: 2 times, light intensity setting value: 30, dark out: OFF,
Sensitivity: High sensitivity

The present invention is a glass substrate interleaf made of a polyethylene resin foam sheet, which is used for a plurality of displays from a single large glass substrate when manufacturing glass panels for various image display devices. A method of cutting and taking a glass substrate is adopted, for example, there is a conventional display glass substrate of 370 × 470 mm to 1000 × 1200 mm, and in recent years, with the increase in the size of the display panel, the glass substrate has a large size, For example, a size of 1500 × 1850 mm or larger is also handled. With the increase in size of the glass substrate, the interleaf interposed between the glass substrates is also required to have a wide width, and a wide width of 1400 to 3200 mm is required. On the other hand, the wider the foam sheet and the thinner the thickness, the more difficult it is to achieve the intended purpose of the present invention. It can cope with. Note that the glass substrate slip of the present invention is not limited to a large glass substrate obtained by cutting the glass panel for display or a cut glass substrate, and includes various known glass substrates. For example, glass substrates for liquid crystal displays, glass substrates for plasma display bodies, glass substrates for thermal heads, various glass substrates such as color filters, etc., or TFTs (thin film transistors) manufactured using these glass substrates Glass substrates such as formed glass substrates and finished panels called liquid crystal cells are included.

  The foam sheet for interleaf of the present invention is a continuous belt-like body produced by an extrusion foaming method and wound up in a roll shape. Although it is used by cutting, the foamed sheet of the present invention is stronger than conventional foamed sheets of the same type, so when used for a slip sheet, it is difficult to cause sag or wrinkle. It can sufficiently handle wide widths and is excellent in workability when removing the foam sheet by suction operation from the glass substrate surface.

The interleaf made of the foamed sheet of the present invention has a surface resistivity after ultrasonic cleaning with ethanol of 1 × 10 ⁸ to 1 × 10 ¹⁴ (Ω), preferably 1 × 10 ^{9 to} 5 × 10 ¹³ (Ω). ), More preferably 1 × 10 ⁹ to 1 × 10 ¹³ (Ω), excellent permanent antistatic properties, suppresses adhesion of dust and dust, and does not contaminate the glass substrate surface. Can be kept clean.
In this specification, “ultrasonic cleaning using ethanol” is performed by placing ethanol at 23 ° C. in a beaker and sinking a test piece (length 100 mm × width 100 mm × thickness: thickness of the test piece) cut out from the foamed sheet. After ultrasonic cleaning for 24 hours, the test piece is left to stand for 36 hours in an atmosphere of 30 ° C. and 30% relative humidity, and dried. The surface resistivity after ultrasonic cleaning with ethanol is measured at an applied voltage of 500 V in accordance with JIS K6271-2001 after adjusting the state of the test piece immediately after the ultrasonic cleaning operation as described above.

  In order to impart antistatic properties to the interleaf made of the foamed sheet of the present invention, a polymer type antistatic agent is added to the polyolefin resin constituting the foamed sheet. The addition amount is 5 to 30 parts by weight, preferably 7 to 20 parts by weight, more preferably 8 to 17 parts by weight, and particularly preferably 9 to 15 parts by weight with respect to 100 parts by weight of the polyolefin resin.

The polymer antistatic agent used is made of a resin having a surface resistivity of less than 1 × 10 ¹² (Ω). Specifically, an ionomer resin containing an alkali metal selected from the group consisting of potassium, rubidium and cesium as metal ions, or a hydrophilic resin such as polyether ester amide or polyether as a main component is preferable. In addition, the polymer antistatic agent improves the compatibility with the polyolefin resin constituting the foamed sheet, imparts an excellent antistatic effect, and suppresses the deterioration of physical properties due to the addition of the antistatic agent. In order to obtain it, it is more preferable to use a resin obtained by block copolymerization of a polyolefin resin.

Particularly preferred polymer type antistatic agents include the compositions described in JP-A-3-103466 and JP-A-2001-278985.
The composition described in JP-A-3-103466 includes (I) a thermoplastic resin, (II) polyethylene oxide or a block copolymer containing 50% by weight or more of a polyethylene oxide block component, and (III) the above (II ), And the composition described in JP-A No. 2001-278985 has a block of polyolefin (a) and a volume resistivity of 1 × 10 ⁵ to It is a block copolymer having a number average molecular weight (Mn) of 2000 to 60000 having a structure in which 1 × 10 ¹¹ Ω · cm blocks of hydrophilic resin (b) are alternately and repeatedly bonded. The block (a) and the block (b) have a structure in which they are alternately and repeatedly bonded through at least one bond selected from an ester bond, an amide bond, an ether bond, a urethane bond, and an imide bond. is there.

  The number average molecular weight of the polymer type antistatic agent used in the present invention is preferably 2000 or more, more preferably 2000 to 100,000, still more preferably 5000 to 60000, and particularly preferably 8000 to 40000. It is distinguished from an antistatic agent consisting of The upper limit of the number average molecular weight of the polymer type antistatic agent is approximately 500,000. By setting the number average molecular weight of the polymer type antistatic agent within the above range, the antistatic performance is more stably expressed regardless of the environment such as humidity, and the antistatic agent is transferred to the package. Contamination of the surface of the package is also suppressed.

  The number average molecular weight is determined using high temperature gel permeation chromatography. For example, when the polymer type antistatic agent is composed mainly of polyetheresteramide or polyether, the sample concentration is 3 mg / ml using orthodichlorobenzene as a solvent, and the column temperature is set to 135 ° C. using polystyrene as a reference substance. Is a measured value. In addition, the kind of said solvent and column temperature are suitably changed according to the kind of polymeric antistatic agent.

  Further, the melting point of the polymer antistatic agent is preferably 70 to 270 ° C., more preferably 80 to 230 ° C., and particularly preferably 80 to 200 ° C. from the viewpoint of expression of the antistatic function.

  The melting point of the polymer antistatic agent can be measured by a method based on JIS K7121-1987. That is, pretreatment is performed under the condition (2) for condition adjustment (2) of the test piece in JIS K7121-1987, and the melting peak is obtained by raising the temperature at 10 ° C / min. The temperature at the top of the obtained melting peak is taken as the melting point. When two or more melting peaks appear, the temperature is the temperature at the top of the main melting peak (the peak with the largest area). When there is another peak having a peak area of 80% or more with respect to the peak area of the peak having the largest area, the sum of the peak temperature of the peak and the peak temperature of the peak having the largest area is added. The average value is adopted as the melting point.

  The polymer antistatic agents can be used alone or in combination. The polymer antistatic agent as described above is commercially available, for example, under the trade names of “SD100” manufactured by Mitsui DuPont Polychemical Co., Ltd. and “Pelestat 300” manufactured by Sanyo Chemical Industries, Ltd.

Next, production examples of the extruded foam sheet of the present invention suitable as a glass substrate slip will be described.
The foam sheet of the present invention is prepared by blending a polymer-type antistatic agent, a bubble regulator and the like into a polyolefin resin, melt-kneading in an extruder, press-fitting the foaming agent into the melt-kneaded material, kneading, and then exiting the extruder It is manufactured by extruding and foaming from an annular die attached to the part, passing through a cooling cylinder, and then cutting it into a sheet.

The interleaf paper for glass substrates made of the polyethylene resin extruded foam sheet of the present invention needs to have a firmness when used as an interleaf paper for glass substrates. In order to obtain a good foamed sheet having sufficient stiffness, the structure of the die attached to the tip of the extruder and the polyolefin resin material to be used are important.

Regarding the die structure, it is necessary to have a shape that suppresses the heat generation of the polyolefin resin as much as possible, and it is designed to increase the cross-sectional area of the resin flow path, and by sliding the inner surface of the resin flow path, etc. For example, a well-known low-heat die technique can be employed. In the foam sheet obtained in a state where the heat generation is large, the bubbles constituting the foam sheet are contracted, the foam wall is not stretched, the center line average roughness of the foam sheet surface is increased, and the foam sheet surface Minor tears may occur. Such a foam sheet has low stiffness.

Regarding the polyolefin resin raw material, the base resin has a melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min so that the base resin exhibits the specific melt tension and melt mass flow rate described above. Is preferably used.

When the melt tension of the polyolefin-based resin is less than 3 cN or the melt mass flow rate exceeds 10 g / 10 minutes, the foamability is lowered, and it is difficult to obtain a foam sheet having the desired apparent density. The closed cell ratio is very low (less than 10%), the cell flatness is too small, and the surface centerline average roughness value may increase. Accordingly, the stiffness of the foam sheet is also reduced, the intended purpose cannot be achieved, and handling as a glass substrate slip sheet becomes difficult. In addition, the thickness accuracy in the width direction of the foam sheet is also adversely affected. If the thickness accuracy is poor, there is a risk of problems such as reduced stacking efficiency when stacked and transported. Decreases. On the other hand, when the melt tension of the polyolefin-based resin exceeds 40 cN or the melt mass flow rate is less than 0.2 g / 10 minutes, heat generation in the die increases as described above, and the bubbles constituting the foam sheet are formed. Shrinkage is observed, the cell walls are not stretched, the centerline average roughness of the surface of the foam sheet may be increased, and a fine tear may occur on the surface of the foam sheet. Therefore, the strength of the stiffness is also reduced as described above, making it difficult to handle as a glass substrate slip. The measurement of the melt tension and melt mass flow rate of the polyolefin resin can be performed in the same manner as the measurement method of the melt tension and melt mass flow rate in the base resin described above, except that the sample is a polyolefin resin.

In relation to the melt tension and melt mass flow rate of the polyolefin resin, the foamed sheet in the present invention has a base resin melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min. Therefore, in combination with other structures such as a bubble structure, it is excellent in lightness, thickness accuracy and appearance, and has a sufficient stiffness.

In the present invention, the following points are important for obtaining a sheet having particularly good thickness accuracy in the width direction of the sheet. In a normal foam sheet, the thickness of the foam sheet is adjusted by adjusting the clearance of the die lip portion at the resin outlet and the balance between the extrusion discharge amount of the foamable molten resin and the take-up speed of the foam sheet. However, since the foamed sheet according to the present invention is an extremely thin polyethylene-based resin extruded foamed sheet and is required to have a wide width, the thickness adjustment method such as the conventional method is absolutely desired. Accuracy cannot be obtained.
Therefore, as a sheet thickness adjusting method for obtaining a foam sheet having a desired thickness accuracy in the present invention, temperature management of the die, particularly the die lip portion, is important. Specifically, the thickness accuracy of the obtained foamed sheet can be improved by setting the temperature control in the circumferential direction of the annular die as division control. Conventionally, only one temperature adjustment has been performed in the circumferential direction, but in the present invention, the temperature is adjusted by dividing into four, preferably 8 to 16, in the circumferential direction. However, even if the temperature is adjusted by dividing the die more finely than necessary, the individual control is not sufficiently reflected in the thickness of the foam sheet. Therefore, the temperature adjustment exceeding 16 divisions is sufficient for making the control complicated. An effect of improving the thickness accuracy cannot be obtained.

Examples of the foaming agent include the following physical foaming agents.
Examples of the physical foaming agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, isohexane and cyclohexane, chlorinated hydrocarbons such as methyl chloride and ethyl chloride, 1,1,1 , 2-tetrafluoroethane, fluorinated hydrocarbons such as 1,1-difluoroethane, ethers such as dimethyl ether and methyl ethyl ether, and other organic physical foaming agents such as dimethyl carbonate, methanol, ethanol, oxygen, nitrogen, dioxide Examples include inorganic foaming agents such as carbon, air, and water. These physical foaming agents can be used in combination of two or more. Among these, an organic physical foaming agent is preferable from the viewpoint of compatibility with the polyolefin resin and foaming properties, and among them, those mainly composed of normal butane, isobutane, or a mixture thereof are preferable. Moreover, although it is not a physical foaming agent, decomposable foaming agents, such as azodicarbonamide, can also be used.

  The amount of the foaming agent added is adjusted according to the type of foaming agent and the target apparent density. In particular, in the present invention, the amount of foaming agent injected is important because the stretching effect due to the formation of the bubble film is related to antistatic properties. That is, when a physical foaming agent such as a butane mixture of 30% by weight of isobutane and 70% by weight of normal butane is used as a foaming agent, 4-35 parts by weight, preferably 5-30 parts by weight per 100 parts by weight of the base resin, More preferably, it is 6-25 weight part.

  Moreover, when manufacturing a foam sheet, a bubble regulator is usually added to the polyolefin resin supplied to the extruder. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic foam regulator include borate metal salts such as zinc borate, magnesium borate, borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, sodium bicarbonate, and the like. Moreover, as an organic type | system | group bubble regulator, phosphoric acid-2,2-methylenebis (4,6-tert- butylphenyl) sodium, sodium benzoate, calcium benzoate, aluminum benzoate, sodium stearate, etc. are mentioned. Also, a combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate, or the like can be used as the air bubble regulator. These bubble regulators can be used in combination of two or more.

  The amount of the cell regulator added is mainly adjusted according to the target cell diameter, but is generally 0.2 to 10 parts by weight, preferably 0.5 to 5 parts per 100 parts by weight of the base resin. Part by weight, more preferably 1 to 3 parts by weight.

In addition, various other commonly used additives such as a colorant, an ultraviolet ray inhibitor and an antioxidant can be blended in the production of the polyethylene resin extruded foam sheet as desired.

Hereinafter, the present invention will be described in more detail based on examples. The results of the following examples and comparative examples disclose the significance of the present invention by comparing the both, and the scope of rights of the present invention is not limited by the results.
As the cell regulator used in Examples 1 to 5 and Comparative Examples 1 to 4, a master batch obtained by blending 20% by weight of talc with low density polyethylene was used.

The following were used as polyolefin resin.
PE1: Low density polyethylene “F102” manufactured by Sumitomo Chemical Co., Ltd. (crystallization temperature: 97.8 ° C., density: 922 g / L, MFR: 0.3 g / 10 min)
PE2: Nippon Unicar Co., Ltd. low density polyethylene “NUC8321” (crystallization temperature: 96.9 ° C., density: 922 g / L, MFR: 2.4 g / 10 min)
PE3: Nippon Unicar Co., Ltd. low density polyethylene “NUC8009” (crystallization temperature: 93.0 ° C., density: 916 g / L, MFR: 9.0 g / 10 min)

As the polymer type antistatic agent, those shown below were used.
P1: Sanyo Kasei Kogyo Co., Ltd. polyether-polypropylene block copolymer “Pelestat 300” (melting point 136 ° C., number average molecular weight 14000, density 990 g / L)

Example 1
As an extruder for producing a foam sheet, a single extruder having an annular die attached to the outlet of an extruder having a diameter of 150 mm was used, and a foam sheet was obtained using the base resin and production conditions shown in Table 1.

  Extruder with a diameter of 150 mm, containing 3.0 parts by weight of a bubble regulator masterbatch with respect to 100 parts by weight of a base resin in which a polyethylene resin and a polymeric antistatic agent are blended in the proportions shown in Table To a raw material charging port, and kneaded by heating to obtain a resin melt adjusted to about 200 ° C. A mixed butane of 70% by weight normal butane and 30% by weight isobutane as a physical foaming agent is press-fitted into the resin melt so as to be 14.6 parts by weight with respect to 100 parts by weight of the base resin, and then cooled and foamed. The foamable resin melt was extruded, and the foamable resin melt was extruded with an annular die to form a cylindrical foamed sheet. The extruded tubular foam sheet was cut along the cooled cylinder while being cut to obtain the desired foam sheet.

Examples 2, 3 and Comparative Examples 2-4
A foam sheet was obtained in the same manner as in Example 1 except that a tandem extruder composed of two extruders having a diameter of 115 mm and a diameter of 180 mm was used and the base resin and production conditions shown in Table 1 were changed.

Example 4, Comparative Example 1
A foam sheet was obtained in the same manner as in Example 1 except that a single extruder having a diameter of 115 mm was used as the extruder, and the base resin and production conditions shown in Table 1 were changed.

Example 5
A foamed sheet was obtained in the same manner as in Example 1 except that the base resin shown in Table 1 was changed to the production conditions.

  In Examples 1 to 5 and Comparative Examples 1 to 4, the number of temperature control divisions of the lip part mold, the type of base resin, the composition, the amount of foaming agent, the amount of foam regulator, the foaming temperature, the die pressure, the blow-up ratio, the take-up The speed and discharge amount are summarized in Table 1, and the addition amount of the polymer type antistatic agent, the melt tension of the base resin, the melt mass flow rate, and the thickness, apparent density, width, and thickness direction of the obtained foamed sheet are shown. The number of bubbles, bubble flatness, surface centerline average roughness, and surface resistivity after ethanol cleaning are summarized in Table 2.

  The parts by weight in Table 1 are values relative to 100 parts by weight of the base resin in the table.

  The parts by weight in Table 2 are values relative to 100 parts by weight of the total weight of the polyolefin resin represented by PE1 to PE3 in the base resin.

  The values regarding the thickness of the obtained foamed sheets in Examples 1 to 5 and Comparative Examples 1 to 4 are collectively shown in Table 3.

In addition, the strength of the stiffness in Table 3 was measured as follows.
A test piece having a width of 100 mm, a length of 200 mm, and a thickness of the foamed sheet thickness was cut out from the foamed sheets obtained in Examples and Comparative Examples so that the extrusion direction of the foamed sheet and the length direction of the test piece coincided, The test piece is supported on a horizontal support base so that a 50 mm portion of the length of 200 mm protrudes from the end of the support base, and the amount of sag (mm) at the tip of the test piece is measured. (Mm). Further, a test piece having a width of 100 mm, a length of 200 mm, and a thickness of the foamed sheet thickness was cut out from the foamed sheets obtained in the examples and comparative examples so that the width direction of the foamed sheet and the length direction of the test piece coincided. The test piece is supported on a horizontal support base so that a 50 mm portion of the length of 200 mm protrudes from the end of the support base, and the amount of sag (mm) at the tip of the test piece is measured. The amount of sag was (mm).

It is explanatory drawing which shows an example of the manufacturing method of this invention foam sheet.

Explanation of symbols

11 Extruder 12 Die I Polyolefin resin
II Polymer antistatic agent
III Physical blowing agent
IV Expandable polyolefin resin fat melt V Foam sheet

Claims (4)

It consists of a polyethylene-based resin extruded foam sheet having a thickness of 0.3 to 1.5 mm and an apparent density of 18 to 180 g / L. In the foamed sheet, a polymer-type antistatic agent is 5 per 100 parts by weight of the polyethylene resin. The base resin of the foam sheet has a melt tension of 3 to 40 cN and a melt mass flow rate of 0.2 to 10 g / 10 min. The number of bubbles in the thickness direction is 4 to 10 / mm, the bubble flatness is 0.1 to 0.6, the surface centerline average roughness is 25 μm or less, and the surface resistivity after ultrasonic cleaning using ethanol is The interleaving paper for a glass substrate, which is 1 × 10 ⁸ to 1 × 10 ¹⁴ (Ω).   The average width of 10 cm intervals calculated based on the thickness (A) [mm] of the foam sheet measured at 1 cm intervals in the width direction of the extruded foam sheet is calculated based on the thickness (A) of the foam sheet. The average thickness (B) [mm] is within the range of (average thickness (B) × 0.8) to (average thickness (B) × 1.2), and the foamed sheet is 5 in the width direction. The gap between glass substrates according to claim 1, wherein the difference between the maximum value and the minimum value in the maximum thickness of the thickness (A) of the foamed sheet of each part is equal to or less than 0.08 mm. paper.   3. The glass substrate interleaving sheet according to claim 1, wherein the extruded foam sheet has a width of 1400 to 3200 mm and an apparent density of 40 to 180 g / L. The polyethylene-type resin foam sheet strip | belt continuous body for cutting and setting it as the interleaving paper for glass substrates in any one of Claims 1-3.

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