JP5732333B2 - Polyethylene resin foam sheet - Google Patents

Description

  The present invention relates to a polyethylene-based resin foam sheet, and more particularly, to a polyethylene-based resin foam sheet having antistatic properties, which is used for packaging materials such as display glass and slip sheets.

Polyethylene resin foam sheets are flexible and have excellent cushioning properties, and are therefore used for packaging materials for electronic parts and home appliances, glass slip sheets, and the like.
For example, a plurality of glass substrates for liquid crystal displays and plasma displays are laminated with a polyethylene resin foam sheet interposed therebetween and supplied from a glass manufacturer to a display manufacturer.
In such an application, the polyethylene-based resin foam sheet is normally used in a state of a sheet roll wound in a roll shape, and is fed out from the sheet roll in accordance with the overlapping of the glass substrates and is predetermined. It is cut into dimensions, and the cut piece is sandwiched between glass substrates and used as a slip sheet.

  By the way, in general, polyethylene-based resin foam sheets are relatively easily charged with static electricity as they are, so that the anti-static charge to the polyethylene-based resin foam sheets is to prevent dust from adhering to the sheet surface due to static electricity. An agent is included.

  As this type of antistatic agent, there are known so-called low-molecular types used as surfactants and so-called high-molecular types such as ion conductive polymers. The inhibitor has a relatively high antistatic effect and has the effect of producing an antistatic effect early after the production of the polyethylene resin foam sheet, while bleeding out to the surface of the polyethylene resin foam sheet, There is a possibility that the glass substrate is contaminated instead of adhering to the sheet conveyance path or the glass surface.

On the other hand, the polymer type antistatic agent has a low migration property and is unlikely to contaminate the glass surface. However, if it is not compounded in a relatively large amount, it will not only exhibit a sufficient antistatic effect, but it is sufficiently expensive. If the antistatic effect is to be exhibited, the cost of the polyethylene resin foam sheet may be increased to a level that is difficult to easily use as a consumable material such as a slip sheet or a packing material.
For this reason, for example, as shown in Patent Document 1 below, the use of a surfactant that functions as a low molecular weight antistatic agent in combination with a high molecular weight antistatic agent has been conventionally studied.

  However, as described above, the surfactant used as a low molecular weight antistatic agent is easily transferred to the counterpart material in contact with the polyethylene resin foam sheet. Even if the amount of the agent used is reduced, it does not shift to the state at all. For example, it is used for applications that touch products that do not like slight contamination such as glass substrates, semiconductor elements, and circuit boards of liquid crystal displays and plasma displays. It is difficult to utilize for a polyethylene resin foam sheet.

  In addition, in the display manufacturer, in order to remove the deposits before using the glass substrate, a process of washing the glass substrate with water is performed, and the surfactant has a certain degree of water solubility. In addition, although it can be removed in this cleaning step, it may remain on the substrate surface if it is in an excessive amount.

JP 2009-62442 A

  On the other hand, it is conceivable to reduce the content of the surfactant in the polyethylene resin foam sheet, but the surfactant does not function immediately after the production of the polyethylene resin foam sheet, and takes some time. In order to demonstrate the antistatic effect by bleeding out to the surface over time, if the content is reduced, it will be used as a slip sheet while the antistatic effect is not manifested, and dust etc. will adhere due to static electricity There is a risk of being used.

In addition, the surfactant is effective in preventing other components contained in the polyethylene-based resin foam sheet from adhering to the counterpart material while easily adhering to the counterpart material in contact with it, so that the surfactant bleeds out. If it is used for a slip sheet of a glass substrate in a state where it is not, there is a possibility that a low molecular weight component originally contained in the polyethylene resin, a decomposition residue during extrusion or the like may adhere to the surface of the glass substrate.
Since such components are usually hydrophobic, they are difficult to remove even by washing, but rather have a greater problem than the adhesion of surfactants.

  As described above, the conventional polyethylene-based resin foam sheet is not sufficiently suppressed to contaminate the counterpart material with which it is in contact, and is suitable as a cushioning material or packaging material for products with high demands on cleanliness. Have the problem of not.

  This invention provides the polyethylene-type resin foam sheet which can suppress the contamination of the partner material which touches, and makes it a subject to provide the polyethylene-type resin foam sheet suitable for the slip sheet etc. of the glass substrate for a display, for example.

  In order to solve the above-mentioned problems, the present inventor is excellent in a polyethylene resin foam sheet in such an amount that it can be easily washed and removed even if there is no risk of shifting to the counterpart material or even if it has shifted. As a result of diligent investigations on surfactants that can exert antistatic effects, specific surfactants exhibit early antistatic effects compared to others, and exhibit excellent effects in small amounts, The present invention has been completed by finding that it can be easily washed and removed with water or the like even if it adheres to the counterpart material.

  That is, the present invention relating to a polyethylene resin foam sheet is a polyethylene resin foam sheet comprising a polymer type antistatic agent and a surfactant together with a polyethylene resin, wherein 100 parts by mass of the polyethylene resin On the other hand, the polymer type antistatic agent is contained in a proportion of 4 to 17 parts by mass, and the surfactant contains 0.3 to 1.2 parts by mass of a fatty acid alkanolamide surfactant. It is characterized by being.

  The fatty acid alkanolamide surfactant is preferably lauric acid diethanolamide, and the polymer antistatic agent is preferably a polyether-polyolefin block copolymer.

The polymer antistatic agent to be used preferably has a crystallization temperature of less than 90 ° C. and a melt mass flow rate of 10 g / 10 min or more and 40 g / 10 min or less, and the polyethylene resin has a density of 925 kg. / M ³ or more and 935 kg / m ³ or less, and the melt mass flow rate is preferably 2 g / 10 min or more and 6 g / 10 min or less.

  Such a polyethylene resin foam sheet can be suitably used as a slip sheet for a glass substrate for display.

  According to the present invention, the polyethylene resin foam sheet can be made excellent in the antistatic effect, and the surfactant can be prevented from migrating from the polyethylene resin foam sheet to the counterpart material.

About the polyethylene-type resin foam sheet of this invention, the embodiment is described, illustrating the case where it utilizes for the slip sheet of the glass substrate for a display.
The polyethylene-based resin foam sheet (hereinafter, also simply referred to as “foam sheet”) is formed by extruding and foaming a polyethylene-based resin composition containing a polymer-type antistatic agent and a surfactant together with a polyethylene-based resin. It is formed.

The polyethylene resin constituting the foamed sheet of the present embodiment has a melt mass flow rate (hereinafter also referred to as “MFR”) of 2 to 6 g / 10 min, and a resin density of 925 kg / m ³ or more and 935 kg / m ³ or less. The low density polyethylene resin is preferable.
The low density polyethylene resin of MFR as described above is preferable, if the MFR is less than 2 g / 10 min, a problem occurs in the kneadability with the polymer type antistatic agent in the extruder and the antistatic performance is lowered. This is because it may be difficult to obtain a good foamed sheet due to foam breakage during extrusion foaming.
On the other hand, if the MFR exceeds 6 g / 10 min, the melt tension becomes too low, and it becomes difficult to obtain a low-density foam, or a scum-like deposit tends to occur at the tip of the die.

  In the present specification, the melt mass flow rate of JIS K 7210: 1999 “Plastic-thermoplastic melt mass flow” is also used for the MFR of the polymer type antistatic agent described below, unless otherwise specified. The value measured by the method described in Method B (however, the test temperature is 190 ° C. and the load is 21.18 N) is intended. “Rate (MFR)” and “Melt Volume Flow Rate (MVR) Test Method”

The polyethylene-based resin constituting the foamed sheet of the present embodiment preferably has the above-described density. When the resin density is less than 925 kg / m ³ , the foaming agent from the foamed sheet after extrusion is used. The resin itself has a low rigidity and the rigidity of the resin itself is small, and the shrinkage may not be suppressed. On the other hand, if the resin density exceeds 935 kg / m ³ , the rigidity of the resin itself is too large and the foam sheet becomes a packaging material. This is because there is a risk of losing cushioning properties.

As the polymer antistatic agent constituting the foamed sheet together with the polyethylene resin, a polymer antistatic agent having a crystallization temperature of less than 90 ° C. and an MFR of 10 to 40 g / 10 min is preferable.
It is preferable that the crystallization temperature of the polymer antistatic agent is less than 90 ° C. If the crystallization temperature is 90 ° C. or more, crystallization progresses in the extruder, resulting in poor dispersion. This is because when the film is stretched, the polymer antistatic agent is not deformed and becomes a lump, and the distance between dispersed particles of the antistatic agent is widened so that it is difficult to develop an antistatic function commensurate with the amount added.

In addition, it is preferable that the MFR of the polymer antistatic agent is within the above-mentioned range. If the MFR of the polymer antistatic agent is less than 10 g / 10 min, the polyethylene resin in the extruder or in the die is used. This is because the dispersion is uneven and the surface resistivity is excellent, but the static electricity decay rate tends to deteriorate.
In addition, when the MFR exceeds 40 g / 10 min, the dispersibility with the polyethylene resin is lowered and the melt tension of the polyethylene resin composition is lowered, so that a low-density foam sheet cannot be obtained or communicated. Such coarse bubbles may be generated.

In the present specification, the crystallization temperature is intended to be a value measured according to the method described in JIS K7122 “Method for measuring transition temperature of plastic” unless otherwise specified.
Specifically, using a differential scanning calorimeter (for example, “DSC 6220” manufactured by S.I. Nano Technology Co., Ltd.), about 6.5 mg of a sample is filled in a measurement container, and the nitrogen gas flow rate is 30 ml / min. The temperature can be raised and cooled between 30 ° C. and 200 ° C. at a heating / cooling rate of 10 ° C./min, and the exothermic peak temperature during cooling can be measured as the crystallization temperature.
In addition, when two or more exothermic peaks appear, the temperature of the peak of the highest temperature peak among the area peaks having 5% or more of the total peak area is defined as the crystallization temperature.

  Examples of the polymer antistatic agent include polyethylene oxide, polypropylene oxide, polyethylene glycol, polyester amide, polyether ester amide, ionomers such as ethylene-methacrylic acid copolymer, and quaternary such as polyethylene glycol methacrylate copolymer. Examples thereof include ammonium salts and copolymers of olefinic blocks and hydrophilic blocks described in JP-A No. 2001-278985.

Among these, a copolymer of an olefin block and a hydrophilic block is preferable, and a polyether-polyolefin block copolymer (a block copolymer of a polyether block and a polyolefin block) is charged with the above-described polymer type charging. It is preferable to make it contain in a polyethylene-type resin composition as an inhibitor.
The polymer type antistatic agent may be a mixture of two or more substances. For the purpose of further improving the antistatic performance, the block copolymer is mixed with polyamide, or a polyamide-based antistatic agent. The block may be further copolymerized.

As the polymer type antistatic agent, those having as a main component a copolymer of an olefin block and a polyether block containing 70 mol% or more of propylene are more preferable.
Here, the “main component” means that the proportion of the polyether-polyolefin block copolymer in all the polymer antistatic agents contained is 50% by mass or more.
In addition, it is preferable that the ratio for which the said polyether-polyolefin block copolymer accounts to a polymer type antistatic agent shall be 70 mass% or more, and it is more preferable to set it as 80 mass% or more.

In the polyethylene resin composition constituting the polyethylene resin foam sheet of the present embodiment, the blending ratio of the polyethylene resin and the polymer-type antistatic agent is as described above with respect to 100 parts by mass of the polyethylene resin. It is important that the molecular antistatic agent has a ratio of 4 to 17 parts by mass.
It is important that the blending ratio of the polymer type antistatic agent in the polyethylene resin composition is within the above range. If it is less than the lower limit of the above range, the antistatic performance of the foamed sheet may be insufficient, and foaming is caused by static electricity. This is because there is a possibility of adhering dust to the sheet. If the content exceeds the upper limit of the above range, it is difficult to expect further improvement in antistatic performance, which not only increases costs but also polyethylene. This is because the foamability of the resin-based resin composition may be reduced and a low-density foam sheet may not be obtained.

The surfactant contained in the polyethylene resin foam sheet together with the polymer antistatic agent functions as an antistatic agent as a so-called low molecular antistatic agent. In the present embodiment, the surfactant is used as the surfactant. It is important to employ a fatty acid alkanolamide surfactant.
The fatty acid alkanolamide-based surfactant is formed from a fatty acid and an alkanolamine. For example, a fatty acid alkanolamide-based surfactant obtained by bonding a saturated or unsaturated fatty acid group having 8 to 20 carbon atoms to the nitrogen atom of alkanolamine. Can be mentioned.
Examples of the alkanolamine include monoethanolamine, diethanolamine, isopropanolamine, diisopropanolamine, ethylethanolamine, butylethanolamine, isopropylethanolamine and the like.
Especially, what consists of capric acid (C10), lauric acid (C12), myristic acid (C14), palmitic acid (C16), and either a diethanolamine or monoethanolamine is preferable, and a lauric acid diethanolamide is especially preferable.

Fatty acid alkanolamide surfactants such as lauric acid diethanolamide can quickly impart an antistatic effect to a polyethylene resin composition in a small amount due to a synergistic effect with the polymer type antistatic agent. In addition, by including the fatty acid alkanolamide-based surfactant, the foamed sheet can be made suitable as a buffer material (interleaf) for a member that dislikes contamination such as a glass substrate for display.
About the blending ratio of the polyethylene resin and the fatty acid alkanolamide surfactant in the polyethylene resin composition constituting the polyethylene resin foam sheet of the present embodiment, the fatty acid alkanol is based on 100 parts by mass of the polyethylene resin. It is important to contain 0.3 to 1.2 parts by mass of an amide surfactant.

  It is important that the blending ratio of the fatty acid alkanolamide surfactant in the polyethylene resin composition is within the above range. If the blending ratio is less than the lower limit of the above range, the antistatic performance of the foam sheet may be insufficient. This is because there is a risk of adhering dust to the foamed sheet. If the content exceeds the upper limit of the above range, no further improvement in antistatic performance can be expected and the surfactant is excessively applied to the glass substrate for display. It is because there exists a possibility that a novel adhesion may arise.

This fatty acid alkanolamide-based surfactant, particularly lauric acid diethanolamide, is also preferable in that it can be easily removed from the glass substrate by washing with water.
By using such a surfactant in combination with a polymer-type antistatic agent, for example, if it is a foam sheet that is used as a slip sheet of a general glass substrate, depending on the blending amount thereof, etc. The surface resistivity can be reduced to less than 10 13 (10 ¹² (Ω / □) order) when 24 hours have passed since the foam sheet was produced.

  In other words, this fatty acid alkanolamide-based surfactant, unlike conventional surfactants, exhibits an antistatic effect quickly, and thus can prevent adhesion of dust and the like due to static electricity without blending in large quantities. Even if the contact time with the glass substrate takes a long time, the amount of migration can be reduced compared to the conventional one, and even if there is a migration, it can be easily removed by washing with alkaline washing water. Therefore, it can be said that it is particularly suitable for a slip sheet of a glass substrate that is not suitable for contamination.

Such a foam sheet can be manufactured by adding a component for imparting foamability to the polyethylene resin composition and selecting a general production method by extrusion foaming.
Examples of the foaming component include a foaming agent and an air conditioner. In addition to these, addition of a heat stabilizer, an ultraviolet absorber, an antioxidant, a colorant, etc., if necessary. An agent can also be added to the polyethylene resin composition.

As the foaming agent, it is preferable to use a foaming agent containing isobutane at 50 mol% or more, preferably 60 mol% or more, particularly preferably 70 mol% or more.
It is preferable to contain isobutane in such a ratio. For the foaming agent having an isobutane amount of less than 50 mol%, the polyethylene resin was selected from those having a resin density of 925 to 935 kg / m ³ suitable for foaming. However, other foaming agents are likely to permeate through the cell membrane, and the shrinkage may be excessively increased.

As the foaming agent component other than isobutane, a halogen-free foaming agent is preferred.
Specific compounds include hydrocarbons such as normal butane, propane, pentane, hexane, cyclobutane and cyclopentane, and inorganic gases such as carbon dioxide and nitrogen.
However, if the isobutane ratio is increased as in the present invention, the open cell ratio of the foam may be increased. Therefore, when a foaming agent component other than isobutane is contained, polyethylene-based rather than isobutane, such as normal butane. It is preferable to contain 2 mol% or more of a foaming agent having excellent compatibility with the resin.

Accordingly, the blowing agent is preferably mixed butane having an isobutane content of 50 mol% or more and a normal butane content of 2 mol% or more.
That is, the blowing agent is preferably a mixed butane of 50 to 98 mol% of isobutane and 2 to 50 mol% of normal butane, more preferably a mixed butane of 60 to 97 mol% of isobutane and 3 to 40 mol% of normal butane, A mixed butane of 70 to 96 mol% and normal butane 4 to 30 mol% is particularly preferred.

  In this way, when isobutane / normal butane mixed butane is used, isobutane suppresses rapid dissipation of the foaming agent in the extrusion foaming process, while normal butane having excellent compatibility with the polyethylene resin is derived from isobutane. Since the increase in the open cell ratio of the foam is suppressed, it is possible to obtain a foam sheet that is less contracted and has a low open cell ratio and excellent cushioning properties.

The amount of the foaming agent depends on the desired degree of foaming, but the density is 925 to 935 kg / m ³ , the MFR is 2 to 6 g / 10 min, the crystallization temperature is less than 90 ° C., and the MFR is 10 to 10. The ratio of the foaming agent to the mixture with the polymer antistatic agent of 40 g / 10 min is usually 5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the mixture.
Usually, such a range is set so that sufficient foaming is difficult to obtain when the addition ratio of the foaming agent is less than 5 parts by mass. It is because there exists a possibility that it may not be obtained.

In addition, as the bubble adjusting agent for adjusting bubbles formed by the foaming agent, polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate (sodium bicarbonate) used as inorganic powders such as talc and silica, or as a decomposable foaming agent And azodicarboxylic acid amide.
These may be used alone or in combination. The addition amount is preferably 0.5 parts by mass or less per 100 parts by mass of the polyethylene resin.

The density (apparent density) of the foamed sheet is not particularly limited, and may be a density that can provide cushioning properties that are generally required as a slip sheet for a glass substrate, and is usually 70 kg / m ^3. Less than, preferably 10 kg / m ³ or more and 60 kg / m ³ or less.
The reason why such a density is selected is that when the density is 70 kg / m ³ or more, there is a possibility that the foam sheet has insufficient flexibility and the buffering property may be low. This is because the foam sheet may not have sufficient strength, and as a result, the cushioning property may be low.
Furthermore, if the thickness of the cell membrane is too thin, the shrinkage increases, and as a result, when a long foam sheet is produced, it is difficult to wind it as a roll.
Accordingly, the density is preferably 10 kg / m ³ or more, and more preferably 15 kg / m ³ or more.

  As an example of the method for producing a foamed sheet according to the present embodiment, an extrusion foaming process in which the polyethylene resin composition is extruded and foamed to produce an extruded foamed sheet, and the extruded sheet is wound up by a winder. Examples include a winding step for producing a raw fabric roll, an aging step for aging the wound raw fabric roll for a certain period, and a decorative winding step for rewinding the raw fabric roll for a product roll with a rewinder.

(Extrusion foaming process)
Specifically, a polyethylene resin having a resin density of 925 to 935 kg / m ³ and an MFR of 2 to 6 g / 10 min, a polymer type antistatic having a crystallization temperature of less than 90 ° C. and an MFR of 10 to 40 g / 10 min. 4 to 17 parts by mass of the polymer type antistatic agent with respect to 100 parts by mass of the polyethylene resin, and the fatty acid alkanolamide-based interface. Blended so that the activator is 0.3-1.2 parts by mass, and further blended a masterbatch containing a bubble regulator, and supplies this blend to an extruder with a circular die connected to the tip. Then melt knead.
At this time, once the kneaded product is heated to a temperature suitable for extrusion to improve the dispersibility of the blowing agent, isobutane is added in an amount of 50 mol% from the blowing agent inlet provided in the middle of the extruder. Add the foaming agent contained above, further melt-knead, then lower the temperature and extrude in a foamed state from the circular opening of the circular die to form a cylindrical foam, the opening provided in front of the circular die The foam is slidably brought into contact with the outer peripheral surface of the cooling mandrel having a larger diameter and cooled while being stretched in the circumferential direction, and the foam that has been cooled is cut along the extrusion direction to open a flat sheet. Let
A continuous belt-like foam sheet can be produced by continuously carrying out the extrusion foaming.

In this method for producing a foam sheet, as described above, a polyethylene resin composition containing a polyethylene resin having an MFR of 2 to 6 g / 10 min and a polymer type antistatic agent having an MFR of 10 to 40 g / 10 min together with a fatty acid alkanolamide. In the extrusion foaming process, the resin temperature can be lowered to a temperature suitable for foaming even in the extrusion foaming process by using a polyethylene resin having a predetermined range of MFR and a polymer antistatic agent. And the amount of extrusion can be increased.
Therefore, foam sheet production can be carried out in a condition with excellent productivity.

(Winding process)
In this step of winding the long foamed sheet obtained in the extrusion foaming step into a roll with a winder, it is preferable to wind it loosely with as little tension as possible during winding.
This is because by loosely winding it with a small tension, it is possible to secure a space where the contracted thickness recovers between the sheets, and when the contracted foam sheet recovers, it tends to be close to the original thickness. is there.
Moreover, the thickness variation in a roll can be decreased more by this.
That is, when the tension is high, the soft, highly foamed polyethylene-based resin foam sheet is not only stretched and stretched, but is wound in a state where the thickness is thinner than the actual thickness, and is also crushed in the thickness direction. The product thickness may be reduced.
On the other hand, if the tension is too small, it becomes difficult to wind in a roll shape. Specifically, the average tension is preferably 4.9 to 29.4 N per 1 m of the sheet width.

Moreover, it is preferable to perform winding by a winder as short as possible after an extrusion foaming process.
By shortening the winding time until winding up after extrusion foaming, the amount of foaming agent dissipated from the foamed sheet to be wound can be reduced, and the thickness reduction of the foamed sheet at the winding stage can be suppressed.
Thereby, the sheet | seat thickness difference of the roll core part and outer peripheral part of a roll can be made small.
Specifically, it is preferable that the time until winding is within 15 minutes, and by setting the time until winding is within 15 minutes, it is possible to wind in a state with less shrinkage.

Further, the diameter of the winding core of the winder is preferably larger, and specifically, the diameter is preferably 140 mm or more.
When the diameter is large, it is easy to control the tension and the whole can be wound with substantially the same tension, so that a thickness difference is unlikely to occur.
On the other hand, if the diameter of the winding core is less than 140 mm, it is difficult to wind unless the tension at the beginning of winding is increased, and the thickness in the vicinity of the winding core portion tends to be thin.
However, on the contrary, if the winding core diameter becomes too large, a large winding facility is required, and therefore the maximum diameter of the winding core is appropriately restricted.

As described above, in the foam sheet manufacturing method, in the extrusion foaming step, the discharge rate can be increased to increase the extrusion amount, so that the winding speed can be increased in the winding step. The winding time can also be shortened.
Accordingly, the roll winding time can be shortened, and the amount of the foaming agent can be reduced. As a result, the shrinkage of the foamed sheet can be reduced.

(Aging process)
In the production of the foamed sheet, the raw roll obtained by winding the sheet after the extrusion foaming in the winding process is left to age for a certain period in a constant atmosphere state. Diversify and remove the foaming agent.
In the case of a foam sheet to which a shrinkage inhibitor is added, it is usually necessary to age for about 10 days.
However, in the method for producing a foam sheet in the present embodiment, when no shrinkage inhibitor is used, the foaming agent is rapidly dissipated and air enters in the aging process, and the aging period can be shortened, approximately 3 to 4 days. Is enough.
In the aging process, in order to make it easier to recover the thickness uniformly in the wound foam sheet, the roll core is left in a suspended state in which the core is level and suspended in the air. Preferably it is done.
Further, when the aging temperature is low, it takes a long time for dimensional recovery or replacement of the foaming agent with air, and when it is high, the foamed sheet may be thermally shrunk, so 15 to 55 ° C is preferable, and 20 to 50 ° C is preferable. More preferred.

(Make-up process)
This decorative winding step is a method for producing a product roll having the same length as the original roll by winding the foamed sheet from the original roll after aging and winding the drawn foam sheet on another winding core, or , A method of making a product roll shorter than the original roll by cutting in the middle, a product roll in which a plurality of foam sheets are connected by joining the tip of another original roll to the end of one original roll It can be implemented by adopting a manufacturing method or the like.
In the foam sheet according to the present embodiment, since the antistatic effect is quickly manifested, it is possible to suppress the generation of static electricity when the foam sheet is unwound from the raw roll in the decorative winding process, and clean without dust and the like being attached. A product roll obtained by winding a foamed sheet for a predetermined length can be produced.

Thus, in this embodiment, a particularly excellent foam sheet can be obtained as a slip sheet for a glass substrate.
In addition, the use of the foamed sheet of the present invention is not limited to the slip sheet of the glass substrate, and can be used for various uses.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
Sanyo Chemical Co., Ltd. with respect to 100 parts by mass of low density polyethylene resin (LDPE) (trade name: “LF580”, density: 928 kg / m ³ , MFR = 4.0 g / 10 min) manufactured by Nippon Polyethylene Co., Ltd. as a polyethylene resin Company-made polymer antistatic agent (polyether-polypropylene block copolymer) (trade name: “Pelestat 300”, crystallization temperature: 85.4 ° C., MFR = 20.2 g / 10 min) 5 parts by mass, Miyoshi Surfactant (lauric acid diethanolamide) (trade name: “Amicol LDE”) 0.3 part by mass, manufactured by Oils and Fats Co., Ltd., 0.5 part by mass of a bubble regulator masterbatch (Cermic MB1023 manufactured by Sankyo Kasei Co., Ltd.) Supplied to the φ90mm first extruder of φ150mm tandem extruder and melted in the extruder, then from the middle of the extruder 13 parts by mass of butane (isobutane / normal butane = 95/5 (molar ratio)) as a foaming agent was injected and kneaded, and then cooled to a temperature range (112 ° C.) suitable for foaming with a second extruder having a diameter of 150 mm. Extrusion foaming was performed in the air from a circular die having a diameter of 145 mm (slit 0.2 mm).
The extruded foamed cylindrical foam was cooled along a cooling mandrel having a diameter of 520 mm, and cut at one point to obtain a sheet-like extruded foamed sheet.

Subsequently, the obtained extruded foamed sheet was wound up in a roll shape with a winding length of 640 m with an average tension of 20 N per 1 m of the sheet width by a winder.
The diameter of the winding core was 150 mm, and the winding diameter was 960 mm. The basis weight of the foamed sheet was 0.03 kg / m ² . The roll-shaped foamed sheet was hung in a room temperature-controlled at 35 ° C. so that the winding core was horizontal and floated in the air, and allowed to age for 24 hours.
Thereafter, the roll-shaped foamed sheet was rewound in a roll shape on a 3-inch paper tube with an average tension of 20 N and a winding length of 620 m per 1 m of the sheet width in a rewinding machine. The roll foamed sheet of this example was obtained by allowing to stand for a period of time.
The density of the foamed sheet of this example was 37 kg / m ³ immediately after winding.
On the other hand, the density of the foamed sheet after being allowed to stand at room temperature for 5 days was 32 kg / m ³ .

(Comparative Example 1)
A foamed sheet was prepared in the same manner as in Example 1 except that the surfactant (lauric acid diethanolamide, 0.3 part by mass) was not added.

(Evaluation)
The following evaluation was performed on the foamed sheet of Example 1 and the foamed sheet of Comparative Example 1.

(Cloudy phenomenon evaluation)
The evaluation of the contamination due to the component transfer to the partner material to be contacted is carried out by placing a foam sheet on the glass plate, leaving it on the weight and observing the degree of dirt on the glass plate with the naked eye. went.
Specifically, the foam sheet is cut into a size of 5 cm × 5 cm, and this is placed on a cleaned and dried glass plate (non-alkali glass OA-10G manufactured by Nippon Electric Glass Co., Ltd.), and further 4 kg of it is placed thereon. A weight was placed (load 15690.64 Pa) and left in a tank at a temperature of 65 ° C. and a relative humidity of 90% for 24 hours, and then naturally cooled at a temperature of 25 ° C. and a relative humidity of 60% for 1 hour.
Then, the foamed sheet was removed, and the occurrence of cloudiness (dirty condition) on the surface of the glass plate was evaluated with the naked eye, and the results were evaluated in five stages as shown below.

(Criteria)
1. I can not confirm the transition at all.
2. If you look closely, you can see the transition.
3. The transition can be confirmed slightly.
4). The transition can be clearly seen at a glance.
5. Migrate can be confirmed on the entire surface.

(Contact angle evaluation)
The contact angle of water to a sample (a glass plate to which the component of the foam sheet was transferred) prepared in the same manner as the sample used for cloudy evaluation was measured at room temperature with a contact angle meter (Kyowa Interface Chemical, CA-X type). .

(Evaluation of cleaning effect)
Cloudiness evaluation and contact angle evaluation The sample was washed with an alkaline cleaning solution (pH 10 aqueous solution), and then cloudy evaluation and contact angle evaluation were performed again to confirm the cleaning effect.
Specifically, the glass plate adjusted in the cloudy evaluation and contact angle evaluation is immersed in an alkaline cleaning solution for 3 minutes, then rinsed with running water, and then rinsed with distilled water and dried, and the cloudy evaluation sample and contact An angular measurement sample was obtained.
Note that this contact angle may be observed to be small due to the adhesion of a highly hydrophilic surfactant, but usually the contact angle decreases as the adhering material is removed after good cleaning. It can be determined that the corner is 10 degrees or less is in a clean state.

(Surface specific resistivity)
With respect to the foam sheets of Examples and Comparative Examples, the value of surface resistivity was measured by the method described in JIS K 6911: 1995 “Thermosetting Plastics—General Test Method”.
Specifically, after a flat square test piece having a side of 10 cm is left in an atmosphere of a temperature of 22 ° C. and a humidity of 60% for 24 hours, a test apparatus (manufactured by Advantest Corporation) under an environment of a temperature of 22 ° C. and a humidity of 60% is used. Using a digital ultra-high resistance / microammeter R8340 and a resiliency chamber R12702A), an electrode is crimped to a test piece with a load of about 30 N, a voltage of 500 V is applied, and a resistance value after one minute has elapsed. Measured and calculated by the following formula.
ρs = π (D + d) / (D−d) × Rs
However,
ρs: surface resistivity (Ω / □)
D: Inner diameter (cm) of the annular electrode on the surface (7 cm for the resiliency chamber R12702A)
d: outer diameter (cm) of inner circle of surface electrode (5 cm for resiliency chamber R12702A)
Rs: Surface resistance (Ω)

The measurement was performed on three sheets, and an arithmetic average was obtained to obtain each surface specific resistivity.

These evaluation results are shown in Table 1 below.

When the surface deposit on the sample subjected to the cloudy test was confirmed by infrared absorption spectrum (IR), the low molecular weight component of polyethylene and the polymer antistatic agent were adhered to the sample of Comparative Example 1. Was confirmed.
This is considered to be because the foam sheet was pressed by the weight of 4 kg, and the components of the foam sheet at the press contact portion were transferred to the glass plate.
On the other hand, in the sample of Example 1, since the surfactant (lauric acid diethanolamide) quickly covers the foam sheet surface, the polymer antistatic agent and polyethylene are prevented from adhering to the glass plate surface. It can be seen that the result of the cloudy test was better than that of Comparative Example 1.
In addition, the sample of Comparative Example 1 shows the same degree of cloudiness after cleaning, whereas the sample of Example 1 has the above-described functions because the deposits are washed away by cleaning. It can be confirmed that it is acting on the sample.

  This also shows that the foamed sheet of the present invention is useful for preventing contamination of the partner to be in contact with the foamed sheet, and is useful for a slip sheet of a glass substrate.

Claims (6)

A polyethylene resin foam sheet comprising a polymer type antistatic agent and a surfactant together with a polyethylene resin,
The polymer type antistatic agent is contained in a proportion of 4 to 17 parts by mass with respect to 100 parts by mass of the polyethylene resin, and the fatty acid alkanolamide surfactant is 0.3 to 3 as the surfactant. A polyethylene resin foam sheet characterized by containing 1.2 parts by mass.   The polyethylene resin foam sheet according to claim 1, wherein the fatty acid alkanolamide-based surfactant is lauric acid diethanolamide.   The polyethylene-based resin foam sheet according to claim 1 or 2, wherein the polymer antistatic agent is a polyether-polyolefin block copolymer.   4. The polyethylene-based resin according to claim 1, wherein the polymer antistatic agent has a crystallization temperature of less than 90 ° C. and a melt mass flow rate of 10 g / 10 min or more and 40 g / 10 min or less. Foam sheet. The polyethylene-based resin according to any one of claims 1 to 4, wherein the polyethylene-based resin has a density of 925 kg / m ³ or more and 935 kg / m ³ or less, and a melt mass flow rate of 2 g / 10 min or more and 6 g / 10 min or less. Resin foam sheet.   The polyethylene-based resin foam sheet according to any one of claims 1 to 5, which is used as a slip sheet for a glass substrate for display.